Effect of Manufacturing Tolerances and Magnetic Anisotropy of Electrical Steel on Surface-Mounted Permanent Magnet Synchronous Motor Cogging Torque

Abstract

Minimizing cogging torque is critical for surface-mounted permanent magnet synchronous motors (SPMSMs) in high-precision applications, such as electric power steering and robotics. While skewing techniques are typically applied to mitigate cogging torque, anomalous cogging torque harmonics frequently arise in mass production due to manufacturing tolerances and the inherent magnetic anisotropy of non-oriented electrical steel. This paper proposes a systematic analysis approach to distinguish the physical origins of these additional harmonics. By decoupling the effects of geometric and material properties, this study reveals that magnetic anisotropy interacts with slot harmonics to generate a distinct harmonic signature-specifically, the 16th-order harmonic for the 8-pole 12-slot SPMSM. Notably, 3D finite element analysis and experimental validation confirm that this anisotropy-induced cogging torque persists even after applying conventional step-skewing. These findings demonstrate that accounting for magnetic anisotropy is essential for the accurate prediction of cogging torque and the design of low-cogging-torque motors.