State-of-Health Estimation for Lithium-Ion Batteries Based on Decoupled Dynamic Characteristic of Constant-Voltage Charging Current

Abstract

State-of-health (SoH) is one of the critical battery states that must be estimated and closely monitored by the on- board battery management system in electric vehicles (EVs). In this study, the battery SoH, especially the capacity fade, is calculated based on the decoupled characteristic of the charging current under the constant-voltage (CV) scenario. First, a dynamic-decoupled parameter identification method is proposed to extract the parameters of the simplified second-order resistor–inductor ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RL</i> ) network-based equivalent circuit model (ECM), developed by the authors. Second, the dynamic characteristics of the decoupled CV charging currents at different aging states are qualitatively investigated, and the corresponding time constant is selected as a feature-of-interest (FoI) to reflect the battery capacity degradation. Third, the aging data based on two types of lithium-ion batteries are employed to evaluate the performance of the proposed method. Verification results demonstrate that the proposed parameter identification method yields a reduced computational cost with a satisfactory fitting performance, compared to the conventional methods. The proposed parameterization method and the selected FoI guarantee the root-mean-square errors of the estimated SoH less than 2%, and the comparative results further validate the superiority of the selected FoI in terms of the SoH estimation accuracy.