IPS - ESTS – DEE - Artigos científicos
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- Physical Layer Aware Network Architecture for the Future InternetPublication . Cardoso, Filipe; Correia, Luís; Mannersalo, Petteri; Frantti, Tapio; Serrador, António; Nunzi, Giorgio; Genay, Naveena; Le Rouzic, EstherIn this article, physical layer awareness inaccess, core, and metro networks is addressed,and a Physical Layer Aware Network Architec-ture Framework for the Future Internet is pre-sented and discussed, as proposed within theframework of the European ICT Project4WARD. Current limitations and shortcomingsof the Internet architecture are driving researchtrends at a global scale toward a novel, secure,and flexible architecture. This Future Internetarchitecture must allow for the co-existence andcooperation of multiple networks on commonplatforms, through the virtualization of networkresources. Possible solutions embrace a fullrange of technologies, from fiber backbones towireless access networks. The virtualization ofphysical networking resources will enhance thepossibility of handling different profiles, whileproviding the impression of mutual isolation.This abstraction strategy implies the use of wellelaborated mechanisms in order to deal withchannel impairments and requirements, in bothwireless (access) and optical (core) environ-ments.
- A computer-based testing system to evaluate protective relays as a tool in power system protection educationPublication . Martins, L. Sousa; Fortunato, Carlos; Pires, V. FernãoTeaching power system relaying is a fundamental issue in a power system high-level course. However, for an effective instruction of this topic an experience with real equipments can be considered as fundamental. To achieve this purpose, in this paper a new approach for the practical learning of power system relaying is presented. This consists of a computer-based testing system of relay-operating characteristic. Different relay types and developed specific software are also an important piece of the laboratory practice. Using this system it is possible to understand the performance and limitations of different protective relay systems and to test a real relay disoperation. The benefit of using this system is not available through traditional lectures and textbooks.
- Fault location in an electrical energy distribution infrastructure with a wireless sensor networkPublication . Fortunato, Carlos; Casaca, Augusto; Grilo, António; Santos, MiguelThis article presents a detailed analysis of the applicability of wireless systems in the localization of faults in the energy distribution network. The hwardware and software architectures of the envised sensor solution will also be described and finally, the integration of this system into Smart Grids will be discussed in terms of automatic fault analysis. A pilot system has been tested in a subset of the Portuguese energy distribution infrastructure operated by EDP Energias de Portugal. It presents a new approach to a fault locator system for the power network. The purpose is to obtain faster and more reliable information about the disruptions in the power distribution network and their location. Furthermore, the wireless sensors allow remote detection of medium and low voltage (MV/LV) power transformer hotspots in order to identify emerging malfunction as well as detection of intrusion in the MV/LV power transformers.
- Energy Efficient TransmissionTechniques for LTEPublication . Cardoso, Filipe; Petersson, Sven; Boldi, Mauro; Mizuta, Shinji; Dietl, Guido; Torrea-Duran, Rodolfo; Desset, Claude; Leinonen, Jouko; Correia, LuísThe goal of the European ICT ProjectEARTH is to enhance energy efficiency of cur-rent LTE cellular networks by 50 percent,enabling operators to provide more extensivecoverage, namely to less densely populatedareas, while ensuring high levels of efficiency,hence, reducing the carbon footprint. In order toachieve this objective, different strategies, at dif-ferent levels, are being addressed. Energy effi-cient transmission techniques for LTE, proposedwithin the framework of EARTH, are addressedand discussed, with an emphasis on beamform-ing and MIMO. It is concluded that the strategicobjective of EARTH is achievable. CombinedMIMO mode selection, resource allocation,scheduling and precoding strategies will allow anenergy consumption reduction of more than 50percent in macro-cells. A reduction in MIMOpower consumption of 91.7 percent (factor of12) can be achieved in pico-cells
- OnDemand Virtual Radio Resource Allocation for Wireless AccessPublication . Caeiro, Luísa; Cardoso, Filipe; Correia, Luís
- Scale Models Formulation of Switched Reluctance Generators for Low Speed Energy ConvertersPublication . Lobato, Pedro; Dente, J. A.; Martins, J.; Pires, A. J.
- Magnetic Flux Density Distribution in the Air Gapof a Ferromagnetic Core With SuperconductingBlocks: Three-Dimensional Analysis andExperimental NMR ResultsPublication . Roque, António; Sousa, Duarte M.; Margato, Elmano; Machado, Vítor; Sebastião, Pedro; Marques, G.D.The design of magnetic cores can be carried out bytaking into account the optimization of different parameters inaccordance with the application requirements. Considering thespecifications of the fast field cycling nuclear magnetic resonance(FFC-NMR) technique, the magnetic flux density distribution,at the sample insertion volume, is one of the core parametersthat needs to be evaluated. Recently, it has been shown that theFFC-NMR magnets can be built on the basis of solenoid coilswith ferromagnetic cores. Since this type of apparatus requiresmagnets with high magnetic flux density uniformity, a new typeof magnet using a ferromagnetic core, copper coils, and supercon-ducting blocks was designed with improved magnetic flux densitydistribution. In this paper, the designing aspects of the magnetare described and discussed with emphasis on the improvement ofthe magnetic flux density homogeneity(ΔB/B0)in the air gap.The magnetic flux density distribution is analyzed based on 3-Dsimulations and NMR experimental results.
- SRM sensorless for position control based on a frequency modulation systemPublication . Rafael, Silviano; Branco, P. J. Costa; Pires, A. J.This paper presents a study of a system to detect the angular position of the shaft of an 8/6 Switched Reluctance Machine (SRM) for position control. The detection system is independent of the machine circuits and is based on the indirect measurement of the induction coefficient, using a diagnostic coil. This induction coefficient, variable with the angular position, is the variable element of an oscillator, producing a frequency modulation. The intrinsic problems that this indirect position measurement system presents, particularly related with position control, are explained. The influence of the machine temperature, of the rotor speed and of the magnetic circuit saturation are also discussed.
- Fast-Field Cycling Nuclear Magnetic Resonance relaxometer's electromagnet with optimized homogeneity and reduced volumePublication . Videira, P.; Sebastião, P.; Roque, António; Sousa, D. M.; Margato, E.In this article a Fast Field Cycling (FFC) Nuclear Magnetic Resonance (NMR) electromagnet with low power consumption (less than 200 W), high field homogeneity and reduced volume is projected and described. The electromagnet is iron and copper based, possessing a high permeability and allowing for good magnetic field homogeneity in the operating range of 0 to 0.33 T. With this solution, it is possible to increase 65% the maximum magnetic field keeping the magnetic field homogeneity in comparison with former similar FFC relaxometers. Electromagnet's experimental and simulation results evaluating the generated magnetic field, field homogeneity, heating effects and cooling requirements are also presented. In addition, some technical aspects of the required coupled systems such as the cooling, sample heating are assessed.
- A Multilevel Fault-Tolerant Power Converter for a Switched Reluctance Machine DrivePublication . Pires, Vítor Fernão; Cordeiro, Armando; Foito, Daniel José Medronho; Pires, A. J.; Martins, João; Chen, HaoReliability in the electrical drives is becoming an important issue in many applications. In this context, the reliability associated to the switched reluctance machine (SRM) is also an important area of research. One of the major problems, that strongly affect its operation, are drive power semiconductors faults. Typical power converter topologies used in SRM drives cannot handle faults in their power semiconductors. So, this paper presents a power converter topology that provides fault-tolerant capabilities to the drive under a switch fault. This power converter will be used considering that a change in the direction of the current that flows in the SRM windings does not affect the behavior of the machine. Besides that, the proposed power converter will allow to generate multilevel phase voltages in order to apply different voltage levels as function of the SRM speed. A laboratory power converter was developed to test the SRM drive in normal and faulty conditions. From the obtained results it was possible to verify the fault-tolerant capability of the drive under switch faults in different devices and failure modes. It was also possible to confirm the multilevel operation of the drive.