Precise Demagnetization Fault Diagnosis Based on Multiple Robust Sliding Mode Observers for PMSMs Under Variable Conditions

This article proposes a high-robustness sliding mode rotor flux observer (SM-RFO) that can detect the real-time air-gap flux linkage to diagnose whether a permanent magnet synchronous motor (PMSM) encounters the demagnetization fault that can reduce motor efficiency. First, based on the electrical property of the PMSM, a flux observer based on the sliding mode variable structure theory is developed, with its stability and applicable conditions discussed. Then, because the accuracy of the SM-RFO is closely related to stator inductances, robust sliding mode d- and q-axis inductance observers that are sequentially executed are developed to eliminate the negative impacts of parameter variations on the flux observation and fault detection strategies. On this basis, the proposed observers and the demagnetization fault diagnosis method can be precisely applied to different working conditions. Finally, simulation and experiment are conducted on both surface-mounted PMSM (SPMSM) and interior PMSM (IPMSM) prototypes to validate the proposed SM-RFO-based demagnetization fault diagnosis strategies.