TEDE Coleção:

Controle Fuzzy T–S Tipo-2 intervalar por modos deslizantes adaptativo acionado por eventos e com garantia de passividade robusta para sistemas com atraso de tempo

Fri, 19 Jun 2026 00:00:00 GMT

Título: Controle Fuzzy T–S Tipo-2 intervalar por modos deslizantes adaptativo acionado por eventos e com garantia de passividade robusta para sistemas com atraso de tempo Autor: NORONHA, Rodrigo Possidônio Primeiro orientador: SERRA, Ginalber Luiz de Oliveira Abstract: This thesis addresses the design of event-triggered adaptive sliding mode control for interval type 2 Takagi–Sugeno (T–S) fuzzy nonlinear systems with time-varying delay, subject to matched perturbations with unknown upper bound and unmatched perturbations, with distinct input matrices among the local linear subsystems. Two control methods are proposed, denoted control method 1 and control method 2, which share the same practical stabilization and robust passivity framework while differing in the adaptive law governing the switching gain. In both methods, practical stabilization and robust passivity within the practical sliding mode region are obtained from the robust passivity inequality, with the storage function defined by a fuzzy Lyapunov Krasovskii functional, from which conditions in the form of delay-dependent linear matrix inequalities are derived, dependent on the maximum delay, the upper bounds on the rates of variation of the delay and of the membership degrees, and the robust passivity coefficient. The feasibility of these conditions determines the sliding variable matrix and provides the decision variables required to derive the practical stabilization conditions, whose practical stability region radius, for both methods, is determined independently of the estimate of the upper bound of the matched perturbation, as is the upper bound of the practical sliding mode region. Control method 1 employs an adaptive law based on monotonic growth, which dispenses with knowledge of this bound and forces the gain to converge once the practical sliding mode region is reached. Control method 2 employs an adaptive law based on a barrier function, which relaxes the dominance of the gain over the matched and unmatched perturbations through a relaxation region, allowing the gain to both increase and decrease and yielding a less aggressive control action than the monotonic strategy. For both methods, the positive invariance of the practical sliding mode region is established under the simultaneous presence of time-varying delay, matched and unmatched perturbations, and event-triggered control, with reaching instants independent of the estimate of the upper bound of the matched perturbation. The event-triggering mechanism is formulated with an analytical guarantee of the absence of Zeno behavior, and certification of the maximum admissible delay is carried out via bisection decoupled from the control design. An upper bound for the triggering threshold is further derived, for each method, as a function of the robust passivity coefficient, establishing an energy-based link between the triggering mechanism and the closed-loop dissipativity, while this same coefficient bounds the impact of the unmatched perturbation on the output. The results are validated through computational simulations that demonstrate the effectiveness and comparative advantages of the proposed methods over existing approaches in the literature. Instituição: Universidade Federal do Maranhão Tipo do documento: Tese

Desenvolvimento de um absorvedor eletromagnético têxtil aplicado às bandas 4G E 5G

Wed, 01 Jul 2026 00:00:00 GMT

Título: Desenvolvimento de um absorvedor eletromagnético têxtil aplicado às bandas 4G E 5G Autor: CARVALHO, Paulo Henrique Bezerra de Primeiro orientador: SANTANA, Ewaldo Eder Carvalho Abstract: Absorbing materials are developed to attenuate electromagnetic radiation and ensure the compatibility of electronic equipment in environments subject to interference. Although microwave frequency transmissions are essential for communication systems, absorber solutions are required to reduce the intensity of unwanted signals. This Thesis presents a flexible and low cost textile electromagnetic absorber designed for 4G and 5G technologies, operating at 2.5 GHz and 3.5 GHz. The developed material consists of a natural graphite and poly(vinyl alcohol) (PVA) composite applied onto a denim substrate. The electromagnetic losses of the device are based on the interaction of the incident wave with the conductivity and permittivity of the material, characterizing it as a resistive-type absorber. To verify the device efficiency, four samples were fabricated and tested, with thicknesses ranging from 0.96 mm to 1.05 mm, whose electromagnetic characterizations were performed using a Vector Network Analyzer (VNA) in the 2 GHz to 4 GHz frequency range. The electrical properties were analyzed to demonstrate its resistive behavior through conductivity and permittivity measurements, using the four-point probe and coaxial probe methods, respectively. To identify the structural and morphological properties of the composite, characterizations were performed by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and Fourier-transform infrared spectroscopy (FTIR). In the frequency band of interest, the results revealed significant attenuation between 2 GHz and 3.5 GHz, with values ranging from -11.89 dB (at 3.5 GHz) to -20.83 dB (at 2.14 GHz). The average attenuation was -16.96 dB in the 2 GHz to 2.5 GHz range; -16.93 dB between 2.5 GHz and 3 GHz; and -14.58 dB between 3 GHz and 3.5 GHz. The sample with the best absorption performance presented a direct current (DC) conductivity of 1.36 S/m, associated with an imaginary permittivity in the range of 1 < 𝜀′′ < 1.2 and a dielectric loss tangent between 0.1 < tan𝛿 < 0.15. These results demonstrated the efficiency of the absorber, which is characterized by electromagnetic losses predominantly driven by Joule heating. Instituição: Universidade Federal do Maranhão Tipo do documento: Tese

Segmentação de acumulações de gás natural em imagens de reflexão sísmica através de técnicas 1D, 1.5D e 2D

Fri, 10 Oct 2025 00:00:00 GMT

Título: Segmentação de acumulações de gás natural em imagens de reflexão sísmica através de técnicas 1D, 1.5D e 2D Autor: MELLO, Henrique Ribeiro de Primeiro orientador: PAIVA, Anselmo Cardoso de Abstract: The most common indirect identification method used by the oil and natural gas industry in the search for natural gas accumulations is conducting a survey based on the principle of seismic reflection. Specialists look for sudden changes in signal intensity, which may indicate the presence of natural gas, oil, or other hydrocarbons. In this thesis, we propose three methods to automate this task using seismic reflection data: one method that uses an Ensemble of U-Nets, a well-established architecture in image segmentation, and two others that make use of the Robustly Optimized Bidirectional Encoder Representation from Transformers Pretraining Approach (RoBERTa), a method originally developed in the context of natural language modeling. The methods are developed in such a way that we simulate what happens in practice, where models are trained in a given region and are used to evaluate unkown areas. To do so, we propose a train-test split policy for the public dataset used that simulates the use of the methods in a new region. The U-Net based method requires the annotation to be considerably larger than the original and is able to determine the annotated region more precisely. The method based on the RoBERTa architecture shows more false positives in areas of high acoustic-impedance variation, but it is capable of identifying possible smaller accumulations, as well as de- lineating much of the structure that stores the natural gas. All three methods present segmentation evaluation metrics superior to the state-of-the-art when considering the model’s generalization capability using a single dataset. On the F3 block dataset in the Netherlands, the methods achieved F1-scores between 0.36 and 0.62 on the proposed test set, while sensitivity varies between 0.65 and 0.79. Instituição: Universidade Federal do Maranhão Tipo do documento: Tese

CONTROL OF INTERNAL LOOPS IN CONVERTERS OPERATING AS VIRTUAL SYNCHRONOUS MACHINES FOR IMPROVED DYNAMIC RESPONSE

Fri, 03 Oct 2025 00:00:00 GMT

Título: CONTROL OF INTERNAL LOOPS IN CONVERTERS OPERATING AS VIRTUAL SYNCHRONOUS MACHINES FOR IMPROVED DYNAMIC RESPONSE Autor: SERRA, Amiron Wolff dos Santos Primeiro orientador: RIBEIRO, Luiz Antonio de Souza Abstract: A crescente integração de fontes renováveis de energia aos sistemas elétricos modernos, impulsionada por preocupações ambientais e pela busca global por soluções sustentáveis, tem transformado significativamente o panorama da geração de energia. Nesse cenário, os recursos baseados em inversores tornaram-se essenciais para a conexão dessas fontes à rede elétrica. Tais recursos geralmente são controlados por estratégias do tipo seguidores de rede ou formadores de rede. Enquanto os inversores seguidores de rede dependem de malha de detecção de fase e requerem uma fonte externa de tensão para sincronização, os inversores formadores de rede são capazes de estabelecer de forma autônoma referências de tensão e frequência, sendo, portanto, adequados para operação tanto conectada à rede quanto isolada. Dentre as estratégias de formadores de rede, destacam-se as máquinas síncronas virtuais por sua capacidade de emular o comportamento inercial e de amortecimento dos geradores síncronos convencionais. Essa característica permite uma resposta dinâmica mais robusta em sistemas com alta penetração de fontes renováveis e baixa inércia. Inversores baseados em máquinas síncronas virtuais são capazes de sustentar a regulação de tensão e frequência, tanto em operação autônoma quanto em coordenação com a rede principal. Esta tese propõe o projeto e o aprimoramento das malhas internas de controle de um inversor baseado em máquina síncrona virtual, com o objetivo de melhorar a estabilidade do sistema elétrico e a resposta dinâmica. Especificamente, é desenvolvido um controlador de corrente com alta largura de faixa, capaz de atenuar a ressonância do filtro LCL e melhorar a rejeição a perturbações. Também é proposto um controlador de tensão com desacoplamento da entrada de perturbação, visando aprimorar a resposta dinâmica da máquina síncrona virtual. Com as malhas de controle internas projetadas, a máquina síncrona virtual apresenta desempenho dinâmico aprimorado quando conectada à rede, mesmo em uma ampla faixa de razões de curto-circuito, assim como durante variações de carga em modo isolado. A máquina síncrona virtual também demonstra melhor desempenho quando operando em uma microrrede, tanto em coordenação com um inversor seguidor de rede quanto em paralelo com outra máquina síncrona virtual. De modo geral, esta tese busca aprimorar as malhas internas de uma máquina síncrona virtual, permitindo que ela atue como uma estratégia eficaz de controle de potência em sistemas elétricos cada vez mais dominados por recursos baseados em inversores. Instituição: Universidade Federal do Maranhão Tipo do documento: Tese