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Item Adaptive real-time power measurement based on IEEE standard 1459-2010.(2015) Ferreira, Silvia Costa; Gonzatti, Robson Bauwelz; Silva, Carlos Henrique da; Silva, Luiz Eduardo Borges da; Pereira, Rondineli Rodrigues; Torres, Germano LambertMostrar mais This article presents the theoretical development and implementation of an adaptive algorithm for real-time measurement of electrical powers under sinusoidal, non-sinusoidal, balanced, and unbalanced conditions according to the definitions given by IEEE Standard 1459-2010. The algorithm is based on adaptive filter notch filter implementation, where the parameters are adjusted by tracking the amplitude and phase variations to improve the accuracy of the power measurement. The algorithm uses the filter coefficients to calculate powers, resulting in low computational burden. The results of computer simulation and practical implementation using a fixed-point digital signal controller are shown in detail, proving the accuracy and efficiency of the algorithm.Mostrar mais Item An auxiliary system discretization approach to Takagi-Sugeno fuzzy models.(2022) Campos, Víctor Costa da Silva; Braga, Marcio Feliciano; Santos, Luciano Antonio FrezzattoMostrar mais This paper proposes a new procedure for discretizing nonlinear systems described by Takagi-Sugeno fuzzy models. The discretization procedure consists of obtaining a linear auxiliary system that approximates the Takagi-Sugeno model over a sampling instant. By discretizing this auxiliary system, a norm bounded uncertain linear discrete-time system is found, which is capable of representing the fuzzy model. This auxiliary system, as well as the norm bounded uncertainty, is found by solving an optimization problem with Linear Matrix Inequality (LMI) constraints. To illustrate the discretization procedure, a constant state observer is synthesized based on simple LMI conditions and then applied to a real nonlinear Chua’s circuit. Additionally, a state-feedback controller based on our discretization approach is synthesized and we obtain larger maximum sampling periods than other tested strategies from the literature.Mostrar mais Item Analysis of the spatiotemporal MVDR filter applied to BCI-SSVEP and a filter bank extension.(2022) Vargas, Guilherme Vettorazzi; Leite, Sarah Negreiros de Carvalho; Boccato, LevyMostrar mais Artifacts inevitably permeate brain signal acquisition by electroencephalography (EEG). Hence, brain-computer interfaces based on steady-state visually evoked potentials (BCI-SSVEP) frequently require a filtering to increase signal-to-noise ratio (SNR) in an attempt to improve its ability to identify a command selected by the user. By combining the signals from different electrodes, the spatiotemporal filtering technique based on the minimum variance distortionless response (MVDR) attenuates undesired frequency components while preserving the spectral content at the visual stimuli frequencies. In this study, we revisit the MVDR filter, further evaluating its behavior with respect to critical factors in a BCI-SSVEP system: proximity amid stimulation frequencies, number of stimuli and stimulation window-length. Additionally, the main parameters of the filter were also varied, such as the order and the number of electrodes to be combined. The experimental analysis confirmed the effectiveness of the MVDR filter for the majority of the scenarios. However, it also revealed a significant difficulty that the MVDR filter has when dealing with short-length time windows, especially when compared with classical filtering techniques, such as CAR and CCA. So, in order to mitigate this limitation, we propose a filter bank MVDR (FBMVDR), where each element is a MVDR filter designed to preserve a single stimulation frequency or harmonic components. This new approach provided an increase of more than 5% in relation to the standard MVDR, reaching a performance of 92.6% in scenarios with 4 visual stimuli and 1s window-length and achieved competitive results with the state-of-the-art technique filter bank CCA (FBCCA).Mostrar mais Item Analytical upper bound for the error on the discretization of uncertain linear systems by using the tensor product model transformation.(2020) Campos, Victor Costa da Silva; Braga, Marcio Feliciano; Santos, Luciano Antonio FrezzattoMostrar mais This work provides analytical upper bounds on the discretization error of uncertain linear systems. The Tensor Product Model Transformation is used to approximate the derived discretized system, with a reduced number of vertices. Digital state feedback controllers are then designed for the discretized system, for comparison to other available work in the current literature.Mostrar mais Item Applied sensor fusion : tuning parameters of CF and KF by means of evolution strategies.(2020) Santos, Talysson Manoel de Oliveira; Barroso, Márcio Falcão Santos; Ricco, Rodrigo AugustoMostrar mais From the point of view of metrology, inertial sensors acting separately present undesirable performance in the measurement of angular position. In order to provide measurements with greater precision and accuracy, the measures of each of these sensors are typically fused by means of filters. The performance parameters of these filters are hard to tune and several works have been using exhaustive search algorithm or manual experimental tests to tuning these parameters. However, the exhaustive search algorithm usually requires a large computational effort and adjusting parameters manually does not guarantee that the estimated parameters are optimized. In this work, it has been proposed the tuning of the Complementary Filter (CF) and the Kalman Filter (KF) through the heuristic method Evolutionary Strategies. Experimental results have shown that our method is a useful tool that considerably reduces the time to find the tuning of the FC and the FK. In addition, the use of the tuned FC and FK improved significantly metrological characteristics of the system. The use of Bland and Altman’s statistical method show that the measurements of the angular position have a good agreement with the actual angular position of a servo motor.Mostrar mais Item Cascaded interleaved DC–DC converter designed for grid-to-vehicle and vehicle-to-grid technologies.(2021) Leal, Wagner Coelho; Bastos, Renan Fernandes; Aguiar, Cassius Rossi de; Godinho, Marcelo Oliveira; Fuzato, Guilherme Henrique Favaro; Piardi, Artur Bohnen; Braggio, Almir Augusto; Sonoda, Dabit G.; Otto, Rodrigo Bueno; Nadal, Zeno L. I.; Machado, Ricardo QuadrosMostrar mais This paper presents a study of a cascaded bidirectional interleaved DC–DC converter applied to an electric charging station, which uses grid-to-vehicle (G2V) and vehicle-to-grid (V2G) technologies. In this context, the interleaved technique is used to reduce the current ripple through the battery of the electric vehicle (EV), which can also absorb or deliver power to the microgrid. Additionally, the small-signal technique is also employed to calculate the gains of the PI controllers for charging and discharging the EV battery. Finally, this paper presents a set of simulations using the software PSIM® and experimental results using a low-cost hardware-in-the-loop (HIL) to support the theoretical study and to demonstrate the effectiveness of the proposed approach.Mostrar mais Item Channel capacity in brain-computer interfaces.(2020) Costa, Thiago Bulhões da Silva; Suarez Uribe, Luisa Fernanda; Leite, Sarah Negreiros de Carvalho; Soriano, Diogo Coutinho; Castellano, Gabriela; Suyama, Ricardo; Attux, Romis Ribeiro de Faissol; Panazio, Cristiano MagalhãesMostrar mais Objective. Adapted from the concept of channel capacity, the information transfer rate (ITR) has been widely used to evaluate the performance of a brain–computer interface (BCI). However, its traditional formula considers the model of a discrete memoryless channel in which the transition matrix presents very particular symmetries. As an alternative to compute the ITR, this work indicates a more general closed-form expression—also based on that channel model, but with less restrictive assumptions—and, with the aid of a selection heuristic based on a wrapper algorithm, extends such formula to detect classes that deteriorate the operation of a BCI system. Approach. The benchmark is a steady-state visually evoked potential (SSVEP)-based BCI dataset with 40 frequencies/classes, in which two scenarios are tested: (1) our proposed formula is used and the classes are gradually evaluated in the order of the class labels provided with the dataset; and (2) the same formula is used but with the classes evaluated progressively by a wrapper algorithm. In both scenarios, the canonical correlation analysis (CCA) is the tool to detect SSVEPs. Main results. Before and after class selection using this alternative ITR, the average capacity among all subjects goes from 3.71 1.68 to 4.79 0.70 bits per symbol, with p -value <0.01, and, for a supposedly BCI-illiterate subject, her/his capacity goes from 1.53 to 3.90 bits per symbol. Significance. Besides indicating a consistent formula to compute ITR, this work provides an efficient method to perform channel assessment in the context of a BCI experiment and argues that such method can be used to study BCI illiteracy.Mostrar mais Item A circuit for automatic measurement of bifurcation diagram in nonlinear electronic oscillators.(2016) Ricco, Rodrigo Augusto; Verly, Anny; Amaral, Gleison Fransoares VasconcelosMostrar mais Experimental bifurcation diagram is very helpful to describe the global behaviour of nonlinear electronic oscillators. The diagram allows insight gain of the oscillators behaviour for a parameter variation. However, when the bifurcation parameter is a resistance, experimental bifurcation diagrams are hard to achieve. In this case, if the potentiometer resistance has been used to change the gain, it is possible to replace the potentiometer by an alternative circuit using operational transconductance amplifier. This kind of circuit is presented in this work and experimental results are provided to piecewise affine Rössler electronic oscillator. The results obtained show a very good matching with the theoretical diagram. Then, if the bifurcation parameter is a resistance, voltage or current, we have implemented a circuit to extract the experimental bifurcation diagram of all nonlinear electronic oscillators.Mostrar mais Item Comparative analysis of strategies for feature extraction and classification in SSVEP BCIs.(2015) Leite, Sarah Negreiros de Carvalho; Costa, Thiago Bulhões da Silva; Suarez Uribe, Luisa Fernanda; Soriano, Diogo Coutinho; Yared, Glauco Ferreira Gazel; Coradine, Luis Cláudius; Attux, Romis Ribeiro de FaissolMostrar mais Brain–computer interface (BCI) systems based on electroencephalography have been increasingly usedin different contexts, engendering applications from entertainment to rehabilitation in a non-invasiveframework. In this study, we perform a comparative analysis of different signal processing techniquesfor each BCI system stage concerning steady state visually evoked potentials (SSVEP), which includes: (1)feature extraction performed by different spectral methods (bank of filters, Welch’s method and the mag-nitude of the short-time Fourier transform); (2) feature selection by means of an incremental wrapper,a filter using Pearson’s method and a cluster measure based on the Davies–Bouldin index, in additionto a scenario with no selection strategy; (3) classification schemes using linear discriminant analysis(LDA), support vector machines (SVM) and extreme learning machines (ELM). The combination of suchmethodologies leads to a representative and helpful comparative overview of robustness and efficiency ofclassical strategies, in addition to the characterization of a relatively new classification approach (definedby ELM) applied to the BCI-SSVEP systems.Mostrar mais Item Comparative performance of three phasor-extraction algorithms for co-simulation of electrical power systems.(2021) Theodoro, Thainan Santos; Barbosa, Pedro Gomes; Tomim, Marcelo Aroca; Lima, Antonio Carlos Siqueira deMostrar mais This work presents a comparison of the three phasor extraction algorithms proposed in the literature for the co-simulation of transient stability and electromagnetic transients programs. Initially, a brief mathematical review of two algorithms widely used in the literature is made: the discrete Fourier transform and the adjustment of the least-squares curve. In addition, a technique proposed by the authors based on the use of the generalized second-order integrator is presented. Then, these three techniques will be implemented and evaluated numerically through a comparative performance study extracting the fundamental phasor component of a test signal.Mostrar mais Item Control of event-triggered quasi-LPV systems based on an exact discretization approach - a linear matrix inequality approach.(2022) Campos, Víctor Costa da Silva; Santos, Luciano Antonio Frezzatto; Oliveira, Tiago Gaiba de; Manzoc, Víctor Estrada; Braga, Marcio FelicianoMostrar mais This paper presents an H∞ event-triggered state-feedback controller design for continuous-time non-linear systems via convex optimization techniques. The proposal is based on an exact discretization and its quasi-linear parameter varying representation. Thus, two sets of design conditions in terms of linear matrix inequalities by means of both parameter-dependent and quadratic Lyapunov functions are proposed. The proposed conditions also provide an estimate to system’s domain of attraction and an extra set of conditions is presented for a guaranteed minimum time between events. Well-known examples are employed to illustrate the effectiveness of the proposal.Mostrar mais Item Demand side management using time of use and elasticity price.(2016) Manso, Juan Carlos Galvis; Costa, AugostinoMostrar mais Demand Side Management (DSM) has been traditionally seen as a mean of reducing peak electricity demand so that utilities can delay building further capacity. In fact, by reducing the overall load on an electricity network, DSM has various beneficial effects, including mitigating electrical system emergencies, reducing the number of blackouts and increasing system reliability. In this paper we propose a methodology to evaluate DSM in electric distribution systems, based on elasticity and time of use pricing concepts. This evaluation is performed through an optimal power flow model considering linear constraints. The results of the proposed method depend, to a great extent, on two parameters: the maximum share of load which consumers are able to shift and the elasticities used to express the consumer's level of participation in the dynamic pricing mechanism. Simulation results confirm the benefits of Time of Use Demand Side Management reducing the peak-toaverage ratio of the total power demand, as well as each user’s individual daily electricity charges.Mostrar mais Item Determination of phase jumps in the measurement of phase velocity of samples obeying a frequency power-law attenuation coefficient using Kramers-Kronig relations.(2020) Elvira, Luis; Tiago, Marcelo Moreira; Yoza, Suelen Akemi Nakazato; Kitano, Claudio; Higuti, Ricardo TokioMostrar mais Ultrasonic phase velocity spectroscopy is a very sensitive technique used in the measurement of material properties. In phase velocity calculation, ambiguities can arise in the spectral phases, in the form of integer multiples of 2π rad, which, if not corrected, result in large errors. In this work we propose a method for determining these ambiguities, more specifically, the number of 2π rad phase jumps, using KramersKronig relations, for samples exhibiting a frequency power-law attenuation coefficient. The method is based on a first estimate of the phase velocity from group velocity and attenuation coefficient, which are not affected by phase jumps. This estimated phase velocity is used to obtain the number of 2π rad phase jumps, which in turn is used to calculate the corrected phase velocity. The method was tested with samples of liquids with frequency power-law attenuation coefficient (exponent y varying from 1.5 to 2) and a solid (PMMA - polymethyl methacrylate) with y ∼ 1, and velocity dispersions ranging from 0 to 34 (cm/s)/MHz.Mostrar mais Item Development and characterization of medical phantoms for ultrasound imaging based on customizable and mouldable polyvinyl alcohol cryogel–based materials and 3-D printing : application to high-frequency cranial ultrasonography in infants.(2019) Elvira, Luis; Durán, Carmen; Higuti, Ricardo Tokio; Tiago, Marcelo Moreira; Ibáñez, Alberto; Parrilla, Montserrat; Valverde, Eva; Jiménez, Javier; Bassat, QuiqueMostrar mais This work presents an affordable and easily customizable methodology for phantom manufacturing, which can be used to mimic different anatomic organs and structures. This methodology is based on the use of polyvinyl alcohol–based cryogels as a physical substitute for biologic soft tissues and of 3-D printed polymers for hard tissues, moulding and supporting elements. Thin and durable soft-tissue mimicking layers and multilayer arrangements can be obtained using these materials. Special attention was paid to the acoustic properties (sound speed, attenuation coefficient and mechanical impedance) of the materials developed to simulate soft tissues. These properties were characterized as a function of the additives concentration (propylene-glycol and alumina particles). The polyvinyl alcohol formulation proposed in this work is stable over several freeze-thaw cycles, allowing the manufacturing of multilayer materials with controlled properties. The manufacturing methodology presented was applied to the development of a phantom for high-frequency cranial ultrasonography in infants. This phantom was able to reproduce the main characteristics of the ultrasound images obtained in neonates through the anterior fontanel, down to 8-mm depth.Mostrar mais Item Digital redesign of analogue dynamic output-feedback controllers for polytopic systems.(2017) Morais, Cecilia de Freitas; Braga, Marcio Feliciano; Tognetti, Eduardo Stockler; Oliveira, Ricardo Coração de Leão Fontoura de; Peres, Pedro Luis DiasMostrar mais This paper is devoted to the problem known as digital redesign, i.e. given a previously designed stabilising continuous-time controller for a continuous-time plant, synthesise a digital controller that provides the hybrid closed-loop system with output trajectories as similar as possible to the continuous-time ones. To accomplish this goal, two distinct optimisation criteria are investigated: (i) the Euclidean norm of the difference between the dynamic matrix of the discretised closed-loop continuous-time system and the dynamic matrix that represents the discretised open-loop system fed back by the designed digital controller; (ii) the H∞ norm of the transfer function from the noise input to the error between the outputs of the two systems. As main novelties with respect to the existing results on digital redesign, the proposed conditions can deal with polytopic systems, and can synthesise reduced-order dynamic output-feedback digital controllers as well.Mostrar mais Item Digital single voltage loop control of a VSI with LC output filter.(2018) Souza, Igor Dias Neto de; Almeida, Pedro Machado de; Barbosa, Pedro Gomes; Duque, Carlos Augusto; Ribeiro, Paulo FernandoMostrar mais This paper deals with the output voltage control problem of a three-phase three-wire voltage source Inverter (VSI) with LC output filter. A novel discrete-time active damping technique is proposed in order to damp the filter resonance without the need of current feedback. The method is based on an inner voltage feedback with digital lead compensator on the feedback path. A modified digital resonant controller is also proposed to reject the current harmonic disturbance drawn by nonlinear loads. The resonant controllers are connected in series and the design is based on its zeros damping. Results from a small scale experimental setup are used to validate the proposed control strategy.Mostrar mais Item Dispatchable distributed generation using a back-to-back converter for grid-forming improvements based on feed-forward action with load current prediction.(2020) Fogli, Gabriel Azevedo; Souza, Igor Dias Neto de; Fernandes, Marcelo Carvalho; Almeida, Pedro Machado de; Barbosa, Pedro GomesMostrar mais This work deals with the control law design and experimental verification of a grid-forming dispatchable distributed generation based on a back-to-back converter. The proposed system brings several improvements to the prime mover as well as to the microgrid voltage quality. The control strategy is based on an inner current and an outer voltage loop for both sides of the converter. The external loop of the back-to-back input side, which is connected to the generator, is responsible for regulating the DC voltage. On the other hand, in the output side, the voltage loop ensures a high-quality AC waveform to feed the loads. A comprehensive discussion regarding the current controller with harmonic mitigation is performed to justify the controller's choice. It is shown that a suitable current controller significantly improves the disturbance rejection. A feed-forward compensation based on the load current prediction without any additional sensor is proposed to improve the output voltage quality. Experimental results are used to validate the proposed control law and to show the improvements and benefits of the system.Mostrar mais Item Distribution network reconfiguration using iterative branch exchange and clustering technique.(2023) Pereira, Ezequiel C.; Barbosa, Carlos Henrique Nogueira de Resende; Vasconcelos, João Antônio deMostrar mais The distribution network reconfiguration problem (DNRP) refers to the challenge of searching for a given power distribution network configuration with better operating conditions, such as minimized energy losses and improved voltage levels. To accomplish that, this paper revisits the branch exchange heuristics and presents a method in which it is coupled with other techniques such as evolutionary metaheuristics and cluster analysis. The methodology is applied to four benchmark networks, the 33-, 70-, 84-, and 136-bus networks, and the results are compared with those available in the literature, using the criteria of the number of power flow executions. The methodology minimized the four systems starting from the initial configuration of the network. The main contributions of this work are the use of clustering techniques to reduce the search space of the DNRP; the consideration of voltage regulation banks and voltage-dependent loads in the feeder, requiring the addition of a constraint to the mono-objective model to guarantee the transferred load will be supplied at the best voltage magnitude level, and the application of the methodology in real distribution networks to solve a set of 81 real DNRPs from CEMIG-D (the distribution branch of the Energy Company of Minas Gerais). Four out of those are presented as case studies to demonstrate the applicability of the approach, which efficiently found configurations with lower power and energy losses with few PF runs.Mostrar mais Item Effects of harmonic pollution on salient pole synchronous generators and on induction generators operating in parallel in isolated systems.(2020) Vanço, Wagner Eduardo; Silva, Fernando Bento; Oliveira, José Mário Menescal de; Monteiro, José Roberto Boffino de AlmeidaMostrar mais This work presents a study of the disturbances caused by harmonic pollution in salient pole synchronous generators (SPSG) and induction generators, when operating in parallel in isolated systems. SPSG are known to operate with induction generators, since the excitation system of the synchronous generator is responsible for the voltage control on the island system. Due to the increase in the employment of power electronics, the loads take on a nonlinear behavior, where these become responsible for the generation of harmonics, due to the switching of electrical devices. Therefore, the analysis of the disturbances that these loads cause in generators, in this proposed and studied architecture, becomes essential. For the synchronous generator, there is also presented the analyses of the oscillations for voltages and currents on the dq0 model, the currents induced on the damper winding, the disturbances on the load angle and on the field current. In terms of the induction generator, the voltage and current oscillations are also analyzed from the dq0 model on the slip frequency. All the identified and quantified disturbances are oscillations on the electric variables, which possess a pulsating nature of frequencies 6ω, 12ω, and 18ω for the synchronous and induction generators, the oscillations of the sixth order and its multiples, will be given in the harmonic slip frequency of their respective harmonic orders in positive and negative sequence. In this way, verification is made as to the appearance of high slippage on the rotor of the induction generator.Mostrar mais Item Estratégias de energização e desenergização de um compensador estático síncrono para distribuição.(2018) Duarte, Samuel Neves; Fogli, Gabriel Azevedo; Almeida, Pedro Machado de; Barbosa, Pedro GomesMostrar mais Este trabalho propõe dois controladores para energizar e desenergizar compensadores estáticos síncronos destinados a serem conectados nas redes de distribuição. O primeiro circuito é baseado em um retificador semi–controlado enquanto o segundo controlador é baseado em um circuito gradador. Os dois controladores propostos são facilmente adaptados a estrutura do compensador estático sem a necessidade de realizar alterações topológicas no conversor. Um modelo matemático é usado para derivar as relações matemáticas usadas para controlar as correntes de energização e de desenergização. Aproximações lineares por partes foram usadas para reduzir o esforço computacional dos algoritmos de controle desenvolvidos. Resultados de simulação e experimentais são apresentados para validar a metodologia proposta.Mostrar mais