Research On SOC Estimate Of Power Battery Based On Multivariable Analysis Method

It brought many negative effects of energy consumptiong and environmental issues with the development of the automotive industry.Developping electric vehicles is a new green transport to decrease the excessive oil consumption and environments issues.The working states of the power batteries are very important to driving safety and operational reliablity of electric vehicles,among which,the reasonable,accurate and rapid assessment of the remaining power is one of the key issues to be solved urgently for new energy vehicles.A timely and accurate understangding of the various operating status,especially the residual State of Charge(SOC)of the battery pack,is one of the key issues to ensure good performance of the battery pack.In this paper,32650 lithium iron phosphate battery is investigated.The main research works of this paper are as follows:First,for a cell battery,the voltage variation characteristics of the power battery at 20?-40 ? with different charging and discharging currents and different aging degrees are analyzed through charging and discharging tests.The corresponding relationships among working voltage,non-charge and discharge stagnated time and balanced electromotive force under various conditions are analyzed.Then,a set of power battery voltage change under different environment parameters is established to provide a set of data base for the power battery SOC evaluation.After that,According to the voltage variations of power batteries under different environmental parameters,the SOC evaluation modes of power batteries are respectively constructed by multivariate model and look-up table method.Experiments show that the SOC evaluation method based on multivariable model has faster speed but lower prediction accuracy.However,the SOC evaluation method based on look-up table method has higher accuracy but slower operation speed.A improved SOC evaluation algorithm based on multivariable model is proposed.By comparing the differences between look-up table method and multivariable model,a correction function is introduced on the basis of the original multivariable model to improve the evaluation accuracy of SOC.Finally,for the power battery pack,the evaluation systems of the cell SOC and the wholeSOC are proposed respectively,and the SOC consistency of the power battery during using is calculated with the standard deviation method.A cell weight index is proposed to evaluate the influence of each cell on the system.In the above theoretical derivation and experimental test,found in different temperature,different power battery charge and discharge current,working voltage and balance under different aging degree of electromotive force difference,the paper proposed according to the phenomenon of power battery SOC evaluation method based on multivariable model and the weight evaluation method of cell battery in the whole system is proposed in this paper.It can provide references for SOC evaluation,system consistency evaluation and system maintenance of power battery packs for new energy vehicles.