| There is a problem of electric-thermal inconsistency which can not be neglected in battery module and battery pack,which has influence on battery charge and discharge efficiency,usable capacity,service life and safety.The electric-thermal inconsistency of the battery is caused by many reasons,the existing research mainly concentrates on the difference of the batteries' performance caused by the production process,the battery self-discharge during the long period of use and the uneven thermal environment of the battery pack,and the inconsistency of charge-discharge depth.In fact,in the process of long-term use,the large number of electrical contacts inside the battery pack are affected by the initial assembly condition,the vehicle vibration condition and the environment corrosion aging,the contact resistance value is different,which affects the current distribution in the battery pack,and is also an important factor that causes the battery inconsistency.Even the loose faults of individual electrical contacts can cause a lot of heat in the interface,and there is a hidden danger of heat out of control.On the basis of considering the difference of battery electric connection,combining the theory of electric contact,battery outer characteristic and battery heat generation,this paper puts forward a set of numerical method system to study the problem of inconsistent battery electrical connection of vehicle battery,analyzes the coupling effect of inconsistent electrical connection on the battery-thermal performance,and takes a certain lithium ion battery as the research object,researches are carried out from two aspects of parallel battery module and series battery module.Firstly,from three aspects of electric connection type,electric contact characteristic and battery working principle,the mechanism of electric connection heat generation and battery heat generation is expounded,and the external characteristics of battery are explained and evaluated.Secondly,the battery performance test platform is built,the initial capacity of the cell,the Ohm resistance,the polarization resistance and the balance potential parameters are identified and fitted by the parameter identification test of the cell,and based on these parameters,the Simulink and Simscape tools are used to build the external characteristic simulation model of the battery,The thermal model with electric contact heat source and the internal heat source of the cell is built.The internal and external heat generation of the battery module is calculated,and the UDF and Profile are written on the Fluent soft platform to realize the loading of the time-varying heat generation rate and time-varying boundary conditions,the temperature field of the battery is solved based on the thermal equilibrium equation.Three groups of contact resistance are designed,respectively,the parallel and series battery modules are analyzed,the influence of different contact resistance size on the module and the influence of the difference of contact resistance in the cells are investigated.The results show that the external characteristic model with electric contact and the thermal model with time-varying multiple heat sources can reflect the inconsistency of electric-thermal state of the battery module caused by the inconsistency of electric connection.In the case of high and low SOC,the electric-thermal parameters of the cells will fluctuate violently,in order to ensure the accuracy of SOC estimation,the maximum contact resistance of each electric connection at 3C discharge can not exceed 30% of the ohmic resistance of the cells.The electric connection acts on the temperature distribution of the parallel module through the heat generation of the contact and the current distribution,and the temperature difference of each cell is small when it is in series. |
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