A Coordinated Frequency Regulation Method for Offshore Wind Farms Integrated by VSC-HVDC

At present, Voltage Source Converter based High Voltage Direct Current Transmission (VSC-HVDC) is widely used in connecting OWF to the main power system. Different from onshore wind farms, OWFs are decoupled from the system frequency due to VSC-HVDC connection, so the traditional onshore wind farm frequency control strategy cannot be directly applied, which brings new challenges to the frequency support in onshore system when The frequency fluctuation. The VSC-HVDC connected OWFs has the rotational kinetic energy in the wind turbines' rotor and the DC capacitor electrostatic energy of the VSC-HVDC system which could be utilized for frequency control. Based on the characteristics of the two power sources, a coordinated frequency control strategy which can suppress secondary frequency drop and assist the rotor speed recovery of the wind turbine was proposed. By means of this strategy, the onshore power system frequency nadir and rate of change of frequency are reduced. And the second frequency drop caused by the rotor speed recovery of wind turbines could be limited. A low-inertia power system model in Matlab/Simulink is used to testify the effectiveness of the strategy.