Design And Optimization Of Lithium Battery Thermal Management System Based On Wind And Liquid Combination

To reduce carbon emissions,on September 22,2020,Chinese President Xi Jinping proposed at the 75 th session of the United Nations General Assembly the development goal of "striving to achieve carbon neutrality by 2060".In this context,the development of new energy vehicles has become a key area of national attention.Lithium battery is a widely used power battery for electric vehicles.It is found that lithium batteries have very strict temperature requirements for the working environment,the best working temperature range is20℃-45℃,the safe temperature range-30℃～60℃,if the working temperature exceeds the safe temperature range,it will cause thermal runaway of lithium batteries,and even the risk of battery spontaneous combustion,while the temperature difference between the battery pack will shorten the service life of the battery pack.Therefore,a thermal management system that can control the surface temperature increase of lithium batteries and improve the surface temperature uniformity of lithium batteries is of great interest.At present,the widely used thermal management systems are air-cooled lithium battery thermal management system,liquid-cooled lithium battery thermal management system and phase change material thermal management system.Considering the advantages and defects between different thermal management systems,this paper combines the air-cooled thermal management system with the liquid-cooled lithium battery thermal management system to design an air-liquid combined lithium battery thermal management system.The specific work is as follows.In order to study the improvement effect of thermal management system on the surface temperature and temperature difference of lithium battery,this paper relies on the P2 D heat production model of lithium battery to establish the simulation model of lithium battery single cell heat production,and establishes the physical field model of wind-liquid combined lithium battery thermal management based on this simulation model and conducts simulation analysis.After establishing the physical field of thermal management,it needs to be optimized.In this paper,we use parametric scanning to obtain the relationship between different air flow rate and coolant flow rate on the surface temperature,surface temperature difference and average power consumption of fan pump of Li-battery.The neural network model between air velocity and coolant flow rate and lithium battery surface temperature,lithium battery surface temperature difference,and average power consumption of fan pump is established using BP neural network algorithm,and the model is solved optimally by NSGA-II algorithm.Finally,a set of optimal solution set is found and the optimal air speed and coolant speed are selected for different working conditions.After completing the modeling and optimization of the physical field of air-liquid combined lithium battery thermal management,the physical field needs to be verified experimentally.In this paper,the thermal management experiment platform is built according to the required experimental conditions,and the driver circuit is designed to drive the fan and collect data such as lithium battery surface temperature,lithium battery surface temperature difference,coolant flow rate,fan power consumption,etc.Meanwhile,the Windows-based host computer is designed and developed to record the data.Finally,the surface temperature of the lithium battery,the temperature difference between the surface of the lithium battery and the average power consumption of the fan pump under natural convection,with the addition of air cooling,with the addition of liquid cooling,and with the addition of air-liquid combined cooling are verified in turn through experiments.The experimental results show that the cooling effect under the condition of adding liquid cooling is better than that of adding air cooling,but both air cooling and liquid cooling will increase the surface temperature difference of the lithium battery when the ambient temperature and the charge/discharge multiplier of the lithium battery are high.By adding the optimal air flow rate and coolant flow rate,the combined air-liquid cooling can better improve the surface temperature and temperature difference of the Li-ion battery with lower power consumption at higher ambient temperature and charge/discharge rate.