Fault Detection and Isolation in Controlled Multi-Robot Systems

Multi-Agent Systems (MASs) have attracted much popularity, since the previous decade due to their potential wide range of applications. Indeed, connected MASs are deployed in order to achieve more complex objectives that could otherwise not be achievable by a single agent. In distributed schemes, agents must share their information with their neighbours, which are then used for common control and fault detection purposes, and thus do not require any central monitoring unit. This translates into the necessity to develop efficient distributed algorithms in terms of robustness and safety. Indeed, the problem of safety in connected cooperative MASs has arisen as a consequence of their complexity and the nature of their operations and wireless communication exchanges, which renders them vulnerable to not only physical faults, but also to cyber-attacks. The main focus of this thesis is the study of distributed fault and attack detection and isolation in connected MASs. First, a distributed methodology for global detection of actuator faults in a class of linear MASs with unknown disturbances is proposed using a cascade of fixed-time Sliding Mode Observers (SMOs), where each agent having access to their state, and neighbouring information exchanges, can give an exact estimate of the state of the overall MAS. An LMI-based approach is then applied to design distributed global robust residual signals at each agent capable of detecting faults anywhere in the network. This is then extended to agents with nonlinear nonholonomic dynamics where a new distributed robust Fault Detection and Isolation (FDI) scheme is proposed using predefined-time stability techniques to derive adequate distributed SMOs. This enables to reconstruct the global system state in a predefined-time and generate proper residual signals. The case of MASs with higher order integrator dynamics, where only the first state variable is measurable and the topology is switching is investigated, where a new approach to identify faults and deception attacks is introduced. The proposed protocol makes an agent act as a central node monitoring the whole system activities in a distributed fashion whereby a bank of distributed predefined-time SMOs for global state estimation are designed, which are then used to generate residual signals capable of identifying cyber-attacks despite the switching topology. The problem of attack and FDI in connected heterogeneous MASs with directed graphs, is then studied. First, the problem of distributed fault detection for a team of heterogeneous MASs with linear dynamics is investigated, where a new output observer scheme is proposed which is effective for both directed and undirected topologies. The main advantage of this approach is that the design, being dependant only on the input-output relations, renders the computational cost, information exchange and scalability very effective compared to other FDI approaches that employ the whole state estimation of the agents and their neighbours as a basis for their design. A more general model is then studied, where actuator, sensor and communication faults/attacks are considered in the robust detection and isolation process for nonlinear heterogeneous MASs with measurement noise, dynamic disturbances and communication parameter uncertainties, where the topology is not required to be undirected. This is done using a distributed finite-frequency mixed H_/H1 nonlinear UIO-based approach. Simulation examples are given for each of the proposed algorithms to show their effectiveness and robustness

Distributed Passive Fault Tolerant Formation Tracking for Uncertain Second Order Multi-Agent Systems

This paper deals with the problem of distributed passive fault tolerant formation tracking control for cooperative second order multi-agent systems (MASs) subject to disturbances and sensor/actuator faults. The proposed scheme is based on decentralized observers used to robustly estimate the actuator and sensor faults in spite of disturbances. These estimates are then injected into a dynamic control law in order to mitigate their effects on the control objective. Using the Hcomethod, graph theory properties and the projection lemma, sufficient conditions in the form of a set of linear matrix inequalities (LMIs) are derived to guarantee the stabilization of the tracking errors while reducing the effects of sensor and actuator faults and disturbances. A numerical simulation illustrates the effectiveness of the proposed passive fault-tolerant control scheme

A Distributed Observer-Based Cyber-Attack Identification Scheme in Cooperative Networked Systems under Switching Communication Topologies

This paper studies an approach for detecting cyber attacks against networked cooperative systems (NCS) that are assumed to be working in a cyber-physical environment. NCS are prone to anomalies both due to cyber and physical attacks and faults. Cyber-attacks being more hazardous given the cooperative nature of the NCS may lead to disastrous consequences and thus need to be detected as soon as they occur by all systems in the network. Our approach deals with two types of malicious attacks aimed at compromising the stability of the NCS: intrusion attacks/local malfunctions on individual systems and deception/cyber-attacks on the communication between the systems. In order to detect and identify such attacks under switching communication topologies, this paper proposes a new distributed methodology that solves global state estimation of the NCS where the aim is identifying anomalies in the networked system using residuals generated by monitoring agents such that coverage of the entire network is assured. A cascade of predefined-time sliding mode switched observers is introduced for each agent to achieve a fast estimate of the global state whereby the settling time is an a priori defined parameter independently of the initial conditions. Then, using the conventional consensus algorithm, a set of residuals are generated by the agents that is capable of detecting and isolating local intrusion attacks and communication cyber-attacks in the network using only locally exchanged information. In order to prove the effectiveness of the proposed method, the framework is tested for a velocity synchronization seeking network of mobile robots

Détection et isolation des défauts dans les systèmes multi-robots contrôlés

Les systèmes multi-agents (SMAs) ont beaucoup attiré depuis la décennie précédente en raison de leur large éventail d’applications. En effet, les SMAs connectés sont déployés afin d’atteindre un objectif plus complexe qui pourrait autrement ne pas être réalisable par un seul agent. Dans les approches distribuées, les agents doivent partager leurs informations avec leurs voisins, qui sont ensuite utilisés à des fins de commande et de détection de défaut, et ne nécessitent donc aucune unité de surveillance centrale. Cela se traduit par la nécessité de développer des algorithmes distribués efficaces en termes de robustesse et de sécurité. En effet, le problème de la sécurité dans les SMAs coopérants et connectés est apparu à la suite de leur complexité, de la nature de leurs opérations et de leurs échanges via communication sans fil, ce qui les rend vulnérables non seulement aux défauts physiques, mais également aux cyber-attaques. L’étude de la détection et de l’isolation distribuées de fautes et des attaques dans les SMAs est la principale contribution de cette thèse. Premièrement, une méthodologie distribuée de détection globale des défauts d’actionneur dans une classe de systèmes multiagents linéaires avec des perturbations inconnues est proposée à l’aide d’une cascade d’observateurs mode glissant à temps fixe, où chaque agent ayant accès à leur état et les échanges d’informations voisins, peuvent donner une estimation exacte de l’état du système global. Une approche basée sur les Inégalités Matricielles Linéaires (IMLs) est ensuite utilisée pour la conception distribuée de résidus robustes au niveau de chaque agent, ces résidus étant capable de détecter des défauts n’importe où dans la flotte. Celle-ci est ensuite étendue aux agents avec une dynamique non linéaire non holonome dans laquelle un nouvel algorithme robuste et distribué de détection et d’isolation de défauts est proposé à l’aide de techniques de stabilité à temps prédéfini afin de construire des observateurs mode glissant distribué. Cela permet de reconstruire l’état du système global dans un temps prédéfini et de générer correctement des signaux résiduels. Le cas des systèmes multi-agents sous forme de chaîne d’intégrateurs, où seule la première variable d’état est mesurable et la topologie est dynamique, est étudié, où une nouvelle approche pour identifier les défauts et les cyber-attaques est introduite. L’algorithme proposé fait en sorte que chaque agent joue le rôle d’une unité de surveillance centrale de l’ensemble des activités du système de manière distribuée, en employant des banques d’observateurs mode glissant basés sur la notion de stabilité prédéfinie, où l’estimation de l’état global et des signaux résiduels duquel ils sont générés se fait avant chaque instant de changement de topologie de communication. Ces résidus sont alors capables de distinguer les cyber-attaques, des fautes physiques malgré la topologie commutée. Le problème de la détection et de l’isolation des attaques et des fautes dans des systèmes hétérogènes connectés avec des topologies dirigées, est ensuite étudié. Premièrement, le problème de la détection distribués des défauts actionneurs pour les systèmes multi-agents linéaires et hétérogènes est traité, où un nouveau système d’observateur de sortie a été proposé pour les topologies dirigées et non dirigées. Le principal avantage de cette approche est que la conception ne dépend que des relations entrées/sorties, ce qui rend le temps de calcul, la quantité d’informations échangées et la flexibilité, très intéressants par rapport à d’autres approches qui utilisent l’estimation de tout l’état des agents et leurs voisins comme base de leur conception....Multi-Agent Systems (MASs) have attracted much popularity, since the previous decade due to their potential wide range of applications. Indeed, connected MASs are deployed in order to achieve more complex objectives that could otherwise not be achievable by a single agent. In distributed schemes, agents must share their information with their neighbours, which are then used for common control and fault detection purposes, and thus do not require any central monitoring unit. This translates into the necessity to develop efficient distributed algorithms in terms of robustness and safety. Indeed, the problem of safety in connected cooperative MASs has arisen as a consequence of their complexity and the nature of their operations and wireless communication exchanges, which renders them vulnerable to not only physical faults, but also to cyber-attacks. The main focus of this thesis is the study of distributed fault and attack detection and isolation in connected MASs. First, a distributed methodology for global detection of actuator faults in a class of linear MASs with unknown disturbances is proposed using a cascade of fixed-time Sliding Mode Observers (SMOs), where each agent having access to their state, and neighbouring information exchanges, can give an exact estimate of the state of the overall MAS. An LMI-based approach is then applied to design distributed global robust residual signals at each agent capable of detecting faults anywhere in the network. This is then extended to agents with nonlinear nonholonomic dynamics where a new distributed robust Fault Detection and Isolation (FDI) scheme is proposed using predefined-time stability techniques to derive adequate distributed SMOs. This enables to reconstruct the global system state in a predefined-time and generate proper residual signals. The case of MASs with higher order integrator dynamics, where only the first state variable is measurable and the topology is switching is investigated, where a new approach to identify faults and deception attacks is introduced. The proposed protocol makes an agent act as a central node monitoring the whole system activities in a distributed fashion whereby a bank of distributed predefined-time SMOs for global state estimation are designed, which are then used to generate residual signals capable of identifying cyber-attacks despite the switching topology. The problem of attack and FDI in connected heterogeneous MASs with directed graphs, is then studied. First, the problem of distributed fault detection for a team of heterogeneous MASs with linear dynamics is investigated, where a new output observer scheme is proposed which is effective for both directed and undirected topologies. The main advantage of this approach is that the design, being dependant only on the input-output relations, renders the computational cost, information exchange and scalability very effective compared to other FDI approaches that employ the whole state estimation of the agents and their neighbours as a basis for their design. A more general model is then studied, where actuator, sensor and communication faults/attacks are considered in the robust detection and isolation process for nonlinear heterogeneous MASs with measurement noise, dynamic disturbances and communication parameter uncertainties, where the topology is not required to be undirected. This is done using a distributed finite-frequency mixed H_/H1 nonlinear UIO-based approach. Simulation examples are given for each of the proposed algorithms to show their effectiveness and robustness

Détection et isolation des défauts dans les systèmes multi-robots contrôlés

Multi-Agent Systems (MASs) have attracted much popularity, since the previous decade due to their potential wide range of applications. Indeed, connected MASs are deployed in order to achieve more complex objectives that could otherwise not be achievable by a single agent. In distributed schemes, agents must share their information with their neighbours, which are then used for common control and fault detection purposes, and thus do not require any central monitoring unit. This translates into the necessity to develop efficient distributed algorithms in terms of robustness and safety. Indeed, the problem of safety in connected cooperative MASs has arisen as a consequence of their complexity and the nature of their operations and wireless communication exchanges, which renders them vulnerable to not only physical faults, but also to cyber-attacks. The main focus of this thesis is the study of distributed fault and attack detection and isolation in connected MASs. First, a distributed methodology for global detection of actuator faults in a class of linear MASs with unknown disturbances is proposed using a cascade of fixed-time Sliding Mode Observers (SMOs), where each agent having access to their state, and neighbouring information exchanges, can give an exact estimate of the state of the overall MAS. An LMI-based approach is then applied to design distributed global robust residual signals at each agent capable of detecting faults anywhere in the network. This is then extended to agents with nonlinear nonholonomic dynamics where a new distributed robust Fault Detection and Isolation (FDI) scheme is proposed using predefined-time stability techniques to derive adequate distributed SMOs. This enables to reconstruct the global system state in a predefined-time and generate proper residual signals. The case of MASs with higher order integrator dynamics, where only the first state variable is measurable and the topology is switching is investigated, where a new approach to identify faults and deception attacks is introduced. The proposed protocol makes an agent act as a central node monitoring the whole system activities in a distributed fashion whereby a bank of distributed predefined-time SMOs for global state estimation are designed, which are then used to generate residual signals capable of identifying cyber-attacks despite the switching topology. The problem of attack and FDI in connected heterogeneous MASs with directed graphs, is then studied. First, the problem of distributed fault detection for a team of heterogeneous MASs with linear dynamics is investigated, where a new output observer scheme is proposed which is effective for both directed and undirected topologies. The main advantage of this approach is that the design, being dependant only on the input-output relations, renders the computational cost, information exchange and scalability very effective compared to other FDI approaches that employ the whole state estimation of the agents and their neighbours as a basis for their design. A more general model is then studied, where actuator, sensor and communication faults/attacks are considered in the robust detection and isolation process for nonlinear heterogeneous MASs with measurement noise, dynamic disturbances and communication parameter uncertainties, where the topology is not required to be undirected. This is done using a distributed finite-frequency mixed H_/H1 nonlinear UIO-based approach. Simulation examples are given for each of the proposed algorithms to show their effectiveness and robustness.Les systèmes multi-agents (SMAs) ont beaucoup attiré depuis la décennie précédente en raison de leur large éventail d’applications. En effet, les SMAs connectés sont déployés afin d’atteindre un objectif plus complexe qui pourrait autrement ne pas être réalisable par un seul agent. Dans les approches distribuées, les agents doivent partager leurs informations avec leurs voisins, qui sont ensuite utilisés à des fins de commande et de détection de défaut, et ne nécessitent donc aucune unité de surveillance centrale. Cela se traduit par la nécessité de développer des algorithmes distribués efficaces en termes de robustesse et de sécurité. En effet, le problème de la sécurité dans les SMAs coopérants et connectés est apparu à la suite de leur complexité, de la nature de leurs opérations et de leurs échanges via communication sans fil, ce qui les rend vulnérables non seulement aux défauts physiques, mais également aux cyber-attaques. L’étude de la détection et de l’isolation distribuées de fautes et des attaques dans les SMAs est la principale contribution de cette thèse. Premièrement, une méthodologie distribuée de détection globale des défauts d’actionneur dans une classe de systèmes multiagents linéaires avec des perturbations inconnues est proposée à l’aide d’une cascade d’observateurs mode glissant à temps fixe, où chaque agent ayant accès à leur état et les échanges d’informations voisins, peuvent donner une estimation exacte de l’état du système global. Une approche basée sur les Inégalités Matricielles Linéaires (IMLs) est ensuite utilisée pour la conception distribuée de résidus robustes au niveau de chaque agent, ces résidus étant capable de détecter des défauts n’importe où dans la flotte. Celle-ci est ensuite étendue aux agents avec une dynamique non linéaire non holonome dans laquelle un nouvel algorithme robuste et distribué de détection et d’isolation de défauts est proposé à l’aide de techniques de stabilité à temps prédéfini afin de construire des observateurs mode glissant distribué. Cela permet de reconstruire l’état du système global dans un temps prédéfini et de générer correctement des signaux résiduels. Le cas des systèmes multi-agents sous forme de chaîne d’intégrateurs, où seule la première variable d’état est mesurable et la topologie est dynamique, est étudié, où une nouvelle approche pour identifier les défauts et les cyber-attaques est introduite. L’algorithme proposé fait en sorte que chaque agent joue le rôle d’une unité de surveillance centrale de l’ensemble des activités du système de manière distribuée, en employant des banques d’observateurs mode glissant basés sur la notion de stabilité prédéfinie, où l’estimation de l’état global et des signaux résiduels duquel ils sont générés se fait avant chaque instant de changement de topologie de communication. Ces résidus sont alors capables de distinguer les cyber-attaques, des fautes physiques malgré la topologie commutée. Le problème de la détection et de l’isolation des attaques et des fautes dans des systèmes hétérogènes connectés avec des topologies dirigées, est ensuite étudié. Premièrement, le problème de la détection distribués des défauts actionneurs pour les systèmes multi-agents linéaires et hétérogènes est traité, où un nouveau système d’observateur de sortie a été proposé pour les topologies dirigées et non dirigées. Le principal avantage de cette approche est que la conception ne dépend que des relations entrées/sorties, ce qui rend le temps de calcul, la quantité d’informations échangées et la flexibilité, très intéressants par rapport à d’autres approches qui utilisent l’estimation de tout l’état des agents et leurs voisins comme base de leur conception...

A distributed fault detection scheme in disturbed heterogeneous networked systems

This paper deals with the problem of distributed fault detection and isolation (FDI) in multi-agent systems (MASs) with disturbed high order dynamics subject to communication uncertainties and faults. Distributed finite-frequency mixed

Distributed global fault detection scheme in multi‐agent systems with chained‐form dynamics

This paper studies the problem of distributed robust actuator fault detection for multi‐agent systems composed of multiple unicycle‐type mobile agents with chained form dynamics. This objective is achieved through the design of cascades of predefined‐time sliding mode observers to give an exact estimate of the global system state, whereby the settling time is a parameter defined in advance, which does not depend on the initial conditions of the system. The system structure allows us to reconstruct the disturbance inputs using the equivalent control concept to generate efficient residual signals. This method ensures global actuator fault detection, where each agent can detect its faults and those occurring elsewhere in the system using only local information

Supported PdZn nanoparticles for selective CO2 conversion, through the grafting of a heterobimetallic complex on CeZrOx

International audienceControlling the stoichiometry of supported bimetallic nanoparticles is essential in many catalytic reactions, notably selective CO2 hydrogenation. Thus, a new strategy to ensure the preferred stoichiometry (1:1) of supported bimetallic PdZn nanoparticles is presented, involving the deposition of a heterobimetallic precursor, [PdZn(μ-OOCMe)4]2 on a CeZrOx support. After calcination and reduction, the material contained mainly a PdZn alloy, as revealed by powder XRD and XAFS, and further supported by XPS, TEM-EDX, elemental analysis and in-situ IR at low temperature using CO as probe molecule. Moreover, a minor phase of oxidized Zn was determined by XAFS. This PdZn/CeZrOx reduced catalyst was combined with SAPO-34 to form a tandem catalytic system for CO2 conversion to hydrocarbons. This system could readily convert CO2 and H2 at high temperature (380 °C) into hydrocarbons with a conversion of 24% and high relative selectivity in light hydrocarbons (C2-C3: 82%) with virtually no deactivation of the catalyst after 16 hours on stream. Controlled experiments were performed with Pd/CeZrOx and Zn/CeZrOx in order to gain supplementary insights on this system: Pd/CeZrOx gave only methane and Zn/CeZrOx gave mainly CO under the same conditions. The latter clearly shows that the control of the formation of PdZn phase has great impact for the selective production of hydrocarbons