| As one of the core technologies of electric vehicles,the safety,specific energy,specific capacity,cycle life,charging and discharging of batteries play an important role in determining the performance of battery modules and battery systems and affecting service life,driving performance and safety of electric vehicles.During charging and discharging,most of the energy is consumed to drive the load,and the other energy is transformed to heat.If the heat couldn't be dissipated in time,the safety of battery system would be directly threatened.Therefore,the thermal management of battery system should be solved.Generally,all main heat sources must be taken into account during design stage of battery thermal management system.Not only battery cells but also busbars connecting batteries are the source of heat.Based on the multi-physical field coupling calculation method,the heating characteristics of lithium battery modules and busbars,forced air-cooling design and liquid-cooling design are simulated and experimentally investigated in this dissertation.The main research contents are as follows:(1)In order to quickly and accurately estimate the heating power of the battery system,quantitatively evaluate the thermal characteristics and performance of power batteries,a new parameter "Battery Heat Dissipation Rate(BHDR)" is proposed.Heating characteristics of lithium iron phosphate battery(LFP),lithium titanate battery(LTO),nickel-cobalt-manganese ternary lithium battery(NCM),lithium manganate battery(LMO),and nickel-metal hydride battery(NiMH)are tested by Accelerating Rate Calorimeter(ARC)under specific working conditions,the effects of chemical system,discharge rate,initial temperature,charge and discharge process and state of charge on the heating performance of the battery module are investigated.The safety,specific energy,specific capacity,and cycle life of a battery system not only depend on the performance of a single battery,but also on the consistency of all batteries.Based on experimental test data of a batch of soft-package lithium and mathematical statistics method,the influence of temperature and state of charge(SOC)on battery capacity,DC internal resistance and open circuit voltage was analyzed.It is revealed that BHDR of LFP,NCM,LMO was less than 5%,and the BHDR of NiMH was between 5%-10% during low-rate discharge(<1C).(2)In designing thermal management system of parallel battery module,it is uncertain whether the influence of the heat of the busbar on the battery should be considered.In view of these problems,thermoelectric coupling numerical calculation and experimental methods are conducted to study the heating characteristics and current balance of the busbar from structural design,welding location,operating conditions and current distribution.The interaction between busbar heating and battery heating under different discharge rates,I/O modes,contact areas and I/O positions is studied by building the connection relationship between the busbar and the battery using thermoelectric coupling numerical calculation method.The effects of parameters on the temperature field and current density of the battery module is also studied.Test results show that the temperature rising error between experimental test and the numerical simulation was within 5%.(3)The cooling unit of lithium battery is used for research,the effect of heat dissipation fins,the air duct inclination angle,the air duct height and the air flow on the cooling effect of the battery system and the uniformity of the battery temperature are explored by CFD.An experimental platform is set up acc ording to a certain wind channel design parameter.In order to ensure the accuracy of numerical calculation,the charging and discharging current data under the operating condition of the automobile are input,the multi-function battery charging and discharging test system are used to test the battery pack.It is shown that it is feasible to use air-cooling heat dissipation when the battery heat dissipation rate is less than 2% and the battery system energy is less than 20 kWh.(4)In order to solve the problem of high temperature and temperature consistency in large-capacity battery system which could be a difficulty in traditional air cooling,CFD method was adopted in studying the heat dissipation performance,temperature distribution and energy consumption of three typical liquid flow channels.Firstly,the effects of flow of parallel channels are investigated.The differences and causes of heat dissipation performance of flow paths under low flow rate were compared and analyzed.Secondly,the influence of the design parameters on the heat dissipation performance of center rotary flow channels was studied,and the influence of the enhanced heat transfer structure on the liquid cooling plate were analyzed.Finally,in order to obtain a better compromise among heat dissipation performance,uniform temperature distribution and energy consumption,the effect of enhanced heat transfer structure on the flow path of liquid cooling plate and the effect of exchange inlet and outlet on the comprehensive performance of liquid cooling unit were studied.In this paper,an evaluation index of "battery heating dissipation rate" was proposed to quantitatively evaluate the heating characteristics and performance of power batteries.An anisotropic three-dimensional equivalent thermoelectric coupling model of the battery pack was established and the interaction between the module busbar and the battery heating was researched.Combining with the battery heat dissipation rate,air cooling capacity was quantitatively evaluated.Three-dimensional models of typical liquid-cooling channels were established.The influence factors of heat dissipation,average temperature,and energy consumption characteristics were studied to provide theoretical support for the design of a liquid-cooling system. |
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