Resolution and efficiency improvements for three-phase cascade multilevel inverters

This paper deals with cascade multilevel inverters. It focuses on asymmetrical topologies where the cell input voltages are of different values. These hybrid topologies may be advantageous for several applications. Nevertheless, the need of DC-DC converters to supply the cells of reversible multilevel converters increases the cost and losses of such inverters. It limits their application field. Furthermore, the simultaneous-commutation problem, which increases the switching losses for some operating points, reduces the design choice to configurations of lower resolution. Combining in series a 3-phase 6-switch voltage source inverter with single phase H-bridges, we obtain a cascaded multilevel inverter with attractive properties in terms of voltage resolution and energetic efficiency. This paper describes how to design and use such a structure and how to increase the inverter resolution.