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This thesis presents controllers that use relative range and bearing measurements to steer unmanned aerial vehicles (UAVs) to circular trajectories around stationary, constantly moving and constantly accelerating targets. The range and bearing to the target, along with their derivaties are estimated. These, along with the estimated local heading of the UAVs, are used in the control law, and to estimate the velocity of the target. In this work, six controllers are presented. The controller for a stationary target is derived using Lyapunov's direct method, and feedback linearization is used for the constant velocity and accelerating targets. A new controller is proposed to control the direction of encirclement for moving targets, using Lyapunov's direct method. Additional terms are introduced to maintain a temporally equi-spaced formation around the targets. Theoretical proofs are provided for all controllers using Lyapunov theory. Numerical simulations show vehicles converging to circular formations around both stationary and moving targets. Results are shown using MATLAB simulations with Gaussian noise added to the measurements. Further, a technique is proposed for information exchange between UAVs, with bounds provided for the time taken to dissipate information throughout the system in a scenario with multiple groups of UAVs tracking multiple targets.

Servoposicionadores pneumáticos são sistemas com tecnologia limpa, pois utiliza o ar comprimido como fluido de trabalho, leves, baratos e apresentam boa relação entre a capacidade de carga e a potência fornecida. Contudo, eles apresentam não-linearidades inerentes ao sistema pneumático, como efeitos devidos à compressibilidade do ar, ao atrito e vazamentos. Por estes motivos os controladores lineares mostram-se ineficientes para estes sistemas e é necessário utilizar estratégias de controle mais elaboradas, como, por exemplo, controle por redes neurais, controle com estrutura variável, controle adaptativo ou baseado em linearização por realimentação. Neste trabalho, foi estudada a aplicação do método de linearização por realimentação aliada ao método de controle por realimentação de estados e projeto por alocação de pólos ao controle de um servoposicionador pneumático. A estratégia de linearização por realimentação utiliza as estimativas das não-linearidades do modelo pneumático para linearizar o comportamento do servoposicionador pneumático e permitir o uso tanto de controladores lineares como não-lineares. A análise e prova das características de estabilidade completa do sistema em malha fechada com parâmetros conhecidos foi realizada, obtendo-se a garantia da convergência dos erros de seguimento para zero. Também foi realizada a análise de robustez, com a análise do comportamento do sistema frente às incertezas dos parâmetros estimados. Simulações e ensaios experimentais foram realizados para avaliar o comportamento e a eficiência do controlador proposto. Os resultados do controlador mostram-se promissores, com uma redução de aproximadamente 50% no erro de posição no seguimento de trajetória e na parada precisa com relação às técnicas lineares usualmente aplicadas a estes sistemas. Entretanto, no posicionamento percebe-se a influência do atrito, indicando que a sua compensação deve ser considerada em futuros desenvolvimentos. / Pneumatic positioning systems are clean, lightweight, cheap and present a good rate between the payload and supply power. However, this system shows a highly non-linear behavior, caused mainly by the compression of the air and the friction force. Linear strategies do not present an efficiently control in this kind of system and an improved design technique of control is needed, as neural network control, adaptive control, variable structure control or feedback linearization. In this work, it is developed the application of a feedback linearization control scheme integrated with the state feedback and pole placement method to a pneumatic positioning system. The feedback linearization strategy uses the non-linearities estimation of the pneumatic model to linearize the pneumatic positioning system and allow the use of linear or non-linear controls technique to control the behavior of the servopositioner. In this work, an analysis of the convergence properties of the closed-loop errors of the system when the proposed controller is employed is provided. It is shown that if the parameters are known than the system presents asymptotic convergence of the tracking errors to zero. The robustness properties analysis of the controller is also presented and the system behavior with the uncertainty parameters is analysed. Simulation and experimental tests were performed to assess the behavior and the efficiency of the feedback linearization control. The result of the proposed control shows to be promising on the reduction of position errors in trajectory tracking and in steadystate behavior. The tests show the presence of a strong influence of the friction force and that the friction comparation in techniques must be studied in futher developments.

Cette thèse traite du problème de la stabilisation d'un système de lancement aéroporté (éventuellement non habité) pour satellites. Le lancement aéroporté consiste à ramener, à l'aide d'un avion, un satellite et son lanceur (fusée) à une certaine hauteur, et d'exécuter son lancement dans les airs (souvent en larguant la fusée). Ceci est similaire au lancement d'un missile par un avion chasseur. La plus grande différence réside dans le rapport de masse entre l'avion et le lanceur qui est beaucoup plus proche de l'unité (fusée lourde comparée à la masse de l'avion). Le système est composé de deux étages: le premier étage est dit avion porteur qui est un véhicule aérien automatisé. Il porte le lanceur qui constitue le deuxième étage (la fusée). Dans la première partie, sont proposées des approches de modélisation pour le système de largage pendant et après le largage. La première approche considère que la phase de séparation est instantanée, mais imparfaite. Par conséquent le système est vu comme un modèle d'aéroplane dont les variables d'état sont avec des larges conditions initiales dues à la séparation imparfaite. Une deuxième approche considère la séparation elle-même, représentée par une forte perturbation (un extrême cas) sur les forces et couples aérodynamiques du modèle au cours d'un intervalle de temps. Dans la deuxième partie, afin de stabiliser le système de largage après la séparation, la commande à intégrateur conditionnel modifié est développée dans un premier temps pour une classe des systèmes non-linéaires multi-entrées multi-sorties, avec comme point de départ la théorie introduite par Khalil et co-auteurs pour des systèmes mono entrée mono sortie. Cette commande a été ensuite étendue pour la commande à servo-compensateur conditionnel modifié pour une classe de systèmes non-linéaires multi-entrées multi-sorties. Les deux stratégies ont été appliquées pour stabiliser le système de largage pendant et après la phase de séparation. Ces techniques ont l'avantage d'être robustes et de pouvoir utiliser des modèles approximatifs. D'un autre côté, il était important d'examiner la possibilité d'obtenir de meilleures performances en utilisant de meilleurs modèles. Pour cette raison, la commande de linéarisation par bouclage dynamique a été étudiée. Finalement, les performances de toutes ces méthodes de commande (ainsi que certaines commandes de base additionnelles) ont été illustrées par des simulations sous Matlab/Simulink sur un modèle non-linéaire de F-16. / This thesis addresses the problem of the stabilization of an (unmanned) airlaunch system. Air launching consists in bringing a satellite and its launcher (rocket) to a certain height using an aircraft, and then launching it from the air (often by dropping the rocket), in a similar way of launching a missile from a fighter. The main difference is that the envisaged mass ratio is much closer to one (heavy rocket compared to aircraft mass). It is then composed of two stages: the first stage called carrier aircraft consists of an <unmanned> aerial vehicle that carries the launcher which constitutes the second stage (rocket). This thesis starts by introducing the problem and objectives, continues by presenting several approaches to model the airlaunch system, and ends by developing different advanced control methods to stabilize it after the launching phase. In the modeling part we propose a firstly approach called the initial condition model which assumes that the separation phase is instantaneous, and then the airlaunch system is composed of an aircraft model after the launching phase but with large initial conditions on its state variables, caused by a non-perfect split phase. A second approach assumes that the separation phase itself is modeled by a disturbance on aerodynamic forces and moments (from a worst case) during a time interval. In the control part a modified conditional integrator controller for a class of nonlinear multi-input multi-output systems is first developed starting from the conditional integrator theory developed by Khalil and co-workers. It is then extended to a modified conditional servocompensator control for a class of nonlinear multi-input multi-output systems. Both control strategies were then applied to stabilize the airlaunch system after the separation phase. They have the advantage of being very robust, and they don't depend so much on reliable models. Even if these control strategies gave good results, it was investigated in this thesis another control approach much more dependent on detailed and reliable models. This approach was based on dynamic feedback linearization theory, and the main idea is to obtain better performance in trade off better models. Finally, all proposed control methods (plus some standard ones) were compared and illustrated by simulations under Matlab/Simulink on a nonlinear F-16 model. These simulations have shown that the results were as expected, and that each control strategy was well fit for a particular situation.

The control theory of nonlinear systems has been receiving increasing attention in recent years, both for its technical importance as well as for its impact in various fields of application. In several key areas, such as aerospace, chemical and petrochemical industries, bioengineering, and robotics, a new practical application for this tool appears every day. System nonlinearity is characterized when at least one component or subsystem is nonlinear. Classical methods used in the study of linear systems, particularly superposition, are not usually applied to the nonlinear systems. It is necessary to use other methods to study the control of these systems. For a wide class of nonlinear systems, a rather important structural feature comes from the strong nonlinearity appearing as coupling between spectrally decoupled parts of the system. Even in the case of low frequencies, where lumped models can still be employed the nonlinear coupling between parts of the system requires specific treatment, using advanced mathematical tools. In this context, an alternative, frequency domain approach is pursued here. In the rest of this work, a specific system form of linearly decoupled but nonlinearly coupled subsystems is examined. The mathematical toolbox of the Hilbert transform is appropriately introduced for obtaining two low-pass subsystems that form an equivalent description of the essential overall system dynamics. The nonlinear coupled dynamics is investigated systematically by partitioning the coupled system state vector in such a way as to fully exploit the low-pass and the band-pass intrinsic features of free dynamics. In particular, by employing the Hilbert Transform, a low-pass equivalent system is derived. Then, a typical case is investigated thoroughly by means of numerical simulation of the original coupled low and band-pass, real-state-variable system and the low-pass-equivalent, complex-state-variable derived one. The nonlinear model equations considered here pave the way for a systematic investigation of nonlinear feedback control options designed to operate mechatronic transducers in energy harvesting, sensing or actuation modes.

Utilizing the universal approximation property of neural networks, we develop several novel approaches to neural network-based adaptive output feedback control of nonlinear systems, and illustrate these approaches for several flight control applications. In particular, we address the problem of non-affine systems and eliminate the fixed point assumption present in earlier work. All of the stability proofs are carried out in a form that eliminates an algebraic loop in the neural network implementation. An approximate input/output feedback linearizing controller is augmented with a neural network using input/output sequences of the uncertain system. These approaches permit adaptation to both parametric uncertainty and unmodeled dynamics. All physical systems also have control position and rate limits, which may either deteriorate performance or cause instability for a sufficiently high control bandwidth. Here we apply a method for protecting an adaptive process from the effects of input saturation and time delays, known as ``pseudo control hedging". This method was originally developed for the state feedback case, and we provide a stability analysis that extends its domain of applicability to the case of output feedback. The approach is illustrated by the design of a pitch-attitude flight control system for a linearized model of an R-50 experimental helicopter, and by the design of a pitch-rate control system for a 58-state model of a flexible aircraft consisting of rigid body dynamics coupled with actuator and flexible modes. A new approach to augmentation of an existing linear controller is introduced. It is especially useful when there is limited information concerning the plant model, and the existing controller. The approach is applied to the design of an adaptive autopilot for a guided munition. Design of a neural network adaptive control that ensures asymptotically stable tracking performance is also addressed.

In this research, nonlinear attitude controllers are designed for a low earth orbit satellite intended to be used in observatory missions. The attitude is represented by the Modified Rodriguez Parameters (MRP) which is a minimal representation providing a fully invertible kinematics. As a difference from the classical satellite models existent in the literature, the model of this work incorporates the dynamics of the reaction wheel (actuator) including a brushless dc motor which is armature controlled. The total model has four group of state vectors which are the attitude, body rates, actuator torque and velocity. The main control approach of this research is developed by utilizing integrator back - stepping which provides a recursive stabilization methodology to the designer. For performance comparison, a second controller based on input output feedback linearization (IOFL) is presented. Both of the approaches produce a torque demand law and this is used for generating a desired reaction wheel velocity command. A reaction wheel controller uses the motor as the actuator and produces the necessary amount of the torque according to the desired wheel velocity command. In addition for the back - stepping based approach, a stability analysis against the external disturbance torques is also provided. Simulations are presented for validating the performance and robustness of the proposed controllers.

Dynamic security limits the power transfer capacity between regions and therefore has an economic impact. The power modulation control of high-voltage direct current (HVDC) links can improve the dynamic security of the power system. Having several HVDC links in a system creates the opportunity to coordinate such control, and coordination also ensures that negative interactions do not occur among the controllable devices. This thesis aims to increase dynamic security by coordinating HVDC links, as an alternative to decreasing the transfer capacity. This thesis contributes four control approaches for increasing the dynamic stability, based on feedforward control, adaptive control, optimal control, and exact-feedback linearization control. Depending on the available measurements, dynamic system model, and system topology, one of the developed methods can be applied. The wide-area measurement system provides the central controller with real-time data and sends control signals to the HVDC links. The feedforward controller applies rapid power dispatch, and the strategy used here is to link the N-1 criterion between two systems. The adaptive controller uses the modal analysis approach; based on forecasted load paths, the controller gains are adaptively adjusted to maximize the damping in the system. The optimal controller is designed based on an estimated reduced-order model; system identification develops the model based on the system response. The exact-feedback linearization approach uses a pre-feedback loop to cancel the nonlinearities; a stabilizing controller is designed for the remaining linear system. The conclusion is that coordinating the HVDC links improves the dynamic stability, which makes it possible to increase the transfer capacity. This conclusion is also supported by simulations of each control approach. / QC 20110302

Este trabalho apresenta a modelagem matemática para um manipulador móvel composto por uma base móvel (o robô móvel Twil) e um manipulador (o manipulador WAM da Barrett). Os modelos cinemático e dinâmico para a base móvel, manipulador e manipulador móvel são apresentados. Como o manipulador móvel é um sistema não linear, uma estratégia de controle baseada em linearização por realimentação da dinâmica da plataforma seguida por uma transformação não suave para tratar a não holonomicidade do modelo cinemático é proposta. Então o método de backstepping é utilizado para obter as entradas do modelo dinâmico. Um controlador de torque calculado é proposto para o manipulador, Estas técnicas de controle são utilizadas simultaneamente para controlar o manipulador móvel. A implementação dos controladores propostos, na forma de plugins para o gerenciador de controladores é feita no ROS, assim os controladores são executados em tempo real. A maioria dos controladores existentes no ROS são do tipo SISO baseados em controle PID e independentes para cada junta, sendo que neste trabalho controladores MIMO não lineares são implementados. / This work presents a mathematical modelling for a mobile manipulator composed by a mobile base (the Twil mobile robot) and a manipulator (the Barrett WAM manipulator). The kinematic and dynamic models for the mobile base, the manipulator and the mobile manipulator are presented. As the the mobilie manipulator is a non-linear system, a control strategy based on feedback linearization of the platform dynamics followed by a non-smooth transform to handle the non-holonomicity of its kinematic model is proposed. Then, the backstepping method is used to obtain the inputs for the dynamic model. A computed torque controller is proposed for the manipulador. These control techniques are used simultaneously to control the mobile manipulator. The implementation of the proposed controllers is done in ROS as plugins for the controller manager so that the controllers run in real-time. Most controllers existing in ROS are independent joint SISO controllers based on the PID control law while in this work MIMO non-linear controllers are implemented.

Os atuadores hidráulicos são usados em muitas aplicações e áreas de trabalho devido à sua capacidade para manipular grandes forças com baixa inércia, pouca vibração e capacidade de trabalho por longos períodos de tempo. Entretanto, o maior problema no uso destes tipos de atuadores são as características dinâmicas tais como não-linearidade e variação de parâmetros, as quais dificultam seu controle em malha fechada. Assim, para controlar sistemas hidráulicos, é necessário o uso de modelos matemáticos não lineares e a aplicação de leis de controle complexas para obter um seguimento de trajetória com alta precisão. O objetivo principal deste trabalho é a obtenção de um sistema que siga com precisão as trajetórias de referência do tipo senoidais. Para tanto, este trabalho aborda o projeto de uma lei de controle por realimentação de estados (feedback linearization) combinada com o princípio do modelo interno para aplicar no sistema hidráulico de atuação de uma máquina de ensaios de fadiga. O princípio do modelo interno é aplicado utilizando um compensador dinâmico (que contém pólos imaginários com a mesma freqüência que o sinal de referência) num laço externo do sistema linearizado por realimentação de estados. Uma lei de controle do tipo realimentação de estados, considerando os estados do sistema linearizado e os do compensador dinâmico, é projetada para garantir estabilidade no sistema de malha fechada. A fim de avaliar a estratégia de controle proposta são discutidos e apresentados simulações do modelo experimental. / Hydraulic actuators are used in many applications due to their ability in driving large forces with low inertia and little vibration for a long period of time. However, the main problem in controlling these kinds of systems concerns their dynamics, which presents several nonlinearities and parameters variations. Thus, to control hydraulic systems, appropriated nonlinear models and complex control techniques to achieve a stable force regulation with a specified performance are necessary. The purpose of this work is the application of a feedback linearization scheme in the design of a force controller for a hydraulic actuator used in a fatigue test machine. The main control objective considered regards the achievement of sinusoidal force reference tracking. With this aim the internal model principle is applied by using a dynamic compensator (containing imaginary poles with the same frequency of the force reference) in an outer regulation loop. A state feedback control law, considering both the states of the feedback linearized hydraulic system and the ones of the dynamic compensator, is therefore designed in order to stabilize the whole closed-loop system. Experimental model identification and simulation control results are presented and discussed.