| With the rapid growth of installed capacity of new energy sources such as wind and solar power,grid frequency regulation is facing an increasingly significant challenge.Battery energy storage technology,with its fast and accurate load tracking capability,has become a hot spot for new auxiliary means of frequency regulation.At present,the commercial model of energy storage technology applied to frequency regulation in China is mainly to assist thermal power units in Automatic Generation Control（AGC）.However,in actual engineering application,thermal power units can produce large power deviations when tracking signals,resulting in a large battery discharge rate,which directly affects the life and economy of battery energy storage systems.To increase the economic benefits,this paper focuses on the system modeling,operation strategy and capacity configuration of energy storage that assists the thermal power units in the second frequency regulation.Firstly,based on the mechanism modeling method,the thermal power unit model is constructed,considering that the command signal will produce losses in the transmission process of different links,the load changing speed is identified by combining the actual output data of the unit.A second-order RC equivalent circuit model of a lithium-ion battery is constructed,and the voltage relative error of the model is only 0.0524%,a coupling model of the energy storage battery and thermal power unit is constructed,and the simulation of different types of AGC instructions is carried out in MATLAB/Simulink.The results show that the relative error of the predicted frequency regulation parameters from the thermal power unit model in this paper is within 6.5%,which is more suitable for obtaining the output curve of the unit for tracking signals,and the simulation proves that the BESS can effectively improve the performance of frequency regulation.Secondly,based on the evaluation system of energy storage to provide secondary frequency regulation auxiliary services,simulation and comparative analysis are carried out for the existing AGC distribution strategies.Then the main factors affecting the life of the Li Fe PO4battery are analyzed,and an improved operation strategy based on differential allocation is proposed,and the control of battery discharge rate is realized by predicting the operating state of the BESS.Simulation results show that appropriate limiting of discharge rate can prolong battery life and increase the economic benefits of the system.Finally,the energy storage capacity configuration method based on the bi-level decision model is proposed.The operation layer optimizes the operation strategy with the goal of maximizing the frequency modulation performance indicators and the whole life cycle benefits,and the planning layer determines the rated capacity and rated power of the BESS with the goal of maximizing the net present value.Based on three different terminal value estimation methods,the calculation results of multi-objective optimization and single-objective optimization of the operation layer are comprehensively compared,to formulate the optimal capacity allocation scheme.The study found that the method proposed in this paper has obvious technical and economic characteristics,which can increase the income of the storage combined with the thermal power system while ensuring the frequency regulation effect,and help to increase the net present value of the planning layer. |
