Enhanced Voltage Drop Control by VSC-HVDC Systems for Improving Wind Farm Fault Ridethrough Capability

This paper presents a new control approach for enhancing the fault ridethrough capability of wind farms connected to the grid through a voltage-source-converter-based high-voltage dc transmission line. A controlled voltage drop in the wind farm collector grid is initiated upon the occurrence of fault in the high-voltage grid in order to achieve fast power reduction. In the process, a dc voltage of defined magnitude and duration is injected by the sending-end converter together with the voltage reduction to suppress the dc component of the short-circuit current arising from the voltage reduction. As a result, the electrical and mechanical stress on the wind turbines, especially on the DFIG-based units and their converters, are mitigated. Using a test network, the improvement in the fault ridethrough capability of the system that can be achieved by employing the proposed method has been demonstrated.