Emergency power control strategies applied for offshore wind farms connected by HVDC system

More and more long-distance, large scale offshore wind farms (OWFs) are developed, and connect to the onshore grid through the voltage source converter (VSC) based HVDC link. Particular attention should be paid to the grid connection requirements as the OWF is decoupled with the onshore grid via the VSC-HVDC link. Power fed into the onshore grid should be controlled to some extent for power dispatching requirement. A special emergency power control (EPC) with 3 control modes and its implementation strategies are introduced as an automatic response to realize temporary or permanent power reduction by cooperating with DC chopper and offshore wind farm. EPC1 is designed to realize full power reduction in a short time with assistance of DC chopper. EPC2 is required to reduce power to a pre-defined level relying upon power control by OWFs. EPC3 is to deactivate the function of EPC2. For avoidance of communication failure, a supplementary control of the offshore system frequency is also considered to trigger power reduction of OWFs. PSCAD simulation results demonstrate the validation of proposed EPC strategies.