A Noninvasive and Robust Diagnostic Method for Open-Circuit Faults of Three-Level Inverters

This paper proposes a noninvasive switch open-circuit (OC) fault diagnosis method for a three-level inverter based on voltage detection. Under both healthy and faulty operation, the possible values of two line voltages are analyzed, and the waveforms are obtained according to the analysis. Faults can be quickly diagnosed by the ratio, the voltage difference, and the arithmetic values of the two line-voltages. The time consumption of the single-switch OC faults diagnosis is less than half of a cycle. When some of two switches failures (double-switch OC faults) occur, faults can also be accurately located using this method, and these fault diagnosis processes can be completed within one cycle. Performance evaluation experiments are carried out to verify the effectiveness of the method. The results show that the proposed method is robust to load variation and immune to certain load OC failures. It was also found in the experiments that the diode OC faults can be distinguished from switch OC faults despite having similar fault features.