The Estimation Of State Of Charge Of Lithium-ion Battery Based On Stirling's Interpolation Filter

With gradual depletion of non-renewable energy resources and increasing environmental pollution, as one of the alternate energy source,Lithium-ion battery is widely used in daily life and industrial applications, due to a wide range of advantages, such as environmentally-friendly and higher energy density. State of charge(SOC) is the foundation of the realization of battery management system. So accurate estimatimation of SOC is significant of high-efficiency and safety implementation.This paper proposed a hardware system for verification of algorithm based on basic charge-discharge charactrization of lithium iron phosphate battery and the estimatition of SOC based on Stirling interpolation filter(DD1?DD2).The basic parameters such as battery capacity, dc internal resistance and open circuit voltage(OCV) demonstrate a high nonlinearity with the changes in factors, such as current and SOC. The OCV curve and internal resistance is studied by a step-input method. And the relationship between capacity and current ratio is studied by steady-state discharge experiments.In order to overcome the defects of EKF, such as the calculatation of Jacobian matrix and requirement of differentiable system function, etc, Stirling's interpolation filter is discussed to estimate the SOC, the finite difference is used as a replacemrnt for differential of taylor expansion, which is closer to the nonlinear characteristics of the system than taylor expansion and does not need to calculate the jacobian matrix. Finally, the DD2, DD1 and EKF are used to estimate SOC on the basis of pulse discharge experiments, and the simulation results show that Stirling's interpolation filter has higher precision of estimation.In the last part of this paper, the preliminary design of hardware platform system for verification of algorithm is introduced, and the whole hardware system is divided into two parts, the control unit and the supervision unit. The supervision unit is mainly responsible for monitoring and displaying the battery state information and uploading state information to the control unit. The control unit is used to estimate the SOC of battery according to state information collected by the supervision unit, and the estimation algorithm is written based on model based design method.