Influence of Rotor Eccentricity on Cogging Torque of 12-slot/10-pole PM Machines with Tooth Bulge

Abstract

Cogging torque is usually very sensitive to the manufacturing tolerances, especially tooth bulge and rotor eccentricity in the modular permanent magnet (PM) machines. This paper investigates the cogging torque worst-case scenario due to interaction between static/dynamic rotor eccentricity and tooth bulge in the 12-slot/10-pole PM machine. Firstly, the tooth bulge worstcase scenario of the machine is predicted by vector analysis. Secondly, the worst-case scenario due to interaction between static/dynamic rotor eccentricity and tooth bulge is investigated through the finite element analysis, considering different rotor eccentricity ratio and angle. It is found that the interaction between two tolerances has a significant influence on the cogging torque. Under static rotor eccentricity and tooth bulge, cogging torque depends on the eccentricity ratio that decides which tolerance is dominant and the eccentricity angle that decides whether the effect of the non-dominant tolerance is cancelling or strengthening. Specifically, the cogging torque due to both tolerances is weakened when the eccentric rotor is close to the outward tooth, whilst the cogging torque is strengthened when the eccentric rotor is close to the inward tooth. Under dynamic rotor eccentricity and tooth bulge, cogging torque solely depends on the eccentricity ratio.