IMPROVED FREQUENCY COORDINATED CONTROL STRATEGY FOR HVDC-INTEGRATED OFFSHORE WIND FARM
To address the problem that offshore wind farms(OWF)connected to the onshore grid by voltage source converter based high-voltage direct current(VSC-HVDC)cannot provide frequency active support,this paper proposes an improved frequency coordination control scheme between the offshore wind farms and the VSC-HVDC.The coordinated control scheme is divided into the level of the VSC station and the level of the offshore wind farms.For the VSC station,the frequency change of the onshore grid is transformed into the change of DC voltage through sag control,and the relationship between the sag control coefficient and the virtual inertia coefficient of the HVDC is analyzed,and then the virtual inertia coefficient is adjusted adaptively considering the index of grid frequency deviation.For the offshore wind farms,an improved power backup method is proposed with the objective of maximizing the rotor kinetic energy of wind farms before the frequency failure,which can effectively reduce the wind energy loss and use this part of energy for subsequent frequency adjustment.Considering the wind speed difference of wind turbines,the frequency control coefficients can be adjusted in real time according to rotor speed after the frequency failure.The proposed control strategy can improve the overall frequency regulation capacity of wind farms,while ensuring the safe and stable operation of the units.The simulation results show that the proposed control method has good frequency regulation performance at different wind speeds as well as wind power penetration rates.
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维普
