No description available.

No description available.

Wave energy converters are devices that are designed to extract power from ocean waves. Existing wave energy converter technologies are not financially viable yet. Control systems have been identified as one of the areas that can contribute the most towards the increase in energy absorption and reduction of loads acting on the structure, whilst incurring only minimal extra hardware costs. In this thesis, control schemes are developed for wave energy converters, with the focus on single isolated devices. Numerical models of increasing complexity are developed for the simulation of a point absorber, which is a type of wave energy converter with small dimensions with respect to the dominating wave length. After investigating state-of-the-art control schemes, the existing control strategies reported in the literature have been found to rely on the model of the system dynamics to determine the optimal control action. This is despite the fact that modelling errors can negatively affect the performance of the device, particularly in highly energetic waves when non-linear effects become more significant. Furthermore, the controller should be adaptive so that changes in the system dynamics, e.g. due to marine growth or non-critical subsystem failure, are accounted for. Hence, machine learning approaches have been investigated as an alternative, with a focus on neural networks and reinforcement learning for control applications. A time-averaged approach will be employed for the development of the control schemes to enable a practical implementation on WECs based on the standard in the industry at the moment. Neural networks are applied to the active control of a point absorber. They are used mainly for system identification, where the mean power is related to the current sea state and parameters of the power take-off unit. The developed control scheme presents a similar performance to optimal active control for the analysed simulations, which rely on linear hydrodynamics. Reinforcement learning is then applied to the passive and active control of a wave energy converter for the first time. The successful development of different control schemes is described in detail, focusing on the encountered challenges in the selection of states, actions and reward function. The performance of reinforcement learning is assessed against state-of-the-art control strategies. Reinforcement learning is shown to learn the optimal behaviour in a reasonable time frame, whilst recognizing each sea state without reliance on any models of the system dynamics. Additionally, the strategy is able to deal with model non-linearities. Furthermore, it is shown that the control scheme is able to adapt to changes in the device dynamics, as for instance due to marine growth.

In the modern world of technology, highly sophisticated electronic systems pave the way for future's information technology breakthroughs. However, rapid growth on complexity and functions in such systems has also been a harbinger for the power increase. Power management techniques have thus been introduced to mitigate this urgent power crisis. Switching power converters are considered to be the best candidate due to their high efficiency and voltage conversion flexibility. Moreover, switching power converter systems are highly nonlinear, discontinuous in time, and variable. This makes it viable over a wide operating range, under various load and line disturbances. However, only one control scheme cannot optimize the whole system in different scenarios. Hybrid control schemes are thus employed in the power converters to operate jointly and seamlessly for performance optimization during start-up, steady state and dynamic voltage/load transient state.In this dissertation, three switching power converter topologies, along with different hybrid control schemes are studied. First, an integrated switching buck converter with a dual-mode control scheme is proposed. A pulse-train (PT) control, employing a combination of four pulse control patterns, is proposed to achieve optimal regulation performance. Meanwhile, a high-frequency pulse-width modulation (PWM) control is adopted to ensure low output ripples and avoid digital limit cycling. Second, an integrated buck-boost converter with a tri-mode digital control is presented. It employs adaptive step-up/down voltage conversion to enable a wide range of output voltage. This is beneficial to ever-increasing dynamic voltage scaling (DVS) enabled, modern power-efficient VLSI systems. DVS adaptively adjusts the supply voltage and operation frequency according to instantaneous power and performance demand, such that a system is constantly operated at the lowest possible power level without compromising its performance. Third, a digital integrated single-inductor multiple-output (SIMO) converter, tailored for DVS-enabled multicore systems is addressed. With a multi-mode control algorithm, DVS tracking speed and line/load regulation are significantly improved, while the converter still retains low cross regulation.All three integrated CMOS DC-DC converters have been designed and fabricated successfully, demonstrating the techniques proposed in this research. The measurements results illustrate superior line and load regulation performances and dynamic response in all these designs.

[pt] O objetivo desta dissertação é realizar uma introdução aos estudos e às aplicações dos Esquemas de Proteção de Sistemas -EPSs- usados para manter a segurança dos Sistemas de Energia Elétrica. Um pequeno conjunto de definições e conceitos das áreas de proteção, confiabilidade e análise de desempenho de sistemas de potência é apresentado com o objetivo de distinguir os EPSs das proteções convencionais de componentes do sistema. Isto também ajuda a entender as funções dos EPSs com mais clareza. Os EPSs são usados para manter a integridade do sistema quando este está submetido a fenômenos que provocam instabilidade ou desligamentos em cascata. A classificação e a descrição destes fenômenos, bem como a aplicação dos EPSs estão mostradas nesta dissertação. A estrutura geral dos EPSs, as formas de classificá-los e as diferentes ações usadas pelos EPSs para controlar as perturbações são objeto de análise do trabalho. Para exemplificar, é dada uma visão de como se situam os EPSs no Sistema Interligado Brasileiro (SIB) e também pelo restante do mundo. Alguns EPSs usados no Brasil mereceram destaque especial.As análises dos principais blecautes ocorridos no Brasil e na América do Norte são apresentadas, de forma resumida, no apêndice I. Dessas análises são tiradas muitas lições para implementar medidas que minimizam o risco de interrupções no suprimento de energia. Também é feita uma comparação do grau de severidade dos grandes blecautes ocorridos no Brasil e, para os dois maiores, é realizada uma estimativa dos seus respectivos custos de interrupção. Procurou-se também, no apêndice II, estabelecer os requisitos básicos para a implantação de EPSs que usem tecnologia baseada em microprocessadores.Com base na experiência vivida nos estudos desenvolvidos pelo grupo que analisou a segurança do SIB após o blecaute de 11-MAR-99, foram estabelecidos critérios e procedimentos para analisar a segurança do sistema e realizar estudos de implantação de EPSs. E, como desfecho, é realizado um breve estudo do SIB, onde é analisado o desempenho dos EPSs para controlar graves emergências que podem ocorrer no presente momento. / [en] The objective of this dissertation is to accomplish an introduction to the studies and the applications of the System Protection Schemes -SPSs- used to maintain the Electric Energy Systems safety. A small group of definitions and concepts from the protection,reliability and power systems performance analysis areas is presented with the objective of distinguishing SPSs from the conventional system component protections. It also helps in understanding the functions of the SPSs with more clarity. The SPSs are used to maintain the integrity of the system when it is submitted to phenomena that provoke instability or cascade circuit outages. The classification and the description of these phenomena, as well as the SPSs application are shown in this dissertation. The general structure of the SPSs, the ways of classifying them and the different actions used by SPSs to control the disturbances are the objectives of the analysis of this work. In order to exemplify, a vision is given of how the SPSs are located in the Brazilian Interconnected System -BIS- and also in the rest of the world. Some SPSs used in Brazil deserved special attention.The analyses of the main blackouts that occurred in Brazil and in North America are presented, in a summarized term, in appendix I. Considerable knowledge is obtained from these analyses, leading to implementation measures that minimize the risk of interruptions in the energy supply. A comparison is also made of the degree of severity of the great blackouts that happened in Brazil and, for the two largest, an estimate of their respective interruption costs is made. In appendix II, an attempt was also made to establish the basic requirements for the SPSs implementation using microprocessing technology. Based on the experience lived during the studies developed by the group that analyzed the safety of the BIS after the blackout on March 11/1999, criteria and procedures to analyze the safety of the system and to accomplish studies of SPSs implantation were established. Finally, a brief study of the BIS is done, where the SPSs performances are analyzed to verify the ability to control serious emergencies that can happen in the present moment.

In recent years, large investments have been made in wind power, and this trend is expected to continue in the coming decades. Integrating more wind power in the production mix offers great opportunities for the society, such as reducing greenhouse gas emissions and the dependence on foreign fuel. Large wind power penetration does, however, require changes in the way power systems are planned and operated. The power transfers across the electrical grid are determined by the load and the production. A secure operation of power systems requires that these power transfers stay within certain limits. Frequency control schemes are crucial for ensuring the balance between the electric demand and the production. They enable system operators to re-dispatch the production (for example via the activation of balancing bids) during real-time operations to follow the load variations. With wind power, these frequency control schemes must not only meet the variations of the load but also those of the wind. An optimal use of the frequency control reserves would allow system operators to operate the system in the most cost effective and secure manner, that is, using the cheapest available resources while taking into account the stability limits of the system and the uncertainty. With no wind power, the load is the main source of uncertainty, and it can be forecasted accurately. This enables system operators to dispatch the generation in the most cost-effective way to meet the load while keeping the system within its stability limits. Adding wind power to power systems, on the other hand, introduces a new source of uncertainty on the production side, which is more difficult to forecast. The tools used today for computing the stability limits and operating the system do not consider the whole range of possible future load and wind power production levels, but only pick a few likely values in this range. In this work, we propose a new approach which accounts for the whole uncertainty in the load and wind power, and gives the optimal re-dispatch which ensures a given level of system security given this uncertainty. The approach is a so-called Stochastic Optimal Power Flow (S-OPF) formulation, developed in the scope of this project for the optimal activation of balancing bids. It is a nonlinear optimization problem with one probabilitistic constraint ensuring a certain level of system security -- computed as the probability that the system stays within its stability limits -- and whose objective function is the minimization of the generation re-dispatch. Compared to what is done today, the S-OPF formulation enables system operators to consider the uncertainty when making decisions. An approximation of the proposed S-OPF formulation is developed to render the problem tractable. In particular, the stability boundary, defined as the set of stability limits, is approximated by second-order approximations. The accuracy of these second-order approximations are analyzed in the IEEE 9 bus system by computing the distance between the actual boundary and its approximation. The S-OPF problem is then solved in the IEEE 39 bus system using the approximated stability boundaries. Monte Carlo simulations are run in order to assess the accuracy of the approximation and check whether the optimal solution of the approximation does ensure the specified level of system security. / <p>QC 20121121</p>

As digital games have become increasingly significant in the entertainment media landscape, the terms “casual” and “hardcore” have become the primary ways to describe gaming audiences, genres, and gameplay. However, these terms are saturated with outdated stereotypes involving gender, age, and class. Focusing on industrial discourse, this thesis examines this dichotomy, emphasizing areas of discontinuity and overlap to question why these terms have become so ubiquitous in gaming discourse and what functions they fulfill for a variety of groups including the industry, advertisers, and audience members. Ultimately, I suggest that these terms need to be replaced in order to move beyond restrictive stereotypes, proposing a new framework for digital games that takes into consideration user motivation, personal investment, and historical specificity.

- / In this thesis new advanced nonlinear control methods that solve the power system stabilization problem in a more efficient and integrated manner are considered. The proposed methods mainly concern with the primary level control of a power system that plays a central role in maintaining transient stability and obtaining a desired system performance. To this end, several new nonlinear control schemes mainly applicable on power system stabilizers (PSS) have been designed and extensively analyzed. For a theoretical assessment of the system operation the concepts of passivity and passivity margin are analyzed while the concept of Ω--passivity is introduced. Using partial feedback linearization and backstepping design techniques on suitable models of the system under consideration (power system) the Ω--passivity property of the system is proved. This property is further improved through the control in the closed-loop design. To this end, several control schemes are developed and a series of different theoretical problems have been solved on using simple output feedback and advanced nonlinear control methods like sliding mode control, adaptive control or a combination of them. A significant breakthrough has been achieved with the use of fuzzy techniques in these schemes yielding designs with combined advantages of both fuzzy and adaptive control methods. A detailed stability analysis, based on Lyapunov functions, has been used to prove that the proposed controllers guarantee either uniform ultimate boundedness or asymptotic stability for the closed-loop system. The proposed schemes are examined assuming that the system operates under parameter uncertainties as well as external disturbances. The theoretical analysis indicates that regulating some design parameters of the proposed controllers one can significantly improve the robustness and the disturbance attenuation capability of the system. Extensive simulations on a two machines infinite bus test system have been carried out to evaluate the effectiveness of the proposed schemes as these are applied on the PSS of each machine. Hard cases of three phase faults or significant power demand changes have been simulated. The simulation results show that the proposed nonlinear controllers enhance the damping of the electromechanical oscillations with respect to classical AVR/PSS and improve their robustness to parameter uncertainties and disturbance attenuation capability. Using similar techniques, speed governor controls (SGC) are also designed. An adaptive control scheme is proposed that ensures asymptotic stabilization of the closed-loop system as proved by standard Lyapunov techniques. Simulations are carried out for the one generator system connected to infinite bus. The simulation results confirm a significant improvement in the electromechanical oscillations damping compared to conventional speed governor controls. An important contribution of the thesis involves the coordination and management of the controls at the primary level. The design is carried out so that each control is not competing with the action of the other and it is cooperating to complement the action of the other. In this frame, first, the coordinated operation of the designed nonlinear power system stabilizers with the classical AVR/PSS is proposed. Particularly, the sequential operation of these controllers is considered in the following way: immediately after a fault, only the nonlinear controller operates but when the fault attenuates the classical AVR/PSS takes over. In this way, significant transient enhancement and voltage regulation after the large transients can be achieved. To implement this kind of operation a soft-switching logic from the one controller to the other is proposed by using a fuzzy logic mechanism to determine which controller will act each time period. In this way, it is avoided a discontinuous switching that can create a number of problems and may even lead to instabilities. The analysis and the simulation results confirm the validity of this approach since it is shown that the coordinated control scheme has an almost identical transient performance with the nonlinear controllers ensuring simultaneously the voltage regulation at the desired set-point. The same approach is used for the coordinated operation of FACTS with the excitation controllers. To this end, a static var compensator (SVC) controller is developed which, during a fault, acts to improve the transient stability. During the transient period, the SVC uses as inputs not the voltage at the connecting point but suitable signals from neighbor stations in order to contribute to the electromechanical oscillations damping; in the sequel, it returns to its normal operation maintaining the voltage level at the connecting point at a specified value. A soft switching scheme is also applied while signal transmission delays are taken into the account. The simulation results of a three phase short-circuit in a system with a single machine connected to infinite bus through a bus that has a SVC attached, indicate that this coordinated control scheme improves the transient stability even more (in comparison to the previous coordinated scheme). Finally, coordinated control logic is used for the design of both the speed governor control and the PSS. This is needed when the operation of the PSS cannot be considered completely independent and decoupled from the speed governor dynamics (in the case of fast valve operation). In this combined system a parallel design of both the SGC and the PSS ensures the uniform ultimate boundedness of the complete closed-loop system. Moreover, the use of continuous switching through fuzzy logic, as mentioned before, between these controllers and the classical AVR/PSS (for the excitation system) and a PID control (for the SGC) is proposed. The simulation results on the two machines infinite bus system clearly confirm the superiority of the coordinated control scheme with respect to the classical AVR/PSS excitation controllers and PID speed governor controllers. As a conclusion, new combined advanced nonlinear control schemes are analyzed and proposed for power systems. From the stability analysis and the simulation results it is clearly confirmed that the application of these nonlinear controls can be effectively improve the transient behavior as well as the robustness and disturbance attenuation of a power system. It is also proved that, without extreme cost, coordinated control schemes implemented through the proposed soft-switching techniques further enhance the transient and dynamic performance of the system.

L'objectif de ce travail est de concevoir une nouvelle interface haptique en vue de son exploitation pour la chirurgie mini-invasive. La technique d'anastomose ciblée consiste à réunir deux parties désolidarisées d'une artère par des sutures et des nœuds. Ceci est effectué par des outils chirurgicaux introduits à travers de petites incisions. Une étude expérimentale de cette tâche a été effectuée en collaboration avec des chirurgiens afin de caractériser leurs gestes. L'enregistrement de l'opération par un système de capture de mouvement a permis d'identifier la nature et les gestes canoniques de cette technique. Une structure parallèle sphérique a été ensuite adoptée comme base de l'interface haptique. Cette architecture présente un centre fixe de rotation semblable au point d'incision réel et offre les trois degrés de liberté de rotation nécessaires autours de ce point. Une étude détaillée de cette architecture suivie d'une phase d'optimisation, a permis d'adapter la structure à l'application chirurgicale. L'optimisation, basée sur un algorithme générique, a porté dans un premier lieu sur l'espace de travail de la tâche. La dextérité de la structure a été ensuite prise en compte. Une phase de conception basée sur les paramètres résultants de cette optimisation a aboutie à la réalisation d'un premier prototype. L'influence des erreurs de fabrication sur l'orientation de la plateforme a été aussi traitée dans ce travail afin de déterminer les plages des défauts admissibles. Une modélisation, utilisant les torseurs de petits déplacements, a été élaborée.La dernière partie de ce travail porte sur la commande a retour d'effort de l'interface. Un banc d'essais à 1 degré de liberté a été réalisé afin de tester les différents schémas de contrôle pour la téléopération. Les essais en simulation on permit de dresser une vue comparative de ces schémas. / The aim of this work is to develop a new haptic interface to perform a minimally invasive surgery. The targeted anastomosis technique consists of the surgical binding of a ruptured blood vessel, using sutures and knots. This task is performed by surgical tools inserted through small incisions. An experimental study of this task was conducted in collaboration with surgeons in order to characterize their gesture. The recording of the operation by a motion capture system helped identifying the nature and the canonical actions of this technique. A spherical parallel mechanism (SPM) was then adopted as a basis for the haptic interface. This architecture has a fixed center of rotation similar to the real incision point and offers the three required degrees of freedom of rotation around that point. A detailed study of the architecture followed by an optimization procedure led to a suitable mechanism for the surgical application. The optimization, which is based on a generic algorithm, used the workspace of the task as a criterion. Then the dexterity of the structure was taken into account. A design phase based on the parameters resulting from this optimization led to building the first prototype.The influence of manufacturing errors on the orientation of the platform was also addressed in this work to determine the ranges of allowable defects. The manufacturing errors are modeled by screws of small displacement in order to determine their effect on the orientation error of the end effector. The last part of this work focuses on the command of the force feedback interface. An experimental setup made out of a one degree of freedom system, was built to test different control schemes for teleoperation. Simulation trials allowed developing a comparative view of these schemes.

No description available.