Faculty Profiles - YAMAMOTO Masayoshi

Papers - YAMAMOTO Masayoshi

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Study on the Imbalanced Voltage of Series-connected Active Power Semiconductor Devices in Power Conversion Systems

Zhang Hongjing, Imaoka Jun, Noah Mostafa, Ishikura Yuki, Yamamoto Masayoshi

2019 IEEE WORKSHOP ON WIDE BANDGAP POWER DEVICES AND APPLICATIONS IN ASIA (WIPDA ASIA 2 2019

Bidirectional Converter with Balancing Capacitor using Multi-stage FET Driving Technique

Ishikura Yiki, Imaoka Jun, Noah Mostafa, Yamamoto Masayoshi

2019 IEEE THIRD INTERNATIONAL CONFERENCE ON DC MICROGRIDS (ICDCM) 2019

Cooperative Control of Multi-Input Modular DC/DC Converter for Electric Off-Highway Vehicles

Piao Qingyun, Konoto Masaaki, Kakisaka Tasuku, Imaoka Jun, Yamamoto Masayoshi

2019 IEEE THIRD INTERNATIONAL CONFERENCE ON DC MICROGRIDS (ICDCM) 2019

Common Mode Conductive Noise Cancellation for Multiphase Converter Using Auxiliary Winding

Sasaki Mamoru, Imaoka Jun, Yamamoto Masayoshi, Nakano Akira, Fuse Koji

2019 IEEE THIRD INTERNATIONAL CONFERENCE ON DC MICROGRIDS (ICDCM) 2019

A Novel Transformer Structure Used in a 1.4 MHz LLC Resonant Converter with GaNFETs

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

Proceedings - 2018 IEEE International Power Electronics and Application Conference and Exposition, PEAC 2018 2018.12

Publisher：Proceedings - 2018 IEEE International Power Electronics and Application Conference and Exposition, PEAC 2018

A novel integrated magnetic structure suitable for a high-frequency switching current resonant converter (LLC) with GaNFETs is proposed in this paper. Creating a leakage inductance to resonate with a capacitor, and the mutual inductance in an LLC resonant converter is the most common solution. However, the volume of leakage inductance is very difficult to be controlled or adjusted. Furthermore, the losses may increase when the leakage fluxes cross the patterns on the PCB board or the primary and secondary coils. In order to tackle this problem, a new magnetic structure core is proposed in this paper. The proposed magnetic structure can decrease the losses of the core, which means the magnetic structure proposed in this paper can improve the efficiency of the converter. A power density of approximately 2.6 W/cm 3 has been realized for the 1.4-MHz LLC resonant converter with the proposed magnetic structure with a maximum efficiency of 96.4%. Along with the theoretical discussion, finite element analysis (FEA) electromagnetic simulation and experimental results are also presented.

DOI： 10.1109/PEAC.2018.8590446

Scopus

Fundamental Experiment of 3-phase Electric Resonant Coupling Wireless Power Transfer Reviewed International journal

Hattori F., Imaoka J., Yamamoto M., Masuda M.

7th International IEEE Conference on Renewable Energy Research and Applications, ICRERA 2018 page： 1417 - 1422 2018.12

Language：English Publishing type：Research paper (scientific journal) Publisher：7th International IEEE Conference on Renewable Energy Research and Applications, ICRERA 2018

Lots of researches of electric coupling is performed for wireless power transfer system. For achieving high power transfer, electric resonant coupling is used. A 3-phase electric resonant coupling is one option for higher power wireless transfer. However, as far as the author knows, much less work has been done for a 3-phase electric resonant coupling. In this paper, fundamental experiment of a 3-phase electric resonant coupling wireless power transfer is performed. From experiment results, the possibility that 3-phase electric resonant coupling can be used for wireless power transfer has been found.

DOI： 10.1109/ICRERA.2018.8566938

Scopus

Magnetic Design and Experimental Evaluation of a Commercially Available Single Integrated Transformer in Three-Phase LLC Resonant Converter Reviewed International coauthorship International journal

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

IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS Vol. 54 ( 6 ) page： 6190 - 6204 2018.11

Core Loss Evaluation in Powder Cores: A Comparative Comparison between Electrical and Calorimetric Methods

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

2018 International Power Electronics Conference, IPEC-Niigata - ECCE Asia 2018 page： 1087 - 1094 2018.10

Language：Japanese Publisher：2018 International Power Electronics Conference, IPEC-Niigata - ECCE Asia 2018

Utilizing powder cores in many power electronics applications have gained interest due to the attractive magnetic properties of powder core materials. For instance, powder cores have soft saturation characteristics and high saturation flux density compared to gapped ferrites. However, due to their low relative-permeability and the low loss characteristics, a precise measurement of the core losses is very difficult to be obtained. One of the common approaches to measure core losses is by measuring the electrical signals of the winding terminals, we hereafter refer it as electrical methods. Another alternative approach is calorimetric methods, which rely on measuring the core temperature rise. Nonetheless, these methods may have huge measurement error in case of powder cores. This paper evaluates the accuracy of measuring core losses in powder cores, and a comparison between the electrical and calorimetrical methods is presented. Along with the theoretical discussion, simulation and experimental tests are conducted.

DOI： 10.23919/IPEC.2018.8508012

Scopus

Multiple Exciting Voltage Control for Maximization of Multi-hop Wireless Power Transfer Efficiency

Sasaki M., Yamamoto M.

2018 International Power Electronics Conference, IPEC-Niigata - ECCE Asia 2018 page： 3344 - 3348 2018.10

Publisher：2018 International Power Electronics Conference, IPEC-Niigata - ECCE Asia 2018

Recently multi-hop wireless power transfer (WPT) systems for the area extension of a wireless battery charging have been addressed by several research groups. This paper describes a discrete exciting voltage control technique for the multi-hop WPT system via magnetic resonant coupling which can maximize the power transfer efficiency in response to the change of coupling status. The theory allows the equations of the wireless power transfer efficiency of the system to be determined at all the ratio of the mutual inductance. The calculated results are included to confirm the advantage to single transmitting multi-hop WPT systems.

DOI： 10.23919/IPEC.2018.8508026

Scopus

Modeling, Magnetic Design, and Simulation Methods Considering DC Superimposition Characteristic of Powder Cores Used in Power Converters

Imaoka J., Okamoto K., Shoyama M., Ishikura Y., Noah M., Yamamoto M.

2018 International Power Electronics Conference, IPEC-Niigata - ECCE Asia 2018 page： 1095 - 1102 2018.10

Publisher：2018 International Power Electronics Conference, IPEC-Niigata - ECCE Asia 2018

Powder cores have been gained much attention as one of the attractive magnetic cores used in power converters due to their superior features such as high saturation flux density or distributed air gaps. However, powder cores have a unique feature that the relative permeability of the magnetic core varies depending on the magnetic field intensity. However, modeling the variable relative permeability, the design method for powder cores, and computer simulation methods of non-linear inductance are well not discussed in the related literature. Therefore, this paper proposes a novel modeling, magnetic design methods, and simulation technique considering dc superimposition characteristics of powder cores. The modeling method uses a novel model equation representing the behavior of relative permeability under the dc current superimposition condition, which is helpful to evaluate the performance of powder cores and to properly design various magnetic components. Theoretical analysis has been presented and the effectiveness and the validity of the proposed methods are evaluated through simulation and experimental tests.

DOI： 10.23919/IPEC.2018.8507874

Scopus

Parasitic Inductance Design Considerations to Suppress Gate Voltage Oscillation of Fast Switching Power Semiconductor Devices Reviewed International journal

Sugihara Y., Nanamori K., Yamamoto M., Kanazawa Y.

2018 International Power Electronics Conference, IPEC-Niigata - ECCE Asia 2018 page： 2789 - 2795 2018.10

Language：English Publishing type：Research paper (scientific journal) Publisher：2018 International Power Electronics Conference, IPEC-Niigata - ECCE Asia 2018

Fast switching power semiconductor devices such as SiC MOSFET and GaN FET have attracting increasing attention because of superior switching capability which contributes to high efficiency and high power density of power converters. However, fast switching capability generates large switching noise. Particularly, parasitic oscillation observed in the gate voltage is a severe problem due to the gate-source breakdown. This paper hypothesized that the gate resonator selectively takes in parasitic oscillation caused by a power circuit because of its frequency characteristic and analyzed the gate voltage oscillation. As a result, the phenomenon is characterized by an oscillation susceptibility which indicates susceptibility of the gate voltage to a drain voltage oscillation. Moreover, the oscillation susceptibility predicts the parasitic inductance dependency of the gate voltage oscillation. Therefore, the parasitic inductance should be designed to suppress this oscillation considering the oscillation susceptibility. Results obtained by simulation and experiment indicated appropriateness of analysis results.

DOI： 10.23919/IPEC.2018.8507433

Scopus

GaN半導体研究拠点としての名古屋における活動紹介

山本真義

電気学会誌 Vol. 138 ( 10 ) page： 695 - 695 2018.10

Effect of inductor parasitic resistances on the voltage gain of high step-up DC-DC converters for electric vehicle applications

Martinez Wilmer, Cortes Camilo, Yamamoto Masayoshi, Imaoka Jun

IET POWER ELECTRONICS Vol. 11 ( 10 ) page： 1628 - 1639 2018.8

Review of Current Balance Mechanism in Multiphase LLC Resonant Converters

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

IEEE International Symposium on Industrial Electronics Vol. 2018-June page： 1030 - 1036 2018.8

Language：Japanese Publisher：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

Scopus

Oscillation analysis and current peak reduction in paralleled SiC MOSFETs

Nanamori Kimihiro, Sugihara Yusuke, Yamamoto Masayoshi

IET CIRCUITS DEVICES & SYSTEMS Vol. 12 ( 4 ) 2018.7

Ankle–brachial pressure index as a predictor of the 2-year outcome after transcatheter aortic valve replacement: data from the Japanese OCEAN-TAVI Registry

Yamawaki M., Araki M., Ito T., Honda Y., Tokuda T., Ito Y., Ueno H., Mizutani K., Tabata M., Higashimori A., Tada N., Takagi K., Yamanaka F., Naganuma T., Watanabe Y., Yamamoto M., Shirai S., Hayashida K.

Heart and Vessels Vol. 33 ( 6 ) page： 640 - 650 2018.6

Language：Japanese Publisher：Heart and Vessels

Peripheral artery disease plays a pivotal role for access site selection in transcatheter aortic valve replacement (TAVR). Abnormal ankle–brachial index (ABI) is a generalized mortality marker in many cardiovascular scenarios. However, the long-term outcomes in high-risk TAVR populations remain unclear. We investigated the association between low ABI and 2-year outcome after TAVR. Of 1613 patients enrolled in the OCEAN-TAVI registry, 1458 (90.4%) who underwent ABI before TAVR were divided into groups: patients with (1) ABI ≥ 0.9 in both legs and (2) ABI < 0.9 in either leg. Primary endpoint was all-cause death within 2 years. ABI < 0.9 was noted in 304 patients (20.8%). ABI < 0.9-group had more frequent and severe comorbidities. Primary endpoint in ABI < 0.9-group was significantly higher than that in ABI ≥ 0.9-group (15.8 vs. 8.7%, p < 0.001). This trend continued in the transfemoral (TF)-approach (14.9 vs. 7.5%, p < 0.001), but not in the alternative approach (17.2 vs. 15.8%, p = 0.815). Within 30 days, ABI < 0.9-group had a higher cardiac death rate (3.1 vs. 1.0%, p = 0.033), whereas between 31 days and 2 years, non-cardiovascular death was more frequently observed (9.2 vs. 5.1%, p = 0.003). In ABI < 0.9-group, in-hospital vascular complications (11.9 vs. 4.9%, p < 0.001) and acute kidney injury (10.8 vs, 5.7%, p = 0.009) were more frequently found when using the transfemoral-approach. In multivariate analysis, ABI < 0.9 was an independent predictor of 2-year mortality (adjusted hazard ratio 1.495, 95% CI 1.007–2.220, p = 0.046). Pre-procedure ABI < 0.9 is a useful prognostic marker for all-cause mortality, even in high-risk TAVR populations.

DOI： 10.1007/s00380-017-1096-y

Scopus

A Current Sharing Method Utilizing Single Balancing Transformer for a Multiphase LLC Resonant Converter With Integrated Magnetics Reviewed International journal

Noah, M; Endo, S; Ishibashi, H; Nanamori, K; Imaoka, J; Umetani, K; Yamamoto, M

IEEE JOURNAL OF EMERGING AND SELECTED TOPICS IN POWER ELECTRONICS Vol. 6 ( 2 ) page： 977 - 992 2018.6

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Journal of Emerging and Selected Topics in Power Electronics

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

DOI： 10.1109/JESTPE.2017.2777508

Web of Science

Scopus

A Magnetic Design Method Considering DC-Biased Magnetization for Integrated Magnetic Components Used in Multiphase Boost Converters Reviewed International journal Open Access

Imaoka, J; Okamoto, K; Kimura, S; Noah, M; Martinez, W; Yamamoto, M; Shoyama, M

IEEE TRANSACTIONS ON POWER ELECTRONICS Vol. 33 ( 4 ) page： 3346 - 3362 2018.4

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Transactions on Power Electronics

High power density and high efficiency in dc/dc converters are required in various applications such as the automotive application. Interleaved multiphase circuits with integrated magnetic components can fulfill these requirements because passive components occupying significant space in power converters can be downsized without high-switching frequency driving of power devices. However, dc-biased magnetization is a drawback of integrated magnetic components because of unbalanced inductor average currents. This imbalance arises from the tolerance among the phase components. To overcome this problem, inductor average current control is implemented in interleaved multiphase dc/dc converters. Nevertheless, the imbalance cannot be completely eliminated because the current sensors inserted into each phase have gain errors. The purpose of this paper is to present a magnetic design method to improve the immunity to unbalanced currents. A comprehensive analysis is carried out with two main objectives: to prevent magnetic saturation, which may arise due to the current unbalance and to downsize the magnetic components by selecting the optimal coupling coefficient taking into consideration the maximum permissible percentage of unbalanced currents. Simulation case studies are presented to support the analysis. Finally, a 1-kW prototype of the interleaved boost converter is built to validate the accuracy of the design method.

DOI： 10.1109/TPEL.2017.2707385

Web of Science

Scopus

Lagrangian dynamics model and practical implementation of an integrated transformer in multi-phase LLC resonant converter Reviewed International coauthorship International journal

Noah Mostafa, Umetani Kazuhiro, Imaoka Jun, Yamamoto Masayoshi

IET POWER ELECTRONICS Vol. 11 ( 2 ) page： 339 - 347 2018.2

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

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

ELECTRONICS LETTERS Vol. 54 ( 3 ) page： 157 - 159 2018.2

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Papers - YAMAMOTO Masayoshi