Percorrer por autor "Silva, Fernando"
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- Fault tolerance capability and semiconductor's hold-off voltage of solid-state bipolar Marx modulatorsPublication . Canacsinh, Hiren; Silva, Fernando; Luis RedondoTwo solid-state bipolar Marx modulators are analyzed and compared regarding hold-off semiconductor voltages and open-fault tolerance capability. Normal and abnormal operating conditions are considered, such as switch synchronization mismatches, failures, and open faults. Ten-stage laboratory prototypes of two bipolar Marx modulators have been assembled using 1200-V insulated gate bipolar transistors and matching diodes, to operate at 500-V dc input voltage. Outputs are 4-kV bipolar pulses, 1% duty ratio, into resistive loads, and 1-kHz frequency. Lack of synchronization and open-fault tests confirm that only topologies with redundant switches can operate without semiconductors being subjected to double hold-off voltages while presenting current paths to clear faults.
- A multilevel converter topology for a STATCOM system based on Four-leg Two-level inverters and cascaded Scott TransformersPublication . Fernao Pires, Vitor; Cordeiro, Armando; Foito, Daniel; Silva, FernandoThis paper presents a new power electronic topology for a STATCOM allowing the generation of multilevel AC voltages. This topology is characterized by a modular configuration since it uses two well known four-leg two-level voltage source inverters. A Scott transformer with multiple secondary windings connects the two four-leg inverters to the grid. One of the important features of the proposed power topology is the capability to generate AC voltages with high number of levels, in spite of using only two four-leg two-level voltage source inverters. To maximize the number of voltage levels a geometric progression ratio of 3 between the windings of the transformers connected in cascade is proposed. However, to reduce the turns-ratio span, alternatively a fractional geometric ratio of 1.5 is also proposed and analyzed. A control strategy adapted to the proposed power converter topology is also presented. Besides the control of the reactive power the regulation of the four-leg inverter DC voltage will also be considered. To support the theoretical studies and assumptions, simulations and experiments are presented. Experimental results were obtained using a low power laboratory prototype. The results shown give evidence to the characteristics and features of the proposed power converter topology and control system.
- Novel incremental conductance feedback method with integral compensator for maximum power point tracking: A comparison using hardware in the loopPublication . André, Sérgio; Silva, Fernando; Pinto, Sónia; Miguens Matutino, PedroResearch on renewable energy sources and power electronic converters has been increasing due to environmental concerns. Many countries have established targets to decrease CO2 emissions and boost the proportion of renewable energy, with solar power being a prominent area of investigation in the recent literature. Techniques are being developed to optimize the energy recovered from PV cells and increase system efficiency, including modeling PV cells, the use of converter topologies to connect PV systems to high-power inverters, and the use of MPPT methods. Certain MPPT algorithms are intricate and demand high processing power. The literature describes several MPPT methods; however, the number of hardware resources required by MPPT algorithms is typically not disclosed. This work proposes a novel MPPT technique based on integral feedback conductance and incremental conductance error, considering the current dynamics of the boost converter. This MPPT algorithm is compared to the most widely used techniques in the literature and evaluates each method’s efficiency, performance, and computational needs using an HIL system. Comparisons are made with well-known MPPT algorithms, such as perturb and observe, incremental conductance, and newer techniques based on fuzzy logic and neural networks (NNs). As the NN that is most widely used in the literature depends on irradiation and temperature, an additional NN that is trained using the proposed method is also investigated.
- Oeste Ecopark: plano de comunicaçãoPublication . Silva, Fernando; Eiró-Gomes, Mafalda; Costa, Joana FriasAs Relações Públicas (RP) são uma disciplina da comunicação aplicada e desempenham uma função estratégica de relevo em qualquer organização, ao permitirem o estabelecimento de uma relação mutuamente benéfica entre a organização e os seus públicos. A concretização deste projeto surge de um desafio real: a realização de um plano de comunicação destinado a um empreendimento turístico, denominado por Oeste Ecopark, na zona da Assenta, Torres Vedras, Portugal. Este plano não tem unicamente o objetivo de informar ou captar novos clientes, mas sobretudo envolver os seus stakeholders e públicos de forma consciencializá-los para uma nova forma de ‘fazer’ turismo – o Ecoturismo. Tudo isto porque, apesar de o turismo ter um grande peso na economia portuguesa e mundial, a sua exploração tem sido cada vez mais intensiva, o que acaba por ter um impacto ambiental e social negativo. É face a este desafio que se procura, através de estratégias de RP, manter uma relação favorável entre o contexto sociocultural e o ecológico – privilegiando ações que se proponham a educar os seus stakeholders e públicos (ex.: comunidade e turistas) rumo à sustentabilidade.
- Rise-time improvement in bipolar pulse solid-state Marx modulatorsPublication . Canacsinh, Hiren; Silva, Fernando; Luis RedondoThis paper presents the effect of stray capacitances in bipolar (negative and/or positive) pulses generated by the two different topologies of the solid-state Marx modulators. According to the analysis, the stray capacitances influence the energy transfer from the Marx modulator capacitors to the load affecting the bipolar (negative and/or positive) pulse rise time. This paper deals with the structure design to reduce the influence of the stray capacitance and to improve the pulse rise time of these bipolar solid-state Marx modulators. A four-stage laboratory prototype of the two topologies has been assembled using 1200-V insulated gate bipolar transistors and diodes, operating with 1000-V dc input voltage and 1-kHz frequency, producing 4-kV bipolar pulses, with 5-mu s pulse duration and 120-ns rise time, into a resistive load.
- Wide voltage gain range bidirectional DC-DC converter with reduced switches count and buck-boost characteristic in both power flow directionsPublication . Fernao Pires, Vitor; Cordeiro, Armando; Foito, Daniel; Amaral, Tito; Silva, FernandoSeveral applications require bidirectional power converters with high-voltage gain. While several topologies have been proposed, none of them exhibit Buck-Boost characteristics in both forward and reverse power transfer. Most proposals behave as a Boost converter in forward direction and as a Buck converter in the reverse direction. Therefore, this paper proposes a novel DC-DC bidirectional power converter that exhibits Buck-Boost characteristics in both power flow directions while providing very high wide voltage gain range. The proposed converter has, in addition, the ability to maintain continuous currents in the input and output. The theoretical analysis of the converter under bidirectional power flow conditions will be presented and examined, along with the design of its components. The validation of the characteristics and behavior of the proposed bidirectional power converter were tested in several laboratory experiments. The experimental results obtained from both power flow directions show agreement with the theoretical considerations.