Research On Large-scale Energy Storage Control Method For Improving Frequency Stability Of Wind Farm

With the rapid development and wide application of new energy generation technology represented by wind power,modern electric power system presents profound changes of high proportion of renewable energy,high degree of electricity electronization and high proportion of power transmission and reception.High permeability wind power and other power generation equipment have significantly changed the original frequency and voltage characteristics of the power system,bringing new challenges to the safe operation of the power grid.The breakthrough and maturity of key application technologies of large-scale distributed energy storage make largescale,large-capacity and highly reliable electrochemical energy storage realize industrialization.The deployment of large-scale energy storage on the grid-connected side of wind power has gradually become the safety operation requirement of power grid and grid-connected guidance of new energy,providing core support for the development of wind power and other new energy sources.In order to carry out large-scale energy storage to improve the frequency stability of wind farms,explore the potential inertial support capacity of wind turbines,and put forward the coordinated control method of combined wind storage system,the following studies are mainly carried out in this paper:(1)Relying on a wind energy storage demonstration project in Hunan,a simulation model of wind storage joint system is built based on DIgSILENT/PowerFactory software platform.Aiming at the simulation modeling of wind turbine,the detailed model of Double Fed Induction Generator(DFIG)including aerodynamic module,wind turbine shafting module,Generator voltage and flux control module is analyzed.On this basis,A simplified DFIG model with controlled voltage source power converter is obtained.For the simulation modeling of energy storage,a Virtual Synchronous Generator(VSG)control strategy with the second-order RC equivalent circuit of lithium ion battery as the body and a State of Charge(SOC),frequency f large-scale distributed electrochemical energy storage model for charge and discharge process management.The above research carried out the modeling work of the ontology and controller of the combined wind storage system in an orderly manner,which provided the theoretical basis and simulation environment for the subsequent in-depth research.(2)An adaptive virtual inertial-damping control method for energy storage for wind power maximization tracking is proposed.By establishing DFIG and small signal model of energy storage,the equivalent superposition method is used to build the small signal model of the combined wind storage system.According to the power Angle response of the system under transient power disturbance,the change process of virtual inertia and damping coefficient is revealed.Based on this,an adaptive virtual inertial-damping control method for energy storage is designed.The derivation process,control block diagram and parameter setting principle of the proposed method are described in detail.The effectiveness of the proposed control method is verified by considering the typical working conditions of three-phase shortcircuit fault and sudden load increase of the wind power grid.(3)A coordinated control method of virtual synchronous wind storage joint system is proposed.In order to effectively improve the frequency response of the wind turbine and fully exploit the potential inertial support capacity of the wind turbine,the indirect voltage DFIG-VSG control strategy is adopted to actively release the hidden kinetic energy of the rotor to participate in the system frequency modulation.Then the shafting energy conversion process and inertial support principle of the virtual synchronous fan are studied.Based on this,the control flow of the coordinated control method of the combined wind storage system considering the energy storage assisted wind turbine speed recovery process is designed.The effectiveness of the proposed coordinated control method is verified under two typical load surge and load rejection conditions.