Browsing by Author "Dixon, JW"

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    A series active power filter based on a sinusoidal current-controlled voltage-source inverter
    (1997) Dixon, JW; Venegas, G; Moran, LA
    A series active power filter working as a sinusoidal current source, in phase with the mains voltage, has been developed and tested. The amplitude of the fundamental current in the series filter is controlled through the error signal generated between the load voltage and a preestablished reference. The control allows an effective correction of power factor, harmonic distortion, and load voltage regulation. Compared with previous methods of control developed for series active filters, this method is simpler to implement, because it is only required to generate a sinusoidal current, in phase with the mains voltage, the amplitude of which is controlled through the error in the load voltage. The proposed system has been studied analytically and tested using computer simulations and experiments. In the experiments, it has been verified that the filter keeps the line current almost sinusoidal and in phase with the line voltage supply. It also responds very fast under sudden changes in the load conditions, reaching its steady state in about two cycles of the fundamental.
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    A simple frequency-independent method for calculating the reactive and harmonic current in a nonlinear load
    (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 1996) Tepper, JS; Dixon, JW; Venegas, G; Moran, L
    A basic criterion that determines the behavior of an active power filter is the method of calculating the reference current, There are many ways of generating this reference, but the methods are generally complex and hard to tune, This paper describes a simple and effective method for calculating the reference current, necessary to feed a shunt active power filter to compensate the power factor and harmonic currents generated by a nonlinear load. Simulations and experimental results are presented, showing that the proposed circuit may operate at frequencies ranging from 40 to 65 Hz without adjustment.
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    Control system for three-phase active power filter which simultaneously compensates power factor and unbalanced loads
    (1995) Dixon, JW; Garcia, JJ; Moran, L
    The effectiveness of an active power filter depends basically on three characteristics: a) the modulation method used; b) the design characteristics of the PWM modulator; and c) the method implemented to generate the reference template, For the last characteristic there are many methods, most of them complicated and hence difficult to implement and adjust, In this paper, a new method, which has simplicity at its main characteristic, is presented, The method is based on ''Sample and Hold'' circuits, synchronized with the peak value of the phase-to-neutral mains voltage, This method is useful for shunt active power filters and is capable to eliminate harmonics, compensate power factor, and correct unbalance problems simultaneously. It also has the ability to slow down sudden transient changes in the load. Experimental results, with the reference template obtained with the method, are presented in the paper.
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    Improving passive filter compensation performance with active techniques
    (IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2003) Rivas, D; Moran, L; Dixon, JW; Espinoza, JR
    This paper presents the performance analysis of a hybrid filter composed of passive and active filters connected in series. The analysis is done by evaluating the influence of passive filter parameters variations and the effects that different active power filter's gain have in the compensation performance of the hybrid scheme. The compensation performance is quantified by evaluating the attenuation factor in a power distribution system energizing high-power nonlinear loads compensated with passive filters and then improved with the connection of a series active power filter. Finally, compensation characteristics of the hybrid topology are tested on a 10-kVA experimental setup.
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    Induction motor speed estimator and synchronous motor position estimator based on a fixed carrier frequency signal
    (1996) Dixon, JW; Rivarola, JN
    A speed and position estimator, based on the introduction of a constant-frequency carrier signal (400-1000 Hz) in the stator currents has been developed. Speed and position are estimated through the detection of irregularities in the rotor and, hence, the results are independent of machine parameters, These irregularities generate amplitude oscillations ire the currents generated by the high frequency carrier, which are proportional to the rotor position. At the same time, the frequency of these amplitude modulations is proportional to machine speed. In induction machines, the amplitude of these signals is too low to estimate position accurately. However, special electronic circuits, designed and implemented with analog multipliers and filters, have permitted measurement of very low speeds with high precision, Computer simulations and some experiments have been carried out, and they have shown that it is possible to measure speeds as low as 20 r/min, In the case of salient-pole synchronous machines, the method is useful to measure rotor position due to the high irregularities produced by the poles, which are easily computed because of the important amplitude variations detected in the high frequency carrier.
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    Open-loop VAr compensator for industrial applications, using a single PWM pattern
    (IEE-INST ELEC ENG, 1997) Dixon, JW; Veas, DR
    The authors present the analysis of an open-loop, three-phase static VAr compensator (SVC) based on a voltage source inverter, using only one fixed pulse width modulation (PWM) pattern. The VAr generation is controlled by shifting this PWM pattern according to the AC-mains voltage. Because the system is naturally stable, there is no need to control the capacitor DC voltage, which takes a particular stable voltage for each power factor operation condition. To prove this particular behaviour, a stability analysis, based on the d-q frame is developed. From this analysis, the circle diagram of the VAr compensator is obtained, which gives all the operating characteristics related to the DC voltage, power angle operation, and reactive power generated. The main characteristics of this compensator are its simplicity and its strong stability, which are particularly suitable for use in industrial loads, such as induction motors, thyristor rectifiers and other low power factor loads. This open-loop system is suitable in the range 1-20kvar. The experimental results confirm the operating characteristics given by computer simulations and analysis.
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    Ultracapacitors plus DC-DC converters in regenerative braking system
    (2002) Dixon, JW; Ortúzar, ME
    An ultracapacitor system for an electric vehicle has been implemented. The purpose of this device is to allow higher accelerations and decelerations of the vehicle with minimal loss of energy and minimal degradation of the main battery pack. The system uses a dc-dc power converter, which is connected between the ultracapacitor and the main battery pack. The design has been optimized in weight and size, by using water-cooled heat sinks for the power converter, and an aluminum coil with air core for the smoothing inductance. The ratings of the ultracapacitor are: nominal voltage: 300 Vdc; nominal current: 200 Adc; capacitance: 20 Farads. The amount of energy stored allows us to have 40 kW of power during 20 seconds, which is enough to accelerate the vehicle without the help of the traction batteries. The vehicle uses a brushless dc motor with a nominal power of 32 kW and a peak power of 53 kW. A control system based on a Digital Signal Processor (DSP) manipulates all the aforementioned variables and controls the Pulse Width Modulation (PWM) switching pattern of the converter transistors. The car used for the implementation of this system is a Chevrolet LUV truck, similar in shape and size to a Chevrolet S-10 which was converted to an electric vehicle at the Catholic University of Chile.