Research On Power Battery Pack Model And Temperature Control Based On Large-plate Heat Pipe Coupled With Air-cooled Heat Dissipation

Due to the shortage of fossil fuels such as petroleum and the impact on environmental issues,new energy vehicles have been developed in various countries.At present,new energy vehicles on the market include four types: pure electric vehicles,hybrid electric vehicles,fuel cell electric vehicles and other new energy vehicles.Among them,pure electric vehicles have the advantages of high energy efficiency and zero emissions,and have been rapidly developed in countries around the world in recent years.Compared with lead-acid batteries,nickel-cadmium batteries,and nickel-hydrogen batteries of the same size,lithium-ion batteries have the largest power reserve,the lightest weight,the longest life,the shortest charging time,and no memory effect,making them a new generation with great potential.Secondary battery products.The temperature of the lithium battery is kept at 20℃～45℃,which can exert its best performance.Excessive temperature will affect the capacity of the battery,reduce the service life,and even cause thermal runaway,burning and explosion;and the temperature unevenness will also cause local deformation of the battery pack.At the same time,due to the existence of the internal thermal resistance of the battery,the temperature of the inner core is higher than that of the outer surface,and the temperature of the inner core of the battery is difficult to directly measure,and the risk of thermal runaway is greater.Therefore,it is necessary to monitor and control the temperature of the battery core and ensure the temperature consistency of the battery pack.In this paper,the thermal management of the ternary lithium prismatic battery pack is based on a large flat heat pipe coupled with air-cooled heat dissipation.The main contents are as follows:The first-order RC circuit is used to simulate the discharge characteristics of the battery.The open circuit voltage,ohm internal resistance,and polarization internal resistance are identified through experiments and the least square method to form an equivalent circuit model.The square battery is divided into three parts: the battery core,the bottom surface of the battery and the heat dissipation end of the large flat heat pipe.Considering the heat dissipation process including the internal heat conduction of the battery,the internal heat exchange of the heat pipe and the convection heat dissipation at the heat dissipation end of the heat pipe,the heat balance equation is established,which is a battery pack based on the heat dissipation of the large flat heat pipe Thermal model.Design PTC(electric heating film)heating module,and measure the heat transfer coefficient of large flat heat pipes at different temperatures through experimental methods.The circuit model transfers the calculated heat generation to the thermal model.After the thermal model obtains the heat generation,the battery core and surface temperature are calculated and transferred to the circuit model,so as to determine the parameters in the circuit model and realize the electro-thermal model coupling.A three-dimensional model of battery heat dissipation with high efficiency and high temperature uniformity based on a large flat heat pipe is built.The battery pack is placed on the large flat heat pipe,and the bottom is supplemented by air-cooled heat dissipation.Using the pulse current method(HPPC)to measure the internal resistance of the battery at different temperatures and SOCs,calculate the heat generation of the battery cell according to the Bernardi model,write the heat generation model into UDF and import it into ANSYS-Fluent in the form of the internal heat source of the battery.At the same time,a battery cooling experiment system based on a large flat heat pipe was built to verify the accuracy of the model under different ambient temperatures and different discharge rates.Furthermore,the temperature characteristic values of the battery pack are calculated by simulation under different cooling air temperatures,different cooling air speeds,and different numbers of fins at the radiating end of the large flat heat pipe.The model predictive controller(MPC)of the battery pack based on the heat dissipation of the large flat heat pipe is established.Enter the target core temperature,and control the battery pack temperature near the target temperature by regulating the wind speed at the entrance of the air duct.Combine the CFD model with the electro-thermal coupling model built by Simulink to perform ANSYS-MATLAB joint simulation.Under certain ambient temperature and cooling wind speed,the battery discharge simulation calculation is performed,an appropriate time interval is set,and the calculated battery surface and core temperature are transferred to the MPC.MPC predicts the temperature change of the battery within a certain period of time,calculates the optimal wind speed and feeds it back to ANSYS,and performs online control of the battery temperature in the simulation calculation.The effects of constant wind speed conditions and the use of MPC on battery heat dissipation are compared under different working conditions,and the effect of the model predictive temperature controller is verified.