AC-DC Bidirectional Fault Ride-through Control Strategy of Flexible DC Distribution Network Based on MMC Active Current Limiting

The flexible DC distribution network based on the modular multilevel converter (MMC) has developed rapidly in recent years. However, the negative sequence voltage and current generated after the AC side fault affect the stable operation of the system, and the surge of fault current after the DC side fault also seriously threatens the equipment safety. Therefore, the fault ride-through issue puts forward new requirements for the control strategy of the converter station. Because of this situation, firstly, the fault current characteristics are analyzed, and the hybrid MMC converter station topology is proposed. Then, based on the idea of positive and negative sequence separation and active current limiting control, and considering the demand of AC and DC bidirectional fault ride-through, the AC and DC bidirectional fault ride-through control strategy is designed. In addition, hybrid modulation technology is proposed to realize the switching of working modes to meet the operation requirements under various working conditions. Finally, a simulation model is built in MATLAB/Simulink to verify the effectiveness of the proposed control strategy.