Voltage Balancing Method for Hybrid MMC Using Negative Voltage Levels

Hybrid modular multilevel converters, consisting of half-bridge and full-bridge submodules, are considered a promising topology for various high- and medium-voltage applications. However, these converters present several technical challenges due to the different topology of the submodules, such as the unbalanced voltage of submodule capacitors. This paper proposes to analyze the internal dynamics of the hybrid modular multilevel converter by implementing a submodule voltage balancing technique that exploits the negative levels generated by the full bridge. In this work, the negative levels are generated as an additional degree of freedom to distribute the stored charge among the capacitors of the submodules. Differing from studies present in the literature, which consider the balancing of submodules in the same way, regardless of their topology, the uniqueness of the proposed approach is that it not only balances voltages with short transients, but also reduces voltage ripple. The effectiveness of the proposed strategy has been validated by simulation, its performance has been assessed in comparison with state-of-theart approaches.