Fault-tolerant operation of some reduced-device-count multilevel inverters with improved performance

Multilevel inverters (MLIs) are attracting wide interest for both high power and medium power applications. The most important limitation of MLIs is requirement of an increased number of power switches. To overcome this limitation, a new class of MLI topologies has evolved. These topologies are known as “reduced device count” MLIs (RDC-MLIs). As the number of power devices is reduced in RDC-MLIs, the redundant states are also reduced. Thus, the possibility of fault-tolerant operation is also affected negatively. This paper deals with the possibility of imparting fault-tolerant characteristics to RDC-MLIs. In this work, some of the RDC-MLI topologies are first analysed in the case of “any single switch failure (ASSF)” and corresponding missing levels are identified. Thereafter, addition of power switch is proposed which enables alternative states for the missing states and hence enables fault-tolerant operation in the event of ASSF. These modified RDC-MLIs are verified using software simulations and experimental setups, and the results are presented.