High-ripple Compact Design of MMC for Medium Voltage Distribution

Application of power electronic and DC distribution are the development trend of medium voltage distribution network in the future. The compactness and miniaturization of power electronic equipment are the technical difficulties that must be overcome in the application process of medium voltage DC distribution. This paper analyzes the quantitative relationship between the number of MMC sub-modules, the capacitor voltage ripple, and the total capacitance consumption, purposing to reduce the capacitance consumption of the whole MMC to achieve a compact design. Meanwhile, in order to ensure the overall modulation performance of the MMC in which number of modules is reduced and the sub-module voltage ripple is increased, a carrier phase-shifting indirect modulation method based on the energy prediction of the bridge arm is proposed, this modulation method is effective to improve the utilization ratio of the sub-module capacitor voltage. Simulation results show that the MMC using the high-ripple compact design performs as well as the MMC using conventional design under various power levels, while the high-ripple compact design has a 30% reduction of total capacitance consumption.