Design And Simulation Verification Of Power Lithium Battery Pack Equalization Scheme For Electric Vehicles

The energy crisis and environmental pollution have become a global issue.Under the background of developing low carbon economy,electric vehicles have been receiving more and more attention due to their diversified energy sources.It will surely become the mainstream of automobile industry in the future.Governments and automobile manufacturers are committed to the technological breakthroughs and ndustrialization of electric vehicles and power batteries,and have made great achievements.The rapid development of electric vehicles is mainly limited by technology and cost control.The key of these two aspects lies in the development of power batteries.Among the mainstream power batteries,lithium batteries have become the first choice with high energy density,long cycle life,low self-discharge rate,no memory effect,and no pollution.In practical applications,the battery packs used in new energy vehicles are mostly a series of lithium battery cells in order to meet the requirements of voltage,power,and mileage.However,there is a certain difference between individual cells in production and manufacture,and this difference will be accumulated after repeated charging and discharging.The inconsistency between the lithium battery cells will seriously affect the capacity utilization and cycle life of the battery.At present,the establishment of balanced control system is an effective method to improve the battery pack inconsistency.In order to reflect the voltage characteristics exhibited by the battery more accurately,the second-order RC loop is used as the equivalent circuit model of power battery.Considering the commonly used equilibrium criteria,the voltage is selected as the indicator of inconsistency degree of the battery pack.On this basis,the equilibrium strategy is formulated.In this paper,the advantages and disadvantages of common equilibrium topology circuits are compared and analyzed.Based on the principle of inductive energy storage and dynamic adjustment of equilibrium paths and equilibrium thresholds,multi-criteria defined equalization circuit are used,which are applied to single-series battery pack and hierarchical battery pack respectively.And the strategy of threshold optimization is proposed.The simulation model is built in Matlab\Simulink environment according to the designed equalization scheme,and the battery pack was subjected to charge and discharge process simulation.The simulation results show that the proposed equilibrium circuit is simple in structure,fast in equalization speed and excellent in equilibrium performance.During the charging process,the voltage of an over-voltage cell or bottom cell module can be reduced.During the dischargeprocess,the voltage of an under-voltage cell or bottom cell module can be increased.Moreover,it can achieve better balance effect by adopting threshold optimization measures.