Intra-arm Balancing Control for Modular Multilevel Converter with Cell Loading Operated under High Power Imbalances

Abstract

Multiport converters with a large number of ports have been explored for integrated generation units or batteries. An attractive candidate multiport converter has been developed based on the modular multilevel converter (MMC) with cell loading. Accordingly, this study proposes a control strategy for a multiport converter based on the MMC operated under high power imbalances among cells. Owing to this power imbalance, the multiport converter requires an additional circulating current (intra-arm balancing current) to provide balanced three-phase grid currents and balanced capacitor voltages in all cells. In a previous study, the minimum required intra-arm balancing current was calculated offline and applied according to the loading condition. This method may require a high-capacity memory for the controller. In contract, this study proposes an active control method for minimizing the intra-arm balancing current online. Experimental results reveal that the multiport converter achieves balanced three-phase currents with a total harmonic distortion of 3.13% and balanced capacitor voltages with an error of 0.1% under maximum power imbalance among cells.