Research On Coordinated Control Strategy Of Wind Power And Energy Storage System For Improving Frequency Stability

The system frequency fluctuates after wind power integration because of randomness and fluctuation in wind power generation.As wind power penetration rate is rising,the influence of wind power integration on power system frequency is obvious.At present,wind turbines adopt maximum power point tracking operation mode and cannot participate in the system frequency regulation.However,deloading operation preserves active power margin,which has generation efficiency loss for wind farm.It is a key issue for establishing grid-friendly wind farm that how to maximize the capacity of frequency regulation under the premise of economic wind power operation.To solve this problem,wind farm active power margin,wind speed threshold and energy storage capacity setting method are researched in this thesis.Considering the complementary advantages of wind turbines and energy storage system in power transmission and capacity of frequency regulation,the coordinated control of wind power and energy storage system is proposed to improve the frequency stability of power system.Firstly,the model of doubly fed induction generator is established in three-phase static coordinates and two-phase rotational coordinates,which accomplishes the decoupling control of active and reactive power of wind power generation system.The dynamic aggregation model is established by equivalent approach.As the basis of simulation analysis,the battery energy storage system model is established according to system structure,mathematical model and working principle.Secondly,the coordinated control strategy of wind power and energy storage system for frequency regulation involving wind speed fluctuation interval is proposed.Wind turbines work on maximum power point tracking operation mode at low speeds,while energy storage system provides frequency regulation reserve.The coordinated control is used to adjust frequency at high speeds,which makes wind turbines work under deloading,have margin of active power and support frequency of power grid coordinating with battery energy storage system.The proposed frequency regulation control method of wind farm and storage coordinated system improves frequency stability of power grid and takes account of operation economy of wind farm.Thirdly,the system frequency regulation theory for coordinated system of wind power and energy storage is analyzed.According to the proposed strategy of coordinated control ofwind power and energy storage system for frequency regulation,the pitch angle control,state of charge zoning control of battery energy storage system and rotor speed recovery control of wind turbines are studied,which combine wind turbines and energy storage frequency regulation control and are applied to frequency regulation control of wind farm and storage coordinated system.Finally,the simulation models of wind farm and storage coordinated system are established in DIgSILENT/Power Factory.The situation of frequency deviation is analyzed respectively at low,high and variable speeds.The results show that the proposed coordinated control strategy of wind power and energy storage system for frequency regulation involving wind speed fluctuation interval improves frequency stability of power grid,raises the system response speed of frequency change and avoids secondary frequency drop.Based on the simulation analysis,semi-physical experiment using RT-LAB is completed to prove the feasibility that coordinated control of wind power and energy storage system participates in frequency regulation.