Research On State Estimation Of Li-ion Battery Considering Electro-Thermal Coupling Behavior

With the gradual consumption of oil resources in the world and the intensification of air pollution caused by automobile exhaust emissions,the electric vehicles with battery as the main power source are becoming more and more popular.It is very important for battery energy management to ensure battery safety and improve battery longevity.As the foundation of battery management system,the accurate estimation of battery state is very important,which is directly related to the optimization of vehicle energy management and control strategy.In this paper,the LiCoO2 battery is used as the research object.The electro-thermal coupled battery model is established,which considers both the electric factors and the thermal factors.The study for the state of charge SOC and the state of charge power SOP of the battery is completed.Accurate battery model is very important to ensure the accurate estimation of battery state.In the battery modeling section of this paper,the experimental data are obtained by the pulse discharge experiment at different temperatures.The parameters of the two order RC equivalent circuit model are identified by the least square method.The relationship of the battery model parameters with the state of charge SOC and temperature of the battery is set up.At the same time,the internal temperature of the battery is obtained according to the electrochemical model that has established.The parameters of the two state heat model of the battery can be identified by the surface temperature and the internal temperature of the battery,and then establish the heat model of the battery.Finally,a more accurate electrothermal coupling model with the combination of the equivalent circuit model and the thermal model is established.Based on the dynamic working condition current input of UDDS,the response of the battery voltage,the battery surface temperature and the battery core temperature are obtained,and the model is verified and analyzed.In the part of state of charge estimation,the extended Kalman filter algorithm is introduced to solve the shortcomings of standard Kalman filter algorithm.The space state equation is set up based on the established electrothermal coupling model and the extended Kalman filter algorithm,and then the SOC estimation algorithm is designed.The SOC algorithm is realized by programming in Matlab.According to the data of pulse discharge experiment,the SOC estimation results of the extended Calman filter algorithm is compared with the SOC results from the experimental current.It shows that the SOC estimation algorithm based on the electrothermal coupling model is more precise.The SOC algorithm is analyzed and verified.By changing the initial value of SOC,we verify the fast convergence ability of the extended Kalman filter algorithm and the ability to quickly correct the initial value error.The single constraint condition of battery SOC constraint,voltage constraint and temperature constraint is introduced in the charging and discharging process of battery.In order to ensure the safety of the battery,the state of power estimation method based on the current-voltage-temperature multi-constraint conditions is proposed in view of the actual use of the battery.By combining the battery model and the battery constraint conditions,the state of power estimation method of battery under multiple constraints is obtained.The state of power algorithm is realized by Matlab programming.The response from current,voltage and temperature of battery under multiple constraints is obtained from the input current of dynamic working condition.The state of power is predicted by estimating the maximum current and voltage of the battery at any time.