Torque ripple minimization in permanent magnet synchronous motor magnet demagnetization

The paper deals with the torque-ripple reduction in permanent magnet synchronous motors (PMSM) drive with magnet demagnetization. The rotor permanent magnet field is variable under demagnetization condition, it induces nonsinusoidal distribution of flux density. Torque pulsations exist in PMSM due to nonsinusoidal flux density distribution around the air-gap. The torque pulsations vary periodically with rotor position and is reflected as speed ripple, which influence the PMSM drive performance. To estimate flux magnitude, a extended Kalman filter(EKF) is built by using stator current and PM flux as state variables. The estimation method can accurately track flux linkage. A current compensation method is presented to reduce the negative influence caused by demagnetization, and a smooth torque is obtained. The compensated currents are derived by estimated flux linkage. Experimental evaluations of the proposed method are carried out on a DSP-controlled PMSM drive platform. Test results demonstrate the effectiveness of the proposed method in reducing torque ripple.