Thermal Management Analysis And Improvement Design Of A New Energy Commercial Vehicle Power Battery

Recently,with the emphasis on the environment,electric vehicles have developed rapidly.At present,the development of electric vehicles is mainly restricted by battery technology.As the main power source of electric vehicles,lithium batteries have the advantages of high working voltage,high specific energy,long life and no pollution.However,its performance is sensitive to temperature.In the low temperature environment,the chemical reaction rate of the lithium battery decreases,and the capacity of the lithium battery is significantly reduced,resulting in a decrease in the cruising range of the electric vehicle.In the high temperature environment,the internal resistance of the battery rises,and the discharge voltage of the battery decreases,and the battery work efficiency decreases.Even if the temperature is too high,the battery is out of control,resulting in a safety accident.Therefore,reasonable battery thermal management is very important.The main research contents of this paper are as follows:This paper first studies the thermal behavior of the battery during its work,including heat generation,heat conduction,convection heat transfer and heat radiation.Simplified model of the battery was established,the battery was subjected to cyclic charge and discharge temperature rise simulation and experiments.The experimental and simulation results were compared to verify that the battery model has good accuracy.The results show that at room temperature,the battery is fully discharged at a maximum sustainable discharge current(2.5 C)and the finally temperature is 54.74 ?.When the ambient temperature exceeds 11.71 ?,the battery will completely discharge at a current of 2.5 C and will exceed 40 ?.The battery PACK in the original battery box is composed of 98 single cells connected in parallel,adopting natural air cooling thermal management.CFD simulation was performed on the original PACK at 25 ? with a full discharge of 2.5 C current in Fluent,the results show that the maximum temperature of the battery in the original PACK reaches 59.37 ?,and the temperature difference reaches 8.2 ?.The original PACK was improved to a single-channel series liquid-cooled PACK.Under the same working conditions,the maximum temperature of the battery was only 32.61 ?,and the temperature difference was 4.83 ?.The analysis shows that the temperature difference between the cells in the PACK is too large due to the excessive temperature difference between the front and rear coolants in the series channel,and then the PACK is improved into a multi-channel series PACK and a multi-channel parallel PACK.By adjusting the pressure angle of the parallel PACK to 2.0°,the maximum temperature of the battery in the PACK is 27.24 ?,and the temperature difference is less than 0.24 ?.Finally,in combination with the geometry of the battery box,the PACK and coolant lines in the battery box are properly arranged.The coolant flow characteristics of the four battery PACK modules are analyzed,and the temperature field simulation of the PACK with poor flow uniformity in the battery module is verified to verify that the batteries in the PACK meets the temperature requirements,which indirectly proves the rationality of the PACK and liquid line arrangement.