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1
Balachandran, Neerajnayan. "Low power memory controller subsystem IP exploration using RTL power flow : An End-to-end power analysis and reduction Methodology". Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-280095.
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With FinFET based Application Specific Integrated Circuit (ASIC) designs delivering on the promises of scalability, performance, and power, the road ahead is bumpy with technical challenges in building efficient ASICs. Designers can no longer rely on the ‘auto-scaling’ power reduction that follows technology node scaling, in these times when 7nm presents itself as a ‘long-lived’ node. This leads to the need for early power analysis and reduction flows that are incorporated into the ASIC Intellectual Property (IP) design flow. This leads to a focus on power-efficient design in addition to being functionally efficient. Power inefficiency related hotspots are the leading causes of chip re-spins, and a guideline methodology to design blocks in a power-efficient manner leads to a power-efficient design of the Integrated Circuits (ICs). This alleviates the intensity of cooling requirements and the cost. The Common Memory controller is one of the leading consumers of power in the ASIC designs at Ericsson. This Thesis focusses on developing a power analysis and reduction flow for the common memory controller by connecting the verification environment of the block to low-level power analysis tools, using motivated test cases to collect power metrics, thereby leading to two main goals of the Thesis, characterization and optimization of the block for power. This work also includes an energy efficiency perspective through the Differential Energy Analysis technique, initiated by Qualcomm and Ansys, to improve the flow by improving the test cases that help uncover power inefficiencies/bugs and therefore optimize the block. The flow developed in the Thesis fulfills the goals of characterizing and optimizing the block. The characterization data is presented to provide an idea of the type of data that can be collected and useful for SoC architects and designers in planning for future designs. The characterization/profiling data collected from the blocks collectively contribute to the Electronic System-level power analysis that helps correlate the ASIC power estimate to silicon. The work also validates the flow by working on a specific sub-block, identifying possible power bugs, modifying the design and validating improved performance and thereby, validating the flow.Med FinFET-baserade applikationsspecifika integrerade kretsar (ASIC) -konstruktioner som ger löften om skalbarhet, prestanda och kraft är vägen framåt ojämn med tekniska utmaningar när det gäller att bygga effektiva ASIC: er. Formgivare kan inte längre lita på den "autoskalande" effektminskningen som följer teknisk nodskalning, i dessa tider då 7nm presenterar sig som en "långlivad" nod. Detta leder till behovet av tidig kraftanalys och reduktionsflöden som är integrerade i ASIC Intellectual Property (IP) designflöde. Detta leder till fokus på energieffektiv design förutom att det är funktionellt effektivt. Krafteffektivitetsrelaterade hotspots är de ledande orsakerna till respins av chip, och en riktlinjemetodik för att konstruera block på ett energieffektivt sätt leder till energieffektiv design av Integrated Circuits (ICs). Detta lindrar intensiteten hos kylbehovet och kostnaden. Common Memory-kontrollen är en av de ledande energikonsumenterna i ASIC-designen hos Ericsson. Denna avhandling fokuserar på att utveckla en effektanalys och reduktionsflöde för den gemensamma minneskontrollern genom att ansluta verifieringsmiljön för blocket till lågnivåeffektanalysverktyg, med hjälp av motiverade test caser för att samla effektmätvärden, vilket leder till två huvudmål för avhandlingen, karakterisering och optimering av blocket för kraft. Detta arbete inkluderar också energieffektivitetsperspektiv genom Differential Energy Analys-teknik, initierad av Qualcomm och Ansys, för att förbättra flödet genom att förbättra test cases som hjälper till att upptäcka effekteffektivitet / buggar och därför optimera blocket. Flödet som utvecklats i avhandlingen uppfyller målen att karakterisera och optimera blocket. Karaktäriseringsdata presenteras för att ge en uppfattning om vilken typ av data som kan samlas in och vara användbara för SoC-arkitekter och designers i planering för framtida mönster. Karaktäriserings/ profileringsdata som samlats in från blocken bidrar tillsammans till effektanalysen för elektronisk systemnivå som hjälper till att korrelera ASIC-effektberäkningen till kisel. Arbetet validerar också flödet genom att arbeta på ett specifikt underblock, identifiera möjliga effektbuggar, modifiera utforma och validera förbättrad prestanda och därmed validera flödet.
2
Canossa, Jâine Henrique. "Um programa interativo para estudos de fluxo de potência /". Ilha Solteira : [s.n.], 2007. http://hdl.handle.net/11449/87243.
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Orientador: Dilson Amâncio AlvesBanca: Sergio Azevedo de Oliveira
Banca: Carlos Alberto Castro Júnior
Resumo: Este trabalho apresenta um programa interativo para a simulação do fluxo de potência e do fluxo de potência continuado. O programa foi desenvolvido no ambiente MATLAB e a simulação é realizada por meio de uma interface gráfica. A interface gráfica não só proporciona um bom desempenho computacional, mas também torna o programa mais amigável para o usuário. Através dela o usuário pode editar os arquivos de entrada e saída e visualizar e analisar os resultados obtidos diretamente na tela do computador. A partir do diagrama unifilar dos sistemas, a interface gráfica permite que o usuário: mude os parâmetros do sistema (dados de barras e de linhas de transmissão); remova uma linha de transmissão com um simples clicar sobre ela; visualize os perfis de tensão nas barras, e os fluxos de potência ativa e reativa nas linhas de transmissão. Todas estas características fazem do programa desenvolvido uma ferramenta recomendada para fins educacionais.
Abstract: This work presents an interactive computing program for power flow and continuation power flow simulations. The power flow and continuation power flow programs were developed in the MATLAB environment and the simulation is accomplished through a graphical user interface. The graphical user interface provides not only a good computational performance, but also an user-friendly teaching software. With the use of this interface the user can edit the input and output data files of the selected systems and can visualize and analyze the results of the program directly in the computer screen. Directly from the system one-line diagrams, the graphical user interface allows the user: to change the parameters of the system (bus and lines system data); to remove the transmission line clicking directly on it; to visualize the bus voltage profile, and the active and reactive power flows. All these characteristics make the developed program recommended for educational purposes.
Mestre
3
Zhang, Xiang. "Dimensional analysis based CFD modelling for power transformers". Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/dimensional-analysis-based-cfd-modelling-for-power-transformers(49cac27d-38b9-4f23-a6ec-b5106422420c).html.
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Reliable thermal modelling approaches are crucial to transformer thermal design and operation. The highest temperature in the winding, usually referred to as the hot-spot temperature, is of the greatest interest because the insulation paper at the hot-spot undergoes the severest thermal ageing, and determines the life expectancy of the transformer insulation. Therefore, the primary objective of transformer thermal design is to control the hot-spot temperature rise over the ambient temperature within certain limit. For liquid-immersed power transformers, the hot-spot temperature rise over the ambient temperature is controlled by the winding geometry, power loss distribution, liquid flow rate and liquid properties. In order to obtain universally applicable thermal modelling results, dimensional analysis is adopted in this PhD thesis to guide computational fluid dynamics (CFD) simulations for disc-type transformer windings in steady state and their experimental verification. The modelling work is split into two parts on oil forced and directed (OD) cooling modes and oil natural (ON) cooling modes. COMSOL software is used for the CFD simulation work For OD cooling modes, volumetric oil flow proportion in each horizontal cooling duct (Pfi) and pressure drop coefficient over the winding (Cpd) are found mainly controlled by the Reynolds number at the winding pass inlet (Re) and the ratio of horizontal duct height to vertical duct width. The correlations for Pfi and Cpd with the dimensionless controlling parameters are derived from CFD parametric sweeps and verified by experimental tests. The effects of different liquid types on the flow distribution and pressure drop are investigated using the correlations derived. Reverse flows at the bottom part of winding passes are shown by both CFD simulations and experimental measurements. The hot-spot factor, H, is interpreted as a dimensionless temperature at the hot-spot and the effects of operational conditions e.g. ambient temperature and loading level on H are analysed. For ON cooling modes, the flow is driven by buoyancy forces and hot-streak dynamics play a vital role in determining fluid flow and temperature distributions. The dimensionless liquid flow and temperature distributions and H are all found to be controlled by Re, Pr and Gr/Re2. An optimal design and operational regime in terms of obtaining the minimum H, is identified from CFD parametric sweeps, where the effects of buoyancy forces are balanced by the effects of inertial forces. Reverse flows are found at the top part of winding passes, opposite to the OD results. The total liquid flow rates of different liquids for the same winding geometry with the same power loss distribution in an ON cooling mode are determined and with these determined total liquid flow rates, the effects of different liquids on fluid flow and temperature distributions are investigated by CFD simulations. The CFD modelling work on disc-type transformer windings in steady state present in this PhD thesis is based on the dimensional analyses on the fluid flow and heat transfer in the windings. Therefore, the results obtained are universally applicable and of the simplest form as well. In addition, the dimensional analyses have provided insight into how the flow and temperature distribution patterns are controlled by the dimensionless controlling parameters, regardless of the transformer operational conditions and the coolant liquid types used.
4
Marin, Manuel. "GPU-enhanced power flow analysis". Thesis, Perpignan, 2015. http://www.theses.fr/2015PERP0041.
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Cette thèse propose un large éventail d'approches afin d'améliorer différents aspects de l'analyse des flux de puissance avec comme fils conducteur l'utilisation du processeurs graphiques (GPU). Si les GPU ont rapidement prouvés leurs efficacités sur des applications régulières pour lesquelles le parallélisme de données était facilement exploitable, il en est tout autrement pour les applications dites irrégulières. Ceci est précisément le cas de la plupart des algorithmes d'analyse de flux de puissance. Pour ce travail, nous nous inscrivons dans cette problématique d'optimisation de l'analyse de flux de puissance à l'aide de coprocesseur de type GPU. L'intérêt est double. Il étend le domaine d'application des GPU à une nouvelle classe de problème et/ou d'algorithme en proposant des solutions originales. Il permet aussi à l'analyse des flux de puissance de rester pertinent dans un contexte de changements continus dans les systèmes énergétiques, et ainsi d'en faciliter leur évolution. Nos principales contributions liées à la programmation sur GPU sont: (i) l'analyse des différentes méthodes de parcours d'arbre pour apporter une réponse au problème de la régularité par rapport à l'équilibrage de charge ; (ii) l'analyse de l'impact du format de représentation sur la performance des implémentations d'arithmétique floue. Nos contributions à l'analyse des flux de puissance sont les suivantes: (ii) une nouvelle méthode pour l'évaluation de l'incertitude dans l'analyse des flux de puissance ; (ii) une nouvelle méthode de point fixe pour l'analyse des flux de puissance, problème que l'on qualifie d'intrinsèquement parallèleThis thesis addresses the utilization of Graphics Processing Units (GPUs) for improving the Power Flow (PF) analysis of modern power systems. Currently, GPUs are challenged by applications exhibiting an irregular computational pattern, as is the case of most known methods for PF analysis. At the same time, the PF analysis needs to be improved in order to cope with new requirements of efficiency and accuracy coming from the Smart Grid concept. The relevance of GPU-enhanced PF analysis is twofold. On one hand, it expands the application domain of GPU to a new class of problems. On the other hand, it consistently increases the computational capacity available for power system operation and design. The present work attempts to achieve that in two complementary ways: (i) by developing novel GPU programming strategies for available PF algorithms, and (ii) by proposing novel PF analysis methods that can exploit the numerous features present in GPU architectures. Specific contributions on GPU computing include: (i) a comparison of two programming paradigms, namely regularity and load-balancing, for implementing the so-called treefix operations; (ii) a study of the impact of the representation format over performance and accuracy, for fuzzy interval algebraic operations; and (iii) the utilization of architecture-specific design, as a novel strategy to improve performance scalability of applications. Contributions on PF analysis include: (i) the design and evaluation of a novel method for the uncertainty assessment, based on the fuzzy interval approach; and (ii) the development of an intrinsically parallel method for PF analysis, which is not affected by the Amdahl's law
5
Bayan, Nima. "Harmonic flow analysis in power distribution networks". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0011/MQ52509.pdf.
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Dandachi, Najib H. "Network flow method for power system analysis". Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47398.
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Yang, J. "Power flow analysis of nonlinear dynamical systems". Thesis, University of Southampton, 2013. https://eprints.soton.ac.uk/355696/.
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The power ow analysis approach, which arose from high frequency vibration problems, has been developed into a powerful technique to characterise the dynamic behaviour of complex structures and coupled systems. It has been extensively used to study various linear systems. However, because of the complexity in modelling and simulation, the power ow behaviour of nonlinear dynamical systems remains largely unexplored. This thesis aims to develop power ow analysis approaches for nonlinear dynamical systems, to investigate the effects of damping and/or stiffness nonlinearities on their power ow behaviour, and to apply the findings to enhance the performance of energy harvesting devices as well as vibration control systems. Power ow characteristics of the Du�ng and the Van der Pol (VDP) oscillators are investigated to address the distinct power input and dissipation behaviour due to stiffness and damping nonlinearities, respectively. It is shown that in a nonlinear velocity response with multiple frequency signatures, only the in-phase component of the same frequency as the harmonic excitation contributes to the time-averaged input power. It is demonstrated that bifurcations can cause significant jumps of time-averaged power ows, whereas the associated time-averaged input power of a chaotic response is insensitive to the initial conditions but tends to an asymptotic value as the averaging time increases. It is also found that the time averaged input power of the unforced VDP oscillator can become negative in some ranges of excitation frequencies. Power ow behaviour of two degrees-of-freedom systems with nonlinear stiffness/- damping is also studied using the developed methods to enhance vibration isolation/absorption performance. It is demonstrated that the stiffness and damping nonlinearities in the system affects time-averaged power ows mainly in a narrow frequency range around resonance frequencies. The work described in this thesis provides new insights into power ow generation, transmission and dissipation mechanisms in nonlinear dynamical systems and facilitates more reliable and effective designs with improved dynamic performance. The ability of the VDP oscillator to extract external energy sheds light on energy harvesting using ow-induced vibrations of a nonlinear apping foil system. A nonlinear isolator with a negative sti�ness mechanism is proposed providing less input power in an enlarged frequency range. These studies thus yield an improved understanding of power ow behaviour in nonlinear dynamical systems.
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Wang, Zhenhong. "Power flow analysis of engineering structure using substructure techniques". Thesis, University of Southampton, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270373.
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Olofsson, Magnus. "Power Flow Analysis of the Swedish Railway Electrical System". Licentiate thesis, Stockholm, 1993. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-223934.
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This thesis deals with analysis of the steady state power flow in the Swedish railway electrical system. Finding the steady state of the system means that all voltages and power flows in the system are known. The trains are supplied from the public grid using frequency converters. This is the major difference compared with ordinary power systems fed from turbine-driven generators. The output voltage phase shift function for the converters is important in the mathematical formulation of the problem. In the system, the locomotives are almost entirely of the Re-type, having a rectifier and d.c.-motors. The fundamental frequency reactive power need is thereby dependent on the train speed, wheel power and line voltage. In this thesis, the converters and thyristor locomotives are modelled and included in the load flow formulation. The method is shown to have good convergence properties. An approximate and fast method for the calculation of the power injections from converters is presented. A necessary condition for this approximate method to be valid is that the converters are strongly interconnected. The construction of a new 130 kV line brings the converters close to each other electrically. Energy input from each of the converters inthe system can be simulated calculating repeated load flows. Measurements in a real system have verified the applicability of the proposed load flow method. Examples of areas where the method can be used are system studies and optimal control of the system. The locomotives act as sources of harmonic currents. In an extended load flow formulation this is taken into account. The fundamental idea behind the method is that harmonic powers caused by the thyristor bridges at first are transferred as fundamental frequency active power from the sinusoidal voltage sources. The method thus gives the fundamental frequency powers injected from the sinusoidal voltage sources to the network. Comparisons with time simulations with detailed models show good agreement.
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Estes, Steven Douglas. "Power system analysis suite for Windows". Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-02132009-170931/.
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Guldbrand, Anna. "Analysis of an induction regulator for power flow control in electric power transmission systems". Thesis, Linköping University, The Department of Physics, Chemistry and Biology, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-5329.
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Controlling the power flow in transmission systems has recently gained increased interest. The difficulties of building new lines and the pressure of having a high utilization of existing assets, makes the flexibility of grid systems increasingly important.
This master thesis work investigates induction regulators as control devices for active power flow in a transmission system. A small change in angle of the rotor affects both the amplitude and the phase of the voltage. The magnetic coupling in the induction regulator can be controlled by changing the permeability of a thermo magnetic material such as gadolinium and can hence give a second independent controlling parameter. An analytical model and calculations in the
FEM software AceTripleC together with Matlab, is used to simulate the influence of the regulators connected to a simple grid in case1, a 400 kV scenario and case 2, a 45 kV scenario.
The analysis was carried out on a small transmission system consisting of two parallel transmission lines connected to source and load. The induction regulators are connected to one of the parallel transmission lines. The regulators modelled in case 1 must be able to control the active power flow in the regulated line to vary between 50 and 150 % of the original power flow through this line.
This shall be done over a range of 0 to 800 MW transmitted power. The regulators modelled in case 2 must be able to control the active power flow in
the regulated line to vary between 0 and 30 MW, if this does not cause the power flow in the parallel line to exceed 30 MW. This shall be done over a range of 0 to
50 MW transmitted power.
The regulators are designed as small and inexpensive as possible while still fulfilling requirements regarding the active power flow controllability in the grid, current density in windings and maximum flux density in core and gap.
The results indicate that the size of the 400 kV solution has to be reduced to become competitive whereas for the 45 kV solution the relative difference to existing solution is smaller. Advantages with the proposed design over a phase shifting transformer are mainly a simpler winding scheme and the absence of a tap changer.
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Min, Liang. "Decomposition algorithms for multi-area power system analysis". Texas A&M University, 2003. http://hdl.handle.net/1969.1/5919.
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A power system with multiple interconnected areas needs to be operated coordinately
for the purposes of the system reliability and economic operation, although
each area has its own ISO under the market environment. In consolidation of different
areas under a common grid coordinator, analysis of a power system becomes more
computationally demanding. Furthermore, the analysis becomes more challenging
because each area cannot obtain the network operating or economic data of other
areas.
This dissertation investigates decomposition algorithms for multi-area power system
transfer capability analysis and economic dispatch analysis. All of the proposed
algorithms assume that areas do not share their network operating and economic
information among themselves, while they are willing to cooperate via a central coordinator
for system wide analyses.
The first proposed algorithm is based on power transfer distribution factors
(PTDFs). A quadratic approximation, developed for the nonlinear PTDFs, is used to
update tie-line power flows calculated by Repeated Power Flow (RPF). These tie-line
power flows are then treated as injections in the TTC calculation of each area, as
the central entity coordinates these results to determine the final system-wide TTC
value.
The second proposed algorithm is based on REI-type network equivalents. It uses
the Continuation Power Flow (CPF) as the computational tool and, thus, the problem of voltage stability is considered in TTC studies. Each area uses REI equivalents of
external areas to compute its TTC via the CPF. The choice and updating procedure
for the continuation parameter employed by the CPF is implemented in a distributed
but coordinated manner.
The third proposed algorithm is based on inexact penalty functions. The traditional
OPF is treated as the optimization problems with global variables. Quadratic
penalty functions are used to relax the compatible constraints between the global
variables and the local variables. The solution is proposed to be implemented by
using a two-level computational architecture.
All of the proposed algorithms are verified by numerical comparisons between the
integrated and proposed decomposition algorithms. The proposed algorithms lead to
potential gains in the computational efficiency with limited data exchanges among
areas.
13
Muggleton, Jennifer Margaret. "Acoustic power flow in fluid filled tubes and cavities". Thesis, University of Southampton, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315492.
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Li, Chen. "State Space Modeling and Power Flow Analysis of Modular Multilevel Converters". Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/71811.
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For the future of sustainable energy, renewable energy will need to significantly penetrate existing utility grids. While various renewable energy sources are networked with high-voltage DC grids, integration between these high-voltage DC grids and the existing AC grids is a significant technical challenge. Among the limited choices available, the modular multi-level converter (MMC) is the most prominent interface converter used between the DC and AC grids. This subject has been widely pursued in recent years. One of the important design challenges when using an MMC is to reduce the capacitor size associated with each module. Currently, a rather large capacitor bank is required to store a certain amount of line-frequency related circulating energy. Several control strategies have been introduced to reduce the capacitor voltage ripples by injecting certain harmonic current. Most of these strategies were developed using trial and error and there is a lack of a systematic means to address this issue. Most recently, Yadong Lyu has proposed to control the modulation index in order to reduce capacitor ripples. The total elimination of the unwanted circulating power associated with both the fundamental line frequency and the second-order harmonic was demonstrated, and this resulted in a dramatic reduction in capacitor size. To gain a better understanding of the intricate operation of the MMC, this thesis proposes a state-space analysis technique in the present paper. Combining the power flow analysis with the state trajectory portrayed on a set of two-dimensional state plans, it clearly delineates the desired power transfer from the unwanted circulating energy, thus leading to an ultimate reduction in the circulation energy and therefore the required capacitor volume.Master of Science
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Bonini, Neto Alfredo. "Técnicas de parametrização geométrica para o método da continuação /". Ilha Solteira : [s.n.], 2011. http://hdl.handle.net/11449/100307.
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Orientador: Dilson Amancio AlvesBanca: Sergio Azevedo de Oliveira
Banca: Francisco Carlos Vieira Malange
Banca: Luiz Carlos Pereira da Silva
Banca: Madson Cortes de Almeida
Resumo: Este trabalho analisa a utilização de técnicas de parametrização global para o fluxo de carga continuado. Essas técnicas são consideradas inadequadas para a obtenção da margem de carregamento de sistemas com problemas de estabilidade de tensão com características fortemente locais. Isto se deve ao fato de que no ponto de máximo carregamento a singularidade da matriz Jacobiana do método de parametrização global coincide com a da matriz Jacobiana do fluxo de carga. Nesses casos, a parametrização local é considerada como a única forma de se eliminar a singularidade. Entretanto, este trabalho mostra que a singularidade também pode ser eficientemente eliminada não só para estes sistemas, mas para qualquer outro, através de uma nova técnica de parametrização (global). A técnica utiliza a equação de uma reta que passa por um ponto no plano determinado pelas variáveis fator de carregamento e a somatória das magnitudes, ou dos ângulos, das tensões nodais de todas as barras do sistema, que são as variáveis comumente usadas pelas técnicas de parametrização global. Os resultados obtidos para diversos sistemas confirmam o aumento da eficiência dos métodos propostos e mostram sua viabilidade para aplicações no planejamento da operação nos atuais sistemas de gerenciamento de energia
Abstract: This work presents an analysis of the use of global parameterization techniques to the continuation power flow. Those techniques are considered inadequate for computation of the loading margin of power systems characterized by strong local static voltage stability. In such systems, at maximum loading point, the singularity of the Jacobian matrices of global parameterization techniques coincide with the one of the power flow Jacobian matrix. In those cases, the local parameterization is considered as the only way to overcome the singularity. However, this paper shows that this kind of singularity can be efficiently eliminated not only for these systems, but also for all others, by a new parameterization technique (global). This technique uses the addition of a line equation, which passes through a point in the plane determined by the sum of all the bus voltage magnitudes, or angles, and loading factor variables, that are variables commonly used by global parameterization techniques. The obtained results for several systems confirm the efficiency increased of the proposed methods and show its viability for applications in the operating planning in a modern energy management system
Doutor
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PIRES, Robson Celso. "Complex-Valued Steady-State Models as Applied to Power Flow Analysis and Power System State Estimation". reponame:Repositório Institucional da UNIFEI, 2018. http://repositorio.unifei.edu.br/xmlui/handle/123456789/1359.
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Nonlinear systems of equations in complex domain are frequently encountered in applied mathematics, e.g., power systems, signal processing, control theory, neural networks and biomedicine, to name a few. The solution of these problems often requires a first- or second-order approximation of these nonlinear functions to generate a new step or descent direction to meet the solution iteratively. However, such methods cannot be applied to real functions of complex variables because they are necessarily non-analytic in their argument, i.e., the Taylor series expansion in their argument alone does not exist. To overcome this problem, the nonlinear function is usually redefined as a function of the real and imaginary parts of its complex argument so that standard methods can be applied. Although not widely known, it is possible to build an expansion of these nonlinear functions in its original complex variables by noting that functions of complex variables can be analytic in their argument and its complex conjugate as a whole. This property lies in the fact that if a function is analytic in the space spanned by ℜ{} and ℑ{}in ℝ, it is also analytic in the space spanned by and * in ℂ. The main contribution of this work is the application of this methodology to a complex Taylor series expansions aiming algorithms commonly used for solving complex-valued nonlinear systems of equations emerged from power systems problems. In our proposal, a complex-valued power ow analysis (CV PFA) model solved by Newton-Raphson method is revisited and enhanced. Nonetheless, especially emphasis is addressed to Gauss-Newton method when derived in complex domain for solving power system state estimation (CV PSSE) problems, whichever they are applied in transmission or distribution systems. The factorization method of the complex Jacobian matrices emerged from CV PFA and CV PSSE approaches is the Three Angle Complex Rotation (TACR) algorithm that comes from the Givens Rotations algorithm in real domain. In this research one demonstrates that Wirtinger derivatives can lead to greater insights in the structure of both problems, i.e., CV PFA & CV PSSE. Moreover, it can often be exploited to mitigate computational overhead, storage cost and enhance the network's component modeling as FACTS devices, e.g., STATCOM, VSC-HVDC, besides easily handle PMU measurements and embedding new technologies towards smart grids. Finally, in order to add numerical robustness, a fourth-order Levenberg-Marquardt algorithm is employed to the CV PFA & CV PSSE approaches because of its nice bi-quadratic convergence property, instead of the well-known quadratic convergence property of the classical Newton-Raphson and Gauss-Newton algorithms. Recall that these latter algorithms are prone to collapse when the power system network is ill-conditioned, i.e., it is heavily loaded or presents branches with high R/X ratio. These results are partially presented in this thesis because they are still under study and development. But most of them will appear in forthcoming papers submitted to IEEE-PES Transactions on Power Systems and coming up Top Conferences.
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Bryan, Grant T. "EXPERIMENTAL AND COMPUTATIONAL FLUID DYNAMIC ANALYSIS OF AXIAL-FLOW HYDRODYNAMIC POWER TURBINE". Monterey, California. Naval Postgraduate School, 2013. http://hdl.handle.net/10945/32801.
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Thorough analysis of drag and power characteristics of hydrodynamic power turbines is necessary for the efficient extraction of energy available at sea. In an effort to obtain these characteristics for a three-bladed, axial-flow hydroturbine, used to provide electric power on small sailing vessels, a load cell and voltage measuring system was installed on a carriage in a towing tank for analysis across a speed range of 0.5 to 1.8 m/s. A high-speed camera was used to determine the precise carriage speed and the rotational speed of the turbine rotor. For validation of concept, two thin flat plates were analyzed using the same drag force measuring system in the tow tank to compare experimentally determined drag coefficients with known literature values. Results are shown for the drag force experienced by the flat plates and both the non-rotating and the rotating turbine configurations. Additional results are shown for the turbines power generation capabilities at rotational speeds between 90 and 500 RPMs. Using computational fluid dynamics for the rectangular flat plate and non-rotational turbine configuration, the experimental and computational results for the drag force characteristics were compared.
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ANDRADE, FELIPE AUGUSTO SILVA DE. "FLUID LINES MODELS FOR TRANSIENTS ANALYSIS AND SIMULATION USING THE POWER FLOW". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2007. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=10668@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROO estudo de fenômenos transitórios em sistemas hidráulicos está presente em diversos ramos da engenharia, encontra-se na área de hidrelétricas e na indústria do petróleo. O presente trabalho apresenta uma análise comparativa deste fenômeno utilizando três abordagens de modelagem distintas: o clássico método das características, a técnica de grafos de ligação e o tratamento através do fluxo de potência. No caso do método das características emprega-se o procedimento proposto por Streeter. Na modelagem através de grafo de ligação adota-se a analogia generalizada entre os sistemas fluido, mecânico e elétrico. Na representação pelo fluxo de potência acopla-se módulos previamente desenvolvidos considerando as relações de causa e efeito entre os componentes de um sistema. Todos os métodos foram implementados em Matlab e foram testados e comparados a partir de simulações em dois sistemas simples compostos de um reservatório, linha fluida e válvula. Os resultados obtidos através da metodologia de fluxo de potência aproximam-se dos encontrados pelas abordagens tradicionais.
The study of transitory phenomena in hydraulic systems is present in several branches of the engineering, in the hydroelectric power stations area and in the petroleum industry. The present work introduce a comparative analysis of this phenomenon using three approaches of distinct modeling: the classic characteristics method, the technique of bond graphs and the treatment through the power flow. In the case of characteristics method is used the procedure proposed by Streeter. In the modeling through bond graphs is adopted the generalized analogy among the fluid, mechanic and electric systems. In the representation by power flow modules previously developed are coupled considering the cause and effect relationships between components of one system. All methods were implemented in Matlab and were tested and compared from simulations in two simple systems composed of a reservoir, fluid lines and valve. The results obtained through the methodology of power flow are near of the discoveries by the traditional approaches.
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McCraney, Joshua Thomas. "Analysis of Capillary Flow in Interior Corners : Perturbed Power Law Similarity Solutions". PDXScholar, 2015. https://pdxscholar.library.pdx.edu/open_access_etds/2725.
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The design of fluid management systems requires accurate models for fluid transport. In the low gravity environment of space, gravity no longer dominates fluid displacement; instead capillary forces often govern flow. This thesis considers the redistribution of fluid along an interior corner. Following a rapid reduction of gravity, fluid advances along the corner measured by the column length z = L(t), which is governed by a nonlinear partial differential equation with dynamical boundary conditions. Three flow types are examined: capillary rise, spreading drop, and tapered corner. The spreading drop regime is shown to exhibit column length growth L ~ t2/5, where a closed form analytic solution exists. No analytic solution is available for the capillary rise problem. However, a perturbed power law similarity solution is pursued to approximate an analytic solution in the near neighborhood of the exact solution for the spreading drop. It is recovered that L ~ t1/2 for the capillary rise problem. The tapered corner problem is not analytically understood and hence its corresponding L is undocumented. Based on the slender corner geometry, it is natural to hypothesize the tapered corner column length initially behaves like the capillary rise regime, but after sufficient time has elapsed, it transitions into the spreading drop regime. This leads to a conjecture that its column length growth L is restricted to t2/5 < L < t1/2. To verify this conjecture an explicit finite difference numerical solution is developed for all three regimes. As will be shown, the finite difference scheme converges towards the analytic solutions for the spreading drop and capillary rise regimes. From this we assume the finite difference scheme is accurate for corner flows of similar geometries, and thus apply this scheme the more onerous criteria of the tapered corner. Numerical results support the conjectured L behavior for the tapered corner. Understanding the dynamics of such flows and responses to various geometries offers design advantages for spacecraft waste-management systems, fuel control, hydration containment, cryogenic flows, and a myriad of other fluid applications.
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Li, Qiang. "ANALYSIS, DESIGN, AND LABORATORY EVALUATION OF A DISTRIBUTED UNIFIED POWER FLOW CONTROLLER CONCEPT". UKnowledge, 2006. http://uknowledge.uky.edu/gradschool_diss/347.
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A single-phase, buck-boost based, dual-output AC-DC converter is studied in this thesis. The converter has two DC outputs with opposite polarities, which share the same ground with the input power line. The power stage performance, including the input filter, is studied and procedure to select power components is given. The circuit model is analyzed to develop appropriate control. Zerocrossing distortion of the source input current is addressed and a solution is proposed. Experimental results are satisfactory in that a high power factor line current results for steady-state operation.
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Khaniya, Dina. "Development of three-phase continuation power flow for voltage stability analysis of distribution systems". Master's thesis, Mississippi State : Mississippi State University, 2008. http://library.msstate.edu/etd/show.asp?etd=etd-11142008-101009.
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Kontos, Adamos C. "Construction of boundary matched equivalents for off-line lead-flow-type studies and transient stability analysis". Diss., Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/13697.
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Carrera, Fernando Henrique. "Estudo numérico para a determinação das pressões devidas a ação do vento em torres metálicas de seção circular /". Ilha Solteira : [s.n.], 2007. http://hdl.handle.net/11449/91496.
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Orientador: Renato Bertolino JúniorBanca: Haroldo de Mayo Bernardes
Banca: João Alberto Venegas Requena
Resumo: O presente trabalho tem por objetivo obter numericamente os valores das distribuições de pressões devidas a ação do vento e seus respectivos coeficientes de pressões de formas externos em torres de seção circular. As distribuições de pressões nas torres são determinadas através da simulação numérica, utilizando-se o programa ANSYS 9.0, considerando-se a interação fluido-estrutura. Para a simulação numérica, a geometria da torre foi modelada tridimensionalmente, considerando como fluido o ar no qual a edificação está inserida. As distribuições de pressão foram determinadas para relações geométricas em planta da torre, entre a altura e o diâmetro (h/d), para valores menores ou iguais a 10. Posteriormente, comparam-se os resultados numéricos obtidos na simulação através do ANSYS com os valores apresentados pela norma NBR-6123:1988, a fim de verificar a viabilidade da utilização da simulação numérica na obtenção das distribuições de pressão em outras estruturas.
Abstract: The present work has for objective to obtain the distributions pressures values the wind actions in tower with circular section. The values of the distributions pressures are obtained to the numeric simulation, using the ANSYS 9.0 software and considering the flow structure interaction. In the numeric simulation, the tower geometry was considered in 3D dimension, and the flowed it is the air. The distributions pressures were certain for geometry relationships between the height and the diameter (h/d), for values smaller or equal than 10. Later, the ANSYS numeric results are compared with the presents values by the NBR 6123:1998, in order to verify the viability numeric simulation used for obtaining the pressures distributions in other structures.
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Sreenivasachar, Kannan. "Unified power flow controller, modeling, stability analysis, control strategy and control system design". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ60570.pdf.
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Zhu, Pengcheng. "A novel Q-limit guided continuation power flow method for voltage stability analysis". Thesis, Brunel University, 2008. http://bura.brunel.ac.uk/handle/2438/5360.
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Voltage security assessment is becoming a more and more important issue due to the fact that electrical power systems are more prone to voltage instability under increased demand, and it can be time-consuming to determine the actual level of voltage security in large power systems. For this reason, this thesis presents a novel method for calculating the margin of voltage collapse that is based on the Continuation Power Flow (CPF) method. The method offers a flexible and reliable solution procedure without suffering from divergence problems even when near the bifurcation point. In addition, the new method accounts for reactive power limits. The algorithmic continuation steps are guided by the prediction of Q-limit breaking point. A Lagrange polynomial interpolation formula is used in this method in order to find the Q-limit breaking point indices that determine when the reactive power output of a generator has reached its limit. The algorithmic continuation steps will then be guided to the closest Q-limit breaking point, consequently reducing the number of continuation steps and saving computational time. The novel method is compared with alternative conventional and enhanced CPF methods. In order to improve CPF further, studies comparing the performance of using direct and iterative solvers in a power flow calculation have also been performed. I first attempt to employ the column approximate minimum degree (AMD) ordering scheme to reset the permutation of the coefficient matrix, which decreases the number of iterations required by iterative solvers. Finally, the novel method has been applied to a range of power system case studies including a 953 bus national grid transmission case study. The results are discussed in detail and compared against exiting CPF methods.
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Harris, Rhydar Lee. "A numerical analysis of the flow field surrounding a solar chimney power plant". Thesis, Stellenbosch : University of Stellenbosch, 2004. http://hdl.handle.net/10019.1/16337.
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Thesis (MScIng)--University of Stellenbosch, 2004.ENGLISH ABSTRACT: This study investigated the flow field above a proposed solar chimney power plant, without a cross wind, using a commercial numerical solver in the form of CFX 4-4 by AEA Technology plc. The governing equations solved are for an incompressible steady state solution. Variation in density due to buoyant effects is modelled with the Boussinesq approximation, and turbulence is approximated by the k-ε model with modifications due to buoyancy. The effect of different turbulence conditions at atmospheric inflows is also investigated. Modifications to the k-ε turbulence model in the context of atmospheric turbulence are investigated and applied to the standard k-ε model. These modifications include the addition of source terms in the turbulence kinetic energy and the turbulence dissipation rate equations to allow for the production/destruction of turbulence due to buoyancy. Other modifications include an additional source term in the turbulence dissipation rate equation accounting for atmospheric stability and the specification of model constants relevant to atmospheric flows. Initial results for the flow field using the Boussinesq approximation show reasonable correlation between the current study and the study by Thiart (2002) whereby the flow field exhibits characteristics of the axially symmetric turbulent jet. One of the primary and most noticeable differences between the current study and that of Thiart (2002) is the difference in height at which air is drawn into the collector. In order to account for variation in density with height, a modification on the Boussinesq approximation, the Deep Boussinesq model, Montavon (1998), is applied to a simplified 100 m by 100 m rectangular geometry. The results obtained are compared to a similar model using the Boussinesq approximation and it is seen that the average velocities reached in the deep Boussinesq model are significantly larger than those obtained in the Boussinesq approximation.
AFRIKAANSE OPSOMMING: Hierdie studie ondersoek die vloeiveld bo 'n aangewese son-skoorsteen kragstasie, deur die gebruik van 'n kommersiële numeriese oplosser in die vorm van CFX 4-4; van AEA Technology plc. Die heersende vergelykings wat opgelos moet word, is vir 'n niesaampersbare, tyd-onafhanklike oplossing. Die wisseling in digtheid as gevolg van saamdrukbaarheids effekte, word gemodelleer met die Boussinesq benadering en turbulensie-skatting deur die k-ε model met aanpassings as gevolg van dryfkrag. Die effek van die verskillende turbulensie-toestande teen atmosferiese invloeing word ook ondersoek. Aanpassings op die k-ε turbulensie-model in die konteks van atmosferies turbulensie word ondersoek en toegepas op die standaard k-ε model. Hierdie veranderinge sluit die byvoeging van bron terme in die turbulente kinetiese energie en die turbulensieverspillings vergelykings om ruimte te laat vir die produksie/afbreking van turbulensie as gevolg van dryfkrag in. Ander aanpassings sluit in 'n bykomende bron term in die turbulensie-verspillings vergelyking wat rekenskap gee vir atmosferiese stabiliteit en die spesifikasie van model onveranderlikes met betrekking tot atmosferiese vloei. Aanvanklike resultate vir die vloeiveld met die gebruik van die Boussinesq benadering dui op geredelike ooreenstemming tussen de huidige studie en die studie van Thiart (2002), waar die vloeiveld eienskappe toon van 'n simmetriese turbulente spilpunt. Een van die mees primêre en duidelikste verskille tussen die huidige studie en diè van Thiart (2002) is die verskil in die hoogte waarteen die lug in die samesteller ingesuig word. Om rekenskep te kan gee vir die verskil in digtheid met betrekking tot hoogte is 'n aanpassing van die Boussinesq benadering, die Diep Bussinesq model, Montavon (1998), aangebring. Hierdie aanpassing word toegepas op ‘n vereenvoudigde 100 m by 100 m reghoek. Die resultate wat verkry word, word vergelyk met 'n soortgelyke model waar die algemene snelheid wat met die diep Boussinesq model bereik word merkbaar groter is as die in die Boussinesq benadering.
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Buxamusa, Adnan. "Wind Flow Analysis and Modeling Power Generation for a Multiple Wind Turbine Installation". Youngstown State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1299607231.
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Manchanda, Antarpreet Singh. "Design Methodology for Differential Power Analysis Resistant Circuits". University of Cincinnati / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1377866652.
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Abuella, Mohamed A. "STUDY OF PARTICLE SWARM FOR OPTIMAL POWER FLOW IN IEEE BENCHMARK SYSTEMS INCLUDING WIND POWER GENERATORS". OpenSIUC, 2012. https://opensiuc.lib.siu.edu/theses/991.
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AN ABSTRACT OF THE THESIS OF Mohamed A. Abuella, for the Master of Science degree in Electrical and Computer Engineering, presented on May 10, 2012, at Southern Illinois University Carbondale. TITLE:STUDY OF PARTICLE SWARM FOR OPTIMAL POWER FLOW IN IEEE BENCHMARK SYSTEMS INCLUDING WIND POWER GENERATORS MAJOR PROFESSOR: Dr. C. Hatziadoniu, The aim of this thesis is the optimal economic dispatch of real power in systems that include wind power. The economic dispatch of wind power units is quite different of conventional thermal units. In addition, the consideration should take the intermittency nature of wind speed and operating constraints as well. Therefore, this thesis uses a model that considers the aforementioned considerations in addition to whether the utility owns wind turbines or not. The optimal power flow (OPF) is solved by using one of the modern optimization algorithms: the particle swarm optimization algorithm (PSO). IEEE 30-bus test system has been adapted to study the implementation PSO algorithm in OPF of conventional-thermal generators. A small and simple 6-bus system has been used to study OPF of a system that includes wind-powered generators besides to thermal generators. The analysis of investigations on power systems is presented in tabulated and illustrative methods to lead to clear conclusions.
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Gallego, Pareja Luis Alfonso. "Fluxo de potência em redes de distribuição de energia elétrica considerando incertezas /". Ilha Solteira : [s.n.], 2009. http://hdl.handle.net/11449/100319.
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Orientador: Antonio Padilha FeltrinBanca: Percival Bueno de Araujo
Banca: Anna Diva Plasencia Lotufo
Banca: José Manuel Arroyo Sanchez
Banca: Paulo Augusto Nepomuceno Garcia
Resumo: Nesta tese é proposta e avaliada uma metodologia alternativa para o cálculo do fluxo de potência quando são consideradas incertezas no sistema de distribuição de energia elétrica. Especificamente é considerada incerteza na demanda dos usuários de baixa tensão, assim como também nas fases em que os usuários estão ligados no sistema. A demanda das unidades consumidoras é modelada através das funções de distribuição de probabilidades. A metodologia proposta vale-se das curvas de carga diárias típicas que foram estimadas através das curvas de carga medidas em uma campanha de medição. O fluxo de potência proposto emprega o método de simulação de Monte Carlo para gerar múltiplos cenários de demanda do sistema de distribuição. O método de fluxo de potência determinístico empregado é o denominado algoritmo Backward-Forward Sweep. Neste trabalho também é realizado um estudo estatístico para determinar quais distribuições de probabilidade podem representar os dados das curvas de carga diárias obtidas na campanha de medições. Muitos trabalhos apresentados no âmbito acadêmico empregam a priori a função de distribuição de probabilidade normal para realizar os diversos estudos, isto pode levar a conclusões inadequadas. Também é realizada uma análise comparativa entre os resultados obtidos pelo fluxo de potência probabilístico, quando são utilizadas duas funções de distribuição de probabilidade diferentes para estimar as curvas de carga diárias (a função de distribuição de probabilidade que ficou no primeiro lugar na análise estatística e a função normal). São apresentados resultados comparativos para diferentes distribuições de probabilidade, quando é considerada incerteza somente na demanda e quando é considerada conjuntamente incertezas na demanda e na conexão das fases
Abstract: In this thesis an alternative methodology to calculate the power flow considering uncertainty in the electrical distribution system is proposed and validated. Specifically, uncertainty is considered in the demand of the low voltage consumers, as well as the phases in which the users are connected to the system. The demand of the consumer units is modeled by means of probability distribution functions. The proposed methodology uses the daily load curves that were estimated by means of the load curves measured in measuring campaign. The proposed power flow uses the Monte Carlo simulation method to generate multiple demand scenarios of the distribution system. The deterministic power flow method implemented is the so called Backward-Forward Sweep algorithm. In this work it is also implemented a statistical study to determine which distribution functions can represent the data of the daily load curves obtained in the measuring campaign. Many research works found in the academic ambit use a priori the normal distribution function to perform diverse studies; this can lead to wrong conclusions. This thesis also presents a comparative analysis between the results obtained by the probabilistic power flow, when two different probability distribution functions are used to estimate the daily load curves (the probability distribution function that was first in the statistical analysis and the normal function). Comparative results are shown for different distribution functions considering uncertainty only in the demand, and considering uncertainty in the demand and the connection of the phases
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Hatzitaki, Vassilia. "Power flow analysis as a method to document coordination disabilities observed in Parkinson's disease". Thesis, McGill University, 1991. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61122.
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The purpose of the present study was to establish the use of the power flow analysis and the subsequent phase breakdown of the movement pattern as an objective and reliable tool to document in detail movement disabilities observed in Parkinson's disease. Movement was reflected in a series of functional phases responsible for detailed muscle function around the joint as the result of the kinematic output.The results revealed the importance of the power flow analysis as a sensitive tool for describing coordination disabilities. Similar muscle phenomena were reflected through the functional movement phases of both ability groups. However, the variability in the number of phases increased as a function of the task complexity. The statistical comparison of selected kinematic and dynamic parameters revealed significantly higher peaks for the able-bodied movement profiles. The analysis also demonstrated that the movement deficiencies observed in Parkinson's Disease cannot simply be attributed to the pure force production by the joint musculature. It seems that there is also a problem in managing and organizing the active and passive forces acting at the joint. (Abstract shortened by UMI.)
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Lukman, Dedek Electrical Engineering & Telecommunications Faculty of Engineering UNSW. "Loss minimization in the modified algorithm of load flow analysis in industrial power system". Awarded by:University of New South Wales, 2002. http://handle.unsw.edu.au/1959.4/35453.
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The research looks at an alternative technique of loss minimization using B-loss formula in solving load flow analysis. A modeling of electrical system elements is first developed. A literature review on the history and development of load flow analysis and loss minimization especially on the use of B-loss formula are delivered. A report on load flow in practice and loss minimization measures based on a utility visit to EnergyAustralia is given. An analysis on three types of industrial power systems is also discussed. A substantial study on EDSA was made to adapt the commercial load flow program and demonstrate voltage control methods to achieve loss minimization. The research thesis work focuses on the use of a load flow analysis program to calculate and minimize losses in large electrical power distribution system such as an industrial power system. A Matlab load flow analysis program has been developed successfully using modified polar Newton-Raphson algorithms based on bus admittance matrix Ybus and the use of B-loss coefficient method. Real power losses are calculated using Blosses coefficients for achieving loss minimization and the technique has been verified with the traditional I2R and/or differential power methods. Modified load flow algorithm is also implemented by applying voltage control methods using either a shunt capacitor or a load tap changing (LTC) transformer. Voltage level is improved whilst minimizing losses. Appropriate modeling of a capacitor and an LTC transformer have been developed proven. A network of a typical meshed secondary selective system of five bus has been chosen and used as the test case. Several case studies with different values of capacitance and tap settings of transformer have been conducted to determine minimum losses. Further sensitivity analysis is carried out by simulating a wide range of load power configurations and line and transformer resistances to verify the robustness of the proposed modified algorithms especially on the use of B-losses algorithm for the chosen network. Results showed that the proposed algorithms ,although less accurate than full I2R calculations, are robust and reliable to achieve loss minimization for various ranges of load and impedance configurations. There is confidence in applying the method to larger systems. This two-year thesis details novel contribution towards loss minimization in power systems by applying B-losses formula into a load flow program, expressing the system losses in terms of active power generations which allows coordination of transmission losses in scheduling output of each generating plant. This gives maximum economy for a given load and achieves loss minimization using voltage control methods. This technique is not possible using standard commercial load flow programs.
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WENG, CHIYUAN. "Transient Stability Analysis of Power Systems with Energy Storage". Case Western Reserve University School of Graduate Studies / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=case1348453228.
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Devlin, Joseph. "A gas energy flow constrained unit commitment analysis of the British and Irish power systems considering high wind power penetrations". Thesis, Queen's University Belfast, 2016. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.706454.
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As members of the European Union (EU), the United Kingdom (UK) and Ireland are legally bound to integrate large penetrations of renewable energy into the power system in pursuit of EU 2020 targets. Wind power has emerged as the main renewable energy technology of choice to meet these targets. As the penetration of wind power continues to increase beyond 2020, a wider lens on the integration problem is required, It has been previously shown that gas generation due to its flexibility provision and traditionally high place in the merit order is the sacrificial generator. The ensuing dispatch schedule reduces energy output and incorporates a high degree of variability. This increasingly variable output profile is ultimately transferred onto gas infrastructure and is a relatively overlooked area of research This work is the first to utilise a fully realistic gas energy flow, security and reserve constrained unit commitment and economic dispatch model to investigate the interactions between power and gas vectors In the Interconnected energy systems of the UK and Ireland. Utilisation of this novel modelling methodology produced four key deliverables, Firstly, the real world impact of high wind power penetrations on gas generators in the SEM during 2011 were analysed in detail The second deliverable, novel utilisation of grid scale electrical storage coupled to a constrained on gas generating unit in the SEM during 2020, was shown to have significant impacts on peak' time system operation. Thirdly, the multi vector analysis conducted enabled the value of gas infrastructure to power system operation in the SEM to be determined, Finally, the research highlights the ability of extreme weather driven gas demand to impact unit commitment decisions in both the SEM and BETTA. Additionally, the presence of gas storage in Ireland is shown to significantly improve power and gas security of supply.
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Wei, Nan. "A Line Outage Study for Prediction of Static Power Flow Redistribution". Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/72887.
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Transmission line is a crucial role in power transmission network which connects generating units to consumers. Some unpredicted failure events such as lightening or system faults can cause transmission line tripped, which may bring about a large interruption to the system and causes damage. When line outage happens, the power flow on the tripped line will be redistributed to the rest of lines in the system. It may cause risk of overload happens on other lines, and results in a cascading failure and system collapse. Reasonably, a single line outage will not affect all other lines in the system. Therefore, when a line outage happens, it is important for the system operator to have a preview of which lines will have serious impact and which lines will not, so that the operator can only focus on monitoring certain lines which will be seriously affected, rather than keeping monitoring the whole system. In this thesis, A Line Outage Distribution Factor (LODF) method is proposed and implemented in the IEEE 118 bus system to estimate active power flow redistribution after a line outage. After that, a definition of Thevenin electrical distance between two transmission lines is derived and applied to calculate electrical distances between the outage line and each line in the system. An exponential convergence tendency is found between maximum possible LODF predicted power flow variations and electrical distance, and an exponential regression method is applied to analyze this tendency. The contribution of this work is a rule has been found that starting from the outage line, the maximum possible active power flow variation on transmission lines exponentially decreases exponentially while the electrical distance increases. With only the information of system's normal operating condition and topological information, the maximum possible active power change on each lines caused by single line outage, and the margin of the impact of single line outage on power flow variations may propagate along electrical distance can be easily and quickly predicted. Ultimately, the goal of this work is to allow operators at the control center can concentrate on lines within a certain electrical distance instead of keeping monitoring the whole system when a line outage happens.Master of Science
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Pereira, Marcia Beatriz Carvalho. "Desenvolvimento de um objeto de aprendizagem para análise de sistemas de energia elétrica /". Ilha Solteira : [s.n.], 2008. http://hdl.handle.net/11449/87248.
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Orientador: Laurence Duarte ColvaraBanca: Sergio Azevedo de Oliveira
Banca: Silvia Galvão de Souza Cervantes
Resumo: Este trabalho tem por objetivo contribuir para o desenvolvimento de técnicas de Educação em Engenharia apresentando uma ferramenta de apoio ao Ensino/Aprendizagem de Sistemas Elétricos de Potência na forma de um software de interface amigável e baixo custo. O software desenvolvido em linguagem C++ segue os padrões de programação orientada a objetos e oferece ao usuário a resolução de fluxos de potência e simulações de casos de contingências transitórias com possibilidade de interatividade, apresentando resultados em ambiente gráfico. Desenvolvido para aplicação na área de Dinâmica e Estabilidade de Sistemas de Potência, suporta sistemas-exemplos clássicos do IEEE e também disponibiliza ao usuário ferramentas para personalização de arquivos de dados de entrada, tornando-se flexível e de fácil acesso aos casos já inseridos no sistema. O usuário também pode criar novos sistemas de acordo com suas necessidades. Os resultados são exibidos em forma numérica e também através de gráficos tridimensionais e animação, possibilitando fácil visualização de resultados, entendimento de fenômenos e análise de influências sobre o desempenho.
Abstract: This work presents a contribution to the development of Engineering Education techniques by means of a Teaching/Learning support tool for Electrical Power System studies resulting in a friendly low cost interface software. It was developed in C++ language and follows the pattern of object oriented programming, offering to the user the resolution of load flow and digital simulations of transient stability with the possibility of interactivity, showing the results in a graphic environment. It was developed for use in applications of Static and Transient Power Systems Stability and it has enclosed classic sample-systems of IEEE and others and also allows the user to customize input data files. Then the tool is flexible and enables easy access to cases formerly inserted in the system. The user also can create new systems according to his needs. The machines rotors movement can be seen in a graphic animation, allowing easy visualization of events, phenomena comprehension and analysis of influences about the performance.
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Magalhães, Elisabete de Mello. "Aplicação do método de Newton desacoplado para o fluxo de carga continuado /". Ilha Solteira : [s.n.], 2010. http://hdl.handle.net/11449/87114.
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Orientador: Dilson Amâncio AlvesBanca: Anna Diva Plasencia Lotufo
Banca: Edmárcio Antonio Belati
Resumo: Este trabalho apresenta o método de Newton desacoplado para o fluxo de carga continuado. O método foi melhorado por uma técnica de parametrização geométrica possibilitando assim o traçado completo das curvas P-V, e o cálculo do ponto de máximo carregamento de sistemas elétricos de potência, sem os problemas de mau condicionamento. O objetivo é o de apresentar de forma didática os passos envolvidos no processo de melhoria do método de Newton Desacoplado a partir da observação das trajetórias de solução do fluxo de carga. A técnica de parametrização geométrica que consiste na adição de uma equação de reta que passa por um ponto no plano formado pelas variáveis: tensão nodal de uma barra k qualquer e o fator de carregamento eliminam os problemas de singularidades das matrizes envolvidas no processo e ampliam o grupo das variáveis de tensão que podem ser usadas como parâmetro da continuação. Os resultados obtidos com a nova metodologia para o sistema teste do IEEE (14, 30, 57, 118 e 300 barras) e também para os sistemas reais de grande porte, o 638 barras do sistema Sul-Sudeste brasileiro e do sistema de 904 barras do sudoeste Americano, mostram que as características do método convencional são melhoradas na região do ponto de máximo carregamento e que a região de convergência ao redor da singularidade é sensivelmente aumentada. São apresentados vários testes com a finalidade de prover um completo entendimento do funcionamento do método proposto e também avaliar seu desempenho
Abstract: This work presents the decoupled Newton method for continuation power flow. The method was improved by using a geometric parameterization technique that allows the complete tracing of P-V curves, and the computation of maximum loading point of a power system, without ill-conditioning problems. The goal is to present in a clear and didactic way the steps involved in the development of the improved decoupled Newton method obtained from the observation of the geometrical behavior of power flow solutions. The geometric parameterization technique that consists of the addition of a line equation, which passes through a point in the plane determined by the bus voltage magnitude and loading factor variables, can eliminate the ill-conditioning problems of matrices used by the method and can enlarge the set of voltage variables that can be used as continuation parameter to P-V curve tracing. The method is applied to the IEEE systems (14, 30, 57, 118 and 300 buses) and two large real systems: the south-southeast Brazilian system (638 buses) and the 904-bus southwestern American system. The results show that the best characteristics of the conventional decoupled Newton's method are improved in the vicinity of the maximum loading point and therefore the region of convergence around it is enlarged. Several tests are presented with the purpose of providing a complete understanding of the behavior of the proposed method and also to evaluate its performance
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Lundin, Rasmus y Benjamin Beitler-Dorch. "Modelling and Analysis of Mobile Energy Transmission for Offshore Wind Power : An analysis of flow batteries as an energy transmission system for offshore wind power". Thesis, Mälardalens högskola, Akademin för ekonomi, samhälle och teknik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:mdh:diva-40082.
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A comparison between a traditional fixed high voltage direct current energy transmission system and a mobile transmission system utilizing vanadium redox flow batteries has been conducted in this degree work. The purpose of this comparison was to evaluate if a mobile energy transmission system could be competitive in terms of energy efficiency and cost-effectiveness for use in offshore wind power applications. A literary study was made to fully grasp the various technologies and to create empirical ground of which cost estimation methods and energy calculations could be derived. A specific scenario was designed to compare the two transmission systems with the same conditions. To perform the comparison, a model was designed and simulated in MATLAB. The results from the model showed that the flow battery system fell behind in energy efficiency with a total energy loss of 33.3 % compared to the 11.7 % of the traditional system, future efficiency estimations landed it at a more competitive 17.5 %. The techno-economic results proved that a mobile flow battery system would be up to nine times more expensive in comparison to a traditional transmission system, with the best-case scenario resulting in it being roughly two times more expensive. The main cause of this was found out to be the expensive energy subsystem, specifically the electrolyte, used in the flow battery system. Several environmental risks arise when using a flow battery system with this electrolyte as well which could harm marine life severely. In conclusion; with further development and cost reductions, a case could be made for the advantages of a truly mobile energy transmission system. Specifically, in terms of the pure flexibility and mobility of the system, allowing it to circumvent certain complications. The mobility of the system gives the possibility of selling energy where the spot prices are at their highest, providing a higher revenue potential compared to a traditional fixed system. As for now though, it is simply too expensive to be a viable solution.
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Booeshaghi, Ali Sina. "Analysis & characterization of a flow thermo-electrochemical cell for power generation & heat convection". Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/112567.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 53-55).
In this thesis, I analyzed and characterized a new flow thermo-electrochemical cell that generates power from waste-heat, while in parallel convecting this heat away from the source. I also reviewed previous research on the topic of thermo-electric energy generation, governing physics behind thermo-electrochemical energy generation, actual device fabrication, device testing, results, and applications of this technology. Thermo-electric devices (TE devices) exhibit the thermo-electric effect, where temperature gradients and material properties work in tandem to drive electron transfer at electrode surfaces, thereby generating electricity. For example, a typical sold-state TE device such as a bismuth telluride TE device, can generate up to 0.300 mV/K [31]. New reseach has emerged [25, 26, 14] focusing on liquid-based thermo-electrochemical (TEC) cells that take advantage of the temperature dependence of oxidation/reduction chemical reactions to generate electricity. One of the major benefits of these TEC devices over traditional TE devices is a much higher S, = 1.5 mV/K; another is the low cost of manufacturing, making them promising for commercial applications. The new TEC device that I fabricated and studied utilizes a flowing electrolyte instead of a stationary electrolyte. With this new configuration, and a heated boundary condition, I studied both the energy generation and convective heat transfer capabilities of the flowing electrolyte TEC cell. Numerically I obtained a maximum power output and heat transfer coefficient for the TEC cell of Pmax = 2.6 [mu]W and h = 340 W/m²K which corroborates well with the experimentally found value of Pmax = 2.0 [mu]W and h = 450 W/m². K. If employed in data centers, as a device for CPU cooling, with the given power output I found that a 100,000 ft² data center can generate about 21.96 MWh of energy, which at a cost of 0.20 $/kWh can save a data center about 5,000 $/year. More generally, the application of this technology in locations where waste-heat is prevalent, will allow for energy recycling and consequent cost savings.
by Ali Sina Booeshaghi.
S.B.
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James, Philippe Pierre. "A technique for the assessment of strength of coupling between statistical energy analysis subsystems". Thesis, University of Southampton, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245304.
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Machado, Danilo Agostini. "Construção de um dispositivo de simulação do escoamento pulsátil em artérias /". Ilha Solteira : [s.n.], 2010. http://hdl.handle.net/11449/94513.
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Resumo: Este projeto visa à análise cinemática de um arranjo experimental capaz de reproduzir o fluxo sanguíneo em artérias. O mecanismo procura realizar esse escoamento através de um sistema came-seguidor juntamente com um sistema hidráulico, utilizando êmbolo e duas válvulas controladoras de fluxo. O mecanismo came-seguidor será utilizado devido a sua versatilidade em garantir que o escoamento sanguíneo ocorra durante um ciclo cardíaco. A came será radial com seguidores de roletes. O seguidor de roletes será ligado ao cilindro hidráulico que controla o fluxo sanguíneo. Um tubo de látex foi acoplado ao sistema hidráulico representando a aorta abdominal, foi confeccionado com as dimensões reais desta artéria e o látex foi escolhido, pois possui um coeficiente de elasticidade muito próximo da artéria. Um manômetro foi acoplado ao sistema para medir a pressão no interior do tubo de látex. Na sequência um tubo de complacência simular as perdas de carga do sistema circulatório. O deslocamento radial do tubo de látex e variação de pressão do manômetro foram monitorados através de filmagem. Posteriormente, os resultados experimentais foram comparados e validados com os resultados numéricos obtidos com o programa ANSYS e com a literaturaAbstract: This project aims to kinematic analysis of an experimental apparatus able to reproduce the blood flow in arteries. The mechanism cam-follower and the hydraulic system using piston and two controlling valves of flow were used to realize the fluid flow. The camfollower mechanism was used to ensure that the fluid flow occurs during the cardiac cycle. The cam is radial with roller followers. The follower roller is connected to the hydraulic cylinder which controls the fluid flow. A latex tube was attached to the hydraulic system representing the abdominal aorta. The latex tube has the same real dimensions of this artery and it was chosen due the modulus of elasticity very close to the artery. A manometer was used to measure the outlet pressure of latex tube. After latex tube there is a complacency tube to control the pressure drop of circulatory system. The radial displacement of the latex tube and pressure variation of the manometer were monitored through filming. The experimental results were compared and validated with numerical results obtained with ANSYS software and with literature
Orientador: Aparecido Carlos Gonçalves
Coorientador: Amarildo Tabone Paschoalini
Banca: João Antonio Pereira
Banca: Cleudmar Amaral de Araújo
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Ratul, Saiful A. "Optimal DG Placement: A Multimethod Analysis". ScholarWorks@UNO, 2016. http://scholarworks.uno.edu/td/2269.
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With Power System being restructured in the vision of Smart Grid, it is important now more than ever to find suitable locations to place Distributed Generators (DG). Distributed generators, which may be renewable, are not limited to specific locations as in the case of conventional generators. Several papers have been published that make suggestions on where the optimal location of DG should be in a system. Objectives ranging from loss minimization to total cost minimization have been the factor for such studies. In this study, a new method is introduced that hopes to improve a current system in three ways by maximizing load, minimizing the locational marginal price and improving line contingency scenarios. The proposed methodology is simulated using MATPOWER’s Optimal Power Flow on the IEEE 14 bus test system.
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Stockinger, Christopher Allen. "Numerical Analysis of Airflow and Output of Solar Chimney Power Plants". Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/71670.
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Computational fluid dynamics was used to simulate solar chimney power plants and investigate modeling techniques and expected energy output from the system. The solar chimney consists of three primary parts: a collector made of a transparent material such as glass, a tower made of concrete located at the center of the collector, and a turbine that is typically placed at the bottom of the tower. The collector absorbs solar radiation and heats the air below, whereby air flows inward towards the tower. As air exits at the top of the tower, more air is drawn below the collector repeating the process. The turbine converts pressure within the flow into power. The study investigated three validation cases to numerically model the system properly. Modeling the turbine as a pressure drop allows for the turbine power output to be calculated while not physically modeling the turbine. The numerical model was used to investigate air properties, such as velocity, temperature, and pressure. The results supported the claim that increasing the energy into the system increased both the velocities and temperatures. Also, increasing the turbine pressure drop decreases the velocities and increases the temperatures within the system. In addition to the numerical model, analytical models representing the vertical velocity without the turbine and the maximum power output from a specific chimney were used to investigate the effects on the flow when varying the geometry. Increasing the height of the tower increased the vertical velocity and power output, and increasing the diameter increased the power output. Dimensionless variables were used in a regression analysis to develop a predictive equation for power output. The predictive equation was tested with new simulations and was shown to be in very good agreement.Master of Science
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Tbaileh, Ahmad Anan. "Robust Non-Matrix Based Power Flow Algorithm for Solving Integrated Transmission and Distribution Systems". Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/89362.
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This work presents an alternative approach to power system computations, Graph Trace Analysis (GTA), and applies GTA to the power flow problem. A novel power flow algorithm is presented, where GTA traces are used to implement a modified Gauss-Seidel algorithm coupled with a continuation method. GTA is derived from the Generic Programming Paradigm of computer science. It uses topology iterators to move through components in a model and perform calculations. Two advantages that GTA brings are the separation of system equations from component equations and the ability to distribute calculations across processors. The implementation of KVL and KCL in GTA is described. The GTA based power flow algorithm is shown to solve IEEE standard transmission models, IEEE standard distribution models, and integrated transmission and distribution models (hybrid models) constructed from modifying IEEE standard models. The GTA power flow is shown to solve a set of robustness testing circuits, and solutions are compared with other power flow algorithms. This comparison illustrates convergence characteristics of different power flow algorithms in the presence of voltage stability concerns. It is also demonstrated that the GTA power flow solves integrated transmission and distribution system models. Advantages that GTA power flow bring are the ability to solve realistic, complex circuit models that pose problems to many traditional algorithms; the ability to solve circuits that are operating far from nominal conditions; and the ability to solve transmission and distribution networks together in the same model.PHD
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Adamsson, Carl. "Dryout and Power Distribution Effects in Boiling Water Reactors". Doctoral thesis, KTH, Reaktorteknologi, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-11343.
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Film flow measurements at several axial positions in round pipes with variousaxial power distributions are presented for conditions corresponding to normaloperation of a BWR. It is confirmed that the film flow rate approaches zero atthe onset of dryout. Selected phenomenological models of annular two-phaseflow are shown to reasonably reproduce the measurements. It is concluded thatmodels are in better agreement with measurements if terms corresponding topossible boiling induced entrainment are excluded. A method to perform film flow analysis in subchannels as a post-processto a standard two-field subchannel code is suggested. It is shown that thisapproach may yield accurate prediction of dryout power in rod bundles to alow computational cost and that the influence of the power distribution is wellpredicted by the model.QC 20100618
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Martins, Luís Fabiano Barone. "Método do look ahead modificado para estudos de colapso de tensão /". Bauru : [s.n.], 2011. http://hdl.handle.net/11449/87190.
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Orientador: André Christovão Pio MartinsBanca: Newton Geraldo Bretas
Banca: Andre Nunes de Souza
Resumo: Neste trabalho foi feita uma análise comparativa entre diferentes escolhas dos pontos utilizados pelo método look ahead na estimação do ponto de máximo carregamento de um sistema elétrico de potência. O Fluxo de Cargo Continuado é utilizado na geração dos pontos de operação utilizados pelo método look ahead e para servir como referência na comparação entre os resultados previstos e o ponto de máximo carregamento real. Uma vez que a exatidão dessa estimativa é fortemente afetada pela escolha desses pontos, o FCC é modificado para fornecer pontos mais adequados para o bom funcionamento do método look ahead. A metodologia proposta é aplicada ao sistema IEEE de 300 barras, os resultados obtidos mostram o seu bom funcionamento
Abstract: Here we did a comparative analysis between different choices of the points used by the look ahead method for estimating maximum loading point of a power system. The Continued Power Flow (CPF) is used in the generation of operating points used by the look ahead method and to serve as a reference in comparison between the predicted results and the real maximum loading point. Since the accurancy of this estimative is strongly affected by choicen of these points, the CPF is modified to provide the most appropriate for the proper functioning of the method look ahead. The proposed methodology system is applied to IEEE 300 buses, the results have shown its good functioning
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Massman, Jeffrey. "NUMERICAL FLOW FIELD ANALYSIS OF AN AIR AUGMENTED ROCKET USING THE AXISYMMETRIC METHOD OF CHARACTERISTICS". DigitalCommons@CalPoly, 2013. https://digitalcommons.calpoly.edu/theses/1141.
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An Axisymmetric Rocket Ejector Simulation (ARES) was developed to numerically analyze various configurations of an air augmented rocket. Primary and secondary flow field visualizations are presented and performance predictions are tabulated. A parametric study on ejector geometry is obtained following a validation of the flow fields and performance values.
The primary flow is calculated using a quasi-2D, irrotational Method of Characteristics and the secondary flow is found using isentropic relations. Primary calculations begin at the throat and extend through the nozzle to the location of the first Mach Disk. Combustion properties are tabulated before analysis to allow for propellant property selection. Secondary flow calculations employ the previously calculated plume boundary and ejector geometry to form an isentropic solution. Primary and secondary flow computations are iterated along the new pressure distributions established by the 1D analysis until a convergence tolerance is met. Thrust augmentation and Specific Impulse values are predicted using a control volume approach.
For the validation test cases, the nozzle characteristic net is very similar to that of previous research. Plume characteristics are in good agreement but fluctuate in accuracy due to flow structure formulation. The individual unit processes utilized by the Method of Characteristics are found to vary their outputs by up to 0.025% when compared to existing sources. Rocket thrust and specific impulse are increased by up to 22% for a static system and 15% for an ejector flow at Mach 0.5. Evidence of Fabri conditions were observed in the flow visualization and graphically through the performance predictions. It was determined that the optimum ejector divergence angle for an air augmented rocket greatly depends on the stagnation pressure ratio between the primary and secondary flows.
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Togiti, Santosh. "Comparative Analysis of Load Flow Techniques for Steady State Loading Margin and Voltage Stability Improvement of Power Systems". ScholarWorks@UNO, 2015. http://scholarworks.uno.edu/td/2042.
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Installation of reactive compensators is widely used for improving power system voltage stability. Reactive compensation also improves the system loading margin resulting in more stable and reliable operation. The improvements in system performance are highly dependent on the location where the reactive compensation is placed in the system. This paper compares three load flow analysis methods - PV curve analysis, QV sensitivity analysis, and Continuation Load Flow - in identifying system weak buses for placing reactive compensation. The methods are applied to three IEEE test systems, including modified IEEE 14-bus system, IEEE 30-bus system, and IEEE 57-bus system. Locations of reactive compensation and corresponding improvements in loading margin and voltages in each test system obtained by the three methods are compared. The author also analyzes the test systems to locate the optimal placement of reactive compensation that yields the maximum loading margin. The results when compared with brute force placement of reactive compensation show the relationship between effectiveness of the three methods and topology of the test systems.
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Lun-Hui, Lee y 李崙暉. "Analysis of Voltage Flicker Power Flow". Thesis, 1998. http://ndltd.ncl.edu.tw/handle/45638622944560925181.
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碩士中原大學
電機工程研究所
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Voltage flickers resulting from arc furnaces in the steel plantsare shown to have a greater impact on the power quality. The investigation of the operation characteristics for the arc furnaceand the impact of the arc furnace on the system are therefore very important.First, this thesis discusses the phenomena of voltage flickers.Then different mathematical models of the arc furnace are examinedfor understanding the theoretic basis, mathematical methods and applicability. Because the problems of voltage flickers exist inthe power systems, many utilities build up their voltage flickerstandards which are described in this thesis. The standards of voltage flicker in the world are not the same; therefore, differentmethods are used to measure the voltage flicker. The 10Hz equivalent value is used for the voltage flicker standardin Taiwan. According to the definition of the 10Hz equivalent value, we propose a method to transfer voltage variation waveformto the 10Hz equivalent value. In this thesis, a method calledflicker power flow method for solving voltage flicker power flowis developed based on stochastic load flow theory and least squareanalysis. The flicker power flow method can obtain the voltageflicker of power systems quickly and exactly. The flicker powerflow method is verified through simulation and experimentation.
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Wang, Chun-Lin y 王俊霖. "Power Flow Analysis of Open Cavities". Thesis, 2018. http://ndltd.ncl.edu.tw/handle/us6guq.
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碩士國立臺灣大學
物理學研究所
106
Open cavities are commonly used in research of gyrotrons . The lack of well-defined geometrical boundary cause the distinctive features that is basically different from close cavity. Hence, we understand its physical peoperty and phenomenon by numerical simulation . We introduce the time domain models and declare the numerical algorithm and the boundary condition. The relation of quality factor and resonant frequency in time domain models is explained. We also discuss the power flow in open cavities . By changing the shapes and materials of open cavities , we analyze the flow and decay of energies. We derive the formula of power flow by electrodynamics and check our guess by numerical simulation. Finally we try to give an appropriate physical explanation for the results.