A Novel Configuration Scheme and Modulation Strategy for Asymmetric Cascaded H-Bridge

Asymmetric multilevel inverters can output more voltage levels without the increase of modules due to optimal configuration of DC voltage source magnitudes. However, the existing asymmetric cascaded H-bridge (ACHB) inverters have limitations either in DC voltage ratio or number of cascaded modules, which are difficult to be widely used in modular cascaded systems. To enhance flexibility and modularity, a novel configuration scheme for ACHB and the corresponding modulation strategy are proposed in this paper, where the DC voltage ratio and number of cascaded modules can be flexibly selected according to practical requirements. Under the modulation strategy, the high-voltage modules work at the fundamental frequency while the low-voltage modules work at the high frequency, which is easy to implement digitally and can achieve power balance among high-voltage modules. The correctness and feasibility of the proposed scheme for ACHB together with its control are verified by simulation.