Research On Multi-stage Constant Current Fast Charging Method Considering Charging Temperature Rise

Since the birth of new energy vehicles,power battery safety has been the focus of the whole society.On June 23,2019,at the International Summit Forum on lithium industry and power battery in China(Qinghai),academician Ouyang Minggao pointed out that the essence of safety accidents of new energy vehicles is that the battery heat is out of control.Temperature is an important factor affecting the performance and safety of the power battery.The research of charging method considering temperature can further improve the performance and safety of the power battery.In this paper,a multi-stage constant current fast charging method considering the charging temperature rise is proposed.This method can ensure the fast charging,control the temperature within the allowable range,and ensure the safety and stability of battery charging.The main research work is as follows:1)This paper analyzes the characteristics of three kinds of circuit models of the battery,and chooses a more accurate Thevenin model,which is more balanced in accuracy and computational complexity.The key parameters in the model are identified by the static method and HPPC(hybrid pulse power characteristic)test,and the reliability of the parameter identification results is verified by the constant current discharge experiment.The experimental results show that the model has high accuracy and small error.Thevenin model can simulate the working characteristics of the battery accurately.2)This paper analyzes the equation of temperature loss in the process of lithium-ion battery charging and discharging,establishes the temperature rise model of lithium-ion battery charging,and validates the model effectively under different charging rate and different initial SOC conditions.3)Based on the temperature rise model,combined with the charging characteristics of lithium battery,an optimization strategy of multi-stage constant current fast charging using weight coefficient to balance the charging temperature rise and charging time is proposed.The genetic algorithm is used to solve the objective function,and the proposed optimal charging method is optimized for different constant current charging methods.The experimental verification of the proposed optimal charging method is carried out under the conditions of different charging rate,different initial SOC and different aging degree of the battery.The results show that the proposed charging method not only reduces the overall charging temperature rise,but also has a higher temperature at the later stage of charging Low,shortens the charging time and indirectly affects the life of lithium battery.