Mitigation of UMP Components by the Parallel Stator Windings in Eccentric-rotor Electrical Machines

In this paper, electromagnetic force acting between the stator and eccentric rotor of an induction machine is computed in a wide whirling frequency range and resolved into several components originating from different sources. Effects of the parallel stator windings on these eccentricity force components are investigated. The results of this study showed that the parallel stator windings effectively attenuate the net eccentricity force by suppressing significantly the eccentricity harmonics arising from the modulation of the fundamental magnetomotive force by the permeance wave due to rotor eccentricity. Slotting harmonics, also considerably contributing to the net eccentricity force, are mitigated evenly in the whole whirling frequency range studied, although not to such a great degree as the eccentricity harmonics. It was shown that the reduction of slotting and eccentricity fields accounts for the major part of the unbalanced magnetic pull mitigation by the parallel stator windings.