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1
Juanuwattanakul, Parachai. "Bus voltage ranking and voltage stability enhancement for unbalanced multiphase networks." Thesis, Curtin University, 2012. http://hdl.handle.net/20.500.11937/301.
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Voltage instabilities and subsequent system collapses are considered as growing concerns in modern multiphase distribution networks as they are progressively forced to operate closer to their stability limits due to many factors such as increasing load level, lack of reactive power sources, high installation of single-phase shunt capacitors and reverse action of voltage control devices. System operators must be able to quickly identify trouble spots and take corrective steps to avoid critical voltage collapses. To achieve this, suitable indices must be defined to assess system security and take corrective control actions when predefined thresholds are reached. In this regard, the identification and ranking of weak buses in a power system is an important research area.The existing conventional bus voltage ranking indices are only defined for single-phase and balanced three-phase networks. This thesis proposes a new bus voltage ranking index (VRI) to identify the weakest single-, two- and three-phase buses of multiphase distribution networks. Then, applications of the proposed bus ranking index will be tested for enhancing the voltage stability of unbalanced multiphase distribution networks.In the first part of this thesis, the definition of conventional voltage ranking indices are modified and generalized to also include unbalanced and multiphase networks using symmetrical components. For the first time, the method of symmetrical components is applied to the three-phase voltages computed from three-phase power flow. The new index is defined as the ratio of the (fundamental) positive-sequence voltage at the point of voltage collapse to the positive-sequence voltage at the base-load source. The former voltage level is determined by increasing the active power of all loads while keeping power factor constant until the point of voltage collapse is reached.In the second part of this thesis, the new VRI is validated through the calculation of grid losses and PV curves based on positive-sequence voltage. Extensive simulations of the IEEE 13 and 34 node test feeders are performed using the DIgSILENT PowerFactory to further validate and compare the performance of the new VRI with three well-known conventional ranking indices.In the third part of the thesis, the new VRI is used to identify the weakest three-phase buses in unbalanced three-phase distribution networks. Then, the index is utilized to place compensation devices at the weakest buses of the modified unbalanced three-phase 13 node test feeder to improve voltage stability and increase the maximum loading factor (MLF) under unbalanced three-phase operating conditions.In the fourth part of the thesis, static analyses are carried out to demonstrate applications of the proposed VRI in increasing MLF and improving voltage stability of multiphase networks under unbalanced loading and/or network conditions. Then, dynamic simulations are performed to further validate the accuracy of the proposed VRI and improving voltage stability under dynamic operating conditions.In the fifth part of the thesis, an online application of the proposed bus ranking is introduced to identify the weakest buses in multiphase smart grids with plug-in electric vehicle (PEV) charging stations.Finally, the proposed voltage ranking and stability enhancement approach are utilized to improve the performance of multiphase distribution networks by proper placement and sizing of distributed generator (DG) units such as doubly-fed induction generators (DFIGs) and single-phase capacitors. An iterative algorithm is proposed for the placement and sizing of DG units and single-phase capacitors in multiphase networks to reduce grid losses and increase MLF while keeping all bus voltages within acceptable limits. The approach consists of utilizing the positive- sequence voltage ratio Vcollapse/Vbase-load to identify the weakest three-phase and single-phase buses for the installation of DG units and shunt capacitors, respectively. DG penetration levels are increased (e.g., 40%) by evaluating their impacts on voltage profile, grid losses, and voltage stability margin while considering the voltage limits at all buses. The impacts of DIFG on voltage profile, active power loss, MLF and voltage unbalance factor are highlighted.
2
朱太秀 and Tai-xiu Zhu. "Knowledge-based assessment and enhancement of voltage stability." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1996. http://hub.hku.hk/bib/B31236455.
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Zhu, Tai-xiu. "Knowledge-based assessment and enhancement of voltage stability /." Hong Kong : University of Hong Kong, 1996. http://sunzi.lib.hku.hk/hkuto/record.jsp?B18061680.
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VEGA, JORGE LEONIDAS LAFITTE. "VOLTAGE STABILITY ASSESSMENT AND ENHANCEMENT IN VOLTAGE-CONTROLLED BUSES BY SYNCHRONOUS GENERATORS AND COMPENSATORS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2009. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=14009@1.
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO<br>Após a incidência de alguns colapsos de tensão em sistemas de
transmissão de energia a nível mundial, a segurança de tensão tornou-se um
assunto de muito interesse nos últimos anos devido à importância do seu
impacto. O fenômeno de estabilidade de tensão deve-se a fluxos de potência
ativa e reativa excessivos na rede de transmissão e está associado às restrições
ambientais e econômicas que impedem a expansão da rede. Atualmente, sabese
da existência de uma máxima carga que pode ser alimentada pela rede e é a
manifestação mais conhecida do fenômeno mas, também, é possível que o
problema manifeste-se pela existência de uma máxima injeção de potência ativa
e reativa na rede por geradores e compensadores síncronos. E mais, em
situações de carregamento elevado da rede, é possível que ações de controle de
tensão tenham efeito oposto ao usual. É apresentado um método seqüencial
iterativo de avaliação e reforço para as condições de carregamento da rede em
barras de tensão controlada, embora na literatura somente as barras de carga
são analisadas. A verificação do comportamento do gerador e compensador
síncrono como dispositivo de controle torna-se necessária já que, se funcionar
de forma inversa, poderá levar o sistema ao colapso por problemas de tensão.
Uma vez que a avaliação do carregamento da rede de transmissão detectou
uma barra de geração crítica em um determinado ponto de operação, o reforço
consiste do cálculo de ações de controle para aumentar a distância ou margem
de potência entre a geração daquela barra e o novo máximo permitido. Muitas
vezes isso pode ser conseguido através da alteração do perfil de tensão com a
conseqüente redução nas perdas. Muitas outras vezes, o redespacho de
potência ativa torna-se necessário. As etapas do método são: identificar a barra
crítica, identificar a sub-rede utilizada para transmitir potência ativa dessa barra
para as cargas, nessa sub-rede determinar o caminho e ramo mais carregados
e, desviar o fluxo de potência do ramo mais carregado para outros. A seqüência
é repetida até que as novas margens de potência sejam consideradas
aceitáveis. Exemplos numéricos ilustrativos reais com o sistema brasileiro são
apresentados. É verificado que o método proposto realmente produz os
resultados desejados.<br>After the incidence of some voltage collapses in the energy transmission
systems in the world, the voltage security became an issue of great interest in the
last years due to the importance of its impact. The phenomenon of voltage
stability is due to the excessive active and reactive power flow in the electrical
transmission network and has been associated with environment questions and
lack of financial resources for transmission system expansion. Nowadays, it is
well-known that there is a maximum power that the network can transmit to a
load bus and is the best known manifestation of the phenomenon, but, is not
familiar to many that there is a maximum power that can be injected by
generators and synchronous compensators into the network. Moreover, in heavy
loading conditions is possible that voltage control actions would have the inverse
effect. It is shown a sequential iterative method for assessment and voltage
security reinforcement in voltage-controlled buses, although the literature only the
load buses are analyzed. The verification of the behaviour of the generator and
synchronous compensator as control device becomes necessary since, if it works
in an inverse way, it can take the system to the voltage collapse. Once the
assessment is performed and is detected one generation critical bus in some
operating point, the objective of the reinforcement function is to calculate
adequate control actions in order to increase the distance or power margin
between the actual generation and the new maximum power flow. Several times
this may be achieved by voltage profile changes and consequent loss reduction.
Sometimes that procedure is not enough and active generation rescheduling is
recommended. The stages of the method are: identify the critical bus, identify the
sub-network used to transmit active power flow from this bus to load buses, in
this sub-network the critical transmission path and critical branch are determined
and redirect the power flow from the branch more loaded to others. The
sequence is repeated until resultant power margins are judged suitable.
Illustrative real life numerical examples with the Brazilian system are provided. It
is verified that the proposed method really produces the desired results.
5
Omura, Ichiro. "High voltage MOS device design: enhancement and negative gate capacitance /." Konstanz : Hartung-Gorre, 2005. http://www.loc.gov/catdir/toc/fy0609/2005477130.html.
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Shahnia, Farhad. "Analysis and correction of voltage profile in low voltage distribution networks containing photovoltaic cells and electric vehicles." Thesis, Queensland University of Technology, 2011. https://eprints.qut.edu.au/50834/1/Farhad_Shahnia_Thesis.pdf.
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Voltage drop and rise at network peak and off–peak periods along with voltage unbalance are the major power quality problems in low voltage distribution networks. Usually, the utilities try to use adjusting the transformer tap changers as a solution for the voltage drop. They also try to distribute the loads equally as a solution for network voltage unbalance problem. On the other hand, the ever increasing energy demand, along with the necessity of cost reduction and higher reliability requirements, are driving the modern power systems towards Distributed Generation (DG) units. This can be in the form of small rooftop photovoltaic cells (PV), Plug–in Electric Vehicles (PEVs) or Micro Grids (MGs). Rooftop PVs, typically with power levels ranging from 1–5 kW installed by the householders are gaining popularity due to their financial benefits for the householders. Also PEVs will be soon emerged in residential distribution networks which behave as a huge residential load when they are being charged while in their later generation, they are also expected to support the network as small DG units which transfer the energy stored in their battery into grid. Furthermore, the MG which is a cluster of loads and several DG units such as diesel generators, PVs, fuel cells and batteries are recently introduced to distribution networks. The voltage unbalance in the network can be increased due to the uncertainties in the random connection point of the PVs and PEVs to the network, their nominal capacity and time of operation. Therefore, it is of high interest to investigate the voltage unbalance in these networks as the result of MGs, PVs and PEVs integration to low voltage networks. In addition, the network might experience non–standard voltage drop due to high penetration of PEVs, being charged at night periods, or non–standard voltage rise due to high penetration of PVs and PEVs generating electricity back into the grid in the network off–peak periods. In this thesis, a voltage unbalance sensitivity analysis and stochastic evaluation is carried out for PVs installed by the householders versus their installation point, their nominal capacity and penetration level as different uncertainties. A similar analysis is carried out for PEVs penetration in the network working in two different modes: Grid to vehicle and Vehicle to grid. Furthermore, the conventional methods are discussed for improving the voltage unbalance within these networks. This is later continued by proposing new and efficient improvement methods for voltage profile improvement at network peak and off–peak periods and voltage unbalance reduction. In addition, voltage unbalance reduction is investigated for MGs and new improvement methods are proposed and applied for the MG test bed, planned to be established at Queensland University of Technology (QUT). MATLAB and PSCAD/EMTDC simulation softwares are used for verification of the analyses and the proposals.
7
Jain, Akshay Kumar. "Enhancing PV Hosting Capacity of Distribution Feeders using Voltage Profile Design." Thesis, Virginia Tech, 2018. http://hdl.handle.net/10919/82481.
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Distribution feeders form the last leg of the bulk power system and have the responsibility of providing reliable power to the customers. These feeders experience voltage drops due to a combination of feeder length, load distribution, and other factors. Traditionally, voltage drop was a major concern. Now, due to an ever-increasing PV penetration, overvoltage has also become a major concern. This limits the amount of solar PV that may be integrated.
Few solutions exist to improve the voltage profile, where the most common is the use of voltage control devices like shunt capacitors and voltage regulators. Due to a large number of design parameters to be considered, the determination of the numbers and locations of these devices is a challenging problem. Significant research has been done to address this problem, utilizing a wide array of optimization techniques. However, many utilities still determine these locations and numbers manually. This is because most algorithms have not been adequately validated. The validation of a voltage profile design (VPD) algorithm has been presented here. The validation of this algorithm was carried out on a set of statistically relevant feeders. These feeders were chosen based on the results obtained from a feeder taxonomy study using clustering analysis. The algorithm was found to be effective in enhancing the amount of solar PV a feeder may host, while still maintaining all the voltages within the ANSI standard limits. Furthermore, the methodology adopted here may also be used for the validation of other algorithms.<br>Master of Science
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Omura, Ichiro. "High voltage MOS device design : injection enhancement and negative gate capacitance /." [S.l.] : [s.n.], 2000. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=14049.
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Ahmed, Faisal Mahmood. "Estimated Droop Control for Parallel Connected Voltage Source Inverters : Stability Enhancement." Thesis, Karlstads universitet, Avdelningen för fysik och elektroteknik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-30794.
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Renewable Energy Sources (RES) are considered as the replacement of conventionalenergy sources. These RES can use wind energy, solar light, bio waste and can alsobe in the form of small hydro power units. These RES has very poor power qualityand contains voltage uctuations and variable frequency. These factors make RES astability risk for the main utility grid. As a solution, currently inverters with dierentdesign techniques are being used as an interface between RES and main utility grid. Thecurrent study proposed a new technique "estimated droop control" for inverter design.The conventional droop control technique which was already used in inverter design, hasdiculty in synchronizing parallel connected inverters with dierent droop gains and lineimpedances. The proposed "estimated droop control" does not use any predened droopvalues for inverters and all inverters are responsible for the estimation of their own droopvalues with respect to their output power. Therefore, inverters are not bound to usesame and static droop values which are considered as a vital communication link. Theproposed design methodology has made inverters independent from this only virtual linkof communication due to which the reliability of a system has increased. The proposeddesign technique has given very good results in a simulation run. When the Simulinkmodel was run in parallel connected inverter with dierent line impedances, it was asuccess as both inverters started operating with same droop values as they were sharingan equal load. The most important test was with dierent line impedances because inconventional droop control it is dicult for inverters to keep their synchronism withdierent line impedances and an unequal load sharing make inverters to deviate fromtheir nominal values and to generate dierent tracking signals for each set. This problemhas been successfully solved with estimated droop control as in this method each inverterset its droop gains according to its output power, which helps an inverter to operate atnominal values with dierent droop gains and line impedance.
10
Lakkireddy, Jahnavi. "Steady State Voltage Stability Enhancement Using Shunt and Series FACTS Devices." ScholarWorks@UNO, 2014. http://scholarworks.uno.edu/td/1881.
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It is specifically important to focus on voltage stability analysis of the power system to avoid worst case scenarios such as voltage collapse. The purpose of this thesis is to identify methods for enhancing the steady-state voltage stability using FACTS devices and determining their impact on real and reactive power losses, improvement of bus voltage magnitude, and transmission line loadability. To achieve this, FACTS devices such as Static VAR Compensator (SVC), Static Synchronous Compensator (STATCOM), and Thyristor Controlled Series Capacitor (TCSC) are used in the test system as three separate test cases. The results obtained assist in drawing conclusions on the effectiveness of each FACTS devices at generator, load and swing buses, on lines between two load buses, and between a load bus and a generator bus, in terms of metrics such as voltage magnitude profile, PV curves, and active and reactive power losses.
11
Zhong, Wanyun. "Demand Uncertainties Management in SCUC and Voltage Security Enhancement for SCED." Case Western Reserve University School of Graduate Studies / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=case1554420443707557.
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Evrenosoglu, Cansin Yaman. "Novel techniques for fault location, voltage profile calculation and visualization of transients." [College Station, Tex. : Texas A&M University, 2006. http://hdl.handle.net/1969.1/ETD-TAMU-1103.
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TRAVASSOS, ROGERIO. "VOLTAGE PROFILE CORRECTION THROUGH A POWER FLOW ALGORITHM WITH REACTIVE IMPLICIT COUPLING." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1992. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=9043@1.
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO<br>Esta dissertação apresenta uma metodologia para a correção
do perfil de tensão dos barramentos de um sistema elétrico
de potência.
Esta correção corresponde a um redespacho de potência
reativa efetuada através de mudança das tensões-base nas
barras com geração variável de potência reativa, da
mudança dos tapes dos transformadores, e do chaveamento de
bancos de capacitores/reatores em paralelo.
O método consiste na resolução da equações nodais não
lineares de fluxo de carga e das equações associadas aos
limites violados. Isto é feito através do método de Newton-
Raphson.
O modelo linearizado, utilizado em cada iteração do método
de Newton-Raphson, é reduzido à parte reativa utilizando-
se a técnica de acoplamento implícito com a parte ativa
(CRIC) sugerida pro J. Carpentier.
Como o sistema linearizado admite infinitas soluções
escolheu-se aquela que minimiza o desvio quadrático da
tensão de todos os barramentos do sistema e dos tapes dos
transformadores. Isto é feito através do uso da matriz
inversa generalizada de Moore-Penrose.<br>This dissertation presents a methodology for correction of
the bus voltage profile of an electric power system.
This correction corresponds to a redispach of reactive
power which is effected by means of voltage set-point
changes in buses with variable generation of reactive
power, transformer tap changes and shunt
capacitors/reactors swithing.
The proposed method consists of solving the non-linear
power flow equations as well as the equatios associated
with violated limits. This is done by using the Newton-
Raphson method.
The linearized model used in each iteration of the Newton-
Raphson method is reduced to the reactive part by means of
Carpentier s Reactive Implicit Coupling (CRIC) technique.
As the linearized system admits several solutions, it is
chosen the one which minimizes the quadratic deviation of
all bus voltages and transformer taps. This is done by
means of Moore-Penrose generalized inverse matrix.
14
Okubo, Hitoshi, Tetsu Shioiri, Mitsutaka Homma, Hiroki Kojima, Ryouki Nishimura, and Keita Aoki. "Enhancement of Breakdown Strength by Microdischarge under Impulse Voltage Applications in Vacuum." IEEE, 2010. http://hdl.handle.net/2237/14534.
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Mohammed, Mahmoud M. Jr. "Development of intelligent systems for evaluating voltage profile and collapse under contingency operation." Diss., Kansas State University, 2011. http://hdl.handle.net/2097/8408.
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Doctor of Philosophy<br>Department of Electrical and Computer Engineering<br>Shelli K. Starrett<br>Monitoring and control of modern power systems have become very complex tasks due to the interconnection of power grids. These large-scale power grids confront system operators with a huge set of system inputs and control parameters. This work develops and compares intelligent systems-based algorithms which may be considered by power system operators or planners to help manage, process, and evaluate large amounts of data due to varying conditions within the system. The methods can be used to provide assistance in making operational control and planning decisions for the system in a timely manner. The effectiveness of the proposed algorithms is tested and validated on four different power systems.
First, Artificial Neural Network (ANN) models are developed and compared for two different voltage collapse indices and utilizing two different-sized sets of inputs. The ANNs monitor and evaluate the voltage profile of a system and generate intelligent conclusions regarding the status of the system from a voltage stability perspective. A feature reduction technique, based on the analysis of generated data, is used to decrease the number of inputs fed to the ANN, decreasing the number of physical quantities that need to be measured.
The major contribution of this work is the development of four different algorithms to control the VAR resources in a system. Four different objectives were also considered in this part of the work, namely: minimization of the number of control changes needed, minimization of the system power losses, minimization of the system's voltage deviations, and consideration of the computational time required. Each of the algorithms is iterative in nature and is designed to take advantage of a method of decoupling the load flow Jacobian matrix to decrease the time needed per iteration. The methods use sensitivity information derived from the load flow Jacobian and augmented with equations relating the desired control and dependent variables. The heuristic-sensitivity based method is compared to two GA-based methods using two different objective functions. In addition, a FL algorithm is added to the heuristic-sensitivity algorithm and compared to a PS-based algorithm.
The last part of this dissertation presents the use of one of the GA-based algorithms to identify the size of shunt capacitor necessary to enhance the voltage profile of a system. A method is presented for utilizing contingency cases with this algorithm to determine required capacitor size.
16
Oluwole, Osaloni Oluwafunso. "Optimal allocation of distributed generation for power loss reduction and voltage profile improvement." Master's thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/20578.
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Distributed generation (DG) integration in a distribution system has increased to high penetration levels. There is a need to improve technical benefits of DG integration by optimal allocation in a power system network. These benefits include electrical power losses reduction and voltage profile improvement. Optimal DG location and sizing in a power system distribution network with the aim of reducing system power losses and improving the voltage profile still remain a major problem. Though much research has been done on optimal DG location and sizing in a power system distribution network with the aim of reducing system power losses and improving the voltage profile, most of the existing works in the literature use several techniques such as computation, artificial intelligence and an analytical approach, but they still suffer from several drawbacks. As a result, much can still be done in coming up with new algorithms to improve the already existing ones so as to address this important issue more efficiently and effectively. The majority of the proposed algorithms emphasize real power losses only in their formulations. They ignore the reactive power losses which are the key to the operation of the power systems. Hence, there is an urgent need for an approach that will incorporate reactive power and voltage profile in the optimization process, such that the effect of high power losses and poor voltage profile can be mitigated. This research used Genetic Algorithm and Improved Particle Swarm Optimization (GA-IPSO) for optimal placement and sizing of DG for power loss reduction and improvement of voltage profile. GA-IPSO is used to optimize DG location and size while considering both real and reactive power losses. The real and reactive power as well as power loss sensitivity factors were utilized in identifying the candidate buses for DG allocation. The GA-IPSO algorithm was programmed in Matlab. This algorithm reduces the search space for the search process, increases its rate of convergence and also eliminates the possibility of being trapped in local minima. Also, the new approach will help in reducing power loss and improve the voltage profile via placement and sizing.
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Wong, Wai Yu. "Supply-independent current-mode slew rate enhancement design /." View abstract or full-text, 2006. http://library.ust.hk/cgi/db/thesis.pl?ELEC%202006%20WONG.
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Fu, Le. "Voltage stability monitoring and enhancement in electrical power systems using transformer tap changers." Thesis, Imperial College London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.506484.
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Anaya-Lara, Olimpo. "Digital control of a multilevel NPC dynamic voltage restorer for power quality enhancement." Thesis, University of Glasgow, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.410730.
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GREENHALGH, ANGELA BARBOSA. "VOLTAGE STABILITY ENHANCEMENT IN THE OPERATION OF POWER SYSTEMS THROUGH AN OPTIMIZATION MODEL." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1998. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=8943@1.
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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR<br>Muito tem sido feito para que se possa entender os
mecanismos que levam o sistema a uma situação de
instabilidade de tensão e até mesmo ao colapso, assim como
também para se suprir a necessidade de ferramentas
analíticas capazes de prever e avaliar a proximidade do
colapso de tensão em sistemas complexos, identificando as
áreas susceptíveis à instabilidade de tensão.
Uma vez detectada a inconveniente proximidade a uma
condição de operação susceptível ao colapso de tensão, é
necessária a identificação de grandezas-chave e
sensibilidades, que forneçam entendimento suficiente, para
ajudar no desenvolvimento de metodologias para reforçar as
condições de estabilidade de tensão. Tendo isto como
objetivo, este trabalho trata do problema de reforço da
estabilidade de tensão através da mudança do perfil de
tensão, utilizando como ferramenta computacional um
algoritmo de otimização.
Há no sistema variáveis de controle que interferem
diretamente no perfil de tensão, tais como, tensão base
nos geradores e compensadores, taps de transformadores, e
capacitadores e reatores usados para compensação de
potência reativa. Entretanto, quando as condições de
estabilidade já se encontram deterioradas, as ações de
controle do perfil de tensão podem levar a resultados
insatisfatórios, podendo mesmo agravar o problema.
Neste trabalho é apresentada uma metodologia, baseada em
algoritmo de otimização, que fornece a lista de variáveis
de controle mais eficientes para o reforço da estabilidade
de tensão, e a direção em que os controles devem ser
acionados. O interesse é obter um ponto de operação viável
mais robusto, do ponto de vista de estabilidade de tensão,
e não necessariamente um ponto de operação ótimo.<br>Much hás been done for the understanding of the voltage
instabilitu mechanisms and to supply the necessity of
analytical tools, which should have the ability tom
predict and evaluate the proximity of voltage collapse in
complex systems, identifying the critical áreas
susceptible to voltage istability.
Once the inconvenient proximity to an operating condition
susceptible to voltage collapse is identified, it is
necessary to look for the key factors and sensitivities
that provide the reinforcement of the voltage stability
conditions. Having it as a goal, this work treats the
problem of reinforcing the voltage stability conditions,
through changes of the voltage profile, using an optimal
algorithm as a computational tool.
There are control variables in the system which directly
interfere on the voltage profile, such as, voltage set
point on generators and compensators, transformer taps,
capacitors and reactors. However, when the voltage
stability conditions are already deteriorated, the voltage
profile control actions may lead to unsatisfactory
results, and may even aggravate the problem.
It is presented a methodology based on an optimal, that
provides the list of the most efficient control variables
for the reinforcement of voltage stability, and the
corresponding direction of movement. The search is for a
feasible operating point, more robust in relation to
voltage stability, and not necessarily for an optimal
operating point.
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West, Paul Martin. "TECHNIQUES FOR DIGITAL LOW DROPOUT REGULATOR MODELING AND TRANSIENT RESPONSE ENHANCEMENT." OpenSIUC, 2016. https://opensiuc.lib.siu.edu/theses/1878.
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Low dropout regulators (LDOs) are important components for power management in modern integrated circuits. With the continued scaling down of power supply voltage, digital LDOs have become a more attractive design choice since they avoid the difficulty of designing high-gain amplifiers with low voltage. This thesis investigates techniques for both modeling and enhancement of digital LDO transient response. It discusses the importance of the resistance in the output stage of an LDO, and proposes a simulation model for examining LDO transient response. In addition, the thesis studies circuit techniques to improve LDO transient response. Different LDO circuits are implemented and compared in this study.
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Monika, Sadia K. "III- Nitride Enhancement Mode Device." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1483535296785214.
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Joseph, Tibin. "Operation and control of voltage source converters in transmission networks for AC system stability enhancement." Thesis, Cardiff University, 2017. http://orca.cf.ac.uk/111498/.
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The rapid expansion in power transmission for the integration of large-scale renewables is foreseen in the future. This will be complemented by infrastructure reinforcements in the form of series compensation and high-voltage direct current (HVDC) links. These changes will bring forth new operability challenges to grid operators. The stability issues pertained to such reinforcements: potential threat of subsynchronous resonance (SSR) and frequency regulation will be investigated in this thesis. Utilising the existing and future voltage source converters (VSC) based HVDC links to support the AC system by proving ancillary services will be of significant importance in the coming decades. The research work presented in this thesis is aimed to address these challenges, in particular, the technical barriers associated with AC/DC interaction and to propose measures to avoid any potential instability. The main contributions of this research work comprise of four parts, namely, (1) analysis of interactions in-terms of SSR in AC/DC grids, (2) design of SSR damping (SSRD) controllers, (3) experimental demonstration of SSRD schemes, and (4) assessment and improvement of frequency regulation in a wind-thermal bundled AC/DC grid. An VSC-HVDC connected series-compensated AC system resembling the Great Britain (GB) power system has been used as the test network to evaluate the operability challenges pertained to the reinforcements. A state-space representation has been formulated and an eigenvalue analysis has been performed to assess the impact of VSC-HVDC on the torsional modes of nearby connected thermal generation plants. This is followed by damping torque investigation for SSR screening with the results compared against time-domain simulations for testing the accuracy of the small-signal models for SSR studies. A series of SSRD schemes is presented which have been integrated with the VSC-HVDC to damp SSR in the series-compensated GB power system. In addition, this thesis proposes an adaptive SSRD method based on the real-time estimation of the subsynchronous frequency v Abstract component present in series-compensated transmission lines–key information for the optimal design of HVDC subsynchronous damping controllers. Furthermore, the combined AC/DC GB network has been implemented in a real-time digital simulator and connected to a VSCHVDC scaled-down test-rig to performhardware-in-the-loop tests. The efficacy and operational performance of the AC/DC network while providing SSR damping is tested through a series of experiments. In order to provide frequency support in a wind-thermal bundled AC/DC system a dualdroop controlmethod is presented. The scheme binds the system frequency with the DC voltage of an HVDC network. For completeness, the performance of the proposed method is compared to conventional frequency regulation schemes. Sensitivity studies and eigenvalue analyses are conducted to assess the impact that wind penetration and changes in the dual-droop coefficient have on grid stability. Experimental validation is performed using a real-time hardware-inthe- loop test-rig, with simulation and experimental results showing a good agreement and evidencing the superior performance of the proposed frequency support scheme.
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Layton, Kent Downing. "Low-Voltage Analog CMOS Architectures and Design Methods." BYU ScholarsArchive, 2007. https://scholarsarchive.byu.edu/etd/1218.
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This dissertation develops design methods and architectures which allow analog circuits to operate at VT + 2Vds,sat, the minimum supply for CMOS circuits with all transistors in the active region where Vds,sat is the drain to source saturation voltage of a MOS transistor. Techniques which meet this criteria for rail-to-rail input stages, gain enhancement stages, and output stages are discussed and developed. These techniques are used to design four fully-differential rail-to-rail amplifiers. The highest gain is shown to be attained using a drain voltage equalization (DVE) or active-bootstrapping technique which produces more than 100dB of gain in a two stage amplifier with a bulk-driven input pair while showing no bandwidth degradation when compared to amplifier architectures with similar biasing. The low voltage design techniques are extended to switching and sampling circuits. A 10-bit digital to analog converter (DAC) and a 10-bit analog to digital converter (ADC) are designed and fabricated in a 0.35um dual-well CMOS process to prove the developed design methods, architectures, and techniques. The 10-bit DAC operates at 1MSPS with near rail-to-rail differential output operation with a 700mV supply voltage. This supply voltage, which is 150mV lower than the VT+2Vds,sat limit, is attained by using a bulk driven threshold voltage lowering technique. The ADC design is a fully-differential pipelined 10-bit converter that operates at 500kSPS with a full scale input range equal to the supply voltage and can operate at supply voltages as low as 650mV, 200mV below the VT + 2Vds,sat limit. The design methods and architectures can be used in advanced processes to maintain gain and minimize supply voltage. These designs show a minimum supply improvement over previously published designs and prove the efficacy of the design architectures and techniques presented in this dissertation.
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Thome, Brian Matthew. "Increasing the scale of electrophoretic true moving bed enantiomer separations using voltage gradients and filtration enhancement." Online access for everyone, 2006. http://www.dissertations.wsu.edu/Dissertations/Fall2006/b_thome_110706.pdf.
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Macrelli, Elena. "Performance and Robustness of low-voltage enhancement-mode GaN-based power HEMTs with p-type gate." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/24039/.
Full textAbstract:
This thesis is a report of the work of a six-months internship in imec, a R&D hub for nano- and
digital technologies based in Leuven, Belgium.
During this internship I worked on the characterization of enhancement-mode GaN-based lateral HEMT devices with p-GaN gate, aiming to understand the impact of different process
variations, device layout and architecture on the electrical performance and reliability of the
devices. After the first essential steps that included the study of the basics about device
structure, fabrication and operations and literature review, I started to plan experiments and
characterization routines with a focus on gate and OFF-state reliability and I performed the
measurements and the data elaboration.
The first chapter of this elaborate will present an overview on the field of power electronics:
its relation to the theme of climate change and the state of its market nowadays.
Then a presentation of p-GaN HEMT devices will follow, explaining the working of the
transistor and all its fabrication options and issues.
After that, the report will get into the real work done during the internship: two chapters will
explain all the experimental details of the measurements and present the obtained results and
observations.
A final chapter will in the end summarize the results and draw some conclusions.
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Zhou, Tong, Haiyang Tang, Ying Han, et al. "Expression profile of mitochondrial voltage-dependent anion channel-1 (VDAC1) influenced genes is associated with pulmonary hypertension." KOREAN JOURNAL OF PHYSIOLOGY & PHARMACOLOGY, 2017. http://hdl.handle.net/10150/624396.
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Several human diseases have been associated with mitochondria! voltage-dependent anion channel-1 (VDAC1) due to its role in calcium ion transportation and apoptosis. Recent studies suggest that VDAC1 may interact with endothelium-dependent nitric oxide synthase (eNOS). Decreased VDAC1 expression may limit the physical interaction between VDAC1 and eNOS and thus impair nitric oxide production, leading to cardiovascular diseases, including pulmonary arterial hypertension (PAH). In this report, we conducted meta-analysis of genome-wide expression data to identify VDAC1 influenced genes implicated in PAH pathobiology. First, we identified the genes differentially expressed between wild-type and Vdac1 knockout mouse embryonic fibroblasts in hypoxic conditions. These genes were deemed to be influenced by VDAC1 deficiency. Gene ontology analysis indicates that the VDAC1 influenced genes are significantly associated with PAH pathobiology. Second, a molecular signature derived from the VDAC1 influenced genes was developed. We suggest that, VDAC1 has a protective role in PAH and the gene expression signature of VDAC1 influenced genes can be used to i) predict severity of pulmonary hypertension secondary to pulmonary diseases, ii) differentiate idiopathic pulmonary artery hypertension (IPAH) patients from controls, and iii) differentiate IPAH from connective tissue disease associated PAH.
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Kanchanaharuthai, Adirak. "Small-Signal Stability, Transient Stability and Voltage Regulation Enhancement of Power Systems with Distributed Renewable Energy Resources." Case Western Reserve University School of Graduate Studies / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=case1321988036.
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Okuda, Takafumi. "Enhancement of Carrier Lifetimes in SiC and Fabrication of Bipolar Junction Transistors." 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/202717.
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Krishnan, Bharat. "DEVELOPMENT OF SIMULATION FRAMEWORK FOR THE ANALYSIS OF NON-IDEAL EFFECTS IN DOPING PROFILE MEASUREMENT USING CAPACITANCE ? VOLTAGE TECHNIQUE." MSSTATE, 2005. http://sun.library.msstate.edu/ETD-db/theses/available/etd-04082005-092339/.
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Silicon Carbide devices are proving to be most promising for high power and high-temperature application in recent times. Efficient and accurate characterization of the device characteristics is key to the fabrication of high quality devices and reproduction of the quality of the devices fabricated. Capacitance-Voltage profiling is one of the most commonly used techniques to measure the doping profiles of semiconductors. However, interpretation of C-V profiling in the presence of traps in the material becomes complicated. Various complications arising from compensation between donors and acceptors, partial ionization of dopants and presence of deep level impurities could yield anomalous measured profile. Silicon Carbide being a wide bandgap semiconductor, many impurities commonly found such as Boron and Aluminum are not completely ionized at Room temperature. This leads to complications in calculating doping profiles when the trap levels are deeper. Other complications arising due to series resistance effect and diode edge effect may also affect the measured profile. Accounting for these complications may be difficult by mere observation of the measured profile. Simulation can be an excellent tool to extract parameters of interest from experimental results that are influenced by non-ideal effects. Fitting of the experimentally obtained data with simulated profile using specific models may be a useful technique to quantitatively account for the deviations from the actual profiles.
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Nilsson, Jim, and Peter Valtersson. "Machine Vision Inspection of the Lapping Process in the Production of Mass Impregnated High Voltage Cables." Thesis, Blekinge Tekniska Högskola, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-16707.
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Background. Mass impregnated high voltage cables are used in, for example, submarine electric power transmission. One of the production steps of such cables is the lapping process in which several hundred layers of special purpose paper are wrapped around the conductor of the cable. It is important for the mechanical and electrical properties of the finished cable that the paper is applied correctly, however there currently exists no reliable way of continuously ensuring that the paper is applied correctly. Objective. The objective of this thesis is to develop a prototype of a cost-effective machine vision system which monitors the lapping process and detects and records any errors that may occur during the process; with an accuracy of at least one tenth of a millimetre. Methods. The requirements of the system are specified and suitable hardware is identified. Using a method where the images are projected down to one axis as well as other signal processing methods, the errors are measured. Experiments are performed where the accuracy and performance of the system is tested in a controlled environment. Results. The results show that the system is able to detect and measure errors accurately down to one tenth of a millimetre while operating at a frame rate of 40 frames per second. The hardware cost of the system is less than €200. Conclusions. A cost-effective machine vision system capable of performing measurements accurate down to one tenth of a millimetre can be implemented using the inexpensive Raspberry Pi 3 and Raspberry Pi Camera Module V2. Th
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Sagha, Hossein. "Development of innovative robust stability enhancement algorithms for distribution systems containing distributed generators." Thesis, Queensland University of Technology, 2015. https://eprints.qut.edu.au/91052/1/Hossein_Sagha_Thesis.pdf.
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This project was a step forward in improving the voltage profile of traditional low voltage distribution networks with high photovoltaic generation or high peak demand. As a practical and economical solution, the developed methods use a Dynamic Voltage Restorer or DVR, which is a series voltage compensator, for continuous and communication-less power quality enhancement. The placement of DVR in the network is optimised in order to minimise its power rating and cost. In addition, new approaches were developed for grid synchronisation and control of DVR which are integrated with the voltage quality improvement algorithm for stable operation.
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Pistacchio, Theresa M. (Theresa Marie). "The Development of a Psychobiologic Profile of Individuals Who Experience and Those Who Do Not Experience Exercise-Related Mood-Enhancement." Thesis, North Texas State University, 1985. https://digital.library.unt.edu/ark:/67531/metadc331491/.
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The present investigation involved the development of a psychobiologic profile of individuals who experience exercise-related mood-enhancement and those who do not. The sample (N=301) consisted of students participating in 10-week exercise classes at North Texas State University. All subjects completed pre-test inventories assessing various psychological (i.e., trait anxiety and depression, attitude toward physical activity, self-estimation of physical ability and attraction to physical activity, expectancies of health benefits from exercise, and self-motivation) and biological (i.e., aerobic capacity and body fat percentage) variables. Trait anxiety and depression were also assessed before and after the 10-week exercise program and state anxiety and depression were assessed on an acute basis on two separate occasions during the program. Multivariate analysis of variance and discriminant function analysis were employed to determine which variables maximally discriminated between individuals who experienced mood-elevations following exercise and those who did not enjoy such rewards. The hypothesis that these two groups of individuals differ significantly from each other was not upheld by the results; thus, an overall psychobiologic profile could not be developed. However, the data did reveal that individuals who held a more positive attitude toward physical activity for the purpose of health and fitness reduced their state anxiety and depression following exercise significantly more than individuals who held more neutral attitudes. The results also confirmed previous research that individuals initially high in trait anxiety and depression showed a significantly greater decrease in these traits than subjects scoring in the low-moderate range at the outset of the exercise class. Recommendations for future research are discussed.
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Sherkat, Masoum Amir. "Online Coordinated Charging of Plug-In Electric Vehicles in Smart Grid to Minimize Cost of Generating Energy and Improve Voltage Profile." Thesis, Curtin University, 2020. http://hdl.handle.net/20.500.11937/80607.
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This Ph.D. research highlights the negative impacts of random vehicle charging on power grid and proposes four practical PEV coordinated charging strategies that reduce network and generation costs by integrating renewable energy resources and real-time pricing while considering utility constraints and consumer concerns.
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Que, Weiguo. "Electric Field and Voltage Distributions along Non-ceramic Insulators." The Ohio State University, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=osu1037387155.
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Han, Xue. "Quantitative Analysis of Distributed Energy Resources in Future Distribution Networks." Thesis, KTH, Industriella informations- och styrsystem, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-98484.
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There has been a large body of statements claiming that the large scale deployment of Distributed Energy Resources (DERs) will eventually reshape the future distribution grid operation in numerous ways. However, there is a lack of evidence specifying to what extent the power system operation will be alternated. In this project, quantitative results in terms of how the future distribution grid will be changed by the deployment of distributed generation, active demand and electric vehicles, are presented. The quantitative analysis is based on the conditions for both a radial and a meshed distribution network. The input parameters are on the basis of the current and envisioned DER deployment scenarios proposed for Sweden. The simulation results indicate that the deployment of DERs can significantly reduce the power losses and voltage drops by compensating power from the local energy resources, and limiting the power transmitted from the external grid. However, it is notable that the opposite results (e.g., severe voltage uctuations, larger power losses) can be obtained due to the intermittent characteristics of DERs and the irrational management of different types of DERs in the DNs. Subsequently, this will lead to challenges for the Distribution System Operator (DSO).
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Nataraj, Sateesh. "Enhancement of evaluation method of journal bearings’ performance in heavy-duty diesel engines." Thesis, KTH, Skolan för industriell teknik och management (ITM), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-299513.
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Journal bearings are being used in various locations of an internal combustion engine. They contribute to a large portion of total engine friction and lowering it means a significant contribution to CO2 reduction. Operating under heavy loads, journal bearings are often subject to mixed regime of lubrication where a part of bearing load is carried by asperities. This necessitates accurate modelling of asperities contact in order to get more realistic predication of friction losses in journal bearings contact. The evaluation method at Scania couples 3D confocal measurement of bearings’ surface roughness to a Multi-body Dynamic Analysis of journal bearings lubrication utilizing AVL EXCITE. During running-in, asperity peaks are reduced due to wear caused by metal-to-metal contact resulting in change of bearing surface profile and different contact zones in axial and circumferential direction. The aim of this thesis is to include these different contact zones and run-in wear profile of the bearing to the existing evaluation method at Scania to simulate run-in effects more precisely. Surface measurements were made on a run-in big end bearing surface at edges, center and region after oil hole. From these measurements, using the existing Local Scale Model at Scania, asperity pressure curve and flow factors were obtained, which were used to perform AVL EXCITE big end bearing simulations with multiple surface contact patches. The results show that the inclusion of multiple surface patches and run-in wear profile lead to a significant change in distribution and also magnitude of bearing performance parameters e.g. pressure, friction losses, clearance height.<br>Glidlager är en av de mest använda komponenterna i motorer. De bidrar till en stor del av motorns totala friktion och en minskning av denna bidrar i hög grad till minskade utsläpp av CO2. Glidlager som arbetar under hög last utsätts ofta för blandfilmssmörjning där en del av lasten bärs av mekanisk kontakt mellan ytornas asperiteter. Detta kräver en noggrann modellering av asperitetskontakter för att få en realistisk prediktion av friktionsförluster i glidlager.Utvärderingsmetoden på Scania kopplar ihop 3D-mätning av lagrets ytfinhet i ett konfokalmikroskåp med en dynamisk tribologiberäkning i MBS-programvaran (Multi Body Simulation) AVL Excite.Under inkörning nöts asperiteterna ner på grund av metallkontakten mellan ytorna vilket påverkar lagerytans profil och ger olika kontaktzoner i axiell och periferiell riktning.Syftet med examensarbetet är att inkludera de olika kontaktzonerna och lagrets profil efter inkörning i Scanias befintliga utvärderingsmetod i syfte att noggrannare kunna simulera inkörning av lagren.Ytfinhetsmätningar utfördes med ett konfoklamikroskop på ett inkört vevlager vid kanterna, i mitten och i närheten av oljehålet.Med hjälp av dessa mätningar och en av Scanias befintliga kontaktmodeller beräknades asperitetstryck och flödesfaktorer vilka användes för att utföra vevlagerberäkningar i AVL Excite med olika kontaktegenskaper i olika regioner.Resultaten visar att införandet av regioner på lagerytan med olika lokala kontaktegenskaper och lagerprofil efter inkörning ger en signifikant förändring av såväl storleken som fördelningen av olika lagerresultat såsom till exempel lagertryck, friktionsförluster och oljefilmstjocklek.
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Irci, Erdinc. "Low-Profile Wideband Antennas Based on Tightly Coupled Dipole and Patch Elements." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1316456337.
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Gilles, Paul M. "Performance Enhancement and Characterization of an Electromagnetic Railgun." DigitalCommons@CalPoly, 2019. https://digitalcommons.calpoly.edu/theses/2107.
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Collision with orbital debris poses a serious threat to spacecraft and astronauts. Hypervelocity impacts resulting from collisions mean that objects with a mass less than 1g can cause mission-ending damage to spacecraft. A means of shielding spacecraft against collisions is necessary. A means of testing candidate shielding methods for their efficacy in mitigating hypervelocity impacts is therefore also necessary. Cal Poly’s Electromagnetic Railgun was designed with the goal of creating a laboratory system capable of simulating hypervelocity (≥ 3 km/s) impacts. Due to several factors, the system was not previously capable of high-velocity (≥ 1 km/s) tests. A deficient projectile design is revised, and a new design is tested. The new projectile design is demonstrated to enable far greater performance than the previous design, with a muzzle velocity ≥ 1 km/sbeing verified during testing, and an energy conversion efficiency of 2.7%. A method of improving contact and controlling wear at the projectile/rail interface using silver plating and conductive silver paste is validated. A mechanism explaining the problem of internal arcing within the railgun barrel is proposed, and design recommendations are made to eliminate arcing on the basis of the work done during testing. The primary structural members are found to be deficient for their application and a failure analysis of a failed member, loading analysis of the railgun barrel, and design of new structures is undertaken and presented.
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Pflugradt, Noah Daniel. "Modellierung von Wasser und Energieverbräuchen in Haushalten." Doctoral thesis, Universitätsbibliothek Chemnitz, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-209036.
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In dieser Arbeit wird ein Modell für die Simulation des Verbraucherverhaltens in Haushalten entwickelt. Das Ziel ist die Erstellung von Lastprofilen für den Strom- und Wasserverbrauch. Das Modell wird in einem Programm implementiert. Die Ergebnisse werden anschließend validiert und verschiedene Kenngrößen mit Literaturwerten verglichen. Abschließend wird eine Parameterstudie durchgeführt, um den Einfluss verschiedener Faktoren wie z.B. das Arbeitszeitmodell oder die Feiertagsmodellierung auf Lastprofile zu quantifizieren. Das Modell basiert auf einem Bedürfnismodell aus der Psychologie und ermöglicht den Verzicht auf die Errechnung von Aktivitäts-Wahrscheinlichkeitsverteilungen<br>In this thesis a model for the simulation of the behaviour of people in residential households is introduced. The goal is to generate load profiles for residential electricity and water consumption. The model is implemented as a Windows program. The results are validated and various metrics are compared with literature values. A parameter study is performed to quantify the influence of various factors such as the working hours or the influence of holidays on the load profile. The model is based on a desire model from the field of psychology and makes it possible to avoid calculating any probabilty distributions
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Bedoya, Bedoya Duvier Rolando. "Obtenção da margem minima de estabilidade de tensão de sistemas eletricos de potencia." [s.n.], 2007. http://repositorio.unicamp.br/jspui/handle/REPOSIP/262020.
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Orientadores: Carlos Alberto de Castro Junior, Luiz Carlos Pereira da Silva<br>Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação<br>Made available in DSpace on 2018-08-08T23:29:31Z (GMT). No. of bitstreams: 1
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Previous issue date: 2007<br>Resumo: Este trabalho apresenta uma nova e rápida metodologia para calcular a margem mínima de estabilidade de tensão de sistemas de potência. O cálculo da margem de estabilidade de tensão (MET) é normalmente requerido no planejamento e operação dos sistemas de potência. Usualmente, a carga é incrementada em uma direção predefinida baseada em históricos ou previsão da demanda (por exemplo, com fator de potência constante, seguido por um incremento proporcional nos MW da geração) até que o ponto de máximo carregamento (PMC) seja obtido. O cálculo da margem mínima METm, permite obter a pior direção de incremento de carga. Além disso, podem se apresentar situações onde incrementos de carga imprevistos em uma barra ou área conduzam a uma margem menor, arriscando a operação do sistema em modo seguro. O objetivo deste trabalho é apresentar uma metodologia nova e eficiente, do ponto de vista computacional, para obter a METm e a correspondente direção que é equivalente à pior direção de incremento de carga. Esta informação, com a margem que usualmente é calculada, permite que os operadores do sistema tomem medidas preventivas de controle para retornar ou manter o sistema em modo de operação seguro. Adicionalmente, é apresentado um estudo de áreas críticas para identificar as regiões ou barras que mais estão contribuindo a perda de estabilidade de tensão. É possível encontrar a melhor ação de controle, como corte de carga ou compensação reativa<br>Abstract: This work presents a new and fast method for computing the minimum voltage stability margin of electric power systems. The computation of the voltage stability margin (VSM) is often required for the planning and operation of power systems. Usually, loads are increased along a predefined direction, which can be estimated based on historical data or load forecast (e.g. with constant power factor, followed by a proportional MW generation increase) up to the system's maximum loading point is reached. The computation of the minimum VSM (mVSM) allows obtaining the load increase worst scenario. Also, situations may occur where variations from the predefined load increase direction, as for example, an unexpected load increase at some bus or area, may result in smaller VSM, taking the system to an insecure operating state. The aim of this work is to propose a new and fast method to compute the mVSM? and the corresponding load increase direction for which it occurs. This information, along with the usual VSM, allows operators to take measures like preventive control actions to move the system to securer operating points. Also a general study of critical areas is shown in order to identify the weakest region and bus that are contributing to the loss of voltage stability. It is possible to _nd the best control actions, like load curtailment or reactive compensation<br>Mestrado<br>Energia Eletrica<br>Mestre em Engenharia Elétrica
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Ferreira, Adriana Scheffer Quintela. "Estrategias de controle preventivo para a manutenção de margens de segurança com relação a estabilidade de tensão em tempo real." [s.n.], 2006. http://repositorio.unicamp.br/jspui/handle/REPOSIP/260657.
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Orientador: Carlos Alberto de Castro Junior<br>Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação<br>Made available in DSpace on 2018-08-07T10:41:53Z (GMT). No. of bitstreams: 1
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Previous issue date: 2006<br>Resumo: O problema de estabilidade de tensão tem recebido uma atenção crescente dos profissionais que atuam na área de análise e operação de sistemas de potência. O aumento das interligações aliado a operação das redes com altos níveis de carregamento torna mais provável a ocorrência de incidentes que podem levá-las à instabilidade de tensão, culminando com o colapso de tensão e grandes prejuízos à qualidade do fornecimento de energia elétrica. Ações de controle preventivo e/ou corretivo devem ser tomadas para melhorar a segurança de sistemas de potência. Este trabalho de pesquisa aborda a manutenção da segurança de redes com relação à estabilidade de tensão, através do estudo e da implementação de estratégias de controle preventivo, ou seja, que impedem a ocorrência de situações de instabilidade de tensão antes destas efetivamente ocorrerem. Além disso, são propostas filosofias práticas da utilização dos recursos disponíveis para mitigar o colapso de tensão, de maneira que uma margem de segurança com relação à estabilidade de tensão (MSET) apropriada e um perfil de tensão (PT) adequado sejam respeitados. Uma característica importante da metodologia proposta é que o problema de programação não linear a ser resolvido tem pequena dimensão, mesmo para sistemas de grande porte, pois apenas os controles mais eficientes são considerados e o número de restrições é limitado. A inovação consiste em atender uma meta de segurança sem a utilização plena de alguns dos recursos disponíveis, preservando os controles mais sensíveis e os pouco disponíveis para futura utilização em caso de emergências, mesmo após a ocorrência de certas contingências. A valia-se o potencial de utilização do processo proposto no ambiente de operação de redes em tempo real. Objetivou-se desenvolver um algoritmo capaz de identificar ações de controle preventivo apropriadas de forma a serem rapidamente implementadas<br>Abstract: The voltage stability problem has been receiving a growing attention from the professionals in the area of analysis and operation of power systems. The growth in interconnections along with the networks' operation with high loading levels makes the occurrence of incidents that can lead to voltage instability more likely, culminating with the volt age collapse and serious damages to the quality of the electric power supply. Preventive and/or corrective control actions should be taken to improve the power systems' security. This research work deals with the maintenance of network' security with respect to voltage stability, through the study and implementation of preventive control strategies, that prevent the occurrence of volt age instability situations before those effectively take place. Moreover, practical philosophies for using the available resources to mitigate the volt age collapse are proposed, so that an appropriate volt age stability security margin (VSSM) and an appropriate voltage profile (VP) be respected. An important feature of the proposed methodology is that the resulting nonlinear programming to be solved is small, even for large systems, since only the most effective controls are considered and the number of constraints is limited. The innovation consists of meeting a security target without the full use of some of the available resources. The proposed formulation preserves the most sensitive and the least available controls for future use in case of further emergencies, even after the occurrence of certain contingencies. The potential of use of the proposed process is evaluated in the real time operation environment. The objective was to develop an algorithm capable of identifying appropriate preventive control actions that can be quickly implemented.<br>Doutorado<br>Energia Eletrica<br>Doutor em Engenharia Elétrica
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Leone, Filho Marcos de Almeida. "Uma metodologia baseada em algoritmos genéticos para melhorar o perfil de tensão diário de sistemas de potência = A genetic-algorithm-based methodology for improving daily voltage profile of power systems." [s.n.], 2012. http://repositorio.unicamp.br/jspui/handle/REPOSIP/261162.
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Orientador: Takaaki Ohishi<br>Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação<br>Made available in DSpace on 2018-08-21T06:33:46Z (GMT). No. of bitstreams: 1
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Previous issue date: 2012<br>Resumo: A principal contribuição desta tese é a proposta de uma metodologia juntamente com a implementação de um sistema de suporte à decisão para dar subsídio à programação diária de sistemas de potência. Basicamente, a metodologia implementada neste trabalho visa melhorar o perfil das tensões em uma rede de transmissão de energia elétrica através de um ajuste fino dos taps dos transformadores. Este processo de otimização dos taps é feito com a utilização de Algoritmos Genéticos de maneira que, ao final deste processo, seja obtido um conjunto de valores de taps que, se aplicados à rede de transmissão, tornará as tensões mais próximas de um mesmo nível de tensão pré-determinado. Além disto, a abordagem proposta não é somente capaz de analisar uma \fotografia" de carga do sistema, mas também é capaz de realizar uma análise diária (em intervalos horários) para melhorar o perfil de tensão durante um dia completo de operação. A metodologia proposta é avaliada inicialmente com os sistemas IEEE-30 barras e IEEE-118 barras para que, finalmente, fosse aplicada para o sistema interligado nacional (SIN) brasileiro. Além disto, um sistema de suporte à decisão foi implementado durante o desenvolvimento deste trabalho. Tal sistema poderia ser usado para proporcionar ao operador do sistema de transmissão meios de avaliar os fluxos da rede através de uma execução de análises de sensibilidade quanto às possíveis utuações de carga em tempo de operação e também avaliar cenários de contingências<br>Abstract: The main contribution of this thesis is the proposal of a new methodology together with the implementation of a decision support system for real-time transmission grid operation. Hence, a methodology for improving voltage pro- _le for power transmission systems is described in this thesis. Basically, it consists in tuning the transformers taps in a way that the buses voltages in the same area would stay around a pre-specified level. Genetic Algorithms are applied for this optimization process in a way that, at the end of this process, a set of taps values that can drive the power system's voltage closer to a desired voltage level (if applied to it) is obtained. Furthermore, the proposed approach is not only able to analyze a static \picture" of power load, but also to cope with the issue of programming the hourly daily tap strategy according to the variations of the daily load profile. The proposed methodology is first evaluated with the \IEEE-30-bus" and with the \IEEE-118-bus" test cases so that it could be finally applied to the Brazilian interconnected national power system. Besides, a decision support system was implemented during the progress of the work. Such system was designed in a way that it could be possibly used by a grid operator in order to evaluate load flows and also to develop many different studies by analyzing the system's sensitiveness to the load variations at real time operation and also by evaluating a variety of contingencies scenarios<br>Doutorado<br>Energia Eletrica<br>Doutor em Engenharia Elétrica
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Olsson, Kevin. "Optimization of gas flow uniformity in enhancement of Metal Organic Chemical Vapor Deposition growth for III-nitrides." Thesis, Linköpings universitet, Halvledarmaterial, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-157378.
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The thesis focuses on the gas flow profile optimization of a non-conventional injector in a hot-wall MOCVD system. The injector’s gas flow profile is simulated with CFD and demonstrates awell-behaved laminar flow with a parabolic profile. To ensure the theory is in coherence with the reality, a qualitative study with five thermocouples in a test graphite piece of the was performed. First the thesis will take you through an introduction of the semiconductor field to arrive in a problem formulation. Then you will read about the principles of MOCVD systems, fluid dynamics principles and thermocouple theory. The experiment’s way of approach is thendescribed through all steps from blue print to results. A discussion about the result and the conclusion will be read before the proposals of future work based on the thesis work. The laminar flow is confirmed according to the resulting data and the limitations of the system is set to two different cases depending on background temperature. At 1000 °C a laminar flow is strongly indicated to be obtained at position 3A, closest to the growth area, within the gas flow range of 25 SLM regardless of background pressure, except for 700 mBar indicating turbulent flow for 15 SLM an up. At 20 and 200 mBar the laminar flow limit is suggested by data to be even higher and reaching a value of 35 SLM. At 450 °C the data indicate a laminar flow up to 20 SLM at position 3A regardless of background pressure condition, except for 700 mBar where the data indicate a laminar flow at 35 and 40 SLM. 50 mBar strongly indicates a laminar flow profile up to a gas flow of 35 SLM. With a background pressure of 20 mBar, the data suggests a laminar flow profile up to at least 25 SLM. At 100 mBar the data indicates a laminar flow within the range of 30 SLM.
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Canoas, Ana Carolina Garcia. "Logica nebulosa e tecnica de otimização particle swarm aplicados ao controle de tensão e de potencia reativa." [s.n.], 2008. http://repositorio.unicamp.br/jspui/handle/REPOSIP/260661.
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Orientador: Carlos Alberto Favarin Murari<br>Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação<br>Made available in DSpace on 2018-08-11T08:34:49Z (GMT). No. of bitstreams: 1
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Previous issue date: 2008<br>Resumo: Devido ao crescente aumento da demanda de energia elétrica e ao retardo de investimento na expansão dos sistemas e energia elétrica (SEE), a operação destes sistemas está cada vez mais próxima de seus limites operacionais, contribuindo para maior complexidade dos SEE. Neste sentido, para satisfazer as rígidas condições de operação, um gerenciamento do perfil de tensão e fluxo de potência tem se tornado cada vez mais importante para as concessionárias, de modo a aumentar a segurança operacional dos sistemas e otimizar o uso de fontes de potência reativa, visando suprir aos consumidores energia dentro de determinados padrões de qualidade e confiabilidade. o objetivo principal desta pesquisa é o desenvolvimento de metodologias com o objetivo de monitorar o perfil de tensão, mantendo-o dentro dos limites operativos, visando não perder a qualidade de fornecimento de energia elétrica. O primeiro método trata-se de uma ferramenta de auxílio à tomada de decisão dos operadores nos centros de controle, baseada em um conjunto de regras nebulosas, o qual é a base do sistema de inferência fuzzy (ou nebulosa) que por sua vez se fundamenta na teoria de conjuntos nebulosos. Considerando que o problema de controle de tensão e de potência reativa apresenta características de natureza não-linear e que envolve variáveis de controle contínuas e discretas, foi desenvolvido um segundo método, o qual utiliza lógica nebulosa em conjunto com a técnica de otimização particle swarm. Este método mostra a possibilidade de incorporar lógica nebulosa em algoritmos baseados em busca, possibilitando a redução das perdas do sistema, satisfazendo as restrições de operação, e garantindo que o perfil de tensão mantenha-se dentro dos limites operativos com uma melhor utilização das fontes de potência reativa<br>Abstract: Due to the growing electrical power demand and the lag of transmission system infrastruc ture, the operation of transmission systems approaches to its limits and increases the complexity of the system operation. ln this context, in order to satisfy the more rigid operating conditions, managing voltage profile and power flow in a more effective way becomes very important to the power companies that have the aim of enhancing the operating conditions and optimiz ing reactive power sources to provide the consumers with an adequate quality and reliability standards. The main objective of this research work is the development of methodologies for monitoring the volt age profile in order to keep it within operating limits and preserving the quality of the energy being served. The first method consists of a tool for helping decision making by system operators in control centres. This method is based on a set of fuzzy rules, which are the base of a fuzzy inference system. Considering that the voltage and reactive power control present nonlinear characteristics and mixed continuous and discrete variables, a hybrid meta-heuristic method based on fuzzy system and particle swarm optimization has been developed. The fuzzy system has been incorporated into swarm intelligence to provide operational point that allows reduction of system losses while satisfies the operationallimits, volt age constraints and the best utilisation of reactive power<br>Doutorado<br>Energia Eletrica<br>Doutor em Engenharia Elétrica
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Hou, Dongbin. "Very High Frequency Integrated POL for CPUs." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/77608.
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Point-of-load (POL) converters are used extensively in IT products. Every piece of the integrated circuit (IC) is powered by a point-of-load (POL) converter, where the proximity of the power supply to the load is very critical in terms of transient performance and efficiency. A compact POL converter with high power density is desired because of current trends toward reducing the size and increasing functionalities of all forms of IT products and portable electronics. To improve the power density, a 3D integrated POL module has been successfully demonstrated at the Center for Power Electronic Systems (CPES) at Virginia Tech. While some challenges still need to be addressed, this research begins by improving the 3D integrated POL module with a reduced DCR for higher efficiency, the vertical module design for a smaller footprint occupation, and the hybrid core structure for non-linear inductance control.
Moreover, as an important category of the POL converter, the voltage regulator (VR) serves an important role in powering processors in today's electronics. The multi-core processors are widely used in almost all kinds of CPUs, ranging from the big servers in data centers to the small smartphones in almost everyone's pocket. When powering multiple processor cores, the energy consumption can be reduced dramatically if the supply voltage can be modulated rapidly based on the power demand of each core by dynamic voltage and frequency scaling (DVFS). However, traditional discrete voltage regulators (VRs) are not able to realize the full potential of DVFS since they are not able to modulate the supply voltage fast enough due to their relatively low switching frequency and the high parasitic interconnect impedance between the VRs and the processors. With these discrete VRs, DVFS has only been applied at a coarse timescale, which can scale voltage levels only in tens of microseconds (which is normally called a coarse-grained DVFS). In order to get the full benefit of DVFS, a concept of an integrated voltage regulator (IVR) is proposed to allow fine-grained DVFS to scale voltage levels in less than a microsecond. Significant interest from both academia and industry has been drawn to IVR research.
Recently, Intel has implemented two generations of very high frequency IVR. The first generation is implemented in Haswell processors, where air core inductors are integrated in the processor's packaging substrate and placed very closely to the processor die. The air core inductors have very limited ability in confining the high frequency magnetic flux noise generated by the very high switching frequency of 140MHz. In the second generation IVR in Broadwell processors, the inductors are moved away from the processor substrate to the 3DL PCB modules in the motherboard level under the die.
Besides computers, small portable electronics such as smartphones are another application that can be greatly helped by IVRs. The smartphone market size is now larger than 400 billion US dollars, and its power consumption is becoming higher and higher as the functionality of smartphones continuously advances. Today's multi-phase VR for smartphone processors is built with a power management integrated circuit (PMIC) with discrete inductors. Today's smartphone VRs operate at 2-8MHz, but the discrete inductor is still bulky, and the VR is not close enough to the processor to support fine-grained DVFS. If the IVR solution can be extended to the smartphone platform, not only can the battery life be greatly improved, but the total power consumption of the smartphone (and associated charging time and charging safety issues) can also be significantly reduced. Intel's IVR may be a viable solution for computing applications, but the air core inductor with un-confined high-frequency magnetic flux would cause very severe problems for smartphones, which have even less of a space budget. This work proposes a three-dimensional (3D) integrated voltage regulator (IVR) structure for smartphone platforms. The proposed 3D IVR will operate with a frequency of tens of MHz. Instead of using an air core, a high-frequency magnetic core without an air gap is applied to confine the very high frequency flux. The inductor is designed with an ultra-low profile and a small footprint to fit the stringent space requirement of smartphones.
A major challenge in the development of the very high frequency IVR inductor is to accurately characterize and compare magnetic materials in the tens of MHz frequency range. Despite the many existing works in this area, the reported measured properties of the magnetics are still very limited and indirect. In regards to permeability, although its value at different frequencies is often reported, its saturation property in real DC-biased working conditions still lacks investigation. In terms of loss property, the previous works usually show the equivalent resistance value only, which is usually measured with small-signal excitation from an impedance/network analyzer and is not able to represent the real magnetic core loss under large-signal excitation in working conditions. The lack of magnetic properties in real working conditions in previous works is due to the significant challenges in the magnetic characterization technique at very high frequencies, and it is a major obstacle to accurately designing and testing the IVR inductors. In this research, an advanced core loss measurement method is proposed for very high frequency (tens of MHz) magnetic characterization for the IVR inductor design. The issues of and solutions for the permeability and loss measurement are demonstrated. The LTCC and NEC flake materials are characterized and compared up to 40MHz for IVR application.
Based on the characterized material properties, both single-phase and multi-phase integrated inductor are designed, fabricated and experimentally tested in 20MHz buck converters, featuring a simple single-via winding structure, small size, ultra-low profile, ultra-low DCR, high current-handling ability, air-gap-free magnetics, multi-phase integration within one magnetic core, and lateral non-uniform flux distribution. It is found that the magnetic core operates at unusually high core loss density, while it is thermally manageable. The PCB copper can effectively dissipate inductor heat with 3D integration. In addition, new GaN device drivers and magnetic materials are evaluated and demonstrated with the ability to increase the IVR frequency to 30MHz and realize a higher density with a smaller loss.
In summary, this research starts with improving the 3D integrated POL module, and then explores the use of the 3D integration technique along with the very high frequency IVR concept to power the smartphone processor. The challenges in a very high frequency magnetic characterization are addressed with a novel core loss measurement method capable of 40MHz loss characterization. The very high frequency multi-phase inductor integrated within one magnetic component is designed and demonstrated for the first time. A 20MHz IVR platform is built and the feasibility of the concept is experimentally verified. Finally, new GaN device drivers and magnetic materials are evaluated and demonstrated with the ability to increase the IVR frequency to 30MHz and realize higher density with smaller loss.<br>Ph. D.
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Chen, Juan [Verfasser], Thomas [Akademischer Betreuer] Arentz, and Amir S. [Akademischer Betreuer] Jadidi. "Extent and spatial distribution of left atrial arrhythmogenic sites, late gadolinium enhancement at magnetic resonance imaging, and low-voltage areas in patients with persistent atrial fibrillation: comparison of imaging vs. electrical parameters of fibrosis and arrhythmogenesis." Freiburg : Universität, 2019. http://d-nb.info/1194312691/34.
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Nguyen, Thi Dak Ha. "Réalisation et caractérisation de HEMTs AlGaN/GaN sur silicium pour applications à haute tension." Phd thesis, Université Paris Sud - Paris XI, 2013. http://tel.archives-ouvertes.fr/tel-00934655.
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Cette thèse est une contribution aux développements de HEMTS AlGaN/GaN sur substrat de silicium pour des applications basses fréquences sous fortes tensions (typiquement 600V) comme les commutateurs pour la domotique ou les circuits de puissance des véhicules électriques. Elle a été menée en collaboration étroite avec Picogiga International qui a réalisé toutes les épitaxies. Elle est composée de trois parties : développement d'une technologie de fabrication, étude des courants de fuite, amélioration du pouvoir isolant de la barrière et recherche d'un comportement "normally off". La réalisation de contacts ohmiques peu résistifs est l'étape cruciale de la fabrication des HEMTs AlGaN/GaN de puissance. Une optimisation de l'empilement des métaux utilisés, de la température et du temps de recuit ainsi que la recherche d'un compromis sur la distance métallisation - gaz d'électrons, nous a permis de réaliser des contacts ohmiques proches de l'état de l'art (0,5 Ohm.mm). L'origine des courants de fuite a été systématiquement étudiée sur cinq types d'épitaxies différentes. La distance grille - drain et les courants de fuites ont été identifiés comme étant les deux facteurs limitant la tension de claquage. Selon la structure, les courants de fuite ont lieu soit à travers la grille (~e-8 A/mm à 210V), soit en parallèle au canal (e-5 A/mm). Dans les deux cas, ces courants sont comparables aux courants de fuite au travers du tampon (i.e. courants mesurés entre deux mésas). Ces courants de fuite, ont été attribués aux couches de transition nécessaires à l'adaptation de l'épitaxie des couches de nitrure sur le substrat de silicium. La réalisation de HEMT AlGaN/GaN sur silicium pour les applications à haute tension passera donc par une amélioration de ces couches tampons.Nous avons démontré qu'il est possible d'améliorer l'isolation de la barrière en AlGaN grâce à une hydrogénation du matériau. En effet un traitement de surface des transistors par un plasma hydrogène permet, par diffusion, d'y incorporer de l'hydrogène qui passive les dislocations traversantes. Après traitement, les courants de fuite de grille sont réduits et la tension de claquage est repoussée à 400V avec des courants de fuite de l'ordre de e-6 A/mm. Dans ces conditions, le claquage a alors lieu en surface de l'échantillon, il n'est plus limité que par la distance grille-drain. Ce résultat ouvre la voie à la réalisation de HEMT à forte tension de claquage (V~600V).L'effet du plasma fluoré SF6 sur les caractéristiques électriques des HEMT (AlN/GaN)/GaN (la barrière est en super-réseaux AlN/GaN) a été étudié pour la première fois dans cette thèse. Les ions fluor incorporés dans cette barrière agissent comme des donneurs qui font augmenter la densité du gaz bi-dimensionnel d'électrons et décaler la tension de pincement vers les tensions négatives. Cet effet est à l'opposé de celui observé dans les HEMT à barrière en AlGaN. Ce résultat élimine la possibilité de réaliser les HEMT (AlN/GaN)/GaN "normally off" par un dopage au fluor, une technique simple et efficace qui donne de bons résultats sur les HEMT à barrière AlGaN. D'autre part, il apporte quelques réponses expérimentales aux prévisions théoriques d'utiliser le fluor pour les dopages de type n ou p dans les nitrures d'éléments III.
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Bastos, Camila Bianka Silva. "Estudo dos impactos de um sistema fotovoltaico conectado à rede elétrica utilizando análises QSTS." Universidade do Estado de Santa Catarina, 2015. http://tede.udesc.br/handle/handle/2081.
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Previous issue date: 2015-02-27<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior<br>This dissertation presents a study of the operation of two different three-phase grid-connected test-grids with the connection of a 1MWp photovoltaic system. Two analysis methods are used to evaluate the impacts of this photovoltaic systeM, these methods being conventional static analysis and the analysis known as Quasi-Static Time-Series Analysis. Despite the fact that all grids have unique characteristics, it is important to use test-grids, which simulate the real grid characteristics, to analyze the kinds of problems that can occur and then look for alternatives, if necessary. The impacts evaluated are related to the system losses, minimized with the allocation study of the generation on the grid, voltage profile and tap position curve, when automatic load tap changers are used. It was verified that the photovoltaic system interconnection point is the most influenced one after its connection to the grid. The Quasi-Static Time-Series Analysis allow the correct evaluation of the load-generation interaction, running the time series power flow through estimated data for the load and irradiance curves during 168 hours. The conventional static analysis only considers critical operation conditions, like minimum and maximum load, and no generation or maximum generation, and does not evaluate different case scenarios that occur in reality. The photovoltaic systems can bring many advantages to the electric systems, like the improvement on the final consumer voltage profile, line losses reduction, and also environmental impacts reduction. However, with the increase of distributed photovoltaic generation on the electrical grid, it s necessary to be aware of the impacts that this may cause by performing interconnection studies.<br>Esta dissertação apresenta um estudo da operação de uma rede teste trifásica de média tensão com a interligação de um sistema fotovoltaico de 1,0 MWp. Dois métodos de análise são utilizados para avaliar os impactos deste sistema fotovoltaico, sendo estes métodos as análises estáticas convencionais eas análises conhecidas como Quasi-Static Time-Series Analysis. Apesar de cada rede elétrica apresentar características únicas, é importante a utilização de sistemas testes, que simulam as características de sistemas reais, para analisar que tipos problemas podem surgir e então buscar alternativas, se necessário. Os impactos avaliados se referem às perdas no sistema, minimizadas com a correta alocação da geração, perfil de tensão e curva de posição do tap, no caso de transformador com comutação automática de tap. Contata-se que o ponto de conexão do sistema fotovoltaico é o mais influenciado pela sua conexão à rede. As análises QSTS possibilitam avaliar corretamente a iteração entre carga e geração, efetuando o fluxo de potência consecutivo através de dados estimados para as curvas de carga e de irradiância solar ao longo de 168 horas. Já as análises convencionais consideram apenas condições críticas de operação, como por exemplo, carga leve ou nominal e geração nula ou máxima, não avaliando então diferentes cenários de operação que ocorrem na prática. Os sistemas fotovoltaicos podem trazer muitos benefícios aos sistemas elétricos, como melhoria do perfil de tensão de atendimento ao consumidor, redução de perdas nas linhas, além da redução nos impactos ambientais. Entretanto, com o aumento de geração fotovoltaica distribuída na rede, é necessário estar atento aos impactos que isto pode causar através de estudos de interconexão.
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Miri, Lavasani Seyed Hossein. "Design and phase-noise modeling of temperature-compensated high frequency MEMS-CMOS reference oscillators." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/41096.
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Frequency reference oscillator is a critical component of modern radio transceivers. Currently, most reference oscillators are based on low-frequency quartz crystals that are inherently bulky and incompatible with standard micro-fabrication processes. Moreover, their frequency limitation (<200MHz) requires large up-conversion ratio in multigigahertz frequency synthesizers, which in turn, degrades the phase-noise. Recent advances in MEMS technology have made realization of high-frequency on-chip low phase-noise MEMS oscillators possible.
Although significant research has been directed toward replacing quartz crystal oscillators with integrated micromechanical oscillators, their phase-noise performance is not well modeled. In addition, little attention has been paid to developing electronic frequency tuning techniques to compensate for temperature/process variation and improve the absolute frequency accuracy.
The objective of this dissertation was to realize high-frequency temperature-compensated high-frequency (>100MHz) micromechanical oscillators and study their phase-noise performance. To this end, low-power low-noise CMOS transimpedance amplifiers (TIA) that employ novel gain and bandwidth enhancement techniques are interfaced with high frequency (>100MHz) micromechanical resonators. The oscillation frequency is varied by a tuning network that uses frequency tuning enhancement techniques to increase the tuning range with minimal effect on the phase-noise performance. Taking advantage of extended frequency tuning range, and on-chip temperature-compensation circuitry is embedded with the sustaining circuitry to electronically temperature-compensate the oscillator. Finally, detailed study of the phase-noise in micromechanical oscillators is performed and analytical phase-noise models are derived.