Multilevel Converter Based on Cascaded Three-Leg Converters with Reduced Voltage and Current

In this paper, a modularity concept using standard three-leg converters is addressed. Three-phase cascaded topologies composed of standard three-leg converters are investigated. They are composed of three, nine, twenty-one, or n three-leg converters. It permits the reduction levels of currents and voltages on switches when compared with a conventional three-phase module or a cascaded H-bridge structure. In this way, three-leg cascaded converters are suitable to be applied in scenarios of high current in which other cascaded topologies become less attractive and high voltage. Furthermore, the proposed arrangement brings advantages such as modularity that leads to convenient construction, easy maintenance, and extension to higher voltage and current levels. A dynamic model is developed and a pulse-width modulation strategy is designed to the converter command accordingly with reference voltage. Discussions about fault tolerance and dc-link capacitor currents are also carried out. Comparisons in terms of converter rating, harmonic distortion, and semiconductor power losses between the proposed and conventional cascaded H-bridge topologies have been carried out. Simulation and experimental results are presented as well.