Asymmetric cascaded H-bridge topology with 25-level output voltage based on modular multilevel DSCC inverters

摘要

This paper introduces an asymmetric cascaded multilevel inverter consisting of series-connected two nine-level (9L) H-bridge cells, which are based on modular multilevel cascade converter (MMCC) with double-star chopper cells (DSCC). An unequal dc voltage ratio of 1:2 is used, so that the proposed topology can generate 25 output voltage levels. A modulation strategy for the inverter is proposed. A comparative analysis is performed, demonstrating that the proposed inverter offers reduced losses in the semiconductor devices and smaller number of components compared to 25-level conventional MMCC. Besides that, in order to maintain the stable system, a circulating current control and voltage balancing algorithm are discussed. At last, simulation and experimental results are presented to validate the proposed system.