Multi-Level Constant Current Based Fast Li-Ion Battery Charging Scheme With LMS Based Online State of Charge Estimation

Abstract

Li-ion battery supports fast charging. However in conventional battery charging schemes, this fast charging capability is restricted by its terminal voltage during constant current charging profile. Furthermore conventional charging schemes neglect battery dynamics for an optimized charging protocol. This paper characterises Li-ion battery into its electrical equivalent circuit model. Additionally, based on the dynamics characterized through battery modelling a multi-level constant current charging protocol is adopted. This paper demonstrates a multi-level constant current charging scheme for faster battery charging with state of charge (SoC) estimation using least mean square (LMS) based algorithm. The implemented modified LMS algorithm with variable learning rate estimates the SoC of the battery accurately. The charging scheme approaches 100% SoC at a relatively higher charging current in comparison to the conventional battery charging schemes making the SoC estimation an important aspect for charge termination. The multi-level constant current charging scheme, inspired by the Taguchi optimization technique is implemented using a DC-DC buck converter as a variable current source. Experimental comparison between multi-level constant current and conventional charging scheme is performed. The hardware results showcase a reduction in charging time over conventional charging schema by 39.28%.