Research On The Driving-cycle-based Cycle Life Prediction For Lithium-ion Battery System

Power battery,as the only energy source for pure electric vehicle,is the core part in pure electric vehicle.The performance of power battery directly affects the development prospects of electric vehicle.Ternary lithium-ion battery with its high energy density,high charge/discharge efficiency,long cycle life and many other advantages has been widely used in the field of pure electric passenger car.This paper takes the ternary lithium-ion battery system used for a self-owned brand pure electric SUV as research object,and the following aspects of the research work are carried out.Firstly,the paper describes the development status of pure electric vehicle and the research status of lithium-ion battery life,also introduces the structure and work principle of lithium-ion battery as well as the commonly used equivalent circuit model.Then,the two-level-RC Thevenin equivalent circuit model is established to lay the foundation for parameter identification and life prediction of lithium-ion battery.Secondly,the parameter identification model is established by Simulink,then according to the battery terminal voltage and current curve obtained from pulse charge/discharge test,the parameter identification of lithium-ion battery model is carried out by using the Parameter Estimation toolbox.In the end,the parameters of battery model are obtained through repeated iterative operation,these parameters are used for the modeling of the pure electric vehicle simulation model.Thirdly,with the ADVISOR software,the pure electric vehicle model is built and the vehicle performance simulation is carried out by using standard cycle condition.Compared the simulation results with the road test results,the results show that the established vehicle simulation model is accurate,can be used to simulate the real vehicle road test.Fourthly,based on the electric vehicle power balance equation,the NEDC condition is converted into the battery dynamic test condition.In order to verify the reliability of the battery dynamic test condition,conducted the battery bench test according to the battery test condition,then conducted the electric vehicle NEDC condition simulation by ADVISOR.Compared the battery bench test results with the NEDC simulation results,it shows that the error of the battery current and power iswithin a reasonable range,thus the battery dynamic test condition can simulate the NEDC condition well.Lastly,Performed the ternary lithium-ion battery system cycle life test on the basis of the battery dynamic test condition,then got the corresponding test data between charge/discharge capacity and NEDC cycle number.Fitted the cycle life test data based on Matlab genetic algorithm toolbox,and the mathematical model of battery capacity fading is obtained to predict the cycle life of ternary lithium-ion battery system.In this paper,the cycle life of ternary lithium-ion battery system is studied,and the battery bench test method for simulating NEDC cycle test is explored.This method can predict the actual life of lithium-ion battery more accurately,and save life test cycles and costs,possess certain applicable value in engineering.