Research On Modeling Of Lithium-ion Battery Energy Storage System And Its Impact On The Stability Of Power System

The large-scale energy storage technologies has been considered widely to be thesixth part as “storage” in electric power system following the traditional parts namely“mining-generation-transmission-distribution-consumption”. The lithium-ion batteryis considered as the most promising battery system because of its low cost, highefficiency, long service life, no pollution, both high specific energy and high specificpower and other specific advantages. The lithium-ion battery has been widely appliedin many fields such as mobile communications, electric automobile, aerospace,electric engineering and so on, brought a revolutionary change in people’s way of lifeand production. Now the lithium-ion battery represented LiFePO4has developed tolarge-scale energy system construction and application from the cell body and smallvolume application, has become of the ideal choice for the modern power system withenergy storage devices. In this paper, the structure characteristics, the workingmechanism of LiFePO4representing the lithium-ion battery are analyzed firstly, thenthe accurate simulation models are established, after that the lithium-ion batteryenergy storage grid connected system is designed, finally the effect on power systemstability of lithium-ion battery energy storage is studied.Firstly the author analyzes the structure characteristics, the performance features,and the operation mechanism of LiFePO4realizes the modeling work in two aspects ofthe electrochemical mechanism and the external characteristic of equivalent circuitbased on a thorough research on the theory of the battery modeling. In the aspect ofelectrochemical modeling, the paper puts forward the average concentration modelingmethod through appropriate assumptions and reasonable simplification, establishesthe lithium-ion battery electrochemical average model with mechanism, accuracy,simplicity and generality. In terms of equivalent circuit modeling the authorestablishes the new comprehensive equivalent circuit model of lithium-ion batterywhich is composed of the voltage response model and the capacity prediction modelthrough improving the hybrid model creatively which has been considered as the bestmodel in the world. There-into the voltage response model takes into account theinfluences of SoC, temperature, current ratio etc, at the same time the general thermalcircuit model of lithium-ion battery is estabilished; the capacity prediction modelrealizes the modeling combined with three storage capacity attenuation, cyclic capacity attenuation, and current dynamic effect through contacting the chemicaltheory and using the comprehensive identification principle. At the same time thecorresponding experimental methods and parameter identification procedure arepresented. The simulation proves that the models of lithium-ion battery realizes thefunction and achieve the desired effect.Based on the cell model, the lithium-ion battery energy storage grid system isstudied in detail, including mainly analysis and modeling of the grid topology, designand calculation of model the new LCL three order filter, choice and application of thecontrol strategies etc. What’s the most important, the PQ real-time power controlstrategy to smooth/stabilize the fluctuation of power and the V/f droop controlstrategy to maintain the stability of system are realized, at the same time the controlflow based on energy constraint conditions for the lithium-ion battery system ispresented. In the end the grid topology, the filter structure and the control strategiesare effective and practical verified by Matlab/simulink.In the last chapter of the paper, the influence on the power system stability of thelithium-ion battery energy storage is studied. The basic model of the battery isamended and justified properly in accordance with the working principle, the internalvoltage relationship and the mathematical relation of power distribution of the DC-ACconverter. And the equivalent circuit of the energy storage inverter system ispresented. Then on the linear increment model suitable for the stability studies basedon the control theory formed. Next the models of a single machine infinite bus systemand the two areas interconnected power system both with the lithium-ion batteryenergy storage system are established. The effect of improving the power anglestability and the frequency stability in the power system is verified respectively in theabove two system models through Matlab/simulink, and the problem of capacityallocation is discussed qualitatively.