Reconfiguration of Bipolar HVDC System for Continuous Transmission Under DC Line Fault

This article proposes a reconfiguration method for the bipolar high voltage dc transmission (HVDC) system connecting offshore wind power plants (WPPs). Conventional bipolar HVDC systems can continue to transmit half the rated power even if a dc fault occurs at one of the two poles. However, the shutdown of half of the entire WPPs is inevitable because WPPs cannot continue operations on their own. Once the WPPs are shut down, they take a long time to restart. The power transmission decreases during the time and it imposes a negative effect on the onshore ac system. The proposed reconfiguration method immediately removes the dc fault and relocates the converters and WPPs from the faulted pole to the healthy pole by disconnecting switches. Furthermore, the reconfiguration is designed based on the fault ride-through (FRT) capability of the WPPs specified by the existing grid code. As a result, the reconfiguration realizes the continuous operation of the entire WPPs even if a dc line fault occurs. Therefore, the proposed method can improve the supply reliability. The validity of the proposed method is verified by electromagnetic transient (EMT) simulations.