Research On The Algorithm Of SOC Based On LiFePO4Dynamic Batteries In Hybrid Electric Vehicles

Because of energy crisis and environmental pollution, the HEVs (hybrid electricvehicles) have been researched all over the world. However many problems aredemanded to be solved in order to develop HEVs, such as the strategy ofestimating SOC (state of charge). SOC is an important parameter of the powerdistribution for engines and electric motors. So an accurate strategy of estimatingSOC has positive effects on the dynamic and fuel economy of HEV.LiFePO4dynamic batteries, which are regarded as the most promising batteriesin HEVs, are chosen to be research objects in this paper. The research wasrespectively taken about experiments of battery characteristics, the equivalentcircuit model, the algorithm of SOC and the simulation of the algorithm.Firstly, the definition of SOC and common equivalent circuit models of batteriesare given as well as the factors influencing SOC. Secondly, a series of experimentsare done to get the characteristics of LiFePO4dynamic batteries, such as therelationship between OCV and SOC. Based on the experiments the equivalentcircuit model of LiFePO4dynamic battery is set up, while the parameters of themodel are identified by data from the experiments. Next after comparison of thecurrent algorithms about SOC, a new strategy of SOC estimation is proposed,which is Kalman Filter with Ah counting method based on the LPV (LinearParameter Varying) system. At last, the simulation model of estimating SOC inHEVs is built in the Matlab/Simulink. The results indicate that the strategy ofestimating SOC proposed in this paper is feasible and accurate.