| Under the pressure of severe environmental protection and petrochemical energy cr isis,the construction of high-permeability clean energy grid has become the mainstream trend of power grids in the world.Due to the random nature of most clean energy s ources,the frequency impact of one of the three major indicators of power system po wer quality is greater.Large-scale energy storage systems are connected to the grid an d are one of the best options for solving such problems.Therefore,it is of great and urgent practical significance to study the participation of large-scale energy storage syst ems in clean energy grid frequency modulation.In the thesis,the characteristics of various types of energy storage and applicable working conditions are studied firstly.Supercapacitors and all-vanadium flow batteries a re selected as the energy storage system batteries involved in power system frequency modulation.An improved equivalent circuit model of all-vanadium flow battery for ene rgy storage participation in FM transient research and an improved second-order RC su percapacitor equivalent circuit model were established.Then study the grid structure and mode of the composite energy storage system.The energy storage access mode,converter and voltage filter are selected and studied s eparately,and their parameter calculation methods are deduced separately.In order to r ealize the task of large-scale composite energy storage system participating in power s ystem frequency modulation,this paper controls the grid-connected converter based on virtual synchronous machine technology,and builds a model in MATLAB/simulink to s imulate and analyze the method feasibility.Compared with the traditional drooping mo de,it verifies the advantages of various parameters of the energy storage frequency mo dulation system based on the principle of virtual synchronous machine in terms of freq uency modulation response time,climbing rate,active output,state of charge and energ y storage.Finally,the calculation method of rated power and rated capacity of composite en ergy storage system is deduced,and the general composite energy storage capacity con figuration method is obtained.Then according to the frequency modulation effect and c omprehensive economy of the composite energy storage system as the two-phase index,the objective function is established,and the state of charge and minimum load dema nd power are used as constraints,and the improved optimal solution is obtained by th e improved particle swarm optimization algorithm.Under this scheme,the composite e nergy storage capacity configuration is performed.Finally,the method is tested by an example,and the capacity allocation scheme of the composite energy storage system w ith the best combination of the best frequency modulation effect and the best overall e conomic efficiency is involved in the clean energy grid frequency modulation. |
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