Demagnetization Fault Detection of Permanent Magnet Synchronous Motor Through Voltage Excitation at Standstill Condition

Permanent magnet demagnetization (PMD) faults can result in reduced motor performance and reliability in the permanent magnet synchronous motor (PMSM) drive system. Existing PMD detection methods can be invasive or easily influenced by machine parameter variations, loading conditions, and other faults of the machine. This article introduces a noninvasive and computationally efficient approach to diagnose PMD faults of PMSMs at standstill which is independent of the machine operating conditions. In the proposed approach, a set of excitation voltages is designed and fed by the inverter to produce a current in the machine, thereby causing a magnetic flux variation in the PMSM at standstill. The PMD fault indicator is defined based on the corresponding current signal. More specifically, the phase currents are measured and processed to determine the PMD level by comparing with the healthy state current. In this article, it is also found that a position-dependent torque oscillation can be generated during the voltage excitation at standstill. Therefore, this article also addresses the torque oscillation issue under all different rotor positions. In addition, the permanent magnet (PM) flux linkage can be determined with the proposed approach. Extensive tests are conducted to validate the proposed approach in detecting PMD faults and determining the PM flux linkage experimentally and in simulations.