Coupled Inductor Based Regenerative Cascaded Multicell Converter for Drives with Reduced Transformer VA Rating and DC-link Capacitor

A regenerative cascaded multicell converter (CMC) is considered one of the most effective and reliable solutions for high-power medium voltage drives. In the existing regenerative CMC-based drives, multilevel voltage and high-quality current are achieved at the output side by connecting multiple cells in series. However, on the input side, the cells are effectively connected in parallel through the transformer, and their two-level operation results in a considerable amount of harmonics in the secondary winding currents, even with a filter inductor used in each cell. This increases the overall VA rating of the transformer. This paper proposes a modified regenerative CMC in which a three-phase active front-end rectifier (AFER) is used at the input side of each cell, and a coupled inductor is used instead of a normal inductor. The coupled inductor effectively suppresses the lower-order switching frequency harmonics from the secondary winding current while offering negligible reactance to the fundamental component. Hence, the overall size and cost of the transformer will be reduced. Due to the three-phase configuration, the cell capacitance is reduced. A simulation-based comparison study between existing and proposed regenerative CMCs is presented.