Low-Voltage Ride-Through Method of the HVDC Transmission System for Feeding Islanded Offshore AC Loads

This paper discusses a low-voltage ride-through (LVRT) method for high-voltage direct current (HVDC) transmission systems that serve as an interconnector between the main onshore ac grid and an islanded offshore ac load. When a line-to-ground fault occurs in the onshore ac grid, a voltage sag will be applied to the HVDC transmission system. This sag will cause fluctuations of the dc voltage, which will cause a shutdown of the entire HVDC system. The proposed LVRT method stabilizes the dc voltage of the HVDC transmission line by reducing the amplitude of the voltage of the offshore ac grid, which is kept constant during normal operation. The proposed method allows the HVDC system to remain connected during voltage sags in the onshore ac grid and enables faster transmission recovery after fault clearance. The validity of the proposed LVRT method is verified by simulations.