A Generalized Scheme With Linear Power Balance and Uniform Switching Loss for Asymmetric Cascaded H-Bridge Multilevel Inverters

Under the traditional hybrid modulation strategy, the output voltage of 2:1:1 asymmetric cascaded H-bridge multilevel inverter is proved to be of high quality. However, the cascaded cells operate in unbalanced power regime and the switching loss of low-voltage cells is extremely uneven. To resolve the mentioned problems, the average power of cascaded cells is analyzed and the internal mechanism of power imbalance is revealed. Based on this, a power balance modulation strategy is proposed in this article. The modulation strategy effectively equalizes the switching loss of cells H2, H3 by modifying the triangular carriers, and then controls the conducting angle of cell H1 achieving a balanced power distribution among cascaded cells under the full modulation indexes. Compared with the existed modulation strategies, the proposed method has the merits of easy implementation, good dynamic performance, balancing low-voltage cells switching loss, and linearizing output power of cascaded cells. In addition, the modulation strategy also offers a generalized scheme, which can achieve a balanced power distribution among cascaded cells with an asymmetric ratio of i:1:1:1…. Finally, the simulation and experiment results confirm the feasibility of the modulation strategy under changes in modulation index and load.