The task in this thesis is the steering of one of Saab Bofors Dynamics robots using Sliding Mode Control, a method they never used before. The robot constitutes a system which in addition to perturbations and uncertainties due to modeling imprecision, hold the difficulty of being highly time variant. In order to be able to keep required performance with uncertainties and modeling imprecision present, the use of robust control methods like Sliding Mode Control is necessary. SMC is based on the states of the system being forced to stay on or in the direct vicinity of a hyper plane in the state space which is chosen in a way that gives the system dynamics desired properties. Other advantages with sliding mode are reduced order dynamics on the switching surface and total insensitivity to some uncertainties and perturbations. The existing metod for controlling the robot is Linear Quadratic Control. To evaluate the SMC-methodology and compare it with the existing solution simulations using SMC and LQ-control are made with uncertainties and modeling imprecision. Our tests show that a control law based on SMC is robust and seems to be a very good alternative to the existing solution.

A methodology of designing an adaptive sliding mode controller for a class of nonlinear systems with matched and mismatched perturbations is proposed in this thesis. A specific designed sliding surface function is presented first, whose coefficients are determined by using Lyapunov stability theorem and linear matrix inequality (LMI) optimization technique. Without requiring the upper bounds of matched perturbations, the controller with adaptive mechanisms embedded is also designed by using Lyapunov stability theorem. The proposed control scheme not only can drive the trajectories of the controlled systems reach sliding surface in finite time, but also is able to suppress the mismatched perturbations when the controlled systems are in the sliding mode, and achieve asymptotic stability. In addition, the proposed control scheme can be directly applied to a class of underactuated systems. A numerical example and a practical experiment are given for demonstrating the feasibility of the proposed control scheme.

Based on the Lyapunov stability theorem, a sliding mode control design methodology is proposed in this thesis for a class of perturbed switched systems. The control of the systems is rest restricted to switching between two different constant values. New sliding mode reaching conditions are proposed for the controllers so that the controlled systems can enter the sliding mode in finite time. Once the switched control system is in the sliding mode, the stability of the system is guaranteed by choosing a suitable sliding surface. In addition, a method for alleviating the infinite switching phenomenon is also provided in this thesis. Finally, a numerical and a practical example with computer simulation results are given for demonstrating the feasibility of the proposed control scheme.

Recently, active suspension has been applied to many commercial automobiles. To develop the control algorithm for active suspension, a quarter-car test bed was built by using a direct-drive tubular linear brushless permanent-magnet motor (LBPMM) as a force-generating component. Two accelerometers and a linear variable differential transformer (LVDT) are used in this quarter-car test bed. Three pulse-width-modulation (PWM) amplifiers supply the currents in three phases. Simulated road disturbance is generated by a rotating cam. Modified lead-lag control, linear-quadratic (LQ) servo control with a Kalman filter, and the fuzzy control methodologies were implemented for active-suspension control. In the case of fuzzy control, asymmetric membership functions were introduced. This controller could attenuate road disturbance by up to 78%. Additionally, a sliding-mode controller (SMC) is developed with a different approach from the other three control methodologies. While SMC is developed for the position control, the other three controllers are developed for the velocity control. SMC showed inferior performance due to the drawback of the implemented chattering-proof method. Both simulation and experimental results are presented to demonstrate the effectiveness of these four control methodologies.

The objective of this research is to develop innovative techniques for modeling and control of network congestion. Most existing network controls have discontinuous actions, but such discontinuity in control actions is commonly omitted in analytical models, and instead continuous models were widely adopted in the literature. This approximation works well under certain conditions, but it does cause significant discrepancy in creating robust, responsive control solutions for congestion management. In this dissertation, I investigated three major topics. I proposed a generic discontinuous congestion control model and its design methodology to guarantee asymptotic stability and eliminate traffic oscillation, based on the sliding mode control (SMC) theory. My scheme shows that discontinuity plays a crucial role in optimization of the I-D based congestion control algorithms. When properly modeled, the simple I-D control laws can be made highly robust to parameter and model uncertainties. I discussed applicability of this model to some existing flow or congestion control schemes, e.g. XON/XOFF, rate and window based AIMD, RED, etc. It can also be effectively applied to design of detection and defense of distributed denial of service (DDoS) attacks. DDoS management can be considered a special case of the flow control problem. Based on my generic discontinuous congestion control model, I developed a backward-propagation feedback control strategy for DDoS detection and defense. It not only prevents DDoS attacks but also provides smooth traffic and bounded queue size. Another application of the congestion control algorithms is design of private group communication networks. I proposed a new technique for protection of group communications by concealment of sender-recipient pairs. The basic approach is to fragment and disperse encrypted messages into packets to be transported along different paths, so that the adversary cannot efficiently determine the source/recipient of a message without correct ordering of all packets. Packet flows among nodes are made balanced, to eliminate traffic patterns related to group activities. I proposed a sliding window-based flow control scheme to control transmission of payload and dummy packets. My algorithms allow flexible tradeoff between traffic concealment and performance requirement.

This thesis describes the implementation of Yao’s adaptive robust control to an aircraft control system. This control law is implemented as a means to maintain stability and tracking performance of the aircraft in the face of failures and changing aerodynamic response. The control methodology is implemented as an outer loop controller to an aircraft under nonlinear dynamic inversion control. The adaptive robust control methodology combines the robustness of sliding mode control to all types of uncertainty with the ability of adaptive control to remove steady state errors. A performance measure is developed in to reflect more subjective qualities a pilot would look for while flying an aircraft. Using this measure, comparisons of the adaptive robust control technique with the sliding mode and adaptive control methodologies are made for various failure conditions. Each control methodology is implemented on a full envelope, high fidelity simulation of the F-15 IFCS aircraft as well as on a lower fidelity full envelope F-5A simulation. Adaptive robust control is found to exhibit the best performance in terms of the introduced measure for several different failure types and amplitudes.

This thesis investigates both theoretical and implementation-level aspects of switching- feedback control strategies for the development of voltage-controlled oscillators. We use a modified sliding-mode compensation scheme based on various norms of the system state to achieve amplitude control for wide-tuning range oscillators. The proposed controller provides amplitude control at minimal cost in area and power consumption. Verification of our theory is achieved with the physical realization of an amplitude controlled negative-Gm LC oscillator. A wide-tuning range RF ring oscillator is developed and simulated, showing the effectiveness of our methods for high speed oscillators. The resulting ring oscillator produces an amplitude controlled sinusoidal signal operating at frequencies ranging from 170 MHz to 2.1 GHz. Total harmonic distortion is maintained below 0:8% for an oscillation amplitude of 2 Vpp over the entire tuning range. Phase noise is measured as -105.6 dBc/Hz at 1.135 GHz with a 1 MHz offset.

The main goal of this thesis is to study the saturation problem arisen from the integrator in a sigma- delta analog- to- digital modulator , especially when the order of the circuit is higher than two .Signal passes through each stage of integrators yield saturation problem. This situation will miss some part of messages .Unable to deliver datas accurately to next stage of the integrator , the output digital signals will be incorrect and can't be recovered to original analog signals . Hence, this thesis proposes an anti-wind-up method by taking sliding mode control theory to avoid integrator saturation. After that, we are going to design and implement two third order sigma-delta modulators based on this method. Simulation and experiment results show the validity of the method and the significant improvement of avoiding saturation problem, and guarantee the designed circuits can translate signals to terminal accurately .

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Η παρούσα διπλωματική εργασία πραγματεύεται τη μελέτη και κατασκευή ενός μετατροπέα συνεχούς τάσης σε εναλλασσόμενη (αντιστροφέας) που προορίζεται για τη σύνδεση ενός φωτοβολταϊκού πλαισίου στο δίκτυο χαμηλής τάσης. Η εργασία εκπονήθηκε στο Εργαστήριο Ηλεκτρομηχανικής Μετατροπής Ενέργειας του Τμήματος Ηλεκτρολόγων Μηχανικών και Τεχνολογίας Υπολογιστών του Πανεπιστημίου Πατρών. Αρχικά, παρουσιάζονται, συνοπτικά, πληροφορίες για τη φωτοβολταϊκή τεχνολογία και για τους τρόπους διασύνδεσής τους με την κατανάλωση ή το δίκτυο. Στη συνέχεια, γίνεται αναφορά στον αντιστροφέα της διπλωματικής εργασίας. Πιο συγκεκριμένα, μελετάται ένας διαφορικός αντιστροφέας τύπου boost, ένα χαρακτηρισμό που τον οφείλει στην δυνατότητα, να επιτευχθεί μέσω αυτού εναλλασσόμενη τάση εξόδου με ενεργό τιμή μεγαλύτερη της συνεχούς τάσης εισόδου. Ο μετατροπέας αυτός αποτελείται στην ουσία από δύο επιμέρους μετατροπείς dc-dc τύπου boost, με τη συνδυασμένη λειτουργία των οποίων επιτυγχάνεται η επιθυμητή μετατροπή. Η ονομαστική ισχύς για την οποία πραγματοποιείται ο σχεδιασμός του μετατροπέα είναι ίση με 250W. Με δεδομένα τα μεγέθη ρευμάτων και τάσεων, καθώς και των κυματώσεων στα ρεύματα των πηνίων και στις τάσεις των πυκνωτών, υπολογίστηκαν οι τιμές των στοιχείων, βάσει των οποίων έγιναν οι προσομοιώσεις. Κατόπιν, δοκιμάστηκαν σε προσομοίωση διάφορες μορφές ελέγχου του αντιστροφέα, με μόνη ικανοποιητική αυτή του έλεγχου με ολίσθηση στο πεδίο καταστάσεων. Αυτός ήταν και ο έλεγχος που τελικά επιλέχθηκε για τη διάταξη που μελετήθηκε, γι’ αυτό και γίνεται αναλυτική περιγραφή του ελέγχου αυτού. Λόγω των απαιτήσεών του αποφασίστηκε ο έλεγχος να υλοποιηθεί χωρίς χρήση μικροελεγκτή, αλλά με χρήση αποκλειστικά ολοκληρωμένων αναλογικών κυκλωμάτων. Ακολουθεί η περιγραφή της διαδικασίας σχεδίασης και κατασκευής του μετατροπέα που έγινε στο Εργαστήριο Ηλεκτρομηχανικής Μετατροπής Ενέργειας και παρουσιάζονται τα επιμέρους στοιχεία και οι συνδεσμολογίες που χρησιμοποιήθηκαν. Τέλος, περιγράφονται τα πειράματα που πραγματοποιήθηκαν και παρατίθενται τα αποτελέσματα που προέκυψαν, αποδεικνύοντας την ορθή λειτουργία της διάταξης. Επίσης, εξάγονται τα ανάλογα συμπεράσματα. / In this diploma thesis, a Power Inverter in order to connect an Alternating Current-Photovoltaic (AC-PV module) to the low voltage grid is analyzed, designed and manufactured. The work was carried out in the Laboratory of Electrical and Mechanical Energy Conversion at the Department of Electrical and Computer Engineering of the Polytechnic School, University of Patras, Greece. At first, some data and information concerning the photovoltaic technology are presented as well as the connection modes of a PV system or module. Secondly, the operation and structure of the inverter is described. Specifically, a differential output boost inverter is examined, the title of which is derived from its ability to produce an output voltage larger than the input voltage. In fact, this converter consists of two boost dc-dc converters, the combined operation of which achieves the desirable operation of the inverter. The nominal power of the inverter is chosen to be equal to 250W. Depending on the expected values of the currents and voltages, as well as on the ripple voltages of the capacitors and the ripple currents of the inductors, the component values were calculated. The following step was to simulate the operation of the converter under different control techniques. The only control method with satisfying results which was eventually applied to the inverter was the sliding mode control, so it is extensively described. Due to its requirements, this control technique was implemented without using a microcontroller, but only using analog integrated circuits. The design and implementation of the inverter is then described along with the selected components and some individual circuits. Finally, the results of the conducted experiments are presented, the good operation of the setup is confirmed and the related conclusions are derived.