Research On SOC Estimation For Lithium Battery Of Electric Bicycle

With the environmental pollution and energy shortage problem become increasingly serious,the trend of the transition from lithium-ion battery to lead-acid battery is becoming inevitable.Electric battery management system has been a key factor which restricts the development of electric vehicles.Based on the function and function of power battery management,this paper focuses on the monitor of battery pack and the estimation of SOC(State of Charge)by 36 V and 8.8Ah lithium battery.The following issues are discussed:(1)Based on the working data of lithium batteries,the charging characteristics,discharge characteristics and internal resistance characteristics of lithium batteries are analyzed on the basis of relevant experimental data.The electrochemical model is established as the mathematical model of battery SOC estimation.At the same time,the internal resistance and parameters of the electrochemical composite model are realized by recursive least squares method.(2)This paper introduces the definition and influencing factors of SOC in lithium battery,analyzes the advantages and disadvantages of the commonly used SOC estimation method,and uses the extended Kalman filter algorithm as the estimation method of SOC estimation.Based on the electrochemical recombination model of lithium battery,the state space equation for estimating the state of charge of the battery is obtained.Then the Anson integral algorithm is combined with the extended Kalman filter algorithm,designed to calculate the lithium battery SOC calculation process.(3)The STM32F103RCT6 microcontroller as the main controller of the SOC estimation system which includes peripheral necessary functional circuit is completed.There are four steps to realize the main function of this system.Firstly,collect current and measure voltage utilizing the timing interrupt function of single-chip.Secondly,achieve reference residual energy based on the proposed method.Thirdly,in order to study the aging of battery,update the total charge of the battery and record it to the Flash when the charge is completed.Finally,display the data on the LCD screen including voltage,current,residual power and so on.(4)The feasibility and accuracy of the SOC estimation is verified in the method of discharge experiment of constant current 3A and 6A.The experimental results show that the EKF algorithm can eliminate the influence of the initial error on the SOC estimation of the battery.Compared with the measured SOC value,the average error is about 2%,and the maximum error is less than 3%.