Faculty Profiles - YAMAMOTO Masayoshi

Papers - YAMAMOTO Masayoshi

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EMI Analysis and Suppression Method Using Ferrite Beads Applied to LLC Converter Reviewed International journal

Okochi, R; Takatsuji, H; Imaoka, J; Yamamoto, M

2021 IEEE INTERNATIONAL FUTURE ENERGY ELECTRONICS CONFERENCE (IFEEC) 2021

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：2021 IEEE International Future Energy Electronics Conference, IFEEC 2021

To operate the LLC converter at high switching frequency,the excitation current flowing through the transformer is increased,which generates a large conducted noise. The peaks in the noise spectrum are caused by the ringing of the switching node voltage and the resonance of the CM equivalent circuit. In this paper,a method using ferrite beads and additional resistors in combination with the input filter is proposed to suppress the ringing. Its effectiveness in reducing the high-frequency noise while maintaining the fast-switching speed is confirmed by simulation and experiment.

DOI： 10.1109/IFEEC53238.2021.9661804

Web of Science

Scopus

Analysis on Parasitic Capacitance to Prevent False Turn-on in GaN HEMT

Iwaki Toshihiro, Sawada Takashi, Imaoka Jun, Yamamoto Masayoshi

2021 IEEE ENERGY CONVERSION CONGRESS AND EXPOSITION (ECCE) page： 5616 - 5621 2021

Language：Japanese Publisher：2021 IEEE Energy Conversion Congress and Exposition, ECCE 2021 - Proceedings

Driving power devices such as GaN HEMTs at high-frequency is one of the successful solutions to miniaturize the magnetic components of circuits. On the other hand, GaN HEMTs have drawbacks in high-speed switching. For example, in a full-bridge inverter configuration, a fast turn-on of one power device can cause a false turn-on of the complementary power device. Therefore, the GaN HEMT might be destroyed by the overcurrent and transient heat caused by the short circuit. The most important factor for the false turn-on of GaN HEMTs is its reverse transfer capacitance (Crss), but other parasitic components such as inductances in PCB should be considered to analyze the false turn-on phenomena. In this paper the theoretical analysis of the capacitance components that may cause the false turn-on is conducted. Based on the theoretical analysis, we propose the conditions of the parasitic component of the gate drive circuit to prevent false turn-on.

DOI： 10.1109/ECCE47101.2021.9595846

Web of Science

Scopus

A Novel Measurement Method for DC Superimposition Characteristics of Three-Phase Coupled Inductors with Powder Cores

Mishima Yamato, Aoki Tatsuya, Matsuta Kazuya, Imaoka Jun, Yamamoto Masayoshi, Yoshimoto Kosuke

2021 IEEE ENERGY CONVERSION CONGRESS AND EXPOSITION (ECCE) page： 5334 - 5341 2021

Language：Japanese Publisher：2021 IEEE Energy Conversion Congress and Exposition, ECCE 2021 - Proceedings

the objective of this research is to build the measurement method of DC superimposition of multiphase coupled inductors with powder cores. From a perspective of magnetic material, powder cores are usually applied to inductor core in high current applications such as E-mobility due to their attractive features. In addition, multiphase DC/DC converters with coupled inductors can effectively downsize passive components that occupy significant space in power converters. However, when applying coupled inductor with powder cores under the dc current superimposed condition, self-inductance and mutual inductance values of coupled inductors are varied depending on dc current values. Furthermore, measurement methods of the dc superimposition characteristics of multiphase coupled inductor have not been discussed in the relevant literature. Therefore, this paper proposes two measurement methods for DC superimposition characteristics of three-phase coupled inductors with powder cores used in three-phase DC-DC converters. The first method is for three-phase coupled inductors with an asymmetric magnetic core structure, and the values of each self-inductance and mutual inductance can be measured separately. The second method is a simplified measurement method limited to multiphase coupled inductors with symmetric magnetic core structures. DC superimposition characteristics of coupled inductors can be measured with a smaller number of measurements than the first method, and it can be extended to N phase coupled inductors. The verification of the two methods has been evaluated through simulation and experiment.

DOI： 10.1109/ECCE47101.2021.9595692

Web of Science

Scopus

Effects of High-frequency Operation on Magnetic Components in Power Converters Reviewed International coauthorship International journal

Imaoka, J; Yu-Hsin, W; Shigematsu, K; Aoki, T; Noah, M; Yamamoto, M

2021 IEEE 12TH ENERGY CONVERSION CONGRESS AND EXPOSITION - ASIA (ECCE ASIA) page： 978 - 984 2021

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of the Energy Conversion Congress and Exposition - Asia, ECCE Asia 2021

Compound semiconductor devices such as Gallium Nitride (GaN) and Silicon Carbide (SiC) are actively adopted in power converters to improve power conversion efficiency, downsize passive components and miniaturize cooling systems. However, in the power converters, magnetic components often become bottlenecks in power converters from size, power losses, and temperature rise perspective. Therefore, in some cases, the attractive performance of GaN and SiC cannot be fully utilized due to the limits imposed by magnetic components. To indicate this matter from an experimental perspective, this paper conducts a fundamental investigation of the downsizing effect of magnetic components and temperature rise when varying switching frequency (85 kHz, 150 kHz, 350 kHz, 1 MHz) of a 1 kW boost converter as a case study. As results of experiments, although high-switching frequency operation contributes to downsizing magnetic component effectively, the thermal runaway of the magnetic core while driving at high frequency is confirmed due to downsized small surface area and increasing iron loss due to temperature dependency of Mn-Zn ferrite magnetic cores. For a fair comparison, the area product approach is used in the design procedure for selecting core size. The effect of the high-frequency drive is discussed from theoretical and experimental viewpoints.

DOI： 10.1109/ECCE-Asia49820.2021.9479365

Web of Science

Scopus

13.56MHz high power half-bridge GaN-HEMT resonant inverter achieving 99% power efficiency Reviewed International journal

Oyane A., Senanayake T., Hattori F., Imaoka J., Yamamoto M., Masuda M.

9th IEEE International Conference on Power Electronics, Drives and Energy Systems, PEDES 2020 2020.12

Language：English Publishing type：Research paper (scientific journal) Publisher：9th IEEE International Conference on Power Electronics, Drives and Energy Systems, PEDES 2020

High-power inverters with high frequency have been required for progressing technologies such as wireless power transfer (WPT) and plasma processing. Recently, gallium nitride high electron mobility transistor (GaN-HEMT) is getting lots of attention from the viewpoint of fast switching ability and low power consumption. However, GaN-HEMT inverters are difficult to be operated in over several kW because of its low drain-source breakdown voltage. In other words, the conventional half-bridge GaN-HEMT inverter can output high power only for the small load resistance less than several-O. This paper overcomes this difficulty by implementing an impedance conversion network in the prior stage of the series resonator. The proposed topology realizes not only high-power from low drain-source voltage but also the sine wave output with very low harmonics. 3kW output to 50O load at 13.56MHz is theoretically designed, and verified by computer simulations. And also, the experimental prototype using GaN-HEMTs achieves the high efficiency of 99.43% at 13.56MHz and 471W.

DOI： 10.1109/PEDES49360.2020.9379451

Scopus

Magnetic Design Method for Multi-Material Inductor to Flatten Efficiency Curve of Power Converters within Wide Load Ranges Invited Reviewed

Ishikura Y, Imaoka J., Noah M., Aoki T, Ito K, Yamamoto M

IEEE Transactions on Magnetics Vol. 56 ( 10 ) page： 1 - 8 2020.10

Magnetic Design Method for Multi-Material Inductor to Flatten Efficiency Curve of Power Converters Within Wide Load Ranges Reviewed International coauthorship International journal

Ishikura Yuki, Imaoka Jun, Noah Mostafa, Aoki Tatsuya, Ito Koichiro, Yamamoto Masayoshi

IEEE TRANSACTIONS ON MAGNETICS Vol. 56 ( 10 ) 2020.10

Output Power Pulsation Suppressed with an Activity Smoothen Buck-Boost Converter to Achieve Electrolytic Capacitor-less AC/DC Converter

Ou T., Namiki S., Tsuruya M., Noah M., Morita K., Mukaiyama D., Imaoka J., Yamamoto M.

12th AEIT International Annual Conference, AEIT 2020 2020.9

Language：Japanese Publisher：12th AEIT International Annual Conference, AEIT 2020

An Activity Smoothen Circuit with bidirectional Buck-Boost Converter (AS-BBC) was approached to smoothen the output power of a power factor correction (PFC) converter, which is an AC/DC converter, without using any electrolytic capacitors in this paper. In order to smoothen the output pulsation current of the PFC converter, electrolytic capacitors have been used generally, since electrolytic capacitors have a large magnitude capacity. However, there is a lifespan to electrolytic capacitors. On the other hand, film capacitors have a semi-permanent lifespan with so much less magnitude capacity than electrolytic capacitors. A way of using the AS-BBC to make a small capacitor work like a large capacitor as a smoothing capacitor to handle the output power is presented in this paper. Approximately 47% of the pulsation output is suppressed with a 4.4μ F film capacitor with the AS-BBC. Since there is no electrolytic capacitor adapted, a semi-permanent lifespan PFC converter is achieved successfully.

DOI： 10.23919/AEIT50178.2020.9241166

Scopus

Temperature Dependency Modeling, Simulation and Experimental Validations of DC Superimposition Characteristics for Gapped-Ferrite Inductor Including Saturation Region

Imaoka J., Aoki T., Shigematsu K., Yamamoto M.

IEEE International Symposium on Industrial Electronics Vol. 2020-June page： 1466 - 1473 2020.6

Language：Japanese Publisher：IEEE International Symposium on Industrial Electronics

To realize the early development of power converters, research on the front-loading design in which the efficiency, control characteristics, converter size, thermal management, and Electromagnetic Compatibility (EMC) are carefully considered before making a prototype, has been attracting. To carefully design and predict these design factors before prototyping, making accurate models of active/passive components operated on simulation of the multi-physical domain such as thermal, magnetic, and electrical is indispensable. This is because these characteristics of active/passive components on power converters are affected by each other. In this background, this paper proposes a nonlinear relative permeability modeling method with a temperature dependency of gapped-ferrite cores. The temperature dependency of the effective relative permeability of the gapped-ferrite core is investigated under core temperature within-50°C-+ 150°C. As features of the proposed modeling method and simulation model, a simple mathematical equation and lookup tables are utilized for simple implementation to the simulator. The validity of the proposed modeling method is confirmed by both simulation and experimental tests under operating conditions including the magnetic saturation regions.

DOI： 10.1109/ISIE45063.2020.9152521

Scopus

Analysis of Common Mode Noise Reduction Mechanism in A Shielded Inductor

Sasaki M., Imaoka J., Yamamoto M., Nakano A., Fuse K.

IEEE International Symposium on Industrial Electronics Vol. 2020-June page： 660 - 665 2020.6

Language：Japanese Publisher：IEEE International Symposium on Industrial Electronics

To achieve high power density, a power converter circuit is often operated at high frequency, and fast switching devices are also combined to reduce switching loss. On the other hand, both high frequency and fast switching greatly increases conductive noise amplitude at frequency over several megahertz. Therefore, electromagnetic compatibility (EMC) is necessary for a high power density converter. However, an additional filter, which consists of large and heavy passive elements, greatly degrades power density. Thus, in this paper, a noise reduction method for noise at frequency band over 10 MHz with small volume increase is presented and investigated. Consequently, the simulation and experimental result verifies that the proposed method decreases MHz-band noise with small volume increase.

DOI： 10.1109/ISIE45063.2020.9152408

Scopus

Comparison of switching performance between GaN and SiC MOSFET via 13. 56MHz Half-bridge Inverter

Xiong Y., Oyane A., Ou T., Thilak S., Imaoka J., Yamamoto M.

IEEE International Symposium on Industrial Electronics Vol. 2020-June page： 672 - 676 2020.6

Language：Japanese Publisher：IEEE International Symposium on Industrial Electronics

Both silicon-carbide (SiC) and gallium-nitride (GaN) are wide bandgap power transistor which are developing rapidly. They are able to be used as the main switches in the high-frequency power conversion systems successfully. These high-frequency switches just meet the high demand of low-size power electronics device in recent years. As the high-frequency system always relies on the switches, we designed and made evaluation boards for both SiC and GaN switches by 13. 56MHz half-bridge inverter. Both simulation and experimental results show that GaN achieved more successfully switching, which made good output waveform with very short dead-time. And in simulation, lower switching loss of GaN is also confirmed. As all above, it is obvious that GaN device is more suitable for high-frequency application.

DOI： 10.1109/ISIE45063.2020.9152253

Scopus

Technical Trend of Power Electronics Systems for Automotive Applications Invited Reviewed

Yamamoto M., Kakisaka T, Imaoka J

Japanese Journal of Applied Physics Vol. 59 ( SG ) page： 0805-1 - 0805-13 2020.4

多段FET駆動技術を用いた双方向コンバータ Invited Reviewed

石倉祐樹 ,細谷達也, 山本真義

電子情報通信学会論文誌 B Vol. J103-B ( No.4 ) page： .154 - 161 2020.4

Technical trend of power electronics systems for automotive applications Reviewed International journal

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 59 2020.4

Bidirectional Converter Using Multi-stage FET Driving Technique

ISHIKURA Yuki, HOSOTANI Tatsuya, YAMAMOTO Masayoshi

Vol. J103-B ( 4 ) page： 154 - 161 2020.4

Language：Japanese

This paper presents a bidirectional converter using by multi-stage FET driving technique. The proposed converter is constructed by implementing series connected low voltage Si-FETs in multi-stage. A driving circuit using multi-stage driving technique can drive series connected FETs from the one power supply without any isolated power supplies and high voltage process ICs. In addition, the balancing capacitors which constructed the converter have voltage averaging function in drain-source voltage to tackle the voltage unbalance between the series connected FETs. Using the figure of merit which can estimate converter losses from the specification of power devices, the usefulness of the circuit configuration which using low voltage Si-FETs instead of SiC-FETs is shown. The effect of the voltage averaging function by the balancing capacitors, the operating principle of the driving circuit and the power conversion mechanism are clarified and presented using the circuit simulator and a converter equivalent circuit. The experimental results show that the proposed driving technique allows the bidirectional converter to achieve a maximum power conversion efficiency of 99.2%.

DOI： 10.14923/transcomj.2019jbp3022

CiNii Research

Bidirectional Converter with Multi-stage FETs Featuring Voltage Balance Control Function Using Variable Capacitors

Ishikura Yuki, Hosotani Tatsuya, Yamamoto Masayoshi

IEEJ Transactions on Industry Applications Vol. 140 ( 3 ) page： 168 - 174 2020.3

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

<p>This paper presents a bidirectional converter with multi-stage FETs featuring voltage balance control function using variable capacitors. The proposed converter is constructed using low-voltage Si-FETs in a series connection, and it improves the voltage balance between the drain-source voltages of the series connected FETs in the OFF period. Using the converter figure of merit (FOM), which can estimate the converter losses from the specifications of the FETs, the effectiveness of the proposed converter is compared to that of a converter using SiC-FETs. The factors of the voltage unbalance are analytically clarified using the equivalent circuit. The principle of voltage balance control function using the variable capacitor is discussed. The experimental results show that the proposed converter can achieve a maximum power conversion efficiency of 99.2%.</p>

DOI： 10.1541/ieejias.140.168

Scopus

CiNii Research

Voltage Balancing Control Method Using Variable Capacitors with Simple Turn-on Adjusting Function for Multi-Stage FET Bidirectional Converter

Ishikura Y., Hosotani T., Noah M., Imaoka J., Yamamoto M.

Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC Vol. 2020-March page： 2944 - 2949 2020.3

Language：Japanese Publisher：Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC

This paper proposes a voltage balancing control method using variable capacitors with simple turn-on adjusting function for multi-stage FET bidirectional converter. The proposed voltage balancing control circuit is composed of a feedback circuit using photocouplers and a delay circuit using variable capacitors with turn-on adjusting diodes. The proposed voltage balancing circuit can reduce the drain-source voltage unbalance which occur during the turn-on and turn-off period of series-connected FETs. The theoretical discussion includes analyzing the unbalanced drain-source voltage in seriesconnected FETs using a simplified converter. Also, the principal of the proposed voltage balancing control method is clarified. The experimental results show that the proposed voltage balancing control method can reduce the drain-source voltage difference Δvds of series-connected FETs from 36 V to 11 V (69% reduction in Δvds) during the turn-off and from 22 V to 11 V (50% reduction in Δvds) during the turn-on period. The multistage FET bidirectional converter can achieve a maximum power conversion efficiency of 99.2%.

DOI： 10.1109/APEC39645.2020.9124221

Scopus

Effects of Secondary Leakage Inductance on the LLC Resonant Converter Reviewed International coauthorship International journal

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

IEEE TRANSACTIONS ON POWER ELECTRONICS Vol. 35 ( 1 ) page： 835 - 852 2020.1

Acute Pain Intensity After Collagenase Clostridium histolyticum Injection in Patients With Dupuytren Contracture

Noto K., Yamamoto M., Iwatsuki K., Kurimoto S., Tatebe M., Hirata H.

Journal of Hand Surgery Global Online Vol. 2 ( 1 ) page： 16 - 20 2020.1

Language：English Publisher：Journal of Hand Surgery Global Online

Purpose: To investigate multidimensional pain intensity and quality after collagenase Clostridium histolyticum (CCH) injection in patients with Dupuytren contracture using a pain visual analog scale (VAS) and the revised version of the Short-Form McGill Pain Questionnaire (SF-MPQ-2). Methods: This prospective observational study was carried out from 2015 to 2017. As a primary end point, patients completed the pain VAS (range, 0 [no pain] to 100) and SF-MPQ-2 before and after CCH injection; 3, 9, and 24 hours after CCH injection; after the extension procedure; and 3 and 7 days after CCH injection. In addition, they reported the dose and duration of supplementary analgesic use during this period. Results: A total of 41 patients were enrolled in this study (51 joints). Mean pain VAS score (mean ± SD, 34 ± 21) was maximal 9 hours after CCH injection and decreased within the following 7 days. The total score of the SF-MPQ-2 significantly increased after CCH treatment and decreased in the 7 days after the injection. Among the SF-MPQ-2 subscales, the highest and lowest scores after CCH injection were recorded for continuous pain and affected descriptors, respectively. Nonsteroidal anti-inflammatory drugs were most frequently self-administered during 7 days after the extension procedure compared with any other study period. Conclusions: The pain VAS and SF-MPQ-2 revealed acute pain after CCH injection. However, all examined pain aspects dramatically improved within 7 days after injection. Pain after CCH injection is characterized by low scores in the Affective Descriptors subscale of the SF-MPQ-2. Type of study/level of evidence: Prognostic Ⅳ.

DOI： 10.1016/j.jhsg.2019.10.004

Scopus

PubMed

A simple gate driver design for GaN-based switching devices with improved surge voltage and switching loss at 1-MHz operation Invited Reviewed

Shota Jodo, Toshihiro Iwaki, Kosuke Uchiyama, Md. Islam, Kensuke Kataoka, Yuki Hayasaka, Jun Imaoka, Masayoshi Yamamoto, Kiichi Niitsu

Japanese Journal of Applied Physics Vol. No. 60 ( SADD02 ) page： SAAD02-1 - SAAD02 2020

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Papers - YAMAMOTO Masayoshi