Analytical Prediction and Analysis of Electromagnetic Forces in a Surface-Mounted Permanent Magnet Synchronous Machine Under Rotor Eccentricity and Magnetic Saturation

This paper presents an analytical model for predicting electromagnetic forces in an 8-pole/12-slot surface-mounted permanent magnet synchronous machine considering static rotor eccentricity and magnetic saturation. The eccentric air gap is represented by an equivalent concentric region with circumferentially varying magnetic permeability, allowing the harmonic analytical formulation to be retained. Magnetic saturation is incorporated through an iterative permeability update. The calculated radial and tangential air-gap flux-density components are used to evaluate the Maxwell-stress distributions, integrated electromagnetic loads, and unbalanced magnetic force under no-load and on-load conditions. The analytical results agree well with nonlinear finite-element analysis. No-load experiments using three stationary axial conductors are further conducted to validate the predicted redistribution of the radial air-gap flux density at different stator positions and eccentricity levels. The results show that rotor eccentricity mainly redistributes the Maxwell-stress distribution, whereas magnetic saturation limits its magnitude under heavy-load operation. Both effects, therefore, need to be considered for accurate analytical force prediction under eccentric operating conditions.