Research on rotor unbalance magnetic pull compensation method based on modular winding d-axis current injection

Due to the dual air-gap topology of the direct-drive permanent magnet motor with inner enhance force (IEF-DDPMM), the radial EM exciting force generated in the inner and outer air gaps when the rotor is eccentric will act on the same rotor, and the unbalanced magnetic pull (UMP) on the rotor will reduce the fatigue life of the rotor structure and bring many problems such as vibration and noise. Therefore, the rotor UMP compensation method of IEF-DDPMM based on modular winding d-axis current injection is proposed to suppress the harm caused by eccentricity. The expression of electromagnetic (EM) exciting force considering the cogging effect and current time harmonic without rotor eccentricity faults is derived by the analytical method. Also, the EM exciting force newly introduced due to the rotor eccentricity is analysed. The effects of different eccentricity types on torque characteristics, the fatigue life of the rotor structure and stator vibration of IEF-DDPMM are compared and analysed by the FEM. Finally, the IEF-DDPMM rotor eccentricity models are optimised based on the method. The performance of the motor before and after rotor UMP compensation is evaluated by FEM. The results show that the proposed method is correct and effective.