An Efficient Method to Evaluate the Effect of Additional Air Gaps on the Cogging Torque for the PM Machines With Modular Stator

Due to the uncertainties in the manufacturing process, the additional air gaps (AAG) between adjacent stator segments in the modular stator machines are inevitable, which might deteriorate the cogging torque performance. To evaluate the influences of the uncertainties, a large number of finite element analysis (FEA) calculations on designs featuring different uncertain combinations are always required. The correspondingly high computational cost is the biggest obstacle to uncertainties analysis and robust design. To solve this problem, an approach based on the worst–uncertain–combination–analysis (WUCA) method is proposed to theoretically find the possible worst-case under uncertainties. With the help of the WUCA approach, the influence of AAG uncertainties on the cogging torque could be estimated by calculating at most two specific combinations. The efficacy of the proposed method is verified by FEA results for different pole/slot configurations. Then, the influence of the connecting tongue shape on cogging torque robustness is comparatively analyzed based on WUCA. It is found that the relatively complex T-shape is preferable from the robustness point. Finally, four prototypes are developed and tested to prove the proposed conclusion, and the experimental results are presented.