Investigation On Battery Thermal Management System(BTMS)with Refrigerant-based Direct Cooling

Battery thermal management system in electric vehicles is critical for maintaining energy storage capacity,driving range,battery longevity,and system safety.As a key technology for power battery,the refrigerant-based direct cooling method has received more and more attention for its excellent cooling effect.In this paper,aiming at the thermal management technology with heat pump refrigerant-based direct cooling,the numerical simulation method is used to explore the basic performance of the power battery by direct cooling.An efficient thermal management system not only needs to quickly control the battery temperature within a reasonable range,but also balance the temperature difference between every individual cell.The research work mainly focuses on the highest temperature and temperature difference of the battery module.The bottom cold bank is used as the battery cooling structure,and the flow channel structure,processes number and size are all designed.Besides,in order to improve the temperature uniformity,some graphite sheets with high thermal conductivity are added to the cooling structure.After comparing different layouts and thicknesses of the thermal conductive sheets,determine to arrange these sheets between every two cells and the two sides of battery module.At this time,the highest temperature difference in the entire module can be successfully reduced.Based on the final cooling structure above,the effect characteristics of refrigerant heat flow parameters under different battery discharge rate are simulated and researched.In order to enhance the battery temperature control,a variable parameter grading cooling method is proposed,which uses different cooling intensity to satisfy different cooling requirement of every discharge stage.It can achieve a high temperature response rate of battery module in the initial stage of cooling,and then gradually tends to guarantee temperature uniformity,and maintain the battery temperature in the reasonable range.The simulation example shows that the highest temperature and uniformity of the battery module under 1C discharge condition have a potential to maintain in 20.83? and 1.22?.The power change of electric vehicles usually causes the heat load change of battery pack.For battery load-varying discharge,the typical simple linear condition is chosen as an example to explore the battery basic variation characteristics in order to study more complex dynamic conditions.And a coping strategy that to control refrigerant flow rate and evaporation pressure to linearly vary with time is proposed.The influence of parameter range and changing time on battery temperature behavior is emphasized.The analysis shows that the temperature rise under battery load-varying discharge condition can be effectively suppressed by this adjustment method.The simulation example shows that the temperature fluctuation in each area of the battery cell can be controlled within 1°C when the discharge rate change from 1C to 2C,which ensures the temperature stability of the module during load-varying discharge.The battery thermal management with refrigerant-based direct cooling technology is still at the forefront of application,needing to be explored and applied more extensively.This paper only studies the basic characteristics of evaporative cold bank,refrigerant heat flow parameters and battery dynamic load condition by simulation analysis,which aims to provide some reference for promoting the exploration of power battery direct cooling thermal control scheme in the future.