Research On SOC Monitoring And Evaluation For Battery Pack Of Electric Vehicle And Its Application

As environmental pollution and energy crisis intensified, electric vehicle with advantages of energy conservation and environmental protection becomes an important development direction of car in the future and is focused on by governments and enterprises. Power battery is an important component as the main power source in electric vehicle. The state of charge is an important parameter to reflect remaining capacity of battery and is an important basis to diagnose SOH(state of health) of battery, generate energy management strategies and judge whether the battery is over-charge or over-discharge. So SOC value of power battery is necessary to be monitored and evaluated in electric vehicle.The definition of SOC is expounded and its main influencing factors are analyzed at first in this paper. Then methods of SOC assessment in current are summarized in detail, their characteristics and applications are compared and analyzed. The development direction of SOC estimation is prospected. After the comprehensive comparison of SOC estimation methods, an improved ampere-hour method is selected to estimate SOC value of battery in real time.Problems of SOC initial value and SOC cumulative error are two defects of ampere-hour method. They are emphatically studied and improved in this thesis. The open circuit voltage method is adopted to calculate initial value of battery SOC. The SOC initial value problem of ampere-hour method is solved in this dissertation. Based on strong capability of error correction in kalman filtering method, a combination of the kalman filtering method and ampere-hour method is used to optimize ampere-hour method and settle the cumulative error problem. During the process of SOC estimation by kalman filtering method, widely used Thevenin equivalent circuit model is chosen and its parameters are identified. With the simulated analysis for improved ampere-hour method in Matlab/Simulink, the feasibility of improved ampere-hour method is verified in this paper. The simulated basis is provided for design of SOC on-line condition evaluation system and SOC estimation algorithm.On the basis of theoretical analysis and research, an on-line condition evaluation system for battery SOC in electric vehicle is designed and realized in this research based on TMS320LF2407, a digital signal processor manufactured by Texas Instruments Company. Under laboratory condition, the relationship between battery SOC and open circuit voltage is demarcated off-line; and the designed SOC on-line condition evaluation system is validated by experiment. The experiment results show that the SOC estimation algorithm and SOC on-line condition evaluation system can realize the function of monitoring for battery status parameters in electric vehicle, and reach the requirements and goal of monitoring and evaluation for battery SOC value. In brief, this reseach has a certain reference value in engineering application.