Rozprawy doktorskie na temat „Load Flow Methods”

A power system will experience voltage collapse when the loads increase up to a certain critical limit, where the system physically cannot support the amount of connected load. This point identified as a Saddle- Node Bifurcation (SNB), corresponds to a generic instability of parameterized differential equation models and represents the intersection point where different branches of equilibria meet. At this point the jacobian matrix of the system is singular and the system loses stability bringing the typical scenario of voltage collapse. To prevent voltage instability and collapse, the computation of the closest distance from a present operating point to the saddle-node bifurcation set can be used as a loadability index useful in power system operation and planning. The power margin is determined by applying the iterative or direct method described in [16]. Numerical examples of both methods applied to IEEE 9-bus system and IEEE 39-bus system shows that the iterative method is more reliable although it requires a longer computation time. The stability of the system is negatively affected in two ways when generators reach their reactive power limits: the voltage stability margin is deteriorated, or immediate voltage instability and collapse is produced.

Orientador: Dílson Amâncio Alves
Banca: Carlos Roberto Minussi
Banca: Francisco Villarreal Alvarado
Banca: Vivaldo Fernando da Costa
Banca: Walmir de Freitas Filho
Resumo: O fluxo de carga convencional é considerado inadequado para a obtenção do ponto de máximo carregamento devido a singularidade da matriz Jacobiana. Os métodos da continuação são ferramentas eficientes para a solução deste tipo de problema, e diferentes parametrizações são utilizadas para evitar a singularidade da matriz. Neste trabalho apresentase uma técnica de parametrização geométrica que possibilita o traçado completo das curvas PV sem os problemas de mal condicionamento. A técnica proposta associa a robustez com a simplicidade e a facilidade de compreensão. A singularidade da matriz Jacobiana é eliminada pela adição da equação de uma reta que passa por um ponto no plano formado pelas variáveis perdas de potência ativa totais e o fator de carregamento, dois parâmetros físicos de fácil compreensão. A técnica, aplicada aos sistemas do IEEE (14, 30, 57, 118 e 300 barras) e ao sistema brasileiro sul-sudeste (638 e 787 barras), mostra que as características do fluxo de carga não só são preservadas, mas também melhoradas. Diversos testes são realizados para proporcionar a comparação do desempenho do esquema de parametrização proposto para o método do fluxo de carga continuado.
Abstract: The conventional Newton's method has been considered inadequate to obtain the maximum loading point of power systems due to the Jacobian matrix singularity. Continuation methods are efficient tools for solving this kind of problem, and different parameterizations are used to avoid the matrix singularity. This paper presents a new geometric parameterization scheme that allows the complete tracing of the PV curves without ill-conditioning problems. The proposed technique associates the robustness to the simplicity and easy understanding. The Jacobian matrix singularity is overcome by the addition of a line equation, which passes through a point in the plane, determined by the real power losses and loading factor variables, two parameters with clear physical meaning. The application of this new technique to the IEEE systems (14, 30, 57, 118 and 300 buses) and to the Brazilian systems south-southeast (638 and 787 buses) shows that the characteristics of the conventional Newton's method are not only preserved but also improved. Several tests are carried out to compare the performance of the proposed parameterization scheme for the continuation power flow method.
Doutor

Este trabalho está dividido em duas partes distintas que constituem contribuições inéditas ao estudo da estabilidade em sistemas elétricos de potência. A primeira parte do trabalho é a mais importante e trata do problema da identificação das soluções de baixa tensão críticas do fluxo de carga. Esta parte do trabalho se presta a análise de estabilidade de tensão a pequenas perturbações. Os últimos capítulos deste trabalho apresentam também uma proposta de função energia estendida que modela as cargas dependentes da tensão segundo o modelo ZIP de carga, considerando a estrutura da rede preservada. Assim, a função energia proposta pode ser utilizada para analisar tanto a estabilidade de tensão como a estabilidade de ângulo em sistemas de potência. Esta proposta também é inédita na literatura. Embora a função energia proposta tenha sido aplicada apenas a sistemas de dimensão reduzidas, os resultados apresentados neste trabalho nos levam a acreditar que essa mesma função energia pode ser utilizada na análise de estabilidade de sistemas de potência de grandes dimensões. Já o método proposto para identificação das soluções de baixa tensão das equações de fluxo de carga se utiliza de um sistema dinâmico auxiliar das equações de fluxo de carga. O sistema dinâmico auxiliar utilizado não tem significado físico, mas pode ser escolhido de tal forma que a solução usual das equações de fluxo de carga seja um ponto de equilíbrio estável do sistema dinâmico auxiliar, eque as soluções de baixa tensão do fluxo de carga sejam pontos de equilíbrio instáveis do sistema dinâmico auxiliar. Dessa forma, é possível calcular as soluções de baixa tensão do fluxo de carga, calculando-se os pontos de equilíbrio instáveis do sistema dinâmico auxiliar. Assim, é possível utilizar partes da teoria de sistemas dinâmicos para estudar as soluções das equações de fluxo de carga. Baseado nestes princípios, foi desenvolvido um programa para calcular trajetórias do sistema dinâmico auxiliar, que se iniciam e se mantêm nas vizinhanças da fronteira da área de atração do ponto de equilíbrio estável do SEP. Dessa forma é possível afirmar que a trajetória calculada tende a convergir para a solução crítica das equações de fluxo de carga. O programa foi inicialmente concebido para calcular as soluções de baixa tensão de sistemas elétricos sem perdas. Em seguida o programa desenvolvido foi adaptado para calcular as soluções de baixa tensão de sistemas de potência completos, incluindo também as resistências das linhas de transmissão. Esta última versão do programa foi testada para os sistemas IEEE 39 e IEEE 118 barras, e os resultados obtidos se mostraram bastante satisfatórios. Assim, o método proposto é uma ferramenta original e eficaz para a solução do problema de calcular a solução crítica das equações de fluxo de carga de sistemas elétricos de potência.
This work may be divided into two distinct parts. Both of them are new contributions to stability analysis of power systems. In the first part it is proposed a new method to calculate the critical load flow low voltage solutions, and it is the main part of this work. Meanwhile, the last two chapters of this work presents a proposed extended energy function that consider the common load ZIP models. It allows the analysis of angle and voltage stability for power systems subjected to large disturbances. This work proposes a method to calculate the low voltage solutions (LVS) of the load flow equations of an electrical power system. The proposed method identifies the LVS involved in the saddle-node bifurcation leading the power system to a voltage collapse. This solution is known as the critical low voltage solution. In order to perform the proposed calculation, an auxiliary dynamical gradient system is used. It is shown that the equilibrium points of that associated auxiliary dynamical gradient system are the solutions of the load flow equations. In such manner, the paper proposes identifying the critical LVS calculating the equilibrium points of an auxiliary dynamical gradient system. The proposed method was tested on the Stagg 5-bus, on the IEEE 39-bus and on IEEE 118-bus test systems, and the results are presented at the end of the text.

Degradation of water resources has become one of the most pressing global concerns currently facing mankind. Constructed Wetlands (CWs) represent a concept to combat deterioration of water resources by acting as buffers between wastewater and receiving water bodies. Still, constructing wetlands for the sole purpose of wastewater treatment is a challenging task. To contribute to this research area, the fundamental question raised in this doctorate thesis was: how do factors such as vegetation and residing water movements (hydraulics) influence wastewater treatment in CWs? Also, effects of different data analysis methods for results of CW hydraulics and wastewater treatment were investigated. Research was focused on  phosphorus (P), ammonium-nitrogen (NH4+-N) and solids (TSS) in wastewater and o n P in macrophyte biomass. Studies were performed in pilot-scale free water surface (FWS) CW systems in Kenya (Chemelil) and Sweden (Halmstad) and as computer simulations. Results from the Chemelil CWs demonstrated that meeting effluent concentration standards simultaneously for all water quality parameters in one CW was difficult. Vegetation harvest, and thus nutrient uptake by young growing macrophytes, was important for maintaining low effluents of NH4+-N and P, especially during dry seasons. On the other hand, mature and dense vegetation growing for at least 4 months secured meeting TSS standards. Phosphorus in above-ground green biomass accounted for almost 1/3 of the total P mass removal, demonstrating high potential for P removal through macrophyte harvest in CWs. Also, results suggested that harvest should be species-specific to achieve high P removal by macrophytes and overall acceptable wastewater treatment in CWs. Still, different methods to estimate evapotranspiration (ET) from the Chemelil CWs showed that water balance calculations greatly impacted estimations of wastewater treatment results. Hydraulic tracer studies performed in the Chemelil and Halmstad CWs showed that mature and dense emergent vegetation in CWs could reduce effective treatment volumes (e-values), which emphasized the importance of regulating this type of vegetation. Also, it was shown that hydraulic tracer studies with lithium chloride performed in CWs with dense emergent vegetation had problems with low tracer recoveries. This problem could be reduced by promoting the distribution of incoming tracer solution into the CW using a barrier near the CW inlet pipe. Computer simulation results showed that the choice of tracer data analysis method greatly influenced quantifications of CW hydraulics and pollutant removal. The e-value could be 50% higher and the pollutant removal 13% higher depending upon used method. Moreover, unrealistic evalues (above 100%) in published literature could to some extent be explained by tracer data analysis method. Hence, to obtain more reliable hydraulic data and wastewater treatment results from CWs, more attention should be paid to the choice of tracer data analysis method.
Konstruerade våtmarker representerar ett koncept för möjligheten att nå en hållbar vattenresurshantering genom att agera som ”filter” mellan föroreningskälla och viktiga vattenresurser såsom sjöar och hav. Mycket kunskap saknas däremot om hur man konstruerar våtmarker med en optimal och pålitlig vattenreningskapacitet. Den här avhandlingen undersöker därför hur vegetation och vattnets väg genom våtmarken (hydrauliken) påverkar avloppsvattenrening i våtmarker. Dessutom undersöktes hur valet av dataanalysmetod av insamlad data påverkar resultaten. Studier genomfördes i Kenya och Sverige i experimentvåtmarker (ca. 40-60 m2) och inkluderadedatainsamling av vattenkvalité, hydraulik (spårämnesexperiment) samt biomassa och fosfor i biomassan av två olika våtmarksväxter. Dessutom genomfördes datorsimuleringar. Resultaten från Kenya visade att växtskörd och efterföljande näringsupptag av nyskördade växter var viktig för att uppnå låga utgående koncentrationer av fosfor och ammonium i en tropisk våtmark, speciellt under torrsäsongen. Däremot var en välutvecklad och tät vegetation viktig för reningen av partiklar. Fosfor i grön växtbiomassa representerade cirka 1/3 av våtmarkernas totala fosforrening, vilket påvisade potentialen i att genom skörd ta bort fosfor från avloppsvatten m.h.a. konstruerade våtmarker. Resultaten pekade också på att skörden bör vara art-specifik för att uppnå en hög fosforrening och generellt bra vattenreningsresultat. Dock visade olika beräkningsmetoder att vattenbalansen i en tropisk våtmark markant kan påverka vattenreningsresultaten. Resultaten från spårämnesexperimenten demonstrerade att den effektiva våtmarksvolymen för vattenrening blev mindre vid hög täthet av övervattensväxter. Detta pekade på att regelbunden växtskörd var viktig för att uppnå god vattenrening i våtmarker. Experiment med spårämnet litium visade att man kan få felaktiga resultat p.g.a. att en del spårämne fasthålls på botten i våtmarken om denna har mycket övervattensväxter. Därför bör spridningen av spårämnet i sådana våtmarker underlättas m.h.a. en spridningsbarriär nära inloppsröret. Simuleringar visade också att valet av dataanalysmetod av spårämnesdata starkt kan påverka resultaten och därmed också vår tolkning av en våtmarks hydraulik och reningskapacitet. Den effektiva volymen kunde vara 50% högre och reningseffekten 13% högre beroende på vilken metod som användes. Likaså kan valet av dataanalysmetod ha bidragit till överskattade och orealistiska effektiva volymer (över 100%) i artiklar publicerade de senaste 25 åren. Genom att fokusera mer på valet av dataanalysmetod och t.ex. jämföra resultaten från två olika metoder kan man minimera risken för bristfälliga resultat och därmed felaktiga slutsatser om en våtmarks vattenreningskapacitet.

The advent of deregulated electricity and the call for sustainable energy practices are major drivers for the continued increase of renewable energy systems within the modern day power network. Dominant among them is the wind energy system whose output is uncertain because of its dependence on the prevailing climatic conditions. This increases the level of uncertainty witnessed within the power system as such, as the penetration of renewable energy systems continue to increase, their effects cannot be trivialised. Probabilistic load flow (PLF) is employed by power system analysts to account for the effect of uncertainty within the power network. The common technique which is based on Monte Carlo Simulation (MCS), though accurate is very time consuming and for large systems it becomes unwieldy. Alternative approaches with the advantages of the MCS method but with reduced computational burden are required. A viable alternative method should therefore require minimum computational time and burden, be able to accurately model various network uncertainties, be applicable to practical small and large systems, be able to account for the effect of dependency among network variables and possess good overall accuracy. This thesis proposes a novel approximate approach referred to as the enhanced unscented transform method to meet the requirements of PLF. The method combines the Gaussian quadrature method and the Stieljes procedure with dimension reduction technique in deciding estimation points while the Cholesky decomposition is incorporated to account for the effect of dependency. The performance of the proposed technique is demonstrated using modified IEEE 6, 14, and 118 test systems and a practical distribution test system all incorporating wind farms. Results obtained for numerous scenarios show a good match between the proposed method and the MCS method but with significant computational burden saving. The performance of the method is also shown to compare favourably with other existing PLF methods.

The rigorous load-flow analysis of Distribution Networks requires the modeling of mutual coupling, multiphase possibilities and unbalanced loading. The Ladder Load-Flow Method meets these requirements, but is limited to radial systems. The Switch Compensation Method presented here, extends the Ladder Load-Flow Method to solve Distribution Networks. A network analysis program has been developed using the Electric Power Research Distribution Engineering Workstation (DEWorkstation). The program uses the pointers provided by the DEWorkstation to represent the connectivity of the system. The use of these pointers increases the speed of execution while naturally handling the sparsity of the system. The user is also provided with "on line" attribute and topological data maintenance. The extension technique is based on Thevenin's Theorem. This approach allows the accurate determination of the equivalent impedance for networks which contain series and shunt elements. The equivalent impedance can be changed during the iterative solution process. This allows the algorithm to simulate the operation of control devices which significantly alter the impedance of the network. A transformer model for the forward and reverse trace of the Ladder Method is also presented.
Ph. D.

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Em planejamento e operação de sistemas de energia elétrica, é necessário realizar diversas avaliações utilizando o algoritmo de fluxo de potência, para obter e monitorar o ponto de operação da rede em estudo. Em sua utilização determinística, devem ser especificados valores de geração e níveis de carga por barra, bem como considerar uma configuração especifica da rede elétrica. Existe, porém, uma restrição evidente em se trabalhar com algoritmo de fluxo de potência determinístico: não há qualquer percepção do impacto gerado por incertezas nas variáveis de entrada que o algoritmo utiliza. O algoritmo de fluxo de potência probabilístico (FPP) visa extrapolar as limitações impostas pelo uso da ferramenta convencional determinística, permitindo a consideração das incertezas de entrada. Obtém-se maior sensibilidade na avaliação dos resultados, visto que possíveis regiões de operação são mais claramente examinadas. Consequentemente, estima-se o risco do sistema funcionar fora de suas condições operativas nominais. Essa dissertação propõe uma metodologia baseada na simulação Monte Carlo (SMC) utilizando técnicas de amostragem por importância via o método de entropia cruzada. Índices de risco para eventos selecionados (e.g., sobrecargas em equipamentos de transmissão) são avaliados, mantendo-se a precisão e flexibilidade permitidas pela SMC convencional, porém em tempo computacional muito reduzido. Ao contrário das técnicas analíticas concebidas para solução do FPP, que visam primordialmente à elaboração de curvas de densidade de probabilidade para as variáveis de saída (fluxos, etc.) e sempre necessitam ter a precisão obtida comparada à SMC, o método proposto avalia somente as áreas das caudas dessas densidades, obtendo resultados com maior exatidão nas regiões de interesse do ponto de vista do risco operativo. O método proposto é aplicado nos sistemas IEEE 14 barras, IEEE RTS e IEEE 118 barras, sendo os resultados obtidos amplamente discutidos. Em todos os casos, há claros ganhos de desempenho computacional, mantendo-se a precisão, quando comparados à SMC convencional. As possíveis aplicações do método e suas derivações futuras também fazem parte da dissertação.
In planning and operation of electric energy systems, it is necessary to perform several evaluations using the power flow algorithm to obtain and monitor the operating point of the network under study. Bearing in mind its deterministic use, generation values and load levels per bus must be specified, as well as a specific configuration of the power network. There is, however, an obvious constraint in running a deterministic power flow tool: there is no perception of the impact produced by uncertainties on the input variables used by the conventional algorithm. The probabilistic power flow (PLF) algorithm aims to solve the limitations imposed by the use of the deterministic conventional tool, allowing the consideration of input uncertainties. Superior sensitivity is obtained in the evaluation of results, as possible regions of operation are more clearly examined. Consequently, the risk of the system operating outside its nominal conditions is duly estimated. This dissertation proposes a methodology based on Monte Carlo simulation (MCS) using importance sampling techniques via the cross-entropy method. Risk indices for selected events (e.g., overloads on transmission equipment) are evaluated, keeping the same accuracy and flexibility tolerable by the conventional MCS, but in much less computational time. Unlike the FPP solution obtained by analytical techniques, which primarily aim at assessing probability density curves for the output variables (flows, etc.) and always need to have the accuracy compared to MCS, the proposed method evaluates only the tail areas of these densities, obtaining results with greater accuracy in the regions of interest from the operational risk point of view. The proposed method is applied to IEEE 14, IEEE RTS and IEEE 118 bus systems, and the results are widely discussed. In all cases, there are clear gains in computational performance, maintaining accuracy when compared to conventional SMC. The possible applications of the method and future developments are also part of the dissertation.

Shear walls are the primary lateral load resisting elements in bearing wall systems used in masonry construction. Horizontal loads due to wind or earthquake are transferred to vertical walls by diaphragms that are rigid such as concrete floor slabs or flexible such as wood floors. With rigid diaphragms, loads are apportioned to the supporting walls based on their relative rigidity. Walls with openings accommodating doors and windows (“perforated walls”) have reduced rigidity that can be determined using available hand calculation methods. These methods primarily focus on analysis procedures, not on the visualization of the load path that is critically important in structural engineering practice. The analogy of springs in series or parallel is used to determine the equivalent stiffness of elastic systems in structural dynamics. This thesis uses this analogy to develop a method that can help visualize load flow in perforated shear walls connected to rigid diaphragms. Rigidities are calculated using existing methods and combined as springs in series or parallel to represent a perforated wall. Loads taken by the wall segments correspond to the electrical current flowing through this imaginary “circuit”. To help visualize the load path, the line drawing representation of springs in series or parallel and the applied lateral load are deliberately oriented in the vertical direction. The application of the analogy is illustrated by several numerical examples of varying complexity taken from text books. Finite element solutions are included in the comparisons to provide a measure of the relative accuracy of hand calculation methods. The analogy can be extended to refine existing hand calculation methods though this increases computational effort. It improves accuracy but only for cases where the aspect ratio of the wall segments is such that shear effects are dominant.

This thesis is the result of an investigation to assess the potential of the continuation method to solve the minimum cost optimal power flow problem. For this purpose, a restart homotopy continuation method algorithm is developed, which contains in essence two phases.
The pertinent steps of the first phase are as follows: (1) Create a sub-problem of the complete optimal power flow problem by relaxing boundary limits on all functional variables, namely voltages at load buses, line flows and reactive generations. (2) Parameterize a subset of the whole set of controls which comprises initially of tap-changers, phase-shifters, shunt controllers, and the voltages at generation buses. (3) Optimize the resulting problem.
The solution in step (3) is used as an initial starting point in a continuation process, designed to track this solution to the optimal solution of the sub-problem defined in step (1). The tracking is accomplished via a predictor-corrector path following algorithm embodying certain special features, such that the solution accuracy can be improved to any desired degree through a flexible restart feature developed in this study. Within the tracking process only a subset (identified in step 2 above) of the whole set of controls require specific monitoring for break-points. This feature greatly reduces the computational burden. Termination of the first phase marks an operating point in which all controls are strictly feasible.
If, following the termination of the first phase, functional variables previously ignored prove to be within their respective bounds, the solution to the sub-problem becomes the solution to the complete optimal power flow problem. However, should functional variables violate their bounds the second phase of the algorithm is invoked, which in essence creates a new sub-problem by changing the roles of the control and violated dependent variables, such that the newly modified sub-problem maintains the same basic structure as its predecessor.
Phase I is invoked again at this juncture to solve the modified sub-problem. This process is repeated in cycles until the Kuhn-Tucker optimality conditions are satisfied. Simulations suggest that convergence is usually achieved within two or three Phase I/II cycles.
This being a method unique to the minimum cost optimal power flow problem, numerous examples (up to 118 buses) have been tested and compared against the commercial code MINOS. The newly proposed algorithm appears to be faster and more reliable.

This paper presents an analytical assessment method for probabilistic power flow analysis using a Multivariate Complex Gaussian Distribution (MCGD) and a Direct Approach for the load flow equations. To provide a reference for comparison and assessment, a standard Monte Carlo (MC) simulation and a Copula coefficient MC simulation were undertaken. Both use the Direct Approach for load flow equations. Details and steps of all methods are provided along with background information deemed relevant to provide a self-contained body of knowledge. This improves accessibility to a less mathematically advanced audience. It will be shown that the proposed technique is significantly quicker to compute and that the magnitude of mean voltages closely match those obtained using the MCSs. Further, it will be shown that standard deviations observed varied up to 45% between methods, at specific load points, and it is concluded that further analysis is required to be able to determine that the proposed method is sufficiently accurate.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
O fluxo de carga convencional é considerado inadequado para a obtenção do ponto de máximo carregamento devido a singularidade da matriz Jacobiana. Os métodos da continuação são ferramentas eficientes para a solução deste tipo de problema, e diferentes parametrizações são utilizadas para evitar a singularidade da matriz. Neste trabalho apresentase uma técnica de parametrização geométrica que possibilita o traçado completo das curvas PV sem os problemas de mal condicionamento. A técnica proposta associa a robustez com a simplicidade e a facilidade de compreensão. A singularidade da matriz Jacobiana é eliminada pela adição da equação de uma reta que passa por um ponto no plano formado pelas variáveis perdas de potência ativa totais e o fator de carregamento, dois parâmetros físicos de fácil compreensão. A técnica, aplicada aos sistemas do IEEE (14, 30, 57, 118 e 300 barras) e ao sistema brasileiro sul-sudeste (638 e 787 barras), mostra que as características do fluxo de carga não só são preservadas, mas também melhoradas. Diversos testes são realizados para proporcionar a comparação do desempenho do esquema de parametrização proposto para o método do fluxo de carga continuado.
The conventional Newton’s method has been considered inadequate to obtain the maximum loading point of power systems due to the Jacobian matrix singularity. Continuation methods are efficient tools for solving this kind of problem, and different parameterizations are used to avoid the matrix singularity. This paper presents a new geometric parameterization scheme that allows the complete tracing of the PV curves without ill-conditioning problems. The proposed technique associates the robustness to the simplicity and easy understanding. The Jacobian matrix singularity is overcome by the addition of a line equation, which passes through a point in the plane, determined by the real power losses and loading factor variables, two parameters with clear physical meaning. The application of this new technique to the IEEE systems (14, 30, 57, 118 and 300 buses) and to the Brazilian systems south-southeast (638 and 787 buses) shows that the characteristics of the conventional Newton’s method are not only preserved but also improved. Several tests are carried out to compare the performance of the proposed parameterization scheme for the continuation power flow method.

This thesis considers three separate but connected problems regarding energy networks: the load flow problem, the optimal power flow problem, and the islanding problem. All three problems are non-convex non linear problems, and so have the potential of returning local solutions. The goal of this thesis is to find solution methods to each of these problems that will minimize the chances of returning a local solution. The thesis first considers the load ow problem and looks into a novel approach to solving load flows, the Holomorphic Embedding Load Flow Method (HELM). The current literature does not provide any HELM models that can accurately handle general power networks containing PV and PQ buses of realistic sizes. This thesis expands upon previous work to present models of HELM capable of solving general networks efficiently, with computational results for the standard IEEE test cases provided for comparison. The thesis next considers the optimal power flow problem, and creates a framework for a load flow-based OPF solver. The OPF solver is designed with incorporating HELM as the load flow solver in mind, and is tested on IEEE test cases to compare it with other available OPF solvers. The OPF solvers are also tested with modified test cases known to have local solutions to show how a LF-OPF solver using HELM is more likely to find the global optimal solution than the other available OPF solvers. The thesis finally investigates solving a full AC-islanding problem, which can be considered as an extension of the transmission switching problem, using a standard MINLP solver and comparing the results to solutions obtained from approximations to the AC problem. Analysing in detail the results of the AC-islanding problem, alterations are made to the standard MINLP solver to allow better results to be obtained, all the while considering the trade-off between results and elapsed time.

This Ph.D. thesis aims to develop numerical models for two-dimensional and three-dimensional shallow water systems over mobile beds. In order to accomplish the goal of this dissertation, the following sub-projects are defined and completed. 1: The first sub-project consists in developing a robust two-dimensional coupled numerical model based on an unstructured mesh, which can simulate rapidly varying flows over an erodible bed involving wet–dry fronts that is a complex yet practically important problem. In this task, the central-upwind scheme is extended to simulation of bed erosion and sediment transport, a modified shallow water system is adopted to improve the model, a wetting and drying scheme is proposed for tracking wet-dry interfaces and stably predict the bed erosion near wet-dry area. The shallow water, sediment transport and bed evolution equations are coupled in the governing system. The proposed model can efficiently track wetting and drying interfaces while preserving stability in simulating the bed erosion near the wet-dry fronts. The additional terms in shallow water equations can improve the accuracy of the simulation when intense sediment-exchange exists; the central-upwind method adopted in the current study shows great accuracy and efficiency compared with other popular solvers; the developed model is robust, efficient and accurate in dealing with various challenging cases. 2: The second sub-project consists in developing a novel numerical scheme for a coupled two-dimensional hyperbolic system consisting of the shallow water equations with friction terms coupled with the equations modeling the sediment transport and bed evolution. The resulting 5*5 hyperbolic system of balance laws is numerically solved using a Godunov-type central-upwind scheme on a triangular grid. A spatially second-order and temporally third-order central-upwind scheme has been derived to discretize the conservative hyperbolic sub-system. However, such schemes need a correct evaluation of local wave speeds to avoid instabilities. To address such an issue, a mathematical result by the Lagrange theorem is used in the proposed scheme. Consequently, a computationally expensive process of finding all of the eigenvalues of the Jacobian matrices is avoided: The upper/lower bounds on the largest/smallest local speeds of propagation are estimated using the Lagrange theorem. In addition, a special discretization of the bed-slope term is proposed to guarantee the well-balanced property of the designed scheme. 3: The third sub-project consists in designing a novel scheme to estimate bed-load fluxes which can produce more accurate results than the previously reported coupled model. Using a pair of local wave speeds different from those used for the flow, a novel wave estimator in conjunction with the central upwind method is proposed and successfully applied to the coupled water-sediment system involving a rapid bed-erosion process. It was demonstrated that, in comparison with the decoupled model, applying the proposed novel scheme to approximate the bed-load fluxes can successfully avoid the numerical oscillations caused by simple and less stable schemes, e.g. simple upwind methods; in comparison with the coupled model using same flux-estimator for both hydrodynamic and morphological systems, the proposed numerical scheme successfully prevents excessive numerical diffusion for prediction of bed evolution. Consequently, the proposed scheme has advantages in terms of accuracy which are shown in several numerical tests. In addition, analytical expressions have been provided for calculating the eigenvalues of the coupled shallow-water-Exner system, which greatly enhances the efficiency of the proposed method. 4: The fourth sub-project consists in developing a three-dimensional numerical model for the simulation of unsteady non-hydrostatic shallow water flows on unstructured grids using the finite volume method. The free surface variations are modeled by a characteristics-based scheme which simulates sub- and super-critical flows. Three-dimensional velocity components are considered in a collocated arrangement with a sigma coordinate system. A special treatment of the pressure term is developed to avoid the water surface oscillations. Convective and diffusive terms are approximated explicitly, and an implicit discretization is used for the pressure term. The unstructured grid in the horizontal direction and the sigma coordinate in the vertical direction facilitate the use of the model in complicated geometries. 5: The fifth sub-project consists in developing a well-balanced three-dimensional shallow water model which is able to simulate shock waves over dry bed. Due to the hydrostatic simplification of the vertical momentum equation, the governing system of equations is not hyperbolic and can not be solved using standard hyperbolic solvers. That is, one can not use a high-order Godunov-type scheme to compute all fluxes through cell-interfaces. This may cause the model to fail in simulations of some unsteady-flows with discontinuities, e.g., dam-break flows and floods. To overcome this difficulty, a novel numerical scheme for the three-dimensional shallow water equations is proposed using a relaxation approach in order to convert the system to a hyperbolic one. Thus, a high-order Godunov-type central-upwind scheme based on the finite volume method can be applied to approximate the numerical fluxes. The proposed model can also preserve the ``lake at rest'' state and positivity of water depth over irregular bottom topographies based on special reconstruction of the corresponding parameters. 6: The sixth sub-project consists in extending the result of the fifth sub-project to development of a three-dimensional numerical model for shallow water flows over mobile beds, which is able to simulate morphological evolutions under shock waves, e.g. dam-break flows. The hydrodynamic model solves the three-dimensional shallow water equations using a finite volume method on prismatic cells in sigma coordinates based on the scheme prposed in sub-project 5. The morphodynamic model solves an Exner equation consisting of bed-load sediment transportation. The performance of the proposed model has been demonstrated by several laboratory experiments of dam-break flows over mobile beds.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Este trabalho apresenta um novo esquema de parametrização geométrico para o fluxo de carga continuado que possibilita o traçado completo das curvas P-V, e o cálculo do ponto de máximo carregamento de sistemas de potência, sem os problemas de mau-condicionamento. O objetivo é o de apresentar de uma forma clara e didática, os passos envolvidos no desenvolvimento de uma técnica de parametrização geométrica a partir da observação das trajetórias de solução do fluxo de carga. A técnica associa robustez com facilidade de compreensão. A singularidade da matriz Jacobiana é eliminada pela adição da equação de uma reta que passa por um ponto no plano formado nas variáveis magnitude da tensão nodal e o fator de carregamento, dois parâmetros físicos de fácil compreensão. O uso desta técnica amplia o grupo das variáveis de tensão que podem ser usadas como parâmetro de continuação. Os resultados obtidos com a nova metodologia para os sistemas testes do IEEE (14, 30, 57, 118 e 300 barras), mostram que as características do método convencional são melhoradas e a região de convergência ao redor da singularidade é ampliada. Vários testes são apresentados com intuito de prover um completo entendimento do método proposto e possibilitar comparação e a avaliação do desempenho do esquema de parametrização proposto.
This work presents a new geometrical parameterization scheme to the continuation power flow that allows the complete tracing of P-V curves and the computation of the maximum loading point of a power system, without ill-conditioning problems. The objective is to present in a clear and didactic way, the steps involved in the development of a geometrical parameterization technique from the observation of the behavior of power flow solutions path. The technique associates robustness with simplicity and easy interpretation. The Jacobian matrix singularity is overcome by the addition of a line equation which passes through a point in the plane determined by variables bus voltage magnitude and the loading factor, two physical parameter of easy understanding. The use of this technique enlarges the group of voltage variables that can be used as continuation parameter. The results obtained with the new methodology for the IEEE systems (14, 30, 57, 118 and 300 buses), show that the characteristics of the conventional method are improved and the region of convergence around the singular solution is enlarged. Many tests are also presented in intention to provide the complete understanding of the proposed method and to allow the comparison and assessment of the performance of the proposed parameterization scheme.

The restructuring of the electric energy market and the proliferation of intermittent renewable-energy based power generation have introduced serious challenges to power system operation emanating from the uncertainties introduced to the system variables (electricity prices, congestion levels etc.). In order to economically operate the system and efficiently run the energy market, a statistical analysis of the system variables under uncertainty is needed. Such statistical analysis can be performed through an estimation of the statistical moments of these variables. In this thesis, the Point Estimate Methods (PEMs) are applied to the optimal power flow (OPF) problem to estimate the statistical moments of the locational marginal prices (LMPs) and total generation cost under system uncertainty. An extensive mathematical examination and risk analysis of existing PEMs are performed and a new PEM scheme is introduced. The applied PEMs consist of two schemes introduced by H.P. Hong, namely, the 2n and 2n+1 schemes, and a proposed combination between Hong's and M. E Harr's schemes. The accuracy of the applied PEMs in estimating the statistical moments of system LMPs is illustrated and the performance of the suggested combination of Harr's and Hong's PEMs is shown. Moreover, the risks of the application of Hong's 2n scheme to the OPF problem are discussed by showing that it can potentially yield inaccurate LMP estimates or run into unfeasibility of the OPF problem. In addition, a new PEM configuration is also introduced. This configuration is derived from a PEM introduced by E. Rosenblueth. It can accommodate asymmetry and correlation of input random variables in a more computationally efficient manner than its Rosenblueth's counterpart.
Master of Science

A number of experimental and theoretical studies, performed in the field of technical flow duct acoustics are presented in this thesis. The acoustical methods treated are implemented on turbocharged IC-engines and engine gas exchange system components. A new method based on the well-known two-load technique has been developed. The method was applied to characterise the source data of various piston-engines with non-linear behaviour including a 6 cylinder turbo-charged truck diesel engine. The source characterisation results were compared to the results obtained using the linear two-load technique. It was demonstrated that the new non-linear multi-load technique gives improved results when the source is slightly non-linear. The use of active one-port models has been tested to characterize an air terminal device (ATD) as a source of flow generated noise. In order to predict the noise generation at different operating points of the device a scaling law was derived and verified. In the experimentally derived scaling law a flow speed dependence of 3 was found for the narrow band spectra, corresponding to a dipole-like behavior of the source in the plane wave range. The proposed technique was validated successfully and the results indicated a good prediction of in-duct sound generation by the air terminal device. Sound reflection from hot flow duct openings has been investigated experimentally. The reflection coefficient was measured for flow temperatures up to 500 ºC and jet velocities up to 108m/s. The results have been compared with famous Munt’s theory. It was concluded that at low Mach number and Helmholz number cases the results agree well with the Munt’s model. This was the first experimental validation of the theory for hot flow conditions. Experimental procedures to determine the sound transmission through automotive turbo-charger compressors were developed and described in detail. An overview of a unique turbocharger testing facility established at KTH CICERO in Stockholm is given. The facility can be used to measure acoustic two-port data for turbo-compressors. Results from measurements on a passenger car turbo-compressor are presented and the influence of operating conditions on the sound transmission is discussed. Current wave action models developed in CMT for computation of the gas exchange processes in I.C. engines have been implemented to determine the acoustic wave transmission through the turbo- compressor. The models are validated with the experimental data and the results are presented for different operating conditions of a Volvo passenger car turbo-compressor.
QC 20100809

Orientador: Dílson Amâncio Alves
Banca: Francisco Villarreal Alvarado
Banca: Eduardo Nobuhiro Asada
Resumo: Este trabalho apresenta um novo esquema de parametrização geométrico para o fluxo de carga continuado que possibilita o traçado completo das curvas P-V, e o cálculo do ponto de máximo carregamento de sistemas de potência, sem os problemas de mau-condicionamento. O objetivo é o de apresentar de uma forma clara e didática, os passos envolvidos no desenvolvimento de uma técnica de parametrização geométrica a partir da observação das trajetórias de solução do fluxo de carga. A técnica associa robustez com facilidade de compreensão. A singularidade da matriz Jacobiana é eliminada pela adição da equação de uma reta que passa por um ponto no plano formado nas variáveis magnitude da tensão nodal e o fator de carregamento, dois parâmetros físicos de fácil compreensão. O uso desta técnica amplia o grupo das variáveis de tensão que podem ser usadas como parâmetro de continuação. Os resultados obtidos com a nova metodologia para os sistemas testes do IEEE (14, 30, 57, 118 e 300 barras), mostram que as características do método convencional são melhoradas e a região de convergência ao redor da singularidade é ampliada. Vários testes são apresentados com intuito de prover um completo entendimento do método proposto e possibilitar comparação e a avaliação do desempenho do esquema de parametrização proposto.
Abstract: This work presents a new geometrical parameterization scheme to the continuation power flow that allows the complete tracing of P-V curves and the computation of the maximum loading point of a power system, without ill-conditioning problems. The objective is to present in a clear and didactic way, the steps involved in the development of a geometrical parameterization technique from the observation of the behavior of power flow solutions path. The technique associates robustness with simplicity and easy interpretation. The Jacobian matrix singularity is overcome by the addition of a line equation which passes through a point in the plane determined by variables bus voltage magnitude and the loading factor, two physical parameter of easy understanding. The use of this technique enlarges the group of voltage variables that can be used as continuation parameter. The results obtained with the new methodology for the IEEE systems (14, 30, 57, 118 and 300 buses), show that the characteristics of the conventional method are improved and the region of convergence around the singular solution is enlarged. Many tests are also presented in intention to provide the complete understanding of the proposed method and to allow the comparison and assessment of the performance of the proposed parameterization scheme.
Mestre

Orientador: Dilson Amâncio Alves
Banca: 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
Mestre

Este trabalho descreve uma abordagem do método primal-dual barreira logarítmica (MPDBL) associado ao método de Newton modificado para a resolução do problema de fluxo de potência para sistemas de distribuição radial. Também foi realizado um estudo comparativo com duas técnicas clássicas de solução do problema de fluxo potência para redes de distribuição radial. São os métodos: Backward/Forward Sweep e o método proposto por M. Baran e F. Wu, que é baseado na técnica de Newton-Raphson. Este método utiliza uma matriz Jacobiana modificada que atende a característica radial dos sistemas de distribuição. Nos testes comparativos serão considerados todos os parâmetros do sistema. Os algoritmos de solução serão analisados em suas propriedades de convergência e será realizado um teste de robustez. Os resultados dos testes realizados em 4 sistemas (4, 10, 34 e 70 barras) e o teste comparativo entre os métodos evidenciam a melhor metodologia na solução do problema de fluxo de potência para sistemas radiais
This work describes an approach on primal-dual logarithmic barrier method (PDLBM) associate to the method of Newton modified for the resolution of the problem of power flow for radial distribution systems. Also a comparative study with two classic techniques of solution of the flow problem was carried through power for nets of radial distribution. They are the methods: Backward/Forward Sweep and the method considered for M. Baran and F. Wu, that is based on the technique of Newton-Raphson. This method uses modified Jacobiana matrix that takes care of the radial characteristic of the distribution systems. In the comparative tests all will be considered the parameters of the system. The solution algorithms will be analyzed in its properties of convergence and will be carried through a robustness test. The results of the tests carried through in 4 systems (4, 10, 34 and 70 bus) and the comparative test between the methods evidence the best methodology in the solution of the problem of power flow for radial systems

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
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
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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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Este trabalho apresenta dois métodos para a análise estática de contingências em Sistemas Elétricos de Potência utilizando o Método da Continuação. No primeiro método a margem de carregamento pós-contingência é obtida a partir do ponto de máximo carregamento do caso base. A magnitude de tensão de uma barra qualquer é usada como parâmetro na etapa de parametrização do fluxo de carga continuado. O ramo selecionado para avaliação da contingência é parametrizado por um fator de escalonamento que possibilita a remoção gradual do ramo e assegura a convergência nos casos em que o método diverge para a retirada total da linha de transmissão. Em geral, para a maioria das contingências analisadas são necessárias poucas iterações para a determinação do ponto de máximo carregamento pós-contingência. Mostra-se que o método pode ser usado como uma técnica alternativa para a averiguação e até mesmo para a obtenção da lista de contingências críticas fornecida pela função de análise de segurança de sistemas elétricos. No outro método, o qual obtém o ponto de máximo carregamento de pós-contingência a partir do caso base, as variáveis ângulo de fase e magnitude de tensão de uma barra k qualquer, e a perda total de potência ativa, são propostas como parâmetros para a etapa de parametrização do fluxo de carga continuado utilizado na averiguação da lista de contingências críticas fornecida pela função de análise de segurança de sistemas elétricos. Nos casos em que há divergência do fluxo de carga, o método proposto possibilita confirmar se esta ocorre devido à deficiência numérica do método em si ou a inexistência de um ponto de operação factível de pós-contingência. O uso da perda total de potência ativa como parâmetro traz como vantagem a possibilidade da determinação de pontos além do ponto de singularidade sem a necessidade...
This work presents two methods for static contingency analysis of electric power systems by using Continuation Methods. In the first the post-contingency loading margin is obtained from the base case maximum loading point. The voltage magnitude of any bus can be used as a parameter in the parameterization step of the proposed continuation power flow. The branch selected for contingency evaluation is parameterized by a scaling factor which allows its the gradual removal and assures the continuation power flow convergence for the cases where the method would diverge for the complete transmission line removal. In general, for most of the analyzed contingencies little iterations are necessary for the determination of the post-contingency maximum loading point. It is shown that the method can be used as an alternative technique to verify and even to obtain the list of critical contingencies supplied by the electric power systems security analysis function. In the other method, which obtains the maximum loading point from the base case, new parameters, namely the voltage magnitudes, phase angles and the total power losses, for evaluating the effects of branch outages. The approach can be used as a verification tool after a list of critical contingencies had been ranked according to their severities by the contingency selection functions. It is then possible to find whether the non-convergence of a power flow is due to a numerical problem or to an infeasible operating situation. The mains advantage of using the total real power losses as a parameter is that it is not necessary to change parameters during the solutions tracing until beyond the simple limit point, where the original Jacobian is singular. The proposed methods facilitate the development and the implementation of continuation methods for contingencies analysis

Orientador: Dilson Amancio Alves
Banca: Percival Bueno de Araujo
Banca: Carlos Roberto Minussi
Banca: Geraldo Roberto Martins da Costa
Banca: Luiz Carlos Pereira da Silva
Resumo: Este trabalho apresenta dois métodos para a análise estática de contingências em Sistemas Elétricos de Potência utilizando o Método da Continuação. No primeiro método a margem de carregamento pós-contingência é obtida a partir do ponto de máximo carregamento do caso base. A magnitude de tensão de uma barra qualquer é usada como parâmetro na etapa de parametrização do fluxo de carga continuado. O ramo selecionado para avaliação da contingência é parametrizado por um fator de escalonamento que possibilita a remoção gradual do ramo e assegura a convergência nos casos em que o método diverge para a retirada total da linha de transmissão. Em geral, para a maioria das contingências analisadas são necessárias poucas iterações para a determinação do ponto de máximo carregamento pós-contingência. Mostra-se que o método pode ser usado como uma técnica alternativa para a averiguação e até mesmo para a obtenção da lista de contingências críticas fornecida pela função de análise de segurança de sistemas elétricos. No outro método, o qual obtém o ponto de máximo carregamento de pós-contingência a partir do caso base, as variáveis ângulo de fase e magnitude de tensão de uma barra k qualquer, e a perda total de potência ativa, são propostas como parâmetros para a etapa de parametrização do fluxo de carga continuado utilizado na averiguação da lista de contingências críticas fornecida pela função de análise de segurança de sistemas elétricos. Nos casos em que há divergência do fluxo de carga, o método proposto possibilita confirmar se esta ocorre devido à deficiência numérica do método em si ou a inexistência de um ponto de operação factível de pós-contingência. O uso da perda total de potência ativa como parâmetro traz como vantagem a possibilidade da determinação de pontos além do ponto de singularidade sem a necessidade...(Resumo completo, clicar acesso eletrônico abaixo)
Abstract: This work presents two methods for static contingency analysis of electric power systems by using Continuation Methods. In the first the post-contingency loading margin is obtained from the base case maximum loading point. The voltage magnitude of any bus can be used as a parameter in the parameterization step of the proposed continuation power flow. The branch selected for contingency evaluation is parameterized by a scaling factor which allows its the gradual removal and assures the continuation power flow convergence for the cases where the method would diverge for the complete transmission line removal. In general, for most of the analyzed contingencies little iterations are necessary for the determination of the post-contingency maximum loading point. It is shown that the method can be used as an alternative technique to verify and even to obtain the list of critical contingencies supplied by the electric power systems security analysis function. In the other method, which obtains the maximum loading point from the base case, new parameters, namely the voltage magnitudes, phase angles and the total power losses, for evaluating the effects of branch outages. The approach can be used as a verification tool after a list of critical contingencies had been ranked according to their severities by the contingency selection functions. It is then possible to find whether the non-convergence of a power flow is due to a numerical problem or to an infeasible operating situation. The mains advantage of using the total real power losses as a parameter is that it is not necessary to change parameters during the solutions tracing until beyond the simple limit point, where the original Jacobian is singular. The proposed methods facilitate the development and the implementation of continuation methods for contingencies analysis
Doutor

Este trabalho apresenta uma nova abordagem para a modelagem e resolução de problemas de fluxo de carga em sistemas elétricos de potência. O modelo proposto é formado simultaneamente pelo conjunto de equações não lineares que representam as restrições de carga do problema e por restrições de complementaridade associadas com as restrições de operação da rede, as quais propiciam o controle implícito das tensões nas barras com controle de geração. Também é proposta uma técnica para a obtenção dos valores discretos dos taps de tranformadores, de maneira que o ajuste dessas variáveis possa ser realizado em passos discretos. A metodologia desenvolvida consiste em tratar o sistema misto de equações e inequações não lineares como um problema de factibilidade não linear e transformá-lo em um problema de mínimos quadrados não lineares, o qual é resolvido por uma sequência de subproblemas linearizados dentro de uma região de confiança. Para a obtenção de soluções aproximadas desse subproblema foi adotado o método do gradiente conjugado de Steihaug, combinando estratégias de região de confiança e filtros multidimensionais para analisar a qualidade das soluções fornecidas. Foram realizados testes numéricos com os sistemas de 14, 30, 57, 118 e 300 barras do IEEE, e com um sistema brasileiro equivalente CESP 53 barras, os quais indicaram boa flexibilidade e robustez do método proposto.
This work presents a new approach to the load flow problem in electrical power systems and develops a methodology for its resolution. The proposed model is simultaneously composed by nonlinear equations and inequations which represent the load and operational restrictions of the system, where a set of complementarity constraints model the relationship between voltage and reactive power generation in controled buses. It is also proposed a new technique to obtaining a discrete solution for the transformer taps, allowing their discrete adjustment. The method developed treats the mixed system of equations and inequations of the load flow problem as a nonlinear feasibility problem and converts it in a nonlinear least squares problem, which is solved by minimizing a sequence of linearized subproblems, whitin a trust region. To obtain approximate solutions at every iteration, we use the Steihaug conjugate gradient method, combining trust region and multidimensional filters techniques to analyse the quality of the provided solution. Numerical results using 14, 30, 57, 118 and 300-bus IEEE power systems, and a real brazilian equivalent system CESP 53-bus, indicate the flexibility and robustness of the proposed method.

La nécessité d’une meilleure compréhension du mécanisme d’entrainement pour l’instabilité à basse fréquence observée dans un écoulement dans une tuyère sur-détendue a été discutée. Le caractère instable de l’onde de choc/couche limite reste un défi pratique important pour les problèmes des écoulements dans les tuyères. De plus, pour une couche limite turbulente incidente donnée, ce type d’écoulement présente généralement des mouvements de choc à basse fréquence plus élevées qui sont moins couplés aux échelles de temps de la turbulence en amont. Cela peut être bon du point de vue d’un expérimentateur, en raison de difficultés à mesurer des fréquences plus élevées, mais c’est plus difficile d’un point de vue calcul numérique en raison de la nécessité d’obtenir des séries temporelles plus longues pour résoudre les mouvements à basse fréquence. En excellent accord avec les résultats expérimentaux, une série de calcul LES de très longue durée a été réalisée, il a été clairement démontré l’existence de mouvements énergétiques à basse fréquence et à large bande près du point de séparation. Des efforts particuliers ont été faits pour éviter tout forçage à basse fréquence en amont, et il a été explicitement démontré que les oscillations de choc à basse fréquence observées n’étaient pas liées à la génération de turbulence d’entrée, excluant la possibilité d’un artefact numérique. Différentes méthodes d’analyse spectrales, et en décomposition en mode dynamique ont été utilisées pour montrer que les échelles de temps impliquées dans un tel mécanisme sont environ deux ordres de grandeur plus grandes que les échelles de temps impliquées dans la turbulence de la couche limite, ce qui est cohérent avec les mouvements de basse fréquence observés. En outre, ces échelles de temps se sont avérées être fortement modulées par la quantité de flux inversé à l’intérieur de la bulle de séparation. Ce scénario peut, en principe, expliquer à la fois l’instabilité des basses fréquences et sa nature à large bande
The need for a better understanding of the driving mechanism for the observed low-frequency unsteadiness in an over-expanded nozzle flows was discussed. The unsteady character of the shock wave/boundary layer remains an important practical challenge for the nozzle flow problems. Additionally, for a given incoming turbulent boundary layer, this kind of flow usually exhibits higher low-frequency shock motions which are less coupled from the timescales of the incoming turbulence. This may be good from an experimenter’s point of view, because of the difficulties in measuring higher frequencies, but it is more challenging from a computational point of view due to the need to obtain long time series to resolve low-frequency movements. In excellent agreement with the experimental findings, a very-long LES simulation run was carried out to demonstrate the existence of energetic broadband low-frequency motions near the separation point. Particular efforts were done in order to avoid any upstream low-frequency forcing, and it was explicitly demonstrated that the observed low-frequency shock oscillations were not connected with the inflow turbulence generation, ruling out the possibility of a numerical artefact. Different methods of spectral analysis and dynamic mode decomposition have been used to show that the timescales involved in such a mechanism are about two orders of magnitude larger than the time scales involved in the turbulence of the boundary layer, which is consistent with the observed low-frequency motions. Furthermore, those timescales were shown to be strongly modulated by the amount of reversed flow inside the separation bubble. This scenario can, in principle, explain both the low-frequency unsteadiness and its broadband nature

Diploma thesis is focused on modeling rotor downwash generated by the main rotor of helicopter and analyzing its effects on the roof structure. Theoretical definition of rotor downwash flow is described in the first part of the text. Governing equations of computational fluid dynamics are briefly explained as well as boundary layer and finite volume method. Next part inquires into numerical simulation of rotor downwash based on height of rotor above the roof, shape of roof plane and climatic conditions. Results are compared with climatic load values provided by actual Czech construction standard in the end of the text.

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CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Neste trabalho é proposta a aplicação de redes neurais artificiais para ajuste de parâmetros de um compensador estático de reativos, para controle de tensão e harmônicos. Devido à intensa produção de correntes harmônicas e possíveis afundamentos de tensão em instalações industriais como o forno a arco, é necessário um sistema de controle eficiente e robusto. Além disso, os sistemas elétricos de potência se encontram em um cenário com a presença cada vez maior de geração distribuída, cargas não-lineares e forte tendência à operação no contexto das smartgrids e microgrids. Sendo assim, o suporte de reativos deve ser adequado a esses sistemas, podendo atuar de forma rápida, precisa e confiável. Uma possível solução é a utilização de um compensador estático de reativos (CER) com função adicional de filtragem no ponto onde se deseja controlar a tensão e a distorção harmônica. Entretanto, para o correto funcionamento, é necessário um sistema preciso para o ajuste dos parâmetros do CER, ou seja, determinar os ângulos de disparo dos tiristores e o número de bancos de capacitores a serem ligados. Neste trabalho é proposta uma estratégia de controle via redes neurais artificiais, treinadas para o reconhecimento de padrões de operação em regime permanente e definição da configuração do CER, conferindo inteligência ao equipamento. Os desenvolvimentos propostos foram implementados no ambiente MatLab®. A validação do método é feita através de simulações em sistemas-teste, presentes na literatura técnica, utilizando o fluxo de potência pelo método de injeção de correntes trifásico harmônico. Os resultados obtidos mostram as vantagens da utilização da estratégia proposta.
In this work, an artificial neural network-based static var compensator tuning is proposed for voltage and harmonic distortion control. Due to intense harmonic current injection and possible voltage sags produced by industrial facilities such as arc furnaces, an efficient robust control system is needed. Besides, electrical power systems face a new scenario with high penetration of distributed generation and non-linear loads and increased smart grid and microgrid trends. Therefore, the available reactive power sources must be able to provide system control in order to operate the system in a fast, accurate and reliable way. The application of a static var compensator (SVC) with additional filtering function at the controlled node is a possible solution. However, a precise SVC parameters tuning is needed, in order to make the system to work properly. In this work, a control strategy based on artificial neural networks is proposed. The neural networks are trained to recognize steadystate operating patterns and give the SVC adjustment. The proposed technique was implemented in the MatLab® environment. The methodology is validated by simulations in test-systems available in technical literature, using the three-phase harmonic current injection method power flow. Results show the advantages of the proposed methodology.

Ерозија земљишта је један од најкомплекснијих проблема и уједно један од најподмуклијих човекових непријатеља. Ерозивни процеси постепено разарају и уништавају земљиште, односе хранљиве супстрате и ремете водни режим. Они доводе становништво многих, често пространих области у беду, сиромаштво и миграцију. Због тога, многе привредне гране морају бити увучене у борбу против ерозије земљишта и њених страховитих последица. Ерозија је веома сложена динамичка појава, која зависи од низа фактора чије је диференцирање врло тешко. Испитивање и утврђивање интензитета водне ерозије спада у групу проблема који се не могу свеобухватно решити. Веома је тешко, скоро немогуће, издвојити све факторе, а потом мултиплицирати све те факторе у свим постојећим комбинацијама. Овим радом сагледано је стање ерозије земљишта у сливу Млаве и Пека, односно Хомољу и Звижду, са више аспеката и утврђен низ појава као што су: концентрација растворених минералних материја, процентуално учешће макроелемената у укупној минерализацији, однос минерализације према протицају, укупан годишњи пронос растворених минералних материја, однос специфичне електричне проводљивости и укупне минерализације, износ хемијске евакуације, износ хемијски растворених минералних материја које потичу од стенског комлекса у сливу, утицај геолошког састава на укупну минерализацију воде, њену структуру и специфичну хемијску ерозију, концентрација суспендованог наноса по профилима, однос суспендованог наноса према протицају, укупан годишњи пронос суспендованог наноса као и специфична ерозија, утицај сезонских фактора на концентрацију силта и износ механичке ерозије, утицај геолошког састава на укупан пронос суспендованог наноса, мерење вученог наноса, однос хемијске и механичке ерозије. Хомоље и Звижд највећим делом припадају брдско – планинском подручју које се одликује водотоковима са релативно великим уздужним падовима, где су углови нагиба од 10 до 40. у Хомољу и Звижду све водотокове карактеришу врло велике разлике између екстремно великих и малих вода, па на неким водотоковима однос максималних и минималних протицаја достиже вредност и хиљаду. Овакав однос између малих и великих вода погодује развоју ерозивних процеса и разарању земљишта. Ерозија у сливу која почиње плувијалном ерозијом, а наставља се денудацијом, доводи до снижавања топографске површине и еродирања  земљишта. Таложењем наноса на дну речног корита оно се издиже, што доводи до смањивања овлаженог профила. Велике поплавне воде због тога не могу да протекну тако оплићалим речним коритом, па због тога долази до њиховог изливања, што се манифестује поплавама. Без земљишта остају горњи делови слива, а поплавама, услед таложења вученог и суспендованог наноса на дну речног корита, бивају изложени доњи делови речних токова. Овакав негативан тренд уочен је и у Хомољу и у Звижду који су последњих година све чешће угрожени поплавним водама које причињавају велике штете како пољопривредном земљишту тако и насељима у сливовима Млаве и Пека. С обзиром на чињеницу да у Хомољу и Звижду постоји велики број бујичних токова који носе огромне количине наноса, реално је очекивање да ће се тај нанос акумулирати у средњем и доњем делу сливова Млаве и Пека. Избор хидротехничког метода за истраживање обима и интензитета ерозије у Хомољу и Звижду, као и коришћење методе професора С. Гавриловића у анализи бујичних токова је покушај прецизнијег утврђивања квантитета овог процеса који последњих година има узлазни тренд. Остварење постављених задатака утврђеном методологијом и постигнуће задатих циљева пружа одговор на питање колики је интензитет и обим процеса ерозије у Хомољу и Звижду на годишњем нивоу, по годишњим добима и месецима. Утврђен је степен деловања физичко – географских фактора који имају утицај на процес ерозије, указано је на обим и врсту примене антиерозивних мера, нарочито у сливовима бујичних токова. Сагледавањем интензитета и обима ерозије у Хомољу и Звижду, односно сливовима Млаве и Пека, успешније ће бити решени водопривредни проблеми који овде постоје. 
Erozija zemljišta je jedan od najkompleksnijih problema i ujedno jedan od najpodmuklijih čovekovih neprijatelja. Erozivni procesi postepeno razaraju i uništavaju zemljište, odnose hranljive supstrate i remete vodni režim. Oni dovode stanovništvo mnogih, često prostranih oblasti u bedu, siromaštvo i migraciju. Zbog toga, mnoge privredne grane moraju biti uvučene u borbu protiv erozije zemljišta i njenih strahovitih posledica. Erozija je veoma složena dinamička pojava, koja zavisi od niza faktora čije je diferenciranje vrlo teško. Ispitivanje i utvrđivanje intenziteta vodne erozije spada u grupu problema koji se ne mogu sveobuhvatno rešiti. Veoma je teško, skoro nemoguće, izdvojiti sve faktore, a potom multiplicirati sve te faktore u svim postojećim kombinacijama. Ovim radom sagledano je stanje erozije zemljišta u slivu Mlave i Peka, odnosno Homolju i Zviždu, sa više aspekata i utvrđen niz pojava kao što su: koncentracija rastvorenih mineralnih materija, procentualno učešće makroelemenata u ukupnoj mineralizaciji, odnos mineralizacije prema proticaju, ukupan godišnji pronos rastvorenih mineralnih materija, odnos specifične električne provodljivosti i ukupne mineralizacije, iznos hemijske evakuacije, iznos hemijski rastvorenih mineralnih materija koje potiču od stenskog komleksa u slivu, uticaj geološkog sastava na ukupnu mineralizaciju vode, njenu strukturu i specifičnu hemijsku eroziju, koncentracija suspendovanog nanosa po profilima, odnos suspendovanog nanosa prema proticaju, ukupan godišnji pronos suspendovanog nanosa kao i specifična erozija, uticaj sezonskih faktora na koncentraciju silta i iznos mehaničke erozije, uticaj geološkog sastava na ukupan pronos suspendovanog nanosa, merenje vučenog nanosa, odnos hemijske i mehaničke erozije. Homolje i Zvižd najvećim delom pripadaju brdsko – planinskom području koje se odlikuje vodotokovima sa relativno velikim uzdužnim padovima, gde su uglovi nagiba od 10 do 40. u Homolju i Zviždu sve vodotokove karakterišu vrlo velike razlike između ekstremno velikih i malih voda, pa na nekim vodotokovima odnos maksimalnih i minimalnih proticaja dostiže vrednost i hiljadu. Ovakav odnos između malih i velikih voda pogoduje razvoju erozivnih procesa i razaranju zemljišta. Erozija u slivu koja počinje pluvijalnom erozijom, a nastavlja se denudacijom, dovodi do snižavanja topografske površine i erodiranja  zemljišta. Taloženjem nanosa na dnu rečnog korita ono se izdiže, što dovodi do smanjivanja ovlaženog profila. Velike poplavne vode zbog toga ne mogu da proteknu tako oplićalim rečnim koritom, pa zbog toga dolazi do njihovog izlivanja, što se manifestuje poplavama. Bez zemljišta ostaju gornji delovi sliva, a poplavama, usled taloženja vučenog i suspendovanog nanosa na dnu rečnog korita, bivaju izloženi donji delovi rečnih tokova. Ovakav negativan trend uočen je i u Homolju i u Zviždu koji su poslednjih godina sve češće ugroženi poplavnim vodama koje pričinjavaju velike štete kako poljoprivrednom zemljištu tako i naseljima u slivovima Mlave i Peka. S obzirom na činjenicu da u Homolju i Zviždu postoji veliki broj bujičnih tokova koji nose ogromne količine nanosa, realno je očekivanje da će se taj nanos akumulirati u srednjem i donjem delu slivova Mlave i Peka. Izbor hidrotehničkog metoda za istraživanje obima i intenziteta erozije u Homolju i Zviždu, kao i korišćenje metode profesora S. Gavrilovića u analizi bujičnih tokova je pokušaj preciznijeg utvrđivanja kvantiteta ovog procesa koji poslednjih godina ima uzlazni trend. Ostvarenje postavljenih zadataka utvrđenom metodologijom i postignuće zadatih ciljeva pruža odgovor na pitanje koliki je intenzitet i obim procesa erozije u Homolju i Zviždu na godišnjem nivou, po godišnjim dobima i mesecima. Utvrđen je stepen delovanja fizičko – geografskih faktora koji imaju uticaj na proces erozije, ukazano je na obim i vrstu primene antierozivnih mera, naročito u slivovima bujičnih tokova. Sagledavanjem intenziteta i obima erozije u Homolju i Zviždu, odnosno slivovima Mlave i Peka, uspešnije će biti rešeni vodoprivredni problemi koji ovde postoje. 
The abstract has been processed with OCR optical text recognition technology.Soil erosion is one of the most complex problems and at the same time one of the most insidious of human enemies. Erosion processes gradually destroy the land, carry away nutritional substrates and disrupt the water regime. They drive many people, often from large areas, to misery and poverty, and cause migration. Therefore, many industries have to be included into the fight against soil erosion and its terrible consequences. Erosion is a very complex and dynamic phenomenon that relies on many factors which are hard to define. Differentiating and determining the intensity of water erosion are among the problems that cannot be comprehensively solved. It is very difficult, almost impossible, to extract all the factors and then multiply all these factors in every possible combination. This paper looks at the situation with soil erosion in the water basins of the rivers Mlava and Pek respectively, that is, in the areas of Homolje and Zvižd, from various aspects, and identifies a series of phenomena such as concentration of dissolved minerals, percentage of macroelements in the total mineralization, the relationship of mineralization to the flow, the total annual transport of dissolved minerals, the ratio of the specific electrical conductivity and total mineralization, the amount of chemical evacuation, the amount of chemically dissolved minerals that come from the rock complex in the basin, the impact of geological composition on the total mineralization of water, its structure and specific chemical erosion, suspended sediment concentration by profiles, the effect of suspended sediment on the flow, the total annual transport of suspended sediment as well as the specific erosion, the impact of seasonal factors on the concentration of silt and the amount of mechanical erosion, the impact of geological composition on the total transport of suspended sediment, bed load measurement, the ratio of chemical and mechanical erosion. Homolje and Zvižd are mostly hilly and mountainous areas characterized by water streams with relatively large vertical drops where the pitch angles may vary from 10° to 40°. In Homolje and Zvižd all the waterways are characterized by very large differences between extremely high and low water, reaching the value of a thousand in some points. This kind of a ratio between high and low waters favors the development of erosion processes and the destruction of land. Erosion in a basin starts with a pluvial erosion and continues with denudation, causing the lowering of the topographic surface and soil erosion. When the sediment deposits at the bottom of the river bed, the bed rises, leading to a reduction of the humidified profile. Therefore great floodwater cannot pass through such a shallow riverbed, which leads to its discharge and causes a flood. The upper parts of the basin lose land, and the lower parts of the basin become exposed to floods due to the deposition of bed load and suspended sediment at the bottom of the riverbed. This negative trend has been observed both in Homolje and Zviždi which in recent years have become increasingly threatened by flood waters which cause great damage to agricultural land and settlements in the basins of the rivers Mlava and Pek. Considering the fact that Homolje and Zvižd there is a large number of torrential streams that carry huge amounts of sediment, it is reasonable to expect the sediment to accumulate in the middle and lower parts of the basins of Mlava and Pek. The selection of the hydrotechnical method to explore the scope and intensity of erosion in Homolje and Zvižd, and the use of Professor S. Gavrilović’s method in the analysis of torrential flows is an attempt to determine more precisely the quantity of this process with an increasing trend in recent years. Fulfillment of tasks and achievement of objectives through suggested methodology and achievement of objectives provides the answer to the question of intensity and extent of erosion in Homolje and Zvižd on an annual basis, according to seasons and months. The paper has determined the degree of impact of physical and geographic factors on the erosion process, and has pointed to the scope and type of application anti-erosion measures, especially in watersheds with torrential flows. If we manage to comprehend the intensity and extent of erosion in Homolje and Zvižd, that is, in the basins of Mlava and Pek, we will be able to solve the existing water management problems more successfully.

碩士
國立中山大學
電機工程研究所
83
Due to higher efficiency and lower memory requirement in solving load flow problems , fast decoupled load flow has been adopted to solve many power system problems that reuqire higher speed in the computation of steady state load flow sloutions. However ,the fast decoupled load flow method is not without deficiencies , for power networks with high R/X ratios , long and/or short transmission lines and larges shunt capacitance due to network reduction , the fast decoupled load flow suffers slower convergence rate and in many cases , it fails to converge. In order to be able to handle these cases , several researchers have proposed many useful methods for improving the convergence characteristics . In this thesis , many of these modified methods are implemented and compared and compared . Suggestions on suitable methods for certain problems are given .

Research Doctorate - Doctor of Philosophy (PhD)
The fundamental role of an electrical power system is to deliver the requested electricity to customers in a secure and economical manner. In general, to realize the proper functionality of a modern power system, efforts should be devoted to operation and planning stages. This research focuses on the operation stage of power systems. Specifically, advanced methods are developed for three essential problems in power system security operation studies: 1) short-term load forecasting (STLF), 2) security-constrained optimal power flow (SCOPF), and 3) dynamic security assessment (DSA). Where the STLF is the basis for system operation, SCOPF aims to economically dispatch the system while satisfying the security constraints, and DSA focuses on the dynamic security issue of the power system. This research is carried out in a logic way to address the three problems. In the area of STLF, a model based on extreme learning machine (ELM) technique is first developed for the Australian National Electricity Market (NEM). The model is an ensemble of a series of strategically arranged individual ELMs. Compared with some existing methods, it is much faster in model training and can provide more accurate load forecasting results. After this, a composite k-nearest neighbor (kNN) model is developed to deal with the situation that limited temperature input is available. The model uses only the minimum and maximum temperature forecasts as the model input and can provide reasonably accurate load forecast results. At last, a hybrid model for time-varying reactive power load forecasting is developed. This model is among the first in filling the gap between the need for accurate reactive load forecast and current industrial practices which are mainly using a fixed power factor to derive the reactive load. The developed hybrid load forecasting model has been practically applied in a real-world distribution network in U.S. In the area of SCOPF, research efforts are firstly devoted to the corrective security-constrained optimal power flow (CSCOPF) problem. In contrast to traditional OPF models, the CSCOPF considers the use of corrective control (CC) actions to regain the system security in the post-contingency state, and is able to provide the same security level with more economical generator dispatching solutions over the conventional OPF models. This research develops a hybrid computational strategy to solve the much more complex CSCOPF problems. Besides of this, this research proposes a preventive-corrective SCOPF (PCSCOPF) model and corresponding solution method. The PCSCOPF aims to optimally coordinate the preventive control (PC) and CC against the probable contingencies during system operations. In the area of DSA, this research applies the intelligent system (IS) strategy which has been identified in recent years as a promising approach for much faster DSA. First, a comprehensive review and systematic classification of existing methods is conducted. Subsequently, for pre-disturbance DSA, a systematic study on feature selection stage is conducted, and two alternative algorithms are introduced to this area. Then, an IS model for on-line voltage stability margin (VSM) prediction is developed. It employs system loading direction as the input and is much faster in model training and more accurate. After this, a novel IS for post-disturbance transient stability assessment (TSA) is proposed. The proposed IS can be fully integrated in the wide-area protection and control (WAPaC) systems. Compared with existing models, it is radically superior as it is self-adaptive in making the right TSA decision at an appropriate earlier time, hence allowing more time to take the remedial control actions against the instability. The developed methods have been numerically validated on a number of benchmark test systems, and shown satisfactory performance. They can be practically applied for enhanced security operation of modern power systems.

碩士
國立臺灣師範大學
科技應用與人力資源發展學系
101
The purpose of this study was to investigate the impact of different media-rich learning methods on flow experience and cognitive load as well as the correlation between flow experience and cognitive load. The research subjects were first-year students of a general curriculum in a university. A total of 103 students participated in this experiment, 50 of them assigned to the experimental group (game-based learning) and while the remaining 53 to the control group (non-game-based learning). The main findings were as follows: 1. Students engaged in game-based learning had significantly better flow experiences than those engaged in non-game-based learning. 2. No significant difference in intrinsic cognitive load was observed between the two groups. 3. Compared to the control group, students engaged in game-based learning had significantly lower extraneous cognitive load and higher germane cognitive load. 4. Flow experience was significantly negatively related to intrinsic cognitive load and extraneous cognitive load but significantly positively related to germane cognitive load.

碩士
國立中央大學
電機工程學系
104
As the penetration of distributed generation goes up rapidly, the traditional power system is faced with challenges. One of the most severe problems for renewable energy is the fluctuation of the output power. If the output power of distributed generators could not be consumed by local loads, inverse load flow may occur. As a result, developing three-phase unbalanced load flow algorithms for distribution system considering distributed generation seem to be particularly important. By means of day-ahead scheduling, operators could take it as a reference to make an optimal decision. This thesis proposes a novel probabilistic load flow method that is based on Taguchi’s orthogonal arrays from Taguchi method. The proposed method only needs to sample probabilistic variables through orthogonal arrays and utilize few deterministic load flows to obtain the mean and standard deviation of bus voltages. An optimal experiment is also achieved through main effects from Taguchi’s method with the largest deviation from the nominal line-flow result. This thesis also presents a more practical model for distributed generators. To proof the well-behavior of this model, some abnormal operation scenarios are demonstrated. When over-voltage or low-voltage situation occurs caused by excess output power from wind turbine and PV, the model will acquire a voltage set point from optimal algorithm in order to absorb or generate reactive power to improve voltage profile considering the deviation of demands and output power from renewable energies. The simulation results were compared with results attained by Monte Carlo simulation (MCS) and point estimate method (PEM). A 25-bus Penghu system, an IEEE 118-bus system and a modified 12-bus feeder in Taiwan are used as test systems. The results show that the proposed method attains both accurate means and standard deviations of bus voltages and line flows and is time-saving.

Power losses in the grid are important, and as the power losses decrease the efficiency increases. Not much research has been done recently on the Newton-Raphson Power Flow (NRPF) method in polar form for systems with High Voltage Direct Current (HVDC) subsystems. The point of departure for this thesis is based on decoupling the NR Power Flow method Power flow problems are solved for many fundamental problems in the operation and planning of the power system. Although many methods are available to solve these problems, this thesis focuses on developing an enhanced HVDC power flow method with improved computational efficiency and convergence stability. A comparison of the results with full Newton-Raphson Power Flow method is presented to evaluate the performance of the proposed method. Simulations were conducted on the 14-bus and 30-bus IEEE systems. Two and three converters are shown to improve the voltage magnitude, active and reactive power profile .The overall results indicate which mode is the best mode compared to others depending on the bus importance.

碩士
國立成功大學
電機工程研究所
82
In this thesis, a so-called ''topology-free method'''' for the power flow analysis in power systems is presented. Without solving the specific networks of the power systems , the fundamental and harmonic power flow solutions can be obtained simultaneously. Using the concept of ''topology- free method'''', two possible applications for the power flow analysis in power systems are demonstrated in both the transmission system and the distribution system. In the first application, the power distribution in various loads and transmission systems will be evaluated from the total system dissipations and the power factors of the various loads. In the second application, the power distribution in distribution systems will be evaluated from the total complex power supplied from the sources and the power factors of the loads partitioned in a ''binary- tree'''' structure. The proposed method offers some new idea for power flow evaluation in power systems. Examples using Taiwan Power( Taipower) system will be used to demonstrate the application of the new approach in power flow analysis.

博士
國立中正大學
電機工程所
96
Load flow analysis is the most fundamental work for power system operation and planning. In transmission systems, the network is always treated as balanced. Then, the load flow problem for transmission system can be dealt by single-phase method. However, the distribution power system is unbalanced inherently because of unsymmetrical network and unbalanced loads. In such situation, the conventional load flow methods for transmission systems are not suitable for distribution systems. In addition, high R/X ratio and radial structure are also to restrict the use of single-phase load flow approaches. Therefore, the three-phase approaches are required for distribution system load flow studies. The thesis proposes an improved forward/backward sweep algorithm for three-phase load flow analysis of radial distribution systems. In the backward sweep, the KCL and KVL are used to calculate each line current and the upstream bus voltage of each line or a transformer branch. Then, linear proportion principle for finding the real and imaginary ratios on each line section and bus index for fast mapping the terminal bus at each branch are exploited in the forward sweep to update the voltage at each junction or each terminal bus. The procedure stops after the mismatch of the calculated and the specified voltages at the substation is less than the predefined convergence tolerance. In the proposed method, the distribution component models including overhead lines, underground cables, different connecting type transformers, spot loads, distributed loads, capacitor banks and cogenerator are in consideration. The proposed solution algorithm has been described in details and tested by IEEE benchmark distribution systems with default system data, different system loadings, different power factors and different R/X ratios at different system loadings. Results show that the algorithm is accurate and computationally efficient in comparing with conventional forward/backward sweep method and ladder iteration method.

The objective of the thesis is to find appropriate methods for creation and classification of an investment project that should be created while using these methods. The variants drawn were: purchase of the investment by a bank loan, fincial leasing with 30% extra refund, distribution of finshed products by hiring transport or hiring the vehicles using operative leasing and discounted cash flow method. Hiring of the transport was found the most reasonable variant for the company. The purchase of own vehicles is disadvantageous.

The modern day power system is witnessing a tremendous change. There has been a rapid rise in the distributed generation, along with this the deregulation has resulted in a more complex system. The power demand is on a rise, the generation and trans-mission infrastructure hasn't yet adapted to this growing demand. The economic and operational constraints have forced the system to be operated close to its design limits, making the system vulnerable to disturbances and possible grid failure. This makes the study of voltage stability of the system important more than ever. Generally, voltage stability studies are carried on a single phase equivalent system assuming that the system is perfectly balanced. However, the three phase power system is not always in balanced state. There are a number of untransposed lines, single phase and double phase lines. This thesis deals with three phase voltage stability analysis, in particular the voltage stability index known as L-Index. The equivalent single phase analysis for voltage stability fails to work in case of any unbalance in the system or in presence of asymmetrical contingency. Moreover, as the system operators are giving importance to synchrophasor measurements, PMUs are being installed throughout the system. Hence, the three phase voltages can be obtained, making three phase analysis easier. To study the effect of unbalanced system on voltage stability a three phase L-Index based on traditional L-Index has been proposed. The proposed index takes into consideration the unbalance resulting due to untransposed transmission lines and unbalanced loads in the system. This index can handle any unbalance in the system and is much more realistic. To obtain bus voltages during unbalanced operation of the system a three phase decoupled Newton Raphson load ow was used. Reactive power distribution in a system can be altered using generators voltage set-ting, transformers OLTC settings and SVC settings. All these settings are usually in balanced mode i.e. all the phases have the same setting. Based on this reactive power optimization using LP technique on an equivalent single phase system is proposed. This method takes into account generator voltage settings, OLTC settings of transformers and SVC settings. The optimal settings so obtained are applied to corresponding three phase system. The effectiveness of the optimal settings during unbalanced scenario is studied. This method ensures better voltage pro les and decrease in power loss. Case studies of the proposed methods are carried on 12 bus and 24 bus EHV systems of southern Indian grid and a modified IEEE 30 bus system. Both balanced and unbalanced systems are studied and the results are compared.