Improved AC Fault Ride Through Control Strategy for MTDC System with Offshore Wind Farms

Based on a five-terminal HVDC system connected with offshore wind farms, this paper investigates a three-level control strategy for AC fault ride through, including voltage droop, power reduction and DC chopper control, in order to enhance the system ac fault ride through capability. The restrictions of individual control level are respectively investigated before a trigger mechanism of the three-level control strategy is defined. With the improved AC fault rid through control, different protection measures will take actions according to the fault severity. The proposed control strategy is validated through PSCAD/EMTDC simulation and the results prove the feasibility of these control strategy in different situations.