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A three-phase AC/AC matrix converter systemGebrehiwet Gebregergis, Abraham 12 1900 (has links)
Thesis (MScIng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: The thesis discusses the analysis and design of a three-phase-to-three-phase direct
AC-AC matrix converter. A background study of the various matrix converter topologies
and their modulation strategies are presented. The associated PWM strategy of each
matrix converter topology is investigated. In addition, a detailed explanation of the three
safe commutation strategies is presented.
The research focuses on the design and analysis of the direct AC-AC matrix converter
topology. That includes the design of the main bi-directional power converter circuit,
gate drive circuit, current direction detection circuit, voltage measurement circuit and
protection circuitry. Moreover, it covers the development of the direct control algorithm
based on the four-step safe current commutation- and the two-step voltage
commutation strategy. A “PEC33” controller board is used to implement the developed
control algorithm. Furthermore, simulation results of the direct and the indirect matrix
converter topologies are presented.
The results obtained from the experimental test performed on the direct AC-AC matrix
converter topology are also presented. The conclusion drawn is discussed at the final
stage of the report. / AFRIKAANSE OPSOMMING: Hierdie tesis bevat die analise en ontwerp van ‘n drie-fase na drie-fase direkte WS-WS
matriksomsetter. ‘n Agtergrondstudie van verskeie ander matriksomsetter topologieë
word aangebied. Die ge-assosieerde PWM beheerstrategie van elke matriksomsetter
topologie is ondersoek. Hierby word ‘n gedetaileerde verduideliking van drie veilige
kommutasie strategieë ingesluit.
Die navorsing fokus op die ontwerp en analise van die direkte WS-WS matriksomsetter
topologie. Dit sluit die volgende in: die ontwerp van die hoof bi-direksionele
drywingsomsetterbaan; die hek aandryfbaan; die stroomrigting deteksiebaan; die
spanningsmeetbaan en die beveiliging stroombane. Dit dek ook die ontwikkeling van die
direkte beheeralgoritme wat gebasseer is op die vier-stap veilige stroomkommutasie- en
die twee-stap spanningskommutasie strategie. ‘n “PEC33” beheerkaart is gebruik om
hierdie beheeralgoritme te implementer. Simulasie resultate van beide die direkte sowel
as die indirekte matriksomsetter topologieë word ingesluit.
Die eksperimentele resultate wat met die direkte WS-WS matriksomsetter topologie
verkry is word aangebied en bespreek. Die gevolgtrekking word in die finale afdeling
van die verslag bespreek.
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A power electronic converter for high voltage step down DC-DC conversion09 November 2010 (has links)
M.Ing.
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Investigation of modulation dynamics and control of modular multilevel converter for high voltage DC gridsNampally, Ashok January 2017 (has links)
Energy security concerns and the impact of traditional sources of power generation on the climate have prompted a rise in renewable energy expansion around the world. Power transmission from remote generation sites to consumers over long distance is most efficient using High-Voltage Direct Current (HVDC) transmission lines. Consequently, HVDC and the integration of renewable resources are considered as key perspectives in the improvement of sustainable energy systems capable of secure and stable electric power supply. With the intention of huge energy demand in the future, the multi-terminal DC grid concept is proposed based on various converter topologies like Line Commutated Converter (LCC), Voltage Sourced Converter (VSC), and Modular Multilevel Converter (MMC) HVDC technologies. These converters play a vital role in integrating remotely-located renewable generation and reinforcing existing power systems. The MMC has become increasingly popular in HVDC transmission compared to conventional line commutated converters, two-level and multilevel voltage source converters. Low generation of harmonics, a low switching frequency of semiconductors, sine formed AC voltages and currents, black start capability and higher overall efficiency are a few of the unique features of MMC. The MMC is characterised by a modular arm structure, formed by a cascade connection of a vast number of simple cells with floating DC capacitors. These cells are called Sub-Modules (SMs) and can be easily assembled into a converter for high voltage power conversion systems. Compared with traditional VSCs, the analytical modelling of MMC is more challenging. This is because of technical issues such as higher order system, the discontinuous and non-linear nature of signal transfer through converters, the complexity of the interaction equations between the AC and DC variables, and harmonic frequency conversion through AC side and DC side of the converter. This work intends to resolve these challenges by developing a detailed non-linear model using fundamental switching Selective Harmonic Elimination (SHE) modulation technique, an average MMC model in DQ0 frame and an analytical dynamic MMC model, which can be suitable for small-signal stability studies, and control design. Firstly, the detailed model of MMC using fundamental switching SHE modulation scheme has been developed using PSCAD/EMTDC (Power systems computer aided design Electromagnetic transients for DC) software. The basic terms and equations of the MMC have been presented along control loops. The significance of the switching frequency on the performance of the MMC has been studied as well as the relation between the switching frequency, the Total Harmonic Distortion (THD) and the number of output voltage levels. Detailed representation of MMC systems in PSCAD/EMTDC programs incorporates the modelling of Insulated-Gate Bipolar Transistor (IGBT) valves and should typically utilise small integration time-steps to represent fast switching events precisely. Computational burden introduced by such detailed models make the study of steady-state and transient events more complex, highlighting the need to implement more efficient models that provide comparative behaviour and dynamic response. Secondly, average DQ0 models has been implemented to accurately replicate the steady-state, dynamic and transient behaviour of MMC in PSCAD/EMTDC programs. These simplified models represent the average response of switching devices and converters by using averaging techniques involving controlled sources and switching functions. Developing the MMC average model in DQ0 frame was a challenging task because of the multiplication terms in the MMC average model in ABC frame. The proposed approach to overcome this challenge is considering generic form for the product variables and multiplying them in ABC frame and then transferring only the DC and fundamental frequency components of the results to DQ0 frame. The comparisons between detailed model and the average model validated the effectiveness of the average model in representing the dynamics of MMC. It is at least one hundred times faster than the detailed model for the same simulation time step. Finally, a dynamic analytical MMC model and associated controls have been proposed. To enable the model application to a broad range of system configurations and various dynamic studies, the model is built on a modular modelling approach using four sub-systems; an AC system, Phase Locked Loop (PLL) system, MMC system and a DC arrangement. The developed MMC system model has been linearized and implemented in state-space form. To select the best open-loop controller gains, eigenvalue analysis is performed for each particular test system. The rationality and correctness of the proposed model are verified against non-linear PSCAD/EMTDC simulations, and good accuracy is obtained in the time domain analysis. Further, the model is also verified in the frequency domain, and it is concluded that the developed model can be employed for dynamic analysis below 300 Hz.
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Exact Modeling of Time-Interval-Modulated Switched NetworksNiu, Weihe 12 February 1993 (has links)
The frequency response analysis of switched networks plays a very important part in designing various kinds of power converter circuits. In this thesis two frequency response techniques for analyzing switching power converters are discussed. One method provides a mathematical description which treats the converter as a periodic time varying system. A linearized small signal model is subsequently derived. The major part of the thesis concentrates on this accurate exact small-signal technique. The derivation involves state space representation and the use of the time varying transfer function. A Fourier analysis is performed to show the relationship between the frequency response of the network and the time varying transfer function. The obtained expressions are in closed form. The method has proven to be exact. The complexity of this technique is overcome by automating its derivation in conjunction with a circuit simulator. An alternative method, relying only on a sampled-data representation, is also derived, which provides a less complicated algorithm. However the accuracy of this method suffers, particularly at high frequencies. The accuracy of the exact small-signal technique is verified by experimentation.
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Improved efficiency in medium-power flyback convertersRuttanapaibooncharoen, Surin 12 December 2003 (has links)
Switch-mode power supplies (SMPS's) not only convert energy, they also
consume it. Typical operational efficiencies are approximately 25 to 60% for linear
power supplies, and approximately 50-90% for switching power supplies. This means
that products whose end-use electronics are dc, such as televisions and DVD players,
could consume 50% less power when operating if the power supply were upgraded from
40% efficiency to 80% efficiency. Savings can occur not only from using SMPS's
instead of linear power supplies, but also from specifying highly efficient switching
power supplies. In many cases, efficiencies are still lagging to keep costs down, since
the power consumption is considered to be relatively low (40W-700W range). Over
time, however, efficiency improvement strategies will pay back based on the cost of
energy. Therefore three common flyback converter topologies have been studied
through this thesis in the Low (15W), Medium (40W), and High (150W) Power levels.
Efficiency analysis on the three power level topologies showed that the greatest
opportunity for efficiency improvement existed in the 40W (medium power) topology.
Efficiency improvement and measurement approaches are investigated and an
optimized medium-power flyback converter is proposed and implemented resulting in
an efficiency improvement from 57.8% to 83.6%. / Graduation date: 2004
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Hardware design and protection issues in an AC/AC converterFaveluke, Alex 25 August 1997 (has links)
An AC/AC converter has been designed and implemented for the purpose of
providing a modular drive system with a Brushless Doubly-Fed Machine (BDFM.) This
converter is to be used in laboratory testing and also as part of a demonstration system in
the field.
All hardware needed to start and run the BDFM is now consolidated into a single
NEMA standard frame electrical equipment box. This allows easy transportation and
setup of the drive system, and will enable the BDFM drive system to be directly
compared with existing induction machine based drive systems.
Converter subsystem overviews in the body of the text and comprehensive
schematics in the appendices of this thesis describe all circuitry included in the drive
system. Sufficient construction detail is given to allow for duplication of this converter
by qualified technical personnel. While not tailored for mass production, this converter
may provide a starting point for a commercially viable design. / Graduation date: 1998
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Hysteretic pulse width modulation with internally generated carrier for a boost dc-dc converterThekkevalappil, Soniya Noormuhamed. January 2005 (has links)
Thesis (M.S.)--University of Florida, 2005. / Title from title page of source document. Document formatted into pages; contains 74 pages. Includes vita. Includes bibliographical references.
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Analysis of losses in power inductor for high-frequency switching power convertersChung, Hok-Yan. January 2001 (has links)
Thesis (M. Phil.)--University of Hong Kong, 2001.
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Realization of switched-capacitor filters employing voltage-inverter switches /Li, Mei-kuen, Margaret. January 1981 (has links)
Thesis--Ph. D., University of Hong Kong, 1981.
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Systematic analysis of switching power converters for long operation lifePang, Hon-man., 彭漢文. January 2010 (has links)
published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy
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