Study On Dynamic Characteristics And SOC Estimation Of Power Lithium Ion Batteries

With the energy crisis and environmental problems intensified,energy-saving environmental protection of the electric car access to the community’s attention quickly developed.Power lithium battery as an electric vehicle energy storage equipment,its performance and application control technology will directly control the development of electric vehicles.Different types of power lithium-ion batteries have their own advantages and disadvantages,different working conditions and environmental factors also affect the lithium-ion battery to show the electrical characteristics.Practical appli cations are often multi-cell in series to get enough capacity and voltage,and monomer inconsistency will make the monomer work between the unbalanced,in order to protect the battery pack efficient and safe operation,we need to establish the battery The management system(BMS)effectively monitors and manages the battery pack.Power battery state(SOC)is a typical representation of the working state of the battery,and it is also a typical representation of the BMS control strategy.The accuracy and spee d of the estimation algorithm play a decisive role in improving the performance of the BMS system.In this paper,lithium iron phosphate battery as the object of study,the use o f n-order RC equivalent circuit model simulation of battery dynamic characteri stics.The system state equation and the observation equation were established.HPPC cycle experiment and least squares method were used to identify the model parameters.The small-current charge-discharge and auxiliary linear nonlinear combination formula were used to establish the OCV model with the gradient descent method.And the data are based on the AIC criterion to determine the optimal order of the model,and the dynamic characteristics of the model are verified by experiments.Based on the RC equivalent circuit model,the SOC estimation method of lithium iron phosphate battery was established by using the extended Kalman filter method.The influence of temperature on SOC was deduced from the SOC estimation principle by introducing the temperature correction term based on voltage and capacity.The algorithm is validated by MATLAB.The feasibility of the algorithm under normal temperature and constant current conditions and the feasibility of the algorithm under complex conditions are verified by exper iments.The robustness of the algorithm is introduced.Experiments show that the SOC algorithm with temperature correction can also accurately estimate the SOC at low temperature.The characteristics of charge and discharge,the effect of temperature on th e charge and discharge performance of the battery were studied by standard charge and discharge experiment,temperature rate experiment and temperature test.Based on the experimental data,verify the voltage characteristics of the model.A standard charge-discharge experiment and magnification experiment were designed for the ternary polymer lithium battery.The performance characteristics of the two kinds of batteries under different working conditions were compared with the lithium iron phosphate battery and the equalization criterion suitable for the working condition was analyzed.