Influence of Magnet Tolerances and Rotor Eccentricities on Cogging Torque of 12-slot/10-pole PM Machines

This paper investigates the influence of PM tolerances and rotor eccentricities on cogging torque of12- slot/10-pole PM machines. The vector analysis is firstly adopted to derive the worst-case scenario of PM tolerances which exhibits the highest cogging torque. Then, the effects of static/dynamic rotor eccentricity ratios, angle, and rotor initial angle are investigated and compared in the machines with the worst-case scenario of PM tolerances by finite element analysis. It is found that (a) PM tolerances always deteriorate the cogging torque whether the machine has static/dynamic rotor eccentricities or not; (b) when the “weak” (e.g. lower remanence) PM is close to the minimum airgap, the cogging torques due to static rotor eccentricity and worst-case PM tolerances have a significant strengthening effect, whilst the cogging torques due to dynamic rotor eccentricity and worst-case PM tolerances only have a slight strengthening effect. However, when the “strong” (e.g. higher remanence) PM is close to the minimum airgap, the cogging torques due to static/dynamic rotor eccentricities and worst-case PM tolerances both have a significant strengthening effect.