Estimating the State of Charge of Lithium Iron Phosphate batteries using the Open-Circuit voltage method.

Abstract

Lithium Iron Phosphate batteries have gained more extensive use in numerous applications from electronics to power tools owing to their high energy, power densities and long cycle life. However, since State of Charge of a battery is an important parameter for the Battery Management System. In the last decade, research has been done extensively on estimating the state of charge of lithium batteries like lithium-ion, lithium iron phosphate batteries. This has given birth to methods like coulomb counting, terminal voltage method, extended Kalman filter among others. With the noticeable drop in the open circuit voltage during the discharge of the battery, this relationship with the state of charge can be established in form of the characteristic graph. A circuit that can accurately estimate the open-circuit voltage of the Lithium Iron Phosphate batteries was designed. The circuit consists of a microcontroller, a 16-bit analog-to-digital converter and display as an OLED screen. This circuit will utilize the open circuit voltage due to that noticeable drop in voltage when a battery charge is drained by a known load.