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

Due to the uncertainties in the manufacturing process, additional air gaps (AAGs) between different stator segments in the modular stator motors are inevitable, which might deteriorate the cogging torque performance. To evaluate the influences of the uncertainties, a mass of finite element analysis (FEA) on designs featuring different uncertain combinations is 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 only at most two specific combinations, while hundreds of uncertain comparisons are usually required if the conventional approach is adopted. The efficacy of the proposed method is verified by FEA results for different pole/slot configurations, indicating its high potential to reduce the high computational burden for robust optimization.