SOC Estimation And Battery Management System Design For Power Lithium Battery Pack

Electric vehicles arouse people’s wide concern as the energy and environment issues become more and more serious, especially the value of PM2.5rises continuously. Electric vehicles develop rapidly, but there is a bottleneck in the process of development—power battery. The research of battery management system arises at this historic moment and becomes the hotspot in the current.This paper explored the estimating method of State-of-Charge (SOC) in the condition of simulating electric vehicles running. An appropriate battery pack management system was developed based on power lithium battery as the research object. The purpose is to improve the estimating precision of SOC, enhance the reliability of battery pack operation and improve the energy utilization ratio of battery pack.The following work has been done in this paper:researching and improving the method of estimating SOC, designing the hardware circuits of battery management system and writing the software programs in LabVIEW.After analysis and comparison, the Kalman Filter algorithm was chosen as the core algorithm of estimating SOC. The algorithm was developed and improved to consummate the estimating SOC.First, the equivalent model of battery was selected. Then the online identification of parameters was completed based on with the Least Square Method (LS) as the core, combining Orthogonal Least Square Method (OLS) and Recursive Least Square Method (RLS). The value of SOC combining Ampere-hour Integral Method and Open Circuit Voltage method wasn initialized and then the SOC using Unscented Kalman Filter algorithm was estimated. In the process of estimating, the noise error was handled with Partical Filter to obtain higher precision of estimating SOC.The battery pack management system was devised with the control unit of CompactRIO (small, solid, flexible, reliable) which was based on LabVIEW development platform. The data sampling circuit, the protective circuit of system, and the control circuit of system were designed. Then the parametric variation in real time was monitored and SOC was estimated in order to prevent the failure problems, such as over-temperature, over-current, over-voltage, and imbalance. With the purpose of completing all the tasks much better, different development frameworks and modes were adopted to achieve the function of each part and optimization of tasks according to characteristics of CompactRIO. Programs were written, including data sampling, data saving and controlling Based on Lab VIEW. The program of estimating SOC was designed combining with Matlab at the same time.After system testing, the battery pack management system designed can sample the precise data about the operation of the power lithium battery pack. And each of the programs is running smoothly without conflicts. The improved algorithm can improve the precision of estimating SOC and reduce the estimation error to less than10%. The design requirements are all met and the whole system runs stably and reliably.