Thesis (Ph.D.(Electronic engineering))--University of Pretoria, 2008. / Summary in English. Includes bibliographical references.

Thesis (M. Phil.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 121-126). Also available in print.

Thesis (Ph. D.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 134-142). Also available on the World Wide Web.

Η παρούσα διπλωματική εργασία ασχολείται με τη μελέτη και τον έλεγχο ενός συστήματος γερανού με προηγμένες τεχνικές. Το σύστημα αποτελείται από έναν κινούμενο φορέα στον οποίο είναι συνδεδεμένο ένα εκκρεμές φορτίο με μεταβαλλόμενο μήκος. Σκοπός είναι η μεταφορά του φορτίου σε μια διαφορετική θέση και ύψος σε ελάχιστο χρόνο με μηδενική υπολειπόμενη ταλάντωση. Αρχικά παρουσιάζεται ο έλεγχος του συστήματος με τη μέθοδο ανατροφοδότησης κατάστασης. Στη συνέχεια αναλύεται η βασική θεωρία του input shaper και προτείνεται μια προσαρμοστική τεχνική για την εφαρμογή του σε σύστημα με μεταβαλλόμενο μήκος σχοινιού. Έπειτα, η τεχνική αυτή βελτιώνεται συνδυάζοντάς την με τον έλεγχο ανατροφοδότησης κατάστασης και τέλος εφαρμόζεται ένας μη γραμμικός ελεγκτής για το πλήρες μη γραμμικό σύστημα. Τα αποτελέσματα παρουσιάζονται με εκτενείς προσομοιώσεις καθώς και με εργαστηριακές μετρήσεις σε κατάλληλη πειραματική διάταξη. / This diploma thesis includes the analysis and control of a crane system using advanced control techniques. The system consists of a carrier mass connected with a playload with a hoisting mechanism. The aim of this work is to transport the payload to a different position and a different level within minimum time period while simutaneously minimizing the residual vibration. At first, a state feedback control is presented. Furthermore, the input shaping technique is analyzed and an adaptive version of the input shaper is proposed including hoisting cases. Moreover, this technique is significally improved when combined with a state feedback control law and finally a nonlinear controller is proposed for the total nonlinear system. The above techniques are justified with both simulation and experimental results from a suitable experimental setup.

Η παρούσα διπλωματική εργασία ασχολείται με τη μελέτη και το σχεδιασμό ενός άμεσου προσαρμοστικού ελεγκτή, για μη γραμμικά συστήματα με αβεβαιότητα και εξωγενείς διαταραχές. Αρχικά παρουσιάζονται οι έννοιες του προσαρμοστικού ελέγχου, των μη γραμμικών συστημάτων και διερευνώνται οι έννοιες της ευστάθειας και των διαταραχών, με ιδιαίτερη έμφαση στην ευστάθεια κατά Lyapunov. Στη συνέχεια προτείνεται ένας προσαρμοστικός ελεγκτής για άμεσο προσαρμοστικό έλεγχο, προσαρμοστική ευστάθεια, απόρριψη διαταραχών και εκτέλεση εντολών, σε μη γραμμικά δυναμικά συστήματα πολλαπλών μεταβλητών, με αβεβαιότητα και εξωγενείς διαταραχές, ο οποίος εγγυάται μερική ασυμπτωτική ευστάθεια του συστήματος κλειστού βρόχου. Το προτεινόμενο πλαίσιο, ειδικεύεται περαιτέρω για τις περιπτώσεις όπου το μη γραμμικό σύστημα παρουσιάζεται σε κανονική μορφή, με ευσταθείς input-to-state internal dynamics, έχει μια είσοδο ή έχει εξωγενείς L2 διαταραχές. Τέλος ο προτεινόμενος ελεγκτής εφαρμόζεται σε αρκετά πειραματικά συστήματα, καθώς και στον έλεγχο της αστάθειας θερμοακουστικής καύσης. / This diploma thesis features the analysis and design of a direct adaptive controller, for nonlinear uncertain systems with exogenous disturbances. At first, we introduce the concept of adaptive control and we underline its’ need in modern applications. Also, we include a brief presentation of nonlinear systems and we inquire into the theory of stabilization and disturbances, with significant emphasis in Lyapunov’s methods. Furthermore we develop a direct adaptive control framework for adaptive stabilization, disturbance rejection, and command following of multivariable nonlinear uncertain dynamical systems with exogenous disturbances, which guarantees partial asymptotic stability of the closed-loop system. The proposed framework is further specialized for the cases where the nonlinear system is represented in normal form with input-to-state stable internal dynamics, has single-input with uncertain dynamics, or exogenous L2 disturbances .Finally we present several illustrative numerical examples and we apply our framework to the control of thermoacoustic combustion instabilities.

CAPES / Este trabalho apresenta um estudo comparativo entre técnicas de controle PID (proporcional integral e derivativo) lineares e não-lineares, aplicada a um conversor abaixador de tensão de topologia Buck. O principal objetivo desse trabalho é a comparação do desempenho das técnicas de controle PID clássico e o controle PID não linear com ganhos baseados em perfil gaussiano. Trata-se de uma técnica de controle adaptativo baseada no controle PID clássico, através de uma metodologia na qual os ganhos são obtidos a partir de uma função gaussiana, buscando obter um aumento do desempenho desse sistema. Foram realizadas simulações computacionais, onde foi feita a varredura paramétrica de cada ganho (proporcional, integral e derivativo). Os resultados alcançados comprovam a eficiência da técnica proposta. / This work presents a comparative study of linear and non-linear PID control techniques (proportional, integral and derivative) applied to a step-down voltage converter in the Buck topology. The main objective of this work is to compare the performance of classical PID control and nonlinear PID control with gains based on Gaussian-shaped functions. It is an adaptive control technique based on the classical PID control, by means of a methodology in which the gains are obtained fro a Gaussian function, aiming to obtain a performance enhancement for this system. Computer simulations were performed, where a parametric sweep on the parameters for each gain (proportional , integral and derivative) were done. The achieved results verify the efficiency of the proposed tecnique.

This dissertation introduces a Dynamical Neural Network (DNN) model based adaptive inverse optimal control design for a class of nonlinear systems. A DNN structure is developed and stabilized based on a control Lyapunov function (CLF). The CLF must satisfy the partial Hamilton Jacobi-Bellman (HJB) equation to solve the cost function in order to prove the optimality. In other words, the control design is derived from the CLF and inversely achieves optimality when the given cost function variables are determined posterior. All the stability of the closed loop system is ensured using the Lyapunov-based analysis. In addition to structure stability, uncertainty/ disturbance presents a problem to a DNN in that it could degrade the system performance. Therefore, the DNN needs a robust control against uncertainty. Sliding mode control (SMC) is added to nominal control design based CLF in order to stabilize and counteract the effects of disturbance from uncertain DNN, also to achieve global asymptotic stability. In the next section, a DNN observer is considered for estimating states of a class of controllable and observable nonlinear systems. A DNN observer-based adaptive inverse optimal control (AIOC) is needed. With weight adaptations, an adaptive technique is introduced in the observer design and its stabilizing control. The AIOC is designed to control a DNN observer and nonlinear system simultaneously while the weight parameters are updated online. This control scheme guarantees the quality of a DNN's state and minimizes the cost function. In addition, a tracking problem is investigated. An inverse optimal adaptive tracking control based on a DNN observer for unknown nonlinear systems is proposed. Within this framework, a time-varying desired trajectory is investigated, which generates a desired trajectory based on the external inputs. The tracking control design forces system states to follow the desired trajectory, while the DNN observer estimates the states and identifies unknown system dynamics. The stability method based on Lyapunov-based analysis is guaranteed a global asymptotic stability. Numerical examples and simulation studies are presented and shown for each section to validate the effectiveness of the proposed methods.

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.

Sistemas pneumáticos se tornaram cada vez mais presentes em vários segmentos do mercado e são amplamente utilizados na indústria, principalmente devido à sua facilidade de manutenção, baixo custo, segurança e aplicabilidade em diversos processos. O desenvolvimento contínuo da tecnologia conduziu a um aumento nas pesquisas relacionadas ao controle de sistemas de servoposicionamento pneumático, resultando em algoritmos que têm avançado na direção da disponibilização de controle mais preciso destes sistemas. O presente trabalho se propõe ao desenvolvimento de um manipulador tipo SCARA composto por dois atuadores rotativos e um prismático, todos pneumáticos. Estes dispositivos apresentam grandes não linearidades, que dificultam seu controle. Assim, visa-se no presente trabalho o desenvolvimento de um controlador baseado em um modelo que possa superar as principais dificuldades relacionadas a essas não linearidades, como o comportamento não linear da relação pressão-vazão na servoválvula, a dinâmica dos gases na aleta e as forças de atrito O principal objetivo dessa tese é propor uma estratégia de controle baseada na Lei do Torque Computado Adaptativo com compensação explícita do atrito que contemple as peculiaridades dinâmicas estruturais deste tipo de sistema com aplicação de controle de trajetória. O modelo matemático para o atuador pneumático rotativo proposto no âmbito do presente trabalho e utilizado na síntese desse controlador foi avaliado por meio de resultados de simulações e experimentos executados em um protótipo projetado e construído também no escopo do presente trabalho. Os resultados da aplicação do controlador proposto, operando em regime de seguimento de trajetórias contínuas indicam que a estratégia de controle do Torque Computado Adaptativo, em conjunto com o esquema de compensação explícita do atrito, leva o sistema a uma redução dos erros de seguimento de trajetória em posição quando comparado com as técnicas do Torque Computado com parâmetros fixos, Torque Computado com parâmetros fixos com compensação explícita do atrito e Torque Computado Adaptativo sem a compensação explícita do atrito. / Pneumatic systems become increasingly present in different segments of the market and are widely used in industry, mainly due to their ease of maintenance, low cost, safety and applicability in various processes. The continued development of technology resulted in an increase in the research related to the control of pneumatic servo drive positioning systems, resulting in algorithms that have advanced in the direction of the availability of more precise control of these systems. This study has the purpose of to develop a type pneumatic driven SCARA manipulator that consists of a prismatic and two rotary actuators. These devices present highly nonlinear, which harder their control. Thus, the target of this work is to develop a controller based on a model that can overcome the main difficulties related to these nonlinearities, such as the nonlinear behavior of the pressure-flow ratio in the servo valve, the gas dynamics in the fin and friction. The main objective of this thesis is to propose a control strategy based on the Adaptive Computed Torque Law with explicit compensation of the friction that contemplates the structural dynamic peculiarities of this type of system with application of trajectory control The mathematical model for the rotary pneumatic actuator proposed in the present work and used in the synthesis of this controller was evaluated through simulations results and experiments executed in a prototype designed and also built in the scope of the present work. The results of the application of the proposed controller, operating in continuous trajectories tracking regime, indicate that the Adaptive Computed Torque control strategy, together with the explicit friction compensation scheme, leads the system to a reduction of the following errors trajectory in position when compared to techniques as Computed Torque with fixed parameters, Torque Computed with explicit friction compensation and Computed Torque Adaptive without explicit friction compensation.

abstract: Buck converters are electronic devices that changes a voltage from one level to a lower one and are present in many everyday applications. However, due to factors like aging, degradation or failures, these devices require a system identification process to track and diagnose their parameters. The system identification process should be performed on-line to not affect the normal operation of the device. Identifying the parameters of the system is essential to design and tune an adaptive proportional-integral-derivative (PID) controller. Three techniques were used to design the PID controller. Phase and gain margin still prevails as one of the easiest methods to design controllers. Pole-zero cancellation is another technique which is based on pole-placement. However, although these controllers can be easily designed, they did not provide the best response compared to the Frequency Loop Shaping (FLS) technique. Therefore, since FLS showed to have a better frequency and time responses compared to the other two controllers, it was selected to perform the adaptation of the system. An on-line system identification process was performed for the buck converter using indirect adaptation and the least square algorithm. The estimation error and the parameter error were computed to determine the rate of convergence of the system. The indirect adaptation required about 2000 points to converge to the true parameters prior designing the controller. These results were compared to the adaptation executed using robust stability condition (RSC) and a switching controller. Two different scenarios were studied consisting of five plants that defined the percentage of deterioration of the capacitor and inductor within the buck converter. The switching logic did not always select the optimal controller for the first scenario because the frequency response of the different plants was not significantly different. However, the second scenario consisted of plants with more noticeable different frequency responses and the switching logic selected the optimal controller all the time in about 500 points. Additionally, a disturbance was introduced at the plant input to observe its effect in the switching controller. However, for reasonable low disturbances no change was detected in the proper selection of controllers. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2016