Mechanism Modeling And State Estimation Of Lithium Ion Battery

Electrification reform in the field of transportation is of great practical significance to promote and implement the strategic decision of carbon peak and carbon neutrality in China.As the pioneer of transportation electrification reform process,the development of new energy vehicles is not only related to the reform of China’s energy consumption structure,but also the key to promote the construction of green and low-carbon energy system.As the main energy source of new energy vehicles,the lithium-ion battery system always affects the power performance,economy and safety of the vehicle.Strengthening the energy management of power battery system and carrying out accurate and efficient state estimation is the key to ensure the efficiency and safety of power battery system and thus establish the confidence of new energy vehicle market.Therefore,the state monitoring and evaluation of power battery system is researched in this paper.The specific contents and main innovations can be summarized as follows:1)A full-order electrochemical-thermal coupling model of lithium-ion battery is established,and its numerical solution is realized based on finite difference method.Based on the pseudo-two-dimensional model and Fourier’s law,the electrochemical-thermal coupling model of lithium-ion battery is built.The different forms of pseudo-two-dimensional model equation in existing literature is reasonably explained by the charge conservation equation.The numerical solution of highly coupled nonlinear partial differential equations is realized based on finite difference method.2)An open circuit voltage hysteresis correction model for lithium-ion battery is proposed,and the accurate assessment of state of charge is realized based on dual center differential Kalman filter algorithm.Considering the open circuit voltage hysteresis phenomenon of lithium ion battery,a modified model is proposed.The long short-term memory algorithm is adapted to modify the relationship between state of charge and open circuit voltage in real time.On this basis,combined with the equivalent circuit model,the dual center differential Kalman filter algorithm is used to realize the collaborative estimation of the model parameters the model state,so as to improve the accuracy of state of charge estimation.3)A minimalist model of lithium-ion battery is proposed,and the equivalent circuit model is used to estimate the state of charge and the state of health.Aiming at the degradation of battery capacity caused by the growth and thickening of solid electrolyte interface film,a minimalist model of lithium ion battery is proposed to quantify the irreversible loss of lithium ion storage.On this basis,combined with the equivalent circuit model,this paper achieves the effective estimation of the available lithium ion stock(i.e.the battery capacity level)of the lithium-ion battery,thus making the assessment results of the state of charge and health timesensitive.4)The joint estimation method of the state of charge and power for lithium-ion battery is constructed,and the estimation accuracy is improved based on sequential quadratic programming algorithm.Taking the state of charge,manufacturer’s specified value and safety voltage threshold as comprehensive constraints,a joint method for state of charge and state of power estimation of lithium-ion battery is constructed based on the equivalent circuit model.Taking terminal voltage error as objective function,sequential quadratic programming algorithm is used to optimize model parameters to improve the accuracy of state of power estimation.5)The electric-thermal coupling prototype simulation system of lithium-ion battery is built based on Matlab/Simulink platform,and the integrated estimation of SOX is realized.Based on Matlab/Simulink platform,the electric-thermal coupling prototype simulation system for multilevel battery system is built,which highly restores the internal and external characteristics of battery cell,module and pack in real application scenarios.On this basis,the integrated evaluation of the state of charge,health and power of the lithium-ion battery is realized by using the experimental data of the prototype simulation system.