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DOI： 10.1109/access.2022.3232843

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DOI： 10.1109/access.2023.3236105

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DOI： 10.1109/icems56177.2022.9983187

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DOI： 10.1109/iecon49645.2022.9968536

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DOI： 10.1109/iecon49645.2022.9968604

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DOI： 10.1109/ecce50734.2022.9948010

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DOI： 10.1109/ecce50734.2022.9948211

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DOI： 10.1109/ecce50734.2022.9947959

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DOI： 10.1109/icem51905.2022.9910903

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

In recent years, there has been growing demand for flat electrical machines in order to minimize system size while also maintaining high efficiency. In general, axial flux machines (AFMs) are more suitable for flat form than radial flux machines (RFMs). AFMs usually employ a soft magnetic composite (SMC) for the stator core, and their efficiency can be improved by employing an SMC that has low iron loss. However, this reduces the average torque because there is generally a tradeoff relationship between iron loss and magnetic permeability in SMCs. This article, therefore, proposes an AFM with a coreless rotor structure in which the torque performance is not easily affected by the permeability of the SMC. This article aims to reveal the ideal SMC characteristics for high efficiency in AFMs. First, many virtual SMC materials with different iron loss and permeability are used for simulations of AFMs in order to investigate sensitivity to material properties. The simulations by virtual SMCs take into account the experimental increase in the iron loss. As a result, guidelines for developing SMCs are constructed based on the experimental results. Finally, prototype AFMs employing new SMCs developed by following the guidelines are shown, and it is found that they offer higher efficiency in all operating area than conventional AFMs. In particular, one prototype achieves an extremely high efficiency of over 96% at 6000 r/min, 0.8 Nm in experiments.

DOI： 10.1109/TIA.2022.3154336

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DOI： 10.1109/ecce47101.2021.9595816

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

Permanent magnet synchronous motors for electric vehicles should meet three criteria: high maximum torque, high efficiency at low torque, and constant output in a wide speed range. However, meeting these criteria has come with a trade-off in terms of the magnitude of the field magnetic flux. We propose a consequent-pole-PM-type axial-gap motor with ferrite PMs and field windings, which has structure variable field magnetic flux. In order to examine the operational characteristics of the proposed motor, we produced and tested a prototype. Experimental results show that the proposed structure meets all of the three criteria above.

DOI： 10.1109/TIA.2021.3084549

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

This article consists of two important topics regarding variable flux memory motors (VFMMs). The first topic is magnetization characteristic analysis of VFMMs having a double-layer permanent magnet (PM). Two-dimensional simulations are executed to clarify relationship between magnetization characteristic and ratio of the double-layer PM. In addition, a prototype of a compact size VFMM is fabricated, and experiments are also carried out to investigate accuracy of magnetization characteristic analysis. The second topic is the proposed VFMM employing double-layer delta-type PM arrangements and extended flux barriers for traction applications. Conventional VFMMs have three critical issues, which are as follows: asymmetric positive and negative magnetizing current pulses, increase in the iron loss due to harmonics caused by demagnetized variable flux PMs (VPMs), and unintentional demagnetization of VPMs under load condition. The proposed VFMM can overcome the abovementioned problems by employing double-layer delta-type PM arrangements and extended flux barriers. In addition, the proposed VFMM achieves much higher efficiency than that of the target motor mounted in TOYOTA Prius fourth-generation over a wide operating range.

DOI： 10.1109/TIA.2021.3068329

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

This study investigates the relationship between filter inductor impedance and dimensional resonance of MnZn ferrite. Experimental results clarify that multiple factors affect inductor impedance resonances. These can be classified into three factors: the inherent characteristics of a magnetic material, self-resonance due to winding stray capacitance, and winding that acts as a distributed constant line. Next, based on the measurement results, the dimensional dependencies of complex permeabilities (dimensional resonance) and the influence of dimensional resonance on inductor impedance are discussed in detail. Finally, this study verifies that the influence of dimensional resonance on complex permeability can be mitigated, and filter inductor impedance can be increased in the high frequency range by core lamination. All experiments are performed using off-the-shelf magnetic core products.

DOI： 10.1002/eej.23302

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This paper describes the methods for improving the performance of an active common-noise canceler (ACC) that suppresses the common-mode (CM) voltage generated by inverters. Whereas the already proposed ACC (ACC0) compatible with space vector pulse width modulation requires two emitter follower circuits, this paper proposes an improved ACC (ACC1) that requires a single emitter follower. In addition, an ACC (ACC2) that improves the CM voltage suppression performance by adding a feedback circuit to ACC1 is also proposed. The experimental results show that ACC1 improved the CM voltage attenuation by -10 dB compared to ACC0, and ACC2 improved the CM voltage attenuation by -20 dB compared to ACC1. ACC2 has a large CM voltage attenuation of up to -53 dB in the wide frequency range from 100 kHz to 5 MHz.

DOI： 10.1002/ecj.12305

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NdFeB permanent magnets (Nd-PM) can achieve a coercivity of up to 21 kOe without dysprosium due to the development of manufacturing technology. However, due to the high-temperature operation characteristics of vehicle traction motors, Nd-PM over 25kOe is mainly applied. In this paper, 21kOe Nd-PM and 5.5kOe ferrite-PM (Fe-PM) are simultaneously applied, and a hybrid PM motor (HPMM) suitable for environmental temperature conditions of vehicle traction motors is proposed. HPMM is divided into serial configuration and parallel configuration according to the arrangement of each PM. This paper compares the pros and cons of each configuration and presents rotor structures that can improve demagnetization durability and torque characteristics. After comparing the performance characteristics of each rotor structure through 2D-FEM, finally, an HPMM suitable for vehicle traction motors is proposed. Also, the proposed HPMM shows the same torque and power density as the traction motor of TOYOTA PRIUS 4th-generation hybrid electric vehicle (HEV), the target motor. At the same time, the proposed HPMM reduced the usage of Nd-PM by 47% and the total PM cost by 10% compared to the target motor.

DOI： 10.1109/iemdc47953.2021.9449493

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INST ELECTRICAL ENGINEERS JAPAN  

This paper proposes a 2.5 MHz high-frequency output inverter based on a frequency multiplying technique with a multi-core transformer using Mn-Zn ferrite materials. The upper limit of the operation frequency for these materials is lower than the output frequency of 2.5 MHz. First, the operation principle of the proposed circuit is explained. Second, a difficulty of using Mn-Zn for transformers at the frequency of 2.5 MHz is discussed. Third, a numerical analysis shows that the proposed circuit can output the frequency over the upper limit of the operation frequency of Mn-Zn ferrite. Finally, through continuous operation, where the proposed circuit outputs approximately 650 W, it is experimentally confirmed that Mn-Zn ferrite can be used without large iron loss at the output frequency of 2.5 MHz. Thus, the proposed circuit can overcome the difficulty of using Mn-Zn for transformers at the frequency of 2.5 MHz.

DOI： 10.1541/ieejjia.20010411

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In recent years, more than half of the electric power generated in the country is being consumed by motors. Therefore, high performance motors are desired especially for industrial applications. In addition, it is desirable to reduce motor size. Recently, motors called axial gap type have been proposed and researched to achieve both high torque and small size. Axial gap motors are generally suitable for applications requiring flat shape such as a disk. Conventional axial gap motors frequently employ Nd sintered permanent magnets (PMs) to achieve high torque. However, axial gap motors with Nd sintered PMs are not very efficient at high rotational speed due to the eddy current loss arising in the PM. Axial gap motors that use ferrite PMs have also been proposed, but torque density is low. In this paper, an axial gap motor using Nd bonded PMs is proposed to achieve high efficiency in the high-speed and high-torque region. The proposed axial gap motor using Nd bonded PM is compared with other axial gap motors employing Nd sintered PM and ferrite PM through 3D-FEA and experiments. Consequently, it was found that the Nd bonded PM is more effective in enhancing the efficiency of an axial gap motor in the high-speed and high-torque region, compared with Nd sintered PM and ferrite PM.

DOI： 10.1541/ieejjia.20004135

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Researches on more electric aircraft (MEA) are actively conducted. It is necessary for realizing MEA to meet aircraft application requirements: high ability, high availability, and high-power density, while aiming to reduce weight and environmental impact. For example, interior permanent magnet synchronous motors (IPMSMs) are expected to be used for aircraft applications of MEA, because IPMSMs can achieve both high-power density and high efficiency at high speed and high torque area compared to other types such as induction motors. In general, IPMSMs with concentrated winding structure are available to utilize limited space effectively. Rectangular windings allow high winding factor and realizing more high-power density motors, whereas eddy current loss in rectangular windings is much higher than that in round windings. In this paper, high-power density concentrated winding IPMSMs that employ rectangular windings are discussed. We have examined three improvements for a reduction of the eddy current loss in the rectangular windings to attain continuous operation with high-power density in this motor. In order to reduce the eddy current loss in the windings situated in front of the rotor, we adopted an asymmetric toot-htip. Moreover, an adequate groove shape between tooth and stator yoke allows to reduce the eddy current loss in stator yoke side windings. Windings, which have optimized unequal cross-sectional area, offer to reduce whole winding loss. Finally, we present a proposed motor employing the three improvements.

DOI： 10.1109/ICIT46573.2021.9453692

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High frequency transformers are used for isolated power converters such as LLC resonant converters since a leakage inductance of the transformer can be utilized as a part of a resonant inductance in addition to electrical isolation. In order to perform ZVS, the leakage inductance of a transformer is designed so that the current phase flowing in switching devices and Q factor of the resonant circuit are appropriate values. However, it is usually difficult to fabricate properly windings, while managing the leakage inductance precisely. In addition, it is necessary to suppress the stray capacitance which flows leading phase current to switching devices. This paper proposes a high frequency transformer with an adjustable leakage inductance and stray capacitance by only changing the thickness and height of the wire guides.

DOI： 10.23919/ICEMS50442.2020.9291023

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To reduce radiated electromagnetic interference (EMI) in a motor drive system with long power cables, it is necessary to suppress both high-frequency (HF) input- and output-side common-mode (CM) current. In a DC-fed motor drive system, due to stray capacitance between power devices and heat sink, it is difficult to suppress both HF DC- and AC-side CM current by using only the conventional AC-side passive EMI filter. In this paper, the authors investigate how to suppress both HF DC- and AC-side CM currents on a DC-fed motor drive system. To achieve the above purpose, the DC-fed motor drive system based on SiC-MOSFET is constructed and DC- and AC-side CM currents are measured and evaluated for each filter condition.

DOI： 10.23919/ICEMS50442.2020.9290991

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

DOI： 10.1109/iecon43393.2020.9254504

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DOI： 10.1109/ecce44975.2020.9236419

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

This article introduces the operational characteristics of an ultra-high-speed bearingless motor with 2-pole concentrated motor windings and 4-pole concentrated suspension windings. Experiments with a prototype machine indicate that iron loss is the largest component of losses in the proposed bearingless motor. Therefore, in order to reduce the iron loss, comparison of the experimental results and the 3D-FEM results is discussed. As a result, because it is turned out that iron loss of the switching frequency component accounts for a large proportion in total iron loss, a method of enhancing efficiency of the proposed bearingless motor by means of high switching frequency using SiC-MOSFET is examined. The experimental results with the examined method show that the prototype machine can attain the high efficiency of 94.3% at rated operation of 1.70 kW and 100,000 r/min in spite of including suspension input power for magnetic levitation. In addition, operational characteristics comparison of the bearingless motor at switching frequency of 40 kHz, 80 kHz and 120 kHz is discussed in detail.

DOI： 10.1109/TIA.2020.2986453

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In recent years, electric motors having flat shape are desired in order to minimize system size as well as enhancing the efficiency. Therefore, axial gap motors (AGMs) have attracted significant attention because they can achieve higher torque density in flat shape than that of conventional radial gap motors (RGMs). In general, AGMs employ the soft magnetic composite (SMC) for the stator core since they have three dimensional magnetic paths unlike RGMs. If AGMs employ the SMC which has low iron loss characteristic, the efficiency can be improved. On the other hand, the average torque is decreased because the SMC basically has tradeoff-relationship between the iron loss characteristic and the permeability. Hence, in this research, an AGM having coreless rotor structure that torque performance is not easily affected by the permeability of the SMC is proposed. In this paper, many virtual SMC materials which have different iron loss and permeability are considered for the proposed AGM employing the coreless rotor structure. Finally, suitable SMC characteristic to enhance the efficiency over a wide operating range is revealed by three-dimensional finite element analysis (3D-FEA).

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Language：Japanese   Publisher：The Institute of Electrical Engineers of Japan  

<p>Inverters using SiC or GaN power devices can achieve high frequency and high efficiency operation. To achieve high efficiency, the switching characteristics of these power devices are important because stray inductances in the main circuit of the inverter have a strong influence on the switching characteristics. To reduce switching loss and surge voltage, minimization of stray inductance in the main circuit is required for a high-frequency PWM inverter. This paper describes design guidelines for high-frequency inverters that achieve low inductance. The PCB design guideline on a thick multilayer PCB is derived from the inductance calculation using 3D-FEA. It is shown experimentally that the stray inductance of the designed PCB can be reduced to the same level as the inductance inside the power devices. Experimental results verify that a prototype can achieve high-speed switching and suppress a surge voltage. A load test is demonstrated to evaluate the main circuit efficiency in a half-bridge inverter at 100kHz.</p>

DOI： 10.1541/ieejias.140.89

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Language：Japanese   Publisher：The Institute of Electrical Engineers of Japan  

<p>This study investigates the relationship between filter inductor impedance and dimensional resonance of MnZn ferrite. Experimental results clarify that multiple factors affect inductor impedance resonances. These can be classified into three factors: the inherent characteristics of a magnetic material, self-resonance due to winding stray capacitance, and winding that acts as a distributed constant line. Next, based on the measurement results, the dimensional dependencies of complex permeabilities (dimensional resonance) and the influence of dimensional resonance on inductor impedance are discussed in detail. Finally, this study verifies that the influence of dimensional resonance on complex permeability can be mitigated, and filter inductor impedance can be increased in the high frequency range by core lamination. All experiments are performed using off-the-shelf magnetic core products.</p>

DOI： 10.1541/ieejias.140.433

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

This paper verifies the iron loss affected by the secondary frequency in the multi-core transformer for the frequency multiplying circuit. In the frequency multiplying circuit, the secondary frequency component also flows through the primary winding although the transformer is excited by the primary switching frequency, which is one-fifth of the secondary frequency. However, the influence of the secondary frequency to the iron loss of the multi-core transformer in the frequency multiplying circuit has not discussed sufficiently. In this paper, three conditions including a no-load test, a resonant test where the inductance of the secondary side is dominant, and a resonant test where the inductance of the primary side is dominant, are demonstrated in order to verify the influence of the secondary frequency to the exciting voltage and the magnetizing current, that is, the influence of the voltage drop on the primary winding to the iron loss. The iron loss of Mn-Zn ferrite (PC40, TDK) is measured by drawing B (magnetic flux density)-H (magnetic field intensity) curves under the switching frequency is around 200 kHz and the secondary frequency is around 1 MHz. Experimental results verified the increment of the iron loss is 5.1% when the inductance of the secondary side is dominant to the total resonant inductance compared to that in the no-load test. In addition, it is confirmed that the increment of the iron loss is increased by the amplitude of the secondary current. On the other hand, experimental results verified that the secondary frequency significantly affects to the iron loss when the inductance of the primary side is dominant to the total resonant inductance because the voltage drop due to the primary winding's parameters and the secondary frequency component in the primary current occurs. The increment of the iron loss is 35.9% compared to that in a no-load test. From these observations, this paper indicates that placing the resonant inductance at the secondary side is effective for suppressing the influence of the secondary frequency to the iron loss of the multi-core transformer for the frequency multiplying circuit.

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This paper proposes a drive control method for a linear compressor driven by a linear motor. Generally, the efficiency of a linear motor itself is relatively lower than that of a rotational motor. However, higher efficiency should be achievable by adding assist springs and driving at the resonant frequency. We have developed a novel resonant frequency estimation method that calculates the phase difference between a supplied voltage and a mover position. Since the phase difference changes according to the drive frequency with respect to the resonant frequency, our method calculates the phase difference by using the arctangent of a Fourier coefficient, which controls the drive frequency to keep the phase difference at 90 degrees. Experimental results show that the proposed method can successfully track to the resonant frequency dynamically even if the mechanical condition is changed.

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Delta-type permanent magnet (PM) arrangement and extended flux barriers are very effective in improving magnetization characteristics of variable flux memory motors (VFMMs). However, the reluctance torque tends to be declined because of small q-axis inductance. Therefore, a conventional VFMM using above two methods needs larger load current for achieving required maximum torque than that of a target traction motor which is mounted in TOYOTA PRIUS 4th generation. Hence, this paper proposes rotor shape that can increase the reluctance torque in order to achieve required maximum torque by applying same load current as that of the target motor. Finally, the proposed VFMM whose reluctance torque is improved can generate the target maximum torque with smaller load current than that of the conventional VFMM. In addition, the proposed VFMM has smaller maximum magnetizing current compared to that of the conventional model, and the proposed VFMM also indicates higher efficiency than that of the target traction motor in high speed region.

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Higher efficiency for a linear motor should be achievable by adding assist springs and driving the motor at the resonant frequency, even if the efficiency of the motor itself is relatively lower than that of a rotational motor. When using a linear motor with assist springs in a sealed chamber such as a compressor, it is difficult to install a position sensor in such an environment; thus, position sensor-less resonant frequency control is essential. This paper proposes a drive control method that realizes resonant frequency driving without a position sensor. The resonant frequency is estimated on the basis of the detected motor phase current, and the position is estimated using only the fundamental component of the current after removing the offset of the detected current with a high-pass filter. Experimental results show that the proposed method can successfully track the resonant frequency dynamically without a position sensor.

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

DOI： 10.1109/ifeec47410.2019.9014917

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

DOI： 10.1109/iecon.2019.8927384

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

In this article, a new active power-decoupling (APD) circuit without an additional discharging inductor is proposed for single-phase power systems. In an APD circuit, a small film capacitor is used to extend the lifespan and remove ripple power derived from power systems. However, to manipulate power pulsation, additional circuits such as inductors, capacitors, and switches are required, which increase the manufacturing cost and parametric uncertainties. In the proposed circuit, rectification and a decoupling function are conducted on a coupled-inductor at the same time to reduce the number of passive elements. Furthermore, a sliding mode control is used to ensure stable operation under parameter variation and disturbance. A design example is presented and the operation of the proposed topology is also verified with a simulation study and experimental results. The results show that the proposed APD method was able to remove passive components and reduce the withstand voltage of a buffer capacitor and insulated gate bipolar transistors (IGBT) while ensuring that both the input current and output voltage of the converter were well regulated under load variation. (c) 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

DOI： 10.1002/tee.22865

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

© 1972-2012 IEEE. The switching speeds of next-generation power semiconductor devices, such as those made of silicon carbide and gallium nitride are roughly ten times those of conventional devices (e.g., silicon insulated-gate bipolar transistors). This increases the frequency range of the electromagnetic noise accompanying the switching operations of pulsewidth modulated (PWM) converters and worsens the influence of radiated noise. The authors have previously proposed an active common-mode filter (ACF) that reduces the radiated noise from the power cables connected to a PWM converter and evaluated its effect in reducing radiated noise by using a function generator as a common-mode (CM) noise source. In this paper, the ACF is applied to a motor drive system fed by a three-phase PWM inverter, and the attenuation characteristics of the CM voltage are evaluated. To avoid saturating the ACF, the combination of an active common-noise canceller and the ACF is discussed. The experimental results show that the system constructed in this paper can suppress the CM voltage produced by the PWM inverter over a wide frequency range from 100 to 100 MHz.

DOI： 10.1109/TIA.2019.2892364

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In this study, we examine how to increase the operating speed of a consequent pole axial gap motor to achieve higher output density. Our research group has been developing a consequent pole axial gap motor with field windings as the traction motor for electric vehicles. A smaller and lighter traction motor is required for better fuel economy and layout of such vehicles, and it is profitable to manufacture a smaller motor with an increased operating speed. To achieve high-speed operation, it is necessary to suppress the line-to-line voltage, and to that end, we examine the slot/pole combination. Moreover, because the rotor outer diameter of an axial gap motor is larger than that of a radial gap motor, the rotor strength should also be considered. We study the use of non-magnetic high-tensile-strength steel for the component that supports the rotor. We present the motor design and the results of spin burst tests, and we confirm that the motor can operate at the target maximum speed and output power density.

DOI： 10.1541/ieejjia.8.497

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This paper proposes an interleaved AC/DC buck-boost converter with active power decoupling(APD) using the modular design method. It also introduces the control method using the sliding mode control (SMC) strategy for the proposed circuit. The contribution of this paper was first proposed by AC/DC Interleaved Converter circuits with APD functions, which allowed the size of input filters and magnetic cores to be reduced. Additionally, we have applied SMC strategies to the control system to be robust for the disturbance or model uncertainty. The effectiveness of the proposed circuit and control method is shown by simulations using MATLAB/SIMULINK.

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This paper proposes a hybrid common-noise canceler to improve the common-mode (CM) voltage suppression performance by using an active feedback circuit. First, the operating principles of a passive canceler and the hybrid canceler are presented. The passive canceler is composed of a non-zero sequence choke and a CM transformer. The CM voltage suppression performance of the passive canceler is degraded by leakage inductances of the non-zero sequence choke and the CM transformer. The proposed hybrid canceler achieves higher CM voltage suppression than the passive canceler because the active feedback circuit reduces the effects of the leakage inductance. Finally, the hybrid canceler performance is evaluated by simulations.

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We propose a frequency multiplying circuit containing a high-frequency output inverter and an impedance matching transformer that contains magnetic materials with an operation frequency lower than the output frequency. The operation principle and power loss of the proposed circuit and a conventional circuit are compared. Simple theoretical analysis shows that the proposed circuit can reduce the iron loss of magnetic materials. However, the conduction loss of semiconductor devices and the copper loss of primary windings in the proposed circuit are higher those in the conventional circuit because the number of phases in the half-bridge inverter is five times that in the conventional circuit. Experimentally, it is revealed that Mn-Zn ferrite can be used at an output frequency of 2.5 MHz, which exceeds the operation frequency of the material.

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In this paper, a novel variable flux memory motor (VFMM) employing delta-type permanent magnet (PM) arrangement and extended flux barriers is proposed. Conventional VFMMs have three main drawbacks as follows: At first, positive and negative current pulse for magnetizing the variable flux PMs are asymmetry due to the diamagnetic field from Neodymium sintered PM as a constant flux PM. As a result of asymmetric magnetizing current, the inverter capacity is increased. Secondly, variable flux PMs are unintentionally demagnetized when applying maximum load current. Thirdly, iron loss is tend to be increased when magnetization reversal is caused by negative magnetizing current pulse because the harmonic flux becomes larger. The proposed VFMM in this paper overcomes the above challenging points at the same time because of delta-type PM arrangement and the extended flux barrier. In addition, the proposed VFMM can achieve lower iron loss and voltage than the target motor mounted in TOYOTA PRIUS fourth-generation. It is obvious that the proposed VFMM has very high performances in terms of magnetization characteristic, efficiency, and torque density.

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This paper deals with electromagnetic interference radiated from air-conditioner piping that acts as an antenna and emits electromagnetic noise. The current distribution on the piping is measured by using a near-field magnetic probe, and the distribution mode is analyzed. The results show that the piping resonates at the frequencies where the piping length accords with lambda/4, 3 lambda/4, and 5 lambda/4, and radiates electromagnetic noise as a monopole antenna. This radiation mechanism is confirmed by simulations using the CST EMC Studio electromagnetic field simulator.

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© 2019 The Institute of Electrical Engineers of Japan. The switching speed of next-generation power devices based on wide-bandgap semiconductors, such as silicon carbide (SiC) and gallium nitride (GaN), are more than ten times those of conventional silicon insulated-gate bipolar transistors (Si-IGBT). This may increase the frequency range of electromagnetic noise produced by pulse-width-modulated converters. Further, the operating frequency ranges of noise filters are limited by the parasitic components of passive elements, so it is difficult to realize a high-frequency (HF) noise filter whose operating frequency exceeds several tens of megahertz. This paper proposes a novel and simple analytical method to calculate the winding stray capacitance of an HF three-phase common-mode (CM) inductor for the purpose of estimating its operating frequency range at the design stage. Results of measuring the CM impedance confirm that the proposed method can estimate the operating frequency range of an HF three-phase CM inductor while ensuring practically sufficient precision. Furthermore, the obtained results also show that the reduction in the number of turns does not always contribute to the enhancement of the operating frequency ranges of filter inductors.

DOI： 10.1541/ieejias.139.339

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High switching speed in next-generation power devices such as silicon carbide allows increased switching frequencies in power converters. Higher switching frequencies increase power densities, but also increase frequencies of electromagnetic noise accompanying switching operations, resulting in more serious electromagnetic interference (EMI). Radiated EMI will thus soon become a major concern when developing power converters. Most previous works have focused on conducted EMI, resulting in a dearth of research on radiated EMI from power converters. We thus investigated the generation mechanism of radiated noise from power converters to identify effective reduction methods. We identify two propagation paths of high-frequency (HF) common-mode (CM) noise currents, primary CM (PCM) and secondary CM (SCM). SCM constructs a large propagation loop, thus becoming a major source of radiated noise. To suppress HF CM current flow through each mode, we fabricate two types of CM inductors (CMI). HF CM currents are measured in a simple buck converter system. CM current measurements verify the effectiveness of CMI for reduction of HF CM currents and clarify how SCM voltage source is generated. The described generation mechanism of SCM voltage source and radiated noise is verified by measurements of radiated noise in a fully anechoic chamber.

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Permanent magnet synchronous motors (PMSM) for electric vehicles (EV) requires three properties; high torque, high efficiency at low torque region, and constant output in wide speed range. However, these have a relation of a trade-off at magnitude of field magnetic flux. In this paper, consequent pole PM type axial-gap motor with the ferrite PMs and the field windings, which has structure variable field magnetic flux, is introduced. Also, in order to examine operation characteristics of the proposed motor, a prototype is produced and tested. Experimental results show that the proposed structure is effective in realizing all of three properties; high torque, high efficiency at low torque region, and constant output in wide speed range.

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This paper explores the relationship between filter inductor impedance and dimensional resonance in magnetic cores. Experimental results were obtained showing multiple factors behind the resonances that appear in the frequency characteristics of inductor impedances: the inherent characteristics of a magnetic material, the self-inductance of an inductor and stray capacitance in its winding, and the winding acting as a distributed constant line. Next, based on the measurement results, the dimensional dependencies of the complex permeabilities ( dimensional resonance) and the influence of dimensional resonance on inductor impedance are discussed in detail. Finally, this paper shows that the effect of dimensional resonance on complex permeability can be mitigated and filter inductor impedance can be increased in the high frequency range by a core lamination. These results are verified by the experiments described in this paper.

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© 2018 EPE Association. Active power decoupling(APD) method is a suitable solution to increase the lifetime of power conversion systems by replacing electrolytic capacitors(E-Caps) with film capacitors using an auxiliary circuit. However, due to the increased non-linearity and uncertainty of the entire circuit, conventional control methods cannot guarantee global stability. This paper proposes nonlinear control strategy based on Lya-punov&#039;s direct method for AC/DC buck-boost converter with an APD circuit. The contribution of this paper is to guarantee global stability of the APD circuit based converters. The effectiveness of the proposed method is shown by experiments using a 100 W drive.

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© 2018 IEEE. An axial gap motor using neodymium bonded magnet, which our research group has proposed, achieved high torque density and high efficiency at high torque region in the previous paper. However, further improvement in efficiency is required in a wide operation range including not only high torque region but also low torque region. Hence, this paper discusses soft magnetic composite (SMC) suitable for high efficiency of the proposed axial gap motor. In the SMC, there is a trade-off relationship between low iron loss characteristic and high magnetic permeability. Therefore, at low torque region, the efficiency of the axial gap motor using the SMC was lower than that of the radial gap motor using the electromagnetic steel sheet. The proposed axial gap motor adopts a coreless rotor structure. Thus, it is possible to suppress the torque reduction, because the magnetic circuit of the proposed axial gap motor is hardly affected by the magnetic permeability of the stator core due to the large magnetic reluctance of the coreless rotor. For the proposed axial gap motor, HX3 of the newly material having lower iron loss characteristic than the electromagnetic steel sheet is developed, even though the magnetic permeability decreases. Consequently, improvement of efficiency and high torque are compatible by HX3. In this paper, we show the material properties of HX3 and the experimental results of a prototype machine of the proposed motor using HX3 of the newly material. From the experimental results, we report that the proposed motor can achieve improvement of efficiency around low torque region.

DOI： 10.1109/ICELMACH.2018.8507200

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© 2018 IEEJ Industry Application Society. This paper presents an examination of increasing operation speed of consequent pole type axial gap motor to achieve higher output density. Our research group has been developing consequent pole type axial gap motor with field windings for traction motor of electric vehicles. From the point of fuel economy and layout, smaller and lighter traction motor is required. It is profitable to increase operation speed for reducing the size of motor. It is necessary to suppress line to line voltage to achieve high speed operation, and we examined pole-slot combination. Moreover, as rotor&#039;s outer diameter of axial gap motor is larger than that of radial gap motor, the strength of rotor should be considered. We studied the adoption of non- magnetic high tensile strength steel for rotor supporting component. Motor design and the result of spin burst test are presented and we confirmed the operation of target maximum speed and output power density can be possible.

DOI： 10.23919/IPEC.2018.8507510

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© 2018 IEEJ Industry Application Society. Switching speed of next-generation power devices such as silicon carbide is about ten times faster than those of silicon devices. This aspect may increase the frequency ranges of common-mode (CM) voltage accompanied by switching operations. Meanwhile, operating frequency ranges of noise filters typically limited by parasitic effects and frequency dependencies of magnetic components. Thus, it is difficult to suppress a wideband noise by installing only conventional passive noise filter. This paper studies about the combination of a conventional low-frequency passive filter and a high-frequency passive filter (HF-PF) which consists of a high-frequency magnetic material such as nickel-zinc ferrite. Furthermore, the proposed active CM voltage feedback circuit is applied for improving the performance of the HF-PF. An insertion effect against CM voltage produced by a pulse-width-modulated inverter is evaluated experimentally. Experimental results show that the constructed system effectively reduce CM voltage in the frequency range from 100 kHz to 100 MHz.

DOI： 10.23919/IPEC.2018.8507810

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© 2018 IEEJ Industry Application Society. Insulated AC/DC converters using matrix converters (MCs) have higher efficiency, smaller size, and longer lifespan compared with conventional ones. For downsizing of high-frequency (HF) transformers in these converters, developments of HF output MC control methods are active. It is expected to improve efficiency by applying soft switching techniques for these converters. However, to achieve soft switching, phase difference between an output voltage and a current is required. As a result, output power factor decreases. In this paper, a relationship between soft switching conditions and output power factor is revealed. Considering this relationship, the authors propose a new MC control method to achieve soft switching and maximum output power factor. Additionally, this method enables to suppress the distortion of input currents and reduce ripple of the output current. Also, the MC can control the output current and instantaneous reactive power. The authors confirm that experimental results show validity of the method.

DOI： 10.23919/IPEC.2018.8507605

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© 2018 IEEJ Industry Application Society. Inverters using SiC or GaN power devices can realize high frequency and high efficiency operation. To achieve high efficiency, the switching characteristics of these power devices are important, because stray inductances in inverter main circuit have strong influence on the switching characteristics. To reduce the switching loss and surge voltage, minimization of stray inductance in the main circuit is required for high-frequency PWM inverter. This paper describes design guidelines for high-frequency inverters that realize low inductance. The PCB design guideline on the thick multilayer PCB is derived from the inductance calculation using 3D-FEA. It is shown experimentally, that the stray inductance of designed PCB can be reduced to the same level as the inductance inside the power devices. Experimental results verify that a prototype can achieve high speed switching and can suppress surge voltage. A load test is demonstrated to evaluate main circuit efficiency in half-bridge inverter at 100 kHz.

DOI： 10.23919/IPEC.2018.8507376

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

In general, radial gap motors employing neodymium sintered permanent magnet (Nd sintered PM) are used to achieve high torque density in many applications. However, the motors are not suited to a flat, disk-like shape because the dead space, such as the coil ends, occupies most of the motor volume. Therefore, axial gap motors are frequently used for flat shape instead of radial gap motors. Nd sintered PM is a well-known high-performance magnet that has high residual magnetic flux density, but eddy current loss easily occurs in the magnet because of its high conductivity. In axial gap motors for industrial applications, it is difficult to take measures against eddy current loss of Nd sintered PM in terms of cost. Therefore, general axial gap motors employing Nd sintered PM often have unsatisfactory characteristics, such as low efficiency, even though the motor produces high torque. On the other hand, radial gap motors can take measures to suppress eddy current in PMs easily if radial gap motors employ interior permanent magnet structure. Accordingly, this paper discusses an axial gap motor employing neodymium bonded permanent magnet (Nd bonded PM) for flat shape. Compared with Nd sintered PM, Nd bonded PM has lower residual magnetic flux density, but also lower cost. In addition, Nd bonded PM has extremely low eddy current loss due to its low conductivity. It is found from three-dimensional finite element analysis and experimental results that the axial gap motor employing Nd bonded PM can achieve higher torque and higher efficiency compared with the radial gap motor employing Nd sintered PM with the same PM weight and a flat shape.

DOI： 10.1109/TIA.2017.2710123

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This paper introduces the operational characteristics of an ultra-high-speed bearingless motor with 2-pole concentrated motor windings and 4-pole concentrated suspension windings. Experiments with a prototype machine indicate that iron loss is the largest component of losses in the proposed bearingless motor. Therefore, in order to reduce the iron loss, comparison of the experimental results and the 3D-FEM results is discussed. As a result, because it is turned out that iron loss of the switching frequency component accounts for a large proportion in total iron loss, a method of enhancing efficiency of the proposed bearingless motor by means of high switching frequency using SiC-MOSFET is examined. The experimental results with the examined method show that the prototype machine can attain the high efficiency of 94.3% at rated operation of 1.70 kW and 100,000 r/min in spite of including suspension input power for magnetic levitation. In addition, operational characteristics comparison of the bearingless motor at switching frequency of 40 kHz, 80 kHz and 120 kHz is discussed in detail.

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This paper investigates secondary winding structures in a multi-core transformer in a MHz inverter using a frequency multiplying method at the output frequency of 2.5 MHz which is five times of the switching frequency of 500 kHz. The proposed circuit can generate high output frequency by using a multi-phase inverter with phase shift control and the multi-core transformer while the switching frequency and an operational frequency of the multi-core transformer is lower than the output frequency. Therefore, an iron loss of the multi-core transformer is reduced, which results in high efficiency. In this paper, two prototypes of the multi-core transformers which have different secondary winding structures are made and compared from the view point of a leakage inductance and a parasitic capacitance viewed from the secondary side of the multi-core transformer. As a result, it is confirmed that the effect of the parasitic capacitance viewed from the secondary side of the multi-core transformer to a series resonant capacitor connected to the secondary side of the multi-core transformer in series is reduced to 1/4 compared with a loosely-coupled multi-core transformer by a highly-coupled multi-core transformer.

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Switching speed of the next-generation power devices based on the wide-bandgap semiconductors such as silicon carbide and gallium nitride are more than ten times faster than the conventional silicon insulated-gate bipolar transistors. This may increase frequency ranges of electromagnetic noise accompanied by switching operations of power converters. Besides, the operating frequency ranges of noise filters are limited due to frequency dependencies of magnetic materials and parasitic components of passive components, thus, the realization of the high-frequency (HF) noise filter with the operating frequency range beyond several ten megahertz is difficult. This paper presents a modeling technique for estimating the operating frequency range of the HF three-phase common-mode (CM) inductors. The proposed method includes a novel simple estimation technique of winding stray capacitance. The CM impedance measurement results validate that the proposing model can estimate the operating frequency range of the HF three-phase CM inductor while securing practically sufficient precision at the design-stage.

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This paper proposes a new control strategy for active power decoupling(APD) function of a bridge-less single-ended primary inductance converter(SEPIC). Without additional components, a change of control method would enable the implementation of APD functions, replacing an electrolytic capacitor(E-Cap) with a small film capacitor. The contribution of this paper is to apply a Lyapunov-function based control method to the control system to ensure global stability and reduce the number of sensors and parameters required for control. The effectiveness of the proposed control method is shown by simulations using MATLAB/SIMULINK.

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© 2017 IEEE. Magnetic suspension pumps have been attracted attention and actively developed. These pumps can realize magnetic suspension and rotation of a rotor shaft integrated with an impeller without mechanical contact. There is now a need to develop a magnetic suspension pump that is capable of 5-axis active control while retaining a small size and low power output. However, conventional structures capable of 5-axis active control are not suited to such requirements. This paper introduces a novel structure of a 5-axis active control type magnetic suspension pump for small size and low power output. The proposed structure reduces pump size by eliminating a dedicated rotor component for a thrust magnetic bearing and generating thrust suspension force in both the positive and negative axial directions with a single electromagnet. 3D-FEM analysis and experiment demonstrate that the proposed structure satisfies requirements for magnetic suspension pump applications.

DOI： 10.1109/IECON.2017.8216340

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

A bearingless motor (BelM) integrates the characteristics of an electric motor and a magnetic bearing. Typically, a surface-mounted permanent magnet (SPM)-type BelM with a ring magnet magnetized in parallel is employed for high-speed operation. It is noteworthy that a carbon fiber bandage is needed to fix the ring magnet. However, when an SPM-type BelM is applied to a high-output motor, it becomes difficult to generate sufficient suspension force because of the wide magnetic gap arising from the carbon fiber bandage and the ring magnet. In addition, the manufacturing cost for the large-scale ring magnet and the carbon fiber bandage is high. Therefore, to realize a high-output and highspeed BelM at a low cost, we have focused on an interior permanent magnet (IPM)-type BelM with 2-pole motor windings and 4-pole suspension windings. Moreover, a rotor structure for suppressing suspension force ripple arising in the IPM-type BelM has been proposed based on a three-dimensional finite element analysis. In this study, a prototype of the IPM-type BelM with the proposed rotor structure is produced. Experiments with this prototype show that the proposed rotor structure is effective in reducing suspension-force ripple. Additionally, the operational characteristics of the prototype are shown in detail.

DOI： 10.1109/TIA.2017.2746668

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DOI： 10.1109/icems.2017.8056376

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

In-wheel type permanent-magnet synchronous motors for electric commuter cars are required to be compact and light to use limited wheel space effectively and reduce unspringing weight. Therefore, our previous papers presented a low-cost in-wheel axial-gap motor that uses ferrite permanent magnets. This motor adopted an open slot structure to reduce production costs. However, to achieve further size and weight reduction, we examine here in detail the adoption of a semiclosed slot structure instead of an open slot structure. Experimental results show that the semiclosed slot structure is effective in realizing size and weight reduction.

DOI： 10.1109/TIA.2017.2684739

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DOI： 10.1109/ifeec.2017.7992313

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This paper proposes a novel type of an active common noise canceler (ACC) combining feedforward and feedback control. The ACC attenuates the common-mode (CM) voltage and suppresses EMI emissions by adding the CM voltage of reverse polarity to the CM voltage generated by inverters in AC motor drive system. The proposed ACC uses feedforward and feedback control whereas the original ACC [19] uses feedforward control only. Experimental evaluation is presented for comparison between the proposed ACC, a feedforward ACC, and common mode chokes (CMCs) which are widely used as passive filters. The experimental results show that the proposed ACC has large CM voltage attenuation of up to 50 dB in the wide frequency range. The attenuation performance of the proposed ACC is larger than the feedforward ACC and a CMC, which uses the same ferrite core and windings used in the proposed ACC.

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In recent years, flat shape motors are desired for many industrial applications such as robot arm, automobiles and so on. Thus, this paper discusses axial gap motors which have advantage for flat shape. In general, axial gap motors have high torque density with flat shape because of its wide air-gap area. Axial gap motors are therefore used for limited space like disk shape instead of radial gap motors which are the most general motor. However, compared with radial gap motors, the acceleration of axial gap motors is relatively lower because of the larger moment of inertia. In this paper, rotor structure to enhance the acceleration of axial gap motors is proposed and analyzed by 3D-FEA. In addition, material for permanent magnet of axial gap motors is properly selected in order to enhance efficiency at high speed and high torque area. Finally, prototypes of both axial and radial gap motor with flat shape are evaluated by some experiments. It is found that proposed axial gap motor can achieve the higher torque and efficiency compared with the radial gap motor with flat shape. Proposed axial gap motor additionally achieved the slightly larger acceleration compared with the radial gap motor.

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Bearingless motors (BelMs), which can realize magnetic levitation rotation with no mechanical contact, have been proposed and developed. In general, in high speed and high output BelMs, distributed winding structure is adopted in order to suppress iron loss, and neodymium sintered permanent magnet (Nd sintered PM) is employed to achieve a high power density. However, output power fall is caused due to long coil end of the distributed winding structure because a shaft length is limited by primary bending mode under high speed rotation. Furthermore, eddy current loss easily occurs in the Nd sintered PM because of its high conductivity. It is difficult to achieve continuous highspeed and high-output operation due to the temperature raising in a rotor. Therefore, in this paper, a high speed and high power density BelM using concentrated winding stator and neodymium bonded permanent magnet (Nd bonded PM) is proposed in order to suppress output power reduction caused by the coil end and eddy current loss generated in PM. In addition, this paper indicates analysis results of various BelM models using distributed winding structure, concentrated winding structure, Nd sintered PM, and Nd bonded PM, respectively. Comparison of these results is discussed in detail and effectiveness of the proposed structure is clarified.

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This paper presents the examination of consequent pole type ferrite PM axial gap motor with field winding. Especially the configuration of magnet and rotor core is analyzed with equivalent magnetic circuit and 3D FEA. The prototype was assembled and the comparison between test result and analysis is also provided. It is confirmed that high torque and efficiency characteristic is achieved when the width of magnet and rotor core are 21 deg. and 15 deg. (mechanical angle) respectively.

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

This paper proposes novel pulsewidth modulation (PWM) schemes for multi-space-vector pulsewidth modulation (MSVPWM), which is used in position sensorless control of interior permanent-magnet synchronous motor drives. The estimation of the rotor position is based on magnetic saliency and employs high-frequency components of voltage and current, which are excited by MSVPWM. The difference between the instantaneously applied voltage vector and the reference voltage vector causes current ripple. Since six or four voltage vectors are generated during a PWM period, the sequences of the error voltage vectors lead to different types of current ripples. In this paper, the proposed MSVPWM schemes employ six sequences for zero-/low-speed operation and 24 sequences for high-speed operation to reduce line current ripple. Experimental results confirm that the proposed MSVPWM schemes lead to significant reduction in harmonic current while maintaining high performance of sensorless estimation.

DOI： 10.1109/TPEL.2015.2500364

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Magnetic bearings (MBs) are useful for suspending the rotor shaft of a high-speed, high-output motor because they can do so without mechanical contact. In [2], we have proposed a three-axis active-control-type MB (3-axis AMB) with a cylindrical rotor whose diameter is equal to that of the rotor of a radial MB (RMB) or a motor. The proposed 3-axis AMB integrates an RMB and a thrust MB in one unit. However, the assembly of the conventional 3-axis AMB is complex, and the rotor iron loss is large. Thus, in order to simplify the assembly of the 3-axis AMB and to reduce rotor iron loss, this paper discusses a novel structure for the 3-axis AMB in which small auxiliary permanent magnets (PMs) are inserted in the radial winding slots. The suspension force and the rotor iron loss of the proposed device are evaluated by 3-D finite-element analysis in comparison with a 3-axis AMB without small auxiliary PMs.

DOI： 10.1109/TMAG.2016.2514604

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

This paper deals with common-mode (CM) electromagnetic interference (EMI) in an inverter-fed motor drive system. A simplified CM equivalent circuit including -type equivalent circuit for the motor winding is proposed by using the waveform of the common-mode current flowing in the ground conductor. Moreover, a parameter identification method applying the computer-aided software modeFRONTIER is proposed to decide objectively the circuit parameters of the proposed simplified equivalent circuit. Validity and effectiveness of the proposed equivalent circuit are confirmed by comparing the measured impedance characteristics with the calculated ones. Finally, the possibility of a nonlinear phenomenon is discussed in this system. It is shown that the accuracy of simulation result can be improved by introducing the nonlinear element. (c) 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

DOI： 10.1002/tee.22212

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Language：Japanese   Publisher：Institute of Electrical Engineers of Japan  

In the analysis of switched reluctance motors (SRMs), the analytical error of 2D FEA caused by the magnetic flux change in the direction of the axis, which is not considered in 2D FEA, is a serious problem. In this paper, a novel method for making a 2D-FEA model of an SRM, which can equivalently consider the influence of the threedimensional effect, is proposed. A 2D-FEA model of an SRM can be easily made by adjusting only the shape of two regions in a rotor by employing the proposed method. The optimum values of two parameters, defined in this paper for adjusting the shapes of the rotor with the proposed method, are easily extrapolated. A comparison of the experimental results with 2D FEA using the proposed method confirms that the proposed method is effective in considering the three-dimensional effect.

DOI： 10.1541/ieejias.136.100

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IPMSMs used for industrial applications generally require high efficiency operation in a certain operating point or area in addition to constant torque operation. In this research, the examined motor demands high efficiency operation at high speed and high torque area. In this case, the current phase angle is small and it is difficult to use reluctance torque effectively. Furthermore, concentrated winding structure has been adopted to cut manufacturing cost and to use limited space effectively. In general, IPMSMs using concentrated winding structure have a difficulty of generating reluctance torque from the perspective of getting q-axis armature reaction magnetic flux. In this paper, to enhance the efficiency of V-shaped IPMSM using concentrated winding structure at high speed and high torque area, the rotor structures which effectively use permanent magnet torque have been examined. Analysis result of 2D-FEA shows that the examined rotor structure, which arranges disproportional gap and large flux barrier on the q-axis magnetic flux path, can enhance the efficiency at high speed and high torque by suppressing the q-axis magnetic flux and by concentrating the field magnetic flux of PMs on the d-axis.

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In general, radial gap motors employing neodymium sintered permanent magnet (Nd sintered PM) are used to achieve high torque density in many applications. However, the motors are not suited to a flat, disk-like shape because the dead space, such as the coil ends, occupies most of the motor volume. Therefore, axial gap motors are frequently used for flat shape instead of radial gap motors. Nd sintered PM is a well-known high-performance magnet that has high residual magnetic flux density, but eddy current loss easily occurs in the magnet because of its high conductivity. In axial gap motors for industrial applications, it is difficult to make measure against eddy current loss of Nd sintered PM in terms of cost. Therefore, general axial gap motors employing Nd sintered PM often have the unsatisfactory characteristics such as low efficiency, even though the motor produces high torque. Accordingly, this paper discusses an axial gap motor employing neodymium bonded permanent magnet (Nd bonded PM) for flat shape. Compared with Nd sintered PM, Nd bonded PM has lower residual magnetic flux density, but also lower cost. In addition, Nd bonded PM has extremely low eddy current loss due to its low conductivity. It is found from 3D-FEA and experimental results that the axial gap motor employing Nd bonded PM can achieve higher torque and higher efficiency compared with the radial gap motor employing Nd sintered PM with the same PM weight and a flat shape.

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In recent years, interior permanent magnet synchronous motors (IPMSMs) using ferrite permanent magnet are being studied for high power density motor application, such as electric vehicles. However, the residual flux density of ferrite magnet is lower than that of rare-earth permanent magnet. Thus, in general, it is difficult for IPMSMs using ferrite magnet to maintain constant high output power in high-speed region. Accordingly, a spoke-type IPMSM using ferrite magnet with specification similar to the currently commercially available IPMSM using rare-earth magnet is examined in this research. Owing to increasing constant output power in high-speed region, analysis with 3D-FEA was conducted and the analysis results show that the constant output characteristics in high-speed region are improved by contriving the shape of the rotor surface. Moreover, experimental results of a prototype of the examined spoke-type IPMSM using ferrite magnet will be presented in this paper.

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

A magnetic bearing (MB) can suspend a rotor shaft with noncontact, so the MB has been used for high-output and high-speed machines. In general, heteropolar-type MB structure is used, because of its simple structure and low cost. However, the heteropolartype MB structure has a problem in terms of rotor iron loss caused by an alternating magnetic field on a rotor core. On the other hand, general homopolar-type MB structure has a low rotor iron loss caused by a dc magnetic field on a rotor core. However, as the general homopolar-type MB has a complicated structure and needs a large magnet for generating the bias flux, it becomes costly. Therefore, this paper discusses a novel homopolar-type MB structure unifying four C-shaped cores for high output and low iron loss. It is shown with three-dimensional finite element analysis that the novel homopolar-type MB has lower iron loss and lower cost than the general homopolar-type MB, which is known for its low iron loss.

DOI： 10.1109/TMAG.2015.2456338

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DOI： 10.1109/icems.2015.7385377

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Language：Japanese   Publisher：Japan Society of Refrigerating and Air Conditioning Engineers  

This paper proposes a method to estimate the stray capacitance between compressor motor windings and stator in operation, and the permittivity of refrigerant and lubricant oil mixture in this area. By applying this method, the complex experiment equipments and sensors are unnecessary. The estimation about the stray capacitance between the motor windings and stator in operation becomes possible according to the equivalent circuit of the inverter air conditioner by analyzing the high frequency leakage current of ground line. Further, the permittivity of refrigerant and lubricant oil mixture can be calculated by comparing the stray capacitance of equivalent circuit in operation with the stray capacitance of the compressor without refrigerant and lubricant oil. It is meaningful to discuss and solve the problem of EMI (electromagnetic interference) noise.

DOI： 10.11322/tjsrae.15-12_OA

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A new switched reluctance (SR) generator was designed for possible application in hybrid electric vehicles. The proposed generator was designed to be mostly competitive with the target interior permanent-magnet (IPM) generator currently used in mass-produced hybrid vehicles. The energy efficiencies of the SR and IPM generators were compared in typical driving cycles, such as US06, HWFET, and UDDS modes. We found that the energy efficiency of the SR generator was close to the IPM generator in high-speed driving cycles because the SR generator has no iron loss during the generator idling period due to the fact that it has no PM.

DOI： 10.1109/TIA.2014.2387478

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DOI： 10.14243/jsaem.23.250

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DOI： 10.1109/intmag.2015.7157788

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

The increased price and the limited supply of rare-earth materials have been recognized as a problem by the international clean energy community. Rare-earth permanent magnets are widely used in electrical motors in hybrid and pure electrical vehicles, which are prized for improving fuel efficiency and reducing carbon dioxide (CO2) emissions. Such motors must have characteristics of high efficiency, compactness, and high torque density, as well as a wide range of operating speeds. So far, these demands have not been achieved without the use of rare-earth permanent magnets. Here, we show that a switched reluctance motor that is competitive with rare-earth permanent-magnet motors can be designed. The developed motor contains no rare-earth permanent magnets, but rather, employs high-silicon steel with low iron loss to improve efficiency. Experiments showed that the developed motor has competitive or better efficiency, torque density, compactness, and range of operating speeds compared with a standard rare-earth permanent-magnet motor. Our results demonstrate how a rare-earth-free motor could be developed to be competitive with rare-earth permanent-magnet motors, for use as a more affordable and sustainable alternative, not only in electric and hybrid vehicles, but also in the wide variety of industrial applications.

DOI： 10.1109/TEC.2014.2343962

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A bearingless motor (BelM) integrates the characteristics of an electric motor and a magnetic bearing. Typically, a surface-mounted permanent magnet (SPM)-type BelM with a ring magnet magnetized in parallel is employed for high-speed operation. It is noteworthy that a carbon fiber bandage is needed to fix the ring magnet. However, when an SPM-type BelM is applied to a high-output motor, it becomes difficult to generate sufficient suspension force because of the wide magnetic gap arising from the carbon fiber bandage and the ring magnet. In addition, the manufacturing cost for the large-scale ring magnet and the carbon fiber bandage is high. Therefore, to realize a high-output and high-speed BelM at a low cost, we have focused on an interior permanent magnet (IPM)-type BelM with 2-pole motor windings and 4-pole suspension windings. Moreover, a rotor structure for suppressing suspension force ripple arising in the IPM-type BelM has been proposed based on three-dimensional finite element analysis. In this study, a prototype of the IPM-type BelM with the proposed rotor structure is produced. Experiments with this prototype show that the proposed rotor structure is effective in reducing suspension-force ripple. Additionally, the operational characteristics of the prototype are shown in detail.

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This paper proposes a new control method for three-phase to high-frequency single-phase matrix converter (MC) based on instantaneous input voltages. Direct conversion of AC input power to AC output power by MC resulting in higher conversion efficiency, longer lifespan, and more compact size compared to the conventional method by using PWM rectifier and PWM inverter. The proposed MC can produce high frequency output equal to its power devices' switching frequency. The feature of the proposed control method is its sophisticated calculation based on instantaneous input voltages, producing unity input power factor and regulating the output voltage according to the reference value at any instant. Some simulation and experiment results are shown to prove the validity and effectiveness of the proposed method.

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An axial-gap motor with Nd-Fe-B magnets was examined by three-dimensional finite element analysis (3D-FEA) in order to achieve high torque density over 66.8 Nm/L under the constraint of a maximum current density of 12 A/mm(2), and it was confirmed that the examined motor could satisfy these conditions. In this examination, suppressing eddy current loss occurring in these magnets by equally dividing a magnet constituting one pole toward radial direction was attempted. However, 3D-FEA results revealed that the eddy current loss density generated in each magnet which was equally divided was not uniform and had a large bias. So, this paper provides examination to make the eddy current loss density uniform in divided magnets by adjusting split width appropriately.

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In general engine generators, the engine and generator are separate units connected by a mechanical coupling. This tends to increase the package size of general engine generators. In this paper, we are able to achieve miniaturization and high output power of the generator by adopting an axial-gap structure through using ferrite permanent magnets. At the same time, the package size is reduced dramatically by integrating the axial-gap generator into the engine. This paper also discusses methods for reducing the eddy current losses that occur in the windings due to the open-slot structure of the stator core and occur in the rotor support component. By using results from three-dimensional finite element analysis, we show that the eddy current loss that occurs in the windings is reduced by using appropriate methods to wind the coils with rectangular wires. In addition, the eddy current loss that occurs in the rotor support component is decreased by appropriately selecting the material and changing the shape of the component. Experimental results show that the studied structure is effective for realizing miniaturization and high output power of the generator, as well as for decreasing the package size of the engine generator.

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Recent models of hybrid vehicles and electric vehicles include traction motors with increasing capacity for rotation speed. Therefore, high-speed testing equipment suitable for use with traction motors and motor components is required in automotive research and development. Induction motors (IMs) with oil-cooling are suitable motors for testing equipment. Solutions for some drawbacks of high-speed IMs will be proposed in this paper. Also, several solutions, such as high-tension magnet steel and transitional analysis via finite element modeling, will be introduced. Test reports are shown for rotation speeds of up to 23,000 rpm.

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

DOI： 10.1109/ecce.2014.6954053

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

This paper proposes a novel magnet polarity identification method for initial position estimation during startup for interior permanent magnet synchronous machine (IPMSM) drives. The rotor's initial position estimation is based on magnetic saliency and employs high-frequency (HF) components of the voltage and current that are excited by the multi space-vector pulse-width modulation (MSVPWM) pattern. However, there is a common trouble in the estimation methods based on the magnetic saliency: it is necessary to identify the magnet polarity in order to distinguish the north and south poles since the estimated position angle is a periodic function with p radians. In this paper, a novel inductance estimation method is presented and the magnet polarity is uniquely identified by the relationship between the estimated inductance and the magnetic saturation effect. Experimental results confirm the advantages of the proposed method: it is reliable, accurate, and convenient, and can be done in real time. (C) 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

DOI： 10.1002/tee.21990

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This paper presents a position-sensorless interior permanent magnet synchronous motor (IPMSM) control system at low and zero speed based on a multi-space-vector pulse-width modulation (MSVPWM) pattern with the elimination of nonlinear inverter effects. In conventional sensorless methods based on the MSVPWM pattern, the high-frequency (HF) components of voltage and current are used to estimate the rotor position information. However, the inverter nonlinear effects, such as forward voltage drops and deadtime, distort the HF components of the voltage and current so that an error occurs in the position estimation. Therefore, an improved position estimation scheme is developed in this paper. The compensated HF components of the voltage taking account of the inverter nonlinear effects can be used to decrease the estimation error. The proposed method can be implemented without increasing any hardware cost. Experimental results confirm the effectiveness of the proposed method. (c) 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

DOI： 10.1002/tee.21959

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Bearingless motors (BelMs), that can realize shaft suspending without mechanical contacts and lubrication by electromagnetic force, have been proposed. However, in outer rotor type BelMs, one-unit structure with small shaft output alone have been developed. Therefore, this paper introduces a two-unit outer rotor type BelM with consequent-pole permanent magnet structure (CPPM) for high shaft output and the magnetic suspension characteristics of the proposed motor with experimental results. It can be verified that the proposed motor is equipped with the sufficient performance in order to make for practical use.

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A centrifugal pump that employs a bearingless motor with 5-axis active control has been developed. In this paper, a novel bearingless canned motor pump is proposed, and differences from the conventional structure are explained. A key difference between the proposed and conventional bearingless canned motor pumps is the use of passive magnetic bearings; in the proposed pump, the amount of permanent magnets (PMs) is reduced by 30% and the length of the rotor is shortened. Despite the decrease in the total volume of PMs, the proposed structure can generate large suspension forces and high torque compared with the conventional design by the use of the passive magnetic bearings. In addition, levitation and rotation experiments demonstrated that the proposed motor is suitable for use as a bearingless canned motor pump.

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Powerful rare earth permanent magnets (PMs) are generally utilized in in-wheel PM synchronous motors for electric city commuters. However, the use of rare earth PMs has become undesirable due to high prices. An in-wheel PM synchronous motor that does not employ rare earth PMs therefore needs to be developed. We have previously proposed an in-wheel axial-gap motor that can generate high torque density and has features such as a coreless rotor structure with ferrite PMs and a reduction gearbox inside the stator. Through further research, we confirmed that suppression of eddy current loss arising in the rotor is important for attaining higher efficiency in high output motors. Accordingly, here we introduce an improved rotor with slits which can suppress eddy current loss. The results of experiments on a new prototype show that the improved rotor is effective in producing high efficiency and can satisfy the properties demanded of the in-wheel motors for electric city commuters.

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This paper proposes a new circuit configuration of the active common-noise canceler (ACC), which is used to reduce electromagnetic interference of a space vector modulation (SVPWM) inverter. The original ACC, which was proposed by the authors, cancels all components of the common-mode voltage and, therefore, cannot be used in an SVPWM inverter owing to the low-frequency component of the common-mode (zero-sequence) voltage. The proposed ACC cancels only the high-frequency component of the common-mode voltage so it can be used in SVPWM inverters. Furthermore, the high-frequency carrier makes a large contribution to downsizing the common-mode transformer. To confirm the suitability and usefulness of the proposed ACC, an experimental system including a 100-kHz SVPWM inverter was constructed and tested. The experimental results show that the proposed ACC can reduce the high-frequency component of the common-mode voltage.

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this paper introduces a novel decoupling method for current regulation in high-speed bearingless motors using AC suspension current. The frequency of the suspension current increases in proportion to rotating speed in the bearingless motors using AC suspension current, and regulating the suspension current is difficult at high speeds rotation. In previous research, a current regulation method is used that convert AC to DC using a rotating coordinate system. However, that method has interference voltages which make the system unstable. In this paper, we propose a novel decoupling method for the suspension current regulation. In the experiment, stable levitation of the bearingless motor is achieved at 30000 min(-1) by using the proposed decoupling controller.

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In general, the in-wheel type permanent magnet synchronous motor (PMSM) for electric city commuters uses powerful rare earth permanent magnets (PMs). However, the employment of the rare earth PMs should be reduced due to high prices. Therefore, it is important to develop an in-wheel PMSM that does not use the rare earth PMs. We proposed 5kW in-wheel type axial gap motor that can generate high torque density and has features such as a coreless rotor structure with ferrite PMs and a reduction gearbox in the inner side of the stator. And we have presented details of experimental results on a prototype. So, in this paper, in order to achieve further higher power output, we considered a 10 kW in-wheel motor with the proposed structure. The motor with 10-kW output was examined by means of using 3D-FEM and experimental results in order to attain the further higher power as a rare earth free motor.

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Language：Japanese   Publisher：一般社団法人 電気学会  

This paper proposes a new feedback-type dead-time compensation method. The proposed method compensates the output voltage by employing two operations. First, the normal compensation matches the width of the output pulse to that of the input pulse with reduced delay time from the input pulse to the output pulse compared with the conventional method. Second, the short pulse compensation generates an output pulse after a few pulses are input so that the average value of the output signal equals that of the input signal. The voltage utilization factor of the proposed method is almost 100%, because there is no limit to the compensation and the decrease in the fundamental output caused by dead time is eliminated. The experimental results using a 100-kHz input signal show that there is no discrepancy between the output pulse width and the input pulse width. Furthermore, the THD of the compensated output current, when the output frequency is 50Hz, is eliminated, compared with that of the output current without compensation. These results show that the proposed method has low distortion and high voltage utilization factor characteristics.

DOI： 10.1541/ieejias.133.970

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Language：Japanese   Publisher：一般社団法人 電気学会  

This paper proposes simulation methods based on the forward Euler method that are suitable for real-time simulators. However, real-time simulation using the forward Euler method has the following problems: A simulation error caused by a time step limitation and a delay in the simulated waveforms. The authors have proposed a simulation method suitable for real-time simulators, but the physical meaning of the state variables is diluted by diagonalization of the system matrix. This paper proposes a simulation method to obtain the same characteristics as the previous method, without diagonalization. Off-line and real-time simulation results demonstrate the validity and usefulness of the proposed simulation method.

DOI： 10.1541/ieejias.133.714

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Language：Japanese   Publisher：The Japan Society of Applied Electromagnetics and Mechanics  

A bearingless motor is characterized by integration of an electrical motor and a magnetic bearing. Electromagnetic force generated by the magnetic bearing function can realize magnetic suspension of a rotor shaft without mechanical contacts. Principal authors have been proposing a non-contact canned motor pump using the bearingless motor. This pump has no expendable parts, such as shaft seals, mechanical bearings and lubricant. Therefore, it can realize next advantages; 1. clean liquid sending. 2. maintenance free 3. longer operating life. 4. high chemical resistance. The previous paper has proposed novel structure which can generate high output and high suspension force compared with conventional structure. A prototype bearingless canned motor pump with the proposed high power structure is produced, and characteristics of suspension force and torque is tested in the prototype machine. This paper introduces the experimental results of the prototype machine with the proposed high power structure in detail.

DOI： 10.14243/jsaem.21.196

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Small electric vehicles called city commuters are used for commuting and traveling short distances within cities. These vehicles have been extensively researched and developed because of their high environmental performance and small battery size. The in-wheel permanent magnet synchronous motor (PMSM) for electric city commuters generally utilizes powerful rare earth permanent magnets (PMs). However, the employment of rare earth PMs should be reduced, owing to increasing prices and export restrictions on rare earth materials, making it necessary to develop an in-wheel PMSM that does not use rare earth PMs. We propose a ferrite PM-type axial gap motor that generates high torque density and has features such as a coreless rotor structure and a reduction gearbox on the inner side of the stator. Detailed operational characteristics of the proposed motor remain unverified by experiment, so this paper presents such operational characteristics as obtained from experimentation on a prototype.

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This paper proposes an inductance-based estimation method for sensorless interior permanent magnet synchronous machine drives. Rotor position estimation is based on magnetic saliency and employs high-frequency components of voltage and current excited by a multiphase space vector pulse width modulation pattern. Unique to this method is that not only the rotor position but also the inductance parameter values can be estimated instantaneously during a period of modulation. Since inductance is an essential parameter for magnet polarity identification and maximum torque per ampere control, this paper presents the principles and performance results of the proposed inductance estimation method. Experimental results confirm that the proposed method is reliable, real-time, accurate, and convenient.

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This paper focuses on the resistance characteristics of power cables in the very high frequency (VHF) band. The resistance characteristics have a significant influence on radiative electromagnetic interference (EMI). However, to the authors' knowledge, as yet there have been no reports regarding the resistance characteristics of power cables in the VHF band. This paper proposes a measurement method based on distributed constant circuit theory and impedance matching theory. By using this method, the resistance characteristics for a single-core wire with polyvinyl chloride insulation are measured in the frequency range from 10 to 100 MHz. The experimental results show that the measured values of the cable resistance are more than 10-fold the theoretical values calculated by taking the skin effect into account, which are often used in EMI analysis and simulation. Furthermore, the measured values are proportional to the frequency raised to a power of approximately 2/3, whereas the theoretical values are proportional to the square root of the frequency. The measured resistance is validated by simulation using the 3D electromagnetic analysis software EMC Studio.

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In light of global warming and the rapidly increasing prices of rare earths, electric vehicles with motors free of rare earths are needed. We are therefore developing an interior permanent magnet synchronous motor (IPMSM) that utilizes ferrite permanent magnets. Because the residual flux density of a ferrite magnet is lower than that of a rare earth magnet, we have adopted a spoke-type IPMSM with radially arranged ferrite magnets. This paper proposes two rotor structure designs for spoke-type IPMSMs with ferrite magnets, and presents the results of two-dimensional finite element analysis (FEA) for the two designs. The results indicate that the performance loss from using ferrite magnets can be moderated by effectively utilizing reluctance torque in a spoketype IPMSM. Finally, a rotor structure that has sufficient performance to be usable in a traction motor free of rare earths is examined through experiments on a prototype and three-dimensional FEA.

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This paper proposes a novel pulse width modulation (PWM) scheme for multiphase space vector pulse width modulation (MSVPWM), which is used in sensorless control of interior permanent-magnet synchronous motor drives. The estimation of the rotor position is based on magnetic saliency and employs high-frequency components of voltage and current which are excited by a MSVPWM pattern. The difference between the instantaneously applied voltage vector and the reference voltage vector causes current ripples. Since six active voltage vectors are generated during a PWM period, the sequences of the six error voltage vectors lead to different types of current ripples. In this paper, the proposed PWM scheme employs six sequences based on angle range to reduce line current ripple. Experimental results confirm that the proposed PWM scheme leads to significant reduction in harmonic current while maintaining high performance of sensorless estimation despite the reduced current ripple.

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This paper presents a discussion on common-mode (CM) electromagnetic interference (EMI) in an inverter-fed motor drive system, and proposes a non-linear CM equivalent circuit. The effectiveness and necessity of the non-linear element introduction are confirmed.

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

Rare earth magnets that have a large energy product are generally used in high-efficiency interior permanent-magnet synchronous motors (IPMSMs). However, efficient rare-earth-free motors are needed because of problems such as the high prices of and export restrictions on rare earth materials. This paper introduces a ferrite-magnet spoke-type IPMSM that employs a W-shaped magnet placement in order to achieve high efficiency. The effectiveness of the W-shaped magnet placement is verified from the results of two-dimensional finite element analysis and experiments on a prototype.

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：IRON STEEL INST JAPAN KEIDANREN KAIKAN  

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

This paper shows a winding design consideration of a 50-kW switched-reluctance motor (SRM) for hybrid-electric-vehicle (HEV) applications. Increasing the number of turns in stator windings is effective in reducing the maximum current; thus, the inverter current rating is reduced. However, motor output power falls significantly at high speed because of the increased back electromotive force. Continuous current operation can enhance output power at high rotational speed. In this operation, phase current is increased, and hence, the motor output power is maintained at high rotational speed. However, continuous current operation results in a decrease in efficiency. Thus, there is a trade-off in selecting the number of series turns. In this paper, two SRMs are constructed with the same dimensions, and their performance results, i.e., torque and efficiency ranges, are compared with those of the automotive industry standard interior-permanent-magnet motor for HEV applications.

DOI： 10.1109/TIA.2012.2227093

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

Electric city commuters are vehicles used for commuting from suburbs to inner cities and for movement within cities. Because of the short distances that they cover and their small battery size, such vehicles are beginning to attract attention. Generally, a high-performance permanent magnet (PM) composed of rare earth elements, such as neodymium and dysprosium, is used in the in-wheel PM synchronous motor (PMSM) of an electric city commuter. However, rising prices of rare earth elements and export restrictions on them are serious problems. Development of an in-wheel PMSM that does not utilize rare earth PMs is therefore highly desirable for electric city commuter vehicles. Accordingly, our research group has focused on a surface PM type axial gap structure that can achieve a high torque density and a short motor length in the axial direction. The designed motor structure with ferrite PMs replacing the rare earth PMs and the results of a 3-D finite element analysis are introduced in detail in this paper. Moreover, to examine the fundamental characteristics of the designed motor, a prototype is produced and tested.

DOI： 10.1109/TMAG.2012.2196685

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Language：Japanese   Publisher：一般社団法人 電気学会  

Permanent magnets made of rare earth materials are used in interior permanent magnet synchronous motors (IPMSMs), which are major component of hybrid electric vehicles. The recent remarkable increase in the cost of rare earth materials is a major concern. A switched reluctance motor (SRM) without permanent magnets is one of the possible alternatives. Two types of SRMs have been designed with different materials. The SRMs have been investigated full loading tests. This paper reports a comparison between experimental and analysis results for the SRMs. The efficiency of both SRMs can exceed 90%, and the output power can be in excess of 50kW.

DOI： 10.1541/ieejias.132.842

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

A switched reluctance motor (SRM) has been developed as one of the possible candidates of rare-earth-free electric motors. A prototype machine has been built and tested. It has competitive dimensions, torque, power, and efficiency with respect to the 50-kW interior permanent magnet synchronous motor employed in the hybrid electric vehicles (Toyota Prius 2003). It is found that competitive power of 50-kW rating and efficiency of 95% are achieved. The prototype motor provided 85% of the target torque. Except the maximum torque, the most speed-torque region is found to be covered by the test SRM. The cause of discrepancy in the measured and calculated torque values is examined. An improved design is attempted, and a new experimental switched reluctance machine is designed and built for testing. The results are given in this paper.

DOI： 10.1109/TIA.2012.2199952

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DOI： 10.1109/ievc.2012.6183265

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This paper reports a comparison of the experimental results and analysis of the SRMs. Two Switched Reluctance Motors (SRMs) have been designed, constructed, and tested. The iron core of these machines is made of 6.5% silicon steel and conventional 3.5% silicon steel. The performance of these SRMs has been investigated in full loading tests. Efficiency of both SRMs has reached more than 90% and output power has reached more than 50 kW.

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

A bearingless motor has integrated characteristics of an electrical motor and a magnetic bearing. In general, surface permanent magnet (SPM) type rotor structure with a ring magnet magnetized in parallel is employed in high-speed PM type bearingless motors. However, in case of increasing motor size for high output, this rotor structure has problems of insufficient suspension force due to a wide air gap and high cost by using the large-diameter ring magnet magnetized in parallel. Therefore, this paper discusses a novel interior permanent magnet (IPM) type rotor structure for the high-speed and high-output bearingless motor. In the novel IPM type rotor structure, suspension force ripple is suppressed by means of arranging flux barriers at the suitable position in a rotor. It is confirmed with 2D-FEM that the proposed rotor structure using the flux barriers is effective in suppressing the suspension force ripple.

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In general, a rare-earth permanent magnet that has large energy product is used for traction motors mounted on hybrid electric vehicles (HEVs). However, it is necessary to develop rare-earth-free motors for the HEV traction motors owing to several problems such as price hike and export restriction of rare-earth materials. In this paper, a ferrite permanent magnet axial gap motor with coreless rotor structure is introduced as the rare-earth-free motor. In addition, the motor structure and the results of 3D-FEA are described in detail.

DOI： 10.1541/ieejjia.3.47

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This paper discusses a dead-time compensation method for high-frequency pulse-width modulation (PWM) inverters. Feedback-type dead-time compensation can eliminate error in the inverter output voltage. With next-generation switching devices using SiC, the switching frequency of inverters is expected to improve to 10-fold that of conventional inverters. However, as switching frequency increases, dead time will more strongly affect output voltage error. This paper proposes a new compensation method, which can reduce the minimum output pulse width and the phase delay of the inverter output voltage. An experimental system was constructed and tested, using highspeed power MOSFETs and a field-programmable gate array controller. Experimental results support the validity and usefulness of the proposed compensation method.

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

Hybrid electric vehicles (HEVs) that emit less carbon dioxide have attracted much attention and rapidly become widespread, but further popularization of HEVs requires further technical advancement of mounted traction motors. Accordingly, our research group focuses on axial gap motors that can realize high torque density. In this paper, an axial gap motor with a novel interior permanent magnet (IPM) rotor structure is proposed and an examination of the proposed motor at the actual motor size of an HEV is presented. For comparison, we selected the newest radial gap-type 60kW IPM synchronous motor equipped in the third-generation Toyota Prius. Under the condition that the size of the proposed motor be the same as the comparison motor, we confirmed through three-dimensional finite-element analysis that the proposed motor could output twice the maximum torque of the comparison motor. In addition, a comparison was made with a previously reported conventional IPM-type axial gap motor, and the proposed motor was found to be more effective in generating reluctance torque. Moreover, the proposed motor exhibited sufficient durability to irreversible demagnetization of the permanent magnets, to stress caused by rotating the rotor, and to unbalanced electromagnetic forces caused by axial rotor eccentricity.

DOI： 10.1109/TMAG.2011.2150206

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DOI： 10.1109/pes.2011.6039302

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

A machine design of a switched reluctance motor having competitive torque and efficiency as well as compactness with respect to an interior permanent-magnet (IPM) synchronous motor (IPMSM) in a hybrid electric vehicle (Toyota Prius 2003) has been investigated. A torque of 400 N . m is set as a target with an outer diameter of 269 mm with an axial length of 156 mm, including coil end lengths. In addition, a 50-kW field weakening capability must be competitive to the IPMSM. The highest efficiency of 95% is also aimed. Stator and rotor structures and iron material are investigated. Test machines are built. Static and light load tests are carried out.

DOI： 10.1109/TIA.2011.2125770

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DOI： 10.1109/icpe.2011.5944612

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DOI： 10.1109/iemdc.2011.5994829

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Switched reluctance motor (SRM) is attractive for the driving motor of electric vehicles (EVs) and hybrid electric vehicles (HEVs) from the view point which does not use rare-earth materials. However, special drive circuit, which is different from general three-phase inverter used for permanent magnet synchronous motor and induction motor, is required in order to drive SRM. By the way, in some of commercial HEVs, boost chopper combined with three-phase inverter is used in order to apply high voltage to motor windings at high-speed range. In this system, the size of the additional reactor, which is required in boost chopper, is a problem. Then, this paper proposes a novel drive circuit with voltage boost function without additional reactor for SRM. In addition, control scheme and controller configuration for the proposed circuit are described. Moreover, the effectiveness of the proposed circuit is verified by simulation and experimental results.

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A switched reluctance motor is one of possible candidates of rare-earth-free-motors. A prototype machine has been designed, having competitive dimensions, torque, power, and efficiency with respect to the IPMSM employed in the HEVs (Toyota Prius 2003). In this paper, test results are presented including a full load test. It is found that competitive power and efficiency of 50kW and 95%, respectively, are achieved, although 85% of the target torque is possible. Despite of the maximum torque, the most speed-torque region is found to be covered by the test SRM. The cause of discrepancy in the measured and calculated torque values is examined. Considering the discrepancy a new machine is designed for the second stage development.

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In newest hybrid electric vehicle (HEV) propulsion systems, permanent magnet synchronous motors (PMSMs) using high-performance rare-earth permanent magnets play an important role. However, rare earth materials employed in the high-performance rare-earth permanent magnets have problems such as price rise and export restriction. Thus, it is necessary to develop a rare-earth-free motor for the HEVs. In this paper, a novel ferrite permanent magnet axial gap motor with segmented rotor structure is introduced. In order to obtain the fundamental characteristics of this motor, a prototype is fabricated and tested. The experiment results of the prototype are shown in detail. It can be confirmed with the experiment results of the prototype that the proposed motor with the segmented rotor structure has the possibility of the development of the rare-earth-free motor enough.

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

A new noncontact drive system has been developed employing a consequent-pole-type bearingless permanent magnet (PM) motor and a thrust magnetic bearing. This bearingless motor has a wide magnetic gap. The wide magnetic gap may cause a decrease in radial magnetic suspension force because of an increase in magnetic reluctance. A thrust magnetic bearing is installed at the end of the shaft because strong thrust force exists in centrifugal pump applications. In this paper, the magnetic suspension forces and rotation characteristics of the experimental prototype are evaluated while the rotor is magnetically suspended. Experimental results are also compared to the calculated ones using the finite-element method. It is demonstrated that the developed consequent-pole-type bearingless PM motor possesses sufficient magnetic suspension force for noncontact operation.

DOI： 10.1109/TEC.2010.2040828

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DOI： 10.1109/ecce.2010.5618025

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DOI： 10.1109/icelmach.2010.5607864

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DOI： 10.1109/ipec.2010.5542387

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DOI： 10.1109/ipec.2010.5543316

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DOI： 10.1109/ipec.2010.5543565

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

DOI： 10.1109/ipec.2010.5544585

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

DOI： 10.1109/ipec.2010.5543687

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Language：Japanese   Publisher：The Institute of Electrical Engineers of Japan  

DOI： 10.1541/ieejias.130.NL2_05

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

This paper shows an operation area consideration of a torque and speed region of a 50kW Switched Reluctance Motor (SRM) for Hybrid Electric Vehicle (HEV) applications. Increasing a number of turns in stator windings is effective to reduce phase current of SRM at low rotational speed, however, motor output power falls significantly at high speed because of an increased back emf.
A continuous current operation can enhance output power at high rotational speed. The continuous current operation can be realized by expanding excitation angle of applied voltage. In this operation, phase current is increased, thus, motor output power is maintained at high rotational speed, which is strongly required in HEV applications. An effectiveness of the continuous current operation is shown for a 50kW SRM aimed for HEV application. The SRM is designed with competitive dimensions, efficiency, weight, voltage and current with respect to HEV IPM motors.

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

In this paper, a design-optimization method for a consequent-pole bearingless motor with a rather large air-gap length is presented. A rotor iron and permanent-magnet structure is proposed which enhances the suspension-force capability during startup. Magnetic saturation in the rotor-iron pole area is solved, and the stator iron is designed so that magnetic saturation is avoided. The design optimization is based on finite-element-method analysis. It is shown that startup is achieved from the touch-down condition in the experiments.

DOI： 10.1109/TIA.2009.2023498

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

Bearingless PM motors which have additional suspension windings have been designed with 3D FEM. To verify satisfactions in practical application, a test machine has been built. In this paper, suspension force is measured with the static forces. Two experimental methods are proposed. It is proved that those procedures are suitable even if it is in limited conditions, only one shaft end can be used for static force applied. Furthermore, the relation of the suspension force and rotor rotational angle is shown.

DOI： 10.1109/TMAG.2009.2018658

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

A bearingless permanent magnet (PM) motor combines functions of non-contact magnetic suspension and torque generation together, thus it can drive without mechanical contact. Unlike conventional bearingless PM motors, such as a surface-mounted PM motor, a consequent-pole type of bearingless PM motor has inherent advantages. It can regulate the radial rotor positions independently of the motor drive and has no tradeoff between radial suspension force and torque. In the consequent-pole bearingless PM motors, distributed or concentrated windings can be employed to the motor winding structure. However, relationship between voltage characteristics and the winding design has not yet been revealed. In this paper, the induced electromotive force (EMF) of the consequent-pole bearingless PM motor is numerically calculated on the basis of the magnetic flux distribution in the airgap around the rotor. It is found that the EMF is distorted by the second harmonic at a specific slot number in a consequent-pole rotor. The calculated EMFs are confirmed with the experimental results in the fabricated test machines.

DOI： 10.1109/TMAG.2009.2018679

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

Thrust magnetic bearings, which can regulate axial displacement of a rotor shaft, have been used for high-speed rotation. However, conventional thrust magnetic bearings have many problems in manufacturing and assembling caused by a large disk rotor of itself. Therefore, we have proposed a novel structure of a thrust magnetic bearing without the large disk rotor. A cylindrical rotor, that has a small diameter as well as a simple shape, is used in the proposed thrust magnetic bearing. This paper introduces the structure and the principle of the proposed thrust magnetic bearing. In addition, it is shown with experiments on high-speed operation that the proposed thrust magnetic bearing is equipped with the sufficient performance in order to make for practical use.

DOI： 10.1109/TMAG.2009.2022178

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Language：English   Publisher：The Japan Society of Mechanical Engineers  

A wide magnetic gap consequent-pole type bearingless motor has been developed. The wide magnetic gap makes it difficult to start up and suspend a shaft with reasonable suspension voltage and current. To provide high current, high voltage rating is demanded, although, high voltage causes bad influence on magnetic suspension. In this paper, the authors have investigated the start-up and rotational characteristics of a prototype bearingless machine driven by voltage source inverters having the rated voltage of 200V and 100V. When the rated voltage is not suitable, significant problems are occurred. The effectiveness of proper selection in the rated voltage is discussed. The result of this study shows that the 100V inverter is a better choice for the bearingless motor.

DOI： 10.1299/jsdd.3.506

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

Bearing less motors are characterized by integration of electrical motors and magnetic bearings. These motors can realize magnetic suspension of rotor shafts without mechanical contacts. Recently, non-contact canned motor pumps without expendable parts by means of using these motors have been vigorously developed. In these pumps, the large magnetic gap length of about 5 mm or more is required of the bearingless motors, because fluid flows into the gap. It becomes difficult to generate sufficient suspension force for magnetic suspension, as the magnetic gap length is increased.Therefore, a novel structure of a 5-axis active control type bearingless motor which can generate the sufficient suspension force under wide-gap condition has been proposed by the principal authors. In general, thrust disks with large outside diameters are used in thrust magnetic bearings. However, in the canned motor pump application, rotational speed is limited to prevent cavitation caused by the large thrust disks. Accordingly, the proposed novel structure is equipped with a cylindrical rotor instead of the large thrust disk, and can generate sufficient suspension force in the axial direction, also. This paper introduces magnetic suspension characteristics of the proposed novel structure with experiments.

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

Magnetic bearings, which can suspend rotor shafts by electromagnetic force without mechanical contacts and lubrication, have been developed and commercialized. In the various types of magnetic bearings, thrust magnetic bearings with thrust disks are generally used for active suspension control of thrust direction. However, the large thrust disks of the thrust magnetic bearings have caused various problems. Therefore, this paper proposes a novel structure of an active thrust magnetic bearing using a cylindrical rotor core without the large thrust disk, and it is shown with 3-D-FEA and experiment that the proposed thrust magnetic bearing with the cylindrical rotor core is effective in producing thrust force.

DOI： 10.1109/TMAG.2008.2002628

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DOI： 10.1541/ieejjournal.128.697

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：WORLD PUBLISHING CORPORATION  

Bearingless motors (BelMs) have two kinds of stator windings composed of motor windings and suspension windings in the same stator. Not only torque but also electromagnetic suspension force can be simultaneously generated in the same stator. Therefore, rotor shaft suspension can be realized without mechanical contacts and lubricant. In addition to advantages of magnetic bearings, the BelMs are expected to have advantageous features such as small size, low cost and high critical speed. This paper introduces reduction effect of suspension input power using rotor eccentricity actively in the BelMs. It is verified experimentally that the rotor eccentricity is effective in reducing the suspension input power.

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

A new non-contact drive system has been developed employing a consequent-pole type bearingless permanent magnet (PM) motor. This bearingless; motor has a much wider gap with respect to its rotor radius. Wide magnetic gaps can cause a decrease in radial magnetic suspension force of the bearingless motor because of an increase in magnetic reluctance. In this paper, the magnetic suspension forces of the fabricated wide gap bearingless drive system are evaluated, when the rotor is magnetically levitated. Experimental results are also compared to the calculated ones using the finite element method. It is demonstrated that the developed consequent-pole type bearingless PM motor with wide magnetic gaps possesses sufficient magnetic suspension force for non-contact operation.

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

DOI： 10.1109/pccon.2007.373171

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

Various kinds of permanent magnet type bearingless motors, which can be characterized by integration of permanent magnet synchronous motors and magnetic bearings, have been proposed and developed. These motors can realize magnetic suspension of rotor shafts by themselves without mechanical contacts or lubrication. However, these motors cannot generate suspension force effectively, because suspension flux necessary for generating suspension force passes through permanent magnets which have large magnetic reluctance. Accordingly, a novel deeply-buried permanent magnet type bearingless motor with 2-pole motor windings and 4-pole suspension windings has been proposed by the principal authors. In the proposed motor, the suspension flux does not pass through the permanent magnets. Thus, it was shown that the proposed motor can generate suspension force effectively in previous papers. In addition, it was confirmed experimentally that the proposed motor has the desired characteristic of high total efficiency considering suspension input power at rated speed. However, irrespective of the proposed motor, no studies have ever tried to make dear the total efficiency of the bearingless motors in wide speed range to the authors' knowledge. Therefore, this paper introduces the total efficiency of the proposed motor in the wide speed range, along with loading test results of a prototype motor.

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

For low speed applications, such as rotating and swing stages, a multi-consequent-pole bearingless motor is proposed. This paper describes basic characteristics of a multi-consequent-pole bearingless motor. Unlike conventional bearingless motors, suspension force generating on consequent-pole type is independent of rotor rotational position. Thus, multi-pole rotors such as 40, 44, and 46 poles are easy without a penalty of high precision in rotating angular position detection. Basic design of pole number selection is discussed with suspension force and average torque capability. Magnetic force error can be reduced with multi-pole rotor configuration. A test machine has been constructed and driven by a compact drive and a CPU unit.

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

Suspension winding design has been investigated for successful magnetic suspension under the limited voltage and current of suspension power electronics circuits. In bearingless motors, winding configuration design is a critical issue. To reduce requirements in suspension winding and its inverter, required current should be reduced. Thus, a large number of series windings with small diameter conductors is preferred. However, the current response in suspension winding becomes slow, and in the worst case, magnetic suspension is not possible. Design consideration of suspension winding is reported with experimental confirmation. Successful start up and operating characteristics are presented.

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

Various types of permanent-magnet type bearingless motors, which have integrated magnetic bearings with permanent magnet synchronous motors, have been developed actively. However, these motors cannot effectively generate electromagnetic suspension force for rotor shaft suspension, because suspension flux is attenuated owing to passing through high magnetic reluctance of permanent magnets. Accordingly, the authors have proposed a novel permanent-magnet type bearingless motor with positive salient pole that inductance L-d in the d-axis direction is greater than inductance L-q in the q-axis direction. In previous papers, it was shown with 2D-FEM that the proposed motor can generate the suspension force effectively, because the suspension flux does not pass through the permanent magnets. This paper introduces basic characteristics of torque and suspension force in the proposed motor with test results of a prototype machine.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SCRIPTA TECHNICA-JOHN WILEY & SONS  

Bearingless switched reluctance motors, which can control rotor radial positions with magnetic force, have been proposed. The bearingless switched reluctance motors are characterized by integration of switched reluctance motors and magnetic bearings. These motors have two kinds of stator windings composed of motor main windings and suspension windings in the same stator in order to produce suspension force that can realize rotor shaft suspension without mechanical contacts or lubrication. For successful stable operation, accurate theoretical formulas of instantaneous torque and suspension force are necessary to a rotational speed controller and a rotor radial position controller. This paper derives the theoretical formulas of the instantaneous torque and the suspension force from an assumption of simple permeance distribution. This derivation process makes an assumption that fringing fluxes are distributed on elliptical lines. It is shown with experimental results that the derived theoretical formulas are very accurate in terms of practical application. (c) 2006 Wiley Periodicals, Inc.

DOI： 10.1002/eej.20157

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

In this paper, a design optimization method for a consequent-pole bearingless motor is presented. This produces stable magnetic suspension under motor torque generation. The suspension force reduction and direction error, which can be caused by torque generation, are limited in the proposed designs. In the optimization routine, the number of suspension and torque winding turns and air-gap length are carefully assessed. Three stators are constructed for experimental verification. The amplitude and direction errors for the suspension force are found to be within acceptable ranges and the operation of the magnetic suspension is acceptable.

DOI： 10.1109/TMAG.2006.879500

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Bearingless switched reluctance motors, which can control rotor radial positions with magnetic force, have been proposed. These motors are characterized by integration of switched reluctance motors and magnetic bearings. It is essential for a control system to consider magnetic saturation in real time in order to realize stable operation at a full torque load. Thus, this paper proposes a method for fast calculation of radial force and torque of a bearingless switched reluctance motor operating in a region of magnetic saturation. It is shown experimentally that the proposed method is effective in calculating the radial force and the torque under conditions of magnetic saturation.

DOI： 10.1109/TIA.2003.821816

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Publishing type：Research paper (scientific journal)  

Bearingless switched reluctance motors, which can control rotor radial positions with magnetic force, have been proposed. The bearingless switched reluctance motors are characterized by integration of switched reluctance motors and magnetic bearings. These motors have two kinds of stator windings composed of motor main windings and suspension windings in the same stator in order to produce suspension force that can realize rotor shaft suspension without mechanical contacts or lubrication. For successful stable operation, accurate theoretical formulae of instantaneous torque and suspension force are necessary to a rotational speed controller and a rotor radial position controller. This paper derives the theoretical formulae of the instantaneous torque and the suspension force from an assumption of simple permeance distribution. This derivation process makes an assumption that fringing fluxes are distributed on elliptical lines. It is shown with experimental results that the derived theoretical formulae are very accurate in terms of practical application.© 2004, The Institute of Electrical Engineers of Japan. All rights reserved.

DOI： 10.1541/ieejias.124.556

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Switched reluctance type bearingless motors are characterized by integration of switched reluctance motors and magnetic bearings. Therefore, these motors can control radial rotor positions with magnetic force actively. Production of suspension force for rotor shaft magnetic suspension is explained with differential stator windings. In the previous paper, accurate theoretical formulae of instantaneous torque and suspension force generated by one phase excitation were derived from an assumption of simple permeance distribution. From the derived theoretical formulae, it is found that there exist cross coupling between the instantaneous torque and the suspension force. This paper derives a possible output area of the instantaneous torque and the suspension force considering the cross coupling in order to realize a stable operation. It is shown with experimental results that the possible output area of the proposed motors is very accurate in terms of practical application.© 2004, The Institute of Electrical Engineers of Japan. All rights reserved.

DOI： 10.1541/ieejias.124.683

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Bearingless switched reluctance motors, which can control rotor radial positions with magnetic force, have been proposed. These motors have combined characteristics of switched reluctance motors and magnetic bearings. This paper proposes a method of determining the advanced angle of square-wave currents in a bearingless switched reluctance motor. Under any torque condition from no load to full load, a stable operation is realized by controlling the advanced angle of square-wave currents with the proposed method. It is shown experimentally that the proposed method is effective in realizing a stable operation.

DOI： 10.1109/28.968181

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Publishing type：Research paper (scientific journal)  

Bearingless switched reluctance motors, which can control rotor radial positions with magnetic force, have been proposed. Bearingless switched reluctance motors have combined characteristics of switched reluctance motors and magnetic bearings. Production of radial force for rotor shaft magnetic suspension is explained with differential stator windings. Mathematical relations between motor currents and radial force are derived by considering cross coupling and fringing fluxes. Theoretical relationships are verified with experimental results at partial overlap positions. © 2001 IEEE.

DOI： 10.1109/28.903123

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In recent years, permanent magnet synchronous motors (PMSMs) are used for many applications because of their high output density and high efficiency. On the other hand, PMSMs having low aspect ratio like flat disk are desired depending on applications. In general, PMSMs employ radial gap structure which has the air gap in radial direction. However, in flat shape, radial gap motors have relatively low torque because their effective surface area of permanent magnet (PM) is small and their coil ends occupy most of the motor volume. Therefore, in flat shape, axial gap structure which has the air gap in axial direction is frequently employed instead of radial gap motors. Since axial gap motors don't have the coil ends in axial direction, they can reduce axial length. Meanwhile, conventional axial gap motors frequently employ double stator structure. Hence, in flatter shape like 'ultra-flat shape', conventional axial gap motors are not suitable because stator back yoke and PM become extremely thin. Instead of those, an axial gap motor employing C-type SMC core is proposed in this paper. Advantages of the proposed axial gap motor using C-type core in ultra-flat shape is illustrated, and then, the proposed motor is analyzed by three-dimensional finite element analysis (3D-FEA).

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Ultra-high-speed motors has frequently been considered for many applications because to increase rotational speed of motors is effective in improving output power density and reducing motor size. In this paper, a 4-pole ultra-high-speed motor with concentrated winding structure is discussed in order to achieve even higher output power density. However, applying 4-pole magnetization to conventional ultra-high-speed motors using Nd sintered permanent magnet (PM) and concentrated winding structure will extremely increase total loss, total loss density, and especially rotor loss density. Therefore, from the viewpoint of cooling and continuous operation, it is important to propose a 4-pole ultra-high-speed motor with concentrated winding structure that can achieve even higher power density without increasing the total loss density and the rotor loss density. This paper shows that there are four important key points in the motor design to realize the proposed motor. It is found that the proposed motor can accomplish 1.5 times higher output power density without increasing the total loss density and the rotor loss density than the conventional 2-pole ultra-high-speed motor with Nd sintered PM and concentrated winding structure.

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This paper deals with stray capacitance in an inverter main circuit on a printed circuit board (PCB), which affects switching characteristics in a voltage source inverter (VSI), and reduction of the stray capacitance. A simulation shows that switching speed is decreased by the stray capacitance on the inverter output electrode pattern. The design guidelines focusing on reduction of the stray capacitance are proposed. Further, based on the guidelines, a SiC-MOSFET VSI to reduce the stray capacitance is designed using a double-sided PCB with 35 mu m-thick standard copper foil. Experiments using SiC-MOSFET VSIs show that the inverter with the redesigned PCB shortens the switching time of the drain-source voltage by 10% for the rise time and by 38% for the fall time compared with an inverter based on our previous design guidelines. Hence, the switching loss is also reduced using the redesigned PCB inverter.

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This paper introduces a matrix converter control method for an isolated AC/DC converter with a resonant circuit that considers non-linearity of the diode rectifier. The method achieves a high output frequency equals to the switching frequency, a constant DC output voltage, sinusoidal input currents, and unity input power factor. Furthermore, soft switching with maximum output power factor is realized by a frequency control. In this type of circuit, the harmonics of the matrix converter output current are caused by the non-linearity of the diode rectifier. A conventional method neglects these harmonics, which cause input current distortion and DC voltage ripple. In a proposed method, the control variables are numerically calculated considering the non-linearity of the diode rectifier and implemented in a lookup table. In addition, a DC voltage feedback is applied to compensate for the effects of parameter error, e.g., voltage drop of the power semiconductor device and deadtime of the MC. The proposed method is evaluated experimentally.

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