Unbalanced magnetic force and cogging torque of PM motors due to the interaction between PM magnetization and stator eccentricity

Abstract

We investigate the characteristics of cogging torque and unbalanced magnetic forces (UMF) due to the interaction between magnetization of permanent magnets (PM) and stator eccentricity in PM motors. We mathematically and numerically show that the third harmonic of PM magnetization with stator eccentricity decreases the amplitude of the pole harmonic of the cogging torque and UMF while at the same time increasing the amplitude of the least common multiple harmonic of the pole and slot numbers of cogging torque and UMF in PM motors. The effects of the third harmonic of PM magnetization in the PM motors with stator eccentricity were experimentally verified by measuring UMF and acoustic noise.