Research On Capacity Estimation And Static And Dynamic Model Of Lithium-ion Battery For Battery Management System

Lithium-ion battery is an important energy storage device for new energy system.Due to the inconsistency between batteries in the battery pack,the state of battery is not the same when the battery is working.In order to ensure the normal operation of the battery pack,the battery management system（BMS）is used to control batteries charge and discharge.This paper research the capacity estimation,the identification of static model parameters and the establishment of dynamic model of lithium-ion battery based on the application of BMS.First,this paper introduces the BMS functions and implementation methods,and analyzes the application of battery capacity estimation and battery model in BMS.It lays the theoretical foundation for the research of capacity estimation method,battery model parameter identification and battery dynamic model in BMS.Secondly,this paper based on the capacity fade mechanism of the LiFePO₄battery,makes use of the incremental capacity analysis（ICA）to establish the relationship between the terminal voltage of the battery and the capacity fade mechanism without destroying the battery structure.Then,battery capacity can be estimated by the latter half charging curve without full charged and discharged.The proposed method is verified through battery cycle aging test.Then,a model parameter identification method based on battery constant current discharge curve is proposed for direct-current internal resistance model of battery.This method is short time consuming,high precision,easy to realize,and can obtain continuous open circuit voltage（OCV）-state of charge（SOC）curve and direct-current internal resistance-SOC curve,which is convenient for more comprehensive analysis of battery performance.The model parameter identification method is verified under different temperature and different current conditions based on LiFePO₄ battery.Finally,this paper aims at the dynamic process of battery step discharge current during the battery test,proposed a dynamic model of battery step discharge current through analyzing the change of matter diffusion in lithium-ion battery during the dynamic process of step discharge current.The model is verified by LiFePO₄ battery,Li（NiCoMn）O₂ battery.And the influence of temperature,current and SOC on the model parameters is analyzed.