Thermal Design Of Lithium-Ion Batteries For Unmanned Aerial Vehicles

In recent years,with the development of new energy technology,electric-powered unmanned aerial vehicles(UAVs)become a research focus in the field of UAVs.Due to high specific energy density and high power density,long cycle life,lithium ion batteries have been widely used in micro electric-powered UAVs.Power demand of the UAV in conditions such as take-off,working and landing is high,so lithium ion batteries should discharge at a higher rate releasing large amount of heat.High temperature will seriously affect battery's performance,life and safety.At the same time,the UAV have compact and performance sensitive to weight and energy.Commonly used fan cooling,water cooling methods can't be applied directly.To improve the stability of the UAVs,it is necessary to design special thermal management system for lithium ion batteries of UAVs.This thesis proposes a battery cooling method,which contains two heat pipes and three copper sheets.Heat is transferred by high heat conduction heat pipe to the large area fuselage,where heat can be absorbed by the heat capacity of the fuselage.A commercial micro electric-powered four-rotor unmanned aerial vehicle is used as the design sample.The systemic thermal design consists of three aspects: heat parameter measurement,thermal design and simulation optimization.Accurate thermal parameters are the basis of the thermal design and precise simulation.Because of the complicated eat and heat transfer process in lithium ion batteries,appropriate simplified models are adopted,that is,the equivalent heat production rate and the equivalent heat transfer parameters.Then,method of combining experiment and parameter fitting is used for the parameters measurement.At last evaluate the accuracy of the parameters.Based on the thermal parameters obtained from the measurement,the lithium ion battery cooling system thermal model is established.For the heat dissipation structure,the following three aspects are mainly studied.(1)The cooling performance of 1C,3C,5C discharge working conditions.The results show that the cooling system can significantly reduce the battery temperature,among which the highest temperature at 3 C rate,most similar to the actual working condition of battery,is no more than 45 ?.(2)The fuselage materials' thermal conductivity effect on the heat dissipation.The results show that even though the fuselage materials have low thermal conductivity,the fuselage with large heat capacity can still absorb heat and achieve good cooling effect.(3)Heat dissipation effect of copper sheets.The results show that the copper sheets can reduce the thermal resistance between heat pipes and the fuselage or battery,playing a key role for heat dissipation.Based on the established model,structure optimization is conducted.After sensitivity analysis,5 copper sheets geometry sizes are selected as the design variables,overall quality of cooling structure and maximum temperature of battery as objective function.Then the response surface method agent model is built.Genetic algorithm is used to solve double objective optimization problem.It turns out that the 108 g weight of the cooling system can make the lithium ion battery temperature no more than 40 ?.