DC fault ride-through method for full-bridge MMC-based MTDC systems

摘要

The DC fault protection is one of the main issues in multi-terminal voltage source converter based high-voltage direct current (VSC–MTDC) transmission systems. In this study, a DC short-circuit fault ride-through method for full-bridge modular multi-level converter (FB-MMC) based MTDC systems is proposed. First, the model of the FB-MMC topology is analysed. Then, the principle of fault current clearing in full-bridge sub-module (FB-SM) is introduced. The converter protection control strategy and the system protection scheme are proposed, benefitting from the capability of quick fault current elimination with the valves blocked using the FB-MMC topology. With this method, the MTDC system could restart quickly after clearance of DC fault without cutting off the AC grid. The proposed protection strategy is demonstrated using the simulation model in PSCAD/EMTDC. Simulation results verify the feasibility and effectiveness of the strategy.