Open-transistor fault diagnostics in voltage-source inverters by analyzing the load current

A novel method is presented for the detection and isolation of open-transistor faults in voltage-source inverters feeding low-power AC motors. The method is based on monitoring two diagnostic signals, one indicating sustained near-zero values of output current and thus permitting fault detection, the other permitting the isolation of the particular transistor which went faulty. The latter signal is the ratio of the average phase current and the average magnitude thereof. The method proves to work reliably, enabling detection and isolation of all possible cases of single and multiple faults. It enjoys high immunity to transients and noise and requires no extra hardware on top of that normally used for basic control purposes.