Open-Circuit Voltage Models for Battery Management Systems: A Review

A battery management system (BMS) plays a crucial role to ensure the safety, efficiency, and reliability of a rechargeable Li-ion battery pack. State of charge (SOC) estimation is an important operation within a BMS. Estimated SOC is required in several BMS operations, such as remaining power and mileage estimation, battery capacity estimation, charge termination, and cell balancing. The open-circuit voltage (OCV) look-up-based SOC estimation approach is widely used in battery management systems. For OCV lookup, the OCV-SOC characteristic is empirically measured and parameterized a priori. The literature shows numerous OCV-SOC models and approaches to characterize them and use them in SOC estimation. However, the selection of an OCV-SOC model must consider several factors: (i) Modeling errors due to approximations, age/temperature effects, and cell-to-cell variations; (ii) Likelihood and severity of errors when the OCV-SOC parameters are rounded; (iii) Computing system requirements to store and process OCV parameters; and (iv) The required computational complexity of real-time OCV lookup algorithms. This paper presents a review of existing OCV-SOC models and proposes a systematic approach to select a suitable OCV-SOC for implementation based on various constraints faced by a BMS designer in practical application.