VP21-07 A Novel Twelve-Phase Variable Magnetic Circuit Memory Machine for Rim Thrusters
Creators: Yiyi Fu
Publisher: name: IEEE
Year: 2025

I.Introduction Shaftless rim thrusters are widely employed in underwater propulsion systems due to the advantages of compact structure and high transmission efficiency [1]. Nevertheless, traditional shaftless rim thrusters mostly use surface-mounted permanent magnet (PM) machines, which suffer from the narrow high-speed efficiency region and operation range. To address the above issues, this paper proposes a novel variable magnetic circuit memory machine (VMCMM) employing the low coercive force (LCF) PMs [2]. The magnetization states (MSs) of the LCF PMs can be adjusted through the imposition of the d-axis pulse current, which can improve the efficiency [3]. Besides, the proposed VMCMM utilize twelve-phase winding to reduce the torque ripple under different MSs [4]. II.Machine Topology The structure of the proposed VMCMM is shown in Fig. 1(a). When the machine is under flux-enhanced state, half part of high coercive force (HCF) PMs close to the inner side of the rotor and LCF PMs form series magnetic circuits, while the half part of HCF PMs close to the air-gap and LCF PMs form parallel magnetic circuits. When the VMCMM is switched to the flux-weakened state, the magnetic circuit of the rotor varies as the magnetization direction of the LCF PMs is reversed, with the LCF and HCF PMs forming parallel magnetic circuit. Fig. 1(b) shows the electromotive force distribution of the winding, which uses a twelve-phase winding consisting of four sets of star-connected three-phase windings for π/12 multiplex offset. III.Electromagnetic Performance The electromagnetic performance is plotted in Fig. 2. Figs. 2 (a)-(b) reveal the excellent flux changeable performance. Besides, the twelve-phase winding enables the machine to have excellent output torque and low torque ripple. Moreover, the efficiency maps exhibit that the machine can expand the high-speed efficiency region through flux adjustment. It is confirmed that the proposed VMCMM can effectively solve the cruising anxiety of the rim thrusters and the problem of high torque ripple.References: [1] X. Yan, X. Liang, W. Ouyang, Z. Liu, B. Liu, and J. Lan, “A review of progress and applications of ship shaft-less rim-driven thrusters,” Ocean Engineering, vol. 144, pp. 142–156, Nov. 2017. [2] V. Ostovic, “Memory motors,” IEEE Ind. Appl. Mag., vol. 9, no. 1, pp. 52–61, Jan. 2003. [3] H. Hua, Z. Q. Zhu, A. Pride, R. Deodhar, and T. Sasaki, “Comparative study on variable flux memory machines with parallel or series hybrid magnets,” IEEE Trans. Ind. Appl., vol. 55, no. 2, pp. 1408–1419, Mar/Apr. 2019. [4] C. Liu, “Emerging electric machines and drives — An overview,” IEEE Trans. Energy Convers., vol. 33, no. 4, pp. 2270–2280, Dec. 2018.
I.Introduction Shaftless rim thrusters are widely employed in underwater propulsion systems due to the advantages of compact structure and high transmission efficiency [1]. Nevertheless, traditional shaftless rim thrusters mostly use surface-mounted permanent magnet (PM) machines, which suffer from the narrow high-speed efficiency region and operation range. To address the above issues, this paper proposes a novel variable magnetic circuit memory machine (VMCMM) employing the low coercive force (LCF) PMs [2]. The magnetization states (MSs) of the LCF PMs can be adjusted through the imposition of the d-axis pulse current, which can improve the efficiency [3]. Besides, the proposed VMCMM utilize twelve-phase winding to reduce the torque ripple under different MSs [4]. II.Machine Topology The structure of the proposed VMCMM is shown in Fig. 1(a). When the machine is under flux-enhanced state, half part of high coercive force (HCF) PMs close to the inner side of the rotor and LCF PMs form series magnetic circuits, while the half part of HCF PMs close to the air-gap and LCF PMs form parallel magnetic circuits. When the VMCMM is switched to the flux-weakened state, the magnetic circuit of the rotor varies as the magnetization direction of the LCF PMs is reversed, with the LCF and HCF PMs forming parallel magnetic circuit. Fig. 1(b) shows the electromotive force distribution of the winding, which uses a twelve-phase winding consisting of four sets of star-connected three-phase windings for π/12 multiplex offset. III.Electromagnetic Performance The electromagnetic performance is plotted in Fig. 2. Figs. 2 (a)-(b) reveal the excellent flux changeable performance. Besides, the twelve-phase winding enables the machine to have excellent output torque and low torque ripple. Moreover, the efficiency maps exhibit that the machine can expand the high-speed efficiency region through flux adjustment. It is confirmed that the proposed VMCMM can effectively solve the cruising anxiety of the rim thrusters and the problem of high torque ripple.References: [1] X. Yan, X. Liang, W. Ouyang, Z. Liu, B. Liu, and J. Lan, “A review of progress and applications of ship shaft-less rim-driven thrusters,” Ocean Engineering, vol. 144, pp. 142–156, Nov. 2017. [2] V. Ostovic, “Memory motors,” IEEE Ind. Appl. Mag., vol. 9, no. 1, pp. 52–61, Jan. 2003. [3] H. Hua, Z. Q. Zhu, A. Pride, R. Deodhar, and T. Sasaki, “Comparative study on variable flux memory machines with parallel or series hybrid magnets,” IEEE Trans. Ind. Appl., vol. 55, no. 2, pp. 1408–1419, Mar/Apr. 2019. [4] C. Liu, “Emerging electric machines and drives — An overview,” IEEE Trans. Energy Convers., vol. 33, no. 4, pp. 2270–2280, Dec. 2018.