Research On Multi-segment Optimized Charging Method And Application Of Power Lithium-ion Battery

In modern life,the transportation industry has brought us great convenience,while the accompanying environmental deterioration and energy shortage are becoming more and more serious.Compared with the fossil energy consumed by traditional fuel vehicles,the electric power required by electric vehicles is a relatively low cost and easy to obtain.Therefore,it is a general trend that traditional fuel vehicles are replaced by new energy vehicles.In recent years,many European countries and China have begun to set a timetable for the ban on the sale of fuel vehicles.As the source of electric vehicles,power batteries are an indispensable part of electric vehicles.Compared with other types of batteries,Li-ion batteries have gained prominence in the field of power batteries and occupied the main market share of electric vehicle industry due to their advantages of high energy density,light weight,low self-discharge rate,no memory effect,long cycle life and environmental protection.However,the charging problem of power Li-ion batteries is a key factor affecting the widespread use of electric vehicles.This problem has also attracted extensive attention and in-depth research by scholars at home and abroad.Charging characteristics testing,modeling analysis,research on battery charging methods and building a safe and reliable charging platform are beneficial to improve battery charging efficiency and speed up charging,thus,the above research can ensure the convenient use and reliable operation of electric vehicles.In this paper,the charging characteristics of Li-ion batteries are analyzed experimentally,and the second-order RC circuit model of batteries is constructed based on the test data of HPPC,etc.The energy consumption model of batteries is obtained on the basis of this circuit model.According to the change of battery SOC,the charging current curve of Li-ion batteries is obtained by particle swarm optimization(PSO)algorithm to achieve multi-objective optimization of the total charging time and energy consumption of charging batteries.According to the actual work needs,a charging circuit based on full bridge topology is built,and the standard constant current charging and constant voltage charging waveforms are realized.This paper is organized as follows:1?The performance of Li-ion batteries was compared with that of other power batteries.The factors related to charging characteristics of power Li-ion batteries were analyzed,including SOC state,temperature,SOH state and voltage and current value. The charging characteristics of Li-ion batteries were deeply studied through the maximum available capacity test,constant current charging test and HPPC charging and discharging test.At the same time,the existing charging methods of Li-ion batteries are analyzed,and the advantages and disadvantages of the mainstream charging methods are compared,which lays a foundation for the optimization strategy of charging.2?Starting from the internal electrochemical reaction mechanism of Li-ion batteries,the second-order RC equivalent model parameters of Li-ion batteries were identified based on HPPC charging and discharging test data.The battery model was built and validated in MATLAB software.Based on the equivalent circuit model,the discrete state expressions of battery energy consumption and SOC are constructed.Aiming at the CC charging stage in the traditional CC-CV charging method,in order to achieve multi-objective optimization of CC charging capacity,i.e.overall charging speed and battery energy consumption,PSO algorithm is used to optimize the current of multi-segment CC charging based on SOC variation.The simulation results show that the smaller the sectional interval is.the more obvious the optimization effect is.Finally,the experimental verification of 2%SOC multi-segment CC charging is carried out.The results show that the optimized multi-segment CC charging-constant voltage charging can effectively accelerate the charging speed without increasing the temperature rise basically compared with the traditional CC-CV charging.3?Considering the need of practical application and the series-parallel connection of batteries in electric vehicles,a DC/DC charging circuit platform based on full bridge topology is built in this paper.The hardware part mainly introduces the choice of the topology,the selection of the key modules of the main circuit of the charging platform,the selection of the controller,and the design of the drive,measurement and protection module.The software part mainly introduces the design of the control program and charging main program.Finally,based on the experimental platform,the experimental waveforms of standard CC charging and CV charging are completed.