Reuse of a Damaged Permanent Magnet Synchronous Motor for Torque Ripple and Acoustic Noise Elimination Using a Novel Repetitive Observer

A lad-used servo permanent magnet synchronous motor has been accidentally damaged due to overcurrent. On the one hand, the mechanical damage, in the end, bearing and break part generates acoustic noise even when rotating the shaft by hand. On the other hand, the back electromotive force of the motor becomes unbalanced and exceedingly high torque ripple is produced. Such torque ripple results in intolerable speed ripple and will increase the acoustic noise. This article aims to reuse this damaged motor by adding a repetitive observer (RO) to the existing speed loop, both the speed control performance and the acoustic noise of the damaged motor can become comparable with its healthy version. The RO is functionally the same as a repetitive controller (RC), but the stability of the RO is independent of the feedback loop, while the stability of the RC will affect and be affected by the rest of the system. Therefore, RO can be applied for both the healthy motor and the damaged motor. This work opens the possibility of further enhancing the fault tolerance ability of a healthy motor or even reusing a damaged motor and still achieve high performance.