Research On Thermal Management Of Electrical Vehicle Power Battery In Extremely Cold Environment

In recent years,the new energy vehicles industry,especially the battery electric vehicle(BEV)industry has developed rapidly around the world.However,in the severe cold region(partial areas with extreme cold climate,such as high altitude areas or high latitude areas),BEV,which equips with conventional thermal management systems,will face problems,such as the failure of charging,the difficult of starting,and the reduction of discharge capacity.These lead the cruising range BEV is greatly shortened or even unable start.If the battery is dispose by heated,it will face the problem of heat accumulation during the battery charging and discharging circle in normal temperature.In this paper,a thermal battery thermal management system of BEV,which can adapt to both cold and normal temperature climate is designed,researched by numerical simulation and experimental.Firstly,nickel-cobalt-manganese ternary material lithium battery(referred to ternary lithium battery)were subjected to discharge experiments under temperature of-35 ～-20°C,and the discharge performance was analyzed.The experimental results show that the batterie has low discharge initial voltage and capacity attenuation.Then,the ternary lithium battery was selected as the main research object,for the specific heat capacity measurement test of the battery cell and its 0.5C,1C,2C discharge temperature rise curve measurement test in the adiabatic environment,and the thermal conductivity measurement test and discharge infrared thermal imaging test were carried out.The thermal properties and discharge characteristics of the battery were fully studied,and experimental data support was provided for subsequent simulation calculations.The heat generation model of the ternary lithium battery cell in the CFD software Fluent,was established by using the experimental data,and the accuracy was verified by the temperature rise curve of the battery cell discharge experiment.The combination of experiment and simulation is used to determine the natural convection coefficient which is closer to the internal thermal environment of the battery pack.Based on this,a heat dissipation structure of battery cells based on composite phase change materials and flow-coupled heat transfer is designed.The effects of various flow rates,and initial temperature of working fluids on heat dissipation are studied through simulation calculation.Two heating schemes based on polyimide metal heating film were designed.The heating efficiency of the two schemes was compared by simulation calculation.It was determined that the better solution would be able to heat the battery cell evenly from-30°C to 10°C in just 600 s.The thermal management system of the battery pack was further designed.The demand for the cooling medium flow under the operating conditions of the battery pack was analyzed.The results showed that the 1.9167 ? 10-4m3/s of required cooling water could control the temperature of the battery pack within 35°C.The automatic preheating cycle system based on BMS control is designed for the low temperature state of the battery.The simulation results show that the system can complete the preheating of the battery within 600 s,and the battery pack can work normal ly within 24 hours of the preheat cycle.