Analysis and Real-Time Calculation of Postfault Current of Standard Surface-Mounted PMSM Drives With Dysfunctional Power Switches

Fault diagnosis and fault-tolerant control significantly rely on the knowledge of fault mechanisms and postfault states. Regarding open circuits in permanent magnet synchronous motor drives, the postfault states, especially phase voltages, depend on whether the faulty phase is conducting. Under the open-switch fault featuring dysfunctional power switches, the faulty phase is possible to conduct through the still functional diodes. In contrast, the open-phase fault completely blocks the faulty phase. However, the mechanism and effects of the open-switch conduction have not been thoroughly studied, which obscures the boundary between the open-switch fault and the open-phase fault, and fails to realize effective diagnosis and optimal fault-tolerant control. This article not only reveals the mechanism of the open-switch conduction, but also proposes a model that can calculate the postfault conducting current in real time. The proposed model provides an estimation value of the postfault current for further utilization and validates the correctness of the analysis. First, equivalent circuits are analyzed to explain the conduction condition. Subsequently, switching states fulfilling the conditions are studied, and finally, the mathematical model of the postfault current is built. The analysis and model are experimentally validated.