Optimal Control Strategy Of Secondary Frequency Regulation For Large Scale Lithium Battery System

The large-scale access of wind power brings huge pressure to the secondary frequency regulation of power system.Energy storage system(ESS)has become one of the effective means of power grid regulation because of its unique advantages.Among them,li-on battery has become the preferred electrochemical medium for ESS due to its excellent capability density and fast response.However,due to the short response time and long standby time,the capacity loss and polarization response of Li-on battery in the secondary frequency regulation task of power grid cannot be ignored,which brings great difficulty to the design of secondary frequency regulation control strategy with the participation of ESS.Based on the operation characteristics of the Li-on battery energy storage system,this paper establishes a battery model suitable for the secondary frequency regulation of the power system,and designs the optimal control strategy of the ESS participating in the secondary frequency regulation on the basis of the model.Firstly,according to the mechanism of secondary frequency regulation in traditional power system,the principle of power grid frequency fluctuation is analyzed.On this basis,the control model of each frequency regulation power supply is given when the ESS is involved in the secondary frequency regulation.According to the characteristics of each frequency regulation power supply,the control strategy is analyzed,which lays a theoretical foundation for the design of optimal control strategy in chapter four.Then,based on the basic principle of the Li-on battery,combined with the requirements of the secondary frequency regulation operation of the power system,the appropriate circuit model is selected as the basic model,and the loss current is converted into the loss power relationship in the capacity loss.The RC circuit of the equivalent circuit model is used to reflect the polarization phenomenon of the battery.The modified Kalman filter SOC estimation method is obtained by improving the traditional Kalman filter SOC estimation.From the above three aspects,the circuit model of single Li-on battery is improved,and the single battery model is expanded to the energy storage unit model.In this chapter,the accuracy of the improved model is verified based on Matlab/Simulink simulation.Finally,based on the improved Li-on battery model,considering the characteristics of capacity loss,capacity loss rate and SOC,the output fuzzy control controller is designed for the ESS,and the SOC adaptive of the energy storage unit is realized.By using the frequency deviation and frequency deviation rate to control the output of the unit,the double-level control strategy of each frequency regulation power supply and energy storage unit is realized.In order to ensure the frequency deviation within the specified range,the capacity loss and the frequency regulation reserve capacity required by the traditional unit are greatly reduced.