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| Analysis and Experiment 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 Zhonghao Electric Technology Co. Ltd Hangzhou 310000 China |
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Abstract Axial flux permanent magnet motor (AFPM) has the advantages of short axial length, lightweight, high power density, and high torque density, which is widely used in electric vehicles, new energy power generation, and other fields. However, due to structural limitations, the heat dissipation of the rotor is difficult, and the eddy current loss in the permanent magnet (PM) can increase the temperature of the rotor, resulting in irreversible demagnetization risk of PM and affecting the normal operation of the motor. Therefore, 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. Extending the 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 motor's finite element (FE) analysis model is established using the FE software. The current density distribution, eddy current loss, and anti-demagnetization ability of the PM before and after optimization are simulated. The results show that the proposed optimization method significantly reduces the eddy current loss and has little influence on the magnetic properties of the PM. Simulation results are 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 by the FE method. Accordingly, the mechanical strength of the PM is improved, and the stress generated by the centrifugal force and the unbalanced magnetic tension do not destroy the mechanical structure of the optimized PM. Finally, the motor efficiency, PM magnetic properties, and PM temperature rise are tested through a prototype, which verifies the effectiveness of the proposed optimization method and the accuracy of theoretical analysis.
The following conclusions can be drawn: (1) The optimization effects of the intermediate retention method (IRM) and the alternating cutting method (ACM) of the PM in AFPM are consistent. Both can effectively reduce PM temperature rise, better than the surface cutting method (SCM) and similar to 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 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 temperatures and high currents, which has little effect on the magnetic properties of PM. (4) The epoxy resin filled in the PM gap can improve the mechanical strength of PM, and the maximum equivalent stress is far less than the yield strength. The stresses generated by centrifugal and unbalanced magnetic forces do not destroy the PM mechanical structure.
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Received: 15 May 2023
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2024, Vol. 39 
