Online Li-ion battery state of health implementation for grid-tied applications

This paper introduces an online method valid to estimate the state of health of Li-ion energy storage systems for grid-tied applications. For this propose, two methods are evaluated. Firstly, a reduced-range incremental capacity analysis (ICA) applied during the last phase of the charging period (above 60-100% approximated) is analyzed, and also, an implementation strategy is proposed. This method has been successfully tested using data gathered during the degradation process of six LFP battery cells of 180 Ah and 100 Ah. However, it requires the energy storage system to be operated up to full charge. For overcoming that limitation, a second method based on adaptive filtering techniques to estimate the impedance evolution at different operating points is also studied. The proposed impedance-based method is analyzed using the data gathered from a cycling test.