Analytical Calculation of Magnetic Field and Cogging Torque in Surface-Mounted Permanent Magnet Machines Accounting for Any Eccentric Rotor Shape

Abstract

This paper presents an improved analytical method for calculating the magnetic field and cogging torque in the surface-mounted permanent-magnet (PM) machines accounting for any eccentric rotor shape. The magnetic field in the surface-mounted PM machines is predicted according to the surface-current method of the PM, the subdomain model, and the superposition principle of vector potential. The cogging torque is calculated based on Maxwell stress theory and the air-gap magnetic field. The investigation shows that harmonic contents of radial flux density can be reduced a lot by changing eccentric distance of eccentric magnet poles compared with conventional surface-mounted PM machines with concentric magnet poles. Moreover, the analysis has made it clear that the cogging torque of motor with eccentric magnet poles is much smaller than the cogging torque of motor with concentric magnet poles. The finite-element results confirm that the developed analytical method has high accuracy for predicting the magnetic field and cogging torque.