T-type Nested Neutral Point Clamped (T-NNPC) Multilevel Inverter: Identification and Diagnosis of IGBT Switch Failures

In recent years, T-type nested neutral point clamped (T-NNPC) multilevel inverter has gained attention in motor drive applications. A lot of insulated gate bipolar transistor (IGBT) switches in the converter considerably increase the probability of switch failure. In this paper, a fast and accurate approach is suggested to identify the open-circuit (OC) failure of IGBT switches in a four-level T-NNPC multilevel inverter. Using the suggested approach, the occurrence and exact place of OC fault are determined in less than one cycle. In the presented fault detection algorithm, the output current and voltage are exploited as detection parameters, in which the predicted and desired values of output waveforms are compared to the actual values. Then, the dissimilarity between the observed and expected values is utilized to find the exactly failed IGBT switch. The four-level T-NNPC multilevel inverter is simulated in MATLAB/Simulink environment, and the feasibility of the suggested method is demonstrated for OC fault conditions. In this regard, the effects of OC faults of switches on the capacitor voltages and output waveforms are investigated. The result of applying the suggested method is shown for all the switches separately.