SOC and diffusion rate estimation in redox flow batteries: An I&I-based high-gain observer approach

© 2021 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting /republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other worksThis paper presents an adaptive non-linear observer for the state of charge estimation in vanadium redox flow batteries. The study is based directly on the use of non-linear equations that describe the evolution of the species concentration inside the system, and a nonlinear cell voltage expression that takes into account the effect of overpotentials. Moreover, a more realistic approach is used which does not consider that the electrolyte concentration is the same in the catholyte and anolyte sides of the system. It is shown that the state of charge can be estimated through the measurement of the output voltage and a high-gain observer. Nonetheless, the accuracy of the estimation is affected by uncertainty in the system diffusion rates. For this reason, the observer is robustified by means of an immersive and invariance adaptive parameter estimation. The results are validated in a numerical simulation.This research was funded by the CSIC under the PTI FLOWBAT 2021 project (ref. 642 201980E101), the Spanish Ministry of Economy and Competitiveness under Project DOVELAR (ref. RTI2018-096001-B-C32), and by the Spanish State Research Agency through the María de Maeztu Seal of Excellence to IRI (MDM-2016-0656).Peer ReviewedPostprint (author's final draft