Browsing by Author "Ortúzar Dworsky, Micah Etan"

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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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    Electric Vehicle Using a Combination of Ultracapacitors and ZEBRA Battery
    (2010) Dixon Rojas, Juan; Nakashima Dueñas, Ian; Arcos Fuentes, Eduardo Fabián; Ortúzar Dworsky, Micah Etan
    The sodium-nickel chloride battery, commonly known as ZEBRA, has been used for an experimental electric vehicle (EV). These batteries are cheaper than Li-ion cells and have a comparable specific energy (in watt-hours per kilogram), but one important limitation is their poor specific power (in watts per kilogram). The main objective of this paper is to demonstrate experimentally that the combination of ZEBRA batteries and ultracapacitors (UCAPs) can solve the lack of specific power, allowing an excellent performance in both acceleration and regenerative braking in an EV. The UCAP system was connected to the ZEBRA battery and to the traction inverter through a buck-boost-type dc-dc converter, which manages the energy flow with the help of DSP controllers. The vehicle uses a brushless dc motor with a nominal power of 32 kW and a peak power of 53 kW. The control system measures and stores the following parameters: battery voltage, car speed to adjust the energy stored in the UCAPs, instantaneous currents in both terminals (battery and UCAPs), and present voltage of the UCAP. The increase in range with UCAPs results in more than 16% in city tests, where the application of this type of vehicle is being oriented. The results also show that this alternative is cheaper than Li-ion powered electric cars.
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    Energy-management system for a hybrid electric vehicle, using ultracapacitors and neural networks
    (2006) Moreno de la Carrera, Jorge Alejandro; Ortúzar Dworsky, Micah Etan; Dixon Rojas, Juan
    A very efficient energy-management system for hybrid electric vehicles (HEVs), using neural networks (NNs), was developed and tested. The system minimizes the energy requirement of the vehicle and can work with different primary power sources like fuel cells, microturbines, zinc-air batteries, or other power supplies with a poor ability to recover energy from a regenerative braking, or with a scarce power capacity for a fast acceleration. The experimental HEV uses lead-acid batteries, an ultracapacitor (UCAP) bank, and a brushless dc motor with nominal power of 32 kW, and a peak power of 53 kW. The digital signal processor (DSP) control system measures and stores the following parameters: primary-source voltage, car speed, instantaneous currents in both terminals (primary source and UCAP), and actual voltage of the UCAP. When UCAPs were installed on the vehicle, the increase in range was around 5.3% in city tests. However, when optimal control with NN was used, this figure increased to 8.9%. The car used for this experiment is a Chevrolet light utility vehicle (LUV) truck, similar in shape and size to Chevrolet S-10, which was converted to an electric vehicle (EV) at the Universidad Catolica de Chile. Numerous experimental tests under different conditions are compared and discussed.
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    Ultracapacitor-Based Auxiliary Energy System for an Electric Vehicle: Implementation and Evaluation
    (IEEE, 2007) Ortúzar Dworsky, Micah Etan; Moreno De La Carrera, Jorge Alejandro; Dixon, Juan
    In the search for better efficiency, an auxiliary energy system (AES) for electric vehicles (EVs) was designed, implemented, and tested. The system, which is composed of an ultracapacitor bank and a buck-boost converter, was installed in an EV, which is powered by a lead-acid battery pack and a 54-kW brushless dc motor. Two control strategies where developed: one based on heuristics and the other based on an optimization model using neural networks. These strategies were translated to algorithms and implemented in a digital signal processor, and their performance was evaluated in urban driving. The results were incorporated to an economic evaluation of the system, which shows that the reduction in costs would only justify the inclusion of this type of system in a lead-acid battery-powered vehicle if the battery life is extended by 50% or more, which is unlikely. The same results were extrapolated to a case in which the lead-acid batteries are replaced by a fuel cell. In this case, the costs of different power support systems were evaluated, such as ultracapacitors and high-specific-power lithium-based batteries. The results showed a significant cost reduction when AES configurations are included in contrast to a system powered by fuel cells only. Also, the cost reduction was higher when using ultracapacitors for this purpose.
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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.
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    Voltage-source active power filter based on multilevel converter and ultracapacitor DC link
    (2006) Ortúzar Dworsky, Micah Etan; Carmi, R. E.; Dixon Rojas, Juan; Moran, L.
    A new topology for active power filters (APF) using an 81-level converter is analyzed. Each phase of the converter is composed of four three-state converters, all of them connected to the same capacitor dc link voltage and their output connected in series through output transformers. The main advantages of this kind of converter are the negligible harmonic distortion obtained and the very low switching frequency operation. The single-phase equivalent circuit is analyzed and their governing equations derived. The dc link voltage control, based on manipulating the converter's voltage phase, is analyzed together with the circuit's characteristics that determine the capability to draw or deliver active and reactive current. Simulation results for this application are compared with conventional pulsewidth-modulated (PWM) converters, showing that this filter can compensate load current harmonics, keeping better-quality sinusoidal currents from the source. The simulated configuration uses a 1-F ultracapacitor in the dc link, making it possible to store energy and deliver it during short voltage dips. This is achieved by applying a modulation control to maintain a stable ac voltage during dc voltage drops. A prototype of the filter was implemented and tested, and the obtained current waveforms showed to be as good as expected.