Electro-thermal Modeling For The Cylindrical Li-ion Power Battery

This thesis constructs the first-order RC(resistance and capacitance)circuit model based on the battery modeling method of equivalent electrical circuits for 18650 cylindrical Li-ion power batteries.Parameters of the battery circuit model are estimated by using the least-squares(LS)technique and the experiment data of battery test.This battery circuit model is also conducted on the Matlab/Simulink? and validated accurate through analysis of voltage errors between simulated and measured battery voltage.By the usage of both whole cell and finite element modeling methods,thermal models of the cylindrical Li-ion batteries are established.The initial ranges of thermal-physics parameters of the Li-ion battery are estimated by using the LS and whole model,the optimum values of which are searched by the genetic algorithm.After that,one dimension(1D)and two dimension(2D)thermal models are built by using the software Fluent?,the heat rate of which is fitted and programmed through the routine of Fluent UDF.Under constant current discharges at constant environment temperatures,both 1D and 2D thermal models are validated effective and reliable by comparing side and central-line temperatures of the battery surface between the simulated and measured values.Due to anisotropic thermal-physics parameters of the Li-ion battery,the 2D thermal model yields better performance than the 1D model.The electro-thermal coupling model(ETCM)is created by using the Fluent software for the Li-ion battery,which runs in cycles of the constant current,DST(dynamic stress test)cycles,and FTP(federal transport procedure).Meanwhile,transient values of the battery current are generated by the UDF routine,by which both the surface temperature and SOC(state of charge)are fed back to interpolate parameter values of the battery circuit model.The ETCM is validated accurate and reliable by the battery surface temperature between the simulated and measured values.By comparison of temperature errors of battery surface,it is found that the ETCM is most simulation accuracy in the three proposed thermal models.In this thesis,an enhanced method of ETCM is proposed to improve the simulated accuracy of battery-surface temperature,adaptive to requirements of real operations of cylindrical Li-ion batteries.