| In recent years,with the continuous promulgation of relevant national energy storage strategies and policies and the rapid development of electrochemical energy storage technology,the application of energy storage systems in the power grid has become more and more extensive.Lithium-ion batteries have become the main battery for energy storage system applications because of their higher energy density,lower self-discharge rate,longer cycle life and less environmental pollution than other kind of batteries.In grid energy storage application,it is often necessary to connect a large number of batteries in series and parallel to meet the capacity and voltage requirements,which will continue to accumulate the very small differences in parameters between single cells during charging and discharging,and ultimately result in decline in energy efficiency and cycle life of battery packs and even explosion accident.Equalization technology can well improve the imbalance caused by the inconsistency of performance parameters between single cells,and has become research priorities in recent years.This paper takes the battery for energy storage in the power rid as the object,and conducts research and experimental verification on the equalization circuit and realization.The main contents are as follows:(1)Based on the analysis of battery characteristics and the characteristics of energy storage applications,this thesis designs a balancing current algorithm for battery packs under charging and discharging conditions.Starting from the research on characteristic parameters and working characteristics of lithium-ion batteries,this algorithm can calculate the maximum equilibrium current for batteries with different capacities in the same battery pack on charging and discharging conditions,so as to converging the actual available capacity of each battery.The experimental results show that the equilibrium result of the designed algorithm satisfies the system current constraints.(2)Through the analysis and comparison of various equalizing circuit structures,a two-way flyback equalization circuit for single battery equalization is designed using a flyback transformer as the main core for energy transfer from the comprehensive consideration of equalization speed,energy transfer efficiency,equalization current amplitude and control complexity.Through modeling simulation,physical circuit production and experimental debugging,it is verified that the designed circuit can realize the two-way transfer of energy between the single cell and the battery pack with better efficiency.(3)Based on the single battery equalization circuit designed before,a hardware and software design scheme for the equalization system of series battery pack is given with the application of the modular strcture and current equalization algorithm.According to the analysis of the functional requirements for the balance of the series battery pack,this thesis designs the balance strategy and provides the hardware design scheme of the balance system and the software programming process.The experimental results show that the equilibrium system scheme given in this thesis has a better equilibrium effect. |
