Torque Improvement Effect of Reverse-Phase Superimposition for Fault-Tolerance in Permanent Magnet Synchronous Motor

This paper presents reverse-phase superimposition method for fault-tolerance in permanent magnet synchronous motor to reduce torque ripple while maintaining torque level. When a motor winding fails, two problems occur: the torque level decreases, and the torque ripple increases. Although previous research solved these problems, maintaining the torque level and reducing the torque ripple simultaneously has not been possible. In the proposed method, the current under the fault condition is separated into zero-, positive-, and reverse-phase, and the reverse-phase current is superimposed on the non-fault phase. By using the proposed method, the torque ripple can be suppressed while maintaining torque levels. To validate the effectiveness, numerical and experimental verification was conducted, and results obtained by the proposed method were compared with the torque performance of the conventional methods. The results revealed that with the proposed method, the advantages of the two conventional methods can be obtained together.