Thesis (M.A.S.)--Memorial University of Newfoundland, 2004. / Restricted until October 2005. Bibliography: leaves 92-100.

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: David A. Kendrick. Vita. Includes bibliographical references.

Thesis (M. Sc.)(Electronic Engineering)--University of Pretoria, 2006. / Includes bibliographical references. Available on the Internet via the World Wide Web.

Inspired by the robustness and flexibility of biological systems, we are developing linguistic and programming tools to allow us to program spatial systems populated by vast numbers of unreliable components interconnected in unknown, irregular, and time-varying ways. We organize our computations around geometry, making the fact that our system is made up of discrete individuals implicit. Geometry allows us to specify requirements in terms of the behavior of the space occupied by the aggregate rather than the behavior of individuals, thereby decreasing complexity. So we describe the behavior of space explicitly, abstracting away the discrete nature of the components. As an example, we present the Amorphous Medium Language, which describes behavior in terms of homeostatic maintenance of constraints on nested regions of space.

Made available in DSpace on 2014-06-11T19:30:49Z (GMT). No. of bitstreams: 0 Previous issue date: 2013-08-30Bitstream added on 2014-06-13T20:21:16Z : No. of bitstreams: 1 souza_wa_dr_ilha.pdf: 2047760 bytes, checksum: 8e0dca06c80251e6c3a1e6e46925aa1a (MD5) / Esta tese propõe novos métodos de projeto de controle chaveado para algumas classes de sistemas: lineares com incertezas politópicas e não lineares incertos descritos por modelos fuzzy Takagi-Sugeno. Inicialmente são propostos métodos que utilizam uma função quadrática de Lyapunov e a estabilidade quadrática é utilizada para projetar vários ganhos do controlador, baseado em desigualdades matriciais lineares (do inglês Linear Matrix Inequalities - LMIs). Os controladores propostos são compostos por um único ganho que é escolhido por uma lei de chaveamento que retorna o menor valor da derivada temporal da função quadrática de Lyapunov. Para o caso linear, os controladores concebidos apresentam um melhor desempenho quando comparados com o controlador que emprega um único ganho de realimentação do estado normalmente implementado, e as LMIs utilizadas para encontrar os ganhos são mais relaxadas. Para o caso não linear, os controladores propostos também apresentaram um bom desempenho e eliminam a necessidade de encontrar as expressões explícitas das funções de pertinência que muitas vezes podem ter expressões longas e/ou complexas, ou serem desconhecidas devido às incertezas na planta. Em seguida foram propostos novos métodos de projeto de controle chaveado e um novo critério de estabilidade para sistemas não lineares incertos descritos por modelos fuzzy Takagi-Sugeno. O projeto do controlador chaveado é baseado na função de Lyapunov quadrática por partes do tipo mínimo e na minimização da derivada temporal desta função de Lyapunov. As condições do novo critério de estabilidade são representadas por um tipo de desigualdades matriciais bilineares (do inglês Bilinear Matrix Inequalities - BMIs) que podem ser resolvidas de forma eficiente pelo método... / This thesis proposes new switched control design methods for some classes of linear systems with polytopic uncertainties and uncertain nonlinear systems described by Takagi-Sugeno fuzzy models. Initially, are proposed methods that use a quadratic Lyapunov function and quadratic stability to design, based on Linear Matrix Inequalities (LMIs), the feedback gains. The controller gain is chosen by a switching law that returns the smallest value of the time derivative of the quadratic Lyapunov function. For the linear case, the proposed methodology presents a better performance when compared with the controller usually implemented which uses only one state feedback gain and the LMIs for finding the switched gains are more relaxed. For nonlinear plants described by Takagi-Sugeno fuzzy models, the proposed controller also presented good performance and eliminates the need to obtain the explicit expressions of the membership functions of the Takagi-Sugeno fuzzy controllers, which can often have long and/or complex expressions, or may not be known, for instance due to the plant uncertainties. The design of the switched controllers is based on a minimum-type piecewise quadratic Lyapunov function and the minimization of the time derivative of this Lyapunov function. The conditions of the new stability criterion are represented by a kind of Bilinear Matrix Inequalities (BMIs) that can be efficiently solved by the path-following method. Furthermore, the proposed switched controller can also operate even with an uncertain reference control signal. To verify the efficacy of the proposed methodology are presented numerical simulations, including robust nonlinear control designs of a ball-and-beam system and of a magnetic levitator, and finally a robust... (Complete abstract click electronic access below)

Orientador: José Paulo Fernandes Garcia / Banca: Jean Marcos de Souza Ribeiro / Banca: Cristiano Quevedo Andrea / Resumo: O principal objetivo do trabalho é explorar a técnica de controle robusto com Modos Deslizantes para a acomodação e atenuação de uma falha no sinal de controle de um helicóptero. Foram projetados dois controladores, o Controle com Estrutura Variável e Modos Deslizantes contínuo no tempo (CEV/MD), e o segundo é o Controle Discreto com Modos Deslizantes (CDMD). Foi usado um modelo matemático não linear que representa um simulador de voo (Helicóptero 3-DOF da Quanser R ), que é um equipamento útil para o ensino, aplicação e desenvolvimento de técnicas de controle robusto. Os resultados experimentais obtidos, fazem uma comparação entre o controle contínuo e o controle discreto. Para que essa comparação seja feita foi inserida uma falha no sinal de controle. Mesmo diante das diferenças na resposta do sinal de controle, entre os controladores, o sistema teve um bom desempenho quando controlado pelo CEV/MD e CDMD, mostrando assim a eficiência da técnica de controle com Modos Deslizantes / Abstract: The main objective of this work is the exploration of the robust control technique with Sliding Mode (VSC-SM) for fault accommodation and attenuation in an aircraft's propulsion system. Two controllers were designed, Variable Structure Control with Sliding Mode (VSCSM) and Discrete Control with Sliding Modes (DCSM). For that, it was used a mathematical model of a flight Simulator of a Quanser's helicopter, named as 3-DOF Helicopter, which is an excellent module for teaching, application and development of robust control techniques. The results obtained in digital simulations show great performance of the system in fault when controlled by VSC-SM and DCSM / Mestre

[pt] Os mercados de ações dos países emergentes tem como principal característica a presença de dias atípicos, os quais fazem impossível o uso, com sucesso, dos modelos de equilíbrio. O principal objetivo desta pesquisa é a de desenvolver uma nova teoria, baseada na estatísica robusta, que possa ser aplicada a estes mercados sem ser seriamente afetada por observações extremas, e que ao mesmo tempo, ofereça resultados eficientes e precisos. / [en] Emergent stock markets are characterized by the presence of atypical days, which make impossible the use of equilibrium models with sucess. The main aim of this research is to define a new theory, based on the robust statistical theory, which could be applied to those markets without being affected by extreme observations and, at the same time, offer efficient and accurate results. / [es] Los mercados de acciones de los países emergentes tienen como principal característica la presencia de días atípicos, lo que hace imposible el uso, con suceso, de los modelos de equilibrio. EL objetivo principal de esta investigación es desarrollar una nueva teoría, basada en la estadística robusta, que pueda ser aplicada a estos mercados sin ser seriamente afectada por observaciones extremas, y que al mismo tiempo, obtenga resultados eficientes y precisos.

This thesis deals with the topic of min-max formulations of robust model predictive control problems. The sets involved in guaranteeing robust feasibility of the min-max program in the presence of state constraints are of particular interest, and expanding the applicability of well understood solvers of linearly constrained quadratic min-max programs is the main focus. To this end, a generalisation for the set of uncertainty is considered: instead of fixed bounds on the uncertainty, state- and input-dependent bounds are used. To deal with state- and input dependent constraint sets a framework for a particular class of set-valued maps is utilised, namely parametrically convex set-valued maps. Relevant properties and operations are developed to accommodate parametrically convex set-valued maps in the context of robust model predictive control. A quintessential part of this work is the study of fundamental properties of piecewise polyhedral set-valued maps which are parametrically convex, we show that one particular property is that their combinatorial structure is constant. The study of polytopic maps with a rigid combinatorial structure allows the use of an optimisation based approach of robustifying constrained control problems with probabilistic constraints. Auxiliary polytopic constraint sets, used to replace probabilistic constraints by deterministic ones, can be optimised to minimise the conservatism introduced while guaranteeing constraint satisfaction of the original probabilistic constraint. We furthermore study the behaviour of the maximal robust positive invariant set for the case of scaled uncertainty and show that this set is continuously polytopic up to a critical scaling factor, which we can approximate a-priori with an arbitrary degree of accuracy. Relevant theoretical statements are developed, discussed and illustrated with examples.

This thesis discusses mathematical optimization techniques for waveform design in cognitive radars. These techniques have been designed with an increasing level of sophistication, starting from a bistatic model (i.e. two transmitters and a single receiver) and ending with a cognitive network (i.e. multiple transmitting and multiple receiving radars). The environment under investigation always features strong signal-dependent clutter and noise. All algorithms are based on an iterative waveform-filter optimization. The waveform optimization is based on convex optimization techniques and the exploitation of initial radar waveforms characterized by desired auto and cross-correlation properties. Finally, robust optimization techniques are introduced to account for the assumptions made by cognitive radars on certain second order statistics such as the covariance matrix of the clutter. More specifically, initial optimization techniques were proposed for the case of bistatic radars. By maximizing the signal to interference and noise ratio (SINR) under certain constraints on the transmitted signals, it was possible to iteratively optimize both the orthogonal transmission waveforms and the receiver filter. Subsequently, the above work was extended to a convex optimization framework for a waveform design technique for bistatic radars where both radars transmit and receive to detect targets. The method exploited prior knowledge of the environment to maximize the accumulated target return signal power while keeping the disturbance power to unity at both radar receivers. The thesis further proposes convex optimization based waveform designs for multiple input multiple output (MIMO) based cognitive radars. All radars within the system are able to both transmit and receive signals for detecting targets. The proposed model investigated two complementary optimization techniques. The first one aims at optimizing the signal to interference and noise ratio (SINR) of a specific radar while keeping the SINR of the remaining radars at desired levels. The second approach optimizes the SINR of all radars using a max-min optimization criterion. To account for possible mismatches between actual parameters and estimated ones, this thesis includes robust optimization techniques. Initially, the multistatic, signal-dependent model was tested against existing worst-case and probabilistic methods. These methods appeared to be over conservative and generic for the considered signal-dependent clutter scenario. Therefore a new approach was derived where uncertainty was assumed directly on the radar cross-section and Doppler parameters of the clutters. Approximations based on Taylor series were invoked to make the optimization problem convex and {subsequently} determine robust waveforms with specific SINR outage constraints. Finally, this thesis introduces robust optimization techniques for through-the-wall radars. These are also cognitive but rely on different optimization techniques than the ones previously discussed. By noticing the similarities between the minimum variance distortionless response (MVDR) problem and the matched-illumination one, this thesis introduces robust optimization techniques that consider uncertainty on environment-related parameters. Various performance analyses demonstrate the effectiveness of all the above algorithms in providing a significant increase in SINR in an environment affected by very strong clutter and noise.

COSTA, M. V. S. Controle MPC robusto aplicado ao conversor Boost CCTE otimizado por inequações matriciais lineares. 2017. 178 f. Tese (Doutorado em Engenharia Elétrica)–Centro de Tecnologia, Universidade Federal do Ceará, Fortaleza, 2017. / Submitted by Marlene Sousa (mmarlene@ufc.br) on 2017-09-06T17:10:36Z No. of bitstreams: 1 2017_tese_mvscosta.pdf: 5929867 bytes, checksum: 81ddf2f8352a8740c1bfba2216f43bfa (MD5) / Approved for entry into archive by Marlene Sousa (mmarlene@ufc.br) on 2017-09-06T17:11:16Z (GMT) No. of bitstreams: 1 2017_tese_mvscosta.pdf: 5929867 bytes, checksum: 81ddf2f8352a8740c1bfba2216f43bfa (MD5) / Made available in DSpace on 2017-09-06T17:11:16Z (GMT). No. of bitstreams: 1 2017_tese_mvscosta.pdf: 5929867 bytes, checksum: 81ddf2f8352a8740c1bfba2216f43bfa (MD5) Previous issue date: 2017-07-21 / This work proposes a MPC predictive control strategy applied to a three-state switching cell boost (3SSC) converter that gives more simplicity and systematization to the control design steps and analysis. The integral gain controller can adjusted, eliminating the re-design the weighting matrices. Besides, the stability elipsoid theory are used to simplify the stability analysis of converter. The proposed MPC begins using the linear time varying (LTV) model plant. The parameters variations are considered polytopic uncertainties using linear matrix inequalities approach (LMIs) with relaxations. Theoretical and experimental aspects are applied and analyzed to a 1 kW 3SSC boost converter with voltage input and load uncertainties. To 500 W experimental test, it is considered load and voltage input steps variations. To 1000 W experimental test, it is only considered load steps variation. Also, the proposed MPC-LMI is compared with a classical LQI known in the literature. Theoretical-experimental aspects are applied and analyzed in a 1 kW converter with uncertainties in the input voltage and load. For the experiments, the voltage and load step tests for the 500 W project and a load step test for the 1000 W one were considered. In addition, to establish a performance reference, the proposed MPC is compared with the classic LQR controller known in the literature. The proposed control strategy presents advantages considering the variations of the model due to load tests in DC-DC 3SSC boost applications, being a feasible proposal in solving problems for high-performance converters. / Este trabalho propõe uma estratégia de controle preditivo MPC aplicado a um conversor boost com célula de comutação em 3 estados (CCTE) que confere mais simplicidade e sistematização nas fases de projeto e análise do controlador. O ganho integral do controlador pode ser ajustável, dispensando o reprojeto nas matrizes de ponderação. Para simplificar a análise de estabilidade do controlador, utiliza-se o conceito de elipsóides de estabilidade. O controle MPC proposto parte da modelagem da planta no espaço de estados médio linear e variante no tempo (LTV). As variações paramétricas, no contexto deste trabalho, são tratadas como incertezas politópicas expressas por meio de desigualdades matriciais lineares (LMIs) com relaxações. Aspectos teórico-experimentais são aplicados e analisados em um conversor boost CCTE de 1 kW com incertezas na tensão de entrada e na carga. Para os ensaios, são considerados os testes de degrau de tensão e de carga para o projeto em 500 W e para o degrau de carga com operação em 1000 W . Além disso, para estabelecer uma base de desempenho, o MPC proposto é comparado com o controlador LQI clássico conhecido na literatura. A estratégia de controle proposta apresenta vantagens considerando as variações do modelo decorrente dos testes de cargas em aplicações boost CC-CC do tipo CCTE, sendo uma proposta viável na solução de problemas em conversores de alto rendimento.