The Study On Estimation Method Aboutthe Capacity Of Power Lithium-ion Battery

With the far-ranging promotion of electric vehicles,more and more attention is paid to the performance examination of power battery,especially to the actual capacity detection of power battery using in the recycling.The total capacity of power lithiumion battery varies with cycle using time.In order to take fast and accurate detection on total capacity of power batteries with unknown service time, two kinds of battery are selected as the experimental object in this paper,they are LFP battery and the ternary lithium-ion battery which is most widely used and has optimal development situation.Then the electrochemical properties of lithium-ion batteries are analyzed under the status of constant current charging.And based on the external curve of the battery characteristic,this article is designed to estimate the battery capacity rapidly through Ah integration method.Regarding the capacity charged with constant current as the practical total capacity, by the way of curve-fitting, discrete data is made continual and some ways including Polynomial-fitting and Gaussian-fitting are compared to prove that Gaussian function is better to be applied in chemical fitting procedure. Furthermore, break-points characteristics of charging curve platform are analyzed with its concavity and convexity. This paper propose the method of using three order derivatives of great value to get the location of break point s. The monotony of first order differential curves can make sure uniformity of all reaction stages when charging with constant current and the method of simulating voltage waveforms of all reaction stages with line-fitting is proposed.By sampling lithium-ion battery recycling charging data at regular intervals, after making a statistics of location of break points as well as the slope changing trend of all reaction stages with aged battery, this paper find all break points and slope during all stages change at equal speed as the battery ages. By the way of line-fitting to simulate charging during all stages with constant current, the charging time with constant current of Fe battery and lithium-ion battery under different capacity situation is estimated. Then the battery capacity at corrsponding state is confirmed as well.With estimating the probabliity distribution of sample, this paper go on researching the applicable condition of all estimating schemes. Before these conditions of all estimation schemes are proposed, some fators’ effects on charging curves including different charging rate, environment temperature as well as the rate of data sampling are analyzed first of all. As for data missing in usage of power battery practically, this paper also design a comprehensive scheme by making up for missing data with history data and point out the disadvantages of this scheme.