Investigation of Electromagnetic Forces under Stator and Rotor Reference Frames in PMSM

The electromagnetic vibration and torque ripple are crucial to the NVH performance of permanent magnet synchronous motor (PMSM). In this paper, take a motor with 9 slots and 6 poles as an example, the spatial and temporal orders of the force harmonics under the stator stationary reference frame and rotor rotating reference frame are derived. Both the theoretical analysis and the finite element method (FEM) demonstrate the differences between the force harmonic characteristics under the two reference frames. Then the radial and tangential vibrations on the stator and rotor are simulated and compared. The orders of force harmonics dominantly causing vibration and torque ripple are identified, respectively. The force harmonics, vibration and torque ripple are compared with motors before and after torque optimization as examples, and the intrinsic relation among them is revealed accordingly to give recommendations for optimization.