A Study on Asymmetry of Electromagnetic Force Modes of Permanent Magnet Synchronous Motors With Rotor Eccentricity

This article deals with electromagnetic forces of permanent magnet synchronous motors (PMSMs) with inclined and parallel rotor eccentricity. The electromagnetic forces have the spatial orders of the main components (multiples of pole numbers) and the sideband components when the rotor is eccentric. Although other studies have reported that each amplitude of an upper and a lower sideband is different, the causes of the asymmetry have not been fully investigated. The rotor eccentricity leads to changes in the gap permeance, the working point of the rotor magnets, and the distribution of gap magnetic flux density. By considering these effects in detail, we develop a new analytical expression of electromagnetic force, which expresses the asymmetry of a pairs of sidebands. The expression is compared with 3-D magnetic field analyses of PMSMs with inclined and parallel rotor eccentricity. As a result, it is found that upper sideband amplitudes are larger than lower sideband amplitudes, and the ratio of an upper sideband to the lower sideband of parallel eccentricity is larger than that of inclined eccentricity.