I. Introduction
Ubalanced MAGNETIC PULL (UMP) is usually associated with larger machines [1], [2], [12]–[14] or other types of machine [15], [16]. Small permanent magnet (PM) machines are subject to UMP [3] even without rotor anomalies. UMP is important because it affects bearing wear, noise, and vibration [4], [5]. There is surprisingly little literature on UMP in PM machines; in [6], several fractional-slot ferrite-magnet motors (9-slot/8-pole machines and 18-slot stator with 12-pole/16-pole/20-pole rotor machines) were investigated—these had surface magnet and consequent pole rotors and considered static rotor eccentricity. Dorrell et al. [6] and Li et al. [17] developed analytical UMP calculations for UMP in PM machines but saturation can lead to inaccuracies [2]. Dynamic rotor eccentricity is addressed in this paper in a higher power 18-slot/4-pole machine with rare-earth surface-mounted magnets and consequent-pole rotors. The equations for the UMP and stresses are implemented using 2-D finite element solutions and investigate the component values of the stress terms and how they vary with load and rotor eccentricity.