Research On Temperature Field Characteristic For Lithium-ion Battery Pack Of Pure Electric Vehicle And Thermal Management System Implementation

In recent years, because the energy crisis and environmental pollution are worsening, allcountries put a lot of energy and money to accelerate the commercialization process of pureelectric vehicles. As the only source of power for electric vehicle, the battery performancedirectly affects the use performance of electric vehicles. Because environmental temperaturehas a significant influence on the performance of the batteries, battery pack thermalmanagement technology, which regards the control of the battery internal temperature rangeand uniformity as the goal, becomes an important research topic. When the battery packwork in the high temperature environment for a long-term, permanent damage that hightemperature does to the battery cannot be restored, the battery life will be drastically reduced.When the batteries temperature reaches a relatively high value, the battery pack will caughtfire. When batteries pack work in low temperatures environment, the battery internalresistance rises sharply as the temperature decreases, available capacity would dropdramatically, and it will result in a short circuit within the battery which leads to accidents.The battery pack thermal management can not only effectively improve the electric car’spower and economy, but also can prevent the occurrence of accidents caused by the batterypack malfunction in the vehicle motion process. This paper designees a battery thermalmanagement system regarding LiFePO4battery for pure electric vehicles as the researchobject, the specific research work is carried out as follows:(1) This paper refers to a large number of documents, analyzes the research status of thebattery thermal management, and identifies the existing problems of battery thermalmanagement system. This paper selects a heat transfer medium and designs structure of thecooling system and heating system for the thermal management according to the actual need.(2) This paper finishes a lot of experimental researches in battery temperature characteristics,analyzes the relationship between temperature and available capacity of the battery pack, theopen circuit voltage (OCV), resistance, longevity and other factors, estimate the battery packthermal physical parameters by designing the experiment, gets the measurement andestimation of the cell the specific heat capacity, thermal conductivity, internal heat rate andother parameters.(3) Firstly, this paper introduces the mechanism of heat energy transfer and conduction, select the research method of thermal field for this papers. This paper establishes athree-dimensional thermal model of the battery cell by using ANSYS simulation softwarestudies the thermal model simulation of the battery cell and verifies the accuracy of themodel by comparing simulation results and experimental values of it. The analysis resultsshow that the model error does not exceed1.5℃, optimizes the design of air flow field in thebattery pack based on the simulation results of simulation.(4) The paper designs the overall framework of battery pack thermal management systemdevelops a battery pack temperature control strategy, designs hardware and software of thethermal management system, writes a display interface by VB software.(5) Finally, the paper verifies the accuracy of the battery pack system simulation model bythe system tests verifies and analyzes the function of the battery box and the temperaturecontrol system, does analysis and experimental study on the thermal management systemenergy consumption under low temperature. The result shows that the temperature at whichbattery pack needs heated.