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Continuous-time systems are usually modelled by differential equations arising from physical laws. However, the use of these models in practice requires discretisation. In this thesis we consider sampled-data models for linear and nonlinear systems. We study some of the issues involved in the sampling process, such as the accuracy of the sampled-data models, the artifacts produced by the particular sampling scheme, and the relations to the underlying continuous-time system. We review, extend and present new results, making extensive use of the delta operator which allows a clearer connection between a sampled-data model and the underlying continuous-time system. In the first part of the thesis we consider sampled-data models for linear systems. In this case exact discrete-time representations can be obtained. These models depend, not only on the continuous-time system, but also on the artifacts involved in the sampling process, namely, the sample and hold devices. In particular, these devices play a key role in determining the sampling zeros of the discrete-time model. We consider robustness issues associated with the use of discrete-time models for continuous-time system identification from sampled data. We show that, by using restricted bandwidth frequency domain maximum likelihood estimation, the identification results are robust to (possible) under-modelling due to the sampling process. Sampled-data models provide a powerful tool also for continuous-time optimal control problems, where the presence of constraints can make the explicit solution impossible to find. We show how this solution can be arbitrarily approximated by an associated sampled-data problem using fast sampling rates. We also show that there is a natural convergence of the singular structure of the optimal control problem from discrete- to continuous-time, as the sampling period goes to zero. In Part II we consider sampled-data models for nonlinear systems. In this case we can only obtain approximate sampled-data models. These discrete-time models are simple and accurate in a well defined sense. For deterministic systems, an insightful observation is that the proposed model contains sampling zero dynamics. Moreover, these correspond to the same dynamics associated with the asymptotic sampling zeros in the linear case. The topics and results presented in the thesis are believed to give important insights into the use of sampled-data models to represent linear and nonlinear continuous-time systems. / PhD Doctorate

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As the IEC 61850 digital substation standard becomes progressively adopted by utilities throughout the world, entirely computerized methods will completely replace traditional strategies for monitoring the power system. Although newer techniques offer enhanced efficiency and controllability, their reliability is not as established as that of conventional practices. Modern approaches require extensive validation and analysis before they can be implemented on a widespread basis. One specific area of interest is the performance of protection systems that utilize voltage and current samples digitized directly at their source. This research presents a complete test bench for evaluating sampled values-based protection schemes and measures their efficacy under several different operating conditions. It is shown that the novel system operates correctly for the situations it is expected to, with minimal latency compared to traditional practices. / Master of Science / Power system infrastrcutures are changing rapidly from analog arrangements to entirely digital methods. This offers numeous benefits such as increased efficiency, lower cost, higher accuracy, and even improved safety. However, digital implementations do not have an as proven track record as compared to conventional practices, leading to concerns about their reliaiblity. This research tests the performance an en entirely digital protection scheme by using various hardware components. The results are analyzed and show that the novel scheme operates correctly, albeit with a slight delay as compared to traditional methods.

This thesis is aimed at analysis of sampled-data feedback systems. Our approach is in the frequency-domain, and stresses the study of sensitivity and complementary sensitivity operators. Frequency-domain methods have proven very successful in the analysis and design of linear time-invariant control systems, for which the importance and utility of sensitivity operators is well-recognized. The extension of these methods to sampled-data systems, however, is not straightforward, since they are inherently time-varying due to the intrinsic sample and hold operations. In this thesis we present a systematic frequency-domain framework to describe sampled-data systems considering full-time information. Using this framework, we develop a theory of design limitations for sampled-data systems. This theory allows us to quantify the essential constraints in design imposed by inherent open-loop characteristics of the analog plant. Our results show that: (i) sampled-data systems inherit the difficulty imposed upon analog feedback design by the plant's non-minimum phase zeros, unstable poles, and time-delays, independently of the type of hold used; (ii) sampled-data systems are subject to additional design limitations imposed by potential non-minimum phase zeros of the hold device; and (iii) sampled-data systems, unlike analog systems, are subject to limits upon the ability of high compensator gain to achieve disturbance rejection. As an application, we quantitatively analyze the sensitivity and robustness characteristics of digital control schemes that rely on the use of generalized sampled-data hold functions, whose frequency-response properties we describe in detail. In addition, we derive closed-form expressions to compute the L2-induced norms of the sampled-data sensitivity and complementary sensitivity operators. These expressions are important both in analysis and design, particularly when uncertainty in the model of the plant is considered. Our methods provide some interesting interpretations in terms of signal spaces, and admit straightforward implementation in a numerically reliable fashion. / PhD Doctorate

Esta dissertação objetiva (1) propor uma perspectiva de análise da música que parte das teses fundantes dos conceitos de intertextualidade, intersemiótica e significância e (2) analisar as músicas sampleadas que constituem o corpus por seus processos de significância. Para tanto, retoma, no capítulo 2, as pesquisas linguísticas e literárias que, desde Bakhtin, apontam para a análise de um texto por sua relação com outros textos da cultura e da história, problematizando o caso da música, que também parece passível de análise em um campo intertextual, e que não se limita, porém, à dimensão verbal. Propõe, portanto, uma primeira passagem: da intertextualidade em sentido estrito à noção de intersemiótica, pela qual é possível pensar também as traduções entre linguagens e sistemas de signos distintos. Revisa autores que pensaram a questão da tradução intersemiótica, partindo de Jakobson, Peirce e Plaza e chegando às teorias das materialidades da comunicação que remetem os fenômenos de significação às redes (midiático-ambientais, no caso de McLuhan, e tecno-discursivas, no caso de Kittler) no seio das quais seu sentido é produzido, e que concebemos como um campo intersemiótico. A significação, desta perspectiva, não se reduz a uma transmissão de sentido, mas é trabalhada por diferentes instâncias semióticas e tecnológicas, em um atravessamento que, da perspectiva pós-estruturalista de Barthes e Kristeva, aponta para a fundação e para a disseminação do sentido em um movimento de significância. Este conceito implica uma segunda passagem: dos estudos do sentido ao pré-sentido, opondo um aspecto fenotextual (estruturado e codificado) a um genotextual (que diferencia as estruturalidades e códigos da comunicação). O capítulo 3, em que este referencial teórico é articulado com nosso objeto de pesquisa, propõe pensar o conceito de sampleamento por uma lógica de disseminação e significância, uma vez que a música sampleada não se limita a sua fabricação intertextual, mas convoca redes intersemióticas em um desenrolar da significação que passa pela apreciação coletiva (principalmente na internet) com seus diferentes interpretantes: repercussão, comentários, críticas, produções de novos materiais a partir das músicas analisadas, e, principalmente, a investigação coletiva dos trechos utilizados em cada música (sample hunting). Neste sentido, é proposta uma torsão do conceito de genotexto no rumo de uma genomusicalidade, que problematiza a fenomusicalidade codificada do ouvir ao instituir novos funcionamentos na comunicação musical. No capítulo 4, é apresentada a metodologia de análise, que se apropria dos pensadores já indicados e também de outros que oferecem semióticas da significação da música (Tatit, Schafer, Tagg) para que, passando por um roteiro de três níveis (intratextual, intersemiótico e diagramático), se possa indicar o tipo de significância em que se processa a significação das cinco músicas que compõem nosso corpus. Quatro delas são do gruopo australiano The Avalanches, que trabalha exclusivamente com música sampleada, e uma de Caetano Veloso, que utiliza o mesmo procedimento em seu Rap Popcreto. Como resultado, chega a cinco diagramas diferentes que dão a ver percursos genomusicais específicos que instauram novos tipos de comunicação: para além do ouvir, surge um germinar, um desvelar, um desenrolar, um recriar e um instituir como práticas que só se apresentam na expansão da análise intratextual da música por um campo intertextual e intersemiótico de materiais. / This work seeks (1) to propose a perspective of music analysis based on the foundational theses of the concepts of intertextuality, intersemiotics and signifiance and (2) to analyze the sampled songs that constitute our corpus in terms of this signifiance. To do so, it revises, in chapter 2, the linguistic and literary researches that, since Bakhtin, point towards the analysis of a text through its relations with other texts (which constitute culture and history), and problematize the case of music, which also seems able to be analyzed in an intertextual field of research, and which is not limited, however, to the verbal dimension. It proposes, therefore, a first passage: from intertextuality in its strict sense towards the notion of intersemiotics, by which it is possible to also think about the translations between distinct languages and systems of signs. It revises authors that thought about the question of intersemiotic translation, from Jakobson and Peirce to Plaza, and arrives at the theories of the materialities of communication that remit the signification phenomena to the networks (of media environments, with McLuhan, and techno-discursivities, with Kittler) in which sense is produced, and which we conceive of as intersemiotic fields. Signification, here, is not reducible to a transmission of signifieds: it is worked by different semiotic and technological instances, in a crossing that, from the post-structuralist point of view of Barthes and Kristeva, indicates the foundation and dissemination of sense in a movement of signifiance. This concept implies a second passage: from studies of sense to those of pre-sense, opposing a phenotextual (structured and codified) aspect to a genotextual aspect (which differentiates the structuralities and codes of communication). Chapter 3, in which this theoretical references are articulated with our object of research, proposes to think about the concept of sampling through a logic of dissemination and significance, once sampled music does not limit itself to a intertextual fabrication. Instead it convokes intersemiotic networks in a development of signification that goes through the collective appreciation (mainly online) that generates a series of different interpretants: repercussion, commentaries, critiques, production of new materials based on the analyzed songs and, primarily, the collective research of the samples used in each song (sample hunting). In this sense, a torsion is proposed to the concept of genotext towards a genomusicality, which problematizes the codified phenomusicality of the ‘to listen’ by instituting new operations in musical communication. The fourth chapter presents the analytical methodology, which stems from the already mentioned authors and also others which offer signification models of music (Tatit, Schafer, Tagg) so that, going through an itinerary of three levels (intratextual, intersemiotic and diagrammatic), we can indicate the types of significance that processes the signification of the five pieces of music which constitute our corpus. Four of them are by the australian group The Avalanches, that works exclusively with sampled music, and one by Caetano Veloso, who utilizes the same procedure in his Rap Popcreto. As conclusions, the work arrives at five different diagrams which present specific genomusical routes that install new types of communication: beyond the ‘to listen’, there emerge a ‘to germinate’, a ‘to unveil’, a ‘to uncoil’, a ‘to recreate’ and a ‘to institute’ as practices that only present themselves through the expansion of the intratextual analysis of music in a intertextual and intersemiotic field of materials.

The majority of computers around us are embedded in productsand dedicated to perform certain tasks. A specific task is thecontrol of a dynamic system. The computers are ofteninterconnected by communication networks forming a distributedsystem. Vehicles and manufacturing equipment are two types ofmechatronic machines which often host dedicated computercontrol systems. A research problem is how the real-timebehaviour of the computer system affects the application,especially the control of the dynamic system. If the internal or external conditions varies over time, itbecomes difficult to assign a fixed resource reservation thatwill work well in all situations. In general, the more time anapplication gets of a resource, the better its gauged orperceived quality will be. A strategy is to alter the resourcereservation when the condition changes. This can be constructedas a negotiation between competing applications, a method forwhich the termquality of control, QoC, has been coined. Scalability isthe ability to change the structure and configuration of asystem. It promotes evolving systems and a can help manage acomplex product family. An architecture for a QoC middleware ontop of a scalable computer system, has been proposed. As aquality measureof a control application, the well-knownweighted quadratic loss function used in optimal control, hasbeen revised to encompass a subset of the so called timingproperties. The timing properties are the periods and thedelays in the control loop, including time-varying period anddelay. They are the interface between control and computerengineering, from a control engineering viewpoint. The qualitymeasure can be used both offline and on-line given a model ofthe sampled-data system and an appropriate description of thetiming properties. In order to use a computer system efficiently and toguarantee its responsiveness, real-time scheduling is a must.In fixed priority scheduling each task arrives periodically andhas a fixed priority. A task with a high priority can preempt alow priority task and gain access to the resource. Thebest-case response time characterizes the delays in the system,which is useful from a control viewpoint. A new algorithm tocalculate thebest-caseresponsetime has been derived. It is based on ascheduling scenario which yields a recurrence equation. Themodel is dual to the well-known worst-case response timeanalysis. Besides the dynamic fixed priority scheduling algorithm,optimal control usingstatic schedulinghas been studied, assuming a limitedcommunication. In the static schedule, which is constructedpre-runtime, each task is assigned a time window within aschedule repeated in eternity. The optimal scheduling sequenceis sought by optimizing the overall control performance. Aninteresting aspect is that the non-specified control periodfalls out as a result of theoptimal schedule. The time-varying delay is accountedfor in the control design. Keywords:Real-time scheduling, sampled-data control,performance measure, quality of control, limited communication,time-varying delay, jitter.

This thesis includes two topics, which are a Self-sampled ALL-MOS ASK Demodulator and a Synchronous DAC with Self-calibration. An all-MOS ASK demodulator with a wide bandwidth for lower ISM band applications is presented in the first half of this thesis. The chip area is reduced without using any passive element. It is very compact to be integrated in an SOC (system-on-chip) for wireless biomedical applications, particularly in biomedical implants. Because of low area cost and low power consumption, the proposed design is also easily to be integrated in other mobile medical devices. The self-sampled loop with a MOS equivalent capacitor compensation mechanism enlarges the bandwidth, which is more than enough to be adopted in any application using lower ISM bands. To demonstrate this technique, an ASK demodulator prototype is implemented and measured using a TSMC 0.35 £gm standard CMOS process. The second topic reveals a synchronous DAC with self-calibration. The main idea is to use a calibration circuit to overcome large error of output voltage caused by the variation of the unit capacitor. When DAC is not calibrated, INL is larger than 1.7 LSB. After calibrated, INL is improved to be smaller than 0.5 LSB. To demonstrate this technique, a DAC prototype is implemented and measured using a TSMC 0.18 £gm standard CMOS process.

¡@¡@We consider output voltage regulation of a novel twin-buck switching power converters with so-called zero voltage switching (ZVS) and zero current switching (ZCS). In order to observe the constraints imposed by ZVS and ZCS, it is necessary to adopt the pulse frequency modulation (PFM) technique, which lead to a switching system with aperiodic operating cycles. The control design is based on a sampled data model of the original switching dynamics and a linear quadratic criterion that takes the at-sampling behaviour into account. The applicability of the proposed controller is validated via numerical simulations written in MATLAB and SIMULINK. The controller is realized using Field Programmable Gate Array (FPGA). The experimental results indicate that the feedback system have good transient response and adequate robustness margin against source and load variation, which verify the applicability of the proposed control design approach.

In this thesis, digital controller design methods for sampled-data nonlinear systems are considered. Although sampled-data nonlinear control has attracted much attention in recent years, the controller design methods for sampled-data nonlinear systems are still limited. Therefore, a range of controller design methods for sampled-data nonlinear systems are developed such as backstepping, adaptive and robust backstepping, reduced-order observer-based output feedback controller design methods based on the Euler approximate model. These controllers are designed to compensate the effects of the discrepancy between the Euler approximate model and exact discrete time model, parameter estimation error in adaptive control and observer error in output feedback control which behave as disturbance. A dual-rate control scheme is presented for output-feedback stabilization of sampled-data nonlinear systems. It is shown that the designed controllers semiglobally practically asymptotically (SPA) stabilize the closed-loop sampled-data nonlinear system. Moreover, various applications of these methods are given and their performances are analyzed with simulations.