Research On Power Battery Preheating And Improved Algorithm Of SOC In Cold Area

Power batteries are the source of power for electric vehicles,battery performance is related to the performance of the vehicle.Many reasons can affect battery performace,but temperature is the most important.The unstable discharge of lithium battery in cold environment seriously affects the performance of electric vehicles,which makes it difficult to promote electric vehicles in cold northern regions.Battery preheating technology is very necessary in cold environment.The Battery Management System(BMS)manages the safety of battery packs.The most critical technology is the estimation of battery state of charge(SOC).Estimating battery SOC in cold environments is difficult,so it is particularly important to estimate battery SOC in cold environment.The research idea of this paper is to preheat the battery pack in a cold environment,and let the battery temperature rise to 20℃ when working,the battery performance is relatively stable.Because low temperature has a great impact on the SOC estimation of the battery,the SOC estimation is not performed when the temperature is lower than 0℃,and the SOC estimation is performed when the temperature is higher than 0℃.Based on this,the following aspects of research are carried out.Firstly,The low temperature discharge test of ternary lithium battery was carried out to analyze its characteristics in low temperature environment.Based on the unstable voltage and serious attenuation of battery capacity in the low temperature environment of terpolymer lithium battery,a heating method combining electric heat film was designed.In the face of different temperatures,PWM signals of different frequencies were output through the microcontroller to change the temperature of the heating film.And the battery pack is heated,which increases the temperature rise rate of battery preheating and solves the problem of uneven internal temperature of battery during traditional heating.Secondly,compare the common equivalent circuit models of batteries.Consider the effect of temperature on battery performance in cold environment,establish the second order Thevenin equivalent circuit model of minxing temperature.The parameters of the model are identified and two different pulse discharge conditions were used to prove the accuracy of the model.Finally,the common algorithms of lithium battery SOC are compared and analyzed.IEKF algorithm was used to estimate SOC at 0℃ and 20℃.In order to improve the accuracy of IEKF algorithm to estimate SOC at low temperature,a fixed smooth interval algorithm was proposed to optimize IEKF algorithm,and the optimized algorithm was obtained.The implementation steps of the method were described.The algorithm is used to estimate the battery SOC,and the results of IEKF algorithm are compared with those of improved IEKF algorithm to verify the accuracy of the algorithm.