Coordinated Control of Offshore Wind Farm and Onshore HVDC Converter for Effective Power Oscillation Damping

摘要

Damping contribution from wind farms (WFs) is likely to become a mandatory requirement as part of the grid codes. For remote offshore WFs, connected through a voltage source converter (VSC)-based direct current (DC) link, the most convenient option for the onshore transmission system operator (TSO) is to modulate the reactive power at the onshore VSC within their own jurisdiction. In this paper, we show that supplementary control through the onshore VSC alone, although attractive for TSOs, could result in unacceptable voltage variations in the onshore power grid. On the other hand, modulation of active power output of the wind turbine generators (WTG) alone turns out to be inadequate due to the limited overload capability of the WTGs and the on- and offshore VSCs. Coordinated control over both onshore VSC and aggregated WF output overcomes the above limitations and is shown to be effective for power oscillation damping. A homotopy approach is used to design the coordinated controller, which can be implemented locally (at offshore WF and onshore converter site) using a decentralized architecture. Case studies on two test systems show that the proposed controller yields similar system dynamic response as supplementary control through the WF alone.