Method for applying OCV tables to enhance SOC accuracy after small discharges

Lithium-ion batteries are widely used as core energy sources in various applications such as electric ships, drones, electric vehicles (EVs), and energy storage systems (ESSs). These batteries can be operated safely with the help of a Battery Management System (BMS). Among the various functions of the BMS, accurately estimating the State of Charge (SOC) is crucial for the efficient use of the battery. One common method for improving SOC estimation accuracy involves using an Open Circuit Voltage (OCV) table. The OCV table is typically divided into a charge OCV table and a discharge OCV table, both of which can be used to correct SOC values. Generally, the charge OCV table is applied after charging, while the discharge OCV table is used after discharging. However, when a small amount of discharge occurs after charging, SOC correction using a simple OCV table may not yield accurate results. In this paper, we examine SOC estimation using both the charge and discharge OCV tables in cases of minor discharge following a charging cycle. We also implemented and tested an optimal compensation logic designed to improve SOC accuracy by evaluating the error associated with each method. The test results show that the proposed logic reduced the SOC estimation error to 1.4% when a 3% discharge occurred without a rest period, and to 1.6% when the same discharge occurred after a 2-h rest. This logic enables accurate SOC estimation even under conditions involving small discharges after charging, thereby enhancing overall estimation reliability.