Research On Cycle Life Prediction Of Power Battery Pack For Low Speed Electric Transport Vehicle

At present,the problems of long test period and difficult cycle life prediction exist in the power battery pack of low speed electric transport vehicle.The life warranty requirements of power battery pack proposed by relevant manufacturing enterprises fail to take the actual driving conditions of the transport vehicles into account.Considering about this,in order to improve the reliability of the cycle life prediction of the low speed electric transport vehicle power battery pack and shorten the cycle life test cycle.The cycle life prediction of power battery pack of low speed electric transport vehicle is studied.The main work content is as follows:Firstly,focusing on the reasons for the decay of power battery cycle life,the charge-discharge ratio,temperature,discharge depth,cycle times and battery pack inconsistency was analyzed.A method for cycle life prediction of power battery pack based on the operating condition of low speed electric transport vehicle was proposed.The advantages and disadvantages of power battery equivalent circuit model were discussed.The third-order RC equivalent circuit model of the power battery was established.Then,the relationship between state of charge(SOC)and open circuit voltage(OCV)was established based on pulse charge and discharge test data of power battery.According to the power battery in the process of pulse charging and discharging voltage hysteresis effect,impedance and capacitive reactance parameters of third-order RC model were identified.The parameters of the power battery model were identified at different temperatures.The identified model parameters were input into the third-order RC equivalent circuit model of power battery.The accuracy of the simulation model of third-order RC equivalent circuit of power battery was verified by comparing the experimental voltage of impulse charge and discharge with the simulated voltage of power battery model.Next,the secondary development was carried out for the existing pure electric vehicle model in the ADVISOR software.The third-order RC equivalent circuit model of power battery was embedded into the whole vehicle model of low speed electric transport vehicle.Parameters of key modules of the vehicle model were defined.The whole vehicle model of low speed electric transport vehicle was set up.Based on the investigation and analysis of typical driving roads of low speed electric transport vehicles,the driving conditions of low speed electric transport vehicles were established and imported into the ADVISOR.The vehicle model was verified by the comparison between simulation of the vehicle model and the test of integrated platform of motor and battery.Based on the power balance equation of the low speed electric logistics vehicle,the dynamic test condition of the power battery pack was established.In order to verify the accuracy of the dynamic test conditions of the power battery pack,the power of the vehicle model and the dynamic test condition power of the cycle life bench test of the power battery pack were compared.Finally,according to the dynamic test condition of the power battery pack of the low speed electric transport vehicle,the cycle life bench test scheme of power battery pack was determined by using the running condition and range of low speed electric transport vehicle.According to the cycle life test data of the power battery,the cycle life curve of the power battery was fitted based on the genetic algorithm.The number of driving conditions was used as the iteration variable,and the sum of the squared errors of the battery capacity retention rate was used as a fitness function.The empirical formula for cycle life prediction of low speed electric transport vehicle power battery pack was obtained by optimizing the optimal coefficient of genetic algorithm.The square sum of the fitting error between the experimental data and the empirical formula of cycle life was only 0.776,the accuracy of the empirical formula of cycle life was verified.This life prediction method can provide a set of reliable cycle life prediction test scheme and empirical formula for the power battery pack of low speed electric transport vehicle,more accurately predict the life of the power battery pack of low speed electric transport vehicle.The life test cycle was shortened.This life prediction method is of practical engineering significance.