VP20-03 A New Asymmetric Permanent Magnet Variable Flux Memory Machine with Magnetic-Field-Shifting Effect
Creators: Wei Liu
Jiamou Zhang
Chi Zhang
Jinhua Chen and Yiyi Fu
Publisher: name: IEEE
Year: 2025

I. Introduction Variable flux memory machines (VFMMs) [1]-[2] employ the low-coercive-force (LCF) PMs to achieve precise adjustment of air-gap flux density, which are considered promising solutions for electric vehicles. Nevertheless, current VFMMs normally suffer from limitations such as narrow flux regulation range and reduced torque under low MS [3]. Therefore, this paper proposes a novel asymmetric PM VFMM (APM-VFMM), which utilizes the magnetic-field-shifting (MFS) effect [4] to adjust the peak angular difference between the PM torque and the reluctance torque, thus contributing to the improvement of torque. Additionally, the multi-parallel magnetic circuit design further enhances the flux regulation range of the VFMM. II. Machine Topology The operation principle and topology of the APM-VFMM are plotted in Fig. 1. It can be seen that only LCF PMs are employed on one side of each pole while the other side has only high-coercive-force (HCF) PMs, thus forming an asymmetric PM design. Moreover, the first layer has two PMs spliced together, with the second layer employing two spoke PM structures. Each layer can form an independent parallel magnetic circuit, which significantly enhances the flux regulation range of the VFMM. Additionally, when the machine is shifted from high MS to low MS, its PM d-axis will be shifted, which will affect the total torque of the APM-VFMM. III. Electromagnetic Performance The electromagnetic characteristics of the APM-VFMM are shown in Fig. 2. The proposed machine exhibits a shift of the PM d-axis at the low MS compared to the high MS due to the presence of the MFS effect. Additionally, this machine achieves more than three times the flux regulation range by magnetization operation. Benefiting from the MFS effect, the torque drop at the low MS can be mitigated. Most importantly, the APM-VFMM can shift the high-efficiency region to the high-speed region at the low MS, implying that the overall high-efficiency characteristics can be achieved by combining different MSs.References: [1] A. N. Charamba, L. Masisi, and M. Ibrahim, “Variable flux machines: A review,” in 2024 32nd Southern African Universities Power Engineering Conference (SAUPEC), Jan. 2024. [2] M. A. Darmani et al., “AFPM machines equipped with multilayer magnets,” IEEE Trans. Energy Convers., early access, 2024. [3] R. Tsunata, M et al., “Variable flux memory motor employing double-layer delta-type PM arrangement and large flux barrier for traction applications,” IEEE Trans. on Ind. Appl., vol. 57, no. 4, pp. 3545–3561, Jul. 2021. [4] Z. Q. Zhu and Y. Xiao, “Novel magnetic-field-shifting techniques in asymmetric rotor pole interior PM machines with enhanced torque density,” IEEE Trans. Magn., vol. 58, no. 2, pp. 1–10, Feb. 2022.
I. Introduction Variable flux memory machines (VFMMs) [1]-[2] employ the low-coercive-force (LCF) PMs to achieve precise adjustment of air-gap flux density, which are considered promising solutions for electric vehicles. Nevertheless, current VFMMs normally suffer from limitations such as narrow flux regulation range and reduced torque under low MS [3]. Therefore, this paper proposes a novel asymmetric PM VFMM (APM-VFMM), which utilizes the magnetic-field-shifting (MFS) effect [4] to adjust the peak angular difference between the PM torque and the reluctance torque, thus contributing to the improvement of torque. Additionally, the multi-parallel magnetic circuit design further enhances the flux regulation range of the VFMM. II. Machine Topology The operation principle and topology of the APM-VFMM are plotted in Fig. 1. It can be seen that only LCF PMs are employed on one side of each pole while the other side has only high-coercive-force (HCF) PMs, thus forming an asymmetric PM design. Moreover, the first layer has two PMs spliced together, with the second layer employing two spoke PM structures. Each layer can form an independent parallel magnetic circuit, which significantly enhances the flux regulation range of the VFMM. Additionally, when the machine is shifted from high MS to low MS, its PM d-axis will be shifted, which will affect the total torque of the APM-VFMM. III. Electromagnetic Performance The electromagnetic characteristics of the APM-VFMM are shown in Fig. 2. The proposed machine exhibits a shift of the PM d-axis at the low MS compared to the high MS due to the presence of the MFS effect. Additionally, this machine achieves more than three times the flux regulation range by magnetization operation. Benefiting from the MFS effect, the torque drop at the low MS can be mitigated. Most importantly, the APM-VFMM can shift the high-efficiency region to the high-speed region at the low MS, implying that the overall high-efficiency characteristics can be achieved by combining different MSs.References: [1] A. N. Charamba, L. Masisi, and M. Ibrahim, “Variable flux machines: A review,” in 2024 32nd Southern African Universities Power Engineering Conference (SAUPEC), Jan. 2024. [2] M. A. Darmani et al., “AFPM machines equipped with multilayer magnets,” IEEE Trans. Energy Convers., early access, 2024. [3] R. Tsunata, M et al., “Variable flux memory motor employing double-layer delta-type PM arrangement and large flux barrier for traction applications,” IEEE Trans. on Ind. Appl., vol. 57, no. 4, pp. 3545–3561, Jul. 2021. [4] Z. Q. Zhu and Y. Xiao, “Novel magnetic-field-shifting techniques in asymmetric rotor pole interior PM machines with enhanced torque density,” IEEE Trans. Magn., vol. 58, no. 2, pp. 1–10, Feb. 2022.