Novel Approach for Battery State of Charge Evaluation through Inductive Sensing

Estimating the State of Charge of the batteries is a crucial operation to ensure the correct functioning of the battery modules, especially when it is necessary to balance the cells adjusting the State of Charge of each and ensure the best performance of the module. Currently, the most used methods to estimate the cells' State of Charge are based on the cell voltage and the current, but both require the galvanic connection, mandatory for voltage measurement and frequent for current measurement, with the battery. Methods based on Non-Destructive Testing are approaching this topic by aiming to obtain the batteries' State of Charge from non-invasive measurements. In particular, methods based on the effect of eddy currents aim to represent a valid alternative for estimating the State of Charge in electrochemical energy storage systems. In this preliminary work, we began to investigate the possibility of estimating the State of Charge by building a measurement set-up that would allow the batteries to be discharged and the characteristic parameters of a coil located outside the battery to be measured. The results show a clear correlation among the battery State of Charge, the inductance, and the parasitic resistance of the complex battery-coil system.