Reduction of Torque Ripple Due to Demagnetization in PMSM Using Current Compensation

Torque pulsations exist in permanent magnet synchronous motors (PMSMs) due to the nonsinusoidal flux density distribution around the air-gap. The rotor permanent magnet field is variable under the condition of demagnetization, which induces nonsinusoidal distribution of flux density. The torque pulsations vary periodically with rotor position and are reflected by speed ripple, which influence the PMSM drive performance. To estimate flux magnitude, an extended Kalman filter is built by using the state variables, such as stator current and PM flux. With this extended Kalman filter method we can accurately track flux linkage. A current compensation method is proposed to reduce the negative influence caused by demagnetization. The compensated currents are derived from the estimated flux linkage. Experiments on a DSP (Digital Signal Processor) controlled platform are developed for the evaluation of the proposed methods. In the experimental results smoother torque or reduced torque ripple is seen by using this current compensation and extended Kalman filter method.