Research On Performance Of Thermal Management System For Power Battery Pack Under All-climate Conditions

Lithium-ion batteries are widely used in electric vehicles due to their high specific energy,low self-discharge rate and long cycle life.Their working performance and life are closely related to ambient temperature.In the low temperature environment,the internal resistance of lithium-ion battery increases and the available capacity decreases.In the charging process,lithium plating is prone to cause irreversible attenuation of battery capacity.In the process of high rate charging,the battery heat production increases,the temperature rise intensifies,the temperature uniformity of the module becomes worse,the performance of the module deteriorates,and the endurance mileage of the electric vehicle is affected.Therefore,it is necessary to carry out thermal management of the battery pack to adapt to the extremely cold and high temperature environment,so as to operate under the whole climate condition.On this basis,the influence of thermal management system on the temperature characteristics of battery pack is further explored to provide reference for the design of thermal management system.In this thesis,the 30 Ah Li Fe PO4 pouch battery was taken as the research object.Firstly,the battery test experimental platform was built,and the related parameters of the battery were tested.According to the theory of battery heat generation and heat transfer,the single battery model was established,and the accuracy of the model was verified by the designed battery charging heat generation experiment.Aiming at the problem that the temperature uniformity of the battery in the external preheating process is poor,the temperature rise of the battery charging process is high and the temperature difference is large,which affects the battery life,an external cooling structure is designed from the perspective of the practical application and economy of the vehicle.Based on the cooling structure,the integrated cooling and preheating system of the battery pack is extended and designed,and the working principle of the thermal management system is expounded.Secondly,in the scheme of preheating the battery module by heating the coolant,the influencing factors of the preheating process are analyzed,and the optimization of the preheating system is carried out from the perspective of improving the temperature distribution uniformity of the module.From the perspective of improving the preheating time,the internal and external combined preheating strategy based on the battery available power is proposed,and the preheating effect of the preheating strategy is verified.Finally,starting from the two influencing factors of coolant flow rate and coolant temperature,the variation law of temperature characteristics of battery pack charging process under the two influencing factors is studied.Based on the above law,the orthogonal simulation scheme of coolant flow rate and temperature is designed to find the control method that meets the requirements of battery pack temperature and temperature difference.Furthermore,according to different cooling objectives,the cooling fluid temperature control strategy is proposed to verify the cooling performance of the control strategy.