A Simple and Novel Precharging Control Strategy for Modular Multilevel Converter

Abstract

Modular multilevel converter (MMC) has been widely concerned due to its inherent excellent performance in recent years. However, in practical engineering, one of the technical challenges of MMC operation control is how to complete the submodule (SM) capacitors precharging safely and effectively, and reduce the impact of overcurrent phenomenon on the converter during the start-up process. In this paper, a simple and novel precharging control strategy is proposed. It can precharging all SMs of the converter at the same time, without the need for capacitor voltage balance algorithm, extra measurements and additional power supplies. It takes advantage of the symmetry of the grid voltage and the structural characteristics of MMC to form boost circuits between the arms by specific switching operations. Furthermore, the proposed method is not limited by the SM topology. The most commonly used SM topologies can also be converted into boost circuits and have the similar precharging process. By selecting appropriate control parameters, the precharging speed and efficiency of the converter can be improved. The effectiveness of the proposed control strategy is verified by simulations and experiments.