| In response to the "double-carbon" goal,vigorously developing the wind power industry is imperative.However,from a technical and economic perspective,large-scale integration of wind power into the grid still has certain limitations.The fluctuation of wind power and the low inertia characteristics of wind turbines have an adverse effect on system frequency adjustment.With the rapid development of energy storage technology,using a configured energy storage method to make wind power have frequency adjustment capabilities has become a hot topic of research.This paper proposes an improved frequency adjustment strategy for Doubly-Fed Induction Generator(DFIG)wind turbines to improve the impact of wind power access on system frequency,and involves energy storage systems on the wind power side to participate in the frequency adjustment.The main work and conclusions are as follows:(1)Firstly,the impact of wind power grid-connected on the power system frequency is analyzed.Through dividing the time scale of frequency response,two power system frequency response models containing only synchronous machines and with wind power access are constructed.The system frequency before and after the connection of wind power is analyzed from three aspects: steady-state frequency value,frequency change rate,and maximum frequency deviation,providing a theoretical basis for the following chapters.(2)Secondly,an improved frequency control strategy is proposed for DFIG.By analyzing the three classic control strategies of DFIG participating in system frequency adjustment,including virtual inertia control,overspeed unloading control and short-time power support control,contrasting their advantages and limitations,an improved frequency adjustment strategy based on the operation status of DFIG is proposed.The strategy can protect the rotor speed not to be lower than the threshold,effectively improve the minimum value of the system frequency,and accelerate the speed recovery to improve the secondary drop of the frequency.(3)Finally,a control strategy for energy storage devices to assist wind turbines in frequency adjustment is proposed.A model of the energy storage device is established,considering the correction of power according to the state of charge,to avoid overcharging and discharging;and a control strategy for the energy storage frequency adjustment is proposed according to the operation state of DFIG;and according to the different wind speeds,a control strategy for the wind-storage combined system to participate in the frequency adjustment is proposed.This control strategy can provide frequency support for the system when the wind turbine is unable to participate in the frequency adjustment according to the different operation conditions of the wind turbine,accelerate the rotor speed recovery of DFIG after the improved frequency control frequency adjustment is completed,avoid the second drop of the system frequency at the same time,and charge to recover the state of charge when the state of charge of the energy storage device is poor and the system frequency is good. |
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