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| Rotor Eddy Current Loss Analytical Model for High-Speed Permanent Magnet Motor Based on Double Layer Permanent Magnet Structure |
| Tong Wenming1, Yang Xiankai1, Lu Jiwen1, Jia Jianguo1, Li Weidong2 |
1. National Engineering Research Center for Rare-Earth Permanent Magnet Machines Shenyang University of Technology Shenyang 110870 China;
2. Shenyang Micro Control New Energy Technology Co. Ltd Shenyang 110178 China |
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Abstract High-speed permanent magnet motor (HSPMM) has the advantages of high efficiency, fast dynamic response, etc. and is widely used in the field of high motor performance requirements. Due to the poor heat dissipation condition of surface-mounted HSPMM, the permanent magnet (PM) will face the risk of irreversible demagnetization if the eddy current loss on the rotor retaining sleeve and PMs is high. The eddy current loss of the double-layer permanent magnet (DLPM) rotor structure can be effectively restrained by using the PM with high resistivity in the outer layer. However, the calculation time of eddy current loss of the rotor in different ratio of the structure by finite element software is long, which is not conducive to the initial design and optimization of the motor. Based on the exact subdomain method, an analytical model of rotor eddy current loss of DLPM structure is established, which can shorten the calculation time of rotor eddy current loss.
The research idea of this paper is as follows Firstly, the motor is divided into 7 subdomains, such as outer permanent magnet subdomain, inner permanent magnet subdomain, retaining sleeve subdomain, etc. Laplacian equation and diffusion equation are written for different subdomains, and the general solution of vector magnetic potential in each subdomain is obtained according to the continuous boundary conditions of vector magnetic potential and tangential magnetic field strength as well as the ferromagnetic boundary conditions of each subdomain. Then the eddy current losses in different subdomains are obtained by Poynting theorem. Secondly, a two-dimensional finite element model is established to compare the air gap flux density obtained by the analytical model and the rotor eddy current loss. The deviation between the analytical model and the finite element is within the allowable range of engineering and meets the accuracy requirements. Finally, the analytical model is verified by the C-type core loss experiment, and the analytical calculation results are compared with the finite element and C-type core experiment results, and the error is less than 5%, which further verifies the accuracy of the analytical model.
In addition, the influence of different material and thickness of outer PM on eddy current loss and magnetic steel cost of HSPMM is investigated by using analytical model. Taking the motor studied in this paper as an example, when the magnetic density of the air gap is unchanged, the outer permanent magnet is bonded NdFeB or Ferrite with the same thickness, and the inhibition effect on eddy current loss of the rotor is similar, but when the bonded NdFeB with strong magnetic properties is used, the amount of sintered NdFeB in the inner layer is reduced by about 20% Therefore, for the DLPM rotor structure, the thickness and material of the outer permanent magnet should be determined by weighing the reduction of eddy current loss of the rotor and the amount of the inner permanent magnet.
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Received: 16 August 2023
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2024, Vol. 39 
