Open switch fault detection in Cascaded H-Bridge Multilevel Inverter using normalised mean voltages

The probability of faults in multilevel inverters increases with increase in the number of switches involved in the power conditioning. The common faults occur in power semiconductor devices are the short-switch fault and open-switch fault. To improve the reliability of multilevel inverter-fed drive systems, a fast and efficient fault detection scheme is required. The fault should be detected as soon as possible to reduce detrimental effects. Many of the earlier methods are complex and the detection time is more than one cycle. This paper presents a simple and fast diagnostic method for single open switch fault in Cascaded H-Bridge Multi-Level Inverters. The proposed fault diagnostic scheme utilises inverter output voltage and voltage across each H-bridge. The variations in the mean values of the measured parameters are used as fault features. The classification algorithm is simple and the fault location identification can be done accurately within one cycle of the output voltage. A Modified Phase Disposition Pulse Width Modulation method is employed for controlling the inverter switches. MATLAB/Simulink simulation of the 5-level Cascaded Multilevel inverter is presented. The simulation results show that proposed fault detection method is performing efficiently under open fault of different switches. This diagnostic method can be extended to higher level inverters.