Rotordynamic Analysis of a Permanent Magnet Synchronous Motor Considering Nonlinear Unbalanced Magnetic Pull

This paper investigates the nonlinear dynamic behavior of a rotordynamic model for permanent magnet synchronous motor (PMSM) incorporating unbalanced magnetic pull (UMP) existing in the air gap between the rotor and stator. The system model comprises a Jeffcott rotor mounted on symmetrically located bearings. The nonlinear UMP is estimated based on the Maxwell stress tensor theory. The harmonic balance approximations and the numerical integration method are applied to solve the governing equations and obtain the steady-state response of the rotor as well as force transmissibility between rotor and bearing. The effects of UMP magnitude, mass unbalance and system damping level on the rotordynamic behavior and vibration transmission characteristics are examined systematically. The results show that the UMP has softening effect on the steady-state frequency response of the rotor. Multiple solutions can be found near resonance frequency of the rotor, demonstrating the complex dynamic behavior of the rotor such as jump phenomenon within the system. The UMP magnitude, mass unbalance and system damping level have large effect on force transmissibility from rotor to the bearing near resonance peak frequency. A small mass eccentricity and large system damping will benefit suppressing the vibration magnitude and force transmission from the rotor to the bearing. These results give a deeper understanding of the effects of UMP on the vibration behavior and vibration transmission within rotordynamic system in PMSM and hence benefit better designs with improved dynamic characteristics.