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

A permanent magnet synchronous motor (PMSM) has its bearing damaged and is irreversibly demagnetized due to overcurrent. Due to the changes in its electromagnetic configuration, the motor suffers from extremely high torque ripple, which produces intolerable speed ripple and acoustic noise. The aim of this paper is to evaluate if a repetitive observer (RO) can be used to smooth the rotational speed and suppress acoustic noise. The RO is functionally the same as a repetitive controller (RC), but is preferred due to its simplicity of tuning. Its effectiveness of reducing acoustic noise will be evaluated in this paper for the first time. Experimental test results show that the speed ripple and acoustic noise are reduced significantly. The work opens the possibility of reusing the damaged motor and still achieve high performance. The RO can also be applied to enhance the fault tolerance capability of a healthy motor.