Demagnetization Detection and Severity Assessment in PMSMs Using Search Coils Exploiting Machine's Symmetry

Magnet demagnetization in permanent magnet synchronous machines (PMSMs) can produce inadmissible performance degradation. Search coils (SCs) have been proven to be a viable option for its detection. Existing methods allow detection of demagnetization of one permanent magnet with three or less SCs. However, detection and severity assessment of the fault has been reported only for the particular case of using one SC per stator slot. This paper proposes two alternative methods for demagnetization detection and severity assessment of PMSMs using a reduced number of SCs. The first method relies on the zero-sequence voltage of three SCs electrically shifted 120 electrical degrees. The second method relies on the differential induced voltage between two SCs electrically shifted 360º. It will be shown that the proposed methods improve the performance of existing methods. Experimental results validating the proposed approach will be provided.