Study On Obtaining Method For Peak Power Reference Value Of Lithium-ion Battery Used For Testing

The accurate estimation of peak power is helpful for the effective formulation of electric vehicle control strategies,which can improve the safety and reliability of the system.The high-accuracy acquisition of the peak power reference value is of great significance for the test evaluation of parameters.In the industry,the estimation of peak power is usually called State of Charge(SOP)estimation.At present,the research on the peak power is mainly based on the steady-state condition,but the polarization voltage will be generated in the practical application of the battery,so the establishment of the peak power reference value acquisition scheme suitable for the initial polarization state is helpful to promote the development of the industry.The initial polarization voltage affects the peak power of the battery through its influence on the terminal voltage.In this paper,the peak power is characterized by the peak current,and the cut-off voltage of charge and discharge is taken as the boundary condition.The 18650 and 26650 lithium-ion battery are taken as the experimental objects.The different polarization voltage is established by discharging the battery at different rate for 5s.The influence of initial polarization voltage in the discharge direction on the peak power of the battery is studied.In order to more accurately reflect the polarization process of the battery,the secondorder RC model is chosen as the equivalent circuit model of the battery.According to the experimental data,the quantitative relationship between the parameters of the model and SOC,discharge rate,initial polarization voltage of the battery is established,and the accuracy of the model is verified by the design of experiments.The peak power can not be obtained continuously by testing.In this paper,the peak power value in some states is obtained by limited fixed-point testing,and then the peak power reference value in the whole region is obtained by high-precision estimation method.Therefore,the acquisition of peak power reference value depends on accurate and efficient test method and high-precision estimation method.Aiming at the problem of time-saving but low precision of HPPC,a peak power test method combining HPPC with second-order model is proposed: Using the peak power(current)obtained from HPPC test to identify the parameters of the second-order RC model,and then using the second-order RC model to obtain the peak power.The relative error of the new test method is concentrated within ± 1%,with high accuracy.Based on the test results,the peak power is estimated.The methods of estimation include secondorder RC model estimation,multiple linear regression estimation and support vector machine estimation.Use statistical indicators to compare the three estimation methods horizontally and test the accuracy of different estimation models.Finally,the peak power reference value is determined by HPPC combined with second-order model test and support vector machine estimation.This paper consists of 56 figures,9 tables and 52 references.