Research On Thermal Characteristics Of Power Battery Pack For Electric Vehicle Based On Air Cooling

With the rapid development of society,the problems of energy shortage and environmental pollution are becoming more and more serious.Excessive use of fossil fuels produces large amounts of greenhouse gases,which lead to global climate change.The electric car have the advantages of little environmental pollution,low noise,high energy efficiency,simple structure,easy to use and maintain.Therefore,more and more people pay attention to it.The power battery pack is the power source of the electric car,it provides power for the vehicle when driving.It directly determines the performance and reliability of new energy vehicles,and plays a key role in safety performance and use cost.When the car is running under different working conditions,the battery temperature will gradually increase due to exothermic reaction and internal resistance.When the temperature exceeds a certain threshold,lithium-ion batteries will suffer irreversible damage.This will reduce battery performance,shorten service life.When the battery heat continues to accumulate and reaches a limit,it will cause a fire and explosion.In addition,when lithium batteries work for a long time at low temperature,the battery life will be shortened,vehicle performance will decline.In the extreme low temperature environment,new energy vehicles can not even start.Therefore,it is necessary to study the thermal characteristics of the electric vehicle’s power battery.The topic of this paper is based on the actual application demand of electric vehicle power battery pack.Based on the main technical parameters of a certain type of automobile,the idea of modularized power battery pack is put forward.This paper constructs the battery pack,and designs the heat dissipation structure and preheating structure for it.The main factors affecting the heat dissipation and heating effect are analyzed by establishing the 3d model and simulation.The structure parameters are optimized with the simulation results.The main contents of this paper are as follows:1.Firstly,the advantages and disadvantages of lead-acid battery,Ni-MH battery and lithium battery are analyzed,and the battery pack is decided to be constructed with lithium iron phosphate battery.Then the internal structure of lithium iron phosphate battery was studied.The working principle,heat generation mechanism and heat transfer characteristics of battery charging and discharging process were analyzed.Finally,the thermal property parameters such as heat generation rate,thermal conductivity and specific heat capacity of single battery were calculated,which provides theoretical basis for the simulation calculation in the following chapters.2.According to the main parameters of the vehicle,the main parameters of the battery pack are determined and the battery pack is preliminarily constructed.The main work is to selected the type of single battery,calculated the number of single battery,determined the number of battery modules and battery placement.In order to overcome the shortcomings of integrated battery pack,the idea of modular battery pack is put forward.In order to improve the temperature uniformity of the battery pack,the air duct with uniform air hole is arranged in the battery box,and the initial heat dissipation structure of the battery pack is designed.3.The geometric model of the initial heat dissipation structure is established and the simulation calculation is carried out.The influence of the number of air outlets,the position of air outlets and the position of air holes on the heat dissipation performance of the battery was analyzed.On this basis,the heat dissipation structure is optimized and its effectiveness is verified under three typical working conditions.4.The preheating structure of the battery pack is designed,and the electric heating film is used to heat the battery in low temperature environment.The initial preheating scheme was proposed,and the influence of the installation position and the area of the electric heating film on the preheating effect of the battery was analyzed.The structure parameters are optimized and the final low temperature preheating structure is determined.