Electric Modeling And Parameter Identification Of Li-ion Battery Based On Electrochemical Properties

Lithium-ion(Li-ion)battery is commonly used in electric vehicles due to its high energy density and high power density.The research on batteries are mainly focused on modeling and parameter identification.Equivalent circuit model(ECM)and electrochemical model are high precise modeling methods we have studied for a long time.ECM is based on a circuit consists of resistances,capacitances and voltage sources which can describe the battery initial reactions.Electrochemical model is based on the partial differential equations(PDEs)of pseudo two-dimension(P2D)model.ECM is easy to build and identify with the sacrifice of estimation accuracy.While the electrochemical model takes full consideration of the microscopic reactions which leads to its superiority in real-time battery performance prediction.But it is time-consuming.The two methods separately cannot reduce the calculation complexity and improve the estimation accuracy at the same time.This paper proposes a novel identification method for the battery ECM parameters considering the electrochemical properties.The estimation accuracy is higher,and the further application,e.g.SOC estimation can be improved as well.In this paper,the progresses are shown as follows.The electrochemical reactions are analyzed.An improved P2 D model is established on the basis of the PDEs,and the terminal voltage is divided into several parts,namely the open circuit voltage,the overpotential of the electrodes,electrolyte potential,internal resistance drop and so on.The model order reduction process is implemented by the simplification of the PDEs using Laplace and inverse Laplace transform,Pade approximation and integral etc.and a unified second order transfer function between cell voltage and current is obtained.The ECM structure is determined based on the diffusion and polarization process.The parameters are identified on-line or off-line.The precision is decided by the order of the model.The higher the order is,the more precise the model is.Analyzing the advantages and disadvantages of the ECM and electrochemical model and find the relationship between the electrical and electrochemical parameters,the ECM is much more accurate,and it may improve further applications,e.g.,SOC estimation.Finally the model is built in MATLAB/Simulink,and the comparisons to the simulation results with COMSOL and experimental results prove the correctness and validity of the proposed methodology.And the hardware-in-loop(HIL)experiment with dSPACE system proves the real time performance.