Design For EV Battery Management System And Estimation Of Battery State Of Health

Electric vehicles as one kind of new energy vehicles, has the dual advantages of energy saving and environment protection, likely to become a substitute for fossil fuel vehicles and representative of the vehicles of the future development direction. In recent years, electric vehicles get more and more attention of national governments all over the world. Power battery is the power source of electric vehicles, playing a crucial role in promoting the development of electric vehicles. So setting up a mature battery management system which can effectively monitor and manage battery, become a key technology of developing electric vehicles.Battery management system is getting more attention both in China and abroad. According to electric vehicles actual requirements for batteries, battery management system needs to realize the monitoring, energy management, state estimation, thermal management and safety protection function for batteries, and communicate with other on-board equipment. Among them, the realization of the internal parameters including state of health estimation for batteries, is an important task in the design of battery management system. The main research work includes the following several aspects.Firstly,according to the electric vehicle batteries requirements for large capacity, high power, long life and other, and the development present situation of battery management system, design a stable, accurate, fast and intelligent battery management system. The battery management system composed of a control unit, monitoring unit, balancing unit, communication unit and related software. It can completes the internal parameter calculation and balance management based on the battery voltage, current, temperature information collection, and exchange information and establish communication with other on-board equipment.Secondly, according to the definition of the state of health of batteries, attenuation factors of batteries and the existing estimation methods, choose to judge battery state of health by internal resistance. Through the analysis of external characteristics when battery works, establish reasonable battery model. Based on appropriate battery model, use least square method to identify the parameters of the battery model. It's proved correct by simulating by MATLAB and calculating offline adopting experience data.Finally, the method of state of health estimation in battery management system is realized. On the basis of parameter identification outline, the double kalman filtering algorithm can estimate the state of charge and internal resistance of batteries at the same time. Simulation and experimental results are given to prove the algorithm used in the system has ability to predict accurately and fast, accomplish the judgment for the battery life.The battery management system developed can accomplish monitoring and communication function well when tested in actual working conditions. It also predict the SOH of batteries well.