Dynamics modeling and analysis of the permanent-magnet synchronous motors bearing-rotor-magnetic field under rotor demagnetize

For the phenomenon of rotor demagnetization of Permanent Magnet Synchronous Motor(PMSM), studying the dynamic modeling and analysis of demagnetization rotor. Firstly, considering the unbalanced magnetic pulling (UMP) of the rotor under the demagnetization and the nonlinear Hertz contact generated by the rolling bearing, the double rectangular coordinate system of the stator and rotor is constructed, and the mathematical model of the unbalanced magnetic pull UMP is constructed with the rectangular coordinate as the variable. Then, the dynamics Jeffcott model of the bearing-rotor- magnetic fields coupling system in the condition of demagnetization is established. Based on this, the demagnetization status of permanent magnet in PMSM is described from three aspects: (1) rotor offset caused by demagnetization, (2) demagnetization angle, (3) decrease of air-gap MMF at the demagnetization angle. Through the analysis, it is found that there is a “saddle” point in the bifurcation plots of the rotor system with the change of demagnetization angle. The position of the “saddle” point in the bifurcation plots with the change of demagnetization angle is related to the speed. The research results of this paper provide a theoretical basis for demagnetization quantitative diagnosis and demagnetization vibration control of permanent magnet synchronous motor.