Analytical Solution for Cogging Torque in Surface-Mounted Permanent-Magnet Motors With Magnet Imperfections and Rotor Eccentricity

Abstract

Cogging torque exhibits a strong correlation with manufacturing tolerances. Aiming for robust design of the mass-produced surface-mounted permanent magnet motors, an analytical solution for the estimation of cogging torque is presented, which considers the magnet imperfections and the rotor eccentricity. In addition, the analytical solution is based on the exact subdomain model and accurate modified magnetization intensity, which takes magnet misplacement, remanence variation, magnetization direction error, pole-arc deviation, thickness error, and recoil permeability variation into consideration. Furthermore, the perturbation method is introduced into the model to describe the effect of rotor eccentricity. The spatial change of magnets and slots resulting from eccentricity is also considered in this paper, which effectively facilitates the calculation precision of cogging torque. Magnetic field distributions and cogging torque calculation by the proposed analytical solution are found to be consistent with the finite-element and experimental results.