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| Analytical Calculation and Parameter Optimization of Eddy Current Loss for Coreless Axial Flux Permanent Magnet Synchronous Machine with Multilayer Flat Wire Winding |
| Wang Xiaoguang1, Yin Hao1, Yu Renwei2 |
1. Hubei Engineering Research Center for Safety Monitoring of New Energy and Power Grid Equipment Hubei University of Technology Wuhan 430068 China;
2. RAYGET Power Generation Technology (Wuhan) Co. Ltd Wuhan 430073 China |
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Abstract Coreless axial flux permanent magnet synchronous machine (CAFPMSM) is increasingly used in industrial applications due to its advantages such as compact structure, low maintenance cost, high power density, high torque ratio, and power efficiency. Preformed flat wire has a relatively regular shape, which is adopted in CAFPMSM winding manufacturing because it can make full use of stator space and increase the power density of the machine. Since the coreless winding is directly exposed to the air gap flux field, the large across section of the flat wire will result in significant eddy current losses and will be more serious when the speed goes higher. Therefore, it is important to calculate the eddy current losses of the winding accurately. Some valuable methods have been presented to calculate the eddy current loss of the traditional round winding, but they are unsuitable for CAFPMSM with flat wire. This paper derives the formula specific to flat wire for the uneven distribution of eddy current losses generated by the air gap flux field. According to the theoretical analysis of eddy current loss and taking the minimum copper loss as the optimization objective, the solution of the optimal parameters of flat wire is established. The calculation formula and parameter optimization method can reduce the eddy current loss and improve efficiency.
Firstly, the distribution characteristics of both the flux field in the axial direction and circumferential direction have been analyzed. Secondly, the amplitude of leakage flux density between the two adjacent permanent magnets is approximately linear with the position in the axial direction. The amplitude of the leakage flux density in different positions can be expressed in terms of the distance in the axial direction. The eddy current loss produced by the leakage flux can be calculated. Thirdly, the amplitude of the main flux density waveform can be expressed by the average value, simplifying the calculation of the eddy current loss produced by the main flux. Finally, the theoretical analysis method has been proposed, and the eddy current loss of the winding can be obtained by the sum of the eddy current loss produced by the main flux and leakage flux. According to the proposed theoretical analysis, the length and width of the cross-section of flat wire are optimized with the constraint of the current density. Furthermore, the method for selecting the length and width of the cross-section is proposed to obtain the lowest eddy current loss of the winding. An equivalent model of the winding by finite element method is established, and the simulation results of the eddy current loss verify the correctness of the theoretical analysis. According to the established model, the prototype is manufactured. The measured results of the eddy current loss prove the accuracy of theoretical analysis, and the error is 6 %.
The following conclusions can be drawn from the analysis: (1) Both axial and circumferential components of the air gap flux field will produce eddy current loss in the rectangular conductor. The eddy current loss caused by the leakage flux field should be considered. (2) The eddy current loss of the machine is related to the length ratio, flat wire section width, and density of the air gap flux field. By changing the ratio of section length to width, the eddy current loss of the winding can be minimized with the same direct current loss. (3) The measured results of the prototype at different speeds are consistent with the theoretical and finite element analysis results, which verifies the correctness of the analytical calculation and finite element results. This paper provides a reference for designing machine windings with different structures.
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Received: 26 May 2022
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2023, Vol. 38 
