Open-circuit fault diagnosis method for the T-type inverter based on analysis of the switched bridge voltage

Multilevel inverter topologies have been widely used in applications of wide-power range. Therefore, fault diagnosis of such circuits is becoming more and more important. The T-type topology, which is one of many multilevel topologies, has an advantage in terms of efficiency compared to the neutral-point-clamped type. This study proposes a new diagnosis method of an open-circuit (OC) fault for a three-level T-type inverter (3LT(2)I). The proposed method is achieved by measuring the bridge voltage and its duration time. The bridge voltage includes information of switching states of 3LT(2)I but not affected by the load. First, according to polarity of the reference voltage and corresponding phase current, working period of the 3LT(2)I is divided into four working regions. Then, the bridge voltage is analysed in detail when an OC fault occurs in different working regions. At last, a fault diagnosis circuit is designed to achieve automatic diagnosis for the OC fault. Simulation and experimental results show that the proposed method can identify the faulty switch exactly and quickly.