Paulo da Costa Branco

The aim of this work is the redesign of the reflector geometry in hybrid concentrating collectors that are currently manufactured by SOLARUS Sunpower AB** to improve the energy efficiency of their solar collectors. The analysis is first accomplished using a numerical model that uses geometrical optics to study the interaction between the sunlight and a concentrating collector along the year. More complex physical models based on open-source and advanced object-oriented Monte Carlo ray tracing programs (SolTrace, Tonatiuh) have been used to study the relation between the collector annual performance and its geometry. On an annual performance basis, a comparative analysis between several solar collector geometries was effectuated to search for higher efficiencies but with controlled costs. Results show that efficiency is deeply influenced by reflector geometry details, collector tilt and location (latitude, longitude) of the solar panel installation and, mostly, by costumer demands. U...

Abstract In the presented paper, we developed a partnership with the Swedish company Solarus AB to study the performance of a CPV/T under very distinct climate zones: Sweden and Portugal. We focus on thermal effects and their influence on the CPV/T’s energy efficiency. Therefore, we develop an electromagnetic-thermal finite element model (FEM) of the CPV/T in 2D and 3D, capable of computing the heat transfer occurring due to the flow of cooling fluid. Furthermore, we use the developed model to evaluate temperature conditions over the different layers of the photovoltaic panel and fluid temperature along the CPV/T. The evaluation shows that it is the CPV/T cooling structure that has a major influence on CPV/T’s performance when it functions in climate zones with very different temperature scales along the year. The shape of cooling channels, for example, must continue to ensure a better heat transfer, leading thus to a more uniform distribution of the temperature along with the receiver. Also, fluid flow rates must be carefully selected to avoid solar cells reach their maximum operating temperatures (85 °C).

Large power transformers are generally associated with a maximum capacity rating of 100 MVA or higher. These large liquid dielectric power transformers are a custom-built piece of equipment, thus very expensive, and a backbone element of the power grid. In extreme cases as, for example, severe geomagnetic disturbances, permanently monitoring their condition will enhance their electrical reliability and resilience to guarantee efficient management of its life cycle. However, some traditional monitoring/diagnosis techniques have singular features when applied to large power transformers and their interlinked subsystems. In this context, and since that information is hardly put in evidence and compiled in the literature, this paper reviews the particularities of monitoring and diagnosing those assets.

This article is to present the Veículo Inteligente Elétrico de Navegaciio Autónoma (VIENA) project - (Intelli-gent Electric Vehicle with Autonomous Driving) - a project made by students, for students. The project scope is to be a multidisciplinary platform for the Electrical and Computer Engineering (ECE) course at Técnico Lisboa to grasp important aspects and concepts that can only be obtained by a practical implementation. Since the objective of this project is to make a semi to a fully autonomous electric car, every aspect of the ECE course applies here: electrical circuitry development, sensor implementation, low and high levels of communication, low and high-level programming, power train design, including battery and electric motor system, and all the control aspects required to make all these parts function as one, as well as for the speed control and autonomous driving. The main goal is to show the work developed so far and how this project contributed to knowledge and curriculum of the students that worked in the project, voluntary, in their master's thesis, or through scholarships.

This work focuses on implementing HTS bulks in the excitation circuit of low-speed synchronous generators as permanent magnets. In addition to the implementation study, it is also addressed to remagnetize HTS bulks in electric generators. To reduce the maintenance costs and time required for the magnetization process, an in-loco remagnetization is used. The HTS bulks are magnetized in their position inside the machine's magnetic circuit. A pulse-field magnetization (PFM) technique is used, using the stator coils of a linear generator. YBCO and GdBCO samples are tested. The experimental procedure starts with the in-loco PFM to magnetize the HTS bulks and, by applying an oscillatory movement to the linear generator's moving part, measuring the magnetic flux density induced voltage is done. Experimental tests show that, for the FeSi core used in the generator, the YBCO material is most suitable for the excitation circuit.

This paper presents an experimentally verified finite-element multiphysics model developed to simulate the coupled electro and thermodynamic processes (electromagnetic, thermal, and fluid-flow with liquid–gas phase transition) occurring between liquid nitrogen (LN2) and HTS YBCO bulks. The model allows estimating: 1) the thermal time constants related to bulk HTS losing/gaining its superconducting state, and mainly 2) the LN2 liquid-to-gas flow rate due to superconductor Joule losses caused by electromagnetic induction heating of it. Model accuracy is evaluated, for example, by comparing the cooling time needed to zero-field-cool the YBCO bulk, and the quantity of LN2 vaporized as the superconductor cool. Other important issues identified were time evolution and spatial distribution of temperature in the superconductor, heat flux, nitrogen liquid flow, and also nitrogen gas concentration for specific cooling scenarios. Full-scale experimental tests in our laboratory allowed us to va...

The aim of this work was to develop a prototype based on an improved version of windings for a spherical induction motor, along with developing its thermal and mechanical project. The improved version of a planar winding configuration was adapted to a spherical configuration to fit into a wooden prototype that was created to test the electromagnetic system and determine its equivalent circuit components. The prototype was successfully built and the new windings shown to generate 133% more torque than the previous version. A CAD model was designed and computational simulations were performed to simulate its mechanical and thermal behavior under nominal conditions. The mechanical simulations shown that the model was sturdy enough to sustain a 1400 N compression load at ease, resulting in a maximum strain of 88 MPa, which is far below the yield strength of the 2014-T6 Aluminum alloy that has been chosen for the project material. The thermal simulations predict a 50 oC reduction of the ...

Abstract The mismatch is a phenomenon intrinsically related to photovoltaic (PV) arrays, either because they are eventually subject to non-uniform irradiance and temperature conditions, or because of inner variations on the components, ageing or occurrence of failures. Despite mismatch losses being so present in the life of a PV system, the available tools for the study of PV arrays response through simulation today present limitations for the handling of mismatch conditions. Most of them do not support non-uniform conditions, and the ones that do, solely explore irradiance and temperature variations, ignoring other causes for mismatches, such as defects on PV cells. This paper proposes a simulation framework that allows manipulation of each parameter in each cell individually to reproduce mismatch conditions, including failures. Each PV cell is represented by the one diode equivalent circuit model, for which two different parameterisation methods were tested: California Energy Commission (CEC) and PVSyst. The proposed simulation framework was validated with laboratory measurements of a PV module under 15 different mismatch conditions of partial shading and failure (short circuit). The results showed a consistent similarity between calculated and measured I–V curves, and errors at the curves’ maximum power points stayed within the instruments’ accuracy range, roughly 1.0 V and 0.2 A. The proposed simulation framework brings great flexibility to the studies of mismatch through simulation, allowing the calculation of the I–V curve of PV strings and small arrays subjected to mismatch conditions due to non-uniform irradiance and temperature profiles, but most significantly failures in the cells.

Reliability assessment in traditional power distribution systems has played a key role in power system planning, design, and operation. Recently, new information and communication technologies have been introduced in power systems automation and asset management, making the distribution network even more complex. In order to achieve efficient energy management, the distribution grid has to adopt a new configuration and operational conditions that are changing the paradigm of the actual electrical system. Therefore, the emergence of the cyber-physical systems concept to face future energetic needs requires alternative approaches for evaluating the reliability of modern distribution systems, especially in the smart grids environment. In this paper, a reliability approach that makes use of failure modes of power and cyber network main components is proposed to evaluate risk analysis in smart electrical distribution systems. We introduce the application of Failure Modes and Effects Anal...

This study proposes and evaluates a predictive control model for the management of the power flow in a hybrid microgeneration power plant with additional storage capacity. The plant integrates a photovoltaic array, a wind turbine, a diesel generator, and a lithium ion battery bank. One objective of the proposed predictive control model is to maximise the use of power from renewable resources looking for the weather predictions and thus minimise the use of fossil power from the diesel generator and corresponding CO 2 emissions. Another aim is to maximise the duration of lithium ion batteries, since extending their lifetime is crucial for the system's economic viability, and since battery disposal brings environmental concerns as well. A numerical evaluation is performed about the evolution of power dispatch decisions and of the batteries state of charge, depending on the available power storage capacity. Model predictive control proves to be a suitable strategy in this system.

The development of electric aircraft is becoming an important technology for achieving the goals set by the European Commission for the reduction of gases emissions by 2050 in the aeronautical transportation system. However, there is a technology gap between the current values of specific power in commercial electric machines and those required for aeronautical applications. Therefore, the search for alternative materials and non-conventional designs is mandatory. One emergent solution is using superconducting machines and systems to overcome the current limits of conventional electrical machines. This work reviews the new hybrid and all-electric aircraft tendencies, complementing it with recent research on the design and development of high specific power superconducting machines. This includes the main topologies for hybrid and all-electric aircraft, with an overview of the ongoing worldwide projects of these aircraft types, systematizing the main characteristics of their propulsi...