| In the context of energy conservation and emission reduction,the development of new energy vehicles is the key decision to solve the energy crisis and environmental pollution.Lithium ion battery is the power source of electric vehicle.The driving conditions of electric vehicle are complex and changeable.It is very easy to have the situation that the temperature of power battery is too high or the temperature difference is too large.If it is not dissipated in time,it will lead to the decline of battery performance and life,and even lead to safety problems.As an important part of the lithium-ion battery management system,the thermal management part of lithium-ion battery is very important for the temperature control of power battery pack.Therefore,it is of great significance to analyze and optimize the liquid cooling heat dissipation of power battery pack.The purpose of this thesis is to improve the heat dissipation performance of power battery pack,firstly,the temperature characteristics of single battery discharge were studied,secondly a cold plate heat dissipation structure of series and parallel channels was designed for the power battery pack,the method of computational fluid dynamics was used to simulate and analyze the liquid-cooled power battery pack,and the method of multi-objective genetic optimization was used to find the optimal cooling mode of the power battery pack,finally,the optimization model of liquid cooling power battery pack is simulated and analyzed under typical working conditions,and the effects of coolant inlet flow and temperature on heat dissipation are studied.The specific research contents are as follows:(1)Firstly,selecting LP2714897 square lithium iron phosphate battery as the research object,and the discharge temperature rise test of single cell was carried out under the conditions of ambient temperature of 27 ℃ and constant current discharge at 1C and2 C rates.Secondly,based on the Bernardi thermogenic rate model,the thermogenic rate of lithium batteries at different discharge rates,and the simulation property parameters are obtained.Finally,CFD simulation analysis of temperature field was conducted on the simplified thermal effect model of single battery,and the accuracy of simulation model and simulation parameters of single battery was verified by comparing simulation and experimental results.(2)A reasonable liquid cold plate model of the power battery pack was preliminarily designed,and series and parallel channels were arranged in the cold plate.Thermal simulation analysis was carried out for the liquid-cooled power battery pack under constant discharge current conditions of 0.5C,1C,1.5C and 2C rate respectively.The results show that the coolant velocity distribution is more uniform when the power battery pack is constantly discharging at a high rate of 2C,the maximum temperature and maximum temperature difference of the power battery pack exceed the target value,and the cooling structure needs to be improved.The CFD thermal simulation analysis of the improved liquid-cooled power battery pack was carried out.The results show that the maximum temperature of the improved power battery pack is 38.78℃,the maximum temperature difference is 3.64℃,and the pressure drop of the inlet and outlet of the pipeline is small,which meets the design requirements.(3)Under the condition of 2C rate discharge,the agent model is constructed based on the experimental design.The multi-objective optimization of the improved liquid cooling battery model is carried out to find the best cooling mode.Comparing the optimized results of temperature difference and pressure drop with the CFD simulation results,the errors are 2.4% and 4.1%,respectively,indicating the accuracy of the optimization method.Compared with the improved liquid-cooled battery pack model,the temperature difference of the battery pack decreases by 4.9% and the inlet and outlet pressure drop of the pipeline increases by 8.5% under the condition that the flow rate decreases by 40%,the width of the series channel increases by 26.7% and the width of the parallel channel decreases by 60%.Using the method of data mining to explore the relationship between design variables and optimization objectives,it is concluded that the coolant flow,the width of series channel and parallel channel can not be ignored in the process of design and optimization.(4)The one-dimensional temperature simulation of single cell is carried out,and the experimental data are compared to verify the accuracy of parameter setting and simulation results;Building the vehicle power model and the optimization model of liquid cooling power battery pack.The power battery pack is discharged at the rate of 0.5C ～ 1C most of the time.Compared with NEDC working condition,the average output current of power battery pack under WLTC working condition is greater;The heat dissipation simulation analysis of liquid-cooled power battery pack under WLTC condition shows that the maximum temperature and temperature difference of the power battery pack meet the requirements.Under the condition of high temperature of 40 ℃,the effects of coolant inlet flow and temperature on the heat dissipation of liquid cooled power battery pack are studied,and the results show that increasing the coolant inlet flow can effectively reduce the maximum temperature of battery pack,when the coolant flow increases to a certain value,the decrease range of the maximum temperature of battery pack decreases;The maximum temperature of the power battery pack increases gradually with the increase of the coolant inlet temperature,and the increase range is larger and larger.In this paper,the cooling and heat dissipation of the power battery pack is studied by using the liquid cooling method,the liquid cooling structure of the series and parallel channels of the power battery pack is designed,and the simulation analysis and optimization of the liquid-cooled power battery pack is conducted by using computational fluid mechanics and multi-objective genetic optimization methods.Multi-objective optimization is rarely used in the field of battery thermal management,the application of multi-objective genetic optimization method in the liquid cooling design and optimization of power battery pack can weigh the relationship between multiple objectives and improve the efficiency of simulation development,so as to obtain the best cooling mode,the research method and content have reference significance for the design and optimization of heat dissipation and liquid cooling structure of power battery pack. |
PDF Full Text Request