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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Agora exibindo 1 - 20 de 199

Acesso aberto (Open Access)
Estudo de secagem por microondas e eólica-solar térmica
(Universidade Federal do Pará, 2003-04-29) PAIVA, Reginaldo Sabóia de; MACÊDO, Emanuel Negrão; http://lattes.cnpq.br/8718370108324505; PINHO, João Tavares; http://lattes.cnpq.br/0847897516772421
With the main objective of studying and developing methodologies of control and simulation of microwave drying processes, this work uses as tool the physical-mathematical modelling of the thermal effects and mass transfer caused by microwave radiation in porous solid materials, taking into account the important variables for each case. Several results are presented, such as simulations of electric field profiles, power density, temperature and humidity inside materials with homogeneous characteristics and with simple geometry for the one, two and three-dimensional excitations. As a complementary study, the thermal process for the sizing of solar and wind dryers is modeled including the presentation of the results of the simulations developed.
Acesso aberto (Open Access)
Detecção, classificação e quantificação automática de variações de tensão de curta duração para aplicação em análise de pós-operação em sistemas de energia elétrica
(Universidade Federal do Pará, 2006-05-19) MACHADO, Raimundo Nonato das Mercês; PELAES, Evaldo Gonçalves; http://lattes.cnpq.br/0255430734381362; BEZERRA, Ubiratan Holanda; http://lattes.cnpq.br/6542769654042813
The analysis of occurrences in electric power systems is of fundamental importance for secure operation of the system, and to maintain quality of the electric energy supplied to the consumers. The electric power utilities use equipments called disturbance registers (DR’s) for monitoring and diagnose of problems in the electric and protection systems. The waveforms usually analyzed in the electric power utilities operation centers, are those generated by events that usually cause the opening of lines due to circuitbreakers operation commanded by the protection devices. However, a great amount of stored data that can contain important information on the behavior and the performance of the system is not analyzed. The proposal of this work is to use the available data in electric power utilities control and operation centers obtained from DR’s equipments, to classify and quantify of automatic form signals that characterize power quality problems, such as, short duration voltage variations: sags, swells and interruptions. The proposed method uses wavelet transform to obtain a characteristic vector for voltages in phases A, B and C, and a probabilistic neural network is used for classification. The classified signals as presenting short-duration variation are quantified for duration and magnitude of the event, using the multiresolution decomposition signal analysis properties. Those parameters, then, will form a database where statistical procedures of analysis can be used to prepare reports regarding power quality features. The results obtained with the application of this proposed methodology to a real system are also presented.
Acesso aberto (Open Access)
Análise de dados e definição de indicadores para a regulação de usinas termelétricas dos sistemas isolados
(Universidade Federal do Pará, 2006-11-28) CONDE, Cláudio Luciano da Rocha; PINHO, João Tavares; http://lattes.cnpq.br/0847897516772421; BRANCO, Tadeu da Mata Medeiros; http://lattes.cnpq.br/8911039344594817
This thesis proposes an efficient and low cost monitoring system of electrical parameters and fuel consumption of thermal plants of the Brazilian isolated electrical systems, almost all located in the Amazon Region. These systems have many operational problems, usually related to the great distances and lack of data necessary to provide power quality and fuel consumption control. The analysis of the acquired data after the implantation of the considered system in four thermal plants in the State of Pará became possible, among other results, the development of an indicator (IMU) that can be used in the short and average planning studies. The viability of the proposed solution for the operative and regulatory control stimulated the development of a methodology to install monitoring systems all over the isolated systems of Brazil, included in a Brazilian Electricity Regulatory Agency (ANEEL) regulatory act.
Acesso aberto (Open Access)
Contribuições aos estudo da compensação de harmônicos em sistemas de energia elétrica
(Universidade Federal do Pará, 2006-12-06) GALHARDO, Marcos André Barros; PINHO, João Tavares; http://lattes.cnpq.br/0847897516772421
This thesis focuses on the study of methods for harmonic compensation in electrical power systems and discusses various aspects related to the presence of harmonics on them, such as the presentation of concepts and definitions in nonsinusoidal systems and strategies of power compensation. Exemplified by measurements and simulations the following topics are emphasized in this study: the influence of supply waveforms on nonlinear loads; the harmonic interaction between the supply voltage and the load currents, due to the system series impedance; and the mutual influence between nonlinear shunt loads, as a possible way of harmonic reduction. To simulate and predict the impact caused by nonlinear loads in a system, as well as the implementation of actions to mitigate these impacts in order to improve power quality, it is necessary to know the response of these loads. As a product of the present work, the development of techniques for modeling nonlinear loads under different supply conditions is emphasized, especially those using computacional intelligence, such as the neuro-fuzzy system and the artificial neural network; as well as the use of Volterra series for load behavior prediction.
Acesso aberto (Open Access)
Um ambiente colaborativo de aprendizagem interdisciplinar apoiado por interfaces adaptativas
(Universidade Federal do Pará, 2006-12-07) LIMA, Paulo Sérgio Rodrigues; SILVA, Orlando Fonseca; http://lattes.cnpq.br/7387718587227127; BARREIROS, José Augusto Lima; http://lattes.cnpq.br/1246564618922453
The use Virtual Learning Environment (VLE) becomes, day by day, more evident in several public teaching institutions, as well as in private and government agencies. Several versions of VLEs are available for free use, each one under its own characteristics. In Brazil there are almost a thousand institutions that have been using these environments, which show the necessity of investments and new research in this area. This theses specifies and develops a VLE, its main objective is to reduce the problems found in many approach of the environment ready for use thus recommending an environment called "Interdiscipline Collaborative Learning Environment" which was prepared to offer an infra-structure which permits to unite cooperative working concepts, learning virtual communities, interdiscipline, interfaces adaptation and in a complementary way allow creation of automatic recommendations to its users based on their profiles.
Acesso aberto (Open Access)
Carimbó: canal de retorno com interatividade condicionada por mecanismo de sinalização contínua e provisionamento de banda orientado QoS
(Universidade Federal do Pará, 2006-12-15) COUTINHO, Mauro Margalho; FRANCÊS, Carlos Renato Lisboa; http://lattes.cnpq.br/7458287841862567; COSTA, João Crisóstomo Weyl Albuquerque; http://lattes.cnpq.br/9622051867672434
This doctoral thesis proposes a framework has controling and management the return network in Digital Television from four components: Digital Television Provider, Interactivity Terminal, Return Channel Provider, and Content Provider. Together, they interact based on a signaling mechanism that propagates QoS restrictions associated to the current interactive programming through the data carrousel system. The set of them also provide an admission control that investigates, periodically, the return channel status allowing or restricting the access according to the necessities of the interactive applications. Moreover, the system is so flexible that admit applications as in large scale as in small scale (local), thanks to the mobility of the service provider. An e-gov/e-health application was development in Xlet Java to evaluate the performance of the system. The performance analysis was proceeded using measurement and modeling techniques according to the system scale. In the last mille, some technologies of low cost and without periodically billing were tested such as wireless local area network. In large scale, the system was evaluated in different scenarios by means of simulation using the Network Simulator.
Acesso aberto (Open Access)
Avaliação da aprendizagem: uma abordagem qualitativa baseada em mapas conceituais, ontologias e algoritmos genéticos
(Universidade Federal do Pará, 2007-05-18) ROCHA, Francisco Edson Lopes da; FAVERO, Eloi Luiz; http://lattes.cnpq.br/1497269209026542
In the last two decades, the development of areas such as Computer Networks and Artificial Intelligence (AI) has favored the growth of other areas of knowledge, like Education. In this area, new discoveries have changed the focus of research from old behaviorist educational theories to constructivism, leading to a better understanding of how learning occurs. Meaningful Learning (ML) is a constructivist theory in evidence nowadays and the Concept Map (CM) is its main cognitive tool. Additionally, the recent developments on Distance Learning (DL) have made it possible to apply the educational process in a larger scale. In this thesis, automatic learning assessment mediated by concept maps is investigated. This is related to a qualitative approach, named as formative assessment, which is compliant with Bloom’s model, a reference for educational processes - teaching, learning, and learning assessment. The proposal presented in this thesis is seen as an alternative solution to an important issue in the area of Education: how to evaluate learning qualitatively, respecting each student’s cognitive processes? The integration of concept maps, domain ontologies, and genetic algorithms allows for advances in automatic learning assessment and assistance. The paradigm of mere quantitative assessment is broken, and a new approach to gradual and continuous assistance in learning is presented. Following this approach, it is possible to accompany students individually, respecting their idiosyncratic ways of learning, and also to group students based on specific cognitive characteristics or development degrees. This thesis begins a new research area, which can be synthesized as "Automatic qualitative assessment of learning centered in Concept Maps, based on AI techniques: ontologies and genetic algorithms". In this new research area, the thesis originated the following contributions: ² a prototype of an environment designed to aid teaching, learning, and learning assessment, founded upon Meaningful Learning, encompassing a concept map editor, an ontology editor, and an assessment module; ² A proposal concerning the use of genetic algorithms and ontologies in qualitative assessment/ assistance of learning, allowing for: – step-by-step individual assistance; – assistance to groups of students; – comparisons among students. Domain ontologies are generated by the teacher, who uses an ontology editor provided by the environment. They comprise the structural knowledge that must be learned by students before they can manage other forms of knowledge. The genetic algorithm was designed to run in two distinct modes: i) generating multiple CMs to compare with the student’s CM, allowing for learning assessment at any moment of the course; this assessment is relative, centered in a determined number of concepts which represent a partial structure of knowledge domain being studied.; and ii) generating an optimal CM according to the ontology created by the teacher, to permit a complete assessment of the learning of the knowledge domain which was studied. The proposed model was evaluated by the implementation of prototypes for the assessment tool. The genetic algorithm developed uses the ontologies as its search spaces. It emulates meaningful learning cognitive processes, and constructs CMs that can be semantically compared to that of the student. Its fitness function represents a way of measuring distances in the cognitive field, being the measurement unit given by a taxonomy that organizes semantic dimensions and, inside these, linking phrases. This taxonomy is used by teachers when they construct their ontologies, and by students when they construct their concept maps. The main challenges faced in the development of the research reported in this thesis were: 1) definition of a domain ontology model that could be applied to learning assessment; 2) definition of a method and a scale that could be applied to the cognitive domain; and 3) definition of a search mechanism in the ontology in accordance with constructivist theories of learning assessment. The research described in this thesis can be further developed with new functionalities or improvements in functionalities already implemented. Some possibilities are suggested in the end of the thesis, the main of which being the deployment of the environment in the Internet. This thesis has generated 7 (seven) scientific contributions, 1 (one) in a qualis A magazine, 1 (one) in a qualis B magazine, 2 (two) in international congresses, and 3(three) in national congresses. The results of this research advance what has already been attained by the AmAm/UFPA research group, in whose context this thesis is inserted.
Acesso aberto (Open Access)
Nova metodologia para análise e síntese de sistemas de aterramento complexos utilizando o método lN-FDTD, computação paralela automática e redes neurais artificiais
(Universidade Federal do Pará, 2008-02-29) OLIVEIRA, Rodrigo Melo e Silva de; SOUZA SOBRINHO, Carlos Leônidas da Silva; http://lattes.cnpq.br/1450994881555781
The FDTD method in General Coordinates (LN-FDTD) was implemented for analyzing structures not coincident to the Cartesian coordinate system. The method solves the Maxwells equations in time domain, allowing the calculation of data concerning the transitory and steady-state responses of such structures. The method is applied to analyze of special grounding electrodes. A new formulation for the truncating technique UPML, for conductive media, referred here as LN-UPML, was developed and implemented in order to make the simulations viable. A new methodology for locating grounding grid faults using two Artificial Neural Networks is presented. The LN-FDTD software was tested and validated though simulations of various grounding systems. A graphical user interface, named LANE SAGS, was implemented to simplify the use and to automate the data processing.
Acesso aberto (Open Access)
Metodologia integrada utilizando sensoriamento remoto em redes neurais artificiais na quantificação do potencial de biomassa florestal na Amazônia
(Universidade Federal do Pará, 2008-04-08) ALMEIDA, Arthur da Costa; ROCHA, Brigida Ramati Pereira da; http://lattes.cnpq.br/9943372249006341
Pattern recognition and pattern classification in digital images is a very important skill, today. With them, it is possible to recognize and identify target objects in those images. This work proposes an integrated methodology for pattern recognition related to biomass in the Amazon tropical rainforest to extract information about bioenergetics potential for electric energy production for use with isolated Amazonian communities. To achieve this aim, information gathered about forest inventory was mixed with pattern classification and recognition in medium resolution satellite imagery such as those from LANDSAT and CBERS. The approach used in this work comes from the computational intelligence area, using artificial neural networks equipped with radial basis functions and Kohonen´s self organizing maps. The results serve as input to a geographical information system application which creates and manages a geographical database for energetic planning with renewable energy resources applicable to isolated Amazonian communities.
Acesso aberto (Open Access)
Nanofabricação, caracterização e modelagem de dispositivos optoeletrônicos nanoestruturados de corantes orgânicos
(Universidade Federal do Pará, 2008-07-28) COSTA, Sheila Cristina dos Santos; DEL NERO, Jordan; http://lattes.cnpq.br/5168545718455899
To better understand the process of miniaturization and the behavior of molecular structures under this effect we appeal to the calculations based in Quantum Mechanics (QM) with the purpose to corroborate theoretical and experimental data as electronic structure as well as electric properties. Another method sufficiently known consists simulate solute-solvent effect through the probabilistic Monte Carlo (MC) method. Of ownership of these computational tools we develop simulations QM/MC that translate the behavior of organic composites Methyl Red (MR) and 1,4-bis (5-phenyl-2-oxazolyl) benzene (POPOP), when suffer structural changes, modification in the optic answers, etc., due miniaturization processes, environment variations, external actions. The Methyl Red composite is known as a sensible dye of pH variation and meets in the basic and acid (isoeletrônico, zwitteriônico) forms is classified as azo-composite for the presence of (– N = N –) bonding in its structure. The POPOP is a luminescent dye of intense fluorescence in the blue region of the UV-Visible spectrum; we stand out that to investigate the functional and mannering principles of this structure we consider two conformational structures protonated derivatives of POPOP: C1 (N+) and C2 (N+). Initially all organic composites structures of MR and POPOP had been optimized through of the quantum methods: semiempirical PM3 (Parametric Method 3) and ab initio HF (Hartree-Fock) and DFT (Density Functional Theory), getting the geometric parameters and the conformations of lowest energy of each system, for the study of the electronic structure. Sequentially, two distinct stages of simulation had been used for the study of composites: 1st) The MR and POPOP structures had been optimized through the method PM3 + External Electric Field (the EEC), getting the geometric parameters and charge parameters. We use this method with the purpose to simulate the electronic transport properties of organic composites as the electric reply characterized by the charge transport (e) curve in function of the variation of the tension (V) in the structures. By means of the electric reply [(e) × V] we characterize this function to use them in nanostructured devices, as photodiodes, photodetector, solar cells, etc. The 2nd stage consists of simulate organic composites through the Monte Carlo method, to investigate its behaviors in liquid. The systems distinct consist of the addition of VM (basic, acid: isoelectronic and zwitterionic) and POPOP [C1 (N+) and C2 (N+)] in 1000 water molecules to analyze the solute-solvent interactions for development of interchange systems optoelectronic systems as sensory. In MC simulation had been carried 1×1010 steps MC for both thermalization and equilibrium stages in NVT ensemble. Generate a set of 105 configurations, from these we select a set reduced of 103 descorrelantion configurations of which we obtain the convergence average of the electronic transitions π→π*. The convergence average of the electronic transitions π→π* for MR: basic s of 434.33 ± 1,0 [436,34 ± 2,0 nm], isoelectronic 485,80 nm ± 2,0 nm [480,66 nm ± 3,0 nm], and zwitterionic [502.13 nm ± 3.0 nm]; for POPOP C1 [361,25 nm ± 2,0 nm], C1(NP+P) [485.0 ± 26.0 nm], C2 [355,39 nm ± 3,0 nm] and C2(NP+P) [472.0 ± 24.0 nm]. The averages of the electronic transitions π→π* had been obtained through semiempirical ZINDO/S-CIS (Zerner Intermediate Neglect of Orbital Diffential Spectroscopic - Configurations Interaction, Single excitation) method that better translates the spectroscopic parameters of the organic molecules in the UV-visible region. Experimentally we develop two distinct types of systems through of the techniques: Sol-Gel that consists in the incorporation of composites in host matrix of APP (Aluminum Polyphosphate), and Blendes that consist in the manufacture of volume devices within active monolayer. The MR and POPOP composites had been diluted in hybrid solution (10% etanol + 90% water), aliquots of these solutions had been incorporated in the synthesis of APP/Gel. The samples obtain for the Sol-Gel process had been submitted to the variation pH and characterized by spectroscopy of absorption in the UV-Visible region, whose bands of maximum absorption are of [431 nm, 513 nm, 511 nm] for MR and [358 nm, 511 nm and 472 nm] for POPOP and values of [355 nm, 361 nm] for POPOP in solution, that corroborate the theoretical results from the averages of the electronic transitions π→π*. The monolayer devices of MR and POPOP had been manufactured by overlapped of thin films in vitreous substrate/FTO (1st electrode)/PEDOT/P3HT/ active monolayer -Aluminum (2nd electrode) and characterized electrically for charge density (J) in function of applied voltage (V), under dark current and under 550 nm monochromatic light. The MR devices present curve (J×V) characteristic of a rectifier junction p-n of higher electric current signal under reverse polarization for dark current, being this signal intensified under light 550 nm; under forward bias the device presents the same behavior how much to the current signal, this is intensified when measured on monochromatic light (550 nm) in comparison with dark current, however under reverse polarization and forward bias the device presents curve characteristic (J×V) analogous of the conventional photodetector and diode tunnel. For POPOP intensification of the electric chain signal is observed under forward bias and reverses when the devices are under monochromatic light in comparison with measures made under dark current, in way that the characteristic curve (J×V) has similar behavior of the conventional photodiodes. The theoretical-experimental results of the electric (J×V) properties of composites had presented similar behaviors in the voltage range [- 2.0 V – 2.97 V] for MR and [- 2.86 V - 2.86V] for POPOP. We development a complete study with polymers of low bandgap (gap 1 eV) based in monomers bridges composition for carbon forming polymeric chains had been investigated by the methods AM1 (Austin Model 1), PM3 and DFT [B3LYP/6-31G] to corroborated the results of the oligomers of CDM (4-dicyano methyllene-4H-cyclopente [2.1 - 3: 4-b'] dithiophene) and BDT (1,3-benzodithiole-4H-cyclopenta [2,1-b: 3,4-b'] dithiophene), derived from the ditiophene. The results show that the growth of the polymeric chain formed by monomers of CDM and BDT provokes the reduction bandgap of the oligomers, analogous behavior to the polymers based on (3-alkylthiophenes) whose electronic transition π→π* energy is of 1.67 eV, the maximum absorption of the CDM and BDT are of 1.28 eV and 1,73 eV, respectively The theoretical methods used in this study to describe satisfactorily this behavior, whose maximum absorption is of approximately 1,28 eV for CDM and 1,74 eV for BDT, these results had been obtain from the polymeric chains formed by 5 monomers units, demonstrating that the geometric conformations of the polymeric chains simulated are equiprobability, proving the trustworthiness of the methods used in our investigation. In general lines, the results presents to demonstrate that the organic composites investigated are good candidates for employ in nanostructured organic devices applied in the molecular electronics and new technology of materials.
Acesso aberto (Open Access)
Controle inteligente LQR neuro-genético para alocação de autoestrutura em sistemas dinâmicos multivariáveis
(Universidade Federal do Pará, 2008-08-30) ABREU, Ivanildo Silva; FONSECA NETO, João Viana da; http://lattes.cnpq.br/0029055473709795
In this thesis is presented a neural-genetic model, oriented to state space controllers synthesis, based on the Linear Quadratic Regulator design, for eigenstructure assignment of multivariable dynamic systems. The neural-genetic model represents a fusion of a genetic algorithm and a recurrent neural network to perform the weighting matrices selection and the algebraic Riccati equation solution, respectively. In order to a assess the LQR design, the procedure was applied in a 6th order aircraft model, 6th order doubly fed induction generator model of a wind plant and a 4th order electric circuit model which were used to evaluate the fusion of the computational intelligence paradigms and the control design method performance.The performance of the neural-genetic models are evaluated by the first and second statistics moments for the genetic algorithm, whereas the neural network is evaluated by surfaces of the energy function and of the norm of the infinity of the algebraic equation of Riccati and the results compared to the results obtained by using Schur’s Method.
Acesso aberto (Open Access)
Modelamento de sistemas móveis celulares em ambiente indoor usando equações parabólicas
(Universidade Federal do Pará, 2009-05-07) MÁGNO, Fátima Nazaré Baraúna; COSTA, Jessé Carvalho; http://lattes.cnpq.br/7294174204296739; CAVALCANTE, Gervásio Protásio dos Santos; http://lattes.cnpq.br/2265948982068382
The progress of the wireless digital communication system during the last years has been remarkable, and today is one of the fields with faster development. There is a growing search in propagation models that provide efficiency and accuracy. The study of the radio propagation in these environments is very important for the determination of the propagation losses in indoor environment, because any object with dimensions in the order of greatness inside of the range of mobile communication wavelength can act as an interference source for the electromagnetic waves. Two types of propagation models are very used for indoor environment: the empirics and the deterministic. The first ones are based on very simple and direct formulas, easy to apply, however they provide local-specific precision. The deterministic models follow propagation of electromagnetic waves physical principles - the most popular are the ray tracing and the numeric solution of the equations of Maxwell (elliptic equations and for approach, parabolic equations). In this work is proposed a model based on the method of parabolic equations, being considered narrow angles (up to 15°) and wide angles (up to 90°) of propagation. For the solution of the parabolic equation for small propagation angles, the implicit finite difference scheme of the Crank-Nicholson type was used; and for the solution of the equation that considers wide propagation angles the mixed Fourier Transforms was used. In order to validate the model proposed, measurement campaigns were carried out in frequencies of 900 MHz and 2.4 GHz and the data obtained from these campaigns were compared to the model proposed in this work. Besides, the model in subject was also compared with some existent models in the literature. The results found in this work validate the method of parabolic equations as an important tool for the calculation of the propagation loss in indoor environment, once a great reduction of computational effort and quantity of necessary memory, when compared the other methods and a better result was observed for wide propagation angles.
Acesso aberto (Open Access)
Modelamento de sistemas móveis celulares em ambiente semi-confinado e misto usando equações parabólicas
(Universidade Federal do Pará, 2009-05-08) SOUZA, João Furtado de; COSTA, Jessé Carvalho; http://lattes.cnpq.br/7294174204296739; CAVALCANTE, Gervásio Protásio dos Santos; http://lattes.cnpq.br/2265948982068382
In the last decades, the use of mobile telephone have become of great importance because of the growing on the use, this become its study very relevant to solve the problems brought from the increase of demand. In this Thesis, it is developed a model for the study of electromagnetic waves propagation loss, using the formalism of parabolic equation applied to mobile communication in an semi-confined and mixed environment. Crank-Nicolson’s finite differences schema is applied to calculate the parabolic equation (PE) solution. The fifteen degrees in the direction paraxial propagation and the complex refractive index were considered respectively. In other to validate the method a campaign of measurement was carried out in different cities in Para state. In Belém,at Braz de Aguiar Avenue, and in Benfica and Marituba, the frequency used was 900 MHz, and in Barcarena and Abaetetuba the frequency was 1,8 GHz. The results were validated by comparison between the simulations via Parabolic Equations and the measurements obtained at those environments. Besides that, the proposed model was compared with others models in the literature, and presented a good performance. An extension to the model was the consideration for angles in the paraxial direction up to 90º. In this case, was used the Fourier transform to solve the parabolic equation. The obtained results presented a good performance with improvement in the results for big angles up to 90°. The computational processing time using the formalism of EP is rather small.
Acesso aberto (Open Access)
Otimização de controladores utilizando algoritmos genéticos para melhoria da capacidade de sobrevivência a afundamentos de tensão de aerogeradores de indução duplamente excitados
(Universidade Federal do Pará, 2009-12-01) VIEIRA, João Paulo Abreu; BEZERRA, Ubiratan Holanda; http://lattes.cnpq.br/6542769654042813; NUNES, Marcus Vinícius Alves; http://lattes.cnpq.br/9533143193581447
It is proposed in this thesis a methodology to obtain optimal controllers gains for the rotorside converter of doubly fed induction generators (DFIGs) using a genetic algorithm approach. The main objective is to enhance the operational security and robustness of the power system, by a more effective contribution of the DFIG controllers to the system controllability. To reach this goal, the crow-bar protection scheme is activated during the fault period when severe voltage sags occur in order to maintain the rotor-side converter connected to the DFIG. Immediately after the fault is cleared the crow-bar protection scheme is deactivated and simultaneously the rotor-side converter optimal controllers are turned on which permits the improvement of the converter ride-through capability and also contribute to enhance the overall power system stability margin. The effectiveness of this proposed methodology was assessed for the DFIG-based plants using a real electrical network, in three different operational conditions.
Acesso aberto (Open Access)
Método para extração de objetos de uma imagem de referência estática com estimativa das variações de iluminação
(Universidade Federal do Pará, 2009-12-04) OLIVEIRA, Jozias Parente de; PELAES, Evaldo Gonçalves; http://lattes.cnpq.br/0255430734381362; FREIRE, Raimundo Carlos Silvério; http://lattes.cnpq.br/4016576596215504
Video segmentation is a fundamental step in many vision systems including video surveillance and traffic monitoring. Background subtraction is a method typically used to segment moving regions in video sequences taken from a static camera by comparing each new frame to a model of the scene background. In this paper, a hardware system for video segmentation is proposed from algorithm to hardware architecture level. The video segmentation algorithm is aimed at fixed-point operations and improves a Gaussian background model by applying a two-stage linear compensation procedure to remove the undesirable subtraction results from noise and illumination changes. First, the algorithm was validated in MATLAB. Then, it was prototyped on an Altera field-programmable gate array platform (DE-2). At a clock rate of 100 MHz, the architecture can process 30 frames per second, where the image resolution is 640 x 507 pixels. The capability of the system is demonstrated for several video sequences.
Acesso aberto (Open Access)
Estratégia de otimização para a melhoria da interpretabilidade de redes bayesianas: aplicações em sistemas elétricos de potência
(Universidade Federal do Pará, 2009-12-10) ROCHA, Cláudio Alex Jorge da; FRANCÊS, Carlos Renato Lisboa; http://lattes.cnpq.br/7458287841862567
The study of methods, techniques and tools that can aid the decision processes in power systems, in its many sections, is a subject of great interest. This decision support can be accomplished through many different techniques, particularly those based on computational intelligence, given their applicability on domains with uncertainty. In this proposal, Bayesian networks are used for the extraction of knowledge models from the available data on power systems. Moreover, given the demands of these systems and some limitations imposed to the inferences in Bayesian networks, a method is proposed, using genetic algorithms, capable of extending the power of comprehensibility of the patterns discovered; it aims at finding the optimal scenario in order to attain a given target, considering the incorporation of a priori knowledge from domain specialists, identifying the most influent variables in the domain for the maximization of the target variable.
Acesso aberto (Open Access)
Solução estrutural para a segurança do suprimento de energia elétrica no estado do Amazonas
(Universidade Federal do Pará, 2009-12-17) FROTA, Willamy Moreira; ROCHA, Brigida Ramati Pereira da; http://lattes.cnpq.br/9943372249006341
The electric energy vector assumes significant importance in the process of the Amazon integration to the national development. The electric energy support on this region, reaches a high priority level among the constitutional objectives on reduction the regional differences (FROTA, 2004). In the Amazon state, it can be stated that the lack of energy is a fact that decreases the regional development, and in many locations, smaller and more isolated, a factor of social, economic and cultural marginalization. The historical situation of the increasing use of fuel derived petroleum to the power generation in the Amazon state brings huge economic and environmental damage to the Brazilian society, and it has to be solved by the energetic Brazilian planning organ, by imposing the need of reaching other cleaner, safer and less expensive sources. The state is different from other regions of the country due to the existence of several isolated systems, mainly from its capital, Manaus, that shows low reliability and quality in its energy service, adding to that the high cost, considering the need of thermal diesel and oil generation, their amount represents about 73% of all fuel that have to be used in Brazil to thermoelectric power generation (GTON, 2009), having a final cost of 3 billions (US$ 1.5 billion) which is supported, most of it, by the sources transferences obtained through the subsidies of the Consumption Account of Fossil Fuels - CCC. Having this in mind, this assignment has as objective to present an approach of the mainly existing problems, as well as a proposal of structural solution for the energy business to the Amazon state, that can contribute to the improvement of the principles that rule, the compatible energetic politics with the goals of the updated institutional model of the Brazilian electric sector, giving birth to a new cycle of development and growing to the Amazon state and to the Amazon region.
Acesso aberto (Open Access)
Avaliação de estratégias de controle de potência reativa de aerogeradores síncronos em redes elétricas
(Universidade Federal do Pará, 2009-18-11) NASCIMENTO, André Cavalcante do; BEZERRA, Ubiratan Holanda; http://lattes.cnpq.br/6542769654042813; NUNES, Marcus Vinícius Alves; http://lattes.cnpq.br/9533143193581447
In the present work a methodology of reactive power injection in electric grids during voltage dips provoked by short-circuit, in connected wind farms, adopted at some countries with technological maturity in the production of wind energy in the world is evaluated. In the developed studies, the direct drive synchronous wind generator was used with full converter due to the high controllability of the converter connected to the electric grid and for possessing high capacity of reactive power supply, compared to other wind generators technologies. In Brazil, the grid code to connect wind farms to the electric grids, defined by the National Operator of the Electrical System, doesn't stipulate yet the need of adoption of such methodology during faults in the electric grid. It just specifies the ride through apability curve for voltage dips that the wind generators should follow to avoid the trip of the undervoltage relay. Criteria of the synchronous wind generators protection are evaluated starting from short-circuit simulations in a test grid with adoption of the Brazilian grid code, without reactive power injection, being compared with those of other countries that adopt reactive power injection curves.
Acesso aberto (Open Access)
Estratégia de planejamento de redes de acesso de alta capilaridade baseada em tecnologia DSL: uma abordagem híbrida empírica e probabilística
(Universidade Federal do Pará, 2010-03-26) CARDOSO, Diego Lisboa; FRANCÊS, Carlos Renato Lisboa; http://lattes.cnpq.br/7458287841862567
Recently, the Next Generation Network (NGN) have emerged as a viable alternative to merge the data, voice and video transmission over a single network, while maintaining reasonable standards for quality of service. However, despite the improvements brought by the NGN philosophy, many developing countries lack the infrastructure necessary to implement such technology. In this context, technologies such as DSL (Digital Subscriber Line) allows universal access to broadband, with reduced cost and time, when compared to others access networks. In many third world countries, DSL can be considered a broadband network of high capillarity, since it uses a combination of the existing telephony infrastructure and transmission technologies However, the DSL network needs to be widely understood, so that its main advantages are not outweighed by the inefficiency of the system. Therefore, the implementation of a planning policy to aid in this process, taking into account the current needs of applications (voice, video and data) is of major importance. This thesis presents an approach based on strategies to facilitate the planning of communication networks which, a priori, were not implemented to support triple play streams (a prerequisite, nowadays, for the current profile of Internet users). It will be shown that, from the use of actual measurements and probabilistic analysis, it is possible to enable the planning of communication networks, considering physical and software parameters, such as the transmission path, the influence of noise in the communication, the protocols used, and traffic of Triple Play (voice, video and data) applications.
Acesso aberto (Open Access)
Desenvolvimento de metodologias para a localização de intruso em ambientes indoor
(Universidade Federal do Pará, 2010-03-30) ARAÚJO, Josivaldo de Souza; SOUZA SOBRINHO, Carlos Leônidas da Silva; http://lattes.cnpq.br/1450994881555781
The present study aims to propose methodologies in order to detect the presence and locate of an intruder in indoor environments 2-D and 3-D which uses a cooperative system of antennas with the latter. This system is based on multi-static radars in both cases. For a high resolution, the radar operates with pulses of Ultra Wide Band which have spectral range up to 1GHz for the 2-D environments and pulses of Wide Band of 200MHz and 500 MHz for the 3-D environments. For the two-dimensional environments, the estimated location is made by the Particle Swarm Optimization (PSO) technique, Newton’s method with Gaussian elimination and least squares method with Gaussian elimination. For the three-dimensional environment, it was developed a methodology based on vectors which estimates a possible region of intruder location. For the simulation of electromagnetic waves, it uses the numerical method Finite Difference Time Domain (FDTD) associated with the absorption technique UPML (Uniaxial Perfectly Matched Layer) which is used to truncate the domain of analysis simulating the spread upwards. For the analysis of 2-D environment, it was developed ACOR-UWB-2-D and in order to build environments in 3-D, it was used LANE SAGS software.