Engenharia Elétrica

URI Permanente desta comunidade

http://repositorio.ufes.br/handle/10/17617

Programa de Pós-Graduação em Engenharia Elétrica

Centro: CT
Telefone: (27) 4009 2663
URL do programa: https://engenhariaeletrica.ufes.br/pt-br/pos-graduacao/PPGEE

Navegar

Agora exibindo 1 - 20 de 454

A brain-computer interface architecture based on motor mental tasks and music imagery
(Universidade Federal do Espírito Santo, 2013-08-30) Benevides, Alessandro Botti; Bastos Filho, Teodiano Freire; Sarcinelli Filho, Mário; Ferreira, André; Frizera Neto, Anselmo; Conci, Aura; Tierra Criollo, Carlos Julio
This present research proposes a Brain-Computer Interface (BCI) architecture adapted to motor mental tasks and music imagery. For that purpose the statistical properties of the electroencephalographic signal (EEG) were studied, such as its probability distribution function, stationarity, correlation and signal-to-noise ratio (SNR), in order to obtain a minimal empirical and well-founded parameter system for online classification. Stationarity tests were used to estimate the length of the time windows and a minimum length of 1.28 s was obtained. Four algorithms for artifact reduction were tested: threshold analysis, EEG filtering and two Independent Component Analysis (ICA) algorithms. This analysis concluded that the algorithm fastICA is suitable for online artifact removal. The feature extraction used the Power Spectral Density (PSD) and three methods were tested for automatic selection of features in order to have a training step independent of the mental task paradigm, with the best performance obtained with the Kullback-Leibler symmetric divergence method. For the classification, the Linear Discriminant Analysis (LDA) was used and a step of reclassification is suggested. A study of four motor mental tasks and a non-motor related mental task is performed by comparing their periodograms, Event-Related desynchronization/synchronization (ERD/ERS) and SNR. The mental tasks are the imagination of either movement of right and left hands, both feet, rotation of a cube and sound imagery. The EEG SNR was estimated by a comparison with the correlation between the ongoing average and the final ERD/ERS curve, in which we concluded that the mental task of sound imagery would need approximately five times more epochs than the motor-related mental tasks. The ERD/ERS could be measured even for frequencies near 100 Hz, but in absolute amplitudes, the energy variation at 100 Hz was one thousand times smaller than for 10 Hz, which implies that there is a small probability of online detection for BCI applications in high frequency. Thus, most of the usable information for online processing and BCIs corresponds to the α/µ band (low frequency). Finally, the ERD/ERS scalp maps show that the main difference between the sound imagery task and the motor-related mentaltasks is the absence of ERD at the µ band, in the central electrodes, and the presence of ERD at the αband in the temporal and lateral-frontal electrodes, which correspond tothe auditory cortex, the Wernickes area and the Brocas area.
A control structure for a bidirectional dc-ac converter with power quality support functions
(Universidade Federal do Espírito Santo, 2022-12-02) Ribeiro, Laila Sindra; Simonetti, Domingos Savio Lyrio; https://orcid.org/0000000159202932; http://lattes.cnpq.br/1107005171102255; Encarnação, Lucas Frizera; Reis, Fernando Soares dos
The expansion of distributed generation, especially photovoltaic, provokes an increase in the number of DC-AC converters connected to the grid. These converters may offer power grid support functions such as power factor correction and compensation of the current harmonic components. Those functions raise the equipment relevance to the grid and contribute to the power system’s confiability and power quality. In this context, the objective of this work is to design a DC-AC converter with the grid support functions as power factor correction and harmonic compensation, besides electrical power interchange. The work focuses on the controller of the converter, with the algorithms embedded in a DSP and power converter in a Hardware In the Loop (HIL). This dissertation includes a theoretical background of the converter topology operation, filter design, and control loops used in the project. Experimental results demonstrate that the converter is capable of operating with grid support functions with a good performance, correcting power factor and compensating 3rd, 5th, and 7th harmonics. Furthermore, the converter can have multiple functions activated, distributing its power capacity to prioritize the chosen operation mode.
A fairness-focused spectrum assignment algorithm for elastic optical networks
(Universidade Federal do Espírito Santo, 2016-09-27) Tessinari, Rodrigo Stange; Garcia, Anilton Salles; Waldman, Hélio; Martins, Joberto Sérgio Barbosa; Resendo, Leandro Colombi; Segatto, Marcelo Eduardo Vieira; Paiva, Marcia Helena Moreira
In the past few years, Elastic Optical Networking (EON) emerged as the next generation core network technology, intended to surpass Wavelength-Division Multiplexing (WDM) weaknesses and limitations. WDM is the most successful and widely used technology in the backbone of the optical networks. However, in recent years Internet traffic in the core network has been doubling almost every two years, and predictions indicate that it will continue to exhibit exponential growth due to emerging applications such as high-definition and real-time video communications. To keep pace with the always greater demand for bandwidth, EON relies on Optical Orthogonal Frequency Division Multiplexing (OOFDM) and advanced modulation technologies which enhance spectral efficiency and flexibility. OOFDM allows the aggregation of multiple sub-carriers to form super-channels, thus changing the paradigm of the network from fixed-size WDM channels to variable-sized EON channels that can reduce spectrum waste up to 60%. EON presents several other benefits such as high spectral and energy efficiency and flexible bandwidth adaptation over time. Despite all benefits, no technology is perfect, and the added EON efficiency and flexibility comes at the price of increased complexity and new problems, such as spectrum fragmentation and service unfairness. A considerable amount of work has been done on both fragmentation and unfairness problems, introducing a broad range of solutions, which raises the following question: "how to compare existent solutions and how to identify which one is better suited for the required scenario?" In this context, it is presented the first contribution of this Doctoral Thesis, ElasticO++, an Elastic Optical Network Simulation Framework for OMNeT++. ElasticO++ is a framework created to enable testing a whole range of routing, modulation, spectrum assignment, defragmentation algorithms, parameters, and topologies. At present, the proposed framework is the first software available capable of working with fragmentation and defragmentation in dynamic network scenarios. The flexibility offered on the proposed tool allows both academia and industry to develop new algorithms and techniques for Elastic Optical Networks. The second contribution of this Doctoral Thesis is the Zone-Based Spectrum Assignment Algorithm. The proposed algorithm is an attempt to solve the unfairness and fragmentation problems, taking advantage of the spectrum management concept. In this Doctoral Thesis, it is presented two versions of the technique: the static version and the dynamic version. The static version is intended to be used in cases where the information regarding the nature of the network traffic is known beforehand, whereas the dynamic version was developed as a solution in cases in which absolutely no information is known.
A Human-Machine Interface Based on Eye Tracking for Controlling and Monitoring a Smart Home Using the Internet of Things
(Universidade Federal do Espírito Santo, 2019-02-20) Bissoli, Alexandre Luís Cardoso; Encarnação, Lucas Frizera; Bastos Filho, Teodiano Freire; Adams, Kimberly; Krishnan, Sridhar; Villa Parra, Ana Cecilia; Ferreira, André
People with severe disabilities may have difficulties when interacting with their home devices, due to the limitations inherent to their disability. Simple home activities may be even impossible for this group of people. Although many works have been devoted to proposing new assistive technologies to improve the lives of people with disabilities, some studies have found that the abandonment of such technologies is quite high. In this sense, this work presents a new and useful assistive system based on eye tracking for controlling and monitoring a smart home based on internet of things, which was developed following concepts of user-centered design and usability. With this system, a person with severe disabilities was able to control everyday equipment of her residence, such as lamps, television, fan and radio. In addition, her caregiver was able to monitor remotely, by internet, her use of the system in real time. Additionally, the user interface developed here has some functionalities that allowed improving the usability of the system as a whole. The experiments were divided into two steps. In the first step, the assistive system was assembled in an actual home, where tests were conducted with 29 participants without disabilities (group of able-bodied participants). In the second step, the system was tested with online monitoring, for seven days, by a person with severe disability (end-user), in her own home, not only to increase convenience and comfort, but also so that the system could be tested where it would in fact be used. At the end of both steps, all the participants answered the SUS questionnaire, which showed that both the group of able-bodied participants and the person with severe disabilities evaluated the assistive system with a mean of 89.9 and 92.5, respectively.Keywords:Human-Machine Interface (HMI); Human-Computer Interaction (HCI); Smart Home; Eye Tracking; Assistive Technology; Usability Evaluation; User-Centered Design (UCD); Home Automation; Internet of Things (IoT).
A methodology for cloud robotics implementation based on open-source software : from human-robot interaction to autonomous applications
(Universidade Federal do Espírito Santo, 2020-11-26) Mello, Ricardo Carminati de; Frizera Neto, Anselmo ; https://orcid.org/0000000206873967; http://lattes.cnpq.br/8928890008799265; https://orcid.org/0000000304204273; http://lattes.cnpq.br/1569638571582691; Ribeiro, Moises Renato Nunes; https://orcid.org/0000000291492391; http://lattes.cnpq.br/1005553714687743; Siqueira, Adriano Almeida Goncalves; https://orcid.org/0000-0003-0663-156X; ttp://lattes.cnpq.br/2935052598064187; Garcia, Carlos Andres Cifuentes; https://orcid.org/0000-0002-6942-865X; http://lattes.cnpq.br/8650937498900305; Diaz, Camilo Arturo Rodriguez; https://orcid.org/0000000196575076; http://lattes.cnpq.br/2410092083336272; Lima, Eduardo Rocon de; https://orcid.org/0000-0001-9618-2176; http://lattes.cnpq.br/6623746131086816
The advent of the cloud robotics paradigm has the potential to unleash a whole new generation of smart robotic devices by allowing robots to communicate with each other and with remote computing platforms to share experiences, sensor data, and to o oad heavy processing applications. This work explores cloud robotics by casting a light on key issues and proposing novel solutions to allow for the widespread adoption of cloud based functionality for research and commercial robots. We investigate the cloud robotics paradigm as an enabler to a series of applications and devices and question how the insertion of network and cloud technologies into such solutions might a ect the interaction between a robot and a human operating it and what are the limiting requirements for cloud-based solutions. We propose a reference architecture for cloud robotics paired with an integrated network solution to allow for uninterrupted connectivity in mobile robotics applications. Furthermore, we present an open communication framework to link robots and cloud platforms, and that suits a large range of applications. Finally, we introduce a methodology for cloud robotics implementation based on open-source software and commercial o-the-shelf devices. Such a methodology leverages our communication framework and provides a common standard that allows reproducing and benchmarking di erent cloud robotics works. Our methodology and communication framework are validated considering di erent applications and multiple cloud con gurations, showing the suitability of our approach and providing insight for other researchers and practitioners
A novel approach of independent brain-computer interface based on SSVEP
(Universidade Federal do Espírito Santo, 2016-09-01) Tello, Richard Junior Manuel Godinez; Ferreira, André; Müller, Sandra Mara Torres; Bastos Filho, Teodiano Freire; Ciarelli, Patrick Marques; Lima, Eduardo Roncon de; Sá, Antônio Maurício Miranda de
Over the past ten years, Brain Computer Interfaces (BCIs) based on Steady- State Visual Evoked Potentials (SSVEP) have attracted the attention of many researchers due to the promissory results and the high accuracy rates achieved. This type of BCI provides to people with severe neuromotor difficulties the possibility to communicate with the world around them using visual attention modulation to blinking lights at a given frequency. This thesis aiming at developing a new approach of Independent BCI, in which users are not required to perform neuromuscular tasks to select visual targets, a feature that distinguishes it from traditional SSVEP-BCIs. Thus, people with severe motor disabilities as Amyotrophic Lateral Sclerosis (ALS) have a new alternative channel to communicate with the world around them using brain signals. Several contributions were done in this thesis, such as: improvement of the feature extractor called Multivariate Synchronization Index (MSI) for detecting evoked potentials; development of a new method for detecting evoked potentials through correlating multidimensional models (tensors); a first study on the influence of colored stimuli in SSVEPs detection using LEDs; the development of the concept of Compressive sensing applied to SSVEPs; and, finally, the development of a novel independent BCI under an approach named Figure-Ground Perception (FGP)
A novel cascaded multilevel converter topology based on three-phase cells
(Universidade Federal do Espírito Santo, 2021-08-24) Camargo, Renner Sartório; Encarnação, Lucas Frizera; https://orcid.org/0000000261627697; http://lattes.cnpq.br/5578918284508758; https://orcid.org/0000-0002-6604-7544; http://lattes.cnpq.br/3539297708118726; Rolim, Luis Guilherme Barbosa; https://orcid.org/0000-0002-4639-1778; http://lattes.cnpq.br/7561722009076484; Simonetti, Domingos Sávio Lyrio; https://orcid.org/0000-0001-5920-2932; http://lattes.cnpq.br/1107005171102255; Aredes, Mauricio; https://orcid.org/0000-0003-4798-7052; http://lattes.cnpq.br/9551383663863628; Nunes, Weder Tótola; https://orcid.org/0000-0001-8091-7035; http://lattes.cnpq.br/7043645987773086; Santos, Walbermark Marques dos; https://orcid.org/0000000298716028; http://lattes.cnpq.br/5558697161842579; Peña, Emilio José Bueno
Due to the structural characteristics of modern electrical grids, the use of equipment based on power electronics to guarantee its perfect functioning has grown sharply, encouraging the study and development of equipment based on these technologies like converters with multiple voltage levels, known in the literature as multilevel converters. Multilevel converters based on H bridge cells, known in the literature as CHB (Cascaded H bridge Converter) are the most outstanding among this converters category, however, the natural switching of the multilevel CHB converter in specific configurations, such as a back-to-back connection (CHB-B2B), presents several short-circuit states, making its performance unfeasible or limiting. This issue may require additional stages of isolation, increasing its implementation cost and reducing its competitiveness. Under these circumstances, this work proposes a new multilevel converter topology based on H bridge cells, without isolation stages, with three-phase characteristics and superiority in some metrics compared to a CHB of the same specifications. It also has a lower number of components, lower construction cost, and similar performance. This newly proposed topology, named SDC-CHB (Cascaded H Bridge Converter with Single DC-link), also features several short-circuit states as well as CHB. However, the use of graph theory and model-based predictive control (MPC) enables the inhibition of the short-circuit stages inherent to the SDC-CHB topology. This work is also dedicated to the mathematic study and the mapping of the SDC-CHB short circuit states in a STATCOM as a power electronic application, and comparing its performance with this device using a CHB converter with similar characteristics. This topology was subjected to simulations in Simulink Matlab software for data analysis and later implemented on a hardware-in-the-loop (HIL) real-time platform from the manufacturer OPAL-RT, model 5700, to prove its applicability and to validate the proposal. To analyze the efficiency of the converter, measurements of losses by conductivity and switching were carried out using the PLECS® Plexim software, where the energy consumption of the converter in different modes of operation can be observed.
A novel framework for Covid-19 detection and clinical triage using multimodal physiological signals on a portable medical assistant
(Universidade Federal do Espírito Santo, 2025-08-15) Silva, Leticia Araújo; Krishnan, Sridhar; https://orcid.org/0000-0002-0321-9273; Bastos Filho, Teodiano Freire; https://orcid.org/0000-0002-1185-2773; http://lattes.cnpq.br/3761585497791105; https://orcid.org/0000-0002-1534-0708; http://lattes.cnpq.br/2690656852231539; Caldeira, Eliete Maria de Oliveira; https://orcid.org/0000-0002-3742-0952; http://lattes.cnpq.br/8508979665054143 ; Andrade, Adriano de Oliveira; https://orcid.org/0000-0002-5689-6606; http://lattes.cnpq.br/1229329519982110; Naves, Eduardo Lazaro Martins; https://orcid.org/0000-0003-4175-723X; http://lattes.cnpq.br/5450557733379720; Rodríguez, Denis Delisle; https://orcid.org/0000-0002-8937-031X; http://lattes.cnpq.br/7140331839822423; Villa Parra, Ana Cecilia; https://orcid.org/0000-0002-7588-9372; http://lattes.cnpq.br/7385634502540480
Emergency and urgent care systems face growing challenges in providing timely and accurate triage, especially in resource-constrained environments where subjectivity, lack of infrastructure, and high patient volumes compromise clinical decisions. These limitations became even more evident during the Coronavirus Disease 2019 (COVID-19) pandemic, which exposed critical gaps in diagnostic capacity and highlighted the absence of scalable, non-invasive tools for autonomous assessment. This research investigates whether multimodal physiological signals — cough, speech, breath, and vital signs — collected through a portable equipment called Integrated Portable Medical Assistant (IPMA) may support intelligent triage and COVID-19 inference via Machine Learning (ML) models. To address this, a two-part experimental design was conducted. The first part focused on COVID-19 detection using public datasets and real-world data collected with the IPMA. Mel-spectrograms were extracted from audio signals, followed by texture-based feature extraction using Local Binary Pattern (LBP) and Local Ternary Pattern (LTP). LBP consistently outperformed LTP across classification tasks, with speech showing the highest discriminative power, and SpO2 and temperature emerging as the most informative physiological indicators. Although trained on public datasets, models achieved moderate generalization to IPMA data, particularly for speech and breath signals. The second part evaluated clinical risk classification based on the Manchester Triage System through a structured approach that included data preprocessing, comparison of ML and Deep Learning (DL) models, and usability assessment. Using a public pediatric dataset, ensemble classifiers such as XGBoost and Stacking achieved F1-scores above 0.99 when trained on comprehensive clinical features. Additionally, promising results were obtained using primarily vital signs and low-subjectivity variables, with models reaching F1-scores around 0.74, demonstrating the potential of objective data for low-bias risk stratification in autonomous systems. However, when tested on adult data collected with IPMA, the models showed limited performance, indicating challenges in generalizing across different populations and clinical contexts. Usability was also a central component of this study. Standardized evaluations using the System Usability Scale (SUS) (and Post-Study System Usability Questionnaire — PSSUQ — for the COVID-19 task) indicated high user acceptance of the IPMA by both patients and healthcare professionals. Reported scores reflect the system’s ease of use and perceived integration into clinical workflows, reinforcing its potential for deployment in real-world triage and screening scenarios.
A novel stimulation paradigm for a brain-computer interface based on SSVEP
(Universidade Federal do Espírito Santo, 2015-11-30) Atencio, Anibal Cotrina; Ferreira, André; Bastos Filho,Teodiano Freire; Frizera Neto, Anselmo; Sarcinelli Filho, Mario; Krohling, Renato Antônio; Sá, Antonio Mauricio Ferreira Leite Miranda de
Brain-computer interfaces (BCIs) are systems that provide a direct connection between users’ brain signals and a computer, generating an alternative channel of communication that does not involve the traditional way as muscles and nerves. They help to restore or replace useful functions of people with paralysis. For instance, BCI systems based on SSVEP (SSVEP-BCI) present a set of stimuli flickering at different frequencies to the users, detect which stimulus is being gazed and associate this information to commands that can be used to control a robotic wheelchair, an exoskeleton, or a speller. Nowadays, SSVEP-BCIs are being widely used due to the high SNR of their response that is achieved when the target stimulus is brought to the center of the user’s field of view. Paradoxically, it is their main disadvantage because bringing a stimulus to the center of the field of view demands muscular activity making them not suitably for paralyzed people who cannot control their head, neck and/or eyeball movements for redirecting their gaze. In optical systems, the range of distance near the point of focus where objects are perceived sharp is referred as Depth-of-field; objects outside this region are defocused and blurred. The mechanism of the visual system that adjusts the eye focal length for focusing does not demand neck, head and/or eyeball movements. Furthermore, ophthalmology studies state that the amplitude and the latency of visual evoked potentials are affected by defocusing. In this context, this Thesis proposes a novel SSVEP-BCI paradigm, in which two stimuli are presented together in the center of the user’s field of view but at different distances from him, ensuring that if one stimulus is focused on, the other one is non-focused, and vice versa; with the aim of providing an alternative way of sending commands through a stimuli selection by a focusing mechanism. In this sense, first, a model of VEP generation for two stimuli is introduced and the hypothesis that distinguishable SSVEP can be elicited by the focused stimulus, regardless of the non-focused stimulus is also present, is tested by employing the SFT-based ORD. Next, a demodulation method based in LPF and HPF is proposed for the case in that two stimuli are present in the field of view; and spatial-temporal retinal response for flickering stimuli is described by using PSF and NPSF functions. Finally, CCA, PSDA, LASSO with EEG signals re-referenced at Pz and CAR are employed to detect the SSVEP pattern. Accuracy rate, Kappa coefficient, AUC, and ITR are used to evaluate the detection performance. As a result of the hypothesis test, the absence of evoked potentials due to a focused stimulus, when a non-focused stimulus is also present was rejected in most of the cases. In SSVEP detection experiments, an average accuracy rate of 0.93 was achieved for a time window of 7s and for eight healthy subjects who were asked to focus on just one stimulus at a time.
A socially assistive robot as a therapeutic tool for applied behavior analysis therapy in children with autism spectrum disorder through dynamically modulated serious games
(Universidade Federal do Espírito Santo, 2024-10-07) Freitas, Éberte Valter da Silva; Bastos Filho, Teodiano Freire; https://orcid.org/0000-0002-1185-2773; Caldeira, Eliete Maria; Cuadros, Marco Antonio de Souza Leite; Valadão, Carlos Torturella; Vasquez, Luiz Fernando Guerrero
This work presents the programming/adaptation of the Socially Assistive Robot (SAR) called Mobile Autonomous Robot for Interaction with Autistics and Trisomy 21 (MARIA T21) to be able to carry out interventions, according to the Applied Behavior Analysis (ABA) therapy, applied to Children with Autism Spectrum Disorder (ASD), Serious Games (SGs), which are projected by MARIA T21, with difficulty modulation dynamics, are used as part of this therapy thus creating a motivating and facilitating effect for children and therapists. The SGs were developed in Unity 3D, using C Sharp language (C#), and modulated according to the child’s performance, eye attention level, and user’s facial emotion, being integrated into the robot through the Robot Operating System (ROS). The child-Robot Interaction (CRI) protocol followed in this research was carried out in a child’s psychotherapy room at the APAE (Association of Parents and Friends of Excepcional People for the acronym in Portuguese) of Vitoria in Espirito Santo state (Brazil), which was instrumented with four video cameras and supervised by a group of researchers. The sample consisted of 18 children with a conclusive diagnosis of ASD, 3 girls and 15 boys, aged 5 to 9 years and presence of stereotyped movements of eyes and/or hands and/or feet. The experiments were separated into three modules for which SGs or specific therapeutic dynamics were applied, namely: Cognitive Module, Physical Module and Functional Module. The first one brings together the games and dynamics applied by MARIA T21 focused on the development and improvement of cognitive learning skills, whereas the physical module brings SGs for motor evaluation and correction, that can be used for physical and postural strengthening by a physiotherapist. Finally, the functional module has applications of SGs and Occupational Therapy dynamics in order to work on the so-called Activities of Daily Living (ADLs) and encourage autonomy in those assisted. In addition to the data recorded by MARIA T21, two evaluation scales– Pediatric Evaluation of Disability Inventory Computer Adaptive Test (PEDI-CAT) and System Usability Scale (SUS)– were applied for each module, and another for the degree of acceptance of the robot in therapy by the child. The results obtained so far enable the use MARIA T21 as an ABA therapeutic tool. In addition, the SGs are capable of dynamically modulating their difficulty, providing greater user adherence and continued attention in the optimal learning zone of the ABA bibliography while carrying out the activities. The technology embedded in the robot has also enabled the identification and quantification of characteristics and parameters, such as the presence and recurrence of stereotypies and postural dysregulations, placing the robot as an innovative and promising tool to assist health professionals in the early diagnosis, conduction and follow-up of therapies.
Adaptação dos modelos de Markov para um sistema de segmentação e classificação de sinais de eletrocardiograma
(Universidade Federal do Espírito Santo, 2006-04-03) Müller, Sandra Mara Torres; Andreão, Rodrigo Varejão; Bastos Filho, Teodiano Freire; Resende Junior, Fernando Gil Vianna; Salles, Evandro Ottoni Teatini
In this work three incremental adaptation methods for the hidden Markov models (HMM) are studied and implemented, which are based on the Expectation-Maximization (EM), Segmental k-Means and Maximum a Posteriori (MAP) algorithms. These methods, already used in the speech recognition field, are applied here in the electrocardiogram (ECG) segmentation problem. For that, it was used an ECG analysis system able to segment and classify cardiac diseases, like premature ventricular contraction (PVC) and ischemia. The use of these methods allow us to adjust the models to the signal fluctuations commonly met during ambulatory recording. The methods can also be implemented for other kinds of biomedical signals, like electroencephalogram (EEG).
Adaptive x-ray tomography image reconstruction
(Universidade Federal do Espírito Santo, 2019-08-08) Wirtti, Tiago Tadeu; Salles, Evandro Ottoni Teatini; https://orcid.org/0000000282873045; http://lattes.cnpq.br/5893731382102675; https://orcid.org/ 0000-0003-0731-6326 ; http://lattes.cnpq.br/3414259707581590; Filho, Mario Sarcinelli; https://orcid.org/0000000276968996; http://lattes.cnpq.br/3459331011913021; Andreao, Rodrigo Varejao; https://orcid.org/0000000268005700; http://lattes.cnpq.br/5589662366089944; Pinto, Luiz Alberto; https://orcid.org/; http://lattes.cnpq.br/; Kim, Hae Yong
In X-ray tomography image reconstruction, one of the most successful approaches involves a statistical modeling with l2 norm function for fidelity regularized by a functional with lp norm, 1 < p < 2, with p ∈ R. Among them stands out, for its results and computational performance, a technique that reconstructs an image by alternating minimization for (i) solving the l2 norm fidelity term by Simultaneous Algebraic Reconstruction Technique (SART) and (ii) constraining the regularization term, defined by a Discrete Gradient Transform (DGT) sparse transformation, using Total Variation (TV) minimization. This work proposes an improvement to the reconstruction process by adding a Bilateral Edge preserving (BEP) regularization term to the objective function, resulting in a three-step method. BEP is a noise reduction framework and has the purpose of adaptively eliminating noise in the initial phase of reconstruction process. BEP improves optimization of the f idelity term and, as a consequence, improves the result of DGT minimization by total variation. Regular dosage experiments shown favorable results compared to classical methods, such as Filtred Backprojection (FBP), and more modern ones, such as l2 norm optimization by using SART, and the l2 norm SART solution regularized by l1 norm TV optimization of DGT (SART+DGT), especially with the Structural Similarity Index Measurement (SSIM) metric. Although not so prominent in the case of regular dosing reconstruction, Peak Signal-to-noise Ratio (PSNR) results are consistent with those of SSIM. For low dosage, the quality of the reconstruction worsens for all methods, but is markedly lower for the FBP and SART methods. In this context of limited number of projections (low dosage), the reconstructions with the method here proposed presents better defined edges, in addition to better contrast and less artifacts in surfaces of regular intensity (low intensity variation). These results are generally obtained with a smaller number of steps compared to the other iterative methods implemented in this Thesis. However, this behavior (of the proposed method) depends on the parameterization of the lp norm, 1 ≤ p ≤ 2, used in the BEP stage. It is experimentally shown that by varying the norm during the reconstruction process it is possible to keep the proposed method stable over a sufficiently large number of iteractions. It is also graphically shown that the method converge, meaning that the SSIM and PSNR metrics can be continuously improved by a sufficiently large number of iteractions. For reconstructions with a limited number of projections (low-dose reconstruction), the proposed method can achieve higher PSNR and SSIM results because it can better control the noise in the initial processing phase.
Adequação ao requisito cintilação em sistemas de comunicação via luz visível mediante uso de sinais OFDM com envoltória constante
(Universidade Federal do Espírito Santo, 2018-09-21) Neves, José Luís Costa; Segatto, Marcelo Eduardo Vieira; Silva, Jair Adriano Lima; Nunes, Reginaldo Barbosa; Pereira, Esequiel da Veiga; Pontes, Maria José
The scarcity of electromagnetic spectrum has been a problem in the development of new wireless applications. To solve this problem, visible light communication has emerged as a promising and complementary technology to radiofrequency due to its advantages such as green technology, unlicensed spectrum, low power consumption, high privacy protection and resistance to electromagnetic interference . Allied to this, because it is a technology that uses light emitting diodes for data transmission, also guaranteeing the lighting function, it allows its use in di erent types of environments. Orthogonal frequency division multiplexing (OFDM) in visible light communication systems has been attractive because of its ability to combat intersymbol interference and ensuring high data rates. However, OFDM signals have large amplitude uctuations, resulting in high peak-to-average power ratio (PAPR) and therefore can degrade the quality of the illumination due to Flicker light. Flickering light is harmful to vision and causes eye fatigue, seizures, headache, malaise, and other problems. The present work presents a simulation and experimental study that evaluates the performance of the OFDM transmission technique that transmits signals with constant envelope (CE-OFDM) in a communication system via visible light, by means of the adequacy of the Flickering requirements. The CE-OFDM system is based on the phase modulation of an electric carrier and reduces the PAPR parameter to 3 dB. The results obtained in the line-of-sight channel using a bandwidth of 5 MHz showed that, by adapting the icker requirements and considering the mapping levels 4, 16 and 64-QAM, the CE-OFDM system presents a upper performance than those presented by the conventional OFDM and ACO-OFDM systems. The results also showed that, in the presence of non-linearities introduced by the LED, the CE-OFDM system presents greater robustness.
Admittance control of a robotic knee orthosis based on motion intention through sEMG of trunk muscles
(Universidade Federal do Espírito Santo, 2017-12-04) Parra, Ana Cecilia Villa; Frizera Neto, Anselmo; Bastos Filho, Teodiano Freire; Ferreira, Andre; Caldeira, Eliete Maria de Oliveira; Rocon, Eduardo; Bó, Antonio Padilha Lanari
The population that requires devices for motion improvement has increased considerably, due to aging and neurological impairments. Robotic devices, such as robotic orthosis, have greatly advanced with the objective of improving both the mobility and quality of life of people. Clinical researches remark that these devices, working in constant interaction with the neuromuscular and skeletal human system, improves functional compensation and rehabilitation. Hence, the users become an active part of the training/rehabilitation, facilitating their involvement and improving their neural plasticity. For this purpose, control approaches based on motion intention have been presented as a novel control framework for robotic devices. This work presents the development of a novel robotic knee exoskeleton controlled by motion intention based on sEMG, which uses admittance modulation to assist people with reduced mobility and improve their locomotion. For recognition of the lower-limb motion intention, sEMG signals from trunk are used, which implies a new approach to control robotic assistive devices. The control system developed here includes a stage for human-motion intention recognition (HMIR) system, which is based on techniques to classify motion classes related to knee joint. The motion classes that are taken into account are: stand-up, sit-down, knee flexionextension, walking, rest in stand-up position and rest sit-down position. For translation of the users intention to a desired state for the robotic knee exoskeleton, the system includes a finite state machine, in addition to admittance, velocity and trajectory controllers, which has also the function of stopping the movement according to the users intention. This work also proposes a method for on-line knee impedance modulation, which generates variable gains through the gait cycle for stance control during gait. The proposed HMIR system showed, in off-line analysis, an accuracy between 76% to 83% to recognize motion intention of lower-limb muscles, and 71% to 77% for trunk. Experimental on-line results of the controller showed that the admittance controller proposed here offers knee support in 50% of the gait cycle, and assists correctly the motion classes. A positive effect of the controller on users regarding safety during gait was also found, with a score of 4 in a scale of 5. Thus the robotic knee exoskeleton introduced here is an alternative method to empower knee movements using motion intention based on sEMG signals from lower limb and trunk muscles.
Algoritmos evolutivos aplicados em projetos de redes ópticas passivas
(Universidade Federal do Espírito Santo, 2019-08-23) Silva, David Moscon Inacio; Rocha, Helder Roberto de Oliveira; https://orcid.org/000000016215664X; http://lattes.cnpq.br/8801325729735529; ; http://lattes.cnpq.br/5946991206561502; Moraes, Renato Elias Nunes de; https://orcid.org/0000-0001-5538-0504; http://lattes.cnpq.br/8323084944042061; Nunes, Reginaldo Barbosa; https://orcid.org/0000-0001-8877-1480; http://lattes.cnpq.br/0301147577506989
Alocação de recursos de uma rede óptica passiva BS-OFDMA-PON usando otimização multiobjetivo
(Universidade Federal do Espírito Santo, 2020-12-18) Flores, Jardel Terci; Rocha, Helder Roberto de Oliveira; https://orcid.org/000000016215664X; http://lattes.cnpq.br/8801325729735529; http://lattes.cnpq.br/0293197276972341; Coura, Daniel Jose Custodio; https://orcid.org/0000-0002-2134-7981; https://orcid.org/0000-0001-8877-1480; http://lattes.cnpq.br/5570995348839001; http://lattes.cnpq.br/0301147577506989; Nunes, Reginaldo Barbosa
With the growing demand for Internet traffic by users and the increased need for transmission rate by applications, it is necessary to use bandwidth efficiently and economically in optical networks, which plays an important role in improving service delivery. Scalability is an important requirement necessary to meet this demand. To serve it, multiple access can be provided through the OFDMA multiplexing technique (Orthogonal Frequency Division Multiple Access), which allows for flexible bandwidth allocation, in addition to being an efficient solution for ISI (Inter Symbol Interference). Through the variation of the signalto-noise ratio OSNR (Optical Signal to Noise Ratio), the level of modulation by subcarrier and the width of the sub-bands of the ONUs (Optical Network Units), this paper approach this important requirement in the architecture BS (Bandwidth Scalable)-OFDMA-PON (Passive Optical Network) in the communication downlink, by means of the optimization of parameters with Multi-Objective Grey Wolf Optimizer algorithm. The results obtained by the numerical simulation demonstrated in optical links that would vary from 20 to 40 km demonstrated the optimization of the resources allocated to the network in order to attend 16 ONUs and 32 ONUs with individual transmission rates equal to 1Gbps, by adopting 4, 8, 16, 32 and 64-QAM e OSNR mappings ranging between 1 e 50 dB. In the first case, 43.17% of the useful subcarriers were allocated to enable a transmission rate of 1 Gbps for all users, for the highest OSNR found, while in the second situation 68.55 % were allocated.
Alocação e dimensionamento de geração distribuída e coordenação otimizada de religador-fusível baseados em algoritmos genéticos
(Universidade Federal do Espírito Santo, 2020-09-18) Ferraz, Renato Santos Freire; Medina, Augusto Cesar Rueda; https://orcid.org/0000000242913153; http://lattes.cnpq.br/7397584412509839; https://orcid.org/0000-0001-7571-1972; http://lattes.cnpq.br/1832936459743268; Trujillo, Joel David Melo; https://orcid.org/0000-0001-5046-1890; http://lattes.cnpq.br/4396532007704107; Fardin, Jussara Farias; https://orcid.org/0000-0003-4785-556X; http://lattes.cnpq.br/1912113095988528
Nowadays, it is possible to notice a growth in the integration of Distributed Energy Resource (DER) in the distribution systems. Despite the many benefits caused by this integration, there are some changes in the load and short-circuit current, which may lead to some issues in the protection system, such as simpathetic tripping, mis-coordination between protective devices, reduction in reach of impedance relays, among others. Moreover, an improper DER integration can generate problems regarding the levels of current, voltage and power factor of the network. Therefore, in this work, the author aimed to conduct a specific study related to the DER optimal allocation and sizing in a distribution feeder, in order to reduce investment and operation costs, regarding the operational and physical limits of the system and generators. In addition, optimal recloser fuse coordination was performed to reduce the actuation time of these protective devices, taking into account the generation and load variation during the day, DER operating modes and all the fault types. In this study, the optimization method adopted was genetic algorithms, due to the adaptive optimization and parallel computing which, based on the selection, crossover and mutation operations, are capable of searching for the optimal solution in the solution space; and the IEEE 34-Node Test Feeder was used to evaluate the proposed methodology. Therefore, from the results, it was possible to notice a 39.420% reduction of the overall cost, from the DER allocation proposed in this analysis. Regarding the coordination between reclosers and fuses, it was possible to achieve a single protection scheme, which is able to coordinate the protective devices for all the analyzed cases simultaneously, avoiding the need for adaptive protection or fault current limiters
Alocação ótima de geração distribuída e de sistemas de baterias em um sistema de distribuição para redução das perdas e controle de tensão nas barras
(Universidade Federal do Espírito Santo, 2021-04-16) Menezes, Luíza Saleme de; Encarnação, Lucas Frizera; https://orcid.org/0000000261627697; http://lattes.cnpq.br/5578918284508758; https://orcid.org/0000-0002-4141-4600; http://lattes.cnpq.br/6971088590764497; Rocha, Helder Roberto de Oliveira; https://orcid.org/0000-0001-6215-664X; http://lattes.cnpq.br/8801325729735529; Donadel, Clainer Bravin; https://orcid.org/0000-0002-3310-2762; http://lattes.cnpq.br/8624415630257203; Medina, Augusto César Rueda; https://orcid.org/0000-0002-4291-3153; http://lattes.cnpq.br/7397584412509839
A proposal of a method to determine the optimal allocation of Battery Banks and photovolvaic painels in a Distribution System. The methodology makes use of the photovoltaic generation profile in the summer season and is based on the load curve of low volt
Alocação ótima de geração distribuída em sistemas de distribuição considerando incertezas no modelo probabilístico de geração
(Universidade Federal do Espírito Santo, 2018-06-08) Pereira, Luan Diego de Lima; Rocha, Helder Roberto de Oliveira; Fardin, Jussara Farias; Donadel, Clainer Bravin; Medina, Augusto César Rueda
This dissertation proposes a methodology to determine a probabilistic model of distributed generation of electrical energy from wind generators and photovoltaic panels and to determine the optimal location of these generators in a distribution network of electric energy, based on technical and economic parameters. The methodology correlates the historical wind speed and solar irradiance data of a particular study region and applies the Monte Carlo simulation to model the power of wind and solar generation, preserving its stochastic nature. The optimization of the location of the distributed generation units aims to minimize the annual losses of active power and the installation costs of the generators connected to the network. The optimization problem also provides for the allocation of capacitor banks in conjunction with the distributed generators, in order to manage the reactive power of the network and, consequently, to improve the voltage profile and minimize the electrical losses. The optimization algorithm used was the Genetic Algorithm, which receives as input the annual data of active power of the wind generators, solar and the demand of the load and search for better solutions to the problem. In order to validate the effectiveness of the proposed model, tests were performed on two real radial feeders, resulting in annual losses of active power, voltage profiles and total investment cost.
Alternativas de topologias retificadoras para aerogeradores síncronos a ímã permanente de baixa potência
(Universidade Federal do Espírito Santo, 2015-12-11) Freitas, Tiara Rodrigues Smarssaro de; Menegáz, Paulo José Mello; Simonetti, Domingos Sávio Lyrio; Antunes, Fernando Luiz Marcelo; Fardin, Jussara Farias; Encarnação, Lucas Frizera; Pinto Filho, Wilson Aragão Correia
Two controlled rectifier topologies applied to low power wind energy conversion system with permanent magnet synchronous generator are presented. For low power or stand-alone operation systems, where the energy from wind generation is a significant part of the total power system, generators and converters have the role of maintaining the grid’s voltage and frequency constant, despite the fluctuations of the wind turbine. In variable speed permanent magnet synchronous generator (PMSG), the preferred solution has been a conversion on two stages: AC-DC-AC. Several converter topologies have been explored, but kind of this conversion has many controlled elements, most of them with 6 controlled switches in AC-DC conversion, making it difficult and more expensive its control; each new topology introduces new aspects and always looking for a converter that best suits the system with minimally influence to the quality of power generation. The topologies presented in the literature are effective for the high power levels, but when it comes to systems with lower power levels, simpler converters (single or three controlled switches) can serve the purpose of rectification with a lower cost and without the conversion quality been reduced. The contribution of this thesis is the development of a new SEPIC rectifier topology using three controlled switches, and the analysis and new application of an existing resonant buck topology, with a single controlled switch, to wind energy system. They are simpler rectifying solutions, applied to low power wind generation based on permanent magnet synchronous generator, offering simplicity and control facility. The converter’s project, the equations that define them, the simulation and experimental results for each converter are presented. It was verified that both topologies could achieve high power-factor and low harmonic distortion employing only one single gate signal, on a wide range of wind speed with no current’s generator closed loop control.

Navegar

Navegando Engenharia Elétrica por Título

Resultados por página

Opções de Ordenação