Browsing by Author "Morán, Luis"

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    A clean four-quadrant sinusoidal power rectifier using multistage converters for subway applications
    (2005) Dixon, Juan; Morán, Luis
    A special 27-level four-quadrant rectifier for subway applications is analyzed. The arrangement uses only three H-bridges per phase, common dc bus, and independent input transformers for each H-bridge. The transformers allow galvanic isolation and power escalation to obtain high-quality voltage waveforms, with total harmonic distortion of less than 1%. Some advantages of this 27-level rectifier are: 1) only one of the three H-bridges, called the main converter, manages more than 80% of the total active power in each phase and 2) it switches at fundamental frequency, reducing the switching losses at a minimum value. The rectifier analyzed in this paper is a current-controlled voltage-source type, with a conventional feedback control loop. Some simulations in a rectifier substation, including power reversal at full load are displayed (750 Vdc, 1200 A). The rectifier shows the ability to produce clean ac and dc waveforms without any ripple, and fast reversal of power. Some experimental results with a small prototype, showing voltage and current waveforms, are finally displayed.
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    A full compensating system for general loads, based on a combination of thyristor binary compensator, and a PWM-IGBT active power filter
    (IEEE, 2001) Dixon Rojas, Juan, 1948-; Del Valle, Yamille; Orchard, Marcos; Ortúzar Dworsky, Micah Etan; Morán, Luis; Maffrand, Carlos
    A full compensating system for distribution networks which is able to eliminate harmonics, correct unbalanced loads and generate or absorb reactive power is presented. The system is based on a combination of a thyristor binary compensator (TBC), and a PWM-IGBT active power filter (APF) connected in cascade. The TBC compensates the fundamental reactive power and balances the load connected to the system. The APF eliminates the harmonics and compensates the small amounts of load unbalances or power factor that the TBC cannot eliminate due to its binary condition. The TBC is based on a chain of binary-scaled capacitors and one inductor per phase. This topology allows, with an adequate number of capacitors, a soft variation of reactive power compensation and a negligible generation of harmonics. The capacitors are switched on when the line voltage reaches its peak value, avoiding inrush currents generation. The inductor helps to balance the load, and absorbs reactive power when required. The APF works by measuring the source currents, forcing them to be sinusoidal. The two converters (TBC and APF) work independently, making the control of the system simpler and more reliable. The system is able to respond to many kinds of transient perturbations in no more than a couple of cycles. The paper analyzes the circuit proposed, the way it works and the results obtained under operation with different types of loads.
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    Voltage source active power filter, based on multi-stage converter and ultracapacitor dc-link
    (IEEE, 2003) Ortúzar Dworsky, Micah Etan; Carmi, Rodrigo; Dixon Rojas, Juan; Morán, Luis
    A multi-stage inverter using three-state converters is being analyzed for active filter and static var compensator applications. Each phase of the converter is composed of four three-state converters, all of them connected to the same dc link and its output connected through output transformers scaled in power of three. The filter can compensate load currents with high harmonic content and low power factor, obtaining sinusoidal currents from the source. A 1F ultracapacitor is used in the dc link, making it possible to obtain a very stable voltage at the dc bus, even with highly contaminated currents. This high capacity also makes it possible to continue feeding the contaminating load during a voltage dip. The capacitor voltage is controlled simply by changing the phase angle of the converter, and thus changing the amount of active current flowing to and from the converter. The control is implemented with a non-linear PI gain and a modulation control to maintain a stable ac voltage during dc voltage drops. The great advantage of this kind of converter is the minimum harmonic distortion obtained. Simulation results for this application are shown and compared with similar results obtained with conventional PWM converters.