Monitoring And SOC Estimation Research Of EV Li-Ion Battery Packs

In the 21st century, as the environmental pollution and energy shortage problems become more and more serious. As an important component of the new energy automobile, the electric vehicle develops rapidly. But the development of the electric vehicle brings a lot of technical problems, the management of battery packs is one of the problems. Considering the role and function of power battery packs, this thesis mainly studies the monitor of the battery and the estimation of SOC (State of Charge).In order to accord with the layout of the battery packs using in the electric vehicle, this paper presents a centralized and distributed structure to realize the monitoring of battery packs. The battery packs is divided into two parts: the first is data acquisition module, it mainly fulfill the voltage collection and temperature gathering of the battery, the data collection adopts linear optocoupler isolation to reduce the crosstalk of large current and high voltage. To minimize electromagnetic interference because of many more wires in the battery packs. the temperature gathering makes full use of 1-wire characteristics of chip DS18B20, designing search algorithm to accomplish multiple points gathering with 1-wire; the second part is main control module, the master control module mainly achieved communication with all the data acquisition module, the CAN communication combines extended remote frames and extended data frame to guarantee the reliability of the data communication.Analyzing the factors of affecting battery SOC estimation, and makes a deep research of discharge rate factor, then proposes through calculating the power loss of internal resistance to accomplish discharge factor correction. Through compare and research the commonly used battery model, establishing linear cell battery model to estimate battery SOC, the resistance of linear cell model uses the recursive least square method to realize the online identification. Comparing and analyzing the advantages and disadvantages of traditional method of SOC estimation. This paper proposes a method which based on the minimum voltage and extended kalman filtering (Vmin-EXF) algorithm to estimate the SOC of battery packs.Finally, through the experiments verified the anti-interference and safety performance of data acquisition module, and the reliability of communication between the data acquisition module and master control module. The Vmin-EXF algorithm eliminates the influence of initial error in SOC estimation. And comparing with traditional SOC estimation method, this method improved the accuracy of the SOC estimation, and satisfying the 8% error requirements of electric vehicle.