Analysis of Cogging Torque under Eccentricity of PMSMs for EV Steer-by-Wire System

Cogging torque is an inherent characteristic of permanent magnet synchronous machines (PMSMs). Eccentricity caused by manufacturing errors and assembly deviations would aggravate cogging torque, further deteriorate control accuracy and torque ripple of electrical machine-based traction systems. In this paper, an improved magnetic co-energy method based on the airgap field modulation theory (AFMT) is developed to investigate the effects of different eccentricity types on the cogging torque of a 22-pole/24-slot outer-rotor surface-mounted PMSM (OR-SPMSM) for electric vehicles (EVs) steer-by-wire systems. The proposed analytical model demonstrates that static eccentricity (SE) induces the specific orders of cogging torque associated with rotor pole multiples, whereas dynamic eccentricity (DE) introduces the orders related to stator slots multiples. For mixed eccentricity (ME), the orders of cogging torque not only contain the main harmonic orders of SE and DE, but also modulate other additional characteristic harmonics.