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DC analysis of quasi-resonant buck and forward converters including effects of parasitic elementsRoufberg, Lewis Marlin 20 November 2012 (has links)
The need for smaller and more efficient power supplies steadily grows. Many power supplies incorporate high-frequency dc-to-dc switching converters to meet these demands. Recently, a new class of switching converters has been introduced which can operate at very high frequencies to further reduce size and increase efficiency. They are called quasi-resonant converters. Previously, the dc characteristics of many of these converters had been determined, assuming ideal components and circuit operating conditions. However, as the frequency of operation increases, the circuit behavior becomes less ideal causing changes in the expected characteristics. This is because resistive losses, semiconductor junction capacitances, and other parasitic (undesirable) elements become more pronounced at higher frequencies.
This thesis investigates the effects of parasitic elements on the dc characteristics of several zero-current-switched, buck-derived quasi-resonant converters. For the quasi-resonant buck converter, it is demonstrated that for certain operating conditions the dc voltage gain can increase when parasitic losses are increased. Design guidelines are given for maximizing this converter's efficiency. Various forward quasi-resonant topologies are investigated, and the effects of parasitic elements on circuit operation are highlighted. A dc analysis is performed for the secondary-resonance forward converter, which has not previously been analyzed. This converter can operate either in full-wave or half-wave mode. Its dc voltage gain in full-wave mode is less sensitive to load variations than other resonant forward topologies that only operate in half-wave mode. / Master of Science Read more
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Design and implementation of a modular converter with application to a solid state transformerWolf, Marko 12 1900 (has links)
Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: The purpose of a solid state transformer (SST) is to use power electronic converters to mimic
the operation of the conventional distribution transformer. These power electronic converters
are proposed to overcome the disadvantages of the conventional distribution transformer. The
advantages of a SST include near perfect voltage regulation and harmonic isolation between the
primary and secondary windings of the transformer.
This thesis discusses the design and development of the different converters in a solid state
transformer (SST). A prototype modular back-to-back converter is developed for the input and
isolation stage of the SST. The isolation stage consists of a high voltage DC-DC converter, which
transfers power across the isolation barrier of the SST. This stage is evaluated in the laboratory
with special attention being paid to the efficiency of the converter.
The second aspect that this thesis addresses is the output stage of the SST, namely a three
phase inverter. The discussion of the output stage focuses on the losses occurring in the inverter.
The switching device losses are calculated by means of an adapted numerical method as opposed
to using conventional analytical methods. The presented numerical method is compared to the
existing analytical method and the findings are discussed.
A double loop control strategy is implemented for the output stage inverter. The inner
current loop utilizes a predictive control strategy. The control analysis of the double loop
controller is discussed and evaluated in the laboratory. All the converters that are discussed in
this thesis are evaluated in the laboratory and the relevant measurements are included. / AFRIKAANSE OPSOMMING: Die doel van ’n drywingselektroniese transformator (DET) is om drywingselektroniese omsetters
te gebruik om die werking van die konvensionele distribusietransformator na te boots. Hierdie
drywingselektroniese omsetters word voorgestel ten einde die nadele van die konvensionele distribusietransformator
te bowe te kom. Die voordele van ’n DET sluit in: feitlik perfekte regulering
van spanning en harmoniese isolasie tussen die primˆere en sekondˆere windings van die
transformator.
Hierdie tesis bespreek die ontwerp en ontwikkeling van die verskillende omsetters in ’n drywingselektroniese
transformator (DET). ’n Prototipe modulˆere rug-aan-rug-omsetter word ontwikkel
vir die intree- en isolasiefase van die DET. Die isolasiefase bestaan uit ’n hoogspanning-
GS-GS omsetter, wat drywing oor die isolasiegrens van die DET heen oordra. Hierdie omsetter
word in die laboratorium ge¨evalueer met besondere aandag aan die doeltreffendheid van die
omsetter.
Die tweede aspek waarna in hierdie tesis gekyk word, is die uittreefase van die DET, naamlik
’n driefaseomsetter. Die bespreking van die uittreefase fokus egter op die verliese wat in die omsetter
voorkom. Die verliese van die skakelaars word bereken deur middel van ’n aangepaste numeriese
metode teenoor die gebruik van konvensionele analitiese metodes. Die numeriese metode
wat aangebied word, word vergelyk met die bestaande analitiese metode en die bevindings word
bespreek.
’n Dubbellus-beheerstrategie word vir die uittreefase-omsetter ge¨ımplementeer. Die binneste
stroomlus word ge¨ımplementeer deur van ’n voorspelbare beheerstrategie gebruik te maak. Die
beheeranalise van die dubbellusbeheerder word bespreek en in die laboratorium ge¨evalueer. Al
die omsetters wat in hierdie tesis bespreek word, word in die laboratorium ge¨evalueer en die
relevante metings word ingesluit. Read more
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A nano-CMOS based universal voltage level converter for multi-VDD SoCs.Vadlmudi, Tripurasuparna 05 1900 (has links)
Power dissipation of integrated circuits is the most demanding issue for very large scale integration (VLSI) design engineers, especially for portable and mobile applications. Use of multiple supply voltages systems, which employs level converter between two voltage islands is one of the most effective ways to reduce power consumption. In this thesis work, a unique level converter known as universal level converter (ULC), capable of four distinct level converting operations, is proposed. The schematic and layout of ULC are built and simulated using CADENCE. The ULC is characterized by performing three analysis such as parametric, power, and load analysis which prove that the design has an average power consumption reduction of about 85-97% and capable of producing stable output at low voltages like 0.45V even under varying load conditions.
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Development of a universal bidirectional galvanic isolated switch module for power converter applicationsMokhalodi, Kopano 06 1900 (has links)
M. Tech. (Engineering: Electrical, Department Electronic Engineering, Faculty of Engineering and Technology), Vaal University of Technology / The global trends towards energy efficiency have facilitated the need for
technological advancements in the design and control of power electronic converters
for energy processing. The proposed design is intended to make the practical
implementation of converters easier.
The development of a universal bidirectional galvanic isolated switch module will be
used to drive any MOSFET or IGBT in any position in any topology whether the
load is AC or DC. Semiconductor switches are required and are also integrated for
fast switching times in power converter applications
The structure of the power switch module consists of an opto-coupler which will
provide an isolation barrier for maximum galvanic isolation between the control
circuitry and power stage. It also consists of a high performance gate drive circuit
for high speed switching applications with a floating supply. / Telkom South Africa Ltd, TFMC Pty Ltd, M-TEC, THRIP
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TIMR : Time Interleaved Multi RailRuggeri, Thomas L. 19 April 2012 (has links)
This work presents a new energy saving technique for modern digital designs. We propose Time Interleaved Multi-Rail (TIMR) - a method for providing two dynamic supply rails to a circuit. This technique uses the first supply rail to mask the transition delay while changing the voltage of the second rail. We examine the design of TIMR as well as the implementation and considerations. We propose a number of control schemes that range from traditional DVFS to "race to sleep". This thesis also shows simulations of the technique using a existing voltage regulator in order to find the time and energy overhead of implementing the design. We find a 100μs switching time delay and 118μJ energy overhead associated with changing the voltage rail. This work concludes with comparisons to current energy saving techniques. / Graduation date: 2012
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Direct AC control of grid assetsSastry, Jyoti 20 May 2011 (has links)
The objective of the proposed research is to investigate feasible approaches to dynamic control of the power grid. Growth in the demand for electric power, and an increase in the penetration of renewable energy resources are causing congestion on an already aging power grid. Conventional grid control involves the use of static assets that operate on long time scales. These assets provide no dynamic control on the grid, and are typically used for scheduled support. Existing solutions (FACTS devices) to dynamic grid control have seen minimal market penetration because of high cost and low reliability. The proposed research provides a solution for dynamic control of the power grid that augments existing grid assets with a thin AC converter (TACC) to realize enhanced dynamic control. The TACC is a direct AC converter with filter elements and no bulk energy storage that dynamically reflects the asset value on the grid. The converter has a fail-normal mode of operation that returns the asset to its initial operating state, thereby not degrading system reliability. Some applications of TACCs include Inverter-Less STATCOMs and Controllable Network Transformers, which are realized by augmenting shunt VAR capacitors and load tap changers respectively. The principle of virtual quadrature sources is proposed to enable conditioning of AC voltages and currents. The concept is a novel method to realize control of phase angle and, or harmonics in single-phase AC converters, with no bulk energy storage. This concept is used to control the TACC and provides the asset with significantly enhanced control capabilities. Scaling of the TACC to utility voltage and power levels has been addressed by proposing a novel multilevel direct AC converter. The concept proposes the use of commercially available low cost semiconductor devices to realize high power converters. The specific application chosen to validate the concept of TACCs, through a medium voltage design, is the Inverter-less STATCOM. Read more
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Modelling a new electrical conversion chain for railways applicationsGrave, Justin. January 2012 (has links)
M. Tech. Electrical Engineering. / Aims to develop these railways applications for a better use of the electrical power to reduce pollution and consumption. The specification of this project is to improve the conversion of the electrical energy. This also involves improving the connection between the train and the electrical networks using the pantograph. In this research, I will propose a new architecture for the converters and a structure to provide to the grid the electricity generated through braking. Another point regards the command of the converters, which is directly involved in the system behaviour. In order to obtain the best behaviour possible, a different control as usual will be described and modelled to reduce the total harmonics distortion rate and reach a better efficiency.
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High-power bi-directional DC/DC converters with controlled device stressesHan, Sangtaek 11 May 2012 (has links)
The objective of the research is to develop a cost-effective high-power bi-directional dc/dc converter with low total-device ratings, reduced system parasitic effects, and a wide input/output range. Additional objectives of the research are to develop a small-signal model and control methods, and to present performance characterizations. Device stresses in the proposed topology are controlled to maintain minimal levels by varying the duty ratio and phase-shift angle between the primary and the secondary bridges, which results in a low total-device rating, when compared to conventional bi-directional dc/dc topologies. In the proposed topology, soft switching, which reduces power loss, can be realized under specific operating conditions. When the condition that causes minimal device stress is satisfied, zero-voltage switching (ZVS) can be obtained. In the research, ZVS capability is explored for a wide range of voltage conditions as well as for the minimal device-stress condition. The performance characterization includes verifying the soft-switching regions and power-loss estimation. Another part of the thesis is the controller design of the converter. Small-signal models and feedback controllers are developed, and the controllers are experimentally validated. Because in the isolated high-frequency converters, transformer saturation is an important issue, a method to prevent transformer saturation is proposed and experimentally validated. Read more
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New current sensing solutions for low-cost high-power-density digitally controlled power convertersZiegler, Silvio January 2009 (has links)
[Truncated abstract] This thesis studies current sensing techniques that are designed to meet the requirements for the next generation of power converters. Power converters are often standardised, so that they can be replaced with a model from another manufacturer without an expensive system redesign. For this reason, the power converter market is highly competitive and relies on cutting-edge technology, which increases power conversion efficiency and power density. High power density and conversion efficiency reduce the system cost, and thus make the power converter more attractive to the customer. Current sensing is a vital task in power converters, where the current information is required for monitoring and control purposes. In order to achieve the above-mentioned goals, existing current sensing techniques have to be improved in terms of cost, power loss and size. Simultaneously, current information needs to be increasingly available in digital form to enable digital control, and to allow the digital transmission of the current information to a centralised monitoring and control unit. All this requires the output signal of a particular current sensing technique to be acquired by an analogue-to-digital converter, and thus the output voltage of the current sensor has to be sufficiently large. This thesis thoroughly reviews contemporary current sensing techniques and identifies suitable techniques that have the potential to meet the performance requirements of the next-generation of power converters. After the review chapter, three novel current sensing techniques are proposed and investigated: 1) The usefulness of the resistive voltage drop across a copper trace, which carries the current to be measured, to detect electrical current is evaluated. Simulations and experiments confirm that this inherently lossless technique can measure high currents at reasonable measurement bandwidth, good accuracy and low cost if the sense wires are connected properly. 2) Based on the mutual inductance theory found during the investigation of the copper trace current sense method, a modification of the well-known lossless inductor current sense method is proposed and analysed. This modification involves the use of a coupled sense winding that significantly improves the frequency response. Hence, it becomes possible to accurately monitor the output current of a power converter with the benefits of being lossless, exhibiting good sensitivity and having small size. 3) A transformer based DC current sense method is developed especially for digitally controlled power converters. This method provides high accuracy, large bandwidth, electrical isolation and very low thermal drift. Overall, it achieves better performance than many contemporary available Hall Effect sensors. At the same time, the cost of this current sensor is significantly lower than that of Hall Effect current sensors. A patent application has been submitted. .... The current sensing techniques have been studied by theory, hardware experiments and simulations. In addition, the suitability of the detection techniques for mass production has been considered in order to access the ability to provide systems at low-cost. Read more
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Modeling and control of fuel cell based distributed generation systemsJung, Jin Woo, January 2005 (has links)
Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xvi, 209 p.; also includes graphics. Includes bibliographical references (p. 202-209). Available online via OhioLINK's ETD Center
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