RCAAP Repository

In recent decades it has been observed the occurrence of voltage collapse phenomenon in several electric power systems around the world. This can be explained by the increase of generation to meet growing consumption without concomitant investment in transmission lines. It is usual to increment the active power transmission capability through the inclusion of reactive support devices. Due to excessive use of this resource, the load busses can become too capacitive. This implies in increase the risk of voltage collapse in these busses, even without transgressing the undervoltage limits. In this scenario the voltage collapse may occur without the actuation of a undervoltage load shedding scheme. In this case it is necessary to improve the undervoltage relay which can be achieved by the inclusion of a load shedding logic based on a voltage collapse proximity indicator. This work proposes a load shedding algorithm based on bus loading margins. In the context of electric power system protection, such methodology should be included in undervoltage digital relays that operate in load busses with capacitive power factor. The operation of the proposed algorithm is illustrated through simulations of situations favorable to voltage collapse using a reduced electric power system, represented by the Thevenin equivalent circuit coupled to a load bus, as well as the IEEE 14- bus power system.

Universidade Federal de Uberlândia

This thesis identifies ways of mitigating the temporal harmonics caused by Non-Linear Loads (NLL) constituted by electronically switched loads which increase constantly, at the present time constituting 65% of the total in countries such as Brazil. The research involved identifies the solution for Distributed Generation (DG), that is to say, in plants fed by their own electrical generators working disconnected from the main, as occurs in situations of maintenance or emergency which lead to the interruption of the main. The solution presented in this study proposes that Synchronous Generators (SGs) of low sub transient reactances should be used as the solution. The research was undertaken by means of the development of the mathematical models used in the simulations by means of which the relationship between the reactances and the wave deformity of the voltage with Non Linear Loads became evident. Laboratory experiments validated the simulations. The spatial harmonics which are focused on only tangentially are disregarded seeing that the Synchronous Generators are produced with excellent wave forms with distortions of only 1% to 3%. The frequent quotation of norms or standards, especially of the IEC, the IEEE and the ABNT is meant to serve as a frame of reference for the thesis as regards the standards used by engineering firms in the projection and implantation of Electrical Generating Plants in Distributed Generation

Virtual Reality (VR) is, by nature, motivating. It enhances interaction and propitiates the evolution of Virtual Environments (VE). It also establishes and expresses a dialogue between users in an attractive way, in the most diverse informational ambiences. It is considered the most advanced and interactive interface to date, in which is possible to present a more natural way of communicating, and provide visually stimulating resources to users. Thus, with the advance of interactive digital technologies, VEs should be developed in such a way that they not only attract and keep the users attention, but also present information in an adequate context. Taking motivation as the starting point, we are led to question the limitations presently found in VEs, like the difficulties in understanding the activity process because the way it was exposed, the use and disposition of navigation controls or even the limitations imposed by information overload. Users with different objectives, preferences, interests or knowledge may help in identifying the demands established for the development of tools in this area. Therefore, it has been hypothesized that the interaction attributes (controls) used for navigating in VEs do not take on board the descriptions of digital resources that seem to users particular needs. VR, as an immersive technology, lacks new elements which can deliver to each user interfaces that respect their individual needs. The recommendations found in the literature for the development of VEs alone do not guarantee the necessary subsidies to have access to interaction in a personal basis. Taking into consideration the points raised above, especially when the objective is training and learning, the objective of this study was to present, through a descriptive exploratory approach, a framework proposal to promote digital interaction elements for the development of VEs for users with individualized profiles. The general objective of this study was to contribute to the elaboration of directed digital environments, as well as to supply recommendations and technologies for the elaboration of parameters for VR interfaces. In a theoretical dimension, this research involves a revision of concepts related to adaptive interfaces and presents a methodology of framework for the development of interaction interfaces in VR environments. To that aim, a search of adaptive VEs characteristics, and of technologies for the development of interfaces for VR, was carried out. In addition to that, a model of Artificial Intelligence (AI) was adopted for information reorganization based on the interaction between the user and the digital context, specific to education, using Usability principles. Hence, VR, AI and Usability elements constitute the basis of this framework to provide a favorable environment to the development of specific interactive approaches with the generation of individualized contexts which, from an educational point of view, can boost learning through the relationship between users and the environment s graphic interface.

The development of computational models that can simulate the behavior of photovoltaic cells is of great importance in understanding this type of device. A new model is proposed to determine the types of dopants used in the manufacturing process, with the estimation of their concentrations. The use of techniques aided by computational intelligence based strategies allowed the creation of a new way to simulate and achieve results, regarding to the processing of mathematical model for photovoltaic cells. This new technique is not only able to get the types of dopants and their concentrations, but also minimize the amount of information required in term of number of variables needed to determine the behavioral characteristics of the solar cell under the parameters of voltage, current and power. The validity of the technique is treated in the theoretical and observed from the examples used during the tests applied software models PMCCF and PC-1D.

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

The volume of timber planted is essential information in a rational and sustainable direction of resources available in the forests. Thus it is very important to quantify it as precisely as possible. The Forestry activity that deals with the quantification of wood in the forest is the Forest Inventory. This inventory is the basis for planning the use of forest resources. Through it is possible to characterize a given area and the qualitative and quantitative knowledge of the species that compose it. Forest inventories are used in various types of surveys for recognition, diagnosis and evaluations in the field of forests. The assessment of timber stock in feasibility studies, planning and preparation of plots of exploitation, as well as exploratory post-diagnosis, require specific inventories. Neural networks, especially multilayer perceptron networks with back-propagation algorithm have been used in several areas due to its high capacity to deal with nonlinear relationships of input-output, highlighting the learning ability and the ability to generalization, association and parallel search. These networks have been applied in various areas such as finance, time series forecasting, pattern classification, among others. Neural networks have also been used in several works modeling to estimate forest trees of various parameters such as diameter, height, volume, and others. In this work we performed the analysis and prediction of diameters and calculation of volumes of trees of genus Eucalyptus. The model uses only three diameters measure from the base of the tree, and recursively, the diameters are predicted. For the proposed model experiments were performed to approaches with the overall height and the minimum commercial diameter. The model performance was compared in the experiments and the results showed that the proposed model showed satisfactory performance in relation to the traditional models used in Forestry.

Universidade do Estado de Minas Gerais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

The aim of this work is to evaluate the potential of Virtual Reality as an assistive technology for students with intellectual disability, especially in the teaching of logicalmathematical concepts. For this purpose, a Virtual Reality game aimed at students with intellectual disability was developed. The game, called VirtualMat, enables the teacher to explore many fundamental mathematical concepts with the students. It has been validated by special education professionals and tested by students with intellectual disability from two inclusive schools. In order to evaluate the efficiency of VirtualMat, it was used an approach both quantitative and qualitative. In the quantitative stage, questionnaires were applied to the teachers. These questionnaires, regarding the skills and knowledge presented by the students, were applied prior to the tests with VirtualMat get started in schools and were reapplied after a period of 3 months of tests. For the statistical analysis it was used the t-test for hypothesis testing and descriptive statistics for exploratory analysis. In the qualitative stage, it was used the observation technique, with a record about what occurred during the application of the software. This set of notes was assembled to be reported later in the present study, aiming to expand the theoretical discussion with what was observed in practice. The results indicate that VirtualMat contributed significantly for students with intellectual disabilities to learn concepts and skills that had not been seized by them in a conventional way, pointing out evidences that Virtual Reality, when used as Technology Assistive, has a positive impact on the process of teaching/learning of these students.

Recently, in order to improve the distribution of electrical energy, and to provide agreement with the power quality standards, especial emphasis on power quality has demanded performance improvement of rectifier structures as a front end power processor. Three-phase diode-bridge rectifiers are very popular in several industrial and rural applications, where an intermediate DC link provides energy for other electronic circuits. However, such standard diode-bridge rectifiers do not meet harmonic current content restrictions, as imposed by several international standards such as IEC 61000-3-4 and IEEE 519-1992. Thus, expensive and bulky passive filters or complex power factor correction and active filter structures must be installed to compensate the inherent harmonic current distortion. Therefore, in the past few years, there has been a tremendous interest in achieving low harmonic current distortion in three-phase AC to DC converters, motivating researches of several front-end multipulse rectifiers. Several structures of multipulse rectifiers have been applied in three-phase applications for mitigation of the input current harmonic content. However, these converters need magnetic circuits such as inter-phase transformers, current balancing transformers or harmonic blocking transformers. They have complex design, are heavy, bulky, expensive and only made by special order. Besides, elimination of interphase transformers is particulary desirable when there are preexisting harmonic voltages in the three-phase power source, because those harmonic voltages cause changes in the DC output leading to further complication in the design of interphase transformers. Therefore, in this thesis, controlled rectifiers operating in parallel to standard threephase diode-bridge rectifier are proposed in contrast to expensive and complex schemes, as long as the overall converter behave as a current source controlled with a suitable strategy. The fundamental idea behind a front-end programmable rectifier is the imposition of a suitable input line current waveform in order to provide low THDI and high input power factor. In conclusion, this work proposes a new concept of multipulse hybrid rectifier for ultra clean power applications. This innovative programmable three-phase power factor correction hybrid multipulse power rectifier is capable to provide ultra clean power without the need of phase-shift transformers, inter-phase transformers, current balancing transformers or harmonic blocking transformers.

Universidade Federal de Uberlândia

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Changes in the process of teaching and learning can be both useful and nonuseful to enhance students learning. This work tried to show that current teaching methods not always meet the needs efficiently when it comes to improve students skills. For that, it relied on experiments with Language Programming subject matter s students. It did so because such a subject matter poses questions whose answers can be answered freely because its codes can be written in many ways , while its assessment is dichotomic. Teacher s didactic procedures, methodology applied in classes, programming language, and the time taken to develop the work proposed were the categories considered in the research. In an experimental group of students, Robert Mager s theory was applied to compare their learning. In such theory, instructional aims are supposed to provide a statement on the information students will get and on their understanding and ability to use them after the course ends. Conclusion is that students skills and performance were improved, that is to say, that there was an increase of knowledge, which can be measured and presented graphically by Rasch model.

Aging is directly linked to adverse impacts related to factors that affect the chronological age-related changes such as heredity, environment, diet, lifestyle, and habit of practicing physical exercises, among other features. The Central Nervous System (CNS) and neuronal signals carry information that represents changes throughout life. In this context, this study seeks to establish some correlation between brain activity as a function of age, from the record of electroencephalographic signals (EEG), in subjects not suffering from neurological disorders, while performing a certain task. There were 59 healthy subjects that voluntarily participated in this study, which were divided into 07 groups, with ages between 20 and 86 years and both sexes. EEG signals were collected \"simultaneously\" in three different experimental protocols during the execution of the Spiral of Archimedes (Ingoing Spiral, Outgoing Spiral and stopped up in the center). The electrodes were positioned according to the international standard 10/20, using the channels C3 and C4 of the central region. Statistical analyses were performed to identify differences and allow discrimination between the characteristics of each group according to the presented changes. The data were processed with software MATLAB. Among the results, significant differences were observed, via LDA-value, Linear Discriminant Analysis (LDA), a technique to optimize the extraction of discriminating information from a data set. The tool has satisfactorily performed the separation of discriminant features, classifying each group of individuals that have high correlation as a function of age. It can be concluded by the analysis of the characteristics used that there is the separability between groups according to age, contributing significantly to register the changes that occurred during the aging process.

This study presents a model for the organization of educational content customized for environments of individual studies. For many students the availability of content in general form can not be efficient. It proposed a multilevel structure of concepts to provide the development of different combinations to show the same content. The work shows that it is possible to customize the content in order to encourage other students with the use of proximal learning standards. These patterns are obtained from the analysis of the action of students with positive results in the individual organization of the content. The formal representation establishes the definition of the student profile, multi-level content, the distribution plan of correction of concepts and teaching career. The structure of the trajectory of student teaching is formally established by the method of finite differences. The system uses artificial intelligence techniques to organize and personalize content reactively. Customization is provided by an artificial neural network that enables the classification of the student profile and assign that profile to a standard proximal learning. To mediate and adjust the contents of a reactive system was inserted into a set of rules from experts in teaching. The experiment showed the applicability and appropriateness of the proposed model. The results indicated the suitability of the approach by automating the organization\'s custom content so adaptive and reactive. The intelligent system to establish the structure of the custom content to be presented was considered efficient, giving the student a better use of the content, with higher and lower final average study time and content presented.

This work demonstrates the theoretical and experimental feasibility of a induction generator to work as an attenuator of the harmonics in main generators of on the electric power system, i.e., the synchronous generators. The induction and synchronous machines were analyzed in physical terms and established mathematical modeling in the frequency domain in order to prove the purpose of the thesis. Computer simulations were also carried out in the time domain and laboratory tests were made to check levels of attenuation of current harmonics (THDi) in accordance with the maximum standardized voltage harmonic distortion (THDv). Furthermore, this work presents a study of technical and economical feasibility of a typical application.

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

A person can be remembered or identified by various physical characteristics. During childhood, a child learns to identify people by voice, the smell, but probably the most remarkable characteristic of a person is face. Due to the fact that looking at the face of a person more information is collected almost simultaneously, such as eye color, mouth shape, hair texture, skin color, etc.. With a larger amount of information, the probability of incorrectly identifying a person is lower, ie it is more precise to recognize a person from the image of his face than from a voice sample. The person recognition from the image face has always been an important task. This recognition may have several objectives such as identifying a criminal, to allow people access to restricted areas, etc.. Thereforewith the improvement of computers various facial recognition techniques were developed, including techniques that use PCA (Principal Component Analysis). The purpose of this research is develop some methods of face recognition that uses less computational resources and are faster. Based on PCA method, two techniques were developed, the methods Segmented PCA and Selective PCA , which had the highest recognition rates and processing times smaller than Advanced PCA. Other three recognition techniques also developed in this thesis and theses techniques using Genetic Algorithms which also performed better than Advanced PCA. The techniques developed in this thesis can also perform facial recognition from facial regions (forehead, eyes, nose, mouth and chin), it is not always the whole picture of a person s face is available to perform the identification, for example, images obtained from security cameras where a burglar is hooded and the camera can record only the eye region.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior