AC Fault Ride-Through Strategy for MMC-Based HVDC Systems with Short Lines

This paper presents a thorough study of the operation of Modular Multilevel Converters (MMC) connected to a back-to-back High Voltage Direct Current (HVDC) grid during AC fault conditions. Fault Ride-Through requirements state that converter stations are required to remain connected to the AC grid during voltage sags while ensuring the stable and safe operation of the DC grid. MMC-HVDC applications with short lines pose additional challenges due to smaller line capacitance which has been addressed in previous publications but an AC fault ride-through (ACFRT) strategy is still lacking for the proposed control method. This Study proposes a converter control strategy for ACFRT operation which ensures the DC grid’s stable operation and also aids in AC grid voltage recovery during AC voltage sags in either converter station.