Abstract:By incorporating the merits of the high torque density, high efficiency, and compact size, the dual-stator low-speed high-torque permanent magnet drive machine (DLHPMDM) is an excellent alternative to the traditional machine in low-speed high-torque applications. For dual-stator machines, the total output torque equals the output torque superposition of inner and outer machines, namely the torque superposition principle of dual-stator machines. This principle can explain the mechanism of reducing the torque ripple of the dual-stator permanent magnet machines. Changing the pole-slot number combination is a crucial method to reduce the torque ripple of machines. However, in analyzing and mitigating torque ripple for the DLHPMDM, considering the inner and outer machines alone needs to be revised and more accurate. More attention should be paid to the superposition reduction effect of inner and outer torque ripple resulting from different phases. The combination number of inner and outer stator slots can affect the torque ripple of the DLHPMDM. Based on the torque superposition principle of dual-stator machines, a design method is proposed to reduce the torque ripple of the DLHPMDM with the inner and outer windings connected in parallel. Generally, the 6th ripple torque accounts for the largest proportion of the torque ripple of permanent magnet machines. Suppose the phase difference between the 6th ripple torque of the inner and outer machines is close to π. In that case, the superposition reduction effect can be achieved, thereby reducing the total torque ripple of the DLHPMDM. When only considering the situation where the fundamental sinusoidal current is passed through the stator windings, the 6th ripple torque is caused by the following two cases. One is the interaction of the fundamental current and the 5th harmonic of the back EMF. The other is the interaction of the fundamental current and the 7th harmonic of the back EMF. The fundamental phases of the inner and outer stator currents are approximately the same. Therefore, when the DLHPMDM is divided into two independent machines for design, the superposition effect of 6th ripple torque of the inner and outer machines can be predicted by the phase relationship of the back-EMFs harmonics. Then, the appropriate winding form combination is determined to reduce the total torque ripple of the DLHPMDM by utilizing the superposition reduction effect. Based on three projects of DLHPMDM with different winding forms installed on the inner stator, the influence of the harmonic phase difference of back EMFs of inner and outer machines on the superposition of the ripple torque is analyzed. By comparing torque performance, the winding form combination of the inner and outer stators is initially selected. Then, considering the influence of harmonic currents from winding harmonics, the torque ripple of DLHPMDM can be effectively reduced (from 8.84% to 5.21%) with a reasonable winding form combination. Finally, a prototype of the DLHPMDM is manufactured and tested. The results are well consistent with the simulated results, which verifies the feasibility of the low torque ripple design method.
刘佶炜, 狄冲, 李仕豪, 鲍晓华. 基于不同绕组形式双定子低速大转矩永磁直驱电机转矩脉动的分析与抑制[J]. 电工技术学报, 2024, 39(12): 3646-3657.
Liu Jiwei, Di Chong, Li Shihao, Bao Xiaohua. Analysis and Mitigation of Torque Ripple of a Dual-Stator Low-Speed High-Torque Permanent Magnet Machine with Different Winding Forms. Transactions of China Electrotechnical Society, 2024, 39(12): 3646-3657.
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