Reduced number of auxiliary H-bridge power cells for post-fault operation of three phase cascaded H-bridge inverter

This work offers a fault-tolerant strategy that uses a combination of a hardware-based and a control-based fault-tolerant methods for multilevel (ML) cascaded H-bridge (CHB) converters. The possibility of a switch failure in an ML converter is higher than a conventional inverter due to the increased number of power electronics switches. Although the event of a single switch failure is more likely, nonetheless, the fault tolerant operation of a ML converter with two or more faulty switches needs to be addressed as well. This article first offers a hardware topology that can bypass the faulty H-bridge cell and replace it with an auxiliary cell, in the event of a single switch failure. Then, it enhances the hardware topology with a modulation-based fault-tolerant method for the event of more than one defective switch. Using this strategy, the CHB converter will be able to operate with maximum achievable output voltage in the post-fault condition. Experimental results are presented for a seven-level CHB converter for the validation of the theoretical outcomes.