Comparative study and improvement of battery open-circuit voltage estimation methods

Due to the steadily-increasing demands on more powerful electronic devices, an accumulator´s operating lifetime plays an essential role for the usability of battery-powered devices. To avoid an insufficient utilization of a cell´s energy and/or lifetime, a reliable and reasonably accurate knowledge of its internal parameters like the state-of-charge (SoC) is indispensable. The determination of the SoC is often directly related to the estimation of a battery´s open-circuit voltage (OCV). In this work, various OCV estimation methods are compared with respect to their inherent accuracy. Additionally, the observability-Gramian-based OCV estimation method is extended to deal with expanded kinds of cell currents. Moreover, interpolation-based methodologies are presented which considerably reduce the average OCV estimation error over the entire SoC range, compared to state-of-the-art implementations.