On state-estimation in weakly-observable scenarios and implicitly regularized observers

© 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 work proposes a framework to design observers for systems that present low observability. It is shown that, in these scenarios, the estimation problem becomes ill-posed, which drastically limits the performance of standard observers, specially in the presence of noise. Consequently, this paper presents a method to design an observer that optimizes some potential function to be defined by the designer. This allows to implicitly regularize the estimation and recover a well-posed problem. The proposed technique is validated in a set of weakly-observable systems and the performance is compared with a common Kalman filter-like observer.This work has been partially funded by the Spanish State Research Agency through the María de Maeztu Seal of Excellence to IRI (MDM-2016-0656) and by the project DOVELAR (ref. RTI2018-096001-B-C32).Peer ReviewedPostprint (author's final draft

Library-based adaptive observation through a sparsity-promoting adaptive observer

© 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 proposes an adaptive observer for a class of nonlinear system with linear parametrization. The main novelty of the technique is that the regressor vector is considered to be unknown. Instead, a library of candidate non-linear functions is implemented, which transforms the original parameter vector into a new one that is characterized by being sparse. In such problem, it is shown that standard adaptive observers cannot recover the original vector due to a lack of persistence of excitation. Instead, a parameter-adaptation with an implicit l1 regularization is implemented. It is shown that this new observer can recover the parameter vector under standard assumptions of sparse signal recovery. The results are validated in a numerical simulation.This work has been partially funded by the Spanish State Research Agency through the María de Maeztu Seal of Excellence to IRI (MDM-2016-0656), by the project DOVELAR (ref. RTI2018-096001-B-C32) and by the PTI FLOWBAT 2021 project (ref. 642 201980E101).Peer ReviewedPostprint (author's final draft

Control adaptatiu d'una pila PEM de càtode obert

En aquest projecte es dissenya un observador capaç d’estimar la saturació d’aigua líquida a la capa catalítica d’una pila de combustible de tipus PEM. En els primers apartats es presenta al lector la idea de la pila de combustible, tant en el seu context històric com dels seus usos i característiques tècniques. Ja que, determinats aspectes del funcionament de la pila són necessaris per entendre el projecte. La pila de combustible és un sistema realment complex de modelar, en el projecte es reutilitza un model (Strahl, 2011) i una simulació del programari Simulink (González, 2017) d’una pila de combustible de característiques similars a la del treball. Partint del model, es dissenyaran diverses estructures d’observador i s’explorarà la seva validesa implementant-los en la simulació. En els següents apartats es dissenya l’observador. Es presenta tres estructures possibles: En llaç obert, en llaç tancat basat en Sliding Mode Control (SMC) i en llaç tancat dissenyat sobre la forma canònica controlable del sistema. Durant aquests apartats, es presenta la teoria necessària per entendre els dissenys i es realitza una sèrie de simulacions per a analitzar la seva validesa. Finalment, es dissenya un diferenciador que permet estimar el valor de certes derivades necessàries per a la implementació de l’observador

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

Online state of charge estimation for a vanadium redox flow battery with unequal flow rates

This study presents an observer-based methodology to estimate, in real-time, the state of charge of a Vanadium redox flow battery. Different from the available results in the literature, this work presents a new estimator that distinguishes between the concentration in the tank and cell parts of the system. Moreover, it presents an estimation of the state of charge that can deal with both balanced and unbalanced situations. The model used for the observer design is a nonlinear electrochemical model. A nonlinear observer is proposed, designed and validated through simulation and in an experimental prototype.Peer ReviewedPostprint (published version

Modelling and estimation in lithium-ion batteries: a literature review

Lithium-ion batteries are widely recognised as the leading technology for electrochemical energy storage. Their applications in the automotive industry and integration with renewable energy grids highlight their current significance and anticipate their substantial future impact. However, battery management systems, which are in charge of the monitoring and control of batteries, need to consider several states, like the state of charge and the state of health, which cannot be directly measured. To estimate these indicators, algorithms utilising mathematical models of the battery and basic measurements like voltage, current or temperature are employed. This review focuses on a comprehensive examination of various models, from complex but close to the physicochemical phenomena to computationally simpler but ignorant of the physics; the estimation problem and a formal basis for the development of algorithms; and algorithms used in Li-ion battery monitoring. The objective is to provide a practical guide that elucidates the different models and helps to navigate the different existing estimation techniques, simplifying the process for the development of new Li-ion battery applications.This research received support from the Spanish Ministry of Science and Innovation under projects MAFALDA (PID2021-126001OB-C31 funded by MCIN/AEI/10.13039/501100011033/ ERDF,EU) and MASHED (TED2021-129927B-I00), and by FI Joan Oró grant (code 2023 FI-1 00827), cofinanced by the European Union.Peer ReviewedPostprint (published version

Estimación del estado de carga y coeficientes de difusión en baterías de flujo redox

Estimation of the state of charge and diffusion coefficients in redox flow batteries. This paper presents an observer for the estimation of the state of charge of redox flow batteries. The observer is high gain and is based on a non-linear dynamic model, which uses a realistic approach differentiating between the total electrolyte concentrations in the two parts of the system. It is shown that the state of charge can be estimated by measuring cell voltage and a high gain observer. However, the precision of the estimate is affected by the uncertainty in the diffusion coefficients of the system. For this reason, the observer is strengthened by estimating adaptive parameters of immersion and invariance. Finally, the results are validated in a numerical simulationPeer ReviewedPostprint (published version

Generalized Lyapunov conditions for k-contraction: analysis and feedback design

Recently, the concept of k-contraction has been introduced as a promising generalization of contraction for dynamical systems. However, the study of k-contraction properties has faced significant challenges due to the reliance on complex mathematical objects called matrix compounds. As a result, related control design methodologies have yet to appear in the literature. In this paper, we overcome existing limitations and propose new sufficient conditions for k-contraction which do not rely on matrix compounds. Our design-oriented conditions stem from a strong geometrical interpretation and establish a connection between kcontraction and p-dominance. Notably, these conditions are also necessary in the linear time-invariant framework. Leveraging on these findings, we propose a feedback design methodology for both the linear and the nonlinear scenarios

Vanadium redox flow batteries real-time State of Charge and State of Health estimation under electrolyte imbalance condition

This paper presents a novel observer architecture capable to estimate online the concentrations of the four vanadium species present in a vanadium redox flow battery (VRFB). The proposed architecture comprises three main stages: (1) a high-gain observer, to estimate the output voltage and its derivatives; (2) a dynamic inverter, to obtain a set of concentration candidate solutions; and (3) a static selector, to determine the actual concentrations. The methodology does not rely on the classic assumption of balanced electrolytes, thus significantly widening the application range in comparison with most of the literature previous studies. Furthermore, to perform the estimation, only a single voltage and current measurements are required, which eliminates the need of including complex and costly additional sensors. To validate the proposal, comprehensive simulation tests are conducted. These tests take into account typical side reactions that cause imbalance in VRFB systems, such as vanadium crossover and oxidation. The observer shows a remarkable performance when dealing with these realistic conditions, allowing to estimate with high accuracy and robustness the four vanadium concentrations, the State of Charge and the State of Health with a relative error below 2%.The project that gave rise to these results received the support of a fellowship from ”la Caixa” Foundation (ID 100010434). The fellowship code is LCF/BQ/DI21/11860023. This research was also supported by the Spanish Ministry of Science and Innovation, under the projects MAFALDA (PID2021-126001OB-C31) and MASHED (TED2021-129927B-I00). This work has been supported by the Spanish Ministry of Universities funded by the European Union - NextGenerationEU (2022UPC-MSC-93823).Peer ReviewedPostprint (published version

On addressing the security and stability issues due to false data injection attacks in DC microgrids an adaptive observer approach

© 2022 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 proposes an observer-based methodology to detect and mitigate false data injection attacks in collaborative DC microgrids. The ability of observers to effectively detect such attacks is complicated by the presence of unknown non-linear constant power loads. This work determines that, in the presence of unknown constant power loads, the considered attack detection and mitigation problem involves non linearities, locally unobservable states, unknown parameters, uncertainty and noise. Taking into account these limitations, a distributed non linear adaptive observer is proposed to overcome these limitations and solve the concerned observation problem. The necessary conditions for the stability of the distributed scheme are found out. Moreover, numerical simulations are performed and then validated in a real experimental prototype, where communication delay, uncertainty and noise are considered.Peer ReviewedPostprint (author's final draft