A Five-Parameter Analytical Curvefit Model for Open-Circuit Voltage Variation with State-of-Charge of a Rechargeable Battery

摘要

Rechargeable batteries, particularly using lithiumion chemistry, are used for energy storage in a wide range of applications. As these batteries charge and discharge, the variation of open-circuit voltage (OCV) is highly non-linear with respect to state-of-charge (SOC). Modelling this phenomenon using the details of the internal electrochemical processes results in a highly complex model that can be hard to build and simulate. In order to focus on the terminal behaviour only, this paper presents a simple five-parameter analytical model that accurately curvefits empirical data of OCV variation with battery SOC. The proposed model uses a summation of a logarithmic function and a polynomial function to capture the non-linearities in the low-SOC and high-SOC regions, respectively. The extent of nonlinearity or bend in each of these two regions can be controlled using separate parameters. Comparison with experimental data during discharge of a Samsung 18650 cell is shown. The proposed battery model is simple and flexible, and can easily cater to a variety of battery types.