Online estimation of state-of-charge using auxiliary load

Abstract

Numerous approaches and methodologies have been established for online (while the load is supplied) estimation of the State-of-Charge of Lithium-ion cells and batteries. However, as battery load consumption fluctuates in real time because of delivered device operations, obtaining a precise online state of charge estimation remains a challenging task. This work proposes a new technique for online open circuit voltage measurement to estimate state of charge of batteries. This novel technique proposes the addition of an auxiliary regulated load that may be utilized to temporarily force specifically defined forms of the battery's current curve under particular conditions, which results in improving and simplifying online open circuit voltage computations. The effectiveness of the proposed technique was successfully validated through several experimental tests. The acquired findings demonstrated its efficiency with an acceptable online state of charge estimation accuracy. Typically, an estimation error of less than 2% was recorded in most tests, while the error was less than 1% when the battery’s state of charge was high.