Diagnosis of Free-Wheeling Diodes in PMSM Drives Based on Residual Current Under Open-Circuit Faults

The diagnosis of open-circuit (OC) faults has been well studied. However, it is necessary to further monitor the free-wheeling diodes (FWDs) in the OC leg, as their conduction affects the phase voltages, currents, and postfault (PF) 5operation. When FWDs are dysfunctional, the phase current is zero, and phase voltages float. When FWDs are functional, the OC leg has residual current and fixed voltages. First, this article analyzes the floating phase voltages under dysfunctional FWDs. Then, based on the phase voltages, the residual current is estimated. After that, a sampling method is designed for the residual current. Furthermore, a diagnostic method is proposed based on the estimated and sampled residual currents. Finally, the methods are validated in experiments.