Research On Cooperative Thermal Management System Of Battery Liquid Cooling And Cabin Air Conditioning

To deal with the dual challenges of energy crisis and environmental pollution,China has invested a lot of human,material and financial resources in the development of electric vehicles in recent years,but the rapid new energy vehicle industrial development has not dispelled people’s worries about driving mileage and battery safety while purchasing electric vehicles.Lithium-ion battery is the first choice of traction battery because of its high energy density.As the only energy storage device of pure electric vehicle,temperature is the key factor which affecting the performance and safety.The ideal working temperature level of lithium-ion battery is relatively low.In order to seek a reliable cold source for the effective thermal management in high temperature environment,the vapor compression refrigeration cycle of electric vehicle provide cooling capacity not only to the air conditioning system of the cabin,but also the traction battery,which makes the overall structure more complex and the control more difficult.This paper aims at the cooperative thermal management system of battery liquid cooling and cabin air conditioning to explore its working characteristics and reasonably and effectively regulate the system.Firstly,in order to determine the real-time and accurate heat production and temperature state of lithium-ion battery,an electrothermal coupling model based on the second-order RC equivalent circuit and lumped thermal parameters is established,and a battery test platform is built.Considering the influence of SOC,discharge current and temperature,a series of experiments are carried out to obtain the parameters of the model and verify the model by the battery discharge temperautre rise experiment.Secondly,a complete physical model including refrigerant cycle,coolant cycle and cabin is established,and the key components are calibrated by steady-state experimental data to ensure the accuracy of the model,which lays the foundation for system performance analysis and system control strategy.Thirdly,the differences between the system and the single cooling VRV system and the dual-evaporator cabin air conditioning system are analyzed.The influence of various factors on the performance of the system is studied through the steady-state simulation,and the control strategy of controlling the compressor speed according to the suction pressure and the variable evaporator air volume flow rate when the cabin and the battery are cooled at the same time is formulated,the effectiveness of the control strategy is verified by dynamic simulation.Finally,in view of the extreme conditions of vehicles soaked in high environmental temperature in summer,the influence of different evaporator air volume flow rate and chiller coolant flow rate on the temperature reduction of battery and cabin is analyzed and compared.The control triggering logic to determine the cooling priority and the control logic to switch the control state of the system according to the decision result are proposed and the corresponding model is established.Through the system simulation at different environmental temperature,the results show that the control strategy can effectively determine the temperature state of battery and cabin,make full use of the system cooling capacity and reasonably adjust the cooling capacity of the system to distribute between the evaporator and chiller according to the corresponding cooling priority,which can make the battery exit the adverse temperature range with the fastest speed,and the temperature drop time of cabin is basically not affected.