掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE Transactions on Power Electronics  

Gallium nitride high-electron-mobility transistors (GaN-HEMTs) are promising for high-speed switching capability and small on-resistance. However, large turn-off surge and limited cooling capability due to their small chip size are hindering their application to high power conversion. To solve these problems, this letter proposes a novel power module structure with small power loop inductance and small thermal resistance based on recently proposed power module structures. The proposed structure comprises two aluminum-clad printed circuit boards (PCBs) that sandwich the GaN-HEMT devices. These PCBs generate eddy current inside the aluminum base to reduce power loop inductance and provide an additional thermal path to improve the cooling performance. These features were tested by an experiment that compared 3-kW half-bridge prototype power modules of the proposed and conventional structures. As a result, the proposed structure revealed power loop inductance of 1.4 nH and thermal resistance of 0.72 K/W, which corresponded to a reduction by 53% and 20%, respectively, compared to the conventional structure.

DOI： 10.1109/TPEL.2024.3431615

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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）  

DOI： 10.1109/ECCE55643.2024.10860887

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）  

DOI： 10.1109/ECCE55643.2024.10860997

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：Conference Proceedings IEEE Applied Power Electronics Conference and Exposition APEC  

LLC converter is well known as an attractive topology however, it suffers from system stability degradation depending on load conditions, which has limited use for many applications. The previous study addressed this problem by proposing a novel control, called the 'power factor (cosθ) control', which adjusts the phase difference θ between the inverter voltage and primary current of the LLC half-bridge instead of adjusting the operating frequency. However, the previous prototype required a complicated analog circuit for the control, which appeared difficult for practical application. This paper aims at achieving a compact implementation of the control circuit. A special "Event-Driven-Timer Based"digital control is adopted which can automatically track the timing and frequency by detecting the resonant trigger point and turning on the main switch. The prototype board exhibited great size reduction of the control circuit as well as excellent controllability, supporting promising features for practical application.

DOI： 10.1109/APEC48139.2024.10509360

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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）   出版者・発行元：INTELEC International Telecommunications Energy Conference Proceedings  

In recent years, with the advent of next-generation semiconductors, circuit boards have been miniaturized to accommodate higher frequencies. Miniaturization also means increased heat density. Further miniaturization of switching converters and inverters requires heat sinks that provide excellent heat dissipation performance in a limited volume, and the cylindrical fin type has been commonly used as a heat sink structure. However, cylindrical fin type heat sinks have the problem of large pressure loss when refrigerant passes through them. To solve this problem, streamlined fins and elliptical fin have been proposed to replace cylindrical fin type heat sinks. Although many studies have compared the heat dissipation performance of elliptical and cylindrical fin, few studies have compared it with that of streamlined fins. Therefore, in this paper, a heat sink structure with multiple streamlined fins is constructed. The change in pressure loss due to the change in fin shape and the resulting heat dissipation performance were verified by thermo-fluid analysis and actual device verification, and compared with the conventional cylindrical fin type. As a result, it was confirmed that the streamlined fin structure slightly increases thermal resistance and significantly reduces pressure loss. Comparison of the thermal resistance-pressure loss characteristics showed that the streamlined fins can sufficiently reduce the pressure loss for the same thermal resistance value. In the case of forced air cooling, the heat dissipation performance of the streamlined fins could be expected to improve with fan selection.

DOI： 10.1109/INTELEC60315.2024.10679005

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掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE Access  

In resonant inductive coupling wireless power transfer systems, a repeater resonator is crucial in expanding the charging area, enabling efficient power supply to receivers, such as small Internet of Things (IoT) devices sparsely distributed in a wide area. However, the repeater current is highly susceptible to deviations in resonance frequency due to manufacturing tolerance and aging, as well as to the magnetic coupling between the transmitter and repeater coils, potentially leading to insufficient amplitude. Consequently, the magnetic field generated by the repeater decreases and the receiver may be difficult to obtain sufficient power from the transmitter via the repeater. To address this problem, this paper proposes a wireless power transfer system with active reactance compensators incorporated in the repeater and the transmitter. The proposed system can equivalently adjust the resonant frequencies of the transmitter and repeater to stably maximize the repeater coil current regardless of the variations in the resonant frequency and the magnetic coupling intensity. Experiments successfully verify that the proposed system can provide a more stable and larger repeater current and output power than the conventional system against the variations in the magnetic field intensity and the resonant frequency of the repeater, validating the feasibility of the proposed system for practical utilization of the repeater in expanding the charging area.

DOI： 10.1109/ACCESS.2024.3428864

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出版者・発行元：2024 IEEE Design Methodologies Conference Dmc 2024  

Heatsink design is a critical aspect of thermal management in power electronics. This paper presents three innovative 3D models of heatsink developed in Ansys Icepak, evaluated against a conventional cross-cut heatsink of the same size but differing in weight and volume. Simulation results demonstrate that the maximum temperature of the new designs is significantly lower than the minimum temperature observed in the conventional heatsink. The maximum temperature for each innovated heatsinks have dropped 11 %, 11.2% and 13.6%. Additional evaluation criteria, such as velocity and heat transfer coefficients, were also compared. Furthermore, the innovative heatsinks offer reduced volume and weight, highlighting their potential for applications where lightweight and efficient thermal dissipation are essential in power electronic.

DOI： 10.1109/DMC62632.2024.10812126

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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）   出版者・発行元：INTELEC International Telecommunications Energy Conference Proceedings  

A high-voltage dc power supply system is an attractive solution for reducing the system cost and improving efficiency. This system needs compact but high-efficiency high-step-down converters to exploit the benefits. This paper proposes a novel converter for a better candidate than traditional converters. The proposed converter is a non-isolated high step-down converter utilizing the switched capacitor technology. Compared to conventional similar topologies, the number of switched capacitor stages can be reduced, enabling the compact converter design. Furthermore, this converter has interleaved output, which can downsize the magnetic devices. The current of the interleaved output is automatically balanced without special control, enabling simple controller implementation. These features were successfully verified by the experiment.

DOI： 10.1109/INTELEC60315.2024.10678985

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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）   出版者・発行元：Conference Proceedings IEEE Applied Power Electronics Conference and Exposition APEC  

In recent years, using SiC devices for fast switching have led to the miniaturization of power modules. However, due to the high di/dt of fast switching, false triggering and parallel oscillation caused by high di/dt have become an issue. A method for extracting equivalent circuits, including parasitic inductance, is essential to solve these issues. In power modules, multiple devices are often connected in parallel to meet the demand for high power density. Therefore, complex mutual coupling between wirings makes it challenging to determine the equivalent circuit, including parasitic inductance. In this paper, we propose an equivalent circuit extraction method for power modules that focuses on current loops instead of focusing on the wiring section as in previous studies. The proposed method can extract the effective inductance considering the mutual coupling between wires with fewer measurements than the conventional method. We first summarize the concept of inductance and explain the advantages of the extraction method, focusi ng on current loops. Next, the equivalent circuit, including the parasitic inductance of a double-pulse test circuit board with SiC-MOSFETs connected in parallel, is extracted using the proposed method. To confirm the validity of the proposed method, a double resonance system was constructed using the test circuit board wiring, and the frequency characteristics of the actual measurement and the simulation based on the extracted parasitic inductance were compared.

DOI： 10.1109/APEC48139.2024.10509099

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出版者・発行元：13th International Conference on Renewable Energy Research and Applications Icrera 2024  

Recently, GaN-HEMTs are expected to be used in high-power applications due to their characteristics. To deal with high-power in GaN-HEMTs, it is necessary to connect in parallel to reduce the current stress. However, the paralleled GaN-HEMTs often suffer from oscillatory false triggering, which is a key issue for preventing the practical application of GaN-HEMTs in high-power applications. The purpose of this study is to develop a new method to avoid the oscillatory false triggering of parallel connection by optimally designing the parasitic capacitance and common-source inductance. To achieve this purpose, this paper derives and analyzes an equivalent circuit after the turn-off transition of the circuit which have half-bridge structure with two-paralleled GaN - HEMTs. As a result, we derived the guideline to prevent the oscillatory false triggering caused between two paralleled GaN - HEMTs. The validity of this guideline was confirmed by experiments.

DOI： 10.1109/ICRERA62673.2024.10815257

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出版者・発行元：2024 IEEE 21st International Power Electronics and Motion Control Conference Pemc 2024  

This paper presents guidelines for suppressing oscillations between paralleled GaN-HEMTs focusing on the harmonics of switching surges. In recent years, false triggering due to oscillation between paralleled GaN-HEMTs has become a practical issue. To suppress this oscillation, it is essential to reduce the noise that triggers the oscillation. This noise is caused by switching surges and inductance imbalances in the PCB layout. However, as more GaN-HEMTs is connected in parallel, it becomes difficult to avoid inductance imbalance in the PCB layout. This paper reveals that the harmonics of the switching surge trigger oscillation in paralleled GaN-HEMTs. These harmonics are caused by nonlinearity of the drain-source capacitance. Based on this insight, we propose parasitic inductance design considering harmonics of switching surge. Experiments have confirmed the transition from switching surges to oscillation. Furthermore, we confirmed through simulation that oscillation between paralleled GaN-HEMTs can be suppressed by designing the resonant frequency between GaN-HEMTs to avoid the harmonics of the switching surge.

DOI： 10.1109/PEMC61721.2024.10726359

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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）  

DOI： 10.1109/IGBSG.2014.6835247

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）  

DOI： 10.1109/ECCEEurope62508.2024.10752048

記述言語：英語   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  

Recently, the resonant inductive coupling wireless power transfer (RIC-WPT) technique is being widely used to charge small IoT devices dispersed in a wide area, e.g., an office desk and warehouse rack. In this application, the repeater is utilized to expand the chargeable area without an additional AC power source. The repeater comprises a LC resonator commonly with a high-quality factor to induce large current in the repeater coil. However, this causes the problem that the repeater performance is highly susceptible to the variation in its resonant frequency due to the manufacturing tolerance of coil inductance and resonant capacitance as well as the variation of the magnetic coupling between the transmitter and repeater coils. To solve this problem, a previous study has proposed a concept of the autonomous resonant frequency tuning circuit to stably maximize repeater coil current, although this study implemented a part of this control system as a practical circuit. This paper aims to develop a complete autonomous resonant frequency tuning circuit that implements the aforementioned concept. The proposed circuit adjusts the resonant frequencies of the transmitter and repeater by utilizing the Automatic Tuning Assist Circuits. These frequencies are optimized using the infrared wireless signal communication from the transmitter to the repeater. Along with the operating principle of the proposed circuit, this study presents detailed circuit design as well as the experimental results, which verified the stable autonomous maximization of the repeater coil current against the variation in the resonant frequency of the repeater resonator.

DOI： 10.1541/ieejjia.22010814

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CiNii Research

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 International Symposium on Industrial Electronics  

The flipped classroom is known as an effective teaching method, particularly for subjects that largely weigh on the exercises. This learning method devotes the class to exercises, whereas the lecture is left to the students' self-study before the class. Therefore, the quality improvement of the self-study has been the major issue for the success of the flipped classroom because the students can easily lose motivation due to the lack of interactive involvement during the lecture. Conventionally, textbooks or teachers' prerecorded lecture videos are commonly provided for self-study. However, these materials are often designed for the efficient display of knowledge but scarcely contain discussion, which may fail to evoke the students' feeling of active involvement in the lecture. This paper addresses this issue by utilizing artificial voice for self-study lecture videos. The artificial voice is used for presenting knowledge through the artificial discussion of multiple persons of a similar age to the students. The teacher designs and creates this discussion carefully to make the lecture appear familiar to the students, thus motivating the students to the topic of the lecture. Along with highlighting the technology of the artificial voice for making the lecture videos, this paper also reports an actual flipped classroom utilizing the lecture videos of artificial discussion, which supports the positive effect of motivating the students and improving their understanding.

DOI： 10.1109/ISIE51358.2023.10228017

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その他リンク： https://dblp.uni-trier.de/db/conf/isie/isie2023.html#UmetaniTIH23

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：2023 IEEE 10th International Conference on E Learning in Industrial Electronics Icelie 2023  

Power electronics is an electric circuit technology for electric power conversion and is taught in many universities due to its importance in modern society. This technology is traditionally taught in lecture courses, which are based on the operation analysis of the power conversion circuits based on the circuit theory. However, unlike other fields regarding the electric circuit, the quality of the power conversion circuits is fundamentally dependent on the non-ideal features of the circuit elements as well as the size including the cooling system. Therefore, the practical design of the power conversion circuit profoundly relies not only on understanding the basic circuit operation but also on the knowledge of the actual circuit elements, including their non-ideal features. The traditional class based on theoretical circuit operation analysis was difficult to cover the latter knowledge, which may have resulted in insufficient educational achievement in power electronics technology. This paper proposes a teaching approach that embeds mini-experiments in the lecture to overcome this difficulty. These mini-experiments are carefully designed to be seamlessly combined with the lecture and shown to the students during the lecture by utilizing IT-based measurement instruments. According to the students' survey, the students felt the improvement of the lecture quality by the embedded experiment, although the difficulty in the time scheduling for the embedded experiment is a remaining problem to be solved in future studies.

DOI： 10.1109/ICELIE58531.2023.10313105

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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）   出版者・発行元：2023 IEEE Energy Conversion Congress and Exposition Ecce 2023  

Gallium nitride high electron mobility transistor (GaN-HEMT) is attractive for fast switching capability and small on-resistance, which motivates researchers to adopt GaN-HEMT for high-power applications. High-power application of GaN-HEMT requires small power loop inductance to suppress switching surge under fast switching but also requires a large power module size for sufficient cooling performance by heat spreading, which results in large wire length and increases the power loop inductance. This paper addresses this problem by proposing a module structure with small power loop inductance and high cooling capability. The proposed module structure incorporates double-sided and single-sided aluminum-clad printed-circuit boards (PCBs) that sandwich the switching devices. These PCBs offer double-sided cooling and small power loop inductance owing to the eddy current generation inside the aluminum clad. A 3kw half-bridge prototype module was constructed to test the proposed structure in comparison with the preceding module structure, which incorporates the double-sided FR4 PCB for the power circuit and the single-sided aluminum-clad PCB for heat spreading. The result successfully revealed that the proposed structure exhibited a small power loop inductance of 1.4nH and a small thermal resistance of 0.72/W, which indicates the reduction in power loop inductance by 53% and in thermal resistance by 20%.

DOI： 10.1109/ECCE53617.2023.10362213

Scopus

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：2023 IEEE 10th International Conference on E Learning in Industrial Electronics Icelie 2023  

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

DOI： 10.1109/ICELIE58531.2023.10313100

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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：2023 IEEE Energy Conversion Congress and Exposition Ecce 2023  

The kelvin-source packages are becoming popular for high-power ultrafast switching devices to reduce the common source inductance (CSI), which induces the noise voltage in the gating circuit at the transitional change of the drain current and causes false triggering. Despite its importance, however, the actual measurement of CSI has not been reported for kelvin-source packages due to their small inductance values. This paper measured the CSI of typical kelvin-source package TO-247-4L. The result revealed that the CSI of this kelvin-source package ranged 0.2nH-0.7nH, which cannot be neglected at a switching speed greater than 1A/ns. Furthermore, this variation in CSI was found to arise from the magnetic coupling between the bonding wires of power source and gating source, implying that separating the bonding wires can further reduce the CSI.

DOI： 10.1109/ECCE53617.2023.10362400

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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）   出版者・発行元：2023 25th European Conference on Power Electronics and Applications EPE 2023 Ecce Europe  

The gallium nitride high electron mobility transistors (GaN-HEMTs) are increasingly applied for high-power switching converters. However, their fast switching in high-power applications tends to generate enormous switching surges at the turn-off, which may destroy the switching device. This problem can be mitigated by optimizing the wire structure to minimize the power loop inductance, although satisfactory reduction of this inductance is difficult in many practical designs. This paper address this issue by optimizing the power loop inductance rather than seeking the entire elimination of this inductance. This paper analytically elucidates the existence of the optimal power loop inductance that ideally generates no turn-off surge with fast-switching GaN-HEMTs. An experiment supported the analytical result, suggesting the optimal design of power loop inductance is promising for the power module design of GaN-HEMTs.

DOI： 10.23919/EPE23ECCEEurope58414.2023.10264302

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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）   出版者・発行元：Icpe 2023 Ecce Asia 11th International Conference on Power Electronics Ecce Asia Green World with Power Electronics  

In many practical LLC DC-DC converters, the isolation transformer is commonly designed to have a secondary-side center-tapped configuration with one-turn secondary windings. Conventionally, the rectification circuit is installed outside the transformer. However, the recent LLC converters are designed to operate at increasingly high switching frequencies, which indispensably causes the proximity effect in the rectification circuit as well as the wire that connects this circuit to the transformer secondary windings, resulting in large copper loss generation outside the transformer. The previous paper addressed this problem by proposing a secondary winding structure integrating the rectification circuit, although this structure caused the parasitic resonance inside the rectification circuit and reduced the rectification efficiency. To prevent the reduction in the rectification efficiency, this paper proposes an improved winding structure based on the printed-circuit-board technology for suppressing parasitic resonance. The experiment revealed further improvement in the rectification efficiency compared to the previously-proposed structure, suggesting the effectiveness of the proposed winding structure.

DOI： 10.23919/ICPE2023-ECCEAsia54778.2023.10213516

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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）   出版者・発行元：2023 IEEE Energy Conversion Congress and Exposition Ecce 2023  

Recently, GaN-HEMTs are expected to be applied to high-power applications because of their high-speed switching and low on-resistance, which enables high-efficiency. In high-power applications, the GaN-HEMT is commonly connected in parallel to reduce the current stress. However, the paralleled GaN-HEMTs often suffer from oscillatory false triggering due to fast switching capability. If oscillatory false triggering is occurred, may damage the circuit so that we must be prevented in industrial products. To solve this problem, the purpose of this study is to elucidate design strategy for the parasitic inductance to prevent the oscillatory false triggering in the paralleled GaN-HEMTs. To achieve the purpose, this paper analyzes an equivalent circuit of the single-pulse test circuit with two paralleled GaN-HEMTs after the turn-off transition. As a result, we derived design strategy for parasitic inductances to prevent the oscillatory false triggering and verified the validity of the design strategy by simulations and experiments.

DOI： 10.1109/ECCE53617.2023.10362878

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担当区分：最終著者   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）  

DOI： 10.1109/icelie55228.2022.9969423

担当区分：筆頭著者   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）  

DOI： 10.1109/icelie55228.2022.9969416

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 Transactions on Industry Applications  

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

DOI： 10.1109/TIA.2022.3172898

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Ieej Transactions on Electrical and Electronic Engineering  

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

DOI： 10.1002/tee.23562

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記述言語：日本語   出版者・発行元：パワーエレクトロニクス学会  

Wireless power supply systems using repeater resonators are expected to be a promising technology for supplying power to small-powered IoT devices distributed over a wide area. However, the detuning of the repeater resonator caused by the manufacturing tolerance as well as magnetic interference with the transmitter can reduce the amplitude of the repeater current, which leads to the reduction in the power transfer. To address this problem, an autonomous resonant frequency adjusting circuit was proposed for the repeater resonator. However, this method suffers from limited tuning capability because the adjustable range of the autonomous resonant frequency adjustment circuit is limited under high frequency operating conditions. This paper proposes an improved circuit based on this preceding autonomous resonant frequency adjustment circuit to expand the adjustable range in high-frequency operation.

DOI： 10.5416/jipe.48.97

CiNii Research

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：2022 IEEE 7th Southern Power Electronics Conference Spec 2022  

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

DOI： 10.1109/SPEC55080.2022.10058227

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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：2022 IEEE Energy Conversion Congress and Exposition Ecce 2022  

Simultaneous wireless powering of mobile devices and home appliances over a wide area using multiple transmitters operating at 6.78 MHz is an attractive application of resonant inductive coupling wireless power transfer. Nevertheless, this application often suffers from two types of cross-interference. The first is cross-interference among the transmitters, which may cause the hard-switching of the inverter within the transmitter. The second is cross-interference among the receivers via the transmitter, which may not only cause the output power reduction but also complicate the power distribution control for the receivers. To solve the two cross-interference, this paper proposes a novel 6.78 MHz multiple-transmitter. The proposed multiple-transmitter adopts a simple active variable reactance component called an automatic tuning assist circuit (ATAC) for each transmitter. The ATAC works to fix the phase of each transmitter current regardless of the magnetic coupling among the transmitter, eliminating the cross-interference among the transmitters. Furthermore, the proposed multiple-transmitter also incorporates inverters with power factor based control effectively utilizing the transmitter current phase fixed by the ATAC. This inverter controls each transmitter current amplitude to be constant regardless of the receiver, removing the cross-interference among the receivers via the transmitter. The effectiveness of the proposed multiple-transmitter was verified by experiments.

DOI： 10.1109/ECCE50734.2022.9947525

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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）   出版者・発行元：2022 IEEE Energy Conversion Congress and Exposition Ecce 2022  

This paper reports the frequency dependence deterioration of the ac resistance found in Litz wires for high power applications. Litz wire is widely utilized for heating coils of the induction heaters as a wire with small ac resistance at high frequency. Particularly, the recent spread of next-generation switching devices resulted in high-frequency operation of high-power induction heaters, which increasingly adopt Litz wire with a large diameter for copper loss reduction. However, little knowledge has been reported on the effect of the Litz wire diameter on the frequency dependence of the ac resistance, which will be important for the design of Litz wire for high power applications. To elucidate the effect, this paper experimentally measured and compared the frequency dependence of the ac resistance among the Litz wires with different diameters. The result revealed that the Litz wire with a large diameter exhibits worse frequency dependence of the ac resistance than that with a small diameter. In other words, the Litz wire with a large diameter increased ratio of the ac resistance to the dc resistance at a lower frequency than that with a small diameter. An analysis of this reason was also carried out using the recently proposed Litz wire copper loss model, which revealed that the copper loss by the internal proximity effect tends to prevail in the large-diameter Litz wire to cause deterioration of the frequency dependence of the ac resistance. The analysis also suggested that sparse distribution of the strands as well as thinner strands can be effective to mitigate this effect, which can be a key to solve this problem in the Litz wire for high power applications.

DOI： 10.1109/ECCE50734.2022.9948072

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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）   出版者・発行元：IEEE International Symposium on Industrial Electronics  

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

DOI： 10.1109/ISIE51582.2022.9831459

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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：2022 IEEE 7th Southern Power Electronics Conference Spec 2022  

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

DOI： 10.1109/SPEC55080.2022.10058371

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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：2022 International Power Electronics Conference IPEC Himeji 2022 Ecce Asia  

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

DOI： 10.23919/IPEC-Himeji2022-ECCE53331.2022.9806826

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記述言語：日本語   出版者・発行元：パワーエレクトロニクス学会  

DOI： 10.5416/jipe.48.134

CiNii Research

記述言語：日本語   出版者・発行元：パワーエレクトロニクス学会  

DOI： 10.5416/jipe.48.147

CiNii Research

記述言語：日本語   出版者・発行元：パワーエレクトロニクス学会  

DOI： 10.5416/jipe.48.133

CiNii Research

記述言語：日本語   出版者・発行元：パワーエレクトロニクス学会  

DOI： 10.5416/jipe.48.146

CiNii Research

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

An altimeter is a critical instrument in planetary missions, for both safe operations and science activities. We present required specifications and link budget calculations for light detection and ranging (LIDAR) onboard the Martian Moons Exploration (MMX) spacecraft. During the mission phase, this LIDAR will continuously measure the distance between the spacecraft and its target. The time-series distance provides important diagnostic information for safe spacecraft operations and important information for geomorphological studies. Because MMX is a sample return mission, its LIDAR must accommodate physical disturbances on the Martian satellite surface. This resulted in changes to the optical system design. Graphical abstract: [Figure not available: see fulltext.].

DOI： 10.1186/s40623-021-01537-7

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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）  

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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 Transactions on Industry Applications  

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

DOI： 10.1109/TIA.2021.3081071

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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 Transactions on Industry Applications  

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

DOI： 10.1109/TIA.2021.3063993

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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 Industrial Electronics Magazine  

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

DOI： 10.1109/MIE.2020.3002488

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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 Industrial Electronics Magazine  

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

DOI： 10.1109/MIE.2020.3032942

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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：2021 IEEE Energy Conversion Congress and Exposition Ecce 2021 Proceedings  

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

DOI： 10.1109/ECCE47101.2021.9595420

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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：IECON Proceedings Industrial Electronics Conference  

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

DOI： 10.1109/IECON48115.2021.9589541

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その他リンク： https://dblp.uni-trier.de/db/conf/iecon/iecon2021.html#HatakenakaUIHT21

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：IECON Proceedings Industrial Electronics Conference  

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

DOI： 10.1109/IECON48115.2021.9589676

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その他リンク： https://dblp.uni-trier.de/db/conf/iecon/iecon2021.html#HirakiIU21

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 International Symposium on Industrial Electronics  

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

DOI： 10.1109/ISIE45552.2021.9576268

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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：2021 IEEE Energy Conversion Congress and Exposition Ecce 2021 Proceedings  

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

DOI： 10.1109/ECCE47101.2021.9595950

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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：IECON Proceedings Industrial Electronics Conference  

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

DOI： 10.1109/IECON48115.2021.9589302

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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：Proceedings 2021 IEEE 19th International Power Electronics and Motion Control Conference Pemc 2021  

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

DOI： 10.1109/PEMC48073.2021.9432579

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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 International Symposium on Industrial Electronics  

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

DOI： 10.1109/ISIE45552.2021.9576373

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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：Proceedings of the IEEE International Conference on Industrial Technology  

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

DOI： 10.1109/ICIT46573.2021.9453467

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Institution of Engineering and Technology ({IET})  

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

DOI： 10.1049/iet-pel.2019.1207

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1109/TIA.2020.3015446

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1109/TPEL.2019.2956732

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1109/TPEL.2019.2911093

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 International Symposium on Industrial Electronics  

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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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：Ecce 2020 IEEE Energy Conversion Congress and Exposition  

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

DOI： 10.1109/ecce44975.2020.9236116

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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：23rd International Conference on Electrical Machines and Systems Icems 2020  

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

DOI： 10.23919/icems50442.2020.9290802

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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：IECON Proceedings Industrial Electronics Conference  

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

DOI： 10.1109/iecon43393.2020.9254677

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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：2020 22nd European Conference on Power Electronics and Applications EPE 2020 Ecce Europe  

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

DOI： 10.23919/epe20ecceeurope43536.2020.9215804

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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 International Symposium on Industrial Electronics  

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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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1109/TIA.2018.2868272

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：2019 21st European Conference on Power Electronics and Applications EPE 2019 Ecce Europe  

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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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1049/iet-pel.2018.5358

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

CiNii Research

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：8th International Conference on Renewable Energy Research and Applications Icrera 2019  

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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Scopus

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：2019 IEEE Energy Conversion Congress and Exposition Ecce 2019  

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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Scopus

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：2019 21st European Conference on Power Electronics and Applications EPE 2019 Ecce Europe  

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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Scopus

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：Conference Proceedings IEEE Applied Power Electronics Conference and Exposition APEC  

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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記述言語：日本語   出版者・発行元：パワーエレクトロニクス学会  

DOI： 10.5416/jipe.45.29

CiNii Research

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：8th International Conference on Renewable Energy Research and Applications Icrera 2019  

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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Scopus

記述言語：日本語   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

CiNii Books

CiNii Research

J-GLOBAL

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：Conference Proceedings IEEE Applied Power Electronics Conference and Exposition APEC  

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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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：2019 IEEE Energy Conversion Congress and Exposition Ecce 2019  

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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Scopus

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：2019 IEEE Energy Conversion Congress and Exposition Ecce 2019  

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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Scopus

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：Proceedings of the IEEE International Conference on Industrial Technology  

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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Scopus

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：Conference Proceedings IEEE Applied Power Electronics Conference and Exposition APEC  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1109/TIA.2018.2856631

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）  

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Scopus

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

CiNii Research

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1049/iet-pel.2017.0485

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）  

DOI： 10.1109/PEDS.2017.8289248

Web of Science

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：2018 IEEE Energy Conversion Congress and Exposition Ecce 2018  

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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Scopus

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 International Symposium on Industrial Electronics  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1541/ieejjia.7.49

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：2018 International Power Electronics Conference IPEC Niigata Ecce Asia 2018  

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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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：INTELEC International Telecommunications Energy Conference Proceedings  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1109/JESTPE.2017.2777508

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1109/TIE.2017.2694411

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：2017 IEEE Energy Conversion Congress and Exposition Ecce 2017  

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

DOI： 10.1109/ECCE.2017.8096668

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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：Proceedings IECON 2017 43rd Annual Conference of the IEEE Industrial Electronics Society  

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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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：2017 19th European Conference on Power Electronics and Applications EPE 2017 Ecce Europe  

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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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：2017 IEEE Energy Conversion Congress and Exposition Ecce 2017  

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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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：2017 19th European Conference on Power Electronics and Applications EPE 2017 Ecce Europe  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：公益社団法人 日本気象学会  

<p>Heat island intensity approaches the maximum during urban <i>Phase A</i> 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 <i>Phase A</i> and is an important value for urban canopy layer thermal inertia.</p>

DOI： 10.2151/sola.2017-011

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CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1049/el.2016.1253

記述言語：英語   掲載種別：研究論文（学術雑誌）  

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）  

DOI： 10.1109/EPE.2016.7695439

担当区分：最終著者   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）  

DOI： 10.1109/INTLEC.2015.7572421

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/tee.22270

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1541/ieejjia.5.276

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.2151/sola.2016-011

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1049/el.2015.0950

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/tee.22180

記述言語：日本語   出版者・発行元：パワーエレクトロニクス学会  

DOI： 10.5416/jipe.41.160

CiNii Research

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担当区分：筆頭著者   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）  

DOI： 10.1109/INTLEC.2015.7572341

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1541/ieejjia.4.728

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

Web of Science

Web of Science

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/tee.21972

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：2014 IEEE Energy Conversion Congress and Exposition Ecce 2014  

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

Web of Science

Scopus

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

DOI： 10.5416/jipe.40.93

CiNii Books

CiNii Research

その他リンク： https://jlc.jst.go.jp/DN/JLC/20022297080?from=CiNii

Web of Science

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）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/tee.21908

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：2013 IEEE Energy Conversion Congress and Exposition Ecce 2013  

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

Web of Science

Scopus

Web of Science

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：日本語   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.

CiNii Books

J-GLOBAL

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

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： https://doi.org/10.1175/2008JTECHA1076.1

記述言語：日本語   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.

CiNii Books

J-GLOBAL

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

開催年月日： 2023年

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記述言語：日本語  

その他リンク： http://id.ndl.go.jp/bib/031287658

開催年月日： 2021年

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記述言語：日本語  

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開催年月日： 2017年9月

記述言語：日本語  

その他リンク： http://id.ndl.go.jp/bib/028595492

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開催年月日： 2016年9月

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開催年月日： 2015年9月

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記述言語：日本語  

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記述言語：日本語  

開催年月日： 2007年10月

記述言語：日本語  

開催年月日： 2007年10月

記述言語：日本語  

開催年月日： 2007年8月

記述言語：日本語  

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

開催年月日： 2007年

開催年月日： 2007年

開催年月日： 2007年

開催年月日： 2007年