Research On Thermal Mariagement Of New Energy Vehicle Power Battery Based On Refrigerant-cooled System

For the cooling method of power battery,the air cooling scheme which is commonly used is difficult to satisfy the heat dissipation when the battery pack is in the condition of high temperature and high rate discharge.In order to achieve the goal of safe use of batteries,the development of an effective battery thermal management system for electric vehicles has attracted more and more attention in the industry.In this paper,the characteristics of charging and discharging temperature,discharging efficiency and discharging capacity of power battery were analyzed.Based on GT-SUITE software,the simulation model of refrigerant-cooled thermal management system of pure electric vehicle power battery was established,and the thermal management performance and system performance law of cooling scheme of single/double thermal expansion valve system were studied.By using the battery pack and cabin collaborative thermal management model based on the vehicle power system,the influence factors of the vehicle thermal management system under the driving condition of NEDC were simulated to provide support for the optimization of the EV thermal management system.The main research results and conclusions are as follows:(1)The thermal management performance of single/double thermal expansion valve system cooling scheme was studied.When the battery temperature drops from 30? to 25?,the cooling time of the dual thermal expansion valve scheme is 67.01% less than that of the single thermal expansion valve scheme.In one cycle,the average power consumption of single valve scheme is 0.55 kw,and that of double valve scheme is 0.92 kw,which increases by 67.27% compared with the former.In the same cycle,the average refrigerating efficiency of the single/double valve scheme was 4.48 and 4.38,respectively,the latter was only 2.23% lower,and the difference between the two schemes was not significant.If the system is running for a long time,the dual-valve scheme has the advantage in battery cooling rate,which is more conducive to the safe operation of the battery pack.(2)The influence of ambient temperature on the performance of double thermal expansion valve refrigerant-cooled system was studied.The ambient temperature is 30?,35? and 40?,respectively.When the car is running at a constant speed,the cooling time of the battery pack to the set temperature increases with the increase of the ambient temperature.For each 5? increase in temperature,the cooling time increases by 68.75% and 53.70%,respectively.The power of the system compressor is periodic pulse,and the power and power consumption are high when the battery pack is cooled.In a pulse cycle,both the power peak and power consumption increase with the increase of ambient temperature,and the increase increases with the increase of temperature.The average increase of unit temperature in the former is 21.06%,and the average increase of unit temperature in the latter is 25.75%.The COP of the system's refrigeration efficiency changes periodically.In one cycle,the refrigeration efficiency decreases with the increase of the ambient temperature,and the decrease decreases with the increase of the temperature,with an average decrease of 15.11%.Ambient temperature changes have different effects on battery pack temperature,compressor power and COP.(3)The influence law of speed change on the performance of double thermal expansion valve refrigerant-cooled system was studied.The vehicle speed is respectively 40km/h,80km/h and 120km/h under three different gradient states: when the ambient temperature is constant,the battery cooling time of the vehicle under the operating condition of 120km/h is relatively long,and the battery temperature rises rapidly.The temperature rise rate under this operating condition reaches 0.441 ?/min.The change of peak power of the compressor is not affected by the speed,but its power consumption is greatly affected by the speed.The simulation shows that the power consumption of the compressor is the smallest when the speed is 80km/h,which is 27.73% lower than that of 40km/h and 16.75% lower than that of 120km/h.In a short period of time,the influence of COP on speed is low,and the performance of COP under the operating condition of 40km/h is higher,5.01% and 27.35% higher than that of 80km/h and 120km/h,respectively.(4)The performance law of double thermal expansion valve cooperative thermal management system in NEDC vehicle running condition was studied.Under working conditions in urban areas,the battery time decreases to 25? and increases with the increase of ambient temperature.In the range of 30?40?,the unit(5?)temperature rise time increases by 59.06 % and 45.72 % respectively.The temperature rise rate of battery pack in suburban working condition is faster than that in urban working condition,and the maximum temperature in suburban working condition reaches 43.61?.Due to the influence of the ambient temperature,the actual temperature and the preset temperature will produce a certain error,and the corresponding steady-state error is within 1?.The compressor speed is higher when the cabin and battery are cooled at the same time than when the cabin is cooled alone,which increases by 211.17%.Compressor power is less affected by ambient temperature and more affected by vehicle speed.When the battery pack cooling system is turned on,the flow of evaporator refrigerant in the cabin will increase,resulting in a brief drop of about 0.2? in the cabin temperature.The heat exchange of battery pack in suburban working condition was large,and the refrigerant flow rate increased by 13.83% when the ambient temperature increased.The peak heat exchange will decrease by 7.40%.The temperature difference between the heat exchanger of the battery and the inlet and outlet of the evaporator in the cabin decreases with the increase of the ambient temperature.