The Coordinated Fault Current Limiting Strategy for a Hybrid Multilevel Modular Converter (MMC) based VSC-HVDC Applications

Background: High-voltage direct current (HVDC) is suitable for high capacity and longdistance power transmission, thus becoming ideal for connecting renewable energies such as solar power and wind power to grids. Objective: Overhead lines in HVDC are vulnerable to short-circuit faults. Non-permanent DC short circuit faults are the most common in HVDC transmission, which can lead to pause in power transmission and interruption in large grids. Thereby, it is crucial to deploy techniques to suppress fault current. Methods: To lower the fault current economically, a coordinated fault current limiting strategy based on a hybrid multilevel modular converter (MMC) is proposed in this paper. Results: Combining hybrid MMC and small-capacity DC circuit breaker reduces total IGBTs required and avoids MMC blocking during pole-to-ground short-circuit fault. This approach is verified using a two-terminal MMC-based system in PSCAD/EMTDC simulation environment. Conclusion: By implementing the introduced scheme, the peak fault current can be lowered by 33.0% using hybrid-MMC with 80% of FBSMs. Economic efficiency can be improved by adopting proposed scheme.