The Research Of New Energy Vehicles Lithium-Ion Battery Thermal Management

As automobile industry flourishes,energy consumption is intensifying.Many cities are often enveloped in a thick haze and PM2.5 has reached a high level.The emission of automobile's tail gas has been the main source of the air pollution.New energy vehicles have dual advantages in energy-saving and environmental protection and become a new development direction of automobile industry."Made in China 2025" pinpoints that new energy vehicles will be a new breakthrough in automotive technology and there will become the future of China's auto industry.Battery,as an energy storage device,is the key component of new energy vehicles.During the charge-discharge process,it will produce a lot of heat which makes the temperature of battery rises rapidly.The internal temperature of the battery and the temperature uniformity between the battery modules effects the battery performance and the cycle life.The requirement for battery performance is very high especially under high power condition and other harsh conditions.To ensure the heat dissipation requirements as well as the security and reliability of new energy vehicles' power battery pack,the development of an effective battery thermal management system and the design of a stable and efficient battery cooling structure have great significance in improving the overall performance of the power battery.Based on the analysis of relevant technology of battery thermal management system and the summary of the research status of air cooling,liquid cooling and phase change material cooling technology of battery thermal management,this paper analyzes and studies the thermal management system of power battery for new energy vehicles.First of all,the basic structure and the reaction principle of LiFeP04 li-ion battery and the heat generation mechanism as well as the heat transfer characteristic when it is working are summarized.The influence of temperature and state of charge on internal resistance of the battery which is needed when calculating the heat rate of single battery are analyzed.The relationship between them are calculated through curve fitting analysisBased on the unsteady heat transfer model of the battery,the numerical model of the square LiFeP04 li-ion single battery is established.According to the fitting formula of the heat rate of the battery and UDF of ANSYS-Fluent which is used to load the heat generation of the battery,the temperature field distribution when the single battery discharges in a constant rate simulated and verified experimentally.AVL-Cruise is used to build a simulation model of a new energy vehicle,and MATLAB/SIMULINK is used to establish the heat generation module of a battery pack.Through the MATLAB DLL interface in Cruise,the vehicle performance simulation under different cycle conditions are conducted.The real-time curve on the state of charge and the electric current of the battery pack as well as the heat generation rate and quantity under driving test cycle are obtained.The model of the power battery pack's liquid cooling system is established by CFD analysis,and the numerical simulations of temperature field and flow field are carried out.Based on the simulation results of the original model,the existing problems are analyzed and the optimization of the cooling system's cooling channel structure is carried out.The temperature field and the flow field of the improved scheme are simulated and evaluated.