Institute of Electrical and Electronics Engineers (IEEE) Acta Medica Okayama 0278-0046 73 4 2026 Transverse- and Axial-Flux Permanent Magnet Machine With C-Type SMC Stator: A Solution for Ultra-Flat Applications 5942 5953 EN Ren Tsunata Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Masatsugu Takemoto Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Jun Imai Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Tatsuya Saito Sumitomo Electric Sintered Alloy Ltd. Tomoyuki Ueno Sumitomo Electric Sintered Alloy Ltd. This article proposes a novel transverse- and axial-flux permanent magnet machine (T-AFPM) using a C-type stator core for reducing system size via an ultra-flat shape. With an axial length of only 19.7 mm, this ultra-flat shape contributes markedly to reducing system size in industrial applications such as water pumps. In general, AFPMs are suitable for a flat shape because of their high torque density with a short axial length. However, it is difficult to use conventional AFPMs to achieve an ultra-flat shape because of structural problems and insufficient performance. By contrast, the proposed T-AFPM achieves a highly manufacturable structure, high efficiency, and the required output power despite its extremely short axial length. Herein, the T-AFPM is compared with conventional AFPMs with various configurations by means of three-dimensional finite-element analysis, and experiments on a T-AFPM prototype are reported. From the simulation and experimental results, the proposed T-AFPM shows high efficiency (IE5 class), the required output power, and suitable structural properties for an ultra-flat shape. No potential conflict of interest relevant to this article was reported.

JSAE Acta Medica Okayama 2025 Development of 50 krpm Ultra-High Speed IPMSM For EV Traction EN Ren Tsunata Okayama University, Graduate School of Environmental, Life, Natural Science and Technology Masaki Kimura Okayama University, Graduate School of Environmental, Life, Natural Science and Technology Masatsugu Takemoto Okayama University, Graduate School of Environmental, Life, Natural Science and Technology Jun Imai Okayama University, Graduate School of Environmental, Life, Natural Science and Technology This paper develops an ultra-high-speed 50 krpm motor for traction applications. A typical IPMSM structure is used for the rotor in this paper. At ultra-high speeds, the winding structure has a large effect on winding losses. Hence, this paper investigates the AC loss of the winding. The AC loss includes the eddy current loss and circulating current loss in the winding. Additionally, the ultra-high speed raises concerns about the rotor's critical speed. Therefore, in this paper, the shaft of the developed motor is manufactured, and the critical speed is evaluated. No potential conflict of interest relevant to this article was reported.

Institute of Electrical and Electronics Engineers (IEEE) Acta Medica Okayama 0093-9994 61 5 2025 Impact of SMC Property on Axial-Flux Permanent Magnet Machine in Traction Applications 6848 6860 EN Ren Tsunata Division of Industrial Innovation Sciences Graduate School of Natural Science and Technology, Okayama University Masatsugu Takemoto Division of Industrial Innovation Sciences Graduate School of Natural Science and Technology, Okayama University Jun Imai Division of Industrial Innovation Sciences Graduate School of Natural Science and Technology, Okayama University Tatsuya Saito Sumitomo Electric Industries Ltd. Tomoyuki Ueno Sumitomo Electric Industries Ltd. This paper investigates the impact of soft magnetic composite (SMC) properties on an axial flux permanent magnet machine (AFPM) employing ferrite permanent magnet (PM) in traction applications. In general, the efficiency of an AFPM increases as the iron loss of the SMC decreases. However, the torque and output power of the AFPM also decrease at higher speed above the base speed due to the decrease in magnetic permeability because, typically, when the iron loss of an SMC decreases, the permeability also decreases. In this paper, many virtual SMC materials with different iron loss and permeability are used for finite element analysis of the proposed AFPM in order to clarify the sensitivity to SMC characteristics. First, the impact of the permeability on the torque and output power is investigated because the output power is very important in traction applications. Additionally, the total energy loss of AFPMs employing various SMCs is evaluated using the WLTC driving cycle. Furthermore, accuracy of simulation is evaluated using experiments of downscaled and actual size prototypes employing some SMC materials. Finally, this paper shows the newly developed SMC materials and discusses suitable SMC properties from the perspective of efficiency and output power in traction applications. No potential conflict of interest relevant to this article was reported.

Institute of Electrical and Electronics Engineers (IEEE) Acta Medica Okayama 2644-1284 6 2025 Time-Efficient and Practical Design Method for Skewed PMSMs: Integrating Numerical Calculations With Limited 3-D-FEA 1370 1386 EN Ren Tsunata Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Yu Ichimura Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Masatsugu Takemoto Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Jun Imai Graduate School of Environmental, Life, Natural Science and Technology, Okayama University This article proposes a time-efficient and practical design method for determining appropriate skew structures for permanent magnet synchronous motors (PMSMs). Various PMSMs use skew to suppress torque ripple, but 3-D finite element analysis (3-D-FEA) is required in order to accurately determine an appropriate structure for skewed PMSMs, resulting in a long analysis time. Therefore, this article constructs a hybrid analysis method that combines numerical calculations and minimal 3-D-FEA. The aim of this method is to be practical and easy to use, even for novice designers, and to accurately and quickly design skewed PMSMs. In this article, the effectiveness of the proposed method is clarified through several case studies, and then, a skewed PMSM designed using the proposed method is verified experimentally. It is also revealed that suppression of voltage harmonics contributes to improving the performance of PMSMs in experiments. No potential conflict of interest relevant to this article was reported.

Institute of Electrical and Electronics Engineers Acta Medica Okayama 2644-1284 5 2024 Skewing Technology for Permanent Magnet Synchronous Motors: A Comprehensive Review and Recent Trends 1251 1273 EN Ren Tsunata Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Masatsugu Takemoto Graduate School of Environmental, Life, Natural Science and Technology, Okayama University This article gives a comprehensive overview of the current research trends in the skewing technique for permanent magnet synchronous motors (PMSMs). The skewing technique has been widely used in many applications to reduce the cogging torque and torque ripple in PMSMs. There are many ways to implement the skew, and new techniques are continually being developed. First, this article summarizes the types of skew structures and presents a survey of existing techniques. Specific emphasis is placed on what kind of skew structure is selected depending on the PMSM configuration. Second, the optimal value of the skew angle for each structure is comprehensively explained, and the discrepancy between theory and finite element analysis is discussed. The definition of skew angle varies across the literature, and one of the purposes of this article is to organize the definition in an easy-to-understand manner. In addition, this article offers three-dimensional finite element analysis (3D-FEA) results of various PMSMs employing the skew for quantitative comparison. Then, this article discusses the properties of PMSMs using the skew by structure and the latest trends, and finally describes future prospects. No potential conflict of interest relevant to this article was reported.

Institute of Electrical and Electronics Engineers (IEEE) Acta Medica Okayama 0093-9994 60 5 2024 Superior Efficiency Under PWM Harmonic Current in an Axial-Flux PM Machine for HEV/EV Traction: Comparison With a Radial-Flux PM Machine 6736 6751 EN Ren Tsunata Division of Industrial Innovation Sciences Graduate School of Natural Science and Technology, Okayama University Masatsugu Takemoto Division of Industrial Innovation Sciences Graduate School of Natural Science and Technology, Okayama University Jun Imai Division of Industrial Innovation Sciences Graduate School of Natural Science and Technology, Okayama University Tatsuya Saito Sumitomo Electric Industries Ltd. Tomoyuki Ueno Sumitomo Electric Industries Ltd. This paper evaluates the harmonic current caused by a pulse width modulation (PWM) inverter and how it affects the efficiency of a novel axial-flux permanent-magnet machine using a ferrite permanent magnet (AF-FePM) in traction applications. First, differences between the finite element analysis (FEA) and experimental results are discussed using a prototype of the proposed AF-FePM. Second, the AF-FePM is compared with a commercially available radial-flux permanent-magnet machine using a Nd-sintered magnet (RF-NdPM). For both machines, the efficiency and loss are calculated using FEA when applying the sinusoidal and harmonic currents. Additionally, we present the superior efficiency of the AF-FePM under the PWM harmonic current during a WLTC driving cycle because the designed model employs the ferrite magnet and a round copper wire, unlike the RF-NdPM. Finally, motor and inverter losses at different switching frequencies are also evaluated. This paper eventually shows that the proposed AF-FePM would be one of the suitable candidates to enhance high efficiency under PWM harmonic current condition based on comprehensive discussion. No potential conflict of interest relevant to this article was reported.

Institute of Electrical and Electronics Engineers (IEEE) Acta Medica Okayama 0093-9994 60 3 2024 Designing and Prototyping an Axial-Flux Machine Using Ferrite PM and Round Wire for Traction Applications: Comparison With a Radial-Flux Machine Using Nd-Fe-B PM and Rectangular Wire 3934 3949 EN Ren Tsunata Division of Industrial Innovation Sciences Graduate School of Natural Science and Technology, Okayama University Kosuke Izumiya Division of Industrial Innovation Sciences Graduate School of Natural Science and Technology, Okayama University Masatsugu Takemoto Division of Industrial Innovation Sciences Graduate School of Natural Science and Technology, Okayama University Jun Imai Division of Industrial Innovation Sciences Graduate School of Natural Science and Technology, Okayama University Tatsuya Saito Sumitomo Electric Industries Ltd. Tomoyuki Ueno Sumitomo Electric Industries Ltd. This paper proposes a novel axial-flux permanent magnet machine (AFPM) employing ferrite permanent magnets (PMs) and round copper wire. The proposed AFPM adopts a novel rotor structure and uses tooth-tips with a suitable trapezoidal shape. These structures compensate for the low magnetomotive force of the round copper wire and ferrite PMs, achieving high performance at low cost. Additionally, compared with an off-the-shelf radial-flux permanent magnet machine (RFPM) using Nd-sintered PMs and rectangular copper wire, the proposed AFPM achieves the same output power and higher efficiency, despite using ferrite PMs and the round copper wire. Finally, a prototype of the proposed AFPM was manufactured and evaluated experimentally. The prototype achieved a high efficiency of over 95% across a wide operating area while maintaining required maximum torque, suggesting its potential for traction applications. No potential conflict of interest relevant to this article was reported.

Institute of Electrical and Electronics Engineers Acta Medica Okayama 2169-3536 11 2023 A Proposal of an Axial-Flux Permanent-Magnet Machine Employing SMC Core With Tooth-Tips Constructed by One-Pressing Process: Improving Torque and Manufacturability 109435 109447 EN Ren Tsunata Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Masatsugu Takemoto Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Jun Imai Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Tatsuya Saito Sumitomo Electric Industries Ltd. Tomoyuki Ueno Sumitomo Electric Industries Ltd. This study aims to improve the torque performance and manufacturability of axial-flux permanent magnet (AFPM) machines. Hence, we propose a novel AFPM machine that employs a soft magnetic composite (SMC) core with tooth-tips constructed by a one-pressing process and die. In this paper, the proposed AFPM machine is compared to two conventional AFPM machines using an SMC core. One of them has open-slot structure without tooth-tips. Another model employs an SMC core with tooth-tips pressed by a conventional pressing process that requires multiple operations and dies. As a result of the comparison, the proposed AFPM machine realizes a much higher torque than the two conventional machines. Additionally, the manufacturability of an SMC core with tooth-tips pressed by the proposed method is superior to the conventional one because the proposed structure can be realized by the one-pressing process and die. Furthermore, two prototypes of the proposed AFPM machine and the conventional one with an open-slot structure are fabricated, and then, they are compared by experiments. Consequently, the proposed AFPM machine achieves a 15.7% higher torque than that of the conventional machine using an open-slot structure. Finally, this paper presents an improved design of an AFPM machine with SMC cores using the proposed pressing process. As a result, the proposed AFPM realizes a 20% larger torque than that of a conventional model employing an open-slot structure. No potential conflict of interest relevant to this article was reported.

Institute of Electrical and Electronics Engineers (IEEE) Acta Medica Okayama 0093-9994 59 3 2023 Comparison of Thermal Characteristics in Various Aspect Ratios for Radial-Flux and Axial-Flux Permanent Magnet Machines 3353 3367 EN Ren Tsunata Division of Industrial Innovation Sciences Graduate School of Natural Science and Technology, Okayama University Masatsugu Takemoto Division of Industrial Innovation Sciences Graduate School of Natural Science and Technology, Okayama University Jun Imai Division of Industrial Innovation Sciences Graduate School of Natural Science and Technology, Okayama University Tatsuya Saito Sumitomo Electric Industries Ltd Tomoyuki Ueno Sumitomo Electric Industries Ltd This paper proposes an axial-flux permanent magnet machine (AFPM) that uses a neodymium-bonded permanent magnet (Nd-bonded PM) and a coreless rotor structure and assesses how it performs in industrial applications requiring high efficiency and low cost. The AFPM is able to achieve high efficiency in high-speed regions because its Nd-bonded PM can restrain eddy current loss. Additionally, the AFPM can continuously function at the rated operating point without a cooling system, so the expenses for one can be eliminated. Hence, the AFPM can simultaneously achieve high efficiency and low-cost mass production. In this paper, a comprehensive comparison including the thermal characteristics of the proposed AFPM and a conventional radial-flux permanent magnet machine (RFPM) is shown. Furthermore, this paper also focuses on how the aspect ratio influences the thermal characteristics of both machines. Finally, the effectiveness of the proposed AFPM in industrial applications is assessed using 3D-FEA and experimental results. No potential conflict of interest relevant to this article was reported.

Institute of Electrical and Electronics Engineers Acta Medica Okayama 2169-3536 11 2023 Design and Analysis of Hybrid-Excitation Variable Flux Memory Motor for Traction Applications: Improving Output Power in High-Speed Area During Six-Step Operation Mode 82024 82036 EN Ren Tsunata Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Keito Yokomichi Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Masatsugu Takemoto Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Jun Imai Graduate School of Environmental, Life, Natural Science and Technology, Okayama University Variable flux motors with adjustable magnetic flux have been gaining attention because of their capability to simultaneously achieve a high torque density and high efficiency. In addition, the output power characteristic, which is related to acceleration performance, in high-speed areas is important in traction applications. However, typical traction motors have lower output power in high-speed areas. In this paper, a Hybrid-Excitation Variable Flux Memory Motor (HE-VFMM) is therefore proposed to enhance output power characteristics under six-step operation mode in high-speed area. The proposed HE-VFMM can perform magnetic flux adjustment with two components: field winding and variable flux permanent magnet (VPM), thus dramatically increasing flux adjustment range. The simulation results show the proposed HE-VFMM achieves 23.7% higher output power at 17,000 rpm than that of an existing traction motor in Prius 4th generation that has the same size while maintaining high efficiency in the frequently used operating area. Additionally, it was found that variable magnetic flux is very effective in enhancing the output power, especially in the high-speed region because the magnetic saturation in the stator core is mitigated by field-weakening control. Consequently, as the rotational speed increases, an increase ratio of the output power caused by the adjustable magnetic flux becomes higher. This paper shows that the proposed HE-VFMM is an effective method for improving the problem of low output power in high-speed regions in traction motors. No potential conflict of interest relevant to this article was reported.

IEEE Acta Medica Okayama 2169-3536 11 2023 Reduction in Eddy Current Loss of Special Rectangular Windings in High-Torque IPMSM Used for Wind Generator 4740 4751 EN Xianji Tao Graduate School of Information and Technology, Hokkaido University Masatsugu Takemoto Graduate School of Natural Science and Technology, Okayama University Ren Tsunata Graduate School of Natural Science and Technology, Okayama University Satoshi Ogasawara Graduate School of Information and Technology, Hokkaido University A special rectangular winding structure, which has different cross-sectional shape but the same cross-sectional area for each turn, has been adopted in a high-torque IPMSM used for a wind generator to improve slot factor and heat dissipation. However, large eddy current loss occurs to the rectangular windings. According to this problem, this paper proposes three improvements to reduce the eddy current loss. Among them, removing a portion of windings and replacing a portion of windings with aluminum are discussed to realize a tradeoff between eddy current and copper losses. And adjusting the tooth-tip shape is discussed to suppress the magnetic flux passing through the windings by mitigating magnetic saturation around the tooth-tip. Additionally, manufacturing costs can also be reduced by adopting a portion of aluminum windings. Moreover, a 3-step-skewed rotor structure is discussed to reduce cogging torque and lower the start-up wind speed. And its influence on losses is also discussed. Furthermore, three models adopting round windings are made and discussed for comparison. The FEM (Finite Element Method) results show that compared with the three round windings models, the proposed model still has a better performance in the reduction of windings eddy current loss. Finally, a prototype machine is manufactured to verify the FEM results, and the experimental results show that the maximum efficiency of the prototype can exceed 97.5%. No potential conflict of interest relevant to this article was reported.

Institute of Electrical and Electronics Engineers (IEEE) Acta Medica Okayama 2169-3536 11 2022 Novel Rotor Structure Employing Large Flux Barrier and Disproportional Airgap for Enhancing Efficiency of IPMSM Adopting Concentrated Winding Structure 2848 2862 EN Xianji Tao Graduate School of Information and Technology, Hokkaido University Masatsugu Takemoto Graduate School of Natural Science and Technology, Okayama University Ren Tsunata Graduate School of Natural Science and Technology, Okayama University Satoshi Ogasawara Graduate School of Information and Technology, Hokkaido University Interior permanent magnetic synchronous motors (IPMSMs) adopting concentrated windings have been widely used in industrial applications. To reduce operating costs, it is an important issue to enhance the efficiency of an IPMSM as much as possible while maintaining manufacturing costs. In general, an IPMSM used for an industrial application always operates in a specific operating area according to the required load. Therefore, this paper has two purposes. The first purpose is to propose a novel rotor structure which can enhance efficiency at the target wide-speed middle-torque operating area without additional manufacturing costs. The second purpose is to clarify the design method for a suitable rotor structure depending on its target operating area. Reducing losses is the key to enhancing efficiency. This paper first examines the effects of adopting large flux barriers and a disproportional airgap on copper and iron losses, and clarifies their merits and respective high-efficiency operating areas. Furthermore, to take advantage of the two rotor structures, a novel rotor structure which employs both large flux barriers and a disproportional airgap has been proposed. 2D-FEM (Finite-Element Method) is used for discussion first, and a prototype machine is manufactured to verify the 2D-FEM results. Both 2D-FEM and experimental results show that the proposed rotor structure can enhance the efficiency of an IPMSM most effectively at the target operating area. Moreover, for a low-speed high-torque operating area, adopting only large flux barriers is most suitable. And for a high-speed low-torque operating area, adopting only a disproportional airgap is most suitable. No potential conflict of interest relevant to this article was reported.