Teses em Engenharia Elétrica (Doutorado) - PPGEE/ITEC
URI Permanente para esta coleçãohttps://repositorio.ufpa.br/handle/2011/2317
O Doutorado Acadêmico inicio-se em 1998 e pertence ao Programa de Pós-Graduação em Engenharia Elétrica (PPGEE) do Instituto de Tecnologia (ITEC) da Universidade Federal do Pará (UFPA).
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Item Acesso aberto (Open Access) Análise de sistemas não-lineares e síntese de operadores inversos por séries de volterra diagonais(Universidade Federal do Pará, 2019-08-22) TEIXEIRA, Raphael Barros; BAYMA, Rafael Suzuki; http://lattes.cnpq.br/6240525080111166; COSTA JÚNIOR, Carlos Tavares da; http://lattes.cnpq.br/6328549183075122This work proposes innovative strategies for the analysis of nonlinear systems and the synthesis of inverse operators using the Volterra diagonal series. By expressing the output explicitly from the input, the Volterra series enable nonlinear analysis in the frequency domain. However, the multidimensional nature of the model confers several difficulties to its systematic use. This work takes a new look at the so-called Volterra series in diagonal coordinates, in which Volterra operators are expressed as a set of linear and one-dimensional filters that process nonlinear polynomial terms of the input. The proposition of the rational form for these filters leads to exact and compact Volterra models, which exhibit a direct connection with modern nonlinear formalisms, notably the Wiener and Hammerstein block structured models, and the non-linear, autoregressive polynomial models with exogenous input (NARX). In particular, it is proposed a strategy to obtain diagonal Volterra models from the polynomial NARX. The strategy is called derivative method, because it depends only on the established results of the differential calculus. This is important because a NARX model can fit relatively well to experimental data to describe a wide variety of practical systems. A subsequent study through the Volterra series comes as an additional natural step of analysis. This result also opens up possibilities for non-linear synthesis. A problem that has received increasing attention in systems engineering is that of the synthesis of inverse nonlinear operators, through which it tries to reverse distortions generated by the underlying system, preserving the integrity of the information of interest. In this case we propose a strategy of synthesis of Volterra inverse diagonal operators for particular classes of nonlinear polynomial models. It is a numerical approach where the synthesis is driven by an optimization problem that is inspired by the classic inverse p-order operator. Keywords: Non-linear systems, Volterra series diagonals, systems identification, nonlinear analysis, dynamic inversionItem Acesso aberto (Open Access) Efeito de interferência quântica no transporte eletrônico de dispositivos "quasi"-unidimensionais(Universidade Federal do Pará, 2018-05-03) OLIVEIRA, Alexandre de Souza; SILVA, Shirsley Joany dos Santos da; http://lattes.cnpq.br/6060351208361634; DEL NERO, Jordan; http://lattes.cnpq.br/5168545718455899The study of electronic transport in nano devices has been of great relevance in the last years, since the work of Aviran and Ratner, based on the properties of electrical conductivity in individual rectifying molecules under the action of an external electric field. The organic conjugated polymers in the pure state have low conductivity, but when doped, treated with reducing agents or connected to gold electrodes (Au) and subjected to an external electric field, they have a metallic behavior, that is, with high conductivity in line with experimental work. In this research we used devices composed of organic polymers conjugated in the pure state and also doped with chains containing simple (σ) and double (σ-π) type bonds, alternating between the carbons and these bound only to hydrogen atoms with gold electrodes (Au) connected at the ends of the individual molecules. This study was proposed for two types of electrodes: pyramid and plane. The model devices were optimized through the Extended Hückel Theory (EHT) and the computation of the electronic transport was performed using EHT combined with the Non-Equilibrium Green Function (NEGF). These devices are either quasi-1D or approximately linear structures and have been divided into two groups: the first, with odd numbers of carbon atoms from five (5) to nineteen (19) carbon atoms in their individual molecule (Group 1) and the second, with even numbers starting at six (6) going up to twenty (20) carbon atoms in its individual molecule (Group 2). The devices were subjected to two conditions: at low voltage, ranging from 0 to 0.1 Volt and then to high voltage, from 0 to 1.0 Volt. In order to compare the current and voltage (I - V) curves and the differential - voltage conductance (G - V) between low and high voltage results, the same voltage range was used, that is, from 0 to 0.1 Volt. For this work, the effects of destructive quantum interference (DQI) as well as constructive quantum interference (CQI) were analyzed. The effects of DQI are produced due to anti-resonance in the transmittance evidenced by unaccessed states observed in the transmission peaks, not allowing the transport to occur without presenting oscillations in the conductivity curve.Item Acesso aberto (Open Access) Investigação e desenvolvimento de um framework para testes de estratégias de controle automático visando melhoria de desempenho em servidores web apache(Universidade Federal do Pará, 2019-08-29) BARRETO, Marcos Vinicius Sadala; BARRA JUNIOR, Walter; http://lattes.cnpq.br/0492699174212608In this work, a study is carried out for the computational development of automatic control tests in computer response systems to “HTTP” “Apache” request. In particular, the implementation details and results in an environment for digital performance control of the HTTP response system are discussed. Thus, it was necessary to design and develop an environment for performing data collection in the computational system that provides the response service to “HTTP” requests and makes interventions in the values of the available parameters in order to control the system automatically in closed loop. The parameter to be obtained as endogenous variable of the computational system is MaxRequestWorks, and the exogenous one will be the amount of memory consumed. The tool developed modifies neither the source code of the response software to the clients’ “HTTP” requests nor the operating system code of the host computer, being non-intrusive regarding original system configuration. A proportional-integral (PI) controller was designed in order to keep the average perceived time response of “HTTP” messages regulated. Experimental tests carried out on an Apache server show the improvement obtained on the system's time response.Item Acesso aberto (Open Access) Projeto de controle robusto de ordem fracionária para sistemas com incerteza paramétrica(Universidade Federal do Pará, 2024-10-21) GOMES, Marcus Ciro Martins; AYRES JÚNIOR, Florindo Antonio de Carvalho; http://lattes.cnpq.br/1919442364965261; COSTA JÚNIOR, Carlos Tavares da; http://lattes.cnpq.br/6328549183075122This research introduces a novel methodology that integrates fractional-order control theory with robust control techniques to address parametric uncertainty, aimed at enhancing the performance of linear time-invariant uncertain systems with integer or fractional orders, referred to as Fractional-Order Robust Control (FORC). Unlike traditional methods, this proposed approach offers a new formulation of inequalitiesbased design, broadening the scope for discovering improved solutions through linear programming optimization. Consequently, fractional-order controllers are tailored to ensure desired transient and steady-state performance in closed-loop systems. In order to facilitate the digital implementation of the designed controller, the impulse response invariant discretization of fractional-order differentiators (IRID-FOD) is used to approximate fractional-order controllers to integer-order transfer functions. Additionally, the Hankel reduction order method is applied, making the controllers suitable for hardware deployment. Experimental tests conducted on a thermal system, along with assessment results based on time-domain responses and robustness analysis supported by performance indices and set value analysis, demonstrate the enhanced and robust performance of the proposed FORC methodology compared to classical robust control under parametric uncertainty.