Percorrer por autor "Pinto, Sónia F."
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- Design of current power sources for a FFC NMR apparatus: a comparisonPublication . Roque, António; Pinto, Sónia F.; Santana, João; Sousa, Duarte; Margato, Elmano; Maia, JoséThe power supply of a Fast Field Cycling Nuclear Magnetic Resonance apparatus is typically a current power source, with characteristics that are not fulfilled by most of the commercially available power supplies. This current source is used to supply a specially designed magnet, and should be able to drive a cycling current with a slew rate lower than 3 A/ms. In this paper, two solutions for this current source are designed and discussed. The first uses two power supplies: the main voltage source and an auxiliary power supply to guarantee the current transitons from the low level to the high level. In the second solution the auxiliary power supply is replaced by a capacitor. To guarantee the required current slews rates, the possibility of using resistors to dissipate the energy store in the magnet is also discussed.
- Grid Integration of Offshore Wind Farms Using Modular Marx Multilevel ConvertersPublication . Encarnação, Luís; Silva, José Fernando; Pinto, Sónia F.; Luis RedondoThis paper proposes the use of a Modular Marx Multilevel Converter, as a solution for energy integration between an offshore Wind Farm and the power grid network. The Marx modular multilevel converter is based on the Marx generator, and solves two typical problems in this type of multilevel topologies: modularity and dc capacitor voltage balancing. This paper details the strategy for dc capacitor voltage equalization. The dynamic models of the converter and power grid are presented in order to design the converter ac output voltages and the dc capacitor voltage controller. The average current control is presented and used for power flow control, harmonics and reactive power compensation. Simulation results are presented in order to show the effectiveness of the proposed (MC)-C-3 topology.
- HVDC transmission systems: Bipolar back-to-back diode clamped multilevel converter with fastoptimum-predictive control and capacitor balancing strategyPublication . Chaves, Miguel; Margato, Elmano; Fernando Silva, J.; Pinto, Sónia F.; Santana, J.Voltage source multilevel power converter structures are being considered for high power high voltage applications where they have well known advantages. Recently, full back-to-back connected multilevel neutral diode clamped converters (NPC) have been used in high voltage direct current (HVDC) transmission systems. Bipolar back-to-back connection of NPCs have advantages in long distance HVDC transmission systems, but highly increased difficulties to balance the dc capacitor voltage dividers on both sending and receiving end NPCs. This paper proposes a fast optimum-predictive controller to balance the dc capacitor voltages and to control the power flow in a long distance HVDCsystem using bipolar back-to-back connected NPCs. For both converter sides, the control strategy considers active and reactive power to establish ac grid currents on sending and receiving ends, while guaranteeing the balancing of both NPC dc bus capacitor voltages. Furthermore, the fast predictivecontroller minimizes the semiconductor switching frequency to reduce global switching losses. The performance and robustness of the new fast predictive control strategy and the associated dc capacitors voltage balancing are evaluated. (C) 2011 Elsevier B.V. All rights reserved.
- A New Modular Marx Derived Multilevel ConverterPublication . Encarnação, Luís; Silva, José Fernando; Pinto, Sónia F.; Luis RedondoA new Modular Marx Multilevel Converter, M(3)C, is presented. The M(3)C topology was developed based on the Marx Generator concept and can contribute to technological innovation for sustainability by enabling wind energy off-shore modular multilevel power switching converters with an arbitrary number of levels. This paper solves both the DC capacitor voltage balancing problem and modularity problems of multilevel converters, using a modified cell of a solid-state Marx modulator, previously developed by authors for high voltage pulsed power applications. The paper details the structure and operation of the M(3)C modules, and their assembling to obtain multilevel converters. Sliding mode control is applied to a M(3)C leg and the vector leading to automatic capacitor voltage equalization is chosen. Simulation results are presented to show the effectiveness of the proposed M(3)C topology.
- On the Problem of Balancing the DC Capacitor Voltage Divider in Back-to-Back Multilevel ConvertersPublication . Chaves, Miguel; Margato, Elmano; Silva, J. Fernando; Pinto, Sónia F.This paper presents a new generalized solution for DC bus capacitors voltage balancing in back-to-back m level diode-clamped multilevel converters connecting AC networks. The solution is based on the DC bus average power flow and exploits the switching configuration redundancies. The proposed balancing solution is particularized for the back-to-back multilevel structure with m=5 levels. This back-to-back converter is studied working with bidirectional power flow, connecting an induction machine to the power grid.
- Solid-State Bipolar Marx Converter with Output Transformer and Energy RecoveryPublication . Canacsinh, Hiren; Silva, José Fernando; Pinto, Sónia F.; Luis Redondo; Santana, JoãoThe purpose of this paper is to present and discuss a general HV topology of the solid-state Marx modulator, for unipolar or bipolar generation connected with a step-up transformer to increase the output voltage applied to a resistive load. Due to the use of an output transformer, discussion about the reset of the transformer is made to guarantee zero average voltage applied to the primary. It is also discussed the transformer magnetizing energy recovering back to the energy storage capacitors. Simulation results for a circuit that generates 100 kV pulses using 1000 V semiconductors are presented and discussed regarding the voltage and current stress on the semiconductors and result obtained.
- Solid-State Bipolar Marx Generator with Voltage Droop CompensationPublication . Canacsinh, Hiren; Silva, José Fernando; Pinto, Sónia F.; Luis RedondoThis paper addresses the voltage droop compensation associated with long pulses generated by solid-stated based high-voltage Marx topologies. In particular a novel design scheme for voltage droop compensation in solid-state based bipolar Marx generators, using low-cost circuitry design and control, is described. The compensation consists of adding one auxiliary PWM stage to the existing Marx stages, without changing the modularity and topology of the circuit, which controls the output voltage and a LC filter that smoothes the voltage droop in both the positive and negative output pulses. Simulation results are presented for 5 stages Marx circuit using 1 kV per stage, with 1 kHz repetition rate and 10% duty cycle.