Minimum Operator Based Discrete-Time Nonlinear Observer Design for the State of Charge Estimation of Li-ion Battery

Abstract

This paper introduces a novel minimum operator-based discrete-time nonlinear observer for estimating the online state of charge (SoC) of Li-ion batteries. This observer ensures finite-time estimation error convergence. The battery’s model employs a second-order resistor-capacitor (2-RC) equivalent circuit, where the parameters are determined via a least-squares fitting method and treated as nonlinear functions. The Lyapunov direct method is used to demonstrate the finite-time convergence of the estimation error in discrete time. The proposed method’s performance is validated under hybrid pulse power characterization (HPPC) and urban dynamometer driving schedule (UDDS) conditions. Simulation and experimental results show that it provides better estimation accuracy and tracking capability than existing discrete-time nonlinear observers. © 2024 IEEE.