Design and Hierarchical Coordinated Optimization of an Outer-Rotor Hybrid-Excitation Flux-Switching Machine for In-Wheel Driving Applications

This article presents an outer-rotor hybrid-excitation flux-switching (OR-HEFS) machine with E-type stator cores, specifically designed for electric vehicle (EV) applications. To address the challenging working conditions encountered in in-wheel driving EVs, an improved hierarchical coordinated optimization (HCO) method is proposed to optimize the proposed machine. This article commences with an introduction to the structural evolution and is followed by the initial design stage of the proposed machine. Subsequently, in order to streamline the optimization process, the HCO method is launched by balancing the dimension reduction and the comprehensive confidence of the optimization results. After optimization, an overall evaluation of the optimized OR-HEFS machine is conducted both by the finite element analysis (FEA) and by prototype experiments. The results indicate that the HCO method improves the performance of the optimized OR-HEFS machine by 18.7% lower iron loss and 5.44% better flux-regulation capability than the initial design. Particularly for the torque characteristic, the optimized 6–19 OR-HEFS machine possesses 22.6% higher average torque and 63.2% lower ripple under the hybrid-excitation condition. Moreover, compared to the conventional outer-rotor flux-switching permanent magnet (OR-FSPM) machine with traditional stator cores, the proposed OR-HEFS machine achieves nearly equivalent output torque with a 50% reduction in PM usage.