Research On Active Balancing Control Strategy Based On The Prediction Of The SOC Of Lithium Battery Pack

As the gradual decrease of petroleum resources the increasing environmental pressure.Voices of people that electric energy replaces conventional fossil fuels and becomes a power source for vehicles become more and louder.Because of its energy density,power characteristics and service life,lithium battery has become the ideal power source for the new generation of electric vehicles.In order to meet the power and performance requirements of electric vehicles,the single battery is often connected to a battery pack.In the process of production,the capacity,SOC,internal resistance and so on of single battery are different.Studies show: With the increase of charging and discharging times of the power battery pack,the difference of single battery will gradually increase.It is shown that some of the cells in the battery pack are not fully charged,and some of the batteries have been charged,as a result that the capacity of the lithium battery pack would be fade and the service life would be shorten.So it is necessary to use an effective energy balance management of the battery in the process of charging and discharging,and to improve the performance and prolong the service life of the battery pack.The paper of battery balancing is support by Changsha technology bureau: heat flow design and control of hybrid vehicle lithium-ion battery pack technology project [KH1601129].The main research works and analysis are as follows:(1)By analyzing the working principle and characteristics of lithium-ion battery,the essence of the inconsistency of lithium battery is SOC inconsistency.The disparity of SOC can be used to describe the degree of battery inconsistency and can be used to study the balance control strategy of lithium battery.(2)Through the analysis of the commonly battery SOC estimation algorithm,EKF algorithm is proposed to estimate the SOC on the basis of the Ampere-Hour integral and open circuit voltage.Then the Simscape battery model is established to estimate battery parameters.Finally the HPPC experiment is used to verify the precision of SOC estimation.Experiments prove that the method of SOC estimation satisfies the requirement of accuracy.(3)The battery balancing control strategy proposed based on the battery inconsistency.The process are as: Voltage and SOC is used as balancing variables in the process of charging while only voltage in the process of discharging,voltage and SOC discrete degree is used as a judgment of the time of beginning and ending balance.At last,the experimental bench is set up to validate the effectiveness of the balancing strategies,the experiment shows that using balanced measures not only can improve cell inconsistency but also can improve the efficiency of the battery in the process of charging and discharging.