| As an irreplaceable power source in electric vehicles,lithium-ion battery has been widely used in the field of electric vehicles due to its high energy density,many cycles and no memory effect.However,lithium-ion battery has great temperature sensitivity,and too high temperature will threaten the driving safety of electric vehicles,so it is imperative to carry out thermal management on the battery.In this dissertation,the thermal characteristics of 18650 power lithium-ion battery and the air cooling and thermal management of lithium-ion battery pack are analyzed.First of all,according to the working principle and heat generation principle of lithium-ion battery,the thermal characteristic parameters of the battery unit are defined.Through the built thermal characteristic test platform,the charge discharge capacitance experiments at 0 ?-50 ? ambient temperature,the internal resistance experiments at20 ?-50 ? and the temperature rise experiments at different discharge rates at 20 ?are carried out.The experimental results show that: with the increase of ambient temperature,the discharge capacity and time gradually increase,the constant current charging time and capacity gradually increase,and the constant voltage charging time and capacity gradually decrease;the total charging capacity changes little with temperature,and the total charging time decreases with the increase of temperature.When SOC is less than 0.2,the internal resistance increases sharply.With the increase of discharge rate,the maximum temperature and temperature difference on the cell surface increase significantly.Then,the monomer model is established in Icepak software,and the power curve is input to simulate the thermal characteristic temperature field of the monomer at 1 C,1.5 C and 2 C discharge rate at 20 ?,and the simulation results are basically consistent with the experimental results,which verifies the accuracy of the simulation model.Then,the air-cooled heat dissipation method with filter plate is proposed,and the influence of the free area ratio of the three parts of the filter plate on the air-cooled heat dissipation effect is studied.The best free area ratio combination is 0.3,0.9 and 0.9.And through the single factor analysis method to study the influence of wind speed,battery spacing,the number of air outlets and the distance between the bottom of the battery on the air cooling heat dissipation effect.Finally,four factors and three levels orthogonal experiment was designed and compared with the intuitive analysis results of the maximum temperature and temperature difference,and the best combination of heat dissipation effect was obtained.Compared with before optimization,the maximum temperature is reduced by 10.1767 ?,the temperature difference is reduced by10.4750 ?,and the temperature consistency of the battery pack is greatly improved.Finally,according to the application scenario of small electric logistics vehicle,an experimental platform is built for a battery module of its power battery pack,and the forced air cooling temperature rise experiment of the battery pack is carried out.The results show that the battery temperature meets the normal working temperature range,which indicates that the air duct has good heat dissipation effect.Under the working condition of 40 ? discharge rate of 1 C,the heat dissipation effect of two kinds of air duct structures,i.e.upper inlet and lower outlet and left inlet and right outlet,is studied.The optimal results of the two structures are obtained by orthogonal experiment and single factor analysis.It is proved that the optimal results meet the normal working temperature range of the battery,and the heat dissipation effect is good. |
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