Browsing by Author "Dixon, J"

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    A fault protection scheme for series active power filters
    (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 1999) Moran, LA; Pastorini, I; Dixon, J; Wallace, R
    A protection scheme for series active power filters is presented and analyzed in this paper. The proposed scheme protects series active power filters when short-circuit faults occur in the power distribution system. The principal protection element is a varistor, which is connected in parallel to the secondary of each current transformer. The current transformers used to connect in series the active power filter present a low-magnetic saturation characteristic increasing current ratio error when high currents circulate through the primary winding, thus generating lower secondary currents. In this way, the power dissipated by the varistors is significantly reduced. After a few cycles of short-circuit currents flowing through the varistor, the gating signals applied to the active power filter switches are removed and the pulsewidth-modulation (PWM) voltage-source inverter (VSI) is short circuited through a couple of antiparallel thyristors.
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    A simple control scheme for hybrid active power filter
    (INST ENGINEERING TECHNOLOGY-IET, 2002) Rivas, D; Moran, L; Dixon, J; Espinoza, J
    A simple control scheme for hybrid active power filters connected in parallel is presented and analysed. The hybrid active power filter combines the compensation characteristics of resonant passive and active power filters. The series active power filter is implemented with a three-phase pluse-width modular (PWM) voltage-source inverter. The proposed scheme is able to compensate displacement power factor and current harmonics simultaneously. The combination of passive and active power filters allows a better performance compensation of high-power nonlinear loads. The proposed control scheme is discussed in tenus of principles of operations under steady-state and transient conditions. The design and implementation of the power and control circuits are reported. Finally, key predicted results are verified experimentally on a 5 kVA prototype model.
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    Practical evaluation of different modulation techniques for current-controlled voltage source inverters
    (INST ENGINEERING TECHNOLOGY-IET, 1996) Dixon, J; Tepper, S; Moran, L
    The quality of the current waveform generated by a current-controlled, voltage source inverter, depends basically on three factors: (a) the switching frequency of the PWM modulator; (b) the type of current waveform being generated; and (c) the modulation method used. In the paper, three modulation methods, whose characteristics are their simplicity, are analysed: periodical sampling control, hysteresis band control, and triangular carrier control. These three methods have been tested with three different waveform templates: sinusoidal, quasisquare and rectifier compensation current. They are compared in terms of the harmonic content and distortion at the same switching frequency. The paper shows that for sinusoidal current generation, the best method is the triangular carrier, followed by the hysteresis band and the periodical sampling. However, for the other two types of reference templates, the analysis showed that, depending on external factors such as inverter inductance, type of load, or delays in the PWM switching signals, one strategy may be better than the others. The paper shows that each control method is affected in a different way by the switching time delays present in the driving circuitry and in the power semiconductors. The results are analysed and compared, with the help of computer simulations and experimental results.
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    Series active power filter compensates current harmonics and voltage unbalance simultaneously
    (INST ENGINEERING TECHNOLOGY-IET, 2000) Moran, L; Pastorini, I; Dixon, J; Wallace, R
    An active power filter connected in series to the power distribution system is presented and analysed, The series active power filter is implemented with a three-phase PWM voltage-source inverter and operates with a resonant LC passive filter connected in parallel to the power lines. The proposed scheme is able to simultaneously compensate current harmonics, the fundamental negative and zero sequence voltage components generated by the voltage source unbalance, and also eliminates the zero sequence current harmonic components that circulate through the neutral conductor. The active power filter is discussed in terms of the principles of operation under steady-state and transient conditions. The design and implementation of the power and control circuits are reported. Key predicted results are verified experimentally on a 5kVA prototype model.