Research On Consistency Of Sorting Parameters For Lithium-ion Power Batteries

As the core component of pure electric vehicles,lithium-ion power battery packs are composed of hundreds of single cells in series and parallel.The consistency of single cells has a great impact on the cycle life and safety of lithium-ion power battery packs.According to the research status of battery consistency sorting at home and abroad,it is easy to obtain the sorting parameters by the static consistency sorting method of single cells,but it lacks the consideration of the dynamic characteristics of the battery,which makes the battery consistency problem in the use of single cells in groups.It will be highlighted;the single battery dynamic characteristic curve sorting method can indirectly reflect the consistency of the battery parameters such as capacity and internal resistance,but the collected data is large and the processing is complicated,and it is difficult to quickly sort the single battery;comprehensive characteristics The sorting method can obtain single cells with higher consistency,but the sorting process is complicated.Therefore,this thesis proposes a method combining Critic weight multi-parameter sorting and dynamic characteristic curve sorting of series single cells（referred to as comprehensive characteristic sorting method）,to carry out consistent sorting of single cells,in order to solve the problem of sorting batteries used in groups.The difference of the rear battery is prominent and the dynamic characteristic curve of the single battery is difficult to quickly sort,so as to achieve the goal of obtaining high-consistency single cells and improving the sorting efficiency of single cells.The main contents of this thesis are as follows.The total factor sorting method and the Critic weight multi-parameter sorting method are used respectively.The Critic weight multi-parameter sorting method obtains the energy,capacity,open circuit voltage and internal resistance sorting parameter data of the battery through the single battery test equipment;calculate these The weight of the sorting parameters;according to the weight,the comprehensive score of each single cell is calculated;according to the comprehensive score,the single cell is sorted for the first time.Using the average discharge capacity and average internal resistance of the battery as indicators,the sorting effect of the single cell was evaluated.Regardless of whether the sorting results are clustered into 4 categories or 5 categories,compared with the total factor sorting method,the single cells sorted by the Critic weight multi-parameter method have a large average discharge capacity,a small average internal resistance or a small average discharge capacity as a whole,the effect of large mean value of internal resistance,the overall sorting effect is better than the total factor sorting method.On the basis of Critic weighted multi-parameter sorting,considering the influence of battery dynamic characteristics on the consistency of single cells,the dynamic characteristic curve sorting method of series single cells is adopted,and then the single cells are sorted with higher consistency.The dynamic characteristic curve of the series single battery refers to the characteristic curve of the voltage and time of each single battery during the constant current discharge and constant current charging process of the series battery pack.If the single cells are tested individually,the current accuracy of each battery branch of the test equipment will be different,which will bring errors to the dynamic characteristic curve of each single cell.currents are equal.During the discharge and charging process of the series-connected single cells,the final discharge voltage of the single cells,which is the basis for the rapid sorting of battery consistency,is measured;by the intermediate interval method,the single cells with the extreme discharge end voltage are quickly eliminated to discharge the cells.The ratio of the standard deviation of the final voltage to the mean valueδis used to evaluate the consistency of the single cell.The results of the sorting experiment show that compared with theδvalue before using this method,theδvalue of the two groups of single series batteries has been reduced by 2.5%and 4.7%respectively.has been improved.In order to verify the group operation of single cells after consistency sorting,a lithium-ion power battery pack test system was designed and built.The hardware of the system includes main circuit,driving circuit,control circuit and acquisition module,and the software includes main control module,data acquisition and processing module,CAN communication and data display and export module.The system can collect,process,display and store the parameters of single cells and battery packs in real time.When the battery packs are discharged,it can feed back electric energy to the power grid.The single cells that have undergone comprehensive characteristic sorting,Critic weight multi-parameter sorting,and total factor sorting are grouped in series,and compared with the non-sorting group,the battery test experimental system is used to conduct cyclic charge-discharge experiments.Experiments have shown that after 50 cycles of charge and discharge experiments,the battery pack discharge capacity decay rate C_dr of the comprehensive characteristic sorting group is the smallest（2.8%）,and the SOH（State of Health）of the battery is the highest（97.2%）,which verifies the sorting.The method is effective and reliable in improving the parameter consistency sorting of single cells.