Design Optimization of a Spoke-Type Axial-Flux PM Machine for In-Wheel Drive Operation

Axial flux machines (AFMs) have huge potential in direct-drive operations such as in-wheel drive operation due to the characteristics of high torque density and short axial length. However, the design optimization of AFMs was limited by the lack of accuracy magnetic circuit model. In this article, a spoke-type axial-flux permanent magnet synchronous machine (spoke-type AFPMSM) is designed and an efficient optimization method for axial flux structure is proposed. The proposed optimization method improves the efficiency of the optimization design by using a 2-D equivalent finite-element model and multilevel optimization strategy. The parameters without end effects will be optimized by a 2-D equivalent model and the parameters with end effects will be optimized by a 3-D model. In this way, the number of finite-element nodes required for optimization calculation can be minimized. Besides, the multilevel strategy and response surface optimization method are also adopted to further improve the efficiency of the optimization. The proposed method improved the cost, efficiency, and torque of the AFPMSM significantly, and some other constraints are also considered in the optimization progress. Finally, experimental results based on a prototype are provided to validate the performance of the proposed AFPMSM. The proposed method can be applied for other design optimization of axial flux operations.