Fault Diagnosis in Five-level CHB Inverter using Normalization Factor and THD Analysis

Multilevel Inverters have been universally accepted for their distinctive performance and wider applications in high power industrial motor drives. They have many advantages over two-level inverters with the cost of extra semiconductor devices. The reliability of any power electronic converter depends on the performance of the semiconductor devices. Due to the interaction of number of switches in multilevel inverter, the possibility of fault occurrence in switching device is a common issue. In this context, to improve the reliability of multilevel structure the accurate fault diagnosis should be done. This paper has presented a simple and effective fault diagnosis technique for five-level cascaded H-bridge (CHB) multilevel inverter. The fault identification is performed on the basis of total harmonic distortion (THD) analysis. The possible switch fault location is determined by the normalization factor (NF) of output current. The fault signal is identified according to the defined threshold level. This method requires one current sensor per phase, which are normally available in closed loop drive operation. The performance of the fault diagnosis method has been validated through the simulation results.