Research On Lithium-ion Batteries Sorting Method Based On Characteristics Of Charging And Discharging

Due to the increasing environmental pollution and the shortage of oil and othernon-renewable resources, new energy vehicles, especially electric vehicles, will becomeincreasingly popular. The single battery could be used after combining with others togenerate the high power and high capacity which the electric vehicle needs. There are stillsome differences between the combined batteries though the performance parameters ofthem are exactly similar. The difference will increase during the recycling use and eventually,this will lead to failure of the battery pack. Thus, it is necessary to sort out the battery ofsimilar performance and combined them into a battery pack. This will not only improve theoverall performance of the batter pack, but also can reduce material waste. More importantly,this can reduce environmental pollution. Although single parameter separation method,multiple parameter separation method, charge and discharge curve separation method andthe combination of the two methods of separation are applied more in the current, butbecause the sorting basis of single parameter separation method is single, so its defect ismore, do not apply to the electric car battery sorting. Multiple parameter separation methodas the feature of extraction is more than single parameter separation method, the sortingadvantage is obvious, but because of not considering the parameters change in the process ofbattery working, thus has certain defects, can’t present the essential differences among thebatteries. Shan Yi proposed the sorting method of based on charge-discharge curves needs toconsider all separation indexs in every time sorting, and has large amount of calculation. Theseparation method combined the multiple parameters selecting with charge and dischargecurves separation can reflect the dynamic characteristics of battery, but only charge anddischarge curve separation method can put the other parameters characterization of battery,combined with multiple parameter separation method is redundant. Therefore, this paper onthe basis of the existing cell sorting method, proposes a new battery sorting method based onthe charging and discharging characteristics. This paper used lithium-ion battery as the research object, by researching thecharacteristics of lithium-ion battery, concluded that access different current to the battery,the change curves of open circuit voltage Voc, ohm internal resistance R, polarizationresistanceRs andRl, polarization capacityC sandC lalong with state of charge SOCis broadly in line, can ignore its influence, express the open circuit voltage, ohminternal resistance, polarization resistance and, polarization capacity andpresented as to a function of state of charge directly. Then using marquardtalgorithm in integrated optimization software package1st0pt to fit out of the functionrelation of open circuit voltage, ohm internal resistance, polarization resistanceand, polarization capacity and with, then set up battery equivalentcircuit model which used as a link, and can simulate the dynamic characteristics ofbattery accurately. Then establish the simulation model of the equivalent model used thesoftware of MATLAB/Simulink. Finally, according to the equivalent circuit model and itssimulation model which is established, to realize the establishment of the battery packequivalent circuit model and simulation model.In this paper, respectively to extract the open circuit voltage, ohm internalresistance, polarization resistance and, polarization capacity and andstate of charge experimental data of every battery, then use marquardt algorithm inthe integrated optimization software package1st0pt to fit the relationship of each batterybetween the open circuit voltage, ohm internal resistance, polarization resistanceand, polarization capacity and and the charged state of separately, toobtain batteries with different parameters, and then use the simulation model of theequivalent model of monomer battery come to the theory charge-discharge curve of stayingsort battery, to provide object features for battery sorting.The battery sorting problem based on the charging and discharging characteristicsbelongs to the pattern sorting problem, namely the pattern classification problems. Theprocedure of pattern classification of battery sorting is: firstly to extract the characteristics ofthe monomer battery, and then to linear or nonlinear classification of feature space, so as to realize the classification of the battery. Therefore, this thesis through to fuzzy characteristicthe voltage value on the battery charge and discharge curve, to get the fuzzy set of the chargeand discharge curves of the staying sorting battery, and then, on the basis of this collection,based on the similarity measurement method of the battery charge and discharge curve,according to the attributed fuzzy sorting steps to write m file in the MATLAB, to realize theautomatic classifying of cells.This paper used the established battery simulation model to appraise the effect of cellsorting. The research result show that when uses battery pack which is made up the batteriesof sorted by the sorting method based on the charging and discharging characteristics, as thedegree of similarity between monomer battery of battery pack rise, stability and reliability ofthe battery pack will improve corresponding, the number of cells which is worked in the bestcondition is also corresponding increase.