Unbalanced Magnetic Pull in Fractional-Slot Brushless PM Motors

Abstract

This paper reports on an investigation into the unbalanced magnetic pull in brushless PM motors due to either magnetic asymmetry or rotor eccentricity. Several machines are investigated. These have different slot and pole number combinations. Some of the windings contain sub-harmonics and these are found to be more susceptible to UMP when there is rotor eccentricity and also to produce vibrating UMP. Consequent rotor poles are also found to produce high UMP under rotor eccentricity conditions.