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In recent years, the engineering field is becoming more and more complicated, and collaboration with other disciplines is becoming more critical. As a result, interdisciplinary programs are rising at the graduate level and higher education stages, centered around universities. One drawback of this trend is that students who lack foundational knowledge related to certain lectures may take specialized courses. This can lead to significant differences in the knowledge acquired by the students, depending on how the lecture content is tailored to accommodate their respective levels. To address this issue, various efforts have been made to solve this problem. This paper presents a case study of introducing a circuit simulator to conduct a semiconductor power conversion engineering, in a class with not a few students who do not have circuit theoretical backgrounds.

DOI： 10.1109/ICELIE58531.2023.10313100

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Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/icelie55228.2022.9969416

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DOI： 10.1109/icelie55228.2022.9969423

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DOI： 10.1109/ecce50734.2022.9948072

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DOI： 10.1109/ecce50734.2022.9947525

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Switched reluctance motors (SRMs) have recently attracted researchers' attention owing to their robust mechanical construction, high thermal tolerance, and strong cost-effectiveness, which are promising for vehicle propulsion. However, they tend to generate large ripples in the torque and input currents to the inverter; this deteriorates the driving comfort, and damages the battery lifetime. Preceding articles have investigated using the phase currents of SRMs to eliminate these ripples. However, these articles had difficulties in sufficiently eliminating these ripples in operations under magnetic saturation. This article further evolves one of these preceding articles, and proposes a derivation method for the phase-current waveform for improving the elimination of the torque and input-current ripples in operation under magnetic saturation. The proposed method analytically determines the phase-current waveform based on a nonlinear behavior model of the SRM while considering the magnetic saturation. A finite-element-method-based simulation and experiment are performed to evaluate the proposed method. These results reveal the successful reduction of the torque and input-current ripples under the magnetic saturation relative to a preceding study, supporting the appropriateness of the proposed method.

DOI： 10.1109/TIA.2022.3172898

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY  

Power balance mode control (PBMC) is a new control method that adds a function of balancing input and output powers to current-mode control (CMC). As the input power is equal to the output power in a static state, PBMC does not operate, and the control changes to CMC. When there is a fluctuation due to a disturbance, the control to balance the power works because the input power and output powers are different. When the fluctuation is large, the control to balance the power works; when the fluctuation is small, it is equivalent to CMC. In this study, the PBMC operation was analyzed in more detail, and it was found that the PBMC operation and CMC operation switched seamlessly depending on the magnitude of fluctuation. Furthermore, a design method for digital PBMC was developed and analyzed comprehensively through experiments. As a result, even though the frequency characteristics of the open-loop transfer function and output impedance of PBMC by small-signal analysis are the same as those of CMC, the output voltage fluctuation is reduced to about 1/3 of that of CMC. Since the PBMC can suppress the output voltage fluctuation without requiring a high gain crossover frequency, it can ensure high response performance, noise rejection, and stability of the control system. In addition, output voltage fluctuations can be suppressed, thus contributing toward downsizing of power conversion circuits and increased power density. (c) 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

DOI： 10.1002/tee.23562

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Publishing type：Research paper (international conference proceedings)  

The solenoid coil is a typical heating coil structure for induction heating of cylindrical heating objects. Conventionally, a bare solenoid coil without any soft-magnetic core has been commonly utilized. However, this conventional structure suffers from worse heating efficiency caused by the large coil copper loss and the low magnetic field induction at the heating object. This paper addresses these difficulties by proposing a novel heating coil structure. In addition to the solenoid coil, the proposed heating coils structure further incorporates the soft-magnetic cores that cover the outer coil periphery and the coil opening edges. These additional cores can reduce the local intense magnetic field around the coil, thus mitigating the eddy current induction inside the wire to reduce the copper loss, and also can increase the magnetic field inside the heating object, thus increasing the heat generation. The simulation was carried out to test the effectiveness of the proposed heating coil structure. The results inferred the reduction of the coil copper loss by 25% and the increase in the heat generation in the heating object by 53%, both of which suggest the promising features of the proposed heating coil structure for heating the cylindrical magnetic material. The heating operation of the proposed heating coil structure was tested by the experiment, although the current prototype was found to have larger power loss than expected from the simulation. The reason may lie in unintended eddy current generation of the metal case of the heating coil, which will be addressed in future work.

DOI： 10.1109/ISIE51582.2022.9831459

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Publishing type：Research paper (international conference proceedings)  

The data centers of the telecommunication infrastructure are recently consuming more electric power than before. This increasing electrical burden is requiring a small but high-power isolated power converter with a high step-down ratio. Conventionally, the LLC converter is regarded to be a promising candidate, although this converter needs vacant space for galvanic isolation due to extremely high voltage caused by the resonance in the primary side, i.e. high voltage side, of the isolation transformer, which hinders the compact implementation inside the server computers in high power design. The purpose of this paper is to propose a novel LLC converter topology to reduce this extremely high voltage by locating the LC resonator on the secondary side. The performance analysis revealed that the proposed converter exhibits a similar frequency-voltage characteristic enabling the boost and buck operation modes as well as the small rectifier conduction loss similar to the full-wave rectifier with a center-tapped transformer. The simulation confirmed the operating principles and reduction of the resonance voltage amplitude of the proposed LLC converter in comparison with the conventional LLC converter. Furthermore, the experiment also supported the operating principles, which suggests the usefulness of the proposed converter for a high voltage dc power supply system.

DOI： 10.23919/IPEC-Himeji2022-ECCE53331.2022.9806826

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Publishing type：Research paper (international conference proceedings)  

Isolated DC-DC converter in data centers are now required to have a high step-down ratio and be suitable for high-power applications. As such DC-DC converters, LLC resonant converters have been attracting attention. However, the LLC resonant converter generates a large resonance voltage at the resonator, so the resonance inductor and resonance capacitor must be large in size. Recently, a previous study proposed a secondary-side resonance LLC converter to reduce the resonant voltages of the passive components. Nevertheless, this LLC converter requires a resonant capacitor in parallel with the rectifier to achieve boost mode operation, which complicates the circuit operation and design. Therefore, we have considered the use of the magnetizing inductance of the coupled transformer of the current doubler rectifier as a method to realize the boost mode operation. In this paper, we propose a new method of boost mode operation for LLC resonant converter using secondary-side resonance and the current doubler rectifier.

DOI： 10.1109/SPEC55080.2022.10058227

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The LLC converter is a very effective topology for miniaturization of power supplies. However, its application is currently limited. That is because of the problem of degraded system stability when the load condition changes. This paper proposed a practical control circuit that controls the power factor cos\theta by adjusting the phase difference \theta between the inverter voltage and primary current of the LLC converter to control the output voltage to address this problem. As a result, experimental result confirm that the proposed control method has robust control characteristics against wide load impedance and shows low output impedance regardless of the output voltage.

DOI： 10.1109/SPEC55080.2022.10058371

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

An altimeter is a critical instrument in planetary missions, for both safe operations and science activities. We present required specifications and link budget calculations for light detection and ranging (LIDAR) onboard the Martian Moons Exploration (MMX) spacecraft. During the mission phase, this LIDAR will continuously measure the distance between the spacecraft and its target. The time-series distance provides important diagnostic information for safe spacecraft operations and important information for geomorphological studies. Because MMX is a sample return mission, its LIDAR must accommodate physical disturbances on the Martian satellite surface. This resulted in changes to the optical system design.

DOI： 10.1186/s40623-021-01537-7

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Reluctance machines such as the switched reluctance machines (SRMs) and the synchronous reluctance machines (SynRMs) are recently investigated for propulsion motors of the electrified vehicles owing to their robust mechanical construction, high thermal tolerance, and cost-competitiveness. However, practical application of the reluctance machines to the vehicle propulsion has been hindered by the fact that the conventional SRMs and SynRMs are difficult to meet all the three preferable features for the vehicular application: 1. High power density, 2. Low torque and input-current ripples, 3. Being drivable by the normal three-phase inverter. This paper addresses this issue by proposing a novel reluctance machine. The prominent features of the proposed reluctance machine are the sinusoidal reluctance profile and the delta-connected phase windings, both of which differ from conventional reluctance machines. Along with the theoretical discussion of the basic operating principles of the proposed reluctance machines, this paper presents a simple performance estimation of the proposed machine, the SRM, and the SynRM, which supported that the proposed machine can meet the three preferable features. Furthermore, the experiment successfully supported the operating principles of the proposed machine, suggesting the feasibility of the proposed machine for vehicle applications.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Multiple-receiver resonant inductive coupling wireless power transfer (RIC-WPT) technique is emerging as a promising charging method for multiple household appliances, mobile devices, and wearable devices. However, this technique often suffers from output power fluctuation owing to the cross-interference among receivers as well as the manufacturing and aging tolerance of the resonant frequency (i.e., resonant frequency tolerance). This article proposes an autonomous RIC-WPT system concept to solve this difficulty. The proposed concept addresses the cross-interference and resonant frequency tolerance by incorporating the following two functions. First, the amplitude of the transmitter current is controlled to have a constant amplitude. Second, the phase of each receiver current is controlled to be orthogonal to that of the transmitter current by using an active reactance compensator installed in each receiver. The experiment of a two-receiver RIC-WPT system successfully verified that the two functions of the proposed system concept can stabilize the output voltage against the cross-interference and resonant frequency tolerance.

DOI： 10.1109/TIA.2021.3081071

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

The resonant inductive coupling wireless power transfer technique (RIC-WPT) is emerging as a promising wireless power transfer method for small mobile devices with comparatively high-power transfer capability and good efficiency. However, the performance of the RIC-WPT system is severely deteriorated by the resonant frequency detuning of the transmitter, repeater, and receiver resonators, which can be naturally caused by the manufacturing tolerance and the aging effect of these resonators. Particularly, the detuning of the repeater resonator tends to severely affect the performance due to its high-quality factor, which should be solved for practical application of RIC-WPT technology. This paper addresses this difficulty by proposing an autonomous resonant frequency tuning controller circuit for the repeater resonator. The controller tunes the resonant frequency of the repeater resonator to the operating frequency of the inverter, driving the transmitter, without an external power supply and wireless communication with the inverter controller, which restricts the freedom of the installation location and therefore preferably be avoided in the wireless power transfer system. The operating principles of the proposed controller were confirmed by the circuit simulator, supporting the feasibility of the proposed controller.

DOI： 10.1109/ISIE45552.2021.9576268

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Gallium-nitride-field-effect transistors (GaN-FETs) are expected as a key component to the power density improvement of switching power converter for electric vehicles (EVs) because of their low on-resistance and fast switching capability. It is well known that the switching loss is influenced by the drain inductance, which is the parasitic inductance of the power loop, and can be minimized in principle by an appropriate design of the drain inductance. However, in switching power converters using Si-based power devices such as the Si-MOSFET and the Si-IGBT, it is usually difficult to design the drain inductance so that the switching loss minimizes because an appropriate drain inductance becomes too large, thus resulting in large surge voltages of the switching device. On the other hand, this may not be the case when using the GaN-FETs because the inductance that can minimize the switching loss may become small due to the high-di/dt switching. Therefore, the purpose of this study is to show the feasibility of the parasitic drain inductance design that the switching loss of the GaN-FET in the bridge circuit can be minimized while keeping the surge voltage of the GaN-FET within acceptable limits. The appropriateness of this insight is verified by simulation.

DOI： 10.1109/ISIE45552.2021.9576373

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Litz wire has been widely utilized in power transformers and inductors as a wire with low copper loss at high-frequency operation. The Litz wire is commonly made of many thin isolated strands twisted in multiple levels. Due to its complicated structure, the copper loss prediction of the Litz wire has been difficult, hindering the design optimization of the Litz wire structure. To overcome this difficulty, preceding studies have investigated the analytical copper loss models of the constituting elements of the Litz wire, i.e., the strands and the bundles of strands. The purpose of this article is to propose an analytical copper loss model of the Litz wire by utilizing these preceding knowledge. The proposed model is formulated only with parameters that can be measured by basic testing instruments. Besides, the proposed model considers the bundle structure of the Litz wire, which affects the local ac current distribution, and the twisting pitch, which causes the inclination of the Litz wire strands. The proposed model was tested by comparing the analytical prediction and experimental measurements of the ac resistance of commercially available Litz wires. As a result, the predicted ac resistance showed good agreement with the measured ac resistance, suggesting the appropriateness of the proposed model.

DOI： 10.1109/TIA.2021.3063993

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Reluctance motors, represented by the switched reluctance motor (SRM) and the synchronous reluctance motor (SynRM), are attractive for vehicle propulsion owing to their high thermal tolerance and simple mechanical construction. However, the SRM exhibits large torque and large input current ripples, deteriorating driving comfort and battery lifespan. Furthermore, a driving system of the SRM requires the special inverter topology with additional switching or rectifying devices, leading to the cost-up. Meanwhile, the SynRM does not have these drawbacks, although this motor tends to be difficult to cover the wide range of the torque and the rotation speed required for vehicle propulsion because of large phase flux induction. To solve the obstacles of these conventional reluctance motors, this paper proposes a novel reluctance motor. The proposed reluctance motor is based on magnetization by the sinusoidal phase flux waveform, whereby the torque and input current ripples are eliminated using a common three-leg inverter without inducing large phase magnetic flux. This paper presents the operating principles of the proposed reluctance motor as well as analysis and simulation results in comparison with the SRM and the SynRM. As a result, the proposed reluctance motor is elucidated to reduce the torque and input current ripples with the three-leg inverter. Furthermore, the proposed reluctance motor can improve the torque range and rotating speed range compared to the SynRM because of the sinusoidal flux waveform with reduced amplitude. These results imply feasibility of the proposed motor for vehicle propulsion.

DOI： 10.1109/PEMC48073.2021.9432579

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Industrial electronics (IE) covers a wide range of technologies and applications, being a key enabling technology for numerous industrial, domestic, and biomedical uses, among others. In this context, IE education has become a relevant and challenging topic for society and industry. This article covers its evolution and state-of-the-art methodologies and provides an overall view of its status around the world. Finally, future trends and challenges in IE education are discussed.

DOI： 10.1109/MIE.2020.3002488

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

The industrial electronics (IE) discipline includes a wide variety of technical areas devoted to the application of electronics and electrical sciences for the enhancement of industrial and manufacturing processes. It inherently acts as a key enabling technology for a diverse number of applications and includes the latest developments in intelligent and computer control systems, robotics, factory communications and automation, flexible manufacturing, data acquisition and signal processing, vision systems, and power electronics, among others, as well as the educational and human factors involved. This makes IE inherently multidisciplinary, and, with many interconnected synergies, it plays a key role as an enabling technology in multiple domestic, biomedical, transportation, and industrial applications.

DOI： 10.1109/MIE.2020.3032942

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

The educational methodologies employed in Industrial Electronics have been affected by Covid-19. In many cases, conventional learning methods relying on face-to-face lectures have been replaced by online methodologies. The whole process has required a fast adaptation and development of the elearning tools to ensure a quality of theoretical, practical and laboratory lectures, as well as the development of new methods for the reliable assessment of the learning process. From this perspective, the present paper deals with the different strategies that have been implemented in institutions of several countries located in different geographical areas, including Portugal, Spain, Japan and Australia. It is shown that the use of methodologies, such as flip teaching, has provided a wide variety of possibilities to adapt to the new educational context. Moreover, for Industrial Electronics degrees, the use of virtual or remote laboratories, portable learning tools and advanced information and communication technologies have also risen as valuable resources. The paper also reports the problems arising during the development of the e-learning tools, their implementation constraints, and the evaluation of their results.

DOI： 10.1109/ICIT46573.2021.9453467

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

GaN-FETs are recently spreading in high-power switching converters, where GaN-FETs are commonly parallel connected to switch the large current. However, the parallel-connected GaN-FETs often suffer from false triggering because the parallel connection incorporates multiple LC resonators of the parasitic capacitance of GaN-FETs and the parasitic inductance of the printed circuit board, which can be easily excited by the switching noise and fluctuate the gate voltage. Particularly, GaN-FETs are susceptible to the self-sustaining repetition of the false triggering, i.e. the oscillatory false triggering, which must be prevented in industrial products. For prevention of this phenomenon in the case of a single GaN-FET, the preceding studies have proposed the design instruction of the parasitic inductance. However, few insights are available for the parallel-connected GaN-FETs. The purpose of this paper is to elucidate the design instruction to prevent the oscillatory false triggering for parallel-connected GaN-FETs through analyzing the equivalent circuit model of this phenomenon. The result revealed that parallel-connected GaN-FETs need the design instruction slightly modified from that for a single GaN-FET. The appropriateness of this modified instruction was verified by the simulation, suggesting the feasibility of this instruction for applying the parallel-connected GaN-FETs in high-power switching converters.

DOI： 10.1109/IECON48115.2021.9589541

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Other Link： https://dblp.uni-trier.de/db/conf/iecon/iecon2021.html#HatakenakaUIHT21

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Due to COVID-19, Okayama University, one of the national universities in Japan, has been unable to enter the campus since March 2020. Therefore, all classes, meetings, and even graduation ceremonies were held online. Even now that large-scale vaccination is in progress, most of the lectures are stil online except for some small-scale classes that can secure the social distance. This paper introduces small attempts to effectively conduct the interactive online lectures of undergraduate and graduate schools.

DOI： 10.1109/IECON48115.2021.9589676

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Other Link： https://dblp.uni-trier.de/db/conf/iecon/iecon2021.html#HirakiIU21

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Power electronics is a complex field of power, electronics, and control. For this reason, the content taught in lectures is extremely broad. In addition, because it deals with circuits that are actually used in the world, unlike other electrical subjects, it also requires a design and development perspective. Conventional education methods for power electronics have centered on lectures that explain the basic operation of various power conversion circuits and hands-on practice using circuit kits. However, even understanding the basic operation is insufficient to gain the knowledge and experience necessary to become a circuit designer. Therefore, in this paper, we propose a lecture for students to acquire a wide range of power electronics technologies, and a coordinated education of basic and applied technologies in which students actually design power conversion circuits. In the lectures, students learn not only the operation of basic power conversion circuits throughout the year, but also the basic design methods of power conversion circuits. In the design of power conversion circuits, students work on circuit fabrication through repeated trial and error based on the design methods introduced in the lectures. In this way, students can acquire not only the basic knowledge but also the knowledge and skills necessary for circuit design more than with conventional educational methods.

DOI： 10.1109/IECON48115.2021.9589302

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

The LLC converter is attractive for its small volume and comparatively high efficiency. However, the application of this converter is limited to the power supply to a static load with almost constant output voltage and current because the LLC design covering a wide range in the output voltage and the load variation can deteriorate the output voltage stability and efficiency. This paper addresses this issue by proposing a novel control method. Unlike the conventional control, which adjusts the operating frequency to stabilize the output voltage, the proposed control adjusts the power factor of the transformer primary-side to achieve the same excellent dynamic performance as the buck chopper. Simulation supported the effectiveness of the proposed control at a wide load variation range.

DOI： 10.1109/ECCE47101.2021.9595420

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Resonant inductive coupling wireless power transfer (RIC-WPT) systems with multiple transmitters and multiple receivers often suffer from cross-interference among transmitters as well as among receivers. The cross-interference causes the fluctuation of the output power of the receiver and hard switching of the inverter on the transmitter. To avoid the cross-interference, controlling the amplitude and the phase of each transmitter current is an effective method. Therefore, this paper proposes a multiple-transmitter that can compensate for the cross-interference influence by implementing two controls. First, adopting the phase-shift control on the full-bridge inverter, the current amplitude is controlled to be constant. Second, applying the reactance control, each phase of the current is controlled to be in phase. In addition to the above operations, especially under a high-frequency operation, zero-voltage switching (ZVS) at a fixed operating frequency is essential for improving the power efficiency while not exceeding an allowable narrow bandwidth. Thus, the reactance control also works to ensure ZVS in all load conditions without adjusting the frequency. The RIC-WPT prototype with two transmitters and a single receiver is built to verify that the proposed multiple-transmitter can compensate for the cross-interference influence while achieving ZVS in different load conditions at a fixed operating frequency.

DOI： 10.1109/ECCE47101.2021.9595950

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The Litz wire is utilized to wireless power transfer system and induction heating according to has small AC resistance in high frequency. Prediction of AC resistance of the Litz wire is important for design optimization of the Litz wire, hence the recent study has proposed analytical AC resistance prediction model of the Litz wire. However, verification in practical coils using the Litz wire is still insufficient. The purpose of this paper is to verify the prediction accuracy of AC resistance using a full analytical model in a practical coil. For practical coil, planer spiral coils are selected, and AC resistance of the planer spiral coil is calculated by combining with the loss model and the FEM analysis. As a result, the Litz wire loss model is found to well predict the measured AC resistance of the Litz wire planer spiral coil, supporting the appropriateness of the Litz wire loss model.

DOI： 10.23919/ICEMS50442.2020.9290802

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INST ENGINEERING TECHNOLOGY-IET  

In recent decades, switched reluctance motors (SRMs) have been attracting increasing attention as a promising type of traction motors for electric vehicle propulsion, owing to their robust construction, elimination of permanent magnets. However, their phase inductance profile contains significant high-order harmonics, which generates input-current and torque ripples under SRM drive with the conventional square phase-current waveform. This study solves this problem by proposing a novel phase-current waveform in replacement of this square waveform. The proposed waveform is a predetermined waveform that can be stored as a look-up table in the inverter controller and can be magnified or attenuated to adjust the output torque, similarly as the conventional square waveform. Certainly, SRMs generally exhibit magnetic non-linearity due to magnetic saturation, which complicates the analysis. Therefore, the proposed waveform is analytically derived under the assumption that the magnetisation of the motor remains below the saturation level because vehicle propulsion tends to require a torque output far smaller than the maximum rating of the motor in normal vehicle travel. The proposed phase-current waveform is experimentally tested in comparison with the conventional square phase-current waveform. Consequently, the proposed waveform revealed smaller ripples in both the input-current and torque, supporting the effectiveness of the proposed phase-current waveform.

DOI： 10.1049/iet-pel.2019.1207

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Switched reluctance motor (SRM) is recently emerging as a cost-effective but mechanically and thermally robust motor for vehicle propulsion. However, the conventional driving method of the SRM causes a large input current and torque ripples, both of which are scarcely acceptable for vehicle application. Recently, a promising driving method has been proposed that tunes the phase current to eliminate the input current and torque ripples simultaneously, although this method suffers from large copper loss when applied to the normal SRMs. To solve this problem, this article proposes simultaneous tuning of the rotor shape in combination with the recently proposed driving method, which includes only tuning of the phase current. Tuning of the rotor shape is targeted at minimizing the copper loss. Meanwhile, the stator structure is the same as the normal SRM design. The proposed approach was revealed to reduce the effective value of the phase current by 18% in simulation and by 23% in experiment compared with the recently proposed driving method, without increasing the input current and torque ripples. This result suggests the effectiveness of tuning both the rotor shape and the phase current for applying SRMs to vehicle propulsion.

DOI： 10.1109/TIA.2020.3015446

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© 2020 EPE Association. The windings of high-frequency high-current transformers are required to reduce the proximity effect loss. Therefore, the Litz wire in parallel connection of interleaved winding layers is usually used as the winding of transformers. However, this can cause unbalanced AC current distribution, hindering effective reduction of the copper loss. This paper solves this problem by optimizing the distance between the winding layers based on the analytical principle called the extremum co-energy principle. The transformers used in the experiment to verify this method consists of three parallel-connected primary winding and two parallel-connected secondary winding, PQ core, thin polypropylene sheets for adjusting the distance between the winding layers. As a result, the copper loss can be recused by homogenizing the AC current distribution, and the effectiveness of this method has been clarified by experiments.

DOI： 10.23919/EPE20ECCEEurope43536.2020.9215804

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

© 1986-2012 IEEE. Series-series (SS) and series-parallel (SP) topologies are widely used in resonant inductive coupling wireless power transfer systems for various applications. However, the selection of an appropriate topology to achieve higher output power or higher efficiency is typically difficult because design optimization of the circuit parameters (e.g., characteristic impedance, load resistance, and mutual inductance) for each topology is generally separately discussed using different equivalent circuits with multiple resonance modes. Therefore, the purpose of this study involves proposing a simple strategy to select an appropriate topology. The proposed strategy is based on quasi-duality between the SS and SP topologies that are elucidated from the novel equivalent circuits derived using Lagrangian dynamics. Based on the quasi-duality, the output power and efficiency of the SP topology are calculated via the equivalent circuit of SS topology. Thus, the quasi-duality offers a simple comparison between the SS and SP topologies. The proposed strategy selects an appropriate topology by comparing only the equivalent ac load resistance, which is the ac resistance including the rectifying circuit and the load resistance, the characteristic impedance, and the ac load resistance that achieves the maximum efficiency or maximum output power of the SS topology. Experiments verify the appropriateness and effectiveness of the proposed strategy.

DOI： 10.1109/TPEL.2019.2956732

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

© 2020 IEEE. Secondary-side center-tapped transformer is a common transformer design of the high step-down forward converters owing to its effective reduction of the copper loss. Particularly, the extremely high step-down converters tend to have one-turn secondary coils to increase the winding turn ratio. However, due to the proximity effect in the terminal and the wire connecting the secondary coils and the rectifier, this design tends to suffer from significant deterioration of the copper loss reduction effect. To mitigate this problem, this paper proposes a novel transformer's secondary-side structure that integrates the one-turn secondary coils and the rectifier. The proposed transformer structure can mitigate the proximity effect in the secondary coils and the rectifier, thus suppressing the local concentration of the current distribution. Experiments revealed effective reduction of the copper loss, supporting the effectiveness of the proposed structure.

DOI： 10.1109/ISIE45063.2020.9152390

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

© 2020 IEEE. With the growth of GaN HEMTs applications in power electronic commercial markets, higher frequency operation became possible allowing different advantages with regards to downsizing of passive components in power converters. High switching and heat performance makes GaN HEMTs a better solution for high power applications. This technology is different from that of conventional Si devices, raising several new challenges to the power converter design procedures. For instance, the effect of the fast transient operation of GaN HEMTs on the operation magnetic components has not been completely understood yet. Consequently, it is important to start analyzing how GaN semiconductors are driven, despite the few gate drivers designed to drive GaN HEMTs. This paper analyzes and summarizes the driving techniques and solutions of E-mode GaN HEMTs and their gate drivers. The commercially products are reviewed. Simulation of E-modes GaN HEMT switching performance is performed and discussed.

DOI： 10.1109/ISIE45063.2020.9152415

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

© 1986-2012 IEEE. It is quite often to utilize the transformer leakage inductance in the resonant tank of the LLC resonant converter to allow for a drastic reduction in the converter cost, weight, size, and volume. The effects of the secondary leakage inductance on the operation of the LLC resonant converter are not well discussed in the relevant literature, and it is the purpose of this paper to give an insight into these effects. The contribution of this paper lies in the following: first, highlighting that it is not always an accurate assumption to consider that the values of the primary and secondary leakage inductance are identical, specifically in asymmetric magnetic core structures. Second, it has been disclosed that the well-known coupling factor (k12) cannot properly express the unequalized leakage inductance distribution in the proposed asymmetric transformer. Therefore, the authors bring the primary coupling factor (k1) and secondary coupling factor (k2) into practice to appropriately express the unequalized leakage distribution on the primary and secondary windings, which can be controlled by the allocation of the relevant winding with respect to the air gap, utilizing the noise absorber, and changing the distance between the winding. Several transformer prototypes had been built and experimentally tested to validate these hypotheses. Third, it has been observed that the transformer voltage gain and efficiency can be improved when the transformer leakage inductance is concentrated on the secondary side to avoid the voltage drop inflicted by the relatively large value of the magnetizing current (im), especially at the light load condition. Fourth, it has been reported that in a transformer structure with a concentrated value of leakage on the secondary side would decrease the resonant tank input impedance, vertically widen the voltage-gain curve of the converter, and eventually increase the frequency control bandwidth with respect to the load variation. Transformer prototypes had been constructed and tested in a 390 V/12 V-220 W LLC resonant converter to evaluate the proposed analysis.

DOI： 10.1109/TPEL.2019.2911093

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Next-generation switching devices as GaN-FETs are recently emerging as promising switching devices capable of extremely high-speed switching. High-speed switching enables the high-frequency operation of the power converters, which can reduce the size of the passive components. However, highspeed switching can induce the resonance between the parasitic capacitance of the switching device and the parasitic inductance of the circuit board wiring, which appears as the gate voltage fluctuation at the switching. Particularly, GaN-FETs tend to have comparatively low gate threshold voltage and therefore are susceptible to the false turn-on, which is caused by the gate voltage fluctuation in the switching device just after the turn-off transition. For preventing this phenomenon, this paper analytically investigates the design requirement of these parasitic parameters to reduce the gate voltage fluctuation after the turn-off transition. As a result, the optimal ratio of the gate-drain capacitance and the common source inductance is elucidated to be the key to minimize the gate voltage fluctuation. The simulation and the experiment supported that the optimal design of this ratio can reduce the gate voltage fluctuation, supporting the usefulness of this novel insight for preventing the false turn-on.

DOI： 10.1109/ECCE44975.2020.9236428

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The Litz wire is widely utilized in recent high frequency switching regulators as a magnetic wire with small AC resistance. The AC resistance of the Litz wire is dependent on the twisting structure of the strands as well as the resultant cross-section geometry of the Litz wire. Therefore, optimization of the Litz wire is becoming important, although the numerical prediction of the AC resistance is difficult due to the complicated structure of the Litz wire. Certainly, a recent study has proposed an analytical AC resistance prediction method. However, this method cannot be applied to Litz wires with the rectangular cross-section, which is recently developed to improve the packing factor of the winding. This paper aims at extending this previous method to cover these Litz wires by partly utilizing a simple static magnetic field FEM analysis. The experiment revealed successful AC resistance prediction of the Litz wire with the rectangular cross-section.

DOI： 10.1109/ECCE44975.2020.9236116

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Power conversion technology is characterized by the comparatively small variation of circuit topologies. Because product competitiveness mainly lies in the performance quality as efficiency and low noise emission, the professional skills of this technology commonly require the ability to improve the quality under the restriction of the space, the material resource, and the cost. The conventional teaching method of the power conversion technology is mainly based on the lecture classes and the hands-on classes, which teach the fixed knowledge of the circuit operation. Therefore, this conventional method tends to be insufficient to cover the various practical strategies to improve the quality. To overcome this difficulty, this paper proposes application of the competition-based learning (CBL), in which teams of the students design their power converters and compete on the efficiency. For many professional engineers, competition among companies is the basic motivation to think of strategies to improve product competitiveness. Therefore, the CBL may be effective for teaching design strategies. For promotion of sharing the know-how, the proposed teaching method introduces the events, in which each team share its design strategies with other teams and improve its design based on the know-hows of other teams These events emulate the economic activity, in which a company investigates its competitors' products to extract the know-how. Along with the basic methodology of the proposed teaching method, this paper also reports the experience of a teaching course.

DOI： 10.1109/IECON43393.2020.9254677

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Recently, a resonant inductive coupling wireless power transfer (RIC-WPT) system with multiple transmitters is emerging as a promising power supply method for household appliances, mobile devices, and wearable devices dispersedly placed in a wide area. However, the multiple-transmitter often suffers from an unstable operation of an inverter, feeding AC current to the transmitter coil, due to the cross-interference (i.e., cross-coupling) among the transmitters. When the cross-interference occurs, the inverter may not achieve high power factor and soft switching, which damages the power density and reliability of the multiple-transmitter. Therefore, this paper proposes a multiple-transmitter, including its controller, that can compensate for the effect of the cross-interference. In the proposed multiple-transmitter, each transmitter has a simple switching circuit that can automatically cancel the induced voltage due to the cross-interference with only simple control. Furthermore, the proposed multiple-transmitter also achieves a load-independent transmitter current by the control of the input voltage of the inverter, which results in a stable magnetic field regardless of load variation. Experiments verify the effectiveness and appropriateness of the proposed multiple-transmitter.

DOI： 10.1109/ECCE44975.2020.9235430

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DOI： 10.5416/jipe.46.114

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DOI： 10.5416/jipe.46.105

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© 2019 IEEE. Recently, as the miniaturization and densification of the power conversion circuit, switching frequency has been increased. To accomplish the densification, it is essential to predict the losses that occur in each part for the optimization of electric components. However, switching loss which needs to consider nonlinear characteristics are difficult to predict. As a solution, considering the dependence of the gate-drain capacitance on gate-source voltage may improve the prediction accuracy of switching loss. The purpose of this study is to evaluate the improvement of prediction accuracy by considering it. First, to construct the simulation model, the wiring parameter in the circuit, static characteristics and the parasitic capacitance of the device was measured. Next, the device model provided by the manufacturer to use in the simulation was adjusted. Also, the characteristics of the gate-drain capacitance on the gate-source voltage were obtained from two types of measurement circuits. As a result, it was verified that the difference which occurred at the rise of the drain-source voltage at the turn-off tended to decrease and prediction accuracy of the turn-off loss was improved by considering the characteristics of the gate-drain capacitance on the gate-source voltage. Therefore, we concluded that this consideration has the ability to the improvement of turn-off waveforms.

DOI： 10.1109/ICRERA47325.2019.8996508

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© 2019 IEEE. All-metal type induction cookers are utilized to heating up the non-iron pans such as the copper and aluminum pans. These cookers are designed to drive the heating coil with extremely high frequency and large AC current. However, the high-frequency large current drive tends to generate a large electromagnetic force which has the direction levitating the pans to be heated and damages the safeties of the induction cooking by moving the hot pans. The purpose of this study is to propose a novel heating coil structure that can reduce the levitation force. The proposed structure coil is similar to the axial gap induction machine. This coil structure generates the electromagnetic force in parallel to the coil surface rather than perpendicular to the surface, thus mitigating the levitation force. In addition, a novel AC power supply is proposed to drive the proposed structure coil. The experiment revealed a successful reduction of the levitation force by approximately 20% compared to the conventional coil structure, supporting the effectiveness of the proposed coil structure.

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© 2019 IEEE. Secondary-side center-tapped transformers are widely utilized for high step-down forward DC-DC converters. For reducing the copper loss, optimization of the winding layer allocation can be a promising approach. However, the optimal allocation pattern has been difficult to be elucidated, particularly if the winding is formed of parallel-connected winding layers or carries the AC and DC current as in a center-tapped winding. This difficulty is addressed in this paper by proposing a copper loss analysis method applicable to parallel-connected winding layers and a center-tapped winding. The proposed analysis method utilizes the Dowell method in combination with the extremum co-energy principle, which has been recently proposed to analyze the current distribution in parallel-connected winding layers. As an example, this paper analyzes the center-tapped transformer each secondary winding of which is made of two parallel-connected winding layers. The optimal winding layer allocation pattern was elucidated by comparing the copper loss among six possible winding layer allocation patterns. Appropriateness of the analysis was verified by simulation, suggesting the effectiveness of the proposed method and the importance of optimizing winding layer allocation in the forward transformer design.

DOI： 10.1109/ECCE.2019.8912519

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© 2019 EPE Association. Placing a repeater, which relays the magnetic field from the transmitter to the receiver, is promising as a method to increase the spatial freedom of resonant inductive coupling wireless power transfer systems (RIC-WPT) working at 6.78MHz. However, the capability of the repeater is often affected by a frequency splitting phenomenon. When this phenomenon occurs, the resonance in the repeater becomes sufficiently small at a fixed operating frequency and make it difficult to improve the spatial freedom. To solve this problem, we apply an impedance matching method using simple switching circuits to the 6.78 RIC-WPT system with the repeater. Then we carry out experiments to verify the effectiveness of the impedance matching method. The experimental results show that the repeater improves the spatial freedom of the 6.78 MHz RIC-WPT regardless of the frequency splitting phenomenon.

DOI： 10.23919/EPE.2019.8915171

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© 2019 IEEE. The ability to charge to multiple receivers simultaneously with a single transmitter is one of the advantages of resonant inductive coupling wireless power transfer (RIC-WPT) technologies. However, in multiple-receiver RIC-WPT systems, each receiver often suffers from the magnetic coupling among receivers, i.e., cross-coupling. The cross-coupling not only complicates the control of the receivers but also significantly decreases the output power of each receiver. Hence, the purpose of this paper is to propose a compensation method of the influence due to the cross-coupling. To achieve this purpose, we first analyze the requirement to compensate for the influence of the cross-coupling. As a result, we reveal that it is necessary to control the phase of the current in all the receiver to be orthogonal to the phase of the transmitter current. Then, we propose the method to adjust the current phase of each receiver automatically to the desired phase by using only the phase information of the transmitter current, which results in the full compensation of the influence due to the cross-coupling. Furthermore, the proposed method also compensates for the influence of a detuning of the resonant frequency of each receiver due to the natural tolerance. Experiments of a two-receiver RIC-WPT system successfully verify the effectiveness of the proposed method.

DOI： 10.1109/ECCE.2019.8913279

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© 2019 IEEE. Switched reluctance motors (SRMs) is beneficial in excellent cost-effectiveness and high thermal tolerance owing to their simple mechanical construction free from permanent magnets. Nevertheless, application of SRMs to vehicular propulsion is often hindered by their comparatively large input current ripple and torque ripple. For mitigating the problem, the previous study has proposed a phase current waveform that eliminates both of these ripples under the magnetization below the magnetic saturation. However, this previous technique still suffers from significant torque and input current ripples at large output torque, which tends to cause the magnetic saturation. This paper proposes an improved phase current waveform that eliminates these ripples even at large output torque. This waveform was derived analytically based on the nonlinear magnetic model of the SRM. The proposed phase current waveform was successfully verified by the experiment, suggesting the usefulness of the proposed technique for applying SRMs to vehicular propulsion.

DOI： 10.1109/ECCE.2019.8912726

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© 2019 EPE Association. The resonant inductive coupling wireless power transfer (RIC-WPT) is a promising technique of the wireless power transfer with comparatively large power and high efficiency. However, the performance of RIC-WPT system is generally highly dependent on the fine adjustment of the resonant frequency between the transmitter, receiver, and repeater resonators, although the natural tolerance of the capacitor and inductance of the coil may easily lead to the significant detuning of the resonant frequency. Particularly, the repeater resonator is the key item that can improve the power transfer to a distantly located receiver resonator. However, the repeater resonator tends to have a high quality-factor; and therefore, its performance can be easily deteriorated by the detuning of the resonant frequency. The purpose of this paper is to propose a simple automatic resonant frequency tuning system for the repeater resonator as a remedy for the performance deterioration due to the resonant frequency detuning. The operation of the automatic resonant frequency tuning system was experimentally tested using the prototype wireless power transfer system. The result exhibited robust power transfer capability regardless of the natural tolerance of the resonant frequency.

DOI： 10.23919/EPE.2019.8914736

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© The Institution of Engineering and Technology 2019 Resonant inductive coupling wireless power transfer is widely known to be a possible convenient power supply method for the small mobile apparatus. However, the limited receiving-coil size tends to lower the efficiency and limit the output power owing to the small mutual inductance and comparatively large stray alternating current (AC) resistance of the receiving-coil. This study mitigates this issue by proposing a novel receiving-coil structure. This proposed structure comprises a coil and a drum core with a thin axis. The coil is wound on the axis to form a single winding layer. The proposed structure can reduce stray AC resistance by suppressing the proximity effect and reducing the wire length without deteriorating the mutual inductance significantly. Therefore, better efficiency and larger output power can be achieved. Simulations and experiments were performed to verify the proposed structure. Consequently, both simulations and experiments supported the reduction in AC resistance compared to the conventional structure. Furthermore, the experiment revealed improvements by the proposed structure in both efficiency and output power. These results support the effectiveness of the proposed structure for wireless power transfer to small mobile apparatus.

DOI： 10.1049/iet-pel.2018.5358

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© 2019 IEEE. Minimizing the transformer magnetizing inductance is essential for the soft switching operation of the LLC resonant converter, despite the fact that it results in higher values of magnetizing current, which deteriorates the converter efficiency. Furthermore, it is a well-known practice to utilize the transformer leakage as an inductive component in the resonant tank to improve the power destiny. This paper reveals that the transformer voltage gain can be improved when the transformer leakage inductance in concentrated on the secondary side to avoid the voltage drop inflicted by the relatively large value of the magnetizing current (im), especially at light load condition. The theoretical discussion relies on the asymmetry of the EI core by placing the secondary winding in a close contact with the magnetic core and placing the primary winding in the vicinity of the air gap. Moreover, noise absorber had been utilized to control the leakage inductance value. The proposed transformer design maximizes the value of the secondary leakage inductance and minimizes the primary leakage inductance. Alongside with the theoretical discussion, experimental tests had been conducted to evaluate the proposed method using a 390V-12V, 220W LLC resonant converter.

DOI： 10.1109/APEC.2019.8721980

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© 2019 IEEE. Resonant converters rely on a precise knowledge of leakage inductance of the equipped transformers. Resonant circuit topologies such as LLC usually utilize the transformer leakage as an inductive component in the resonant tank, allowing for a drastic reduction in the converter weight, size and volume. The existence of the secondary leakage inductance affects the whole operation of the LLC resonant converter. This paper reveals that placing the secondary winding near the air gap would increase the resonant tank input impedance, vertically shrink the voltage-gain curve of the converter, and consequently minimize the frequency range (i.e frequency bandwidth with respect to load variation). On contrary, placing the secondary winding in a close contact with the magnetic core would decrease the resonant tank input impedance, vertically stretches the voltage-gain curve of the converter, and widen the frequency variation range. It has been reported that the winding location with respect to the air gap has an impact on the leakage inductance value. In other words, placing the secondary winding in a close contact with the magnetic core (zero mmf position) would maximize the leakage energy storage originated from the secondary winding, and hence maximize the secondary leakage inductance and vice versa. The theoretical discussion is presented which is merely based on Ampere's law and Dowell's model. Furthermore, transformer prototypes had been constructed and tested in a 390V/12V-220W LLC converter prototype to evaluate the proposed analysis.

DOI： 10.1109/APEC.2019.8722190

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© 2019 IEEE. The Litz wire has been widely utilized as a wire with a low copper loss under high-frequency operation. However, design optimization of the Litz wire is difficult because this wire generally has a complicated structure of thin strands twisted in multiple levels, which hinders both of the analytical and numerical prediction of the copper loss. To overcome this issue, recent studies have proposed the analytical models of the copper loss in the bundle of twisted strands, which is the basic components constituting the Litz wire. This paper constructs a simple analytical copper loss model of the Litz wire based on these preceding insights. In addition to these insights, the proposed model further considers the effect of the inclination angle of the strands to the Litz wire on the proximity effect loss. The proposed model was tested in comparison with the experimentally measured AC resistance of commercially available Litz wires. As a result, the predicted AC resistance showed good agreement with the measured ac resistance, suggesting the effectiveness of the proposed model.

DOI： 10.1109/APEC.2019.8721827

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© 2019 The Korean Institute of Power Electronics (KIPE). The high-frequency transformers used for isolated DC-DC converters tend to have large volume compared with the other components. Therefore, increasing the power density of the transformer is indispensable for increasing the power density of the DC-DC converter. Reducing the dead space of the transformer is one of the effective solutions. It is well-known that the thinly extended core structure reduces the dead space around the transformer formed by the windings protruding to the outside of the core. However, it has not been clarified how much the thinly extended core structure affects the reducing power loss of the transformer. In this paper, the effect of introducing the thinly extended core structure into the transformer is quantified by the optimization of the convertible design parameters of the transformer with systematic round-robin calculation. The result revealed the volume reduction effect by the thinly extended core was greater than the simply dead space reduction effect.

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© 2019 IEEE. To estimate the core loss in SRMs, core loss estimation by equivalent circuit is preferable especially in the EV development because of its simple calculation. However, previously proposed models may limit applicable operating condition. These models refer instantaneous value, whereas hysteresis loop is a key factor to estimate core loss and the hysteresis loop directly associates with the history of magnetic flux. This paper focuses on the relation between the width of hysteresis loop and the peak to peak value of magnetic flux because the relation directly expresses the core loss. Therefore, the purpose of this paper is to propose a novel core loss model for equivalent circuit which estimates core loss in SRMs. This paper refers the peak to peak value of magnetic flux linkage and electrical angle. Along with the theoretical formulation of the model, this paper presents the model construction method. As a result, the proposed model successfully estimated core loss.

DOI： 10.1109/ICIT.2019.8754931

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© 2018 IEEE. Recent progress of the semiconductor switching devices enabled the high-frequency design of the switching power converters, which successfully led to the miniaturization of the circuit elements. However, the heat sink has scarcely been miniaturized during past decades. Now, the heat sinks are one of the major obstacles that hinder further size reduction of the switching power converters. Conventionally, the heat sinks are designed to have a number of flat aluminum fins extending from the aluminum base. However, these flat fins tend to make the laminar airflow passing through the fins. This laminar airflow keeps the air contacting the fin surface to remain on the surface. As a result, the fin surface is covered with the air already heated in the upstream and the fresh open air is prevented from contacting with the fin surface, thus deteriorating the cooling performance of the heat sinks. To overcome this issue, this paper proposes a heat sink structure with a novel fin geometry. The proposed fin geometry incorporates two sizes of the louvers, which are disposed to form a fractal-like pattern. These louvers are intended to break the laminar flow on the fin surface, thus promoting the mixing of the air to improve the cooling performance. FEM simulation of the heat transfer was carried out to verify this concept. The result showed improvement in the heat transfer coefficient, implying the effectiveness of the proposed structure for miniaturization of the heat sink.

DOI： 10.1109/INTLEC.2018.8612377

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In order to reduce copper loss, high step-down DC-DC converter often employs center-tapped rectifier. In addition, a plate shape one turn coil is utilized for transformer for making a high step-down ratio. We focused on the proximity effect in plate shape one turn coil, and investigate the cause of worsening the copper loss. In this paper, based on this investigation, we propose rectification method using winding integrated with rectifier. In addition, we discuss practical issues of the proposed method and present the solution strategy. The proposed method is verified by experiments, which suggests the effectiveness of the proposed method to high current applications.

DOI： 10.5416/jipe.45.121

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© 1972-2012 IEEE. Gallium-nitride-field-effect transistors (GaN-FETs) are promising switching devices with fast switching capability. However, they commonly have low gate threshold voltage, suffering from susceptibility to the false triggering. Particularly, the oscillatory false triggering, i.e., a self-sustaining repetitive false triggering, can occur after a fast switching, which is a severe obstacle for industrial applications. The purpose of this paper is to elucidate the design instruction for preventing this phenomenon. The oscillatory false triggering is known to be caused by the parasitic oscillator circuit formed of a GaN-FET, its parasitic capacitance and the parasitic inductance of the wiring. This paper analyzed the nonoscillatory condition of this oscillator. The result revealed an appropriate ratio between the gate-drain capacitance and the common-source inductance is a key to prevent the oscillatory false triggering. Experiment successfully verified this analysis result, supporting the effectiveness of the appropriate design of this ratio for preventing the oscillatory false triggering.

DOI： 10.1109/TIA.2018.2868272

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© 2018 IEEE. Litz wire is widely utilized for heating coils of the induction cookers to suppress the proximity effect. However, low space factor of the Litz wire often significantly increases the heating coil height, which may be an obstacle of wide-spread of the induction cookers. In order to overcome this problem, a preceding study has proposed a heating coil structure of the copper foil, which suppresses the proximity effect without using the Litz wire. The preceding study has proven effective suppression of the proximity effect, when the material to be heated is placed to cover the heating coil. However, this heating coil structure still suffers from large A C resistance, when the material to be heated does not exist or partially covers the heating coil. Furthermore, the ferrite walls, installed to suppress the proximity effect, need larger height than the coil, hindering effective reduction of the total heating coil height. The purpose of this paper is to propose an improved heating coil structure. The proposed heating coil structure further incorporates a thin layer of low-permeability soft-magnetic material covering the top of the coil. This layer enables elimination of the proximity effect regardless of the existence or the disposition of the material to be heated. Furthermore, this layer enables the ferrite walls to have the same height as the coil, thus further reducing the total heating coil height. The F E M based simulation was carried out to verify the operating principle of this structure. The result supported reduction of the heating coil height and effective suppression of the A C resistance regardless of the existence and the disposition of the material to be heated.

DOI： 10.1109/IECON.2018.8591462

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© 2018 IEEE. esonant inverters are widely utilized to generate high-frequency high voltage A C power for the power supply to the plasma generator. These inverters commonly require the load impedance to be inductive for achieving soft-switching operation. However, the impedance often fluctuates to be momentarily capacitive due to the unstable state of the plasma, thus causing enormous switching loss and possibly destroying the inverters. This paper addresses this difficulty by using a recently-proposed resonant inverter that can achieve soft-switching operation under the capacitive load impedance. For this purpose, this paper proposes a novel soft-switching controller for applying this inverter for plasma generator application. The proposed controller observes the load impedance and controls the resonant inverter according to the impedance value. Because of the high-frequency A C power supply to the plasma generator, the voltage and current measurement are difficult for estimation of the load impedance. Therefore, the proposed controller estimates the load impedance based on traveling and reflected wave measurement. The experiment revealed successful control of the inverter according to the load impedance, suggesting high feasibility for applying the inverter to the plasma generator.

DOI： 10.1109/IECON.2018.8592832

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© 2018 IEEE. Intermediate resonators (repeaters) of resonant inductive coupling wireless power transfer systems can improve the transmission distance as well as the output power. However, frequency bandwidths in which the repeater can operate effectively are very narrow because the repeater usually has a high quality-factor. Furthermore, these frequency bandwidths shift for the following two factors. The first factor is the intensity of the magnetic coupling between the repeater and the other resonator. The second factor is the variation in the natural resonance frequency of the resonators due to a production error, temperature characteristic, and aging degradation. Therefore, the repeater is not practical because the repeater requires accurate adjusting of the circuit parameters every time according to the various conditions. To address this problem, we propose an impedance matching method for the repeater. The proposed method can maximize the induced current in the repeater in wide frequency bandwidth regardless of the variations in the intensity of the magnetic coupling and the natural resonance frequency. Therefore, the proposed method can realize the repeater which can stably improve the performance of the wireless power transfer. Experiment and simulation successfully verified the effectiveness of the proposed method as well as the appropriateness of the theoretical analysis.

DOI： 10.1109/ECCE.2018.8557827

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© 2018 IEEE. Switched reluctance motors (SRMs) are attractive motors for electric vehicle propulsion because of their cost-effectiveness or robust structures. However, SRMs suffer from input current ripple and torque ripple. The authors have proposed derivation method of phase current profile which suppresses input current ripple and torque ripple and experimentally verified the suppression of both ripples. However, the rms value of derived phase current was much greater than square wave current, which is implemented widely, and increased copper loss. For the EV application, the rms value should be reduced. To break through the issue, the author addressed the characteristic that phase current profiles are shaped based on each reluctance profile, which is shaped by motor configuration, and noticed that phase current profile with low rms value may be derived by a novel rotor configuration. Therefore, this paper proposes a novel rotor configuration which can reduce the copper loss. The proposed rotor configuration is designed to satisfy the reluctance profile which is derived by previously proposed derivation method of phase current. This paper also presents the experiment for the evaluation of the reduction of copper loss.

DOI： 10.1109/ECCE.2018.8558173

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© 1972-2012 IEEE. Multiphase topologies are preferably employed in power conversion systems to lessen the per-phase circuit current, conduction losses, devices thermal stresses, and to reduce the output current ripples. A multiphase LLC resonant dc/dc converter usually possesses a number of magnetic cores equal to the number of phases. These magnetic cores are the major contributors to supply volume, weight, and size. For these reasons, circuit designers tend to select the topologies that have a minimal number of magnetic cores. In this paper, the authors aim to promote the industrial applications of the three-phase LLC resonant converter by integrating three transformers into a single commercially available magnetic core to reduce the volume, weight, and cost of the power converter. A comprehensive magnetic analysis for the three-phase-integrated transformer is conducted. Finite element method (FEM) simulation and experimental tests are carried out to validate the proper operation of the integrated transformer utilized in a 390-/12-V to 500-W prototype. Furthermore, the power losses distribution has been presented. The proposed integrated transformer has been proven effective, and it realized a uniform thermal distribution along the core compared to the three-discrete transformers.

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© 2018 EPE Association. Intermediate resonators (repeaters) for resonant inductive coupling wireless power transfer have been widely studied as a method of improving not only the transmission distance but also the output power. For the repeater to operate effectively, it is needed to induce a large current in the repeater to enhance the magnetic field far from a transmitting resonator. However, it is often difficult to induce a large current in the repeater due to frequency splitting phenomenon. This phenomenon easily occurs when the resonator having high quality factor such as the repeater is used. The frequency characteristic of the induced current in the repeater has multiple peaks when the frequency splitting phenomenon occurs. In addition, these multiple peaks shift according to slight variation in the parameters of the coil and the capacitor that constitute the resonator. This slight variation is easily caused by production error, temperature characteristic, and aging degradation of the coil and the capacitor. The induced current in the repeater is significantly decreased by the slight variation in the parameters, namely, the slight variation in the resonance frequency. Therefore, the repeater has low robustness against variation in the resonance frequency. To address these difficulties, we apply an auxiliary circuit to the repeater. The auxiliary circuit can dynamically adjust a phase of the induced current in the repeater, namely, the resonance frequency without complicated control. As a result, a large induced current can be maintained even if the frequencies corresponding to the peaks shift. Consequently, we can provide the repeater having a stable characteristic against the variation in the resonance frequency. The effectiveness of the repeater applied the auxiliary circuit and the appropriateness of analysis results are supported with simulation and experimental results.

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© 2018 EPE Association. Induction heating is the technique that heats the conductive material by high frequency large AC magnetic field. For efficient generation of the AC magnetic field, induction heating technique commonly utilizes the resonance between the heating coil and the resonating capacitor. The resonance is generally excited by applying the AC voltage of the resonant frequency. However, the resonant frequency is unstable because this frequency is susceptible to the disposition of the material to be heated. As a result, high efficiency high power induction heating system often suffers from unstable operation. This paper addresses this problem by proposing application of a simple automatic resonant frequency tuning circuit to the induction heating. This circuit can automatically achieve equivalent adjustment of the resonance frequency at the operating frequency without special control or the circuit sensing. In addition, this paper elucidated the control method of this tuning circuit to achieve the soft-switching operation in both of the inverter that drives the heating coil and the tuning circuit itself. The experiment revealed successful stabilization of the resonant frequency as well as satisfaction of the soft-switching condition both of the inverter and the tuning circuit, supporting effectiveness of the tuning circuit for induction heating.

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© 2018 IEEJ Industry Application Society. Intermediate resonator (repeater) in resonant inductive coupling wireless power transfer (RIC-WPT) systems can increase the transmission distance between the transmitting and receiving coils. The induced current in the repeater is easily affected by the frequency splitting phenomenon because the quality factor (Q-factor) of the repeater is generally as high as several hundreds. If this phenomenon occurs, induction of large current is often difficult in the repeater because the one peak characteristic of the induced current is no longer expected and the single peak of resonance splits into multiple peaks which shift the resonant frequency corresponding to the circuit parameters. In this paper, we approach this difficulty by applying an auxiliary circuit to the RIC-WPT system with the repeater. As a result, under the fixed operating frequency, the induced current in the repeater can be kept large even if the frequency splitting phenomenon occurs. The effectiveness of proposed system was supported by the simulation and experiment.

DOI： 10.23919/IPEC.2018.8507768

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© 2018 IEEJ Industry Application Society. Litz wire is commonly employed as the heating coil of induction cookers. In order to realize further low cost and profile, the solid wire with simple construction and high space factor is required. However, the solid wire is may suffer from the large copper loss increased by the skin and proximity effect. Then, the previous study proposed the novel coil structure, which can suppress these effects, only by the FEM simulation. Therefore, the purpose of this paper is to verify this structure experimentally in comparison with the Litz wire coil. The result revealed that the proposed structure can have similar AC resistance and the similar height with the same surface area and the same number of turns. Moreover, the experimental result showed a possibility to further height reduction by optimization of the magnetic and winding isolation design. Consequently, the experiment supported practical effectiveness of the proposed structure for induction heating.

DOI： 10.23919/IPEC.2018.8507826

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© 2018 IEEJ Industry Application Society. Resonant inductive coupling wireless power transfer (RIC-WPT) is the promising wireless power supply method to mobile applications. It is well-known that the efficiency and the power transfer capability of RIC-WPT systems deeply depend on the quality factor of the receiver-side resonator, which tends to decline by the conduction loss at rectifying diodes. Therefore, the synchronous rectification is one of the effective solutions. However, the unique characteristics of RIC-WPT, that is the weak magnetic coupling between the transmitter-side and the receiver-side resonator, tend to make the introduction of the synchronous rectification difficult. In order to address this issue, this paper newly proposes a self-driven synchronous rectifier controller suitable for RIC-WPT. This synchronous rectifier controller consists of basic analog elements and gate drivers, and no additional power supply is necessary for driving itself. In addition, the controller doesn't require any information from the transmitter-side resonator. Experiments successfully verified the operating principle as well as the efficiency improvement and clarified the usefulness of the synchronous rectifier with proposed controller for practical application of RIC-WPT.

DOI： 10.23919/IPEC.2018.8507636

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© 2018 IEEE. In multi-phase power conversion circuits, achieving an equalized current sharing between the paralleled modules is a challenge. Especially, in the LLC resonant converter topology, where the voltage gain is very sensitive to a minor change in the resonant tank parameters. In practical applications, the resonant tank parameters are never exactly identical among the phases, leading to unbalanced current sharing between the paralleled modules. This paper reviews the state of the art of current balance mechanisms proposed previously in the literature and revisits a newly proposed method to improve the current balance, which relies on a single balancing transformer connected in series with the paralleled resonant tanks. A comparison between the proposed method and connecting the three transformers in star is conducted. While evaluating the current balancing methods, the following sources of unbalance have been considered: a) resonant and magnetizing inductances b) resonant capacitors. c) on-resistances of the switching devices. d) propagation delay of the gate drivers.

DOI： 10.1109/ISIE.2018.8433827

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© 2018 IEEE. Switched reluctance motors (SRMs) are promising for propulsion motors of electric vehicles (EVs) because of their robust mechanical construction and cost effectiveness. However, practical application of SRMs to vehicular propulsion is hindered by comparatively large torque ripple and radial force ripple, which cause noise vibration and acoustic noise. Previous studies have proposed phase current profiles which suppress both ripples. However, in the derivation process of phase current, these previous studies need numerical calculation hindering the EV development speed. The purpose of this paper is to propose a novel phase current profile to suppress both the torque ripple and the radial force ripple of SRMs without numerical calculation. The profile can be straightforwardly calculated using a simple analytical model of the SRMs. In addition, the profile can be determined for any reluctance profiles of actual SRMs. Experiment was carried out to verify the proposed method. The result supported suppression of the torque ripple and the acoustic noise by the proposed method.

DOI： 10.1109/ISIE.2018.8433685

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© 2013 IEEE. Integrated magnetics is applied to replace the three-discrete transformers by a single core transformer in a three-phase LLC resonant converter. The magnetic circuit of the integrated transformer is analyzed to derive coupling factors between the phases; these coupling factors are intentionally minimized to realize the magnetic behavior of the three-discrete transformers, with the benefit of eliminating the dead space between them. However, in a practical design, the transformer parameters in a multiphase LLC resonant converter are never exactly identical among the phases, leading to unbalanced current sharing between the paralleled modules. In this regard, a current balancing method is proposed in this paper. The proposed method can improve the current sharing between the paralleled phases relying on a single balancing transformer, and its theory is based on Ampere's law, by forcing the sum of the three resonant currents to zero. Theoretically, if an ideal balancing transformer has been utilized, it would impose the same effect of connecting the integrated transformer in a solid star connection. However, as the core permeability of the balancing transformer is finite, the unbalanced current cannot be completely suppressed. Nonetheless, utilizing a single balancing transformer has an advantage over the star connection, as it keeps the interleaving structure simple which allows for traditional phase-shedding techniques, and it can be a solution for the other multiphase topologies where realizing a star connection is not feasible. Along with the theoretical discussion, simulation and experimental results are also presented to evaluate the proposed method considering various sources of the unbalance such as a mismatch in: 1) resonant and magnetizing inductances; 2) resonant capacitors; 3) transistor on-resistances of the MOSFETS; and 4) propagation delay of the gate drivers.

DOI： 10.1109/JESTPE.2017.2777508

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© The Institution of Engineering and Technology. In conventional arrangements of three-phase LLC converters, there are at least three magnetic components that occupy a considerable volume and mass of the power converter. Although, the three-phase LLC topology has many advantages over the single-phase one, circuit designers tend to select the single-phase topology because it has the minimal number of magnetic components. The purpose of this study is to reduce the number of the magnetic components of the three-phase topology, by integrating the three-discrete transformers into a single magnetic core, based on a theoretical framework. Lagrangian dynamics is applied to theoretically prove that it is possible to replace the three-discrete transformers by a single integrated transformer. The Lagrangian dynamics theory allowed us to derive a physically motivated model for the integrated transformer, in which each component of the integrated transformer has its own Lagrangian parameter. The Lagrangian model reveals that in a symmetrical design, there is no interphase coupling, and as a result the magnetic components can be downsized owing to the ac flux cancellation. Along with the theoretical discussion, the practical merits of implementing the integrated transformer is reported. Furthermore, the experimental tests are conducted utilizing a 500 W-390 V/12 V-200 kHz prototype.

DOI： 10.1049/iet-pel.2017.0485

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© 2017 IEEE. Series-Series (SS) and Series-Parallel (SP) topologies are widely utilized in practical resonant inductive coupling wireless power transfer (RIC-WPT) systems owing to their simple circuit configurations. Conventionally, design optimization of the circuit parameters of these topologies were investigated separately, because these topologies are expressed by different equivalent circuits. However, analysis of these equivalent circuits is generally complicated due to the multiple resonant modes contained in the operation, which may cause difficulty in comparing the performance between the SS and SP topologies after design optimization of these topologies. This difficulty may prevent elucidating the methodology to select an appropriate topology that offers better output power or efficiency after design optimization. The purpose of this paper is to suggest a selection methodology of the SS and SP topologies by elucidating a novel insight that these topologies have the quasi-duality relation, in which the SP topology works approximately as the dual of the SS topology. This insight enables to share the analysis results between the topologies. As a result, both of these topologies were found to be expressed by a same novel equivalent circuit. Furthermore, the only difference between the SS and SP topologies were found to be the equivalent load resistance of this equivalent circuit, thus reducing the topology selection into selection of preferable load resistance. The appropriateness of the quasi-duality relation and the resultant equivalent circuit was successfully confirmed by the simulation and the experiment.

DOI： 10.1109/PEDS.2017.8289248

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It is a common practice in the LLC resonant converter to utilise the transformer leakage inductance as an inductive component in the resonant tank. Nonetheless, the leakage does not exist only on the primary side but also on the secondary side. This Letter proposes a winding orientation method to minimise the undesirable secondary leakage in the transformer. The basic theory of the proposed method relies on Dowell's model and Ampere's law to minimise the stored magnetic energy originated from the secondary windings. Along with the theoretical analysis, experimental tests have been conducted to evaluate the proposed method. The measurements of the leakage inductance are consistent with the expectations of the proposed winding orientation method.

DOI： 10.1049/el.2017.4013

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© 2018 The Institute of Electrical Engineers of Japan. This paper proposes a novel control method to improve the responsiveness and the robustness of the boost DC-DC converter. The proposed control method is a feedback control incorporating a minor control that works to balance the input and output power. Experiment was carried out to verify the responsiveness and the robustness of the proposed control in comparison with the conventional voltage-mode and current-mode control. As a result, the proposed method revealed both of the fast response and the robust output voltage regulation against the load change.

DOI： 10.1541/ieejeiss.138.395

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© 2018 The Institute of Electrical Engineers of Japan. Recently, the dual transmitting resonator wireless power transfer system (DTR- WPT) has been proposed as a promising technique for the power supply of mobile apparatus. Although this technique has been reported to be effective for increasing the output power as well as for covering a wide area during wireless power transfer, the complicated magnetic coupling among two transmitting resonators and one receiving resonator makes it difficult to develop practical design optimization methods, thus hindering practical applications of this technique. The purpose of this paper is to propose a design optimization method for the load impedance of DTR- WPT. This method is derived based on a novel simple equivalent circuit model of the DTR- WPT. The optimum impedance derived using this method as well as the appropriateness of the equivalent circuit were verified experimentally, thus validating usefulness of the proposed method for the practical application of DTR- WPT.

DOI： 10.1541/ieejjia.7.49

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© 2017 IEEE. Three-phase power factor correction (PFC) converters have been widely utilized in industrial power applications to improve the power factor and reduce current harmonics in three-phase power grid. The PFC converters commonly incorporate large-sized inductors as a noise filter to suppress the noise emission to the grid. However, as many other power converters, the PFC converters are intensely required to achieve high power density by reducing the size of the inductors. The purpose of this paper is to propose a magnetic structure to miniaturize the inductors. The proposed magnetic structure consists of an integrated magnetic component and a three-phase common-mode choke. By integrating the inductors, the proposed magnetic structure can miniaturize the magnetic core volume, while keeping the saturation current level and the noise filtering capability unchanged. Experiment was carried out to evaluate the appropriateness of the proposed magnetic structure as well as possible volume reduction. As a result, 32.2% volume reduction was found in the proposed magnetic structure without deterioration of the filtering capability.

DOI： 10.1109/IECON.2017.8216165

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© 2017 IEEE. Recently, resonant inverters have been employed to generate high voltage high frequency AC power for plasma generator of the semiconductor processing equipment. This inverter is beneficial in low switching loss owing to its natural soft-switching capability under inductive load impedance. Generally, the resonant inverter for plasma generator is designed to have inductive load using an impedance matching circuit that interfaces the inverter and the plasma reactor. However, the load impedance often fluctuates according to the state of the plasma, momentarily causing the capacitive load impedance. In this case, the inverter is generally controlled to restrict the output power for circuit protection from excessive switching loss, although this will result in unstable plasma, deteriorating the quality of the semiconductor processing. This paper addressed this difficulty by applying a soft-switching technique to the resonant inverter. This soft-switching technique can be utilized regardless to the capacitive or inductive load. Experiment was carried out to evaluate the effectiveness of the proposed technique. As a result, the effective reduction of the switching loss was successfully verified even under the capacitive load impedance.

DOI： 10.1109/IECON.2017.8216264

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© 2017 IEEE. Resonant inductive coupling wireless power transfer (RIC-WPT) is attracting attention as a convenient power supply method to small mobile apparatus. The efficiency and the power transfer capability of RIC-WPT has been known to be profoundly dependent on the quality factor of the receiving resonator. However, the quality factor of the receiving resonator tends to be deteriorated because of the conduction loss at the diode rectifier, particularly for low output voltage applications. In order to improve the efficiency and the power transfer capability, this paper propose a novel simple synchronous rectifier, which can reduce the conduction loss. The proposed rectifier has simple circuit configuration, which contributes to straightforward application to the wireless power transfer to small mobile apparatus with limited installation space. Experiment was carried out to verify the operation principle of the proposed rectifier. As a result, the proposed rectifier revealed successful suppression of the conduction loss. In addition, the experimental wireless power transfer system verified successful improvement in the rectification efficiency, supporting usefulness of the proposed rectifier for practical applications of the RIC-WPT for small mobile apparatus.

DOI： 10.1109/INTLEC.2017.8214163

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© The Institution of Engineering and Technology. One of the main problems in electric vehicles is the volume of their electrical systems because their bulky components carry additional mass and high cost to the total system. On this topic, interleaving-phases and magnetic coupling techniques have been reported as effective methods for increasing the power density of the DC-DC converters that work between the storage unit and the motor inverter. In that sense, a volume assessment of these topologies would provide a better understanding of the problems to be faced when an electric power train is designed. In this paper, a volume modelling methodology is introduced with the purpose of comparing four different DC-DC converters: Single-Phase Boost, Two-Phase Interleaved with non-coupled inductors, Loosely Coupled Inductor (LCI), and Integrated Winding Coupled Inductor (IWCI). The analysis considers the volume of magnetic components, power devices (conventional and next-generation), cooling devices and capacitors. The methodology can be used as a part of an optimization procedure to minimize the volume of DC-DC converters. Conclusively, LCI and IWCI were found effective to miniaturize power converters with a power density of 8.4 W/cc and 9.66 W/cc, respectively. Moreover, a maximum efficiency of 98.04% and 97.61% was obtained for a 1kW LCI and IWCI prototypes, respectively.

DOI： 10.1049/iet-pel.2017.0157

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© 2017 Assigned jointly to the European Power Electronics and Drives Association & the Institute of Electrical and Electronics Engineers (IEEE). Parallel-connected windings are widely utilized for power transformers to reduce the copper loss. However, this reduction effect is often hindered by the proximity effect, which causes concentrated current distribution in parallel-connected windings. This paper addresses this issue by proposing a design optimization method of winding turn allocation among winding layers. This optimization method is based on the recently proposed insight on the proximity effect, referred to as the extremum co-energy principle. Experiment on a planar transformer with four primary winding layers was carried out to verify the proposed method. As a result, the proposed method successfully optimized the allocation of the winding turns to minimize the AC resistance.

DOI： 10.23919/EPE17ECCEEurope.2017.8099115

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© assigned jointly to the European Power Electronics and Drives Association & the Institute of Electrical and Electronics Engineers (IEEE). In the LLC resonant converter,the transformer core is usually gapped to realize the designed value of magnetizing inductance that allows for soft switching. The air gap length which is in a scale of millimeters may be affected by the humidity and long working hours of the ferrite material, resulting into a variation of the core permeability. Moreover, a slight variation of the transformer core permeability may be encountered with any possible change in the core temperature. In a proper transformer design, the transformer shall operate with an optimum value of effective permeability where the sum of both copper and core losses is minimal. In this paper, the transformer optimal design is presented. Moreover, the influence of the permeability on the transformer's copper and core losses is revealed. Furthermore, with the help of newly derived equations, the effect of the transformer's effective permeability on the LLC converter conduction turn-on and turn-off losses is reported. Along with the theoretical discussion,the analysis is supported with simulation and experimental results utilizing a 250W 200kHz prototype.

DOI： 10.23919/EPE17ECCEEurope.2017.8099301

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© 2017 IEEE. GaN- FETs are attractive switching devices for their fast switching capability. However, they often suffer from the oscillatory false triggering, i.e. a series of self-sustaining repetitive false triggering induced after a fast switching. The purpose of this paper is to derive a design instruction to prevent this phenomenon. According to the previous study, the oscillatory false triggering was found to be caused by a parasitic oscillator circuit formed of a GaN- FET, its parasitic capacitance, and the parasitic inductance of the wiring. This paper analyzed the oscillatory condition to elucidate the design requirement to prevent the oscillatory false triggering. As a result, balancing the gate-drain parasitic capacitance and the common source inductance to achieve an appropriate ratio was found to be essential for preventing the oscillatory false triggering. Experiment successfully supported prevention of this phenomenon by balancing these two factors.

DOI： 10.1109/ECCE.2017.8095811

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© 2017 IEEE. SiC-MOSFETs have attracting increasing attention because of their outstanding characteristics that contributes to high efficiency and high power density of power converters. However, compared to conventional Si-IGBTs, SiC-MOSFETs are susceptible to false triggering, because they tend to generate large switching noise due to ultrafast switching capability and have a lower threshold voltage in high temperature operation. Particularly, disastrous oscillation of repetitive false triggering can occur after a fast turn-off, which is the severe issue for practical application of SiC-MOSFETs. The purpose of this paper is to give an instruction to avoid this phenomenon. This paper hypothesized that the repetitive false triggering is the parasitic oscillation caused by parasitic capacitance of SiC-MOSFET, and parasitic inductance of wiring. Based on this hypothesis, this paper analyzed the oscillatory condition of the parasitic oscillator to propose a design instruction to avoid the oscillatory false triggering. The result revealed that the parasitic inductance of the gate, drain, and source wiring should be designed so that the resonance frequency of the parasitic LC resonator in the gating circuit is far apart from that of the power circuit. This paper also presents experimental results that support appropriateness of the proposed design instruction.

DOI： 10.1109/ECCE.2017.8096861

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© 2017 IEEE. In conventional arrangements of three-phase LLC converters, there are at least three magnetic components that occupy a considerable volume and mass of the power converter. Although, the three-phase LLC topology has many advantages over the single-phase one, circuit designers tend to select the singlephase topology because it has a minimal number of magnetic components. In this paper, with the purpose of promoting the industrial applications of the three-phase topology, Lagrangian dynamics is applied to theoretically prove that it is possible to replace the three-discrete transformers by a single integrated transformer. The Lagrangian dynamics theory allowed us to derive a physically motivated model for the integrated transformer, in which each component of the integrated transformer has its own Lagrangian parameter. The remarkable result to emerge from the Lagrangian model is that in a symmetrical design, there is no interphase coupling; this is regardless of the value of the coupling coefficient between the phases. This means that there is no return path for the three ac fluxes, and as a result the magnetic components can be downsized. Therefore, the major advantages of using integrated magnetics in the LLC converter can be concluded as: cost-reduction, reduced weight, and realizing higher power density. Along with the theoretical discussion, experimental validation is provided utilizing a 500W - 390V/12V - 200kHz prototype.

DOI： 10.1109/ECCE.2017.8096668

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© 1982-2012 IEEE. Recent progress of widebandgap semiconductor switching devices enabled extremely high-frequency operation of power converters owing to their ultrafast switching capability. Fast switching may cause large switching noise at the common source inductance, which may increase the switching loss and lead to false triggering. Therefore, measurement of the common source inductance is often intensely required in practical design of fast switching power converters. However, measurement of the common source inductance is difficult, because 1) the wiring path hidden beneath the molded package significantly contributes to this inductance, 2) the mutual inductance between the gating circuit and the power circuit also contributes to this inductance, and 3) this inductance cannot be defined as the stray inductance of a loop wiring path. These difficulties are addressed in this paper by proposing a novel measurement method of the common source inductance. The proposed method is applicable to already-mounted power circuits. In addition, the proposed method offers a straightforward measurement procedure with common instruments, such as a signal generator, an oscilloscope, and voltage and current probes. Along with the measurement principle, this paper also presents an experiment to evaluate the proposed method.

DOI： 10.1109/TIE.2017.2694411

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© 2017 IEEE. The common source inductance is one of the major causes of deterioration of the switching speed and susceptibility of the false triggering for semiconductor switching devices. Practical design of this inductance requires selection of an appropriate semiconductor package because this inductance is greatly dependent on the physical package structure. However, few studies have reported a list of the common source inductance of commercially available packages. In order to list and compare the common source inductance among typical semiconductor packages, this paper carried out measurement of this inductance of actual switching devices mounted on experimental PCBs. This paper employed a recently proposed straightforward measurement technique directly applicable to switching devices mounted on PCBs. As a result, a basic database of the common source inductance of typical packages was presented. The common source inductance was found to be determined mainly by the package type. However, in TO-247 and TO-220 packages, approximately one-third of the total common source inductance was found to possibly vary among the switching devices of the same package due to the dependence on the current rating. Investigation of the physical package structure implied that this dependence was caused by the stray inductance of the bonding wires connecting the semiconductor chip to the source terminal.

DOI： 10.1109/IFEEC.2017.7992207

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© 2017 IEEE. A non-isolated high step-up DC-DC converter with coupled inductor is developed for large voltage gain applications such as electric mobility and renewable energies. This converter combines the concepts of magnetic integration and interleaving phases that are effective for downsizing of power converters. The developed converter offers a good performance of voltage gain vs. converter size, because, compared with the conventional two-phase interleaved boost converter, it only needs the addition of two diodes and one winding. Nevertheless, in order to describe the design method of the developed high step-up converter, the coupled inductor characterization is required. Therefore, the current ripple characterization of the coupled inductor is analyzed and evaluated in this paper. A 100W prototype is constructed and experimental results are provided to verify the characterization analysis.

DOI： 10.1109/IFEEC.2017.7992192

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© 2017 IEEE. This paper proposes a simple control technique for switched reluctance motors to eliminate both the source current ripple and the torque ripple simultaneously. The proposed control is a current tracking control based on a pre-computed magnetic flux profile. This profile is derived using a simple analytical SRM model without the magnetic saturation. Conventionally, the magnetic saturation is commonly utilized for limiting excessive magnetic flux induction to improve the torque output. However, in the proposed control, the magnetic flux profile is utilized for limiting the magnetic flux by control. By controlling without the magnetic saturation, elimination of the source current ripple and the torque ripple can be achieved regardless to the output power. Along with theoretical derivation of the magnetic flux profile, an experiment is carried out to evaluate the proposed control. The results revealed suppression of the source current ripple and the torque ripple simultaneously in comparison with the conventional square-wave current control.

DOI： 10.1109/APEC.2017.7931146

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© 2017 IEEE. The aim of this work is to present a novel topology of a three-phase LLC converter with integrated magnetics. The converter operation and the comprehensive theoretical analysis are presented; this analysis follows the first harmonic approximation (FHA) approach to simplify the system model. Usually, LLC converter achieves zero voltage switching (ZVS) as long as it working in the inductive region. Therefore, the turn off losses are considered as the main source of the switching losses in the converter. In this paper the design in optimized to minimize the switching losses. On the other hand, adapting three discrete transformer cores in this topology will definitely increase the size and volume of the converter. As a result, a novel magnetic integration concept is introduced where all magnetic components of the three-phases are advantageously combined into a single magnetic core to increase the converter power density. Finally, the experimental results are presented to verify the optimized design by showing a reduction in the turn-off losses and the effectiveness of adapting the proposed integrated transformer, in which an increment of 56% in the power density of the converter could be attained.

DOI： 10.1109/APEC.2017.7930712

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© 2016 The Institute of Electrical Engineers of Japan. Inductor winding is often composed as parallel-connected wires to suppress the copper loss. However, in high frequency inductors, the proximity effect can cause concentrated AC current distribution, hindering suppression of the copper loss. Therefore, optimization of the physical inductor structure requires predicting the AC current distribution. Although simulators are commonly employed for predicting the AC current distribution, simple analytical methods are also required for effective design or invention of the inductor structure with less copper loss. The purpose of this paper is to propose a novel analysis method of the AC current distribution in parallel-connected wires of high frequency inductors. The proposed method is based on a novel insight that the AC current is distributed to give an extremum of the magnetic co-energy contributed by the AC flux and the AC current under the given total AC current. Experiments are presented in this paper to verify the proposed method.

DOI： 10.1541/ieejjia.7.35

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© 2016 The Institute of Electrical Engineers of Japan. Resonant inductive coupling wireless power transfer (RIC-WPT) is attractive as a convenient power supply method to small mobile apparatus. However, limited size of the receiving coil can limit the efficiency and the power transfer capability. This paper addresses this difficulty by proposing a novel receiving coil structure. The proposed structure has a coil wound on a drum core with a thin axis. The top and the bottom of the drum core has large surface area to effectively collect the magnetic flux for large mutual inductance. In addition, the thin axis can reduce the wire length, thus reducing the parasitic AC resistance. The AC resistance is further reduced by suppressing the proximity effect. Simulation supported probable improvement in the efficiency as well as the power transfer capability. In addition, experiment verified that the proposed structure improved the efficiency by 66% and the power transfer capability by 109%.

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© 2016 The Institute of Electrical Engineers of Japan. Litz wire has been widely utilized for heating coils of high frequency induction cookers. However, these coils often suffer from large winding height due to low space factor of Litz wire. Certainly, rectangular wire may reduce the winding height of the coil owing to its high space factor. However, the rectangular wire tends to suffer from large copper loss caused by the skin effect and the proximity effect. In the conventional coil structure of the rectangular wire, these effects cause concentrated AC current distribution, which leads to excessive copper loss. This paper addresses this issue by proposing a novel heating coil structure of the rectangular wire that can homogenize the AC current distribution. This paper also presents the simulation results that successfully verified the effectiveness of the proposed structure.

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Heat island intensity approaches the maximum during urban Phase A period, which constitutes a few hours around sunset when radiative cooling primarily determines the temperature decrease. To evaluate the thermal inertia of urban and rural canopy layer, we suggested a local effective thermal inertia (LETI) that corresponds to a canopy layer thermal inertia, excluding advection effects caused by such as heat island circulation, and estimated the value by observing a 30-min temperature variation and radiation flux when clouds appeared during night. The urban area LETI is approximately two times higher than the rural value. LETI has a close relationship to the cooling rate in Phase A and is an important value for urban canopy layer thermal inertia.

DOI： 10.2151/sola.2017-011

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© 2016 IEEE. The Dowell model is widely utilized for copper loss analysis of forward transformers. However, this model is not directly applicable to transformers with parallel-connected windings. The reason is that the Dowell model requires determining the AC current of all the windings in advance of analysis, although the AC current distribution in parallel-connected windings is severely affected by disposition of the windings. This issue is addressed in this paper by employing the Dowell model in combination with a novel insight that the AC current is distributed in parallel-connected windings to give an extremum of the magnetic co-energy of the transformer. Simulation and experiment were carried out; and, the results supported appropriateness of the proposed copper loss analysis method.

DOI： 10.1109/IECON.2016.7793013

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© 2016 IEEE. Switched reluctance motors (SRMs) are expected to be applied to propulsion systems of electric vehicles for their robust mechanical construction and cost-effectiveness. On the other hand, their large source current ripple and large torque ripple are main obstacles in practical applications of SRMs to vehicle propulsion. Certainly, a number of studies have been dedicated to address the torque ripple. However, unlike other motors driven by sinusoidal phase current waveforms, the large source current ripple of SRMs generally remains, even if the torque ripple is removed. The purpose of this paper is to propose a simple control technique of SRMs for vehicular propulsion by eliminating the source current ripple as well as the torque ripple. The proposed control is a current tracking control based on a pre-computed current profile. Because vehicular propulsion requires to instantaneously output large torque in sudden acceleration, SRMs tend to be designed to be propelled below the magnetic saturation in normal vehicle travel. Therefore, this proposed current profile is derived using a simple SRM analytical model without the magnetic saturation. In addition, the proposed current profile is determined so that the peak magnetic flux is minimized to offer high-speed current response at a high rotating velocity. Along with theoretical derivation of the proposed control, this paper also presents an experiment to verify the principle of the proposed control technique, which successfully revealed reduction of both the source current ripple and the torque ripple.

DOI： 10.1109/IECON.2016.7793324

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© The Institution of Engineering and Technology 2016. Series-series (SS) topology and series-parallel (SP) topology of the electric-field coupling wireless power transfer system are widely utilised for practical applications. However, selecting the appropriate circuit topology, which maximise the output power by design optimisation, is often difficult, because these circuit topologies are generally analysed using different circuit models. This difficulty by analysing novel equivalent circuits for SS and SP topologies is addressed. As a result, the output power of SP topology is found to be approximated by that in SS topology with transformed load impedance. This result can offer a simple strategy for topology selection as well as design optimisation.

DOI： 10.1049/el.2016.1253

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© 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. Gallium nitride field-effect transistors (GaN-FETs) are attractive devices because of its low on-state resistance and fast switching capability. However, they can suffer from false triggering caused by fast switching. Particularly, a disastrous oscillation of repetitive false triggering can occur after a turn-off, which may deteriorate the reliability of power converters. To address this issue, we give a design guideline to prevent this phenomenon. We analyze a simple circuit model to derive the condition of occurrence of this phenomenon, which is then verified experimentally. Results show that the parasitic inductance of the gating circuit, Lg, and that of the decoupling circuit, Ld, should be designed so that the LC resonance frequency of Lg and the gate–source capacitance of the GaN-FET does not coincide with that of Ld and the drain–source capacitance, respectively. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

DOI： 10.1002/tee.22339

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© 2016 IEEE and EPE Association. This paper proposes a novel analysis method for the dual transmitting resonators wireless power transfer (DTR-WPT) system. The DTR-WPT is attractive for its higher efficiency and greater power transfer capability compared with the conventional single transmitting resonator wireless power transfer (STR-WPT) system. However, analytical understanding of the DTR-WPT is difficult due to its complicated operating principle caused by two transmitting resonators and a receiving resonator, which are all magnetically coupled each other. Therefore, practical applications of the DTR-WPT may be hindered by difficulty in establishing a design optimization method and a control scheme. This difficulty is addressed in this paper by proposing a novel simple equivalent circuit model of the DTR-WPT. Lagrangian dynamics is employed to derive this model. Brief analysis of this model showed improvement in the efficiency and the power transfer capability by the DTR-WPT compared with the conventional STR-WPT. In addition, the power transfer of the DTR-WPT system was found to be expressed by the same equivalent circuit model as the STR-WPT system. Therefore, similar design optimization methods and similar control schemes as for the STR-WPT are applicable to the DTR-WPT. Along with the theory, this paper presents experiments that verified appropriateness of the proposed model as well as the analysis results based on this model.

DOI： 10.1109/EPE.2016.7695439

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© 2015 IEEE. Nowadays, high power density has become essential in networking, telecommunications and computing applications. Additionally, the electronic equipment used in these applications requires a very-low voltage feeding even when its power supply has a much higher voltage rating. Therefore, high step-down converters with high power density performance are required for these applications. Consequently, a novel two-phase interleaved high step-down converter is proposed in order to fulfill the requirements of high power density and high step-down conversion ratio of these applications. The proposed converter addresses the objective by a particular coupled inductor where three windings are only installed in one core. As a result, the proposed converter can achieve higher step-down ratio than the conventional topologies by adding a winding and two switches to the interleaved two phase buck converter, besides the coupled-inductor configuration. In this paper, the novel topology is introduced and analyzed in order to find its conversion ratio operation. Then, the proposed topology is compared to conventional topologies and some improved high step-down converters recently proposed. Finally, the proposed converter is experimentally validated and the results revealed that the proposed converter shows higher step-down conversion ratio than the conventional buck converter with a further increment of 40% in the conversion ratio when the converter is operating at a duty cycle of 30% and ratio of turns of 2.

DOI： 10.1109/INTLEC.2015.7572421

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© 2015 IEEE. Communication relay stations often suffer from common-mode noise generated by high speed switching in a boost chopper equipped for power supply. This problem can be addressed by applying soft-switching techniques to the boost chopper, although this can lead to significant increase in the circuit volume. To address this difficulty, this paper proposes a novel passive regenerative turn-off snubber applicable to the two-phase interleaved boost chopper. The proposed snubber can add small circuit volume because it is implementable only by two diodes and a capacitor. Experiments are carried out to verify the operating principles of the proposed snubber. The results successfully verified suppression of the rising speed of the drain voltage at the turn-off in both of the phases without apparent deterioration of the efficiency.

DOI： 10.1109/INTLEC.2015.7572341

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© 2016 IEEE. A number of analytical models for switched reluctance motors have been proposed to promote development of control techniques that can alleviate the torque and source current ripples. However, these models can suffer from a large database of the nonlinearity as well as complicated derivation process of the torque and the voltage-current relation. The purpose of this paper is to propose a simple practical behavior model with small database and straightforward derivation of the torque and the voltage-current relation. The proposed model has a simple database of the magnetic energy as a matrix. The flux linkage and the electrical angle are chosen as the state variables. Along with theoretical formulation of the model, this paper presents a practical method of the model construction. In addition, experiments successfully predicted both torque and current waveforms, supporting appropriateness of the proposed model.

DOI： 10.1109/IPEMC.2016.7512270

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© 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. This paper proposes a novel method for deriving dual converters, namely deriving current-source converters from voltage-source counterparts, and vice versa. The conventional derivation method is based on the transformation of circuit topology, in which series connections are converted into parallel connections, and vice versa. However, this method cannot be directly applied to nonplanar circuits because they do not allow perfect topological transformation, although many of them are known to have duals. Lagrangian dynamics does not depend on the topological relation to transform a system into another equivalent system; therefore, it possibly avoids problems related to topological transformation and may provide a universal and systematic method that can be consistently applied to nonplanar circuits. This paper discusses the derivation of duals using Lagrangian dynamics. Along with the theory, this paper presents two examples of Lagrangian derivation of duals. One derives a dual of a planar circuit, to which the topological transformation is applicable. The other derives two duals of a nonplanar circuit. Consequently, these examples suggest that the proposed method is a prospective candidate for universal and systematic derivation of duals. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

DOI： 10.1002/tee.22270

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© 2016 The Institute of Electrical Engineers of Japan. Integrated magnetic components for interleaved converters have been developed in order to fulfill the demand for high power density and high efficiency in power conversion systems. The close-coupled inductor and the loosely coupled inductor methods for interleaved converters are well known as attractive techniques to downsize magnetic components or improve the power conversion efficiency. Moreover, the integrated winding coupled inductor has already been proposed. However, the advantages of the interleaved converter with the integrated winding coupled inductor over the other methods have not been fully elucidated. Consequently, this paper analyzes and evaluates the integrated winding coupled inductor, specifically, the characteristics of the inductor ripple current and the magnetic flux in the core. The analysis shows that the integrated winding coupled inductor provides attractive features compared with the other methods. The effectiveness of the integrated winding coupled inductor is discussed from theoretical and experimental points of view.

DOI： 10.1541/ieejjia.5.276

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：METEOROLOGICAL SOC JAPAN  

© 2016, the Meteorological Society of Japan. Detailed observations of temperature evolution are required to clarify the mechanism of the nocturnal evolution of urban heat island. We conducted spatial and temporal high-density observation of temperature and longwave radiation in Kyoto City, Japan. The results suggest that the time evolution associated with temperature phase shift is one type of urban heat island evolution. Moreover, the phase shift appears to be closely related to a change in wind direction. Two phases, before and after the phase shift, are suggested to be controlled by two different mechanisms: radiative cooling and advection.

DOI： 10.2151/sola.2016-011

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© 2016 IEEE. Recently, Electric Vehicles (EVs) have required high power density and high efficiency systems in order to save energy and costs. Specifically, in the DC-DC converter that feeds the non-propulsive loads in these vehicles, where the output voltage is much lower than the one of the energy storage unit. Therefore, the output current becomes quite high, and the efficiency and power density are reduced due to the high current ratings. Furthermore, magnetic components usually are the biggest contributors to the mass and volume in these converters. This paper proposes a Three-phase LLC resonant converter with one integrated transformer where all the windings of the three independent transformers are installed into only one core. Using this technique, a high reduction in the core size and thereby an increment in the power density and a reduction of the production cost are obtained. In addition, this integrated transformer is intended to be applied in the novel Three-phase LLC resonant converter with Star connection that is expected to offer reduction of the imbalanced output current, which is produced by tolerances between the phase components. Finally, the proposed converter with the novel integrated transformer is discussed and evaluated from the experimental point of view. As a result, a 70% reduction in the mass of the magnetic cores was achieved.

DOI： 10.1109/ECCE.2016.7855520

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© 2015 The Institution of Engineering and Technology. Practical applications of switched reluctance motors (SRMs) require control techniques that can solve large torque ripple and large current ripple in power supply. To promote development of these techniques, a simple Lagrangian formulation for flux-based nonlinear SRM models is proposed. This formulation can be analysed in combination with Lagrangian circuit models of motor drivers. The properness of the formulation is supported by an example of the analysis of the operation of a simple SRM driving system.

DOI： 10.1049/el.2015.0950

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© 2015 IEEE. This paper describes mid-range electrical resonance wireless power transfer in kHz range. Wireless power transfer using electrical field is minor since this method is understood only for close-range applications. However, our experimental units, the resonance frequency of which is 85 kHz, achieved 180 mm distance power transmission by vector network analyzer (VNA) measurement while keeping peak efficiency 68 %. In case of frequency response analyzer (FRA) measurement, the units can transfer power the most to the load at 300 mm but the efficiency is low. The closer the distance between the units, the better the efficiency is.

DOI： 10.1109/ECCE.2015.7310109

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© 2015 IEEE. This paper proposes a novel non-isolated high step-up converter suitable for miniaturization by high frequency design. High step-up converters with voltage multipliers are promising for high frequency design because many of them can be free from coupled inductors or transformers, which may lower the voltage gain due to the leakage inductance or may cause significant AC conduction loss in the primary winding. However, two issues can still hinder further miniaturization. One is that many multiplier stages may be needed to achieve extremely high voltage gain. The other is that high switching frequency may be restricted by severe turn-off voltage surge caused by high speed switching. The proposed converter addresses the former by applying a recently reported technique to a non-isolated boost converter. Additionally, the converter addresses the latter by proposing a simple passive regenerative turn-off snubber implementable only by two diodes and a capacitor. Experiments verified that the proposed converter achieves high voltage gain with fewer voltage multiplier stages compared to prior non-isolated high step-up converters. Additionally, the snubber successfully reduced the turn-off surge into half approximately without apparent deterioration of the efficiency.

DOI： 10.1109/ECCE.2015.7309679

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© 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. Electric-field coupling wireless power transfer has been commonly analyzed using the circuit model. However, the circuit behavior of this model is not necessarily apparent because their resonant modes can be far complicated than the basic LC oscillation. This issue is addressed in this paper by proposing a novel equivalent circuit for a basic wireless power transfer system. This equivalent circuit has a simpler topology than the conventional circuit model. Furthermore, the equivalent circuit allows intuitive understanding of three types of the resonant modes. Along with theoretical derivation of the proposed equivalent circuit, this paper also presents simulation results, which verified the appropriateness of the equivalent circuit.

DOI： 10.1002/tee.22180

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© 2015 Korean Institute of Power Electronics. High step-up converters are widely used in sustainable energy systems and recently used in automotive applications due to their high voltage gain capability. Nevertheless, with the purpose of obtaining a higher voltage gain, in comparison with conventional boost converters, current high step-up converters often employ additional multiplier cells, which may lead to significant cost-up and low power density. Therefore, a novel two-phase interleaved high step-up converter is proposed in order to minimize additional circuit volume used to achieve large voltage gain. The proposed converter addresses the purpose by a particular coupled inductor where three windings are installed in one or two cores. As a result, the proposed converter can achieve higher voltage gain than the conventional topologies by adding a winding and two diodes to the interleaved two phase boost chopper, besides the coupled-inductor configuration. This paper evaluates two arrangements of the coupled-inductor configuration of the proposed high step-up converter: 1. Three windings integrated in only one core and 2. Two independent inductors with a shared winding. The result revealed that the proposed converter shows higher voltage gain than the normal boost converter and the magnetic integration in the coupled-inductor configuration further increases the voltage gain by 20%.

DOI： 10.1109/ICPE.2015.7168088

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

© 1972-2012 IEEE. Recently, Lagrangian dynamics have been applied to transforming integrated magnetic components into equivalent circuits of transformers and inductors. This Lagrangian method is expected to yield an equivalent circuit with few components, when applied to an integrated magnetic component with few flux paths that can be magnetized independently. However, properness of this method has not been verified. As a case study, this paper derives the equivalent circuit of the integrated winding coupled inductor using the Lagrangian method to evaluate consistency with the magnetic circuit model and experimental behavior. As a result, the Lagrangian method yielded a simpler equivalent circuit than those by the conventional methods. Additionally, the equivalent circuit of the Lagrangian method is found to be functionally equivalent to the magnetic circuit model and consistent with the experiment. These results support that the Lagrangian method provides proper equivalent circuits and is useful for deriving simple equivalent circuits in some cases.

DOI： 10.1109/TIA.2014.2330071

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© 2015 The Institute of Electrical Engineers of Japan. The integration of differential-mode (DM) and common-mode (CM) inductors onto a single core has been expected to miniaturize EMC filters. On the other hand, this technique possibly leads to lower tolerance to magnetic saturation caused by the DC flux, hindering the miniaturization effect due to integration. Particularly, this problem seems to be exacerbated in the previously reported magnetic structure. The reason may lie in the fact that this conventional structure tends to induce a large DC flux because its equivalent number of turns for the DM inductance is restricted to only half of the total number of turns. This paper addresses this problem by proposing a novel structure that assigns more turns to the DM inductance to suppress the DC flux more effectively. A theoretical analysis and experiments verified that the proposed structure is equivalent to series-connected DM and CM inductors. Additionally, an analytical estimation revealed that the proposed structure reduced the core volume by 41% compared to the conventional structure for the same wire length. These results demonstrate effectiveness of the proposed structure for miniaturizing EMC filters.

DOI： 10.1541/ieejjia.4.166

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© 2015 The Institute of Electrical Engineers of Japan. Sliding-mode control for power converters is gaining significant research interest for achieving a fast transient response to a step load change in a wide operating range. However, power converters also require better dynamic load regulation against load current fluctuations slower than the step change. This paper addresses this issue by deriving a novel control method for synchronous buck converters using Lagrangian dynamics. Simulation results verified improvement in dynamic load regulation against slow sinusoidal load current fluctuations.

DOI： 10.1541/ieejjia.4.728

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© 2015 IEEE. High step-up DC-DC converters are widely used in many industrial appliances and recently introduced in renewable energy systems and automotive applications due to their high voltage gain capability. Nevertheless, current high step-up converters often employ additional circuitry with the purpose of increasing the voltage gain. Consequently, the converter will be bulky, heavy and expensive, because the use of these additional passive and active components influences the power density and the cost of the whole application. Therefore, the well-known techniques of interleaving phases and magnetic coupling are applied in a novel high step-up converter with the purpose of helping tackle these problems. Using these techniques, high voltage gain and reduction of circuit elements can be achieved. In this paper, the operating principle of this converter is summarized and the voltage gain is analyzed. Moreover, the analyzed topology is compared with several outstanding high step-up converters recently proposed that use the concept of interleaving phases and magnetic coupling. Finally, the analyzed converter was experimentally tested and the effectiveness in terms of higher voltage gain and number of components than the current topologies is validated.

DOI： 10.1109/ICRERA.2015.7418524

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© 2014 IEEE. The DC magnetization is one of the common causes of operational faults in forward DC-DC converters because it may promote magnetic saturation in the transformers. A useful remedy is to detect the DC magnetization using a sensor and eliminate it by a controller. The purpose of this paper is to propose a simple but reliable sensor. Although a number of sensors have been proposed in prior works, they often suffer from complicated implementation or from influence of the load current on the sensor output. The proposed method, on the other hand, can be implemented only by a search coil equipped on the power transformer without adding any special physical structure except a through-hole on the core. Despite of the simple implementation, the method is not affected by the load current and can detect the DC magnetization before apparent magnetic saturation occurs. This paper also presents an experiment, which verified that the load current does not affect the sensor output and that the DC magnetization can be detected even under the flux density below the saturation level. These results support usefulness of the proposed sensor in practical applications.

DOI： 10.1109/ECCE.2014.6953909

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This paper proposes a novel soft-switching boost chopper with a lossless LC snubber, suitable for improving the efficiency of the electric propulsion system of vehicles. The snubber circuit is beneficial owing to the following features: zero-current switching turn-on and zero-voltage switching turn-off are achieved regardless of the operating conditions; it requires only one additional switch with smaller current rating compared to the main switch; the additional switch can be controlled by basic arithmetic; and the main switch is free from additional voltage or current stress caused by the soft-switching operation. Along with theoretical discussions, experimental results are also presented on the circuit behavior and the resulting improvement of the energy conversion efficiency. These results show the usefulness of the chopper for improving the efficiency of electric vehicles. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

DOI： 10.1002/tee.21972

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Institute of Power Electronics  

In order to downsize the storage unit of Hybrid Electric Vehicles, a novel high step-up interleaved boost converter has been proposed. This converter is suitable for automotive applications due to its expected high voltage gain. However, the actual voltage conversion ratio may be significantly reduced by the parasitic resistance effect of the circuit because the input current tends to be large at a high step-up operation and therefore the voltage drop at the parasitic resistance may not be ignorable. This paper analyzes the effect of the parasitic resistance on the voltage gain and evaluates the result experimentally. Consequently, it is found that parasitic resistance affects the voltage gain largely as the ratio of the number of turns in the integrated magnetic component of the proposed converter increases and particularly when the duty cycle is larger than 0.5.

DOI： 10.5416/jipe.40.93

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Integrating differential-mode (DM) and common-mode (CM) inductors onto a single core has been expected to miniaturize EMI filters. However, the previously-reported magnetic structure often suffers from saturation by DC current, hindering miniaturization by integration. This problem seems exacerbated by the fact that this conventional structure tends to induce large DC flux because its equivalent number of turns for the DM inductance is restricted to only half of the total number of turns. This paper addresses the problem by proposing a novel structure that assigns more turns to the DM inductance to suppress the DC flux more effectively. This paper confirmed theoretically and experimentally that the proposed structure is equivalent to series-connected DM and CM inductors. Additionally, analytical estimation revealed that the proposed structure reduced core volume by 41% compared to the conventional structure under the same amount of copper. These results suggest effectiveness of the proposed structure for miniaturizing EMI filters. © 2014 IEEE.

DOI： 10.1109/IPEC.2014.6869598

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Environmental issues related to global warming and resources dryness, increase the global concern for reducing the energy consumption using high efficiency and high power density systems. Therefore, home energy management systems (HEMS) deal with these problems by monitoring and controlling the power consumption of home electronics. However, expanding of human living space increases intense requirements to downsize electronic systems. In order to enhance HEMS and optimize the household living space, this paper shows the design and power loss analysis of a high power density DC-DC converter capable to achieve high efficiency with low weight and low volume components. This converter, developed for home electronics and electric vehicles, uses a novel magnetic coupling technique capable to reduce the size of magnetic components and of the converter itself. As a result, a 1 kW interleaved boost converter with integrated winding coupled inductors (IWCI) was designed and experimentally validated obtaining a volumetric power density of 145 cc/kW. © 2014 IEEE.

DOI： 10.1109/IGBSG.2014.6835247

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A new core structure is proposed to improve the saturation property of an inductor made of iron powder core. In the conventional structure made of a single core material, converging flux lines cause local magnetic saturation at the inner side of the corners of the magnetic path. Therefore, the conventional inductor shows worse saturation property than expected from its core material. This degradation mechanism is solved in the proposed core structure through homogenization of the flux distribution at the corners. Experiments are performed to evaluate the flux homogenization and improvement of the saturation property. Results show a homogenized flux distribution in the proposed core structure. Furthermore, the flux level improved by 28% while the inductance decreased by 40% of its initial value. Both these results are consistent with theoretical expectations, except that a larger improvement is found in the experiment compared to the 16% improvement predicted by numerical calculation. © 2013 Institute of Electrical Engineers of Japan.

DOI： 10.1002/tee.21908

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The integrated magnetic component for interleaved converters has been developed in order to satisfy the demand for high power density of converters. The close-coupled inductor method and the loosely coupled inductor method are well known as techniques that can achieve downsizing of magnetic components. As another approach, the integrated winding coupled inductor has already been proposed. However, the advantages of interleaved converter with the integrated winding coupled inductor have yet to be elucidated fully as compared with the other methods. Therefore, characteristics of inductor ripple current and magnetic flux in the core for the integrated winding coupled inductor are analyzed and evaluated in this paper. As a result of the analysis, integrated winding coupled inductor method provides three attractive features as compared with loosely coupled inductor. The effectiveness of the integrated winding coupled inductor is discussed from theoretical and experimental point of view. © 2013 IEEE.

DOI： 10.1109/ECCE.2013.6647191

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Recently Lagrangian dynamics has been applied to transforming integrated magnetic components into equivalent circuits of basic magnetic components such as transformers and inductors. Although the method is beneficial in simple and systematic derivation in many cases, it sometimes leads to different circuits from those by conventional methods. Hence, the Lagrangian method needs equivalence evaluation of transformation. As a case study, this paper derives equivalent circuits of the integrated winding coupled inductor using the Lagrangian method and a conventional method. The equivalent circuits are investigated to verify their consistency with magnetic circuit model and experimental behavior. As a result, the Lagrangian method yields a simpler circuit than that by the conventional method. Nonetheless, both circuits are found functionally equivalent to the magnetic circuit model and consistent with the experiment. The result suggests that the Lagrangian method provides proper transformation and is useful for deriving simple equivalent circuits. © 2013 IEEE.

DOI： 10.1109/ECCE.2013.6646742

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A generalized Lagrangian is proposed to enable systematic analysis of integrated magnetic components. Although a few conventional theories are known that handle magnetic circuit, they cause difficulties in modeling or analysis, especially when applied to a highly integrated core. These difficulties are avoided in the proposed theory, as its Lagrangian is configurable directly from the physical core structure. As an example, the Lagrangian of the trans-linked three-phase boost converter is presented. Along with the Lagrangian, two types of circuit analysis are also presented: one is to obtain the state-space model of the converter; the other is to translate the integrated magnetic component into an equivalent circuit of basic components such as transformers and inductors. The analyses show the usefulness of the proposed method in practical applications. © 2012 Institute of Electrical Engineers of Japan.

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A simple directional pyrgeometer is tested and compared with a conventional standard pyrgeometer. The system presented in this article has a narrow directional response and points to the representative zenith angle of 52.5°. Because of its directional response, it can be used in a street canyon or in a forest provided that a small part of the sky is visible at the representative angle. The system can be assembled using inexpensive parts that are widely used in household appliances. As this system does not have a flat spectral sensitivity, a spectral correction method is also presented. The results show that the output of the new system agrees well with that from a conventional pyrgeometer (Kipp & Zonen CG3). The correlation coefficient is 0.995 and the standard deviation is 5.6 W m-2 for 1-h averaged values. © 2009 American Meteorological Society.

DOI： 10.1175/2008JTECHA1076.1

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We newly developed a technique of radiation thermometry using a Sony's consumer digital camcorder. Our system is not only convenience and cost effective but with a better performance than previous infrared thermometers, particularly in the place like a crater of volcano where is abundant in gas. This is because our system uses the submicron wavelength band, in which radiation is less influenced by absorption of gas than in the thermal infrared wavelength (>3 μm). We carried out observations of red glow at Aso volcano and succeeded in measuring the temperature of about 800°C, which is much more acceptable than previously reported values of 200-400°C. When we measure the temperature of about 300-700°C and 600-900°C in the place where is abundant in gas, using the camcorder with the near-infrared and with the visible wavelength mode is better than the thermal infrared region, respectively. Copy right © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences; TERRAPUB.

DOI： 10.1186/bf03352550

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Event date： 2021

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Event date： 2021

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Event date： 2021

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Event date： 2021

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Event date： 2021

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Event date： 2021

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Event date： 2020.9.1

Language：Japanese  

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Event date： 2020

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Event date： 2020

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Event date： 2020

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Event date： 2020

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Event date： 2020

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Event date： 2020

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Event date： 2019.12.6

Language：Japanese  

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Event date： 2019.12.6

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Other Link： http://id.ndl.go.jp/bib/030192971

Event date： 2019.8.3

Language：Japanese  

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Event date： 2019.6.1

Language：Japanese  

Our laboratory focuses on a variety of electric power systems based on power electronics and super conductivity. Further details are found on our laboratory's Web-site (http://www.ec.okayama-u.ac.jp/~epc/).

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Event date： 2019

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Event date： 2019

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Event date： 2019

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Event date： 2019

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Event date： 2019

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Event date： 2019

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Event date： 2018.6.16

Language：English  

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Event date： 2018

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Event date： 2018

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Event date： 2017.9.22

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Event date： 2017.9.22

Language：Japanese  

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Other Link： http://id.ndl.go.jp/bib/028595492

Event date： 2017

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Event date： 2017

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Event date： 2016.12.3

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Event date： 2016.9.2 - 2016.9.4

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Event date： 2016.8.31 - 2016.9.3

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Event date： 2016.8.30 - 2016.9.1

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Event date： 2016.8.30 - 2016.9.1

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Event date： 2016.8.30 - 2016.9.1

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Event date： 2016.8.30 - 2016.9.1

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Event date： 2016.8.30 - 2016.9.1

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Event date： 2016.8.30 - 2016.9.1

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Event date： 2016.8.30 - 2016.9.1

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Event date： 2016.8.30 - 2016.9.1

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Event date： 2016.1.1

Language：Japanese  

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Event date： 2016

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Event date： 2016

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Event date： 2015.12.19

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Event date： 2015.10.29

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Event date： 2015.10.29

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Event date： 2015.9.2 - 2015.9.4

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Event date： 2015.9.2 - 2015.9.4

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Event date： 2015.9.2 - 2015.9.4

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Event date： 2015.9.2 - 2015.9.4

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Event date： 2015.9.2 - 2015.9.4

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Event date： 2015.7.6

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Event date： 2015

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Event date： 2015

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Event date： 2014.10.31

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Event date： 2013.8.28 - 2013.8.30

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Event date： 2012.8.21 - 2012.8.23

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Event date： 2011.9.21 - 2011.9.22

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Event date： 2011.9.6 - 2011.9.8

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Event date： 2011

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Event date： 2010.8.24 - 2010.8.26

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Event date： 2009.5.28 - 2009.5.31

Language：Japanese  

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Event date： 2009

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Event date： 2007.10.14 - 2007.10.16

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Event date： 2007.10.14 - 2007.10.16

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Event date： 2007.10.14 - 2007.10.16

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Event date： 2007.8.6 - 2007.8.8

Language：Japanese  

High density observations of the air temperature and the long wave radiation were done in Kyoto city for two years. Clear heat islands were observed in clear nights while no air temperature difference between the urban area and the rural area was observed in the daytime. The analysis shows that the main cause of the heat island in Kyoto city is a high thermal inertia in the urban area. The anthropogenic heat release has little effect. An object with small thermal inertia is expected to have high surface temperature under the sunshine, but the surface temperature of the rural area does not show high temperature comparing with that in urban area. The possible reason is also presented.

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Event date： 2007

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Event date： 2007

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Event date： 2006.4.30

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Event date： 2006.4.30

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Event date： 2006.4.30

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Event date： 2006.4.30

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Event date： 2006.4.30

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Event date： 2006.4.30

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Event date： 2006

Language：Japanese  

身の回りの素材を利用して気象観測用の装置を製作し,京都市内の気温分布を高密度に測定した。観測機器は通常の気象観測機器と比べて一桁安く,高校生でも製作可能である。これを用いて京都市内約40点での同時連続観測を行い明瞭なヒートアイランド現象を確認した。さらに,ヒートアイランド強度が最大になる時刻は,一般に言われている夜明け前ではなく日没後であること,また,雲の出現によって夜間の郊外では気温が一時的に上昇することなど,これまで知られていなかった現象を発見した。これらのことから,京都のヒートアイランド現象には人口廃熱より,都市部のビルなどによる熱容量の増加が大きく効いていることがわかった。

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Event date： 2005.5.15

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Event date： 2005.5.15

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Event date： 2005.5.15

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Event date： 2005.5.15

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Event date： 2005.5.15

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Event date： 2005

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Event date： 2004.5.16

Language：Japanese  

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Applicant：パナソニックIPマネジメント株式会社

Application no：特願2018-194552  Date applied：2018.10.15

Announcement no：特開2020-064722  Date announced：2020.4.23

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Applicant：株式会社デンソー

Application no：特願2014-192967  Date applied：2014.9.22

Announcement no：特開2016-067071  Date announced：2016.4.28

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Applicant：株式会社デンソー

Application no：特願2014-188864  Date applied：2014.9.17

Announcement no：特開2016-063596  Date announced：2016.4.25

Patent/Registration no：特許第6303947号  Date registered：2018.3.16 

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Applicant：株式会社デンソー

Application no：特願2014-188864  Date applied：2014.9.17

Announcement no：特開2016-063596  Date announced：2016.4.25

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Applicant：株式会社デンソー

Application no：特願2014-166688  Date applied：2014.8.19

Announcement no：特開2016-046819  Date announced：2016.4.4

Patent/Registration no：特許第6172088号  Date registered：2017.7.14 

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Applicant：株式会社デンソー

Application no：特願2014-166688  Date applied：2014.8.19

Announcement no：特開2016-046819  Date announced：2016.4.4

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Applicant：株式会社デンソー

Application no：特願2014-140436  Date applied：2014.7.8

Announcement no：特開2016-018882  Date announced：2016.2.1

Patent/Registration no：特許第6464582号  Date registered：2019.1.18 

2016-18882

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Applicant：株式会社デンソー

Application no：特願2014-140436  Date applied：2014.7.8

Announcement no：特開2016-018882  Date announced：2016.2.1

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Applicant：株式会社デンソー

Application no：特願2014-114861  Date applied：2014.6.3

Announcement no：特開2015-230904  Date announced：2015.12.21

Patent/Registration no：特許第6318874号  Date registered：2018.4.13 

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Applicant：株式会社デンソー

Application no：特願2014-114861  Date applied：2014.6.3

Announcement no：特開2015-230904  Date announced：2015.12.21

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Applicant：株式会社デンソー

Application no：特願2014-078622  Date applied：2014.4.7

Announcement no：特開2015-201942  Date announced：2015.11.12

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Applicant：株式会社デンソー

Application no：特願2014-077068  Date applied：2014.4.3

Announcement no：特開2015-008622  Date announced：2015.1.15

Patent/Registration no：特許第6052221号  Date registered：2016.12.9 

2015-142482

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Applicant：株式会社デンソー

Application no：特願2014-077068  Date applied：2014.4.3

Announcement no：特開2015-008622  Date announced：2015.1.15

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Applicant：株式会社デンソー

Application no：特願2014-015605  Date applied：2014.1.30

Announcement no：特開2015-142482  Date announced：2015.8.3

Patent/Registration no：特許第6213268号  Date registered：2017.9.29 

2012-70485

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Applicant：株式会社デンソー

Application no：特願2014-015605  Date applied：2014.1.30

Announcement no：特開2015-142482  Date announced：2015.8.3

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Applicant：株式会社デンソー

Application no：特願2014-003350  Date applied：2014.1.10

Announcement no：特開2015-133378  Date announced：2015.7.23

Patent/Registration no：特許第5983637号  Date registered：2016.8.12 

2015-133378

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Applicant：株式会社デンソー

Application no：特願2014-003350  Date applied：2014.1.10

Announcement no：特開2015-133378  Date announced：2015.7.23

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Applicant：株式会社デンソー

Application no：特願2013-084937  Date applied：2013.4.15

Announcement no：特開2014-207373  Date announced：2014.10.30

Patent/Registration no：特許第5790700号  Date registered：2015.8.14 

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Applicant：株式会社デンソー

Application no：特願2013-084937  Date applied：2013.4.15

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Applicant：株式会社デンソー

Application no：特願2013-059959  Date applied：2013.3.22

Announcement no：特開2014-187479  Date announced：2014.10.2

Patent/Registration no：特許第5733330号  Date registered：2015.4.24 

2013-201883

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Applicant：株式会社デンソー

Application no：特願2013-059959  Date applied：2013.3.22

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Applicant：株式会社デンソー

Application no：特願2013-018642  Date applied：2013.2.1

Announcement no：特開2014-150183  Date announced：2014.8.21

Patent/Registration no：特許第5783191号  Date registered：2015.7.31 

2014-150183

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Applicant：株式会社デンソー

Application no：特願2013-018642  Date applied：2013.2.1

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Applicant：株式会社デンソー

Application no：特願2013-014480  Date applied：2013.1.29

Announcement no：特開2014-147224  Date announced：2014.8.14

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Applicant：株式会社デンソー

Application no：特願2013-008080  Date applied：2013.1.21

Announcement no：特開2014-140263  Date announced：2014.7.31

Patent/Registration no：特許第5838977号  Date registered：2015.11.20 

2014-140263

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Applicant：株式会社デンソー

Application no：特願2013-008080  Date applied：2013.1.21

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Applicant：株式会社デンソー

Application no：特願2013-005569  Date applied：2013.1.16

Announcement no：特開2014-138479  Date announced：2014.7.28

Patent/Registration no：特許第5803946号  Date registered：2015.9.11 

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Application no：特願2013-005569  Date applied：2013.1.16

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Applicant：株式会社デンソー

Application no：特願2012-284933  Date applied：2012.12.27

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Patent/Registration no：特許第5561352号  Date registered：2014.6.20 

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Applicant：株式会社デンソー

Application no：特願2012-284933  Date applied：2012.12.27

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Applicant：株式会社デンソー

Application no：特願2012-222164  Date applied：2012.10.4

Announcement no：特開2014-075275  Date announced：2014.4.24

Patent/Registration no：特許第5751453号  Date registered：2015.5.29 

2014-75275

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Applicant：株式会社デンソー

Application no：特願2012-222164  Date applied：2012.10.4

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Applicant：株式会社デンソー

Application no：特願2011-277164  Date applied：2011.12.19

Announcement no：特開2013-127709  Date announced：2013.6.27

Patent/Registration no：特許第5664536号  Date registered：2014.12.19 

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Applicant：株式会社デンソー

Application no：特願2011-277165  Date applied：2011.12.19

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Patent/Registration no：特許第6008079号  Date registered：2016.9.23 

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Applicant：株式会社デンソー

Application no：特願2011-277165  Date applied：2011.12.19

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Applicant：株式会社デンソー

Application no：特願2011-277164  Date applied：2011.12.19