Research On The Modeling And Optimization Of Vehicle System-level Battery Cooling System

At present,lithium-ion battery is the most widely used energy source in electric vehicles.It will aggravate the aging of the battery and bring the risk of thermal runaway when the temperature of Lithium-ion batteries is too high.Therefore,it is necessary to design and develop an effective battery cooling system.To cope with the challenges caused by different driving conditions,ambient temperature,battery status and other external conditions in the process of designing and optimizing the battery cooling system,the vehicle system-level battery cooling system including the power supply system,drive system,car body system,external environment and driving conditions is taken as the research object,and the key technologies such as system design and modeling,evaluation index and analysis,control parameter and optimization are studied.The main research contents are as follows:(1)To achieve the modeling of vehicle system-level battery cooling system,the modular modeling method was used to establish the vehicle system-level battery cooling system representing the Nissan Leaf;The accuracy of the model was verified by comparing the simulation results with the test data of Argonne laboratory;To meet the cooling demand under extreme conditions,the Chiller-based secondary loop liquid cooling scheme for the Nissan Leaf was designed as an optimized scheme;The parameters of key components were determined and the optimized vehicle system-level battery cooling system model was established.The simulation results show that the designed secondary loop liquid cooling scheme can reduce the battery pack temperature by 10 ℃ in 10 min under extreme conditions,meeting the cooling requirements under extreme conditions,and the attenuation capacity of battery is only46% of the original scheme,but the energy consumption is relatively high,which can be further optimized.(2)To reduce the energy consumption of battery cooling system and the attenuation capacity of battery,the factors affecting the energy consumption and the attenuation capacity of battery within a given driving time were analyzed.Through theoretical analysis and simulation verification,it was found that the influencing factors include battery SOC,battery aging degree,ambient temperature,driving conditions and preset battery cooling target temperature,and the influence law was further determined.The system energy consumption can be reduced by setting a higher battery cooling target temperature,but the battery will attenuate more while the energy consumption is reduced.In addition,when setting the battery cooling target temperature,it is necessary to consider the impact of different external initial conditions on energy consumption and battery attenuation capacity.The trade-off between system energy consumption and battery life,as well as the influence of external conditions,brings difficulties to the setting of the cooling target temperature.(3)To achieve the optimization of battery cooling target temperature under different external initial conditions,the energy consumption cost and aging cost caused by battery cooling system energy consumption and battery attenuation capacity was analyzed and quantified from the economic perspective,and the minimum total cost was proposed to optimize the cooling target temperature;The variation of optimal cooling target temperature with driving time was analyzed when the external initial conditions were NEDC conditions,65% initial SOC,8% initial aging and 36 ℃ambient temperature.It is found that the optimal cooling target temperature decreases gradually with driving time and tends to a fixed value.The optimal cooling target temperature under different external initial conditions was obtained and compared:compared to NEDC driving cycle,the optimal cooling target temperature is higher under HFWET and lower under UDDS;compared to 65% initial SOC,the optimal cooling target temperature under 40% is higher and basically the same at 90%;compared to 8% initial aging,16% The optimal cooling target temperature is higher and lower at 4%;relative to the 36℃ ambient temperature,the optimal cooling target temperature is higher at 40℃ and lower at 32℃.According to the simulation results,the variation law of optimal cooling target temperature under different external initial conditions was analyzed,which provides reference guidance for setting the cooling target temperature of battery.