Fault Ride-Through Strategy for MMC-Based MTDC System Integrated with Offshore Wind Farms to Reduce Dynamic Braking System

This paper developed an energy recovery method for modular multilevel converter-based multi-terminal direct current (MMC-MTDC) system integrated with offshore wind farms (OWFs) to achieve onshore AC fault ride-through. By using the capacitor energy margin of the MTDC system to recover the surplus power during onshore AC faults, the installation of the dynamic braking system (DBS) can be reduced. First, an energy coordination control strategy is developed to achieve synchronous regulation of the capacitor energy in multiple MMCs, while improving overall energy utilization efficiency. Then, preset DC voltage trajectories under two types of AC faults are designed to manage the capacitor energy in MMCs properly during AC faults. Finally, a simulation model of the four-terminal HVDC system integrated with OWFs was built in PSCAD/EMTDC to verify the effectiveness of the proposed energy recovery method.