Browsing by Author "Ferreira, Ângela P."
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- Abordagens para a ligação à rede de sistemas pico-hidroelétricosPublication . Leite, Vicente; Ferreira, Ângela P.; Couto, José; Batista, JoséOs aproveitamentos hidroelétricos de pequena escala apresentam um impacte ambiental reduzido. Existe um enorme potencial inexplorado, apresentando portanto uma capacidade significativa para satisfazer a crescente procura de energia elétrica com muitas vantagens. Os sistemas pico-hídricos ligados à rede são uma solução emergente para um grande número de aplicações, tais como em sistemas de fornecimento de água para uso doméstico, em estações de tratamento de águas residuais e melhoramento de sistemas de controlo e otimização da geração como parte de sistemas de gestão integrada da água. Também são muito promissores para a integração em microrredes em muitos países em desenvolvimento. Este artigo apresenta e discute três principais abordagens para a ligação à rede de sistemas pico-hidroelétricos: utilizando conversores de energia especificamente concebidos, utilizando inversores eólicos estandardizados e utilizando inversores fotovoltaicos estandardizados. Estas últimas abordagens, baseadas em inversores convencionais, são soluções práticas capazes de explorar uma grande quantidade de locais viáveis com pequena e muito pequena queda de água. Além disso, os micro inversores fotovoltaicos, recentemente lançados no mercado, são propostos para os geradores de potência reduzida (250-300 W). Estas abordagens melhoram a eficiência, reduzem os custos e os impactes ambientais e melhoram a fiabilidade dos sistemas de conversão. A avaliação experimental do desempenho em regime permanente e em condições dinâmicas comprova a viabilidade destas abordagens inovadoras.
- An axial flux permanent magnet synchronous generator for a gearless wind energy systemPublication . Ferreira, Ângela P.; Silva, Amândio M.; Costa, A.F.In low speed applications such as wind energy conversion systems, the use of direct driven generators, instead of geared machines, reduces the number of drive components, which offers the opportunity to reduce costs and increases system reliability and efficiency. The Axial Flux Permanent Magnet (AFPM) generator is particularly suited for such application, since it can be designed with a large pole number and a high torque density. This paper presents the design, construction and experimental validation of a double-sided AFPM synchronous generator prototype, with internal rotor and slotted stators. Design objectives embrace achieving a good compromise between performance characteristics and feasibility of construction, which results in a cost competitive machine.
- An improved GA-based approach for reduced non-discriminatory renewable energy curtailmentPublication . Pedroso, André Felipe Pereira; Zanatta, Giuseppe; Ferreira, Ângela P.; Pereira, Ana I.; Amoura, Yahia; Lopes, Rui Pedro; Angelos, Eduardo Werley S. dos; Vasconcelos, Fillipe Matos de; Lemos, Manuel; Pino, GabrielThe active management of the networks with high penetration of renewable energy sources faces several challenges. To maximize the utilization of low carbon electricity, the curtailment of generator units using renewables should be limited and fair among units. In this work, an attempt has been made to solve the optimal power flow using an improved Genetic Algorithm. The optimal flow formulation is oriented to the efficiency of the network, under the boundary restrictions of limited curtailment of the output of distributed generators based on renewables and non-discriminatory behaviour. The results obtained from a IEEE 14-bus test system have demonstrated the feasibility of this approach.
- An innovative optimization approach for energy management of a microgrid systemPublication . Amoura, Yahia; Pereira, Ana I.; Lima, José; Ferreira, Ângela P.; Boukli-Hacene, Fouad; Torres, SantiagoThe local association of electrical generator including renewable energies and storage technologies approximately installed to the client made way for a small-scale power grid called a microgrid. In certain cases, the random nature of renewable energy sources, combined with the variable pattern of demand, results in issues concerning the sustainability and reliability of the microgrid system. Furthermore, the cost of the energy coming from conventional sources is considering as matter to the private consumer due to its high fees. An improved methodology combining the simplex-based linear programming with the particle swarm optimisation approach is employed to implement an integrated power management system. The energy scheduling is done by assuming the consumption profile of a smart city. two scenarios of energy management have been suggested to illustrate the behaviour of cost and gas emissions for an optimised energy management. The results showed the reliability of the energy management system using an improvemed approach in scheduling of the energy flows for the microgrid producers, limiting the utility’s cost versus an experiment that had already been done for a similar system using the identical data. The outcome of the computation identified the ideal set points of the power generators in a smart city supplied by a microgrid, while guaranteeing the comfort of the customers i.e without intermetency in the supply, also, reducing the emissions of greenhouse gases and providing an optimal exploitation cost for all smart city users. Morover, the proposed energy management system gave an inverse relation between economic and environmental aspects, in fact, a multi-objective optimization approach is performed as a continuation of the work proposed in this paper
- Análise do funcionamento do gerador de ímanes permanentes, com anisotropia inversa, isolado, alimentando uma carga resistivaPublication . Ferreira, Ângela P.A utilização da máquina de ímanes permanentes como gerador isolado tem vindo a ser estimulada pelo aumento das potências disponíveis, através do desenvolvimento dos materiais magnéticos permanentes, nomeadamente nos últimos vinte anos, caracterizado pelo aparecimento das ligas de terras raras e por uma selecção adequada dos parâmetros da máquina. A análise do funcionamento do gerador de ímanes permanentes isolado, alimentando uma carga resistiva, baseada no modelo de Blondel simplificado, permite demonstrar uma vantagem funcional do circuito magnético anisotrópico inverso, sendo possível obter tensões superiores à força electromotriz induzida em vazio; estudos preditivos e experimentais permitem avaliar a dependência da regulação dos efeitos de saturação e da resistência do estator.
- Analysis of the operation of a microgrid with renewable distributed generationPublication . Leite, Vicente; Ferreira, Ângela P.; Batista, José; Couto, JoséThis article reports the ongoing research on the performance assessment of an experimental microgrid which integrates various renewable energy sources. The microgrid is based on a modular commercial solution, up to a rated power of 5 kW, integrating storage devices, a backup diesel generator and various renewable energy sources and also distributed energy sources developed under ongoing R&D projects, such as the integration of a pico hydropower plant with an interface able to perform power factor compensation of the microgrid, which is introduced briefly. The performance assessment of this microgrid is conducted through a characterization of different operational states and also a preliminary energy balance of the microgrid during a time span of 4 days.
- Analytical and numerical thermal modelling of a low power transformerPublication . Mendes, Gabriel Dias; Ferreira, Ângela P.; Miotto, EdneiIn past decades, thermal modelling of electric machines was overlooked and based on empirical experience. Due to modern requirements, using novel materials and innovative configurations, the thermal model became a crucial component in the modern design process. The thermal modelling can be performed by analytical methods, as the thermal resistance network (TRN) or by numeric methods as the finite element analysis (FEA). This work presents a methodological approach to thermal modelling, addressing both approaches and applying them to a study case of a low power shell-type single-phase transformer. The results from both approaches are compared with experimental results, achieving relative errors of 5.70% and 21.24% on the determination of windings' temperature, for the FEA and TRN model respectively, which helps define model improvements.
- Assessing the deployment of electric mobility: a reviewPublication . Gruetzmacher, Sarah; Vaz, Clara B.; Ferreira, Ângela P.The transport sector of the European Union is the only sector of the economy that has been increasing its emissions since 2014. To reduce the use of fossil fuels and achieve the greenhouse gas emissions mitigation target, many countries are focusing on the deployment of electric vehicles. This paper aims at analysing recent literature on the deployment of electric vehicles (EV) and typifying objectives, methods and indicators generally exploited, to better understand the state of the art on this topic. The Web of Science database was used and the results showed that the interest in the topic of electric vehicles has been increasing exponentially since 2010. The main significant indicators and the assessment methodologies were analysed. The indicators identified were aggregated in four main clusters: environmental, economic, social and technical indicators. Although the factors that contribute to EV deployment can vary depending on the regions specific characteristics, most of the research studies pointed out that the main contributors are the high density of recharging points, the existence of government monetary incentives and the lower operational cost of EV.
- Assessing the sustainable performance of the transport sector in European countries using alternative benefit-of-the-doubt modelsPublication . Gruetzmacher, Sarah; Vaz, Clara B.; Ferreira, Ângela P.The energy policy of the European Union stresses the need for sustainable energy consumption, improvements in energy efficiency and lower fossil fuel dependence in a decoupling strategy from unstable democracies. Transportation still represents a sector largely dependent on fossil fuels, which come with several negative impacts. Measuring and assessing the sustainability of the transport sector becomes necessary. This study aims to assess the sustainability performance of the transport sector across 28 European countries over a four-year period, aligned with the policy agenda outlined in strategic documents. The methodological approach involves applying Benefit-of-the-Doubt (BoD) models, comparing a version that uses transformation methods for antiisotonic sub-indicators with a variant that directly incorporates these sub-indicators as reverse indicators. In general, the European countries have improved the sustainability performance of their transport sector during the time span analyzed according to the results of both models. For the inefficient units, two improvement strategies are presented based on the profiles identified on the benchmarks from both models, which can be alternative stages to achieve the robust best practices of the benchmarks.
- Assessment of the transport sustainability performance in the European UnionPublication . Gruetzmacher, Sarah; Vaz, Clara B.; Ferreira, Ângela P.The transport sector plays a fundamental role in the European economy. By 2017, the transport sector employed directly more than 11 million people, around 57c of the total workforce, and its activities accounted for about 5% of Europe's Gross Domestic Product (GDP). Promoting efficient transport services and infrastructure is fundamental for making the most of the European's economic strengths, supporting the internal market and its growth. Unfortunately, the European Union transport sector still remains heavily dependent on oil resources and, therefore, it is responsible for a large part of the air pollution. The emissions from the sector have reduced in the last decade, but not enough to limit its impact on the environment and climate. Reducing its pressure on the environment is critical to achieve long-term sustainability. The European Union has been promoting diverse initiatives to- wards sustainable transport development and environment protection by setting targets for changes in the sector, as those proposed in the 2011 White Paper on transport [1]. This study aims at evaluating the sustainable performance of the transport sector in the 28 European Union countries, from 2015 to 2017, towards the policy agenda established in strategic documents. The assessment of the transport environmental performance was made through the aggregation of seven sub-indicators into a compos- ite indicator using a Data Envelopment Analysis approach. The model used to determine the weights to aggregate the sub-indicators is based on a variant of the Benefit of the Doubt model with virtual proportional weights restrictions as proposed by Färe et a1. [2] . The results indicate that, overall, the European Union countries had almost no variation on its transport environmental performance during the time span under analysis. The inefficient countries can improve the transport sustainability mainly by drastically reducing the greenhouse gas emissions from fossil fuels combustion, increasing the share of freight transport that uses rail and waterways and also the share of transport energy from renewable sources.