Coupled Inductor Based Regenerative Cascaded Multicell Converter for Drives With Multilevel Voltage Operation at Both Input and Output Sides

Cascaded multicell converter (CMC) is one of the effective solutions for medium-voltage high-power drives. The inability to regenerate power back to the source is one of the limitations of this converter. The regeneration capability is obtained by using a pulsewidth-modulated active rectifier instead of a conventional three-phase passive rectifier in each cell. However, due to their two-level voltage operation at the input side, an inductor is required for each cell to filter out the switching frequency components from the input current. This paper proposes a new configuration of regenerative CMC based on coupled inductor to achieve multilevel voltage at the transformer secondary terminals. This allows us to operate the rectifier devices at reduced switching frequency. The coupled inductor reduces the total harmonic distortion (THD) of the transformer secondary current and thus the transformer size. The size of the filter inductor and the transformer ratings are compared. The operating principle and the detailed analysis are presented. A technique to bypass a faulty module is proposed. The working of the converter is verified through simulation and experimental studies.