Control strategy for balancing capacitor voltage of modular multilevel converter

The Modular Multilevel Converter (MMC), based on cascaded multi-module structure, is suitable for highvoltage/power applications. However, among hundreds of modules, their voltage-balancing is a key problem which is attracting scholars´ much attention. Therefore, in this paper, a control strategy based on PI controller is proposed for balancing capacitor voltages of Modular Multilevel Converter (MMC). The proposed control strategy includes the voltage-balancing and circulating current-limiting links. The effectiveness of the strategy is conformed using Matlab/Simulink platform. The simulation results show that the fluctuation of capacitor voltages as well as the circulating current can be confined into acceptable range. In addition, the MMC´s switching frequency and system loss can be reduced significantly, since the equivalent switching frequency is promoted to a great extent.