Abstract：The torque ripple of the interior permanent magnet synchronous motor (IPMSM) which affects the driving experience of electric vehicles (EVs), is the most important factor in assessing the quality of driving motors for EVs. Optimizing the rotor structure of the IPMSM is a solution to this drawback that does not significantly increase manufacturing costs. The traditional analytical methods for optimizing the rotor structure are mainly of two kinds: The first method is to make the rotor magnetomotive force (MMF) as close as possible to a sinusoidal waveform by optimizing the magnet distribution; The other method is to make the air gap flux density closer to a sinusoidal waveform by designing an uneven magnetic resistance. However, these methods did not consider the effect of the rotor structure on the air gap relative permeability. This paper proposes an analytical model for calculating the torque ripple of IPMSM, which takes into account the influence of rotor structure on the air gap relative permeability. The optimal design of the rotor structure can be quickly determined by analyzing the analytical model. Firstly, based on the assumption of deep magnetic saturation of the ferromagnetic material at the flux barrier, the flux barrier is abstracted as a rotor virtual slot. Secondly, an air gap relative permeability equation is derived, which takes into account the effect of stator slotting and rotor virtual slotting on the air gap relative permeability. Thirdly, an analytical expression for the torque of IPMSM is obtained, by utilizing the stator MMF equation, rotor MMF equation and the air gap relative permeability equation. The relationship between the position of rotor virtual slot and torque ripple is derived by analyzing the analytical expression, based on which the design principle of IPMSM with low torque ripple is summarized. Finally, an IPMSM for EV with a rated power of 30 kW is optimally designed. The main electromagnetic properties of the original motorand the optimized motor are calculated. The torque ripple is significantly reduced after optimization, without affecting other electromagnetic performance. For torque performance, compared to the original motor, the torque ripple of the optimized motor decreased from 25.5% to 6.8%, a decrease of 18.7%. For the cogging torque performance, compared to the original motor, the cogging torque of the optimized motor decreased from 3.87 Nm to 0.98 Nm. That is to say, optimizing design is beneficial for reducing cogging torque. For inductance performance, the d-axis inductance before and after optimization is 0.243 7 mH, 0.243 9 mH, and the q-axis inductance is 0.838 3 mH and 0.837 1 mH, respectively. The simulation results show that the inductance remains unchanged before and after optimization. Due to the influence of the inductance of IPMSM on its flux weaken ability and reluctance torque utilization, the unchanged inductance means that these properties remain unchanged. For voltage performance, compared to the original motor, the optimized back electromotive force increased from 41.5 V to 43.3 V. For efficiency performance, compared to the original motor, the optimized efficiency increased from 96.55% to 96.66%. The optimization design has little impact on voltage and efficiency performance. Meanwhile, the torque ripple under all operating conditions has been suppressed by optimized design, especially in the flux-weakened region of the maximum current. The following conclusions can be drawn: The rotor virtual slot affects the torque ripple of IPMSM by affecting the air gap relative permeability. By optimizing the position of the rotor virtual slot, it is possible to make the value of the air gap relative permeability 0 for some specific order. For a ZS-slot p-pole IPMSM, the air gap relative permeability with ZS/p order can cause most of the torque ripple. By optimizing the position of the virtual slot, the torque ripple can be reduced without significantly altering the other main electromagnetic performance of the motor. This method is effective for all operating conditions of electric vehicles.
王力新, 王晓远, 高鹏, 刘双双. 电动汽车用内置式永磁同步电机转矩脉动分析及抑制[J]. 电工技术学报, 2024, 39(20): 6386-6396.
Wang Lixin, Wang Xiaoyuan, Gao Peng, Liu Shuangshuang. Torque Ripple Reduction Analysis of Interior Permanent Magnet Synchronous Motor for Electric Vehicle. Transactions of China Electrotechnical Society, 2024, 39(20): 6386-6396.
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