Heat Transfer Analysis And Control Method Research On Liquid Cooling System For Power Battery Pack

The problem of power and environment is increasing intensification,EV is an important method to solve these problems.Battery is only power for EV,it's an important factor to influence EV development.The performance of battery is easily influence by temperature.The higher temperature will cause problem of safety and lifetime.The lower temperature will influence battery efficiency of charge and discharge.The temperature inconformity will cause the performance inconformity among batteries.So battery thermal management system is essential for EV's safety,performance and lifetime.Combining with the National Science Foundation project “Extreme load estimation and intelligent extrapolation optimization of hybrid engineering vehicle in whole working condition”(No.51375202),The research and analysis of battery temperature characteristics,temperature uniformity,battery cooling system control strategy is done.It heat transfer characteristics and temperature distribution characteristics is analyzed by CFD simulation.And the cooling method of high temperature is studied.The battery thermal management system control strategy is built based on different ambient temperature.The main research contents of this paper are listed as following:(1)The battery heat production model is built and thermophysical parameters is computed.It's foundation for CFD simulation.(2)The liquid cooling BTMS is built with 15 batteries.Battery heat transfer characteristics is analyzed by CFD software Fluent.It includes the influence of inlet flow rate and temperature.The contact thermal resistance between battery and cold plate is studied.Contact thermal resistance causes battery temperature higher.The influence is more significant with increasing of heat production.The cooling rate and temperature of the battery with higher initial temperature are influenced by contact thermal resistance.(3)The battery surface temperature inconformity is analyzed and the optimized methods are proposed.Inlet rate,location of inlet and outlet,high thermal conductivity materials,coldplate material have influence for battery surface temperature uniformity.The cold plate material focus on thermophysical parameters.Conductivity is have important influence for battery surface temperature uniformity.And density and thermal capacity almost no influence for battery surface temperature uniformity.(4)The extreme high battery temperature cooling is analyzed.The lower inlet temperature could increase rate of cooling.But it cause big temperature difference in battery module.So,the step cooling method is proposed to increase cooling rate and decrease temperature difference.The every step of temperature difference and the step time is select by orthogonal experiment.(5)After the CFD simulation,the battery cooling circulation is built by AMESim.The battery number,motor parameters and cooling system parameters are computed.The BTMS control method is proposed.It focus on temperature difference between battery and ambient,coolant rate,ambient temperature,coolant temperature and the target temperature of air condition.Different ambient temperature and circulation work condition are analyze by one dimension simulation.