Research On Improved Charging Method Of Constant Current Section Based On The SOH Of Lithium-ion Battery

In recent years,electric vehicles have developed rapidly by virtue of their advantages such as energy saving and environmental friendliness.Under the background of "carbon peaking and carbon neutrality",electric vehicles still have good development prospects.With the rapid growth of the number of electric vehicles in my country,accurate estimation of the health status of lithium-ion power batteries is conducive to ensuring the safe operation of electric vehicles.In addition,improving the charging mode is helpful to further promote the large-scale application of electric vehicles.Aiming at the inaccuracy of the current lithium-ion battery online estimation method and the serious aging of the battery caused by the constant current and constant voltage charging method with a fixed charging current value during the whole life cycle of the lithium-ion power battery,the following researches are carried out in this thesis:Firstly,the realization process of power lithium ion battery charging system is described,and the application scenarios of online estimation of the health state of the power battery and optimized charging are briefly introduced,and the charging process is introduced by taking the constant current and constant voltage charging method as an example.Parameter response for medium lithium-ion batteries.Then,the operation characteristics of lithium-ion batteries are analyzed,and the working principle,aging mechanism and main performance parameters of the battery are introduced.The characteristics of several basic models of power batteries are compared,and the aging characteristics of batteries are described by establishing a lithium-ion capacity decay model,which provides a basis for the subsequent research on optimal charging of power lithium-ion batteries that age too quickly.Secondly,based on the constant current and constant voltage charging process of the battery,there is an approximate linear relationship between the amount of electricity charged in a certain voltage range and the actual capacity of the battery,an equivalent health factor is established,and it is verified by the correlation index check.Due to the different degree of correlation between the equivalent health factor and the actual state of health of the battery under different charging voltage intervals,the charging voltage interval is optimized by genetic algorithm.On this basis,the charging capacity in the accurately estimated voltage range of SOH is used as the optimized equivalent health factor,and the state of health is estimated online for lithium-ion batteries.The validity of the proposed state of health estimation method is verified by battery aging estimation experiments.Finally,the whole life cycle of lithium-ion batteries is divided into sub-intervals,with the goal of minimizing the decline rate of battery capacity,and based on the estimated health status of the battery,the database dynamic programming is used to optimize the decision current of each sub-interval,and the full life cycle is obtained.The optimized charging current distribution,replaces the fixed empirical value of the constant current process of the constant current and constant voltage charging method,conducts aging simulation through the lithium-ion battery capacity decay model,quantitatively analyzes the impact of different charging current rates on the aging of battery life,and based on the optimization current The distribution analyzes the aging characteristics of the battery.The results show that the proposed optimized charging method can effectively delay the problem of rapid aging of lithium-ion batteries,and provide users with more choices of charging methods.