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First principle calculation: current density in AC electric fieldZhang, Lei, 張磊 January 2009 (has links)
published_or_final_version / Physics / Master / Master of Philosophy
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Measurement and analysis of critical current and AC loss of HTS tapes in a superconducting machinePei, Ruilin January 2010 (has links)
No description available.
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Programmed harmonic reduction in single phase and three phase voltage-source invertersKumar, Rajiv. January 1996 (has links)
Thesis (M.S.)--Ohio University, August, 1996. / Title from PDF t.p.
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Comprehensive optimization for thermoelectric refrigeration devicesTaylor, Robert A., January 2005 (has links)
Thesis (M.S.)--University of Missouri-Columbia, 2005. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (December 20, 2006) Includes bibliographical references.
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Use of alternating current field measurement (ACFM) technique for sizing internal surface defects on thin-walled austenitic stainless steel pipes /Putra, Wing Hendroprasetyo Akbar, January 1999 (has links)
Thesis (M.Eng.)--Memorial University of Newfoundland, 1999. / Bibliography: leaves 111-113.
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High voltage direct current strategy solving power delivery shortages to localized area of national gridSmith, Johan January 2009 (has links)
Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2009 / The industrial and population growth of a nation can cause power delivery problems to
localized areas of a national grid through their increased demand for electrical energy. One
reason for these power shortages is the insufficient current carrying capacity of existing high
voltage alternating current, (HVAC), transmission lines supplying the area. High voltage
direct current (HVDC) transmission lines are a possible solution as they provide better power
delivery than HVAC lines.
New or upgraded HVAC lines, or HVDC lines or combinations of HVAC and HVDC lines are
possible solutions to improve power delivery. This research investigates the various line
possibilities using theory. and cutting edge frequency and time domain software tools. The
challenge is how to approach this problem. What methodology or structure should be used?
Thus one of the contributions of this work is the development of a strategy (flow chart), for
solving power delivery problems to localized areas of a national grid through individual or
combinations (e.g. parallel operation) of HVAC and/or HVDC transmission lines. The main
contribution is the evaluation of a HVDC system as a solution to overcoming power delivery
shortages to a localized area of a national grid.
Three different software packages (two industrial and one academic) namely,
PSCAD/EMTDC (time domain), DlgSILENT PowerFactory (frequency domain) and MathCAD
software are evaluated for their capability to perform the simulation studies necessary to
prove the possible solutions given in the developed flow chart. The PSCAD/EMTDC software
package is evaluated for integrated HVAC/HVDC load flow analyses, DlgSILENT for
individual and parallel combinations of HVAC lines and MathCAD to prove hand calculations
to software results.
Five case studies are conducted. The first case study demonstrates a healthy system with no
delivery shortcomings, the second case study portrays the delivery shortcoming due to
increased localized area demand, and the remaining three case studies explore possible
solutions to solve the problem. The first possible solution is to construct an identical HVAC
line in parallel to the existing line.
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A load management system for fixed appliances in a safe DC RDP houseJooste, Kritzman Phillip January 2017 (has links)
Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2017. / This dissertation represents the design and development of a load management system for fixed appliances in a safe direct current (DC) Reconstruction and Development Programme (RDP) house. A combination of valley filling, load shifting and peak clipping load management techniques were employed to assist in reducing the peaks observed in the RDP house load profile during peak hours.
A DC RDP house laboratory model was developed. The study is based on the assumption that the normally 220 V alternative current (AC) grid is replaced by a 350 V DC grid. The assumption is thus that 350 V DC is available at the distribution box in the RDP house laboratory model. All theoretical work was based on a 350 V DC system, but due to the lack of a laboratory 350 V DC supply, all physical tests were conducted by making use of a 300 V DC supply which was available. Consequently all calculations were thus based on 300 V DC as well.
The geyser was the main fixed appliance focused on since it contributes to a significant portion of the power used. An AC geyser was successfully modified in order to be used in the DC network. Safety of the system was considered in order to interrupt the power in case of overcurrent or to isolate the power. Electronic switches were also developed and implemented to ensure that the DC power could be safely switched on and off and that the low power DC was isolated from the high power DC.
LabVIEW allowed all other appliances in the DC RDP house to be virtually represented so that a holistic view of the power use of the house could be represented. This also allowed the system to be successfully simulated before any physical work was conducted.
The load management system was successfully implemented by making use of power line communication. This proved to be a cost effective means to apply the load management algorithm. The algorithm consisted mainly of power on / off instructions that were executed during peak and off-peak times. It follows the normal use of timers used in the AC system to help reduce demand.
It was found that the load management system successfully reduced the demand during peak hours without compromising the basic needs of the user. The power line communication modem proved to be very reliable in implementing the load management algorithm.
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Optimalisasie van stelsels met wisselspanningstussenkringmutators as elektroniese koppelstelsels tussen wisselspanningsnette en gelykspanningsnetteFerreira, Jan Abraham 03 April 2014 (has links)
M.Ing. (Electrical and Electronic Engineering) / The possibilities and technology of converters with an alternating voltage link are investigated for high specific power conversion at high frequencies. With a view to the functional description of these power converters, s i muLat i on techniques are considered for both system and circuit analysis. A thorough investigation is made into the design of high frequency power transformers, which play an important role in this class of power circuits. This includes a theoretical analysis in conjunction with the 'practical implementation of a design procedure for minimal eddy current losses in the windings as well as experimental work on losses in ferrite cores. For the remainder of the study, attention is focussed on the two pulse inverter which is responsible for the generation of the alternating voltage in the high frequency link. The suitability of bipolar and field effect transistors for power switching, is critically examined and a voltage compensation on the bipolar Darlington, which reduces on-state losses, yielded good results upon application. A study on the feasibility of non-dissipative snubber techniques on the centre tapped inverter is presented, thus supplying a practical way of reducing switching losses without affecting the efficiency of the system. An additional, yet simple, network is added to the snubber circuits of the two pulse inverter which is operational during low load conditions.' in order also to have low switching losses under these circumstances. Finally a 50 k~v, 10 kHz centre tapped inverter was developed and built.
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The electrolytic production of peroxydisulfuric acid using periodically reversed direct current and alternating current superimposed on direct currentFan, Sin-Chou January 1956 (has links)
It was the purpose of this investigation to study the effect of varying the direct to reverse time ratio of periodically-reversed, direct current from 1.0 to 20.0 at an anode current density of 4.5 amperes per square centimeter, and to study the effect of alternating current of 60, 240, and 500 cycles per second, 0.2 to 4.5 amperes per square centimeter, superimposed on direct current on the electrolytic production of peroxydisulfuric acid.
Electrolyses of 200 milliliters of sulfuric acid of specific gravity 1.4, at a temperature of 5 to 10 °C were performed with direct current. The anode current density was varied. The surface area of platinum anode and lead cathode was 2.0 and 221.8 square centimeters, respectively. For one hour of electrolysis, the yields were 7.9, 14.0, 20.2, and 22.9 grams of peroxydisulfuric acid at the anode current density of 1.5, 3.0, 4.5, and 6.0 amperes per square centimeter, respectively. The current efficiencies corresponding to these anode current densities were 85.0, 77.0, 61.5, and 53.4 per cent. The results showed that the yield was increased and the current efficiency was decreased with increase in the anode current density.
Electrolysis of the same concentration and volume of sulfuric acid using periodically-reversed, direct current yielded 14.2 grams at an anode current density of 4.5 amperes per square centimeter and at a temperature of 5 to 8 °C. The time of electrolysis was one hour and the time ratio of direct to reverse electrolysis was 20. The current efficiency obtained under these conditions was 42.6 per cent. Decreasing the direct to reverse time ratio gave lower yields and current efficiencies. Apparently, there is no advantage in using periodically-reversed, direct current over the use of direct current for this reaction under the above experimental conditions.
Electrolyses of 200 milliliters of sulfuric acid of the same concentration were performed with 60 cycles per second, alternating current superimposed on direct current. The direct current density was 4.5 amperes per square centimeter for the ten tests, but the surface area of the platinum anode was changed from two to one square centimeter and the direct current was decreased from 9.0 to 4.5 amperes. The current efficiency decreased sharply from 61.5 to approximately 31.0 per cent as the ratio of peak alternating to direct current increased from zero to 0.2 and then it remained constant until the ratio reached one. The current efficiency decreased suddenly to almost zero when the ratio was greater than one.
The same sulfuric acid was electrolyzed under the same experimental conditions with 240 and 500 cycles per second, alternating current superimposed on direct current. Both direct and alternating anode current densities were varied. The direct current density was 2.2 and 4.5 amperes per square centimeter. The current efficiencies obtained during these tests were almost the same as that obtained with 60 cycles per second, alternating current within a specific limit of the ratio of peak alternating to direct current. The ratio of peak alternating current to direct current at which the current efficiencies suddenly dropped to zero was 0.75 for 240 cycles per second, and 0.5 for 500 cycles per second, instead of one for 60 cycles per second, superimposed alternating current.
The platinum anode was activated and dissolved into the sulfuric acid when the ratio of peak alternating to direct current was greater than 1.0, 0.75, and 0.5 for 60, 240, and 500 cycles per second, alternating current superimposed on direct current.
Apparently, there is no advantage in using alternating current superimposed on direct current over the use of direct current for electrolytic production of peroxydisulfuric acid. / Master of Science
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Manhattan Converter Family: Partial Power Processing, Module Stacking with Linear Complexity, Efficiency and Power Density, in DC and AC ApplicationsJahnes, Matthew January 2024 (has links)
A modularized three-dimensional power electronics environment will become increasingly necessary as power converters are more intertwined with the dynamic desires of modern society. This is driven by ever-changing requirements, combined with the desire for quick design cycles, and then further compounded by the increased penetration of electrified technologies. The high demand for various power converters presents a design, manufacturing, and validation burden which can be lessened with a three-dimensional power electronics environment, where power converters of any arbitrary set of voltage, current, or quantity of independent input/outpt requirements can be assembled from a grouping of pre-existing converter modules. This, however, has drawbacks when compared with bespoke power converter designs. Modularization can be complex, lossy, and large, and the resulting converter's overall efficiency and power density will then suffer. To compensate for these costs of modularization, the individual modules must be first be power dense and efficient, and then the framework for grouping modules together must be simple.
This dissertation first proposes a high performance Power Conversion Unit (PCU) which is achieved through a unique combination of techniques. The first of these techniques is modification to the ubiqutioius buck converter topology in a form of an adjustment to its output filter. This topological modification results in decreased current ripple handling requirements of the filter, which can be used to reduce its volume. The second topological technique is an additional capacitance placed across the drain-source terminals of each FET, which is used to reduce their turn-off switching energy at the expense of their turn-on switching energy. A variable frequency soft-switching scheme is utitlized to prevent the converter from incurring turn-on losses, and a duty cycle compensation scheme is developed to mitigate the distortions caused by this increased drain-source capacitance. Finally, a process for balancing the PCU design parameters that results in a Pareto frontier of efficiency-power density optimal points is defined, one selected, and a protoype PCU constructed and tested in a three-phase inverter configuration.
A framework for the vertical stacking of PCUs is then shown. This framework, named the Manhattan Topology, is a multilevel power converter topology which is defined by a set of series stacked capacitances where there exists a method to transfer power between capacitances. This framework has linear complexity and switching device stress scaling with the number of levels, which yields a simple methodology for grouping modules together in the vertical dimension. Furthermore, it exhibits Partial Power Processing (PPP) characteristics as the power processed internally to the overall converter is less than its output power. This framework is validated for both DC/DC and AC/DC applications and control and conversion of voltages greater than the rating of any individual component within the converter is experimentally demonstrated. Lastly, another three-phase inverter is built using this topological framework and the performance of this vertically-modularized inverter is compared with the non-modularized inverter. It is shown that the three-dimensional modular power electronics environment with optimized PCUs, despite the costs of modularization, is still performance-competitive with the non-modular power electronics environment.
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