Analysis and Experimental Study of Eddy Current Loss of Axial Flux Permanent Magnet Motor Based on Rotor Segment Optimization
Liu Xiping1, Zhu Zhiguo1, Chen Dong2, Shi Zihao1, Sun Guojian2
1. School of Electrical Engineering and Automation, Jiangxi University of Science and Technology Ganzhou 341000 China;
2. Hangzhou Zhong hao Electric Technology Co. Ltd Hangzhou 310000 China
Axial flux permanent magnet motor (AFPM) has the advantages of short axial length, light weight, high power density and high torque density, which is widely used in electric vehicles, new energy power generation and other fields. However, due to the structural limitations, the heat dissipation of rotor is difficult, and the eddy current loss in the permanent magnet (PM) will increase the temperature of rotor, resulting in the risk of irreversible demagnetization of PM and affecting the normal operation of motor. To address this problem, three new optimization methods for the partial segmentation of PM are proposed based on the complete segmentation of PM.
Firstly, the mathematical model of eddy current loss of PM of AFPM is derived. It is analyzed that extending eddy current path on the surface of PM and reducing the surface area of PM can effectively reduce the eddy current loss, which provides a theoretical basis for the proposed optimization method. Secondly, the finite element (FE) analysis model of the motor is established by using the FE software, the current density distribution, eddy current loss and anti-demagnetization ability of the PM before and after optimization are simulated and analyzed. The results show that the proposed optimization method can significantly reduce the eddy current loss and has little influence on the magnetic properties of PM. The simulation analysis results are basically consistent with the theoretical analysis. Besides, the appropriate number of segments and the reserved size of the PM are obtained. Then, the cutting gap of the optimized PM is modeled separately and filled with epoxy resin glue. Moreover, the mechanical strength of the PM is calculated and analyzed by the FE method. The results show that the mechanical strength of the PM is improved, the stress generated by the centrifugal force and the unbalanced magnetic tension will not destroy the mechanical structure of the optimized PM. Finally, a prototype was fabricated, the efficiency of motor, the magnetic properties of PM and the temperature rise of PM were tested, which verified the effectiveness of proposed optimization method and the accuracy of theoretical analysis.
The following conclusions can be drawn from the simulation and experimental results: (1) The optimization effects of the intermediate retention method (IRM) and the alternating cutting method (ACM) of the PM in AFPM are basically the same, both can effectively reduce the temperature rise of PM, which are better than the surface cutting method (SCM). In the rated state, the effect is similar to that of the complete segmentation method (CSM). Under the rated working conditions and the same number of partial segments, compared with the original PM, the reduction ratio of the average eddy current loss of IRM and ACM is about 36.8%, 13% higher than that of SCM, and 9% worse than that of the CSM. Therefore, IRM and ACM are preferred. (2) The eddy current loss of PM decreases with the increase of the number of partial segments, and the eddy current loss increases with the increase of the retention size. (3) The proposed optimization method does not affect the anti-demagnetization ability of PM at high temperature and high current, which has little effect on the magnetic properties of PM. (4) The epoxy resin filled in the gap of PM can improve the mechanical strength of PM, and the maximum equivalent stress is far less than the yield strength. The PM mechanical structure is not destroyed by the stresses generated by centrifugal forces and unbalanced magnetic forces.
刘细平, 朱治国, 陈栋, 史梓豪, 孙国建. 基于转子永磁分段优化的轴向磁通永磁电机涡流损耗分析与试验研究[J]. 电工技术学报, 0, (): 239632-239632.
Liu Xiping, Zhu Zhiguo, Chen Dong, Shi Zihao, Sun Guojian. Analysis and Experimental Study of Eddy Current Loss of Axial Flux Permanent Magnet Motor Based on Rotor Segment Optimization. Transactions of China Electrotechnical Society, 0, (): 239632-239632.
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