| At present,with the attention paid to energy and environment,pure electric vehicles have become the focus of the development of various countries.Due to the advantages of zero fuel consumption,no pollution and low noise,pure electric vehicles are gradually replacing traditional fuel vehicles.As the power source of electric vehicles,lithium battery is often used as the power battery of new energy vehicles because of its high energy density,high safety characteristics and long cycle life.The performance of lithium battery determines the vehicle safety,range and service life.However,there are still many security problems in use.In the running process of electric vehicles,the complex road conditions make the discharge rate of the battery in a dynamic change.In long-time climbing and other working conditions,the battery continues to discharge at a large rate,which will cause heat accumulation,resulting in a sharp rise in the battery temperature and an increase in the temperature difference of the battery pack.Beyond the safe working range,the service life and capacity of the battery will be affected,in severe cases,thermal runaway occurs.The appropriate temperature range can effectively play the performance of the battery,which is of great significance for the safety performance of the vehicle.Therefore,it is very necessary to design an effective battery thermal management and cooling system.In this paper,the efficient heat dissipation of lithium-ion battery pack is analyzed,including the following aspects:(1)The structure and working principle of lithium-ion battery were summarized,and the reasons of thermal runaway were pointed out.The internal heat generation mechanism and heat transfer characteristics of lithium-ion battery were summarized.(2)The heat generation characteristics of single lithium-ion battery are simulated and verified,and the error is within 1~oC.At the same time,the heat dissipation structure of the microchannel liquid cooling plate of the battery pack was explored,and the simulation analysis and optimization of the liquid cooling plate were carried out by changing Re,the inlet temperature of the coolant,the length width ratio of the microchannel channel section and the position of the coolant inlet and outlet.(3)The dynamic model of pure electric vehicle is built by using Matlab/Advisor simulation platform,and the limit current value of the vehicle under four typical working conditions is obtained.It is found that the current value under four working conditions is less than the 2C rate discharge current of the battery pack,which provides a numerical basis for the liquid cooling simulation of the battery pack thermal management system.(4)The liquid cooling system of battery pack was studied by limiting discharge rate under dynamic condition.The liquid cooling plate adopted S-shaped structure with single inlet and single outlet.The maximum temperature and temperature difference of battery pack were analyzed by changing the inlet flow rate of coolant,temperature of coolant and type of heat exchange medium,at the end of discharge,the maximum temperature of the battery pack is close to 60~oC.The simulation analysis of the battery pack is carried out by introducing the single in and single out microchannel liquid cooling plate cooling system.The results show that when the ambient temperature is 25~oC and the inlet flow rate is0.09m/s,the maximum temperature of the battery pack is not more than 40~oC,and the maximum temperature difference of the battery pack is 7.25~oC at the end of discharge,it is within the safe working range of 10~oC. |
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