Group dynamic self-tuning MMC capacitor voltage balancing strategy and its application in ship MVDC system

To overcome long calculation time, low allocation efficiency of sub-modules and other problems for the classical sorting-based MMC(modular multilevel converter) capacitor voltage balancing strategy, a group dynamic self-tuning MMC capacitor voltage balancing strategy is studied. According to the voltage flucturate range and current direction of sub-module capacitors in each group, this strategy can assign different number of sub-modules to each group in real time, and significantly reduces the amount of computation caused by sorting. It is proved by simulations that: compared with non-grouping or average grouping situations for sub-modules, the studied strategy is of not only rapid operation but also the stability of the capacitor voltage of sub-modules among groups and in a group, which can further improve the overall efficiency of the ship medium voltage direct current(MVDC) system.