Comparison of Simple Battery Model and Thevenin Battery Model for SOC Estimation Based on OCV Method

Abstract

State of Charge (SOC) is a component of Battery Management System (BMS) which gives information on the remaining capacity of a battery. For monitoring purpose, SOC estimation is represented as ratio of the remaining capacity to the nominal capacity of a battery. In this paper, SOC estimation is carried out by using Open-Circuit-Voltage (OCV) method, i.e. converting OCV estimate to SOC estimate based on SOC-OCV relationship. For comparison purpose, Thevenin battery model and simple Battery model are considered. The OCV estimation is conducted by using Recursive-Least-Square (RLS) algorithm with forgetting factor in which the model parameters are also simultaneously estimated. To demonstrate the effectiveness of the proposed method, experiment is utilized by employing hardware devices for measuring terminal voltage and current of battery which serve as inputs to the RLS algorithm. Accordingly, a forgetting factor of 0.985 for Thevenin battery model and 0,97 for Simple Battery model is obtained to yield accurate OCV estimation with OCV estimation error of 0.014% for Thevenin battery model and Simple Battery Model 0.012%.