Overview of Reactive Power and Voltage Control of Offshore Wind Farms

With the concern of global warming, the amount of renewable energy integration is increasing recently. A high penetration of wind power generation causes not only frequency instability but also voltage instability. In order to maintain the voltage in an acceptable range, supporting reactive power by wind turbines play a vital role. This paper provides a complete introduction to the reactive power and voltage control of offshore wind farms. Three conventional control modes of wind turbines include power factor control mode, voltage control mode and reactive power control mode. Typically, system operators request that the power factor of the point of connection (POC) of a wind farm is adjusted within a certain range; e.g., from 0.95 lagging to 0.95 leading. If the wind farm has insufficient capability to maintain an appropriate voltage range, the system needs other appropriate measures, such as the adaptive Q-V scheme or other methods. Additionally, the efficiency of High Voltage Direct Current (HVDC) transmission system has been improved significantly. A HVDC system is competitive for a long distance, and it controls the active power and reactive power independently. Thus, this paper also discusses about the reactive power and voltage control by voltage-source-converter based HVDC systems.