Unbalanced magnetic force in permanent magnet machines having asymmetric windings and static/ rotating eccentricities

This paper presents finite element investigation and experimental validation on the characteristics of unbalanced magnetic force (UMF) with static/rotating rotor eccentricities in permanent magnet machines having asymmetric windings. It shows that the magnitude of UMF due to eccentricity increases with the pole number, p. The open-circuit UMF varies linearly with the eccentricity ratio. The static/rotating eccentricities result in similar average UMF. However, the harmonic contents of either x/y components or magnitude of the UMF due to static eccentricity as well as the x/y components of the UMF due to rotating eccentricity are the constant, and the (4p)th, the (8p)th, ...., whilst the harmonic contents of the magnitude of the UMF due to rotating eccentricity are the constant, and the 3^rd, the 6^th, ..., of which the constant and the triplen one close to the pole number are the main components. The experiments on two 9-slot machines validate the prediction.