Research On SOC Estimation And Charging Optimization Strategy Of Power Battery

The battery state of charge(SOC)is an important parameter in battery management system,which accuracy is the base of monitoring and optimization management in the charge-discharge cycle process.As the result of complex chemical reactions in batteries,its external parameters are also changing in the various operation and usage mode while the performance,safety and life of the battery will be affected.For fear of capacity fade,potential safety hazard and life length reduction,accurate estimation of SOC is of great significance.Moreover,due to the fact that the endurance capacity of the power battery cannot meet the demand of consumer obviously,the charging time is longer and longer after increasing the battery capacity.First,a precise and accurate algorithm of SOC estimation is studied for lithium iron phosphate battery.Then,the comprehensive fast charging strategy is designed based on the battery SOC.The main contributions of the thesis is:1.For battery voltage hysteresis and fixed model parameters,the battery model is limited.Nonlinear model of open circuit voltage,current,internal resistance and other parameters of the battery is built using the thought of modeling.The model with dynamic parameter contains hysteresis voltage based on data.Then,the dynamic parameters of the model are identified in Matlab/Simscape.The average error of simulation fitting is 12.7mV,which verifies the accuracy of the model.2.In view of the low precision and unstable calculation of the traditional methods,a square root Untraced Kalman filtering algorithm is proposed based on the Kalman filter algorithm and variable parameter battery hysteresis model to estimate the battery SOC.The stability of the calculation in the iterative process is improved.The simulation results show that the SR-UKF algorithm has higher accuracy compared with the commonly frequently-used EKF filtering algorithm,and the error is about 3.5% which verifies the accuracy and fast convergence of the algorithm.3.Aimed at the polarization in battery charging,a comprehensive fast charging strategy based on SOC is designed because the current main charging methods in charging process is insufficient.The charging time is reduced effectively and the charging safety and reliability improved.