State of Charge and State of Health Estimation Over the Battery Lifespan

Abstract

The battery management system (BMS) plays a critical role in battery packs especially for the lithium-ion battery chemistry. Protecting the cells from overcharge and overdischarge, controlling the temperature at the desired level, prolonging the life of the battery pack, guaranteeing the safety and indicating the available power and energy of the battery are the key functionalities of a BMS. In this chapter, two important concepts of a BMS are discussed: (i) battery state-of-charge (SoC) and (ii) battery state-of-health (SoH). Battery SoC and SoH are variables which should be determined precisely in order to use the battery optimally and safely. Batteries are time-varying systems that behave very differently at various states. In other words, the internal states of a battery tell us what we should expect from it. Depending on the battery chemistry, various techniques have been developed in the literature for SoC and SoH estimation. This covers a wide range from simple integration of current over time (i.e. coulomb counting) to advanced estimation techniques such as Kalman filter. In this study, almost all the existing battery SoC and SoH estimation approaches are reviewed and proper references are cited for further studies in each category.