Research On Heat Generation Model And Estimation Of Dynamic Charge And Discharge Process Of Lithium-ion Battery For Vehicle

Lithium-ion batteries are one of the most commonly used on-board energy sources in electric vehicles.A large amount of energy is released during the charging and discharging of the battery,which causes the external environment temperature of the lithium-ion battery to rise sharply.When the working environment is too high,the charge and discharge capacity characteristics will decrease,accelerate the aging of the lithium-ion battery,and even cause dangers such as "thermal runaway".As a key parameter of battery temperature monitoring,the heat production rate of the battery is extremely critical for ensuring the safety and power of the vehicle battery.Therefore,the research is carried out on the heat production estimation method of the vehicle power lithium-ion battery under different aging conditions.The specific content is as follows:(1)The heat generated by the lithium-ion battery in the working process is mainly composed of two parts: reversible heat and irreversible heat.Based on the heat generation mechanism,the Bernardi battery heat generation rate model is proposed to express the two parts of heat in a mathematical model;In addition,a new Hybrid Pulse Power Characterization(HPPC)ohm internal resistance and polarization internal resistance measurement method is proposed based on the key parameters of irreversible heat in the Bernardi battery heat generation rate model.Realize high-precision and high-efficiency testing of ohm internal resistance and polarization internal resistance.(2)Multi-factor dynamic ohm internal resistance and polarization internal resistance model research: The proposed HPPC method is used to test the ohm internal resistance and polarization internal resistance of the battery under the influence of multiple factors under different aging conditions.By analyzing the relationship between battery state of health(SOH),temperature,state of charge(SOC),and charge-discharge rate with ohm internal resistance and polarization internal resistance,respectively,a simulation based on binary polynomials Combined with cubic spline interpolation method is proposed,and then constructed multi-factor dynamic charge-discharge ohm internal resistance and polarization internal resistance models under different health conditions.The validity of the proposed multi-factor dynamic ohm internal resistance and polarization internal resistance models is verified by changing the temperature,SOC,and charge-discharge rate.It is found that the accuracy of the remaining models is higher except for the more aging model that has poor fitting effect.For this reason,it is proposed to use binary cubic spline interpolation theory to compensate the errors of models with poor accuracy.Experiments prove that the multi-factor dynamic ohm internal resistance and polarization internal resistance models with error compensation strategy have higher estimation accuracy.(3)Research on dynamic charge-discharge temperature entropy coefficient model of SOH under different aging states: Compared with the existing measurement methods of open circuit voltage,select the direct measurement method to measure the open circuit voltage under different aging states,temperatures and DOD;Based on the least squares theory,a dynamic charge-discharge open-circuit voltage model with temperature and DOD as independent variables and open-circuit voltage as the dependent variable under different health conditions is constructed.The open circuit voltage models of different aging are verified by changing the temperature and the depth of discharge.The result is that the accuracy of all the constructed open circuit voltage models are in the range of 0.83% to 4.7%,which shows that the model can achieve accurate estimation of the open circuit voltage.In order to further realize the intuitive expression of the reversible heat of the battery,it is proposed to use advanced differential calculus to find the tangent of the three-dimensional horizontal axis temperature of the constructed open circuit voltage model,and obtain the dynamic charge and discharge temperature entropy coefficient model under different aging states.(4)Research on the model of battery dynamic heat generation rate:Firstly,build a battery thermal effect model based on the lumped thermal properties of the battery and the energy conservation equation in the finite element analysis theory.Then,based on the Bernardi battery heat generation rate model,the multi-factor dynamic ohmic resistance and polarization internal resistance models with error compensation strategies under different aging states and the dynamic charge-discharge temperature entropy coefficient model under different aging states are adopted.By introducing SOC and The method of DOD estimation is to construct a battery dynamic heat generation rate model.Using MATLAB language to compile the program of the battery dynamic heat generation rate model under various charging and discharging conditions;And use Comsol Multiphysics to simulate the temperature characteristics and temperature field distribution of the battery under various charge and discharge conditions.Finally,the experiment tests the temperature change process,thermal field characteristics and thermal field distribution of the battery under the same working conditions to verify the validity of the battery thermal effect model and the battery dynamic heat generation rate model.