Transient orbital analysis of rotor with mixed eccentricity for permanent magnet synchronous motor of electric vehicles

The unbalanced magnetic pull (UMP) induced by rotor eccentricity has been studied for permanent magnet synchronous motors (PMSMs); however, the electromagnetic excitation only considers the magnetic field of the rotor. Meanwhile, the harmonics of UMPs induced by electromagnetic field interaction of stator and rotor, also its influence on the critical speed and the transient vibration of rotor have not been fully investigated. Through the analysis of magnetomotive force (MMF) harmonics of stator, rotor, and air-gap permeances with rotor static and dynamic eccentricity, the analytical expressions of UMP harmonics for rotor mixed eccentricity are derived with the Maxwell stress tensor (MST) method in this study. The impact of the typical harmonics of UMPs on the critical speeds and transient whirl orbits of rotor system is studied through rotordynamic simulation. It is found that more critical speeds are generated with harmonics of UMPs, and the transient vibration responses are different for two types of eccentricities in the axial direction. This study contributes to understand critical speeds of PMSMs and detection of different types of rotor eccentricities.