Research On The Diagnosis Methods For Gearbox Based On Multivaraite Signals Analysis

The low temperature performance deterioration of lithium-ion batteries with graphite negative electrode has severely affected the diffusion of electric vehicles in cold areas.To improve the cell low-temperature performance,preheating it to a life-friendly temperature before charging or using is an applicable and effective strategy,when without changing the existing cell material.Among the various preheating methods,alternating current preheating(ACP)has attracted a wide attention due to its high preheating efficiency and uniform temperature distribution in the signal cell.However,most of previous studies on ACP mainly focused on the single cell,and the work,implementing the ACP on the cell module,is relatively few.When extending the ACP to the scenario of cell module from that of single cell,some problems exist as follows:Regarding the method development at the cell level,the ACP method using square wave alternating current(SWAC)has high applicability and energy efficiency,yet related studies is a few,and lacks the guidance on how to set the control parameter to achieve minimal life degradation;Regarding the application of ACP at module/pack level,the cellto-cell variations(CtCVs)have a significant effect on the difference of the cell temperature and the difference of the cell lithium plating condition.However,the existing studies have not involved in these issues.Considering the existing problems above,this paper systematically studies the method development of ACP using SWAC at the cell level,and explores how to suppress the effect of CtCVs on the difference of the cells’ temperature and the difference of the cells’ lithium plating condition at the module/pack level.Firstly,a rapid and lossless square wave preheating method,capable of heating up the cell in short time and with minimal life degradation,is developed at the cell level.Based on the limitations in terms of anode potential and terminal voltage,the current constraints of preventing lithium plating and other side reactions are proposed.According to the measurement results of electrochemical impedance spectroscopy(EIS),the maximum permissible current usage boundaries at different temperatures(each boundary is composed of current amplitude and frequency)are obtained.By comparing these two kinds of usage boundaries,the applicable range of frequency of the two constraints is determined,and the usage boundaries in terms of maximum permissible current are provided at different temperatures by simultaneously considering the lithium plating prevention and the side reactions prevention.Besides,according to the usage boundary in terms of maximum permissible current,a temperature adaptive preheating procedure for square wave preheating is developed.In addition,by comparing the low temperature impedance of the positive electrode and the negative electrode,a strategy of engineering implementation of using the full cell impedance instead of the negative electrode impedance is proposed to eliminate the requirement of the reference electrode during parameters acquisition.Through comparing the preheating performance of implementing different strategies,the alternative strategy is proved feasible.Secondly,a methodology to suppress the effect of CtCVs on the temperature difference(△T)among cells is developed at the cell pack level.By applying phase plane analysis,the temperature evolution of the cells in both series and parallel configuration is explored in the simplified scenario,and the type of portrait with △T=0℃ is acquired.By utilizing bifurcation analysis,the feasible region of control parameters with △T=0℃(also named non-bifurcation region)is obtained.The influential factors,including the frequency,acceptable △ T,target temperature and preheating time,on the feasible region are examined,in addition to providing the corresponding feasible regions of control parameters,which are capable of meeting the requirements of different targets.Besides,the mathematical constant to obtain the feasible regions of control parameters are introduced for the module with more cells in parallel,thereby establishing a methodology of suppressing the influence of CtCVs on △T among cells.Thirdly,utilizing the aforementioned methodology of suppressing the influence of CtCVs on △T among cells,the temperature evolution of the cells in both series and parallel configuration is explored in complex scenario of considering more CtCVs,the corresponding feasible regions of control parameters and the structure optimization strategies to suppress the effect of CtCVs are obtained,thereby providing some theoretical guidances in both thermal design and thermal management for improving the temperature uniformity among cells.Finally,a mathematical method to suppress the influence of CtCVs on the difference of the cells’ lithium plating condition is proposed at the cell pack level.Through statistical analysis and dimensionless comparison of CtCVs related to the lithium plating,it is found that the level of CtCVs in terms of the negative electrode impedance is more significant than that of negative electrode equilibrium potential after aging of the cells,and is demonstrated to be the major influential factor of the lithium plating distribution after the sensitivity analysis and normalization processing.Based on the current constraints of preventing lithium plating and the nature of the low-temperature impedance in positive electrode and negative electrode,the key to prevent lithium plating of the cells in both series and parallel configuration is demonstrated to obtain the lowest usage boundary of the cluster consisting of different cells’ usage boundaries of preventing lithium plating.Furtherly,the maximum permissible current of ensuring each cell in the module/pack without incurring lithium plating is provided through the maximum value analysis of multivariate functions.In addition,by combining the nonbifurcation region of suppressing the temperature nonuniformity with the lowest boundary of preventing lithium plating for cell pack,the optimal usage region of control parameters,capable of meeting the multi-objective requirements,is provided.By combining the square wave preheating method at the cell level with the aforementioned optimal usage region of control parameters,theoretical support and technical solutions can be provided to implement the ACP at the level of cell module.