Design and control of asymmetrical multi-level inverters

This paper deals with asymmetrical multi-level inverters. The investigated topologies consist of series connected cells with different input voltages. Some combinations of different input voltages have been proposed to improve the converter resolution. This paper has a general approach. It describes the rules to obtain a uniform step with these topologies. It points out the switching problem of some of these asymmetrical solutions, describes the rules to avoid this problem, resulting in a solution where the number of commutations and hence the switching losses may be reduced. For this purpose, it also proposes an adapted optimal control strategy based on a geometrical approach, and a scheme for the control of multi-level inverters.