Research On The Method Of Obtaining Parametric Function And Determining Excitation Signal Of Lithium-ion Battery

Lithium-ion battery which is the main component of microgrid energy storage unit and key subsystem of electric vehicles has become a hot research in recent years.The battery is a non-linear system whose internal physical and chemical processes are very complex and the external available information is extremely limited.In order to accurately estimate the battery status to fully use the battery,the battery parameters need be identified accurately by limited information.Therefore,the method of obtaining the parametric function and determining the excitation signal of lithium-ion battery are researched in this paper.The main research contents and innovations are as follows:Firstly,the relationships between the basic parameters of lithium-ion battery and current,ambient temperature and SOC are studied.According to the designed constant current test flow,the Li Fe PO₄ and Li Ni Co Mn O₂ are experimented at different ambient temperatures with different currents.By processing experimental data,the relationships are analyzed comparatively which are terminal voltage,open circuit voltage,capacity and direct current internal resistance and current,ambient temperature,SOC of two kinds of lithium-ion battery,which can lay the foundation for the later study.Secondly,the method of obtaining the parametric function in the DCIR model with relatively simple structure and extensive application is studied.Based on the?DCIR-SOC?curves which are identified in different ambient temperatures and currents,and the existing thermal model,the relationship of DCIR and current,temperature and SOC are established by curve fitting and proportional correction.And the scope of application of the method is given by case analysis.The DCIR in any current,ambient temperature,SOC can be obtained,the DCIR consistency in thermal characteristics can be evaluated by parametric function which is established by a small amount of experiments.Finally,based on the dynamic model which can reflect the real operation of lithium-ion battery,a method of determining the excitation signal is proposed.Firstly,the true value expression of the parameter is deduced based on the circuit model and the parameter identification method.Then,the parametric expression of the relative error is deduced by considering the influence of the measurement error of the experimental equipment and the nonlinearity of the battery.By minimizing the expression,the appropriate excitation signal can be got.The proposed method not only provides the basis for the selection of experimental equipment and test conditions,but also analyzes the error of parameter identification results,and makes the dynamic model more practical.The above methods are validated on off-line experimental equipment of lithium-ion battery in laboratory.