Research And Application Of Multi-stage Constant Current And Constant Voltage Charging Strategy For Lithium Ion Batteries

At present,environmental pollution and energy crisis are becoming increasingly serious.Electric vehicles have the characteristics of high energy conversion efficiency with electrochemical energy storage and conversion devices,and can reduce environmental pollution and primary energy consumption when they are used to replace internal combustion engine vehicles.As the only source of power for electric vehicles,power batteries directly affect the user’s driving experience and the performance of the entire vehicle.Among them,charging is a necessary part of the use of electric vehicles,and the charging time and service life are directly impact on the user experience.When fast charging is pursued with high current,the temperature rise speed increases,which greatly affects the aging of the battery.if low current charging is pursued with battery life,it cannot meet people’s needs for fast charging.Therefore,it is particularly important and urgent to find a fast,safe and reliable charging method.In response to this scientific problem,this article first established a battery cell model coupled with electrothermal aging,and proposed an adaptive multi-stage constant current and constant voltage charging strategy.The charging curve is optimized by the particle swarm optimization algorithm(PSO).Secondly,a complete battery pack model was established.The relationship between charging time,aging and energy consumption in battery pack charging is studied.Finally,in order to solve the problem of low-temperature charging,a low-temperature heating coupled charging strategy based on waste heat recovery is proposed.The specific research content and results are as follows:1)An electrothermal aging coupled single battery model including RC electrical model based on physics,a thermal network model,and a battery aging model based on a semi-empirical formula has been established.And through experiments to identify and verify the parameters of the model.On this basis,a multi-stage constant current and constant voltage charging strategy with adaptive order based on the PSO algorithm is proposed.A multi-objective non-linear optimization model with charging time and battery aging as the optimization objectives is established.The optimization obtained the optimized charging curve under different weighting factors and revealed the influence of voltage threshold and constant voltage switching timing on the charging strategy.2)Established a complete battery pack model including a coupled electric and thermal aging model of the series battery pack,a battery pack thermal management model,and a battery pack equilibrium model.The genetic algorithm is used to optimize the battery pack charging strategy,revealing the relationship between charging time,aging and energy consumption.Discuss the difference between battery pack charging strategy and single battery charging strategy.3)In order to solve the problem of low-temperature charging of lithium-ion batteries,a low-temperature heating coupled charging strategy based on waste heat recovery is proposed.Combining the optimized charging strategy and the low-temperature heating strategy,the combination forms a low-temperature heating and charging joint control strategy.The influence of heating medium temperature and fan flow rate on total time and total energy consumption is analyzed and discussed.Finally,according to the environmental factors and the setting parameters of the heating and charging strategy,the performance influence of the heating and charging process is analyzed.