Overvoltage Suppression Strategy for Offshore Wind Farm Integrated into AC Grid Through VSC-HVDC

Overvoltage usually occurs when an ac failure is applied to an onshore system that includes an offshore wind farm. The onshore converter station's output power rapidly decreases under these conditions. Due to the coupling between the VSC-HVDC transmission line and the offshore wind farms, if no proper measures to regulate the active power are taken on the wind turbine or the VSC-HVDC transmission line, it will lead to the collapse of the whole system. While, if all wind turbine power is injected into the system according to the rated value, a surplus of energy will result in significant voltage surges, thus, it will cause serious damage to electrical equipment or a reduction in the expected life of electrical insulation. Then the whole VSC-HVDC transmission system will be turned off, and the overall stability of the electrical system may be jeopardized. An overvoltage suppression control strategy is proposed and tested on an offshore wind power system that is integrated into an ac system using VSCHVDC in this paper. To suppress overvoltage, the power regulation capacity of both the wind farms and the dc lines is used. To validate the proposed control strategy, an electromagnetic transient model is built which can simulate the dynamic performance of the wind farm integrating to ac grid through VSC-HVDC under various faults. The simulation results demonstrate that the proposed strategy can effectively suppress dc overvoltage. And it can ensure that the power of wind farms produced does not exceed the limits under various types of faults.