abstract: Unmanned aerial vehicles have received increased attention in the last decade due to their versatility, as well as the availability of inexpensive sensors (e.g. GPS, IMU) for their navigation and control. Multirotor vehicles, specifically quadrotors, have formed a fast growing field in robotics, with the range of applications spanning from surveil- lance and reconnaissance to agriculture and large area mapping. Although in most applications single quadrotors are used, there is an increasing interest in architectures controlling multiple quadrotors executing a collaborative task. This thesis introduces a new concept of control involving more than one quadrotors, according to which two quadrotors can be physically coupled in mid-flight. This concept equips the quadro- tors with new capabilities, e.g. increased payload or pursuit and capturing of other quadrotors. A comprehensive simulation of the approach is built to simulate coupled quadrotors. The dynamics and modeling of the coupled system is presented together with a discussion regarding the coupling mechanism, impact modeling and additional considerations that have been investigated. Simulation results are presented for cases of static coupling as well as enemy quadrotor pursuit and capture, together with an analysis of control methodology and gain tuning. Practical implementations are introduced as results show the feasibility of this design. / Dissertation/Thesis / Masters Thesis Aerospace Engineering 2016

La première partie de la thèse est consacrée à la commande avec contraintes de systèmes différentiellement plats. Deux types de systèmes sont étudiés : les systèmes non linéaires de dimension finie et les systèmes linéaires à retards. Nous présentons une approche unifiée pour intégrer les contraintes d'entrée/état/sortie dans la planification des trajectoires. Pour cela, nous spécialisons les sorties plates (ou les trajectoires de référence) sous forme de courbes de Bézier. En utilisant la propriété de platitude, les entrées/états du système peuvent être exprimés sous la forme d'une combinaison de sorties plates (courbes de Bézier) et de leurs dérivées. Par conséquent, nous obtenons explicitement les expressions des points de contrôle des courbes de Bézier d'entrées/états comme une combinaison des points de contrôle des sorties plates. En appliquant les contraintes souhaitées à ces derniers points de contrôle, nous trouvons les régions faisables pour les points de contrôle de Bézier de sortie, c'est-à-dire un ensemble de trajectoires de référence faisables. Ce cadre permet d’éviter le recours, en général fort coûteux d’un point de vue informatique, aux schémas d’optimisation. Pour résoudre les incertitudes liées à l'imprécision de l'identification et modélisation des modèles et les perturbations, nous utilisons la commande sans modèle (Model Free Control-MFC) et dans la deuxième partie de la thèse, nous présentons deux applications démontrant l'efficacité de notre approche : 1. Nous proposons une conception de contrôleur qui évite les procédures d'identification du système du quadrotor tout en restant robuste par rapport aux perturbations endogènes (la performance de contrôle est indépendante de tout changement de masse, inertie, effets gyroscopiques ou aérodynamiques) et aux perturbations exogènes (vent, bruit de mesure). Pour atteindre notre objectif en se basant sur la structure en cascade d'un quadrotor, nous divisons le système en deux sous-systèmes de position et d'attitude contrôlés chacun indépendamment par la commande sans modèle de deuxième ordre dynamique. Nous validons notre approche de contrôle avec trois scénarios réalistes : en présence d'un bruit inconnu, en présence d’un vent variant dans le temps et en présence des variations inconnues de masse, tout en suivant des manœuvres agressives. 2. Nous utilisons la commande sans modèle et les correcteurs « intelligents » associés, pour contrôler (maintenir) l'élasticité horizontale d'un système de Cloud Computing. Comparée aux algorithmes commerciaux d’Auto-Scaling, notre approche facilement implémentable se comporte mieux, même avec de fluctuations aigües de charge. Ceci est confirmé par des expériences sur le cloud public Amazon Web Services (AWS). / The first part of the thesis is devoted to the control of differentially flat systems with constraints. Two types of systems are studied: non-linear finite dimensional systems and linear time-delay systems. We present an approach to embed the input/state/output constraints in a unified manner into the trajectory design for differentially flat systems. To that purpose, we specialize the flat outputs (or the reference trajectories) as Bézier curves. Using the flatness property, the system’s inputs/states can be expressed as a combination of Bézier curved flat outputs and their derivatives. Consequently, we explicitly obtain the expressions of the control points of the inputs/states Bézier curves as a combination of the control points of the flat outputs. By applying desired constraints to the latter control points, we find the feasible regions for the output Bézier control points i.e. a set of feasible reference trajectories. This framework avoids the use of generally high computing cost optimization schemes.    To resolve the uncertainties arising from imprecise model identification and the unknown pertubations, we employ the Model-Free Control (MFC) and in the second part of the thesis we present two applications demonstrating the effectiveness of our approach: 1. We propose a controller design that avoids the quadrotor’s system identification procedures while staying robust with respect to the endogenous (the control performance is independent of any mass change, inertia, gyroscopic or aerodynamic effects) and exogenous disturbances (wind, measurement noise). To reach our goal, based on the cascaded structure of a quadrotor, we divide the system into positional and attitude subsystems each controlled by an independent Model-Free controller of second order dynamics. We validate our control approach in three realistic scenarios: in presence of unknown measurement noise, with unknown time-varying wind disturbances and mass variation while tracking aggressive manoeuvres. 2. We employ the Model-Free Control to control (maintain) the “horizontal elasticity” of a Cloud Computing system. When compared to the commercial “Auto-Scaling” algorithms, our easily implementable approach behaves better, even with sharp workload fluctuations. This is confirmed by experiments on the Amazon Web Services (AWS) public cloud.

Unmanned Aerial Vehicles (UAV) control has become a very important point of scientific study. The control design challenges of a UAV make it one of the most researched areas in modern control applications. This thesis specifically chooses the Quadrotor as the UAV platform. Considering the quadrotor has 4 rotors and 6 degrees of freedom, it is an underactuated system and is dynamically unstable that has to be stabilized by a suitable control algorithm in order to operate autonomously. This thesis focuses on the quaternion representation of the quadrotor system dynamics and develops an adaptive control for its trajectory tracking problem. The control design uses the certainty equivalence principle where adaptive tracking controls are designed separately for each of the translational and rotational subsystems. With this approach, the success of the outer loop translational control relies on the fast convergence of the inner loop rotational control in order to guarantee the system’s stability while achieving the tracking objective. For the translational subsystem in the outer loop, a modified geometric control technique is considered with an adaptive component for the estimation of the uncertain mass of the quadrotor. For the rotational subsystem in the inner loop a backstepping based control design is adopted due to its systematic design and intuitive approach. An adaptive component is further integrated with it to estimate the integrated components of the uncertain Moment of Inertia matrix and other constant parameters in the system dynamics to guarantee the stability of the inner loop system while achieving the tracking objective. Furthermore, a complete backstepping control design methodology is presented which overcomes the issues of certainty equivalence principle where the inner loop needs to execute significantly faster than the outer loop to stabilize the system.

abstract: Control algorithm development for quadrotor is usually based solely on rigid body dynamics neglecting aerodynamics. Recent work has demonstrated that such a model is suited only when operating at or near hover conditions and low-speed flight. When operating in confined spaces or during aggressive maneuvers destabilizing forces and moments are induced due to aerodynamic effects. Studies indicate that blade flapping, induced drag, and propeller drag influence forward flight performance while other effects like vortex ring state, ground effect affect vertical flight performance. In this thesis, an offboard data-driven approach is used to derive models for parasitic (bare-airframe) drag and propeller drag. Moreover, thrust and torque coefficients are identified from static bench tests. Among the two, parasitic drag is compensated for in the position controller module in the PX4 firmware. 2-D circular, straight line, and minimum snap rectangular trajectories with corridor constraints are tested exploiting differential flatness property wherein altitude and yaw angle are constant. Flight tests are conducted at ASU Drone Studio and results of tracking performance with default controller and with drag compensated position controller are presented. Root mean squared tracking error in individual axes is used as a metric to evaluate the model performance. Results indicate that, for circular trajectory, the root mean squared error in the x-axis has reduced by 44.54% and in the y-axis by 39.47%. Compensation in turn degrades the tracking in both axis by a maximum under 12% when compared to the default controller for rectangular trajectory case. The x-axis tracking error for the straight-line case has improved by 44.96% with almost no observable change in the y-axis. / Dissertation/Thesis / Real-time Flight Test of Circular Trajectories / Masters Thesis Aerospace Engineering 2020

Wind turbines have been used for decades to harvest wind energy. They are suitable only to work on close to ground, and have several drawbacks that are related to the availability of the wind and the amount of extracted power compared with the cost of construction. On the other hand, there is an abundant wind power that is available at high altitudes. The wind jet streams at high elevations 8 - 12 kms are pervasive and persistent, and can potentially produce immense wind energy. Even at moderate elevations of 4 - 5 kms, wind power densities are much higher than on ground and more consistent. Consequently, in this thesis research, we investigate the topic of harvesting energy from high altitudes. First, we provide a comprehensive review of two existing theoretical methods that are proposed for airborne wind energy harvesting, the tethered airfoil, and the static autogyro. The latter approach has inherent advantages that warrant further investigation. Autorotation is a well-known phenomenon where a rotor sustains its angular velocity and maintains significant lift in the presence of strong aerodynamic forces and torques generated by interaction with a strong wind field. Autorotation has been researched in the context of free descent of helicopters but has not been considered for energy harvesting. Existing models have mainly focused on statics analysis. In this research, we propose a simple dynamic model of the Autogyro, with the goal of ultimately realizing an Autorotation Energy System (AES). The focus of our work is to provide a preliminary dynamic analysis of autorotation, which is largely absent in current literature, to explore the possibility of using autorotation for designing a multipurpose system that can simultaneously fly at high altitudes and generate energy from the wind. The proposed preliminary dynamic model is used to generate a simulation platform, which is used to explore the autogyros rudimentary maneuvers. Extensive simulation results are provided to evaluate the dynamic performance of AES. Energy harvesting analyses and results are also presented. It is expected that the results will guide the choice of actuations and control that will be necessary for generating combined autorotation and powered flights that would be net energy generating or energy efficient. The research will be relevant for both tethered and untethered AES and could also be incorporated into multi-rotor based UAVs such as quadrotors.

Esta dissertação visa a modelagem, simulação e controle de um veículo aéreo não tripulado (VANT) do tipo quadricóptero, utilizando-se as técnicas de controle ótimo e controle robusto no espaço de estados. O quadricóptero deve realizar as funções de decolagem, voo em cruzeiro e pouso de maneira autônoma. A dissertação inclui a síntese e análise comparativa entre um observador de estados de ordem plena de Luenberger e um filtro de Kalman. Além disso, um controlador linear quadrático gaussiano e um controlador robusto serão sintetizados e avaliados, procurando-se avaliar qual tem o melhor desempenho nas diversas tarefas do VANT. / This dissertation includes the modeling, simulation and control of a quadrotor unmanned aerial vehicle by using optimum control and robust control techniques on the space state. The quadrotor must perform the takeoff, cruise flight and landing in an autonomous way. This report also presents the synthesis and comparative analysis between a Luenberger full order state observer and a Kalman filter. A linear quadratic gaussian controller and a robust controller will be also synthetized and analyzed, to compare which one exhibits the best performance on the UAV tasks.

Esta dissertação visa a modelagem, simulação e controle de um veículo aéreo não tripulado (VANT) do tipo quadricóptero, utilizando-se as técnicas de controle ótimo e controle robusto no espaço de estados. O quadricóptero deve realizar as funções de decolagem, voo em cruzeiro e pouso de maneira autônoma. A dissertação inclui a síntese e análise comparativa entre um observador de estados de ordem plena de Luenberger e um filtro de Kalman. Além disso, um controlador linear quadrático gaussiano e um controlador robusto serão sintetizados e avaliados, procurando-se avaliar qual tem o melhor desempenho nas diversas tarefas do VANT. / This dissertation includes the modeling, simulation and control of a quadrotor unmanned aerial vehicle by using optimum control and robust control techniques on the space state. The quadrotor must perform the takeoff, cruise flight and landing in an autonomous way. This report also presents the synthesis and comparative analysis between a Luenberger full order state observer and a Kalman filter. A linear quadratic gaussian controller and a robust controller will be also synthetized and analyzed, to compare which one exhibits the best performance on the UAV tasks.

abstract: Toward the ambitious long-term goal of a fleet of cooperating Flexible Autonomous Machines operating in an uncertain Environment (FAME), this thesis addresses various perception and control problems in autonomous aerial robotics. The objective of this thesis is to motivate the use of perspective cues in single images for the planning and control of quadrotors in indoor environments. In addition to providing empirical evidence for the abundance of such cues in indoor environments, the usefulness of these perspective cues is demonstrated by designing a control algorithm for navigating a quadrotor in indoor corridors. An Extended Kalman Filter (EKF), implemented on top of the vision algorithm, serves to improve the robustness of the algorithm to changing illumination. In this thesis, vanishing points are the perspective cues used to control and navigate a quadrotor in an indoor corridor. Indoor corridors are an abundant source of parallel lines. As a consequence of perspective projection, parallel lines in the real world, that are not parallel to the plane of the camera, intersect at a point in the image. This point is called the vanishing point of the image. The vanishing point is sensitive to the lateral motion of the camera and hence the quadrotor. By tracking the position of the vanishing point in every image frame, the quadrotor can navigate along the center of the corridor. Experiments are conducted using the Augmented Reality (AR) Drone 2.0. The drone is equipped with the following componenets: (1) 720p forward facing camera for vanishing point detection, (2) 240p downward facing camera, (3) Inertial Measurement Unit (IMU) for attitude control , (4) Ultrasonic sensor for estimating altitude, (5) On-board 1 GHz Processor for processing low level commands. The reliability of the vision algorithm is presented by flying the drone in indoor corridors. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2018

L'objectif de ce travail de thèse est de concevoir des algorithmes de commande et de navigation pour le suivi des cibles dynamiques au sol en utilisant des véhicules aériens. Les quaternions, qui fournissent une alternative aux représentations classiques de la dynamique des véhicules aériens, ont été choisis comme une base pour développer des contrôleurs robustes et des algorithmes de navigation agile, en raison de leurs avantages tels que l'absence de singularités et discontinuités, et leur simplicité mathématique lors de la manipulation des rotations. Les approches de commande explorées à l'aide de quaternions dans cette thèse commencent par le retour d'état, la passivité, et des contrôleurs basés sur l'énergie, jusqu'à des modes glissants, et des approches de saturation en trois dimensions. Ensuite, des stratégies de navigation autonomes et semi-autonomes pour quadrirotors ont été explorées. Un algorithme a été développé pour le pilotage d'un quadrirotor en utilisant des gestes d'un utilisateur portant un bracelet. Afin de faciliter le fonctionnement des multi rotors dans des scénarios défavorables, une stratégie de déploiement agressive a été proposée ou un quadrirotor est lancé à la main avec ses moteurs éteints. Finalement, des techniques de navigation autonomes pour le suivi des cibles dynamiques ont été conçues. Un algorithme de génération de trajectoire basée sur des équations différentielles a été introduit pour le suivi d'un véhicule terrestre tout en décrivant des cercles. Enfin un algorithme de planification de chemin distribué a été développé pour une flottille de drones, afin de suivre de façon autonome des cibles au sol, en résolvant un problème d'optimisation en ligne. / The objective of this thesis work is to design control and navigation algorithms for tracking of dynamic ground targets using aerial vehicles. Quaternions, which provide an alternative to the classical representations of aerial vehicle dynamics, have been chosen as a basement to develop robust controllers and agile navigation algorithm, due to their advantages such as the absence of singularities and discontinuities and their mathematical simplicity when handling rotations. The quaternion-based control approaches explored in this thesis range from state feedback, passivity, and energy-based controllers, up to sliding modes, and three-dimensional saturation approaches. Then, autonomous and semi-autonomous navigation strategies for quadrotors were explored. An algorithm has been developed for controlling a quadrotor using gestures from a user wearing an armband. To facilitate the operation of multirotors in adverse scenarios, an aggressive deployment strategy has been proposed where a quadrotor is launched by hand With its motors turned off. Finally, autonomous navigation techniques for tracking dynamic targets have been designed. A trajectory generation algorithm based on differential equations has been introduced to track a land vehicle while describing circles. Finally a distributed path planning algorithm has been developed for a fleet of drones to autonomously track ground targets by solving an online optimization problem.

Ces dernières années, l’émergence des nouvelles technologies tels que la miniaturisation des composants, les dispositifs de communication sans fils, l’augmentation de la taille de stockage et les capacités de calcul, a permis la conception de systèmes multi-agents coopératifs de plus en plus complexes. L’un des plus grands axes de recherche dans cette thématique concerne la commande en formation de flottes de véhicules autonomes. Un grand nombre d’applications et de missions, civiles et militaires, telles que l’exploration, la surveillance, et la maintenance, ont alors été développées et réalisées dans des milieux variés (terre, air, eau). Durant l’exécution de ces tâches, les véhicules doivent interagir avec leur environnement et entre eux pour se coordonner. Les outils de communication disponibles disposent souvent d’une portée limitée. La préservation de la connexion au sein du groupe devient alors un des objectifs à satisfaire pour que la tâche puisse être accomplie avec succès. Une des possibilités pour garantir cette contrainte est le déplacement en formation permettant de préserver les distances et la structure géométrique du groupe. Il est toutefois nécessaire de disposer d’outils et de méthodes d’analyse et de commande de ces types de systèmes afin d’exploiter au maximum leurs potentiels. Cette thèse s’inscrit dans cette direction de recherche en présentant une synthèse et une analyse des systèmes dynamiques multi-agents et plus particulièrement la commande en formation de véhicules autonomes. Les lois de commande développées dans la littérature pour la commande en formation permettent d’accomplir un grand nombre de missions avec un niveau de performance élevé. Toutefois, si un défaut/défaillant apparaît dans la formation, ces lois de commandes peuvent s’avérer très limitées, engendrant un comportement instable du système. Le développement de commandes tolérantes aux défauts devient alors primordial pour maintenir les performances de commande en présence de défauts. Cette problématique sera traitée dans ce mémoire de thèse et concernera le développement et la conception de commandes en formation tolérantes au défaut dévolu à une flotte de véhicules autonomes suivant différente configuration/structuration / In recent years, the emergence of new technologies such as miniaturization of components, wireless communication devices, increased storage size and computing capabilities have allowed the design of increasingly complex cooperative multi-agent systems. One of the main research axes in this topic concerns the formation control of fleets of autonomous vehicles. Many applications and missions, civilian and military, such as exploration, surveillance, and maintenance, were developed and carried out in various environments. During the execution of these tasks, the vehicles must interact with their environment and among themselves to coordinate. The available communication tools are often limited in scope. The preservation of the connection within the group then becomes one of the objectives to be satisfied in order to carry out the task successfully. One of the possibilities to guarantee this constraint is the training displacement, which makes it possible to preserve the distances and the geometrical structure of the group. However, it is necessary to have tools and methods for analyzing and controlling these types of systems in order to make the most of their potential. This thesis is part of this research direction by presenting a synthesis and analysis of multi-agent dynamical systems and more particularly the formation control of autonomous vehicles. The control laws developed in the literature for formation control allow to carry out a large number of missions with a high level of performance. However, if a fault/failure occurs in the training, these control laws can be very limited, resulting in unstable system behavior. The development of fault tolerant controls becomes paramount to maintaining control performance in the presence of faults. This problem will be dealt with in more detail in this thesis and will concern the development and design of Fault tolerant controls devolved to a fleet of autonomous vehicles according to different configuration/structuring