A Modified State of Charge Estimation Method for Li-ion Batteries

Abstract

Accurate estimation of state of charge (SOC) of a battery pack is one of the critical asset in electric vehicles and static power banks. Lithium iron phosphate (LFP) and Nickle Manganese Cobalt Oxide (NMC) are extensively used for these applications. It’s quite challenging to estimate the true SOC of the battery pack with LFP cells because of the flat nature of their SOC vs open circuit voltage (OCV) curve. The problem gets worse for a battery pack with a series arrangement of cells having slightly different capacities and/or different age. This paper proposes a novel and computationally efficient methodology which by-passes this limitation and predicts accurate SOC of the battery pack. The methodology can be easily extended to other cell chemistries like NMC.