2021/10/11 更新

写真a

ウメタニ カズヒロ
梅谷 和弘
UMETANI Kazuhiro
所属
自然科学学域 准教授
職名
准教授
外部リンク

研究キーワード

  • パワーエレクトロニクス

研究分野

  • ものづくり技術(機械・電気電子・化学工学) / 電力工学

学歴

  • 島根大学   大学院総合理工学研究科  

    2014年4月 - 2015年9月

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経歴

  • 東北大学大学院工学研究科   准教授

    2020年4月

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  • 岡山大学自然科学研究科   助教

    2014年10月 - 2020年3月

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  • 株式会社デンソー 会社員

    2008年 - 2014年

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  • 株式会社東芝 会社員

    2007年 - 2008年

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論文

  • Strategy of Topology Selection Based on Quasi-Duality between Series-Series and Series-Parallel Topologies of Resonant Inductive Coupling Wireless Power Transfer Systems 査読

    Masataka Ishihara, Kazuhiro Umetani, Eiji Hiraki

    IEEE Transactions on Power Electronics   35 ( 7 )   6785 - 6798   2020年7月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

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

    DOI: 10.1109/TPEL.2019.2956732

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  • Secondary-Side Center-Tapped Transformer Structure with One-Turn Secondary Coils Integrating Rectifier for Reducing Copper Loss of Forward Converter 査読

    Tomohide Shirakawa, Kazuhiro Umetani, Eiji Hiraki, Wilmar Martinez

    IEEE International Symposium on Industrial Electronics   2020-June   1459 - 1465   2020年6月

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    掲載種別:研究論文(国際会議プロシーディングス)  

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

    DOI: 10.1109/ISIE45063.2020.9152390

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  • Gate Drivers Techniques and Solutions for GaN HEMTs in High Frequency Applications 査読

    Wei Ren Lin, Camilo Suarez, Kazuhiro Umetani, Wilmar Martinez

    IEEE International Symposium on Industrial Electronics   2020-June   712 - 716   2020年6月

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    掲載種別:研究論文(国際会議プロシーディングス)  

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

    DOI: 10.1109/ISIE45063.2020.9152415

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  • Effects of secondary leakage inductance on the LLC resonant converter 査読

    Mostafa Noah, Tomohide Shirakawa, Kazuhiro Umetani, Jun Imaoka, Masayoshi Yamamoto, Eiji Hiraki

    IEEE Transactions on Power Electronics   35 ( 1 )   835 - 852   2020年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

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

    DOI: 10.1109/TPEL.2019.2911093

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  • Axial heating coil structure for reducing magnetic levitation force of all-metal type induction cookers 査読

    Koki Kamaeguchi, Kazuhiro Umetani, Eiji Hiraki

    8th International Conference on Renewable Energy Research and Applications, ICRERA 2019   793 - 798   2019年11月

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    掲載種別:研究論文(国際会議プロシーディングス)  

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

    DOI: 10.1109/ICRERA47325.2019.8997068

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  • Verification of device model by measuring capacitance and static characteristics for predicting switching waveform 査読

    Kengo Koki, Masahiko Yoshioka, Kazuhiro Umetani, Eiji Hiraki

    8th International Conference on Renewable Energy Research and Applications, ICRERA 2019   786 - 792   2019年11月

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    掲載種別:研究論文(国際会議プロシーディングス)  

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

    DOI: 10.1109/ICRERA47325.2019.8996508

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  • Optimal Winding Layer Allocation for Minimizing Copper Loss of Secondary-Side Center-Tapped Forward Transformer with Parallel-Connected Secondary Windings 査読

    Tomohide Shirakawa, Kazuhiro Umetani, Eiji Hiraki, Yuki Itoh, Takashi Hyodo

    2019 IEEE Energy Conversion Congress and Exposition, ECCE 2019   6206 - 6213   2019年9月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/ECCE.2019.8912519

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  • Experimental verification of impedance matching method for repeater to improve spatial freedom of 6.78 MHz resonant inductive coupling wireless power transfer systems 査読

    Keita Fujiki, Masataka Ishihara, Kazuhiro Umetani, Eiji Hiraki

    2019 21st European Conference on Power Electronics and Applications, EPE 2019 ECCE Europe   2019年9月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.23919/EPE.2019.8915171

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  • Automatic active compensation method of cross-coupling in multiple-receiver resonant inductive coupling wireless power transfer systems 査読

    Masataka Ishihara, Keita Fujiki, Kazuhiro Umetani, Eiji Hiraki

    2019 IEEE Energy Conversion Congress and Exposition, ECCE 2019   4584 - 4591   2019年9月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/ECCE.2019.8913279

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  • Analytical Derivation of Phase Current Waveform Eliminating Torque Ripple and Input Current Ripple of Switched Reluctance Motors under Magnetically Saturated Operation 査読

    Takayuki Kusumi, Kosuke Kobayashi, Kazuhiro Umetani, Eiji Hiraki

    2019 IEEE Energy Conversion Congress and Exposition, ECCE 2019   6540 - 6547   2019年9月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/ECCE.2019.8912726

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  • Resonant frequency tuning system for repeater resonator of resonant inductive coupling wireless power transfer 査読

    Akihiro Konishi, Keita Fujiki, Kazuhiro Umetani, Eiji Hiraki

    2019 21st European Conference on Power Electronics and Applications, EPE 2019 ECCE Europe   2019年9月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.23919/EPE.2019.8914736

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  • Receiving-coil structure reducing stray AC resistance for resonant coupling wireless power transfer 査読

    Kazuhiro Umetani, Toru Honjo, Takahiro Koyama, Masataka Ishihara, Eiji Hiraki

    IET Power Electronics   12 ( 9 )   2338 - 2344   2019年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:INST ENGINEERING TECHNOLOGY-IET  

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

    DOI: 10.1049/iet-pel.2018.5358

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  • Effects of secondary leakage inductance on the LLC resonant converter - Part I: Transformer voltage gain and efficiency 査読

    Mostafa Noah, Tomohide Shirakawa, Kazuhiro Umetani, Jun Imaoka, Masayoshi Yamamoto, Eiji Hiraki

    Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC   2019-March   780 - 786   2019年5月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/APEC.2019.8721980

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  • Effects of secondary leakage inductance on the LLC resonant converter - Part II: Frequency control bandwidth with respect to load variation 査読

    Mostafa Noah, Tomohide Shirakawa, Kazuhiro Umetani, Jun Imaoka, Masayoshi Yamamoto, Eiji Hiraki

    Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC   2019-March   1408 - 1414   2019年5月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/APEC.2019.8722190

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  • Simple fully analytical copper loss model of litz wire made of strands twisted in multiple levels 査読

    Kazuhiro Umetani, Jesus Acero, Hector Sarnago, Oscar Lucia, Eiji Hiraki

    Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC   2019-March   1257 - 1264   2019年5月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/APEC.2019.8721827

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  • Volume Reduction Effect of Thinly Extended Core Structure for Transformer in Isolated DC-DC Converter 査読

    R. Murata, T. Shirakawa, K. Umetani, E. Hiraki

    ICPE 2019 - ECCE Asia - 10th International Conference on Power Electronics - ECCE Asia   2132 - 2138   2019年5月

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    掲載種別:研究論文(国際会議プロシーディングス)  

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

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  • Core loss modeling based on equivalent circuit for switched reluctance motors 査読

    Takayuki Kusumi, Kosuke Kobayashi, Takuto Hara, Kazuhiro Umetani, Eiji Hiraki

    Proceedings of the IEEE International Conference on Industrial Technology   2019-February   1743 - 1748   2019年2月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/ICIT.2019.8754931

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  • Feasibility study of fractal-fin heat sink for improving cooling performance of switching power converters 査読

    Shogo Ikegami, Kazuhiro Umetani, Eiji Hiraki, Satoshi Sakai, Satoshi Higashino

    INTELEC, International Telecommunications Energy Conference (Proceedings)   2018-October   2019年1月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/INTLEC.2018.8612377

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  • Prevention of oscillatory false triggering of GaN-FETs by balancing gate-drain capacitance and common-source inductance 査読

    Kazuhiro Umetani, Ryunosuke Matsumoto, Eiji Hiraki

    IEEE Transactions on Industry Applications   55 ( 1 )   610 - 619   2019年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

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

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  • 板状ワンターンコイルを採用した 高降圧中点タップ整流方式の銅損低減に関する取り組み 査読

    白川 知秀, 梅谷 和弘, 平木 英治

    パワーエレクトロニクス学会誌   45 ( 0 )   121 - 129   2019年

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    記述言語:日本語   掲載種別:研究論文(学術雑誌)   出版者・発行元:パワーエレクトロニクス学会  

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

    DOI: 10.5416/jipe.45.121

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  • Improved thin heating coil structure of copper foil feasible for induction cookers 査読

    Kazuhiro Umetani, Tomohiro Mishima, Eiji Hiraki, Takayuki Hirokawa, Makoto Imai, Hideki Sadakata

    Proceedings: IECON 2018 - 44th Annual Conference of the IEEE Industrial Electronics Society   3503 - 3508   2018年12月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/IECON.2018.8591462

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  • Soft-switching control circuit based on traveling and reflected waves for high-frequency resonant inverter applicable to capacitive load impedance 査読

    Aoi Oyane, Koji Itakura, Kazuhiro Umetani, Eiji Hiraki, Tatsuya Ikenari, Shingo Kawano

    Proceedings: IECON 2018 - 44th Annual Conference of the IEEE Industrial Electronics Society   3051 - 3056   2018年12月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/IECON.2018.8592832

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  • Impedance Matching to Maximize Induced Current in Repeater of Resonant Inductive Coupling Wireless Power Transfer Systems 査読

    Masataka Ishihara, Kazuhiro Umetani, Eiji Hiraki

    2018 IEEE Energy Conversion Congress and Exposition, ECCE 2018   6194 - 6201   2018年12月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/ECCE.2018.8557827

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  • Rotor Configuration Which Reduces Copper Loss of Switched Reluctance Motors with Suppression of Torque Ripple and Input Current Ripple 査読

    Takayuki Kusumi, Takuto Hara, Kazuhiro Umetani, Eiji Hiraki

    2018 IEEE Energy Conversion Congress and Exposition, ECCE 2018   6097 - 6103   2018年12月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/ECCE.2018.8558173

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  • Magnetic Design and Experimental Evaluation of a Commercially Available Single Integrated Transformer in Three-Phase LLC Resonant Converter 査読

    Mostafa Noah, Shota Kimura, Jun Imaoka, Wilmar Martinez, Shun Endo, Masayoshi Yamamoto, Kazuhiro Umetani

    IEEE Transactions on Industry Applications   54 ( 6 )   6190 - 6204   2018年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

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

    DOI: 10.1109/TIA.2018.2856631

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  • Improving Robustness Against Variation in Resonance Frequency for Repeater of Resonant Inductive Coupling Wireless Power Transfer Systems 査読

    Masataka Ishihara, Shoma Ohata, Keita Fujiki, Kazuhiro Umetani, Eiji Hiraki

    2018 20th European Conference on Power Electronics and Applications, EPE 2018 ECCE Europe   2018年10月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

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  • Application of Automatic Resonant Frequency Tuning Circuit to Induction Heating System 査読

    Koki Kamaeguchi, Kazuhiro Umetani, Eiji Hiraki

    2018 20th European Conference on Power Electronics and Applications, EPE 2018 ECCE Europe   2018年10月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

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  • Automatic Resonance Frequency Tuning Method for Repeater in Resonant Inductive Coupling Wireless Power Transfer Systems 査読

    Masataka Ishihara, Kazuhiro Umetani, Eiji Hiraki

    2018 International Power Electronics Conference, IPEC-Niigata - ECCE Asia 2018   1610 - 1616   2018年10月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.23919/IPEC.2018.8507768

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  • Verification of the Reduction of the Copper Loss by the Thin Coil Structure for Induction Cookers 査読

    Morimasa Hataya, Koki Kamaeguchi, Eiji Hiraki, Kazuhiro Umetani, Takayuki Hirokawa, Makoto Imai, Hideki Sadakata

    2018 International Power Electronics Conference, IPEC-Niigata - ECCE Asia 2018   410 - 415   2018年10月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.23919/IPEC.2018.8507826

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  • High-frequency Self-Driven Synchronous Rectifier Controller for WPT Systems 査読

    Akihiro Konishi, Kazuhiro Umetani, Eiji Hiraki

    2018 International Power Electronics Conference, IPEC-Niigata - ECCE Asia 2018   1602 - 1609   2018年10月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.23919/IPEC.2018.8507636

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  • Review of Current Balance Mechanism in Multiphase LLC Resonant Converters 査読

    Mostafa Noah, Jun Imaoka, Yuki Ishikura, Kazuhiro Umetani, Masayoshi Yamamoto

    IEEE International Symposium on Industrial Electronics   2018-June   1030 - 1036   2018年8月

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    掲載種別:研究論文(国際会議プロシーディングス)  

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

    DOI: 10.1109/ISIE.2018.8433827

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  • Theoretical Derivation of Phase Current Profile for Switched Reluctance Motors to Suppress Radial Force Ripple and Torque Ripple 査読

    Takayuki Kusumi, Takuto Hara, Kazuhiro Umetani, Eiji Hiraki

    IEEE International Symposium on Industrial Electronics   2018-June   1037 - 1042   2018年8月

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    掲載種別:研究論文(国際会議プロシーディングス)  

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

    DOI: 10.1109/ISIE.2018.8433685

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  • A Current Sharing Method Utilizing Single Balancing Transformer for a Multiphase LLC Resonant Converter with Integrated Magnetics 査読

    Mostafa Noah, Shun Endo, Hiroki Ishibashi, Kimihiro Nanamori, Jun Imaoka, Kazuhiro Umetani, Masayoshi Yamamoto

    IEEE Journal of Emerging and Selected Topics in Power Electronics   6 ( 2 )   977 - 992   2018年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

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

    DOI: 10.1109/JESTPE.2017.2777508

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  • Lagrangian dynamics model and practical implementation of an integrated transformer in multi-phase LLC resonant converter 査読

    Mostafa Noah, Kazuhiro Umetani, Jun Imaoka, Masayoshi Yamamoto

    IET Power Electronics   11 ( 2 )   339 - 347   2018年2月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:INST ENGINEERING TECHNOLOGY-IET  

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

    DOI: 10.1049/iet-pel.2017.0485

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  • Elucidation of quasi-duality between series-series and series-parallel topologies of resonant inductive coupling wireless power transfer systems 査読

    Masataka Ishihara, Kazuhiro Umetani, Eiji Hiraki

    Proceedings of the International Conference on Power Electronics and Drive Systems   2017-December   674 - 679   2018年2月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/PEDS.2017.8289248

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  • Winding orientation method to minimise the secondary leakage of a gapped transformer utilised in LLC resonant converter 査読

    M. Noah, K. Umetani, M. Yamamoto, J. Imaoka

    Electronics Letters   54 ( 3 )   157 - 159   2018年2月

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    掲載種別:研究論文(学術雑誌)  

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

    DOI: 10.1049/el.2017.4013

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  • Design optimization method for the load impedance to maximize the output power in dual transmitting resonator wireless power transfer system 査読

    Takahiro Koyama, Kazuhiro Umetani, Eiji Hiraki

    IEEJ Journal of Industry Applications   7 ( 1 )   49 - 55   2018年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:INST ELECTRICAL ENGINEERS JAPAN  

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

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  • 昇圧型DC-DCコンバータにおける高い速応性とロバスト性を有する新制御手法の提案 査読

    川上 太知, 原田 敏和, 山本 真義, 梅谷 和弘

    電気学会論文誌. C   138 ( 4 )   395 - 404   2018年

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    記述言語:日本語   掲載種別:研究論文(学術雑誌)   出版者・発行元:一般社団法人 電気学会  

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

    DOI: 10.1541/ieejeiss.138.395

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  • Compact three-phase AC inductor network for PFC converter using magnetic coupled technique 査読

    Takuya Ozaki, Hiroki Nakaido, Kazuhiro Umetani, Eiji Hiraki, Tatsuya Ikenari, Shingo Kawano

    Proceedings IECON 2017 - 43rd Annual Conference of the IEEE Industrial Electronics Society   2017-January   958 - 963   2017年12月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/IECON.2017.8216165

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  • Soft-switching technique applicable to capacitive load for resonant inverter of plasma generator 査読

    Koji Itakura, Hiroaki Kakemizu, Hiroki Nakaido, Kazuhiro Umetani, Eiji Hiraki, Tatsuya Ikenari, Shingo Kawano

    Proceedings IECON 2017 - 43rd Annual Conference of the IEEE Industrial Electronics Society   2017-January   1556 - 1562   2017年12月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/IECON.2017.8216264

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  • Simple self-driven synchronous rectifier for resonant inductive coupling wireless power transfer 査読

    Takahiro Koyama, Toru Honjo, Masataka Ishihara, Kazuhiro Umetani, Eiji Hiraki

    INTELEC, International Telecommunications Energy Conference (Proceedings)   2017-October   363 - 368   2017年12月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/INTLEC.2017.8214163

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  • Total volume evaluation of high-power density non-isolated DC-DC converters with integrated magnetics for electric vehicles 査読

    Wilmar Martinez, Camilo Cortes, Masayoshi Yamamoto, Jun Imaoka, Kazuhiro Umetani

    IET Power Electronics   10 ( 14 )   2010 - 2020   2017年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:INST ENGINEERING TECHNOLOGY-IET  

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

    DOI: 10.1049/iet-pel.2017.0157

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  • Application of extremum co-energy principle for homogenizing current distribution in parallel-connected windings in transformers: Design optimization of winding turn allocation among winding layers 査読

    Tomohide Shirakawa, Kazuhiro Umetani, Eiji Hiraki

    2017 19th European Conference on Power Electronics and Applications, EPE 2017 ECCE Europe   2017-January   P1 - P10   2017年11月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.23919/EPE17ECCEEurope.2017.8099115

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  • An investigation into a slight-variation of the transformer effective permeability in LLC resonant converter 査読

    Mostafa Noah, Shun Endo, Shota Kimura, Masayoshi Yamamoto, Jun Imaoka, Kazuhiro Umetani, Eiji Hiraki

    2017 19th European Conference on Power Electronics and Applications, EPE 2017 ECCE Europe   2017-January   2017年11月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.23919/EPE17ECCEEurope.2017.8099301

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  • Optimization of the balance between the gate-Drain capacitance and the common source inductance for preventing the oscillatory false triggering of fast switching GaN- FETs 査読

    Rynosuke Matsumoto, Kazuhiro Umetani, Eiji Hiraki

    2017 IEEE Energy Conversion Congress and Exposition, ECCE 2017   2017-January   405 - 412   2017年11月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/ECCE.2017.8095811

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  • Analytical investigation on design instruction to avoid oscillatory false triggering of fast switching SiC-MOSFETs 査読

    Yusuke Sugihara, Kimihiro Nanamori, Seiya Ishiwaki, Yuma Hayashi, Kyota Aikawa, Kazuhiro Umetani, Eiji Hiraki, Masayoshi Yamamoto

    2017 IEEE Energy Conversion Congress and Exposition, ECCE 2017   2017-January   5113 - 5118   2017年11月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/ECCE.2017.8096861

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  • A Lagrangian dynamics model of integrated transformer incorporated in a multi-phase LLC resonant converter 査読

    Mostafa Noah, Kazuhiro Umetani, Shun Endo, Hiraki Ishibashi, Jun Imaoka, Masayoshi Yamamoto

    2017 IEEE Energy Conversion Congress and Exposition, ECCE 2017   2017-January   3781 - 3787   2017年11月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

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  • Straightforward Measurement Method of Common Source Inductance for Fast Switching Semiconductor Devices Mounted on Board 査読

    Kazuhiro Umetani, Kyota Aikawa, Eiji Hiraki

    IEEE Transactions on Industrial Electronics   64 ( 10 )   8258 - 8267   2017年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

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

    DOI: 10.1109/TIE.2017.2694411

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  • Measurement of the common source inductance of typical switching device packages 査読

    Kyota Aikawa, Tomohumi Shiida, Ryunosuke Matsumoto, Kazuhiro Umetani, Eiji Hiraki

    2017 IEEE 3rd International Future Energy Electronics Conference and ECCE Asia, IFEEC - ECCE Asia 2017   1172 - 1177   2017年7月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/IFEEC.2017.7992207

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  • Current ripple modeling of an interleaved high step-up converter with coupled inductor 査読

    Wilmar Martinez, Camilo A. Cortes, Jun Imaoka, Kazuhiro Umetani, Masayoshi Yamamoto

    2017 IEEE 3rd International Future Energy Electronics Conference and ECCE Asia, IFEEC - ECCE Asia 2017   1084 - 1089   2017年7月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/IFEEC.2017.7992192

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  • Simple analytical derivation of magnetic flux profile eliminating source current ripple and torque ripple of switched reluctance motors for electric vehicle propulsion 査読

    Takayuki Kusumi, Takuto Hara, Kazuhiro Umetani, Eiji Hiraki

    Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC   3142 - 3149   2017年5月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/APEC.2017.7931146

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  • A novel three-phase LLC resonant converter with integrated magnetics for lower turn-off losses and higher power density 査読

    Mostafa Noah, Shota Kimura, Shun Endo, Masayoshi Yamamoto, Jun Imaoka, Kazuhiro Umetani, Wilmar Martinez

    Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC   322 - 329   2017年5月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/APEC.2017.7930712

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  • Extremum co-energy principle for analyzing AC current distribution in parallel-connected wires of high frequency power inductors 査読

    T. Shirakawa, G. Yamasaki, K. Umetani, E. Hiraki

    19th International Conference on Electrical Machines and Systems, ICEMS 2016   7 ( 1 )   35 - 42   2017年1月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:INST ELECTRICAL ENGINEERS JAPAN  

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

    DOI: 10.1541/ieejjia.7.35

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  • Novel receiving coil structure for improving efficiency and power transfer capability of resonant inductive coupling wireless power transfer 査読

    T. Honjo, T. Koyama, K. Umetani, E. Hiraki

    19th International Conference on Electrical Machines and Systems, ICEMS 2016   2017年1月

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    掲載種別:研究論文(国際会議プロシーディングス)  

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

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  • Novel thin heating coil structure with reduced copper loss for high frequency induction cookers 査読

    M. Hataya, Y. Oka, K. Umetani, E. Hiraki, T. Hirokawa, M. Imai

    19th International Conference on Electrical Machines and Systems, ICEMS 2016   2017年1月

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    掲載種別:研究論文(国際会議プロシーディングス)  

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

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  • Local Effective Thermal Inertia Estimated by Cloud Appearance 査読

    Masanori Onishi, Isao Iizawa, Kazuhiro Umetani, Aya Ito, Arata Yajima, Kosaku Ono, Naoki Amemura, Satoshi Sakai

    SOLA   13   59 - 62   2017年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:METEOROLOGICAL SOC JAPAN  

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

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  • Copper loss analysis based on extremum co-energy principle for high frequency forward transformers with parallel-connected windings 査読

    Tomohide Shirakawa, Genki Yamasaki, Kazuhiro Umetani, Eiji Hiraki

    IECON Proceedings (Industrial Electronics Conference)   1099 - 1105   2016年12月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/IECON.2016.7793013

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  • Simple control technique to eliminate source current ripple and torque ripple of switched reluctance motors for electric vehicle propulsion 査読

    Takayuki Kusumi, Takuto Hara, Kazuhiro Umetani, Eiji Hiraki

    IECON Proceedings (Industrial Electronics Conference)   1876 - 1881   2016年12月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/IECON.2016.7793324

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  • Quasi-duality between SS and SP topologies of basic electric-field coupling wireless power transfer system 査読

    M. Ishihara, K. Umetani, H. Umegami, E. Hiraki, M. Yamamoto

    Electronics Letters   52 ( 25 )   2057 - 2059   2016年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:INST ENGINEERING TECHNOLOGY-IET  

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

    DOI: 10.1049/el.2016.1253

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  • A design guideline of parasitic inductance for preventing oscillatory false triggering of fast switching GaN-FET 査読

    Kazuhiro Umetani, Keisuke Yagyu, Eiji Hiraki

    IEEJ Transactions on Electrical and Electronic Engineering   11   S84 - S90   2016年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:WILEY  

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

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  • Lagrangian derivation and analysis of a simple equivalent circuit model of wireless power transfer system with dual transmitting resonators 査読

    Takahiro Koyama, Toru Honjo, Kazuhiro Umetani, Eiji Hiraki

    2016 18th European Conference on Power Electronics and Applications, EPE 2016 ECCE Europe   2016年10月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/EPE.2016.7695439

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  • A novel high step-down interleaved converter with coupled inductor 査読

    Wilmar Martinez, Jun Imaoka, Yuki Itoh, Masayoshi Yamamoto, Kazuhiro Umetani

    INTELEC, International Telecommunications Energy Conference (Proceedings)   2016-September   2016年9月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/INTLEC.2015.7572421

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  • Passive regenerative turn-off snubber composed of two diodes and a capacitor for two-phase interleaved boost chopper 査読

    Kazuhiro Umetani, Eiji Hiraki, Masayoshi Yamamoto

    INTELEC, International Telecommunications Energy Conference (Proceedings)   2016-September   2016年9月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/INTLEC.2015.7572341

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  • A simple behavior model for switched reluctance motors based on magnetic energy 査読

    Takuto Hara, Takayuki Kusumi, Kazuhiro Umetani, Eiji Hiraki

    2016 IEEE 8th International Power Electronics and Motion Control Conference, IPEMC-ECCE Asia 2016   109 - 115   2016年7月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/IPEMC.2016.7512270

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  • Lagrangian method for deriving electrically dual power converters applicable to nonplanar circuit topologies 査読

    Kazuhiro Umetani

    IEEJ Transactions on Electrical and Electronic Engineering   11 ( 4 )   521 - 530   2016年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:WILEY-BLACKWELL  

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

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  • Three-phase LLC resonant converter with integrated magnetics 査読

    Wilmar Martinez, Mostafa Noah, Shun Endo, Kimihiro Nanamori, Shota Kimura, Yuki Itoh, Masayoshi Yamamoto, Jun Imaoka, Kazuhiro Umetani

    ECCE 2016 - IEEE Energy Conversion Congress and Exposition, Proceedings   2016年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/ECCE.2016.7855520

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  • Magnetic analysis, design, and experimental evaluations of integrated winding coupled inductors in interleaved converters 査読

    Jun Imaoka, Kazuhiro Umetani, Shota Kimura, Willmar Martinez, Masayoshi Yamamoto, Seikoh Arimura, Tetsuo Hirano

    IEEJ Journal of Industry Applications   5 ( 3 )   276 - 288   2016年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:INST ELECTRICAL ENGINEERS JAPAN  

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

    DOI: 10.1541/ieejjia.5.276

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  • Time evolution of an urban heat island from high-density observations in Kyoto city 査読

    Isao Iizawa, Kazuhiro Umetani, Aya Ito, Arata Yajima, Kosaku Ono, Naoki Amemura, Masanori Onishi, Satoshi Sakai

    Scientific Online Letters on the Atmosphere   12 ( 1 )   51 - 54   2016年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:METEOROLOGICAL SOC JAPAN  

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

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  • Simple flux-based Lagrangian formulation to model nonlinearity of concentrated-winding switched reluctance motors 査読

    K. Umetani, M. Yamamoto, E. Hiraki

    Electronics Letters   51 ( 24 )   1984 - 1986   2015年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:INST ENGINEERING TECHNOLOGY-IET  

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

    DOI: 10.1049/el.2015.0950

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  • Mid-range kHz electric resonance coupling wireless power tranfser 査読

    Hirokatsu Umegami, Masataka Ishihara, Fumiya Hattori, Mitsuru Masuda, Masayoshi Yamamoto, Kazuhiro Umetani

    2015 IEEE Energy Conversion Congress and Exposition, ECCE 2015   3197 - 3202   2015年10月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/ECCE.2015.7310109

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  • Non-isolated interleaved high step-up converter with reduced voltage multiplier stages and a regenerative turn-off snubber 査読

    Kazuhiro Umetani, Eiji Hiraki, Masayoshi Yamamoto

    2015 IEEE Energy Conversion Congress and Exposition, ECCE 2015   125 - 132   2015年10月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/ECCE.2015.7309679

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  • Lagrangian-based equivalent circuit of basic electric-field coupling wireless power transfer system 査読

    Hirokatsu Umegami, Kazuhiro Umetani, Masayoshi Yamamoto, Eiji Hiraki

    IEEJ Transactions on Electrical and Electronic Engineering   10   S168 - S170   2015年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:WILEY-BLACKWELL  

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

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  • Analysis of coupled-inductor configuration for an interleaved high step-up converter 査読

    Wilmar Martinez, Jun Imaoka, Yuki Itoh, Masayoshi Yamamoto, Kazuhiro Umetani

    9th International Conference on Power Electronics - ECCE Asia: "Green World with Power Electronics", ICPE 2015-ECCE Asia   2241 - 2248   2015年7月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

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  • Evaluation of the lagrangian method for deriving equivalent circuits of integrated magnetic components: A case study using the integrated winding coupled inductor 査読

    Kazuhiro Umetani, Jun Imaoka, Masayoshi Yamamoto, Seikoh Arimura, Tetsuo Hirano

    IEEE Transactions on Industry Applications   51 ( 1 )   547 - 555   2015年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

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

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  • High Step-Up Interleaved Converter for Renewable Energy and Automotive Applications 査読

    Wilmar Martinez, Jun Imaoka, Masayoshi Yamamoto, Kazuhiro Umetani

    2015 International Conference on Renewable Energy Research and Applications, ICRERA 2015   809 - 814   2015年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/ICRERA.2015.7418524

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  • A magnetic structure integrating differential-mode and common-mode inductors with improved tolerance to DC saturation 査読

    Kazuhiro Umetani, Takahiro Tera, Kazuhrio Shirakawa

    IEEJ Journal of Industry Applications   4 ( 3 )   166 - 173   2015年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:INST ELECTRICAL ENGINEERS JAPAN  

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

    DOI: 10.1541/ieejjia.4.166

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  • Lagrangian-based derivation of a novel sliding-mode control for synchronous buck converters 査読

    Kazuhiro Umetani, Masayoshi Yamamoto, Eiji Hiraki

    IEEJ Journal of Industry Applications   4 ( 6 )   728 - 729   2015年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:INST ELECTRICAL ENGINEERS JAPAN  

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

    DOI: 10.1541/ieejjia.4.728

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  • A detection method of DC magnetization utilizing local inhomogeneity of flux distribution in power transformer core 査読

    Kazuhiro Umetani, Yuki Itoh, Masayoshi Yamamoto

    2014 IEEE Energy Conversion Congress and Exposition, ECCE 2014   3739 - 3746   2014年11月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/ECCE.2014.6953909

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  • A unidirectional boost chopper with snubber energy regeneration using a coupled inductor 査読

    Kazuhiro Umetani, Fujiyuki Iwamoto, Keisuke Yagyu

    IEEJ Transactions on Electrical and Electronic Engineering   9 ( 3 )   315 - 323   2014年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:WILEY  

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

    DOI: 10.1002/tee.21972

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  • High power density DC-DC converter for home energy management systems 査読

    Wilmar Martinez, Shota Kimura, Jun Imaoka, Masayoshi Yamamoto, Kazuhiro Umetani, Seikoh Arimura, Tetsuo Hirano

    Proceedings of 2014 International Conference on Intelligent Green Building and Smart Grid, IGBSG 2014   2014年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/IGBSG.2014.6835247

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  • Parasitic Resistance Analysis in a Novel High Step-Up Interleaved Converter for Hybrid Electric Vehicles (共著) 査読

    Wilmar Martinez, Jun Imaoka, Masayoshi Yamamoto, Kazuhiro Umetani

    パワーエレクトロニクス学会誌   40 ( 0 )   93 - 104   2014年

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.5416/jipe.40.93

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  • Novel magnetic structure of integrated differential-mode and common-mode inductors to suppress DC saturation 査読

    Kazuhiro Umetani, Takahiro Tera, Kazuhiro Shirakawa

    2014 International Power Electronics Conference, IPEC-Hiroshima - ECCE Asia 2014   304 - 311   2014年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/IPEC.2014.6869598

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  • Improvement of saturation property of iron powder core by flux homogenizing structure 査読

    Kazuhiro Umetani

    IEEJ Transactions on Electrical and Electronic Engineering   8 ( 6 )   640 - 648   2013年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:WILEY-BLACKWELL  

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

    DOI: 10.1002/tee.21908

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  • Characteristics analysis and performance evaluation for interleaved boost converter with integrated winding coupled inductor 査読

    Jun Imaoka, Masayoshi Yamamoto, Kazuhiro Umetani, Seikoh Arimura, Tetsuo Hirano

    2013 IEEE Energy Conversion Congress and Exposition, ECCE 2013   3711 - 3718   2013年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/ECCE.2013.6647191

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  • Evaluation of the Lagrangian method for deriving equivalent circuits of integrated magnetic components: A case study using the integrated winding coupled inductor 査読

    Kazuhiro Umetani, Seikoh Arimura, Tetsuo Hirano, Jun Imaoka, Masayoshi Yamamoto

    2013 IEEE Energy Conversion Congress and Exposition, ECCE 2013   495 - 502   2013年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IEEE  

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

    DOI: 10.1109/ECCE.2013.6646742

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  • A generalized method for Lagrangian modeling of power conversion circuit with integrated magnetic components 査読

    Kazuhiro Umetani

    IEEJ Transactions on Electrical and Electronic Engineering   7 ( SUPPL. 1 )   S146 - S152   2012年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:WILEY  

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

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  • 都市熱環境観測システムの開発研究 査読

    酒井 敏, 梅谷 和弘, 飯澤 功, 伊藤 文, 小野 耕作, 矢島 新, 飴村 尚起, 森永 修司

    天気   56 ( 5 )   337 - 351   2009年5月

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    記述言語:日本語   掲載種別:研究論文(学術雑誌)   出版者・発行元:日本気象学会  

    ヒートアイランド現象など都市の熱環境を観測するための多点観測システムを開発した.都市部での観測では設置場所などの制約が大きく,小型軽量の観測機材が求められる.特に,熱的な応答を調べるために必要な放射計は,従来かなり大掛かりで都市部での観測は困難であった.ここでは,気温測定などのための基本的な温度センサに加えて,これらの放射に関するセンサを含め,市販の安価な部品を使って製作し,従来の熱環境を観測するシステムとほぼ同等の精度を有することを示す.

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    その他リンク: http://dl.ndl.go.jp/info:ndljp/pid/10607961

  • A Practical Pyrgeometer Using the Representative Angle (共著) 査読

    S. Sakai, A. Ito, K. Umetani, I. Iizawa, M. Onishi

    Journal of atmospheric and oceanic technologies   26 ( 3 )   647 - 655   2009年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1175/2008JTECHA1076.1

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  • 局地気象観測のための微気圧計の開発 査読

    梅谷 和弘, 酒井 敏

    天気   54 ( 3 )   215 - 224   2007年3月

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    記述言語:日本語   掲載種別:研究論文(学術雑誌)   出版者・発行元:日本気象学会  

    通常数十分程度までの短い周期の圧力変動を計測するために用いられる微気圧計を利用して,数分程度から1日程度までの気圧変動を手軽に広帯域で測定する手法を開発し性能を評価した.この手法では振幅の大きな長周期の圧力変動の感度を下げ,短周期の変動と同程度の振幅に均して計測することで,広い周波帯でほぼ同じS/N比となるため,大気圧変動の計測では絶対圧計よりも利点が多い.同時に記録した絶対圧計と微気圧計の出力比較によって性能評価を行った結果,温度変化が小さい場所では誤差が周波数によらず振幅の2%程度となることが分かった.この精度は,ヒートアイランド現象によって駆動されるヒートアイランド循環に伴う熱的な圧力差を分解できるものであり,従来の微気圧計で観測されてきた重力波の観測からより長周期の現象である局地循環まで幅広い現象を一つの測定器で測定できる見通しが立った.

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    その他リンク: http://dl.ndl.go.jp/info:ndljp/pid/10607000

  • A new technique of radiation thermometry using a consumer digital camcorder: Observations of red glow at Aso volcano, Japan (共著) 査読

    T. Saito, S. Sakai, I. Iizawa, E. Suda, K. Umetani, K. Kaneko, Y. Furukawa, T. Ohkura

    Earth, Planets and Space   57 ( 2 )   e5 - e8   2005年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1186/bf03352550

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MISC

  • 研究グループ紹介:岡山大学 大学院自然科学研究科 電力変換システム工学研究室

    梅谷 和弘, 七戸 希, 平木 英治

    電気学会論文誌D(産業応用部門誌)   139 ( 6 )   NL6_8 - NL6_8   2019年

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    記述言語:日本語   出版者・発行元:一般社団法人 電気学会  

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

    DOI: 10.1541/ieejias.139.NL6_8

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  • 学界情報 国際会議レポート:The 12<sup>th</sup> IEEE International Conference on Power Electronics and Drive Systems (PEDS 2017), December 12-15, 2017, Honolulu, Hawaii, USA

    梅谷 和弘

    電気学会論文誌. D, 産業応用部門誌   138 ( 5 )   NL5_10 - NL5_10   2018年

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    記述言語:日本語   出版者・発行元:一般社団法人 電気学会  

    DOI: 10.1541/ieejias.138.NL5_10

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  • 火星環境模擬チャンバーを用いた探査機器の耐環境試験

    千秋 博紀, 大野 宗祐, 乙部 直人, 山本 真行, 仲吉 信人, はしもと じょーじ, 梅谷 和弘, 池原 光介, 藤津 裕亮

    千葉工業大学研究報告 = Report of Chiba Institute of Technology   ( 63 )   69 - 74   2016年1月

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    記述言語:日本語   出版者・発行元:Chiba Institute of Technology  

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  • 手作りの測機で身近な気象を観測し新事実に挑む参加型科学プロジェクト : 素朴な科学への挑戦(ヘッドライン:新世紀型理数科系教育の展開研究II)

    酒井 敏, 飯澤 功, 梅谷 和弘

    化学と教育   54 ( 6 )   322 - 325   2006年

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    記述言語:日本語   出版者・発行元:公益社団法人 日本化学会  

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

    DOI: 10.20665/kakyoshi.54.6_322

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講演・口頭発表等

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受賞

  • 電気学会優秀論文発表賞(産業応用部門表彰)

    2016年  

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    受賞国:日本国

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  • 電気学会優秀論文発表A賞

    2014年  

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    受賞国:日本国

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  • 電気学会優秀論文発表賞(産業応用部門表彰)

    2011年  

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担当授業科目

  • パワーエレクトロニクス (2021年度) 第4学期  - 月7,月8,木1,木2

  • 現代パワーエレクトロニクス論 (2021年度) 前期  - その他

  • 表現技法1 (2021年度) 前期  - その他

  • 表現技法2 (2021年度) 後期  - その他

  • 電力回路設計論 (2021年度) 後期  - 木5~6

  • 電力変換システム工学演習 (2021年度) 通年  - その他

  • 電子情報システム工学特別研究 (2021年度) 通年  - その他

  • 電気通信系実験B (2021年度) 3・4学期  - 水2,水3,水4,水5,水6

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