Distributed commutations pulse-width modulation technique for high-power AC/DC multi-level converters

This study presents a novel dedicated pulse-width modulation (PWM) technique for use with single-phase multi-level cascaded H-bridge (CHB) converters. The proposed modulation strategy aims to minimise the converter commutations and distribute them, for any amplitude of the voltage reference, among the different converter cells to evenly distribute the heating and stress on the power switches, improving their reliability without compromising the quality of the voltage waveform. Such characteristics are particularly important in high-power grid-connected converters used as an interface for renewable energy sources or smart grid applications. The technique is described in detail along with the verification of the modulation effectiveness provided by a simulation comparison with other common modulation strategies. Finally, the proposed strategy is experimentally validated by means of different tests using a seven level CHB converter.