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- An open-source UFBGA m-board for wearable devicesPublication . A. Antunes, R.; Palma, Luís BritoThis paper presents the development of an open-source, low-sized, BGA microcontroller breakout board, that can be used for the development of wearable and cyber-physical prototypes. The board is based on the low power, 8-bit, ATtiny20-CCU Microchip AVR microcontroller. The ATtiny20-CCU can be programmed without bootloader, using the Atmel Tiny Programming Interface (TPI), instead of In-System Programming (ISP). The C code used to program the microcontroller can be written and compiled using the Microchip Studio freeware platform. The ATtiny20-CCU Ultra Fine-pitch Ball Grid Array (UFBGA) packaging technology allows the shrinkage of the conceived Electroless NickelImmersion Gold (ENIG) Printed Circuit Board (PCB) to a size of only 15.5 13 mm. Its low cost also makes it a viable option for developing many educational electronic projects, especially for Instrumentation and Assistive Technology. The contribution of this paper is mainly the hardware prototype design, the PCB manufacturing, building and test of a very low-sized open source m-breakout PCB board, for wearable Instrumentation applications, towards the emergent Society/Industry 5.0.
- 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.
- DC Microgrids: Benefits, Architectures, Perspectives and ChallengesPublication . Pires, Vítor Fernão; Pires, A. J.; Cordeiro, ArmandoOne of the major paradigm shifts that will be predictably observed in the energy mix is related to distribution networks. Until now, this type of electrical grid was characterized by an AC transmission. However, a new concept is emerging, as the electrical distribution networks characterized by DC transmission are beginning to be considered as a promising solution due to technological advances. In fact, we are now witnessing a proliferation of DC equipment associated with renewable energy sources, storage systems and loads. Thus, such equipment is beginning to be considered in different contexts. In this way, taking into consideration the requirement for the fast integration of this equipment into the existing electrical network, DC networks have started to become important. On the other hand, the importance of the development of these DC networks is not only due to the fact that the amount of DC equipment is becoming huge. When compared with the classical AC transmission systems, the DC networks are considered more efficient and reliable, not having any issues regarding the reactive power and frequency control and synchronization. Although much research work has been conducted, several technical aspects have not yet been defined as standard. This uncertainty is still an obstacle to a faster transition to this type of network. There are also other aspects that still need to be a focus of study and research in order to allow this technology to become a day-to-day solution. Finally, there are also many applications in which this kind of DC microgrid can be used, but they have still not been addressed. Thus, all these aspects are considered important challenges that need to be tackled. In this context, this paper presents an overview of the existing and possible solutions for this type of microgrid, as well as the challenges that need to be faced now.
- Dual Output and High Voltage Gain DC-DC Converter for PV and Fuel Cell Generators Connected to DC Bipolar MicrogridsPublication . Pires, Vitor Fernão; Cordeiro, Armando; Foito, Daniel José Medronho; Silva, J. Fernando A.This paper introduces a new topology for a DC-DC converter with bipolar output and high voltage gain. The topology was designed with the aim to use only one active power switch. Besides the bipolar multiport output and high voltage gain this converter has another important feature, namely, it has a continuous input current. Due to the self-balancing bipolar outputs, the proposed topology is suitable for bipolar DC microgrids. Indeed, the topology balancing capability can achieve the two symmetrical voltage poles of bipolar DC microgrids. Furthermore, it is possible to create a midpoint in the output of the converter that can be directly connected to the ground of the DC power supply, avoiding common-mode leakage currents in critical applications such as transformerless grid-connect PV systems. The operating principle of the proposed topology will be supported by mathematical analysis. To validate and verify the characteristics of the presented topology, several experimental results are shown.
- 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
- 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.
- Fault Detection in PV Tracking Systems Using an Image Processing Algorithm Based on PCAPublication . Amaral, Tito G.; Pires, Vitor Fernão; Pires, A. J.Photovoltaic power plants nowadays play an important role in the context of energy generation based on renewable sources. With the purpose of obtaining maximum efficiency, the PV modules of these power plants are installed in trackers. However, the mobile structure of the trackers is subject to faults, which can compromise the desired perpendicular position between the PV modules and the brightest point in the sky. So, the diagnosis of a fault in the trackers is fundamental to ensure the maximum energy production. Approaches based on sensors and statistical methods have been researched but they are expensive and time consuming. To overcome these problems, a new method is proposed for the fault diagnosis in the trackers of the PV systems based on a machine learning approach. In this type of approach the developed method can be classified into two major categories: supervised and unsupervised. In accordance with this, to implement the desired fault diagnosis, an unsupervised method based on a new image processing algorithm to determine the PV slopes is proposed. The fault detection is obtained comparing the slopes of several modules. This algorithm is based on a new image processing approach in which principal component analysis (PCA) is used. Instead of using the PCA to reduce the data dimension, as is usual, it is proposed to use it to determine the slope of an object. The use of the proposed approach presents several benefits, namely, avoiding the use of a wide range of data and specific sensors, fast detection and reliability even with incomplete images due to reflections and other problems. Based on this algorithm, a deviation index is also proposed that will be used to discriminate the panel(s) under fault. Several test cases are used to test and validate the proposed approach. From the obtained results, it is possible to verify that the PCA can successfully be adapted and used in image processing algorithms to determine the slope of the PV modules and so effectively detect a fault in the tracker, even when there are incomplete parts of an object in the image.
- 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.
- Fault-Tolerant SRM Drive with a Diagnosis Method Based on the Entropy Feature ApproachPublication . Pires, Vitor Fernão; Amaral, Tito G.; Cordeiro, Armando; Foito, Daniel José Medronho; Pires, A. J.; Martins, João F.The power electronic converter design is essential for the operation of the switched reluctance motor (SRM). Thus, a fault-tolerant power converter is fundamental to ensure high reliability and extend the drive operation. To achieve fault tolerance, fault detection and diagnosis methods are critical in order to identify, as soon as possible, the failure mode of the drive. To provide such capability, it is proposed in this paper a new fault-tolerant power converter scheme combined with a fault detection method regarding the most common power semiconductors failures in SRM drives. The fast and reliable proposed diagnosis method is based on the entropy theory. Based on this theory, normalized indexes (diagnostic variables) are created, which are independent from the load and speed of the motor. Through this method, it is possible to identify the faulty leg, as well as the type of power semiconductor fault. To test and evaluate the proposed solution several laboratory experiments were carried out using a 2 kW four-phase 8 / 6 SRM.
- 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.