Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers (IEEE)  

DOI： 10.1109/tia.2023.3255845

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Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers (IEEE)  

DOI： 10.1109/access.2023.3236105

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Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers (IEEE)  

DOI： 10.1109/access.2022.3232843

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

DOI： 10.1109/icems56177.2022.9983187

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

DOI： 10.1109/iecon49645.2022.9968536

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/ecce50734.2022.9948211

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

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

DOI： 10.1109/ecce50734.2022.9947959

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

DOI： 10.1109/icem51905.2022.9910903

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

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

DOI： 10.1109/TIA.2022.3154336

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

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

DOI： 10.1541/ieejjia.20004135

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

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

DOI： 10.1109/TIA.2021.3068329

Web of Science

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

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

DOI： 10.1109/IEMDC47953.2021.9449493

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

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Publishing type：Research paper (scientific journal)  

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

DOI： 10.1541/ieejias.140.949

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electrical Engineers of Japan  

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

DOI： 10.1541/ieejias.140.939

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Other Link： http://id.ndl.go.jp/bib/030793591

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

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

DOI： 10.1109/ECCE44975.2020.9235600

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

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

DOI： 10.1109/ICEM49940.2020.9270995

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Applied Electromagnetics and Mechanics  

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

DOI： 10.14243/jsaem.28.146

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

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

DOI： 10.1109/IECON.2019.8927384

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

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

DOI： 10.1109/ECCE.2019.8913191

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

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

DOI： 10.1109/TIA.2017.2710123

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

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

DOI： 10.1109/ICMECH.2017.7921117

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

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

DOI： 10.1109/ICELMACH.2016.7732538

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Language：Japanese  

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Authorship：Corresponding author   Language：Japanese  

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Authorship：Lead author,　Corresponding author   Language：Japanese  

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J-GLOBAL

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J-GLOBAL

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J-GLOBAL

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J-GLOBAL

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J-GLOBAL

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J-GLOBAL

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J-GLOBAL

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Authorship：Lead author,　Corresponding author  

J-GLOBAL

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J-GLOBAL

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