| Development of electric vehicle has become the major direction of future auto industry facing the growing problems of energy shortage and environment pollution. Power battery, as the power source of electric vehicle, is a key technology for the development of electric vehicle industry. Manage battery effectively, bring battery into full play, and extend the operating life of battery are the purposes of BMS. Estimation of SOC(State of Charge) is the most important technology in BMS, and it’s also the most diffecult part to calculate. However, the definition of SOC which is based on battery capacity leaves out the voltage variation when the battery is working, therefore it can’t reflect actual battery energy state accurately. So, this paper proposes a new definition of SOE(State of Energy) which is based on battery energy, SOE of battery can predict the max range of electric vehicle, and prevent the over charge/discharge of battery, therefore the service efficiency of battery can be promoted, and the cost of electric vehicle will be reduced to some extent.In order to reflect actual energy state of battery under complex condition accurately, this paper proposes a new definition of SOE and its estimation method based on the conservation of energy principle. Steps of estimation are as follows: Firstly, the process of static initial estimation, ECU will calculate the initial SOE on the basis of open-circuit voltage, battery standing time and battery state before standing. Secondly, the process of dynamic cycle estimation, according to the environment temperature and SOH of battery, ECU can correct the inaccuracy of battery total energy, furthermore, it will also calculate the EMF of battery based on the model of SOE-EMF. Then, ECU can calculate the variation of energy by using EMF and current. Lastly, ECU need to correct the loss energy which is caused by self-discharge. In this way, ECU will circular estimate the SOE from one moment to the next, and provide real-time update for SOE, thus reflecting actual battery energy state.Under different condition, co-simulation is experimented with dynamic model of electric vehicle built by CRUISE and SOE estimation model built by Simulink. According to the result of simulation, the method has high accuracy, strong real-time and low estimation error. The model can reflect actual battery energy state, keep its security and efficiency under different condition, thus providing a good protection for running safety and stability of electric vehicle. |
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