Phase-controlled multilevel converters based on dual structure associations

Multilevel converters, like neutral-point-clamped inverters or multilevel choppers, are particularly attractive in high-power applications. Nevertheless, in these structures, all switches are confronted to commutation stresses caused by their turn-on and turn-off control. Furthermore, the methods to balance the capacitor voltages or to control the neutral point voltage are complex enough. In this paper, the authors propose new multilevel converters based on series connection of zero-current-source (ZCS) inverter cells and parallel connection of zero-voltage-source (ZVS) inverters. These dual structure associations give soft-switching operation for all switches and allow the use of semiconductors, normally destined for medium-power applications, in high-power converters (up to 1 MW). The authors consider the structure design for several topologies to achieve DC-DC or DC-AC converters. The simulation results validate the simplicity of phase control techniques and give out the principal features of different topologies