Browsing by Author "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.
- 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.