| In recent years,with the global warming,energy shortage and environmental pollution issues becoming increasingly prominent,electric vehicles have gradually become the main research hotspot in the automotive industry due to their advantages of low pollution,low noise,high energy efficiency,simple structure,convenient use and maintenance,etc..During the driving of an electric vehicle,the power battery pack will continue to discharge,especially under special conditions such as acceleration and climbing,and the current amplitude will rise rapidly.When the battery pack is in the process of discharging,the internal chemical substances will accumulate a large amount of heat with time,causing the battery temperature to increase,causing the battery capacity to decrease,and the service life to decay.In severe cases,it will cause the battery pack to explode.Therefore,it is necessary to design a reasonable thermal management system to effectively control the temperature of the battery pack,which is of great significance for maintaining the safety and other performance of the battery pack and the efficient and stable operation of the electric vehicle.In this paper,the lithium ion battery is taken as the research object.On the basis of the design of the cooling flow circuit,the battery is dissipated by liquid cooling.At the same time,the lithium ion battery is combined with the heat generation characteristics during the charge and discharge process.The model building method and temperature control algorithm of lithium-ion batteries are studied.The main research contents are as follows:First,the battery heat generation model is established according to the Bernardi heat generation rate model,and then the battery heat dissipation model based on the liquid flow rate in the pipeline and the flow rate and the heat transfer coefficient is established according to Newton's cooling law,and the single cell is established using the law of energy conservation Thermal model.After that,the thermal model of the battery pack is simplified to establish the thermal model of the battery pack in combination with the temperature characteristics of the fluid in the pipe entering the heat dissipating pipe under the liquid cooling method.In AMESim,the simulation model of the battery cooling system was built,the structure of the cooling system was designed and optimized,and the reliability of the battery pack thermal model was verified.The simulation results show that the thermal model of the battery pack can accurately describe the temperature changes in the battery pack.Then a battery temperature control strategy based on Iterative Dynamic Programming(Iterative Dynamic Programming,IDP)algorithm is designed,using liquid flow rate as the control quantity and battery temperature as the state quantity,and a temperature cost function is designed for the influence of temperature on battery performance.Temperature and energy consumption are used as system performance indicators to achieve the goal of controlling battery temperature consistency and minimum energy consumption.At the same time,a PID-based battery temperature controller was designed under the same experimental conditions.Under the selected two cycle conditions of European NEDC standard conditions and Japanese JC08 conditions,iterative dynamic programming algorithm and PID control algorithm were compared.Finally,through the joint simulation of Matlab and AMESim,the liquid cooling system pipeline model,the electric vehicle model and the air conditioning loop system model are built.At the same time,under the selected two cycle conditions of European NEDC standard conditions and Japanese JC08 conditions,the iterative dynamic programming algorithm and PID control strategy were compared and analyzed.The energy consumption and battery temperature control effects of the two were compared and verified.The effectiveness and superiority of the optimal control strategy of iterative dynamic programming are verified. |
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