Design considerations on the DC capacitor of each chopper cell in a modular multilevel cascade inverters (MMCI-DSCC) for medium-voltage motor drives

This paper describes an adjustable-speed motor with a quadratic-torque load such as fans, blowers, pumps, and compressors. The motor is characterized by being driven by the modular multilevel cascaded inverter based on doublestar chopper cells (MMCI-DSCC) A design for both mean dc-capacitor voltage and ac-voltage fluctuation in each dc capacitor used within DSCC is carried out to provide a design consideration on capacitance values of each dc capacitor. Experimental waveforms obtained from a 400-V, 15-kW downscaled system verify the validity of the theoretical analysis, and stable driving performance from a standstill to a motor mechanical speed of 1334 min <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> with quadratic-torque load.