Consistency And Capacity Estimation Of Lithium Ion Batteries For Vehicles

As the energy supply part of electric vehicle,battery pack plays a decisive role in the overall performance of electric vehicle.There are still some problems to be solved urgently in the application of batteries in electric vehicles,such as the safety of batteries in use,the service life of batteries and the charging and discharging capacity of batteries.The decisive factor for these problems is the consistency of the individual batteries that make up the battery pack.Therefore,the consistency of the battery pack is studied in this paper,and the capacity of the battery is estimated by using the estimation algorithm.The detailed working arrangements are as follows:(1)In view of the large error and poor applicability of the consistency evaluation model based on terminal voltage and SOC,a piecewise SOC consistency evaluation model considering voltage effect is proposed to evaluate the consistency of batteries.On the basis of analyzing the characteristics of lithium-ion batteries,the first-order Davidinian model is chosen to analyze,in order to prepare for the subsequent consistency study and capacity estimation.At the same time,the consistency performance rules of several battery parameters are given,and specific solutions are given to improve the consistency between batteries.A piecewise SOC consistency evaluation model considering voltage effect is established to study and evaluate the consistency of battery packs.The results show that the evaluation effect of the piecewise SOC consistency evaluation model considering voltage effect is better.(2)Aiming at the cumulative error of the time-integration method and the limitation of Kalman filter algorithm by system noise,an adaptive extended Kalman filter algorithm is proposed to estimate the cell capacity.Firstly,the ampere-time integral method is used to integrate the current,and the charge and discharge of the battery are obtained.Then,according to the actual measurement voltage of the battery,the charge and discharge of the battery are corrected by using the adaptive extended Kalman filter algorithm.The estimation results are compared and analyzed.The feasibility of the algorithm is verified by using MATLAB simulation software.The comparison results show that the estimation effect of the algorithm with adaptive control is more accurate.(3)Aiming at the problem of inaccurate estimation accuracy of structure logic tree estimation algorithm,an improved structure logic tree algorithm is proposed to estimate battery capacity.Battery packs are composed of many single batteries which are mixed in series and parallel.So the capacity of single batteries is estimated first inthis paper,and then the capacity of battery packs is estimated according to the calculation rule of structure logic tree proposed in this paper.The rationality and stability of structure logic tree estimation algorithm are verified by using MATLAB software.Compared with other estimation algorithms,it can be seen that the estimation error of structure logic tree algorithm is smaller.