Programa de Pós-graduação em Engenharia Elétrica e da Computação
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Item Aplicação da teoria da propagação do campo magnético na análise da máquina síncrona(Universidade Federal de Goiás, 2020-06-17) Alves, Renato Silva; Alvarenga, Bernardo Pinheiro de; http://lattes.cnpq.br/9850449311607643; Alvarenga, Bernardo Pinheiro de; Paula, Geyverson Teixeira de; Silva, Rui Vagner Rodrigues daThis work presents a methodology of analysis of the smooth poles synchronous machine in steady state using the theory of magnetic field propagation to obtain the V curve for a given active operating power and various operating factors. This theory is based on the division of the synchronous machine into layers and the application of Maxwell’s equations. This methodology is capable of considering magnetic saturation and the anisotropy of electric steel. The predefined current model is used to estimate the radial and tangential flow density of the layer. The results obtained are compared with the Park equations in steady state. For the validation of the methodology, it was a threephase synchronous four-pole smooth generator is used. The results obtained were very promising when compared to the Park equations on a permanent basis.Item Otimização de vazão em sistema NOMA MIMO utilizando alocação adaptativa de potência, seleção de usuários e conformação de feixe(Universidade Federal de Goiás, 2020-04-14) Carvalho, Marcos Nogueira Lobo de; Vieira, Flávio Henrique Teles; http://lattes.cnpq.br/0920629723928382; Vieira, Flávio Henrique Teles; Lemos, Rodrigo Pinto; Deus Júnior, Getúlio Antero de; Cardoso, Álisson AssisThe combination of Non-Orthogonal Multiple Access (NOMA) and Multiple Input and Multiple Output (MIMO) systems is considered a promising approach for 5G mobile communication networks. However, optimization techniques such as user selection and beamforming can be applied to improve some system performance parameters. In this context, we propose an adaptive power allocation algorithm in conjunction with user selection and beamforming for the downlink of a massive NOMA MIMO system in order to maximize the users' throughput. To this end, we present a novel optimal beamforming solution scheme based on the adaptive computation of signal power values to maximize system throughput, considering the less interfering users. As interference elimination techniques between users in the transmitter the Block Diagonalization with Zero-Forcing and the Dirty Paper Coding are considered. In order to evaluate the performance of the proposed algorithm, simulations were performed considering different power allocation algorithms of the users. The results obtained in the simulations indicate that the proposed algorithm provides higher data throughput values transmitted to the users than the other algorithms considered.Item Contribuições à modelagem e análise de fluxo de carga de redes elétricas com geração distribuída fotovoltaica(Universidade Federal de Goiás, 2020-04-03) Corrêa, Henrique Pires; Vieira, Flávio Henrique Teles; http://lattes.cnpq.br/0920629723928382; Vieira, Flávio Henrique Teles; Brito, Leonardo da Cunha; Garcés Negrete, Lina Paola; Kopcak, IgorThis work presents new contributions to the modeling of photovoltaic panels and the analysis of power systems by means of load flow, with emphasis on distribution networks with associated distributed generation. Such contributions consist of: (a) an equivalent parameter estimation method for photovoltaic cells and panels, which possesses greater accuracy in comparison to similar methods in the literature; (b) matrix equations for the power-mismatch Newton-Raphson load flow algorithm, which provides concise notation for polyphase load flow and reduces execution time due to usage of matrix operations; and (c) a method for the approximate computation of neutral voltages in three-phase systems, whose advantage consists in reducing the computational complexity associated to the study of neutral-earth voltages as functions of grounding impedances. All proposed methods are validated by means of computer simulations based on real data pertaining to distribution networks; the obtained results are compared to those provided by different methods in the literature. In order to expand the analysis to distribution grids with penetration of distributed photovoltaic generation, the simulations are carried out via the Monte Carlo method, by means of which the randomness of power injection and allocation of generators is emulated. The results confirm the validity of the proposed methods and suggest their applicability to problems involving photovoltaic panels and/or load flow in grids with distributed generation.Item Detecção de imagens falsificadas baseada em descritores locais de textura e rede neural convolucional(Universidade Federal de Goiás, 2020-06-30) Ferreira, William Divino; Soares, Fabrizzio Alphonsus Alves de Melo Nunes; http://lattes.cnpq.br/7206645857721831; Cruz Júnior, Gélson da; http://lattes.cnpq.br/4370555454162131; Cruz Júnior, Gélson da; Pedrini, Hélio; Salvini, Rogério Lopes; Costa, Ronaldo Martins da; Lemos, Rodrigo PintoNowadays, digital image transformation has become a widespread activity. Hence, image copying, cloning, and resizing are easily performed, making it challenging to check image integrity and authenticity. Moreover, a criminal investigation from digital images becomes extremely hard, because using those images as proof demands to ensure its legitimately,under a risk to implicate the whole legal process.In this sense, this work develops a model for forged images based on local texture descriptors with convolutional neural networks. Henceforth, in this work, firstly, we evaluated fourteen local texture descriptors in five public image texture datasets, and then we selected descriptors with the best efficacy. Second, the selected descriptors are applied to four public datasets to extract texture features from forged and legit images. Finally, those features are used to train a residual convolutional neural network, and then, classifying images as authentic or forged with a Support Vector Machine Classifier. A result of the proposed model provides enthusiasm, mainly when applied to a dataset with a small number of images.Item Modelagem e proteção de reatores shunt do tipo seco com núcleo a ar(Universidade Federal de Goiás, 2020-02-27) Ribeiro, Jan Augusto Rocha; Almeida, Maria Leonor Silva de; http://lattes.cnpq.br/7955955842189669; Almeida, Maria Leonor Silva de; Silva, Kleber Melo e; Kopcak, IgorThe use of long and high voltage level transmission lines is common in countries with large territorial extensions, since they allow the transmission of electric energy between regions physically distant from each other. Despite of this advantage, long lines with high voltage level operate with high capacitive effect, which results in the increase of the voltage in some points of the system. These overvoltages are harmful because they result in heating, compromising the integrity of electrical equipment. In order to overcome overvoltage problems due to line capacitive effect, there can be used reactors in parallel to the line. These reactors absorb the excess of capacitive reactives in the line, improving voltage regulation. Therefore, due to its importance for line and electrical system operation, it is essential to ensure the shunt reactor’s correct operation. Normally in systems with voltages equal to or greater than 230 kV, iron core reactors immersed in oil are used. However, due to technological advances, air-core reactors have been developed to be installed at systems with voltages up to 345 kV. Since it does not have oil or iron core, this type of reactor causes less losses, is easier to install and requires less maintenance. Considering the benefits of aircore shunt reactors and their relevance to the system’s correct operation, this work proposes to develop both a model and a protection applicable to this equipment. The proposed model allows the analysis of the reactor’s behavior under nominal operating conditions and also in different situations of internal faults (turn-to-ground and turnto-turn faults). For the evaluation of the proposed model, reactor currents are verified against the influences of fault type, number of turns involved in faults, dispersion factor, position of the fault in the coil and value of fault resistance. Furthermore, it is proposed a differential protection which compares zero sequence currente on phase winding to current in ground winding. This current signals comparation is based on an adapted alpha plane. In order to validate the developed proposals, simulations were carried out using Alternative Transient Program software (ATP), wherein is simulated a 230 kV transmission line, 380 km with 50% shunt compensation. In this scenario, different faults were applied to the reactor in order to evaluate the proposed model and it’s protection. In addition, the proposed protection is compared with a protection traditionally employed for a correspondent reactor, restricted earth fault (REF), which confirms the best performance of the proposed protection. Finally, is concluded that the proposed model is a good alternative to represent the air-core dry reactors. In addition, it is concluded that the proposed protection guarantees the integrity of this equipment against different types of faults.