Overfrequency Limiting Control by VSC-HVDC Connected Offshore WFs

Offshore wind farms (WFs) connected to the grid via voltage-source converter based high voltage DC (VSC-HVDC) do not inherently participate in the primary frequency control of the main grid. This paper discusses possible approaches for participation of the offshore WF in the frequency control focusing on the primary frequency response during an overfrequency event caused by a sudden change in the generation -load balance in the grid. Offshore WF generation units can respond to frequency increase by reducing their active power output. A new strategy is proposed in this paper to utilize the HVDC chopper to limit the transferred active power from the offshore WF to the grid by dissipating a defined amount of energy through the chopper resistance during the primary frequency response period. Simulation results are presented using a test grid to demonstrate the functionality of the proposed strategy.