Research On Control Strategy Of Wind-Storage Combined Primary Frequency Regulation

With the increasing scale of wind power integration year by year,the ’ zero inertia ’characteristics of doubly-fed wind turbines,as the mainstream model,pose a great threat to the safe and stable operation of the power system.When the doubly-fed wind turbine uses rotor kinetic energy and overspeed load shedding to participate in frequency modulation,its frequency modulation capability is greatly affected by the operating state of the unit.The blade angle load shedding will cause economic losses in the wind field and wear of the mechanical components of the wind turbine.Battery energy storage has been well applied in the field of frequency modulation due to its advantages of fast response and flexible control.The joint frequency regulation of wind power and energy storage can realize the coordination and complementarity of resources.Therefore,this paper makes an in-depth study on the joint frequency regulation control strategy of wind power and energy storage,aiming at fully tapping the frequency regulation potential of wind power and energy storage system,improving the inertia response and primary frequency regulation ability of wind power and energy storage system,and further improving the frequency stability of the system.The main work of this paper is as follows :Firstly,the mathematical model of each component is established based on the operation principle of doubly-fed wind turbine.Based on the operating characteristics of energy storage,the mathematical models of energy storage system and converter are established.Secondly,through the derivation and analysis of the frequency dynamic model of the regional power grid,a frequency modulation control strategy based on the frequency change rate partition is proposed.The proposed control strategy is applied to the maximum power operation state and the overspeed load shedding state respectively.After fully considering the relationship between the frequency regulation capability of wind turbines and the active power imbalance of the system,corresponding improved control strategies are proposed for each frequency regulation control interval to improve the system frequency stability under different load disturbance degrees.A two-machine two-area power grid simulation model is built on the Matlab / Simulink platform for verification,The results show that the control strategy proposed in this paper can ensure that the unit speed and power do not exceed the limit under different load disturbance conditions,and has good frequency support ability,which has obvious advantages.Then,considering the operating characteristics of the energy storage,the corresponding control strategies are designed for the frequency regulation state and the recovery state respectively.Based on the integrated inertia control,the energy storage integrated output coefficient and the feedback coefficient of frequency change rate maximum are introduced to dynamically adjust the active power output,and logistic function and segmentation function are established to constrain the two respectively.For the energy storage recovery state,based on the ultra-short-term load forecasting curve data,a dynamic SOC base value control strategy is designed.Based on fuzzy control,a control strategy of energy storage recovery output considering SOC recovery demand and grid frequency deviation is designed.Finally,on the basis of the traditional wind speed range division,the medium wind speed range is divided into an over-speed load shedding zone and a rotor kinetic energy release zone,taking into account the system frequency regulation requirements and the wind turbine’s own load shedding capacity.Considering the limitation of frequency regulation ability of wind turbines in each wind speed interval,the energy storage system participates in frequency regulation in wind speed intervals 1 and 4.In the wind speed interval 2 and 3,firstly,the threshold values of each frequency regulation action interval of the doubly-fed wind turbine under different operating conditions are analyzed and calculated,and then the energy storage dynamically adjusts the output according to the change of the frequency regulation state of the wind turbine,so as to realize the flexible complementarity of the frequency regulation output of the wind storage system.Based on the two-machine two-area simulation model,the effectiveness of the control strategy is verified.The results show that the proposed control strategy can provide frequency support under full wind speed conditions,suppress the secondary frequency drop,and further enhance the system frequency stability.