Unmanned Underwater Vehicles (UUVs) are widely used in commercial, scientific, and military missions for various purposes. What makes this technology challenging is the increasing mission duration and unknown environment. It is necessary to embed fault-tolerant control paradigms into UUVs to increase the reliability of the vehicles and enable them to execute and finalize complex missions. Specifically, fault-tolerant control (FTC) comprises fault detection, identification, and control reconfiguration for fault compensation. Literature review shows that there have been no systematic methods for fault-tolerant control of UUVs in earlier investigations. This study presents a hierarchical methodology of fault detection, identification and compensation (HFDIC) that integrates these functions systematically in different levels. The method uses adaptive finite-impulse-response (FIR) modeling and analysis in its first level to detect failure occurrences. Specifically, it incorporates a FIR filter for on-line adaptive modeling, and a least-mean-squares (LMS) algorithm to minimize the output error between the monitored system and the filter in the modeling process. By analyzing the resulting adaptive filter coefficients, we extract the information on the fault occurrence. The HFDIC also includes a two-stage design of parallel Kalman filters in levels two and three for fault identification using the multiple-model adaptive estimation (MMAE). The algorithm activates latter levels only when the failure is detected, and can return back to the monitoring loop in case of false failures. On the basis of MMAE, we use multiple sliding-mode controllers and reconfigure the control law with a probability-weighted average of all the elemental control signals, in order to compensate for the fault. We validate the HFDIC on the steering and diving subsystems of Naval Postgraduate School (NPS) UUVs for various simulated actuator and/or sensor failures, and test the hierarchical fault detection and identification (HFDI) with realistic data from at-sea experiment of the Florida Atlantic University (FAU) Autonomous Underwater Vehicles (AUVs). For both occasions, we model actuator and sensor failures as additive parameter changes in the observation matrix and the output equation, respectively. Simulation results demonstrate the ability of the HFDIC to detect failures in real time, identify failures accurately with a low computational overhead, and compensate actuator and sensor failures with control reconfiguration. In particular, verification of HFDI with FAU data confirms the performance of the fault detection and identification methodology, and provides important information on the vehicle performance. / Ph. D.

This dissertation focused on the IRIS design since this will likely be one of the designs of choice for future deployment in the U.S and developing countries. With a net 335 MWe output IRIS novel design falls in the “medium” size category and it is a potential candidate for the so called modular reactors, which may be appropriate for base load electricity generation, especially in regions with smaller electricity grids, but especially well suited for more specialized non-electrical energy applications such as district heating and process steam for desalination. The first objective of this dissertation is to evaluate and quantify the performance of a Nuclear Power Plant (NPP) comprised of two IRIS reactor modules operating simultaneously with a common steam header, which in turn is connected to a single turbine, resulting in a steam-mixing control problem with respect to “load-following” scenarios, such as varying load during the day or reduced consumption during the weekend. To solve this problem a single-module IRIS SIMULINK model previously developed by another researcher is modified to include a second module and was used to quantify the responses from both modules. In order to develop research related to instrumentation and control, and equipment and sensor monitoring, the second objective is to build a two-tank multivariate loop in the Nuclear Engineering Department at the University of Tennessee. This loop provides the framework necessary to investigate and test control strategies and fault detection in sensors, equipment and actuators. The third objective is to experimentally develop and demonstrate a fault-tolerant control strategy using this loop. Using six correlated variables in a single-tank configuration, five inferential models and one Auto-Associative Kernel Regression (AAKR) model were developed to detect faults in process sensors. Once detected the faulty measurements were successfully substituted with prediction values, which would provide the necessary flexibility and time to find the source of discrepancy and resolve it, such as in an operating power plant. Finally, using the same empirical models, an actuator failure was simulated and once detected the control was automatically transferred and reconfigured from one tank to another, providing survivability to the system.

Avec le développement de l’éolien, les prescriptions techniques de raccordement de cette technologie obligeront le maintient de sa connexion lors d’incidents sur la tension du réseau électrique. L’enjeu pour le gestionnaire du réseau est de pouvoir utiliser tous les générateurs pour garantir la stabilité du système électrique.A partir d’un modèle dynamique d’une éolienne à base de Machine Asynchrone à Double Alimentation (MADA), une commande vectorielle améliorée a été proposée en prenant en compte la dynamique du flux statorique engendrée par la chute de tension. Les performances supérieures en terme de maintient de la production ont été établies par comparaison avec la méthode de commande classique. Son domaine d’utilisation a été également déterminé.Pendant les creux de tension importants, une protection matérielle (crowbar) est implémentée avec un contrôle de la démagnétisation de la MADA. En outre, de la puissance réactive peut être produite à la fois par la MADA et par le convertisseur connecté au réseau électrique au cours de la défaillance du réseau.Un contrôle vectoriel à hystérésis des courants pour les deux convertisseurs électroniques multiniveaux est proposé et évalué pour améliorer la réponse dynamique de ces convertisseurs et pour réduire les effets des variations des paramètres sur les performances de la commande. Selon la durée du défaut, des objectifs différents de contrôle doivent être réalisés en priorité pour empêcher des surintensités rotoriques et pour fournir de la puissance réactive. Une reconfiguration complète du dispositif de commande de cette éolienne est détaillée pour renforcer le maintient de la production éolienne lors de défaillances / With the massive development of wind energy, the technical requirements for connecting this technology will require the improvement of the fault ride-through capability of grid-connected wind turbines. The task for the grid system operator is to use all generators to ensure the stability of the electrical system.From a dynamic model of a Doubly Fed Induction Generator (DFIG) based wind generator, an improved vector control has been proposed by taking into account the dynamics of the magnetic flux, which are generated by the voltage dip. The higher performances have been established by comparison with the conventional control method. The operation domain was also determined.During serious voltage dips, a hysteresis control scheme of the active Crowbar is proposed to protect the system within a demagnetization method of the DFIG. Moreover, additional reactive power can be produced both by the MADA and the grid-side converter in order to support the electric network during the grid fault.A space vector hysteresis current control strategy of both three-level converters is proposed to improve the dynamic response of the system and to reduce the parameter variation effects on the control performanceDepending on the grid fault duration, different control objectives have to be achieved with priority to restrain the rotor over-current or to supply reactive power. Then the reconfiguration scheme of the control strategies of high power DFIG wind turbine system is proposed to enhance the fault ride-through capability of the DFIG system. With this specific methodology, the DFIG can stay connected and can supply maximal reactive current during voltage dips to help voltage recovery

Les travaux menés durant cette thèse s'intéressent principalement aux avantages que peut offrir la machine asynchrone à double alimentation (MADA) dans un système de propulsion navale. Ceci est obtenu à travers les degrés de libertés additionnels qu'elle apporte, d'une part, par l'exploitation de la redondance structurelle naturelle, et d'autre part , par les stratégies de contrôle qui lui sont appliquées. La première partie de ce mémoire, présente la modélisation du propulseur innovant. Ce dernier est conçu principalement autour de la MADA comme moteur de propulsion. Il est alimenté par deux onduleurs de tension à Modulation de Largeur d'Impulsion (MLI), et entrainant une hélice à trois pales fixes et symétriques. Plusieurs stratégies de commande ont été introduites pour piloter le système. En effet, des lois de contrôle de type linéaires et non linéaires, associées à des divers modulateurs MLI ont été validées et appliquées à cette structure de propulsion. L'innovation apportée dans le cadre de ces travaux consiste à associer à l'optimisation par conception (machine et convertisseurs d'alimentation), une optimisation par la commande et ce en évaluant l'influence de ces techniques pour deux critères de dimensionnement majeurs, à savoir, les pertes dans les convertisseurs de puissances, et les bruits acoustiques et vibratoires. La propulsion navale, comme tout système embarqué, possède des exigences en matière de qualité de service non seulement en termes de performances mais aussi de fiabilité et de disponibilité. En effet, les systèmes conçus pour ce type d'application doivent assurer et garantir une continuité de service en cas d'apparition de défauts au sein des constituants du système. L'utilisation de la MADA dans les systèmes de propulsion offre une redondance structurelle naturelle et analytique, introduite par la commande, qui permet d'assurer une continuité de service du système en présence d'une défaillance dans la structure. Deux défauts sont ainsi considérés dans cette étude, un défaut de semi-conducteur de puissance dans le convertisseur de puissance et un défaut de capteur vitesse/position. Les stratégies de contrôle proposées, les modèles de propulseur établis ainsi que les reconfigurations adoptées suite aux défauts ont été validées expérimentalement sur les bancs développés au LAPLACE dans le cadre de ces travaux. / This study focuses on the benefits that can be induced by the use of the Double Fed Induction Machine (DFIM) operating in motor mode for marine propulsion systems. It can be achieved by the additional degree of freedom it provides, firstly, by exploiting the natural structural redundancy, and secondly, by the alytical redundancy introduced by applied control strategies. The first part of this thesis presents the modeling of a propeller architected mainly around the DFIM and its load such as a propeller with three fixed and symmetrical blades. Several control strategies have been introduced to control the system, in fact, linear and nonlinear control laws type associated with various modulators have been validated and applied to the propulsion structure. The objective was to evaluate the influence of these techniques for two major design criteria, namely, losses in power converters, and noise and vibration noise. Naval propulsion as any embedded system has requirements for the quality of service not only in performance but also reliability and availability. Indeed, the systems designed for these types of applications must ensure and guarantee continuity of service in response to the failures in system components. The use of MADA in propulsion systems provides a natural structural and analytical redundancies which ensure system service continuity in the presence of a fault in this structure. Two faults are considered in this study, a power semiconductor fault in the power converter and a speed sensor / position failure. Control strategies proposed, the propeller modeling established and reconfigurations adopted following settings have been validated by simulation and experimentally on the real laboratory or industrial benches developed in the context of this study.

The need for efficiency, reliability and continuous operation has lead over the years to the development of fault-tolerant electrical drives for various industrial purposes and for transport applications. Permanent-magnet synchronous machines have also been gaining interest due to their high torque-to-mass ratio and high efficiency, which make them a very good candidate to reduce the weight and volume of the equipment.<p><p>In this work, a multidisciplinary approach for the design of fault-tolerant permanent-magnet synchronous machine drives is presented. <p><p>The drive components are described, including the electrical machine, the IGBT-based two-level inverter, the capacitors, the sensors, the controller, the electrical source and interfaces. A literature review of the failure mechanisms and of the reliability model of most of these components is performed. This allows understanding how to take benefit of the redundancy generally introduced in fault-tolerant systems.<p><p>A necessary step towards fault tolerance is the modelling of the electrical drive, both in healthy and faulty operations. A general model of multi-phase machines (with a number of phases equal to or larger than three) and associated converters is proposed. Next, control algorithms for multi-phase machines are derived. The impact of a closed-loop controller upon the occurrence of faults is also examined through simulation analysis and verified by experimental results.<p><p>Condition monitoring of electrical machines has expanded these last decades. New techniques relying on various measurements have emerged, which allow a better planning of maintenance operations and an optimization of the uptime of electrical machines. Regarding drives, a number of sensors are inherently present for control and basic protection functions. The utilization of these sensors for advanced condition monitoring is thus particularly interesting since they are available at no cost. <p><p>A novel fault detection and isolation scheme based on the available measurements (phase currents, DC-link voltage and mechanical position) is developed and validated experimentally. Change-detection algorithms are used for this purpose. Special attention is paid to sensor faults as well, what avoids diagnosis errors.<p><p>Fault-tolerant control can be implemented with passive and active approaches. The former consists in deriving a control scheme that gives acceptable performance for all operating conditions, including faulty conditions. The latter consists in applying dedicated solutions upon the occurrence of faults, i.e. by reconfiguring the control. Both approaches are investigated and implemented. <p><p>Finally, design considerations are discussed throughout the thesis. The advantages and drawbacks of various topologies are analyzed, which eventually leads to the design of a five-phase fault-tolerant permanent-magnet synchronous machine. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Ce travail s’intéresse à l’étude d’un système de pompage turbinage à vitesse variable avec une machine asynchrone doublement alimentée face aux perturbations de réseau électrique. L’objectif est d’assurer la continuité de service de cet élément stabilisateur de réseau électrique de sorte qu’il reste connecté au réseau même en cas de perturbations. Le contrôle du système dans les différentes phases de fonctionnement en mode sain a été tout d’abord développé ainsi qu'une étude de stabilité de système utilisant l’analyse modale. Les différents outils nécessaires pour cette analyse ont été tout d’abord mis en oeuvre. Ensuite, les limites de stabilité du système ont été étudiées tenant compte de la variation de longueur de ligne. Le comportement du système en présence des défauts a été par la suite étudié. Les défauts de réseau considérés sont les défauts symétriques et les défauts asymétriques. Une solution basée sur la modification de la stratégie de contrôle a été adoptée pour le cas des défauts symétriques et une solution basée sur l’ajout d’éléments au circuit de puissance a été adoptée pour les cas des défauts asymétriques. Un dispositif expérimental de 4kW a été mis en oeuvre pour la validation des développements menés dans le cadre de cette thèse. / This work focuses on the study of a variable speed pumped storage system based on a doubly fed induction machine in case of grid disturbances. Thus the main objective is to improve the fault ride through capabilities of this grid stabilizer and to guarantee its connection with the grid even under disturbances. The system control in the different operating phases in healthy conditions is developed and then a system stability study is conducted using the eigenvalue analysis. The system stability limits have been investigated taking into account the variation of grid line length so the grid impedance variation. Then the system behavior under disturbances is analyzed. Theconsidered grid faults are symmetric and asymmetric faults. The investigated fault ride through capabilities of the pumped storage system consist of two solutions, one based on the modification of the control strategy was adopted for the symmetric faults and one based on hardware modification has been adopted for the asymmetric ones. A 4kW laboratory set-up has been developed for experimental validation.