Transmission line reactance is an important parameter in carrying out stability studies. The model proposed here utilizes available real time synchrophasor data and information about the generation in the ERCOT grid to determine the Thevenin equivalent reactance of a line. Synchrophasors provide the advantage of synchronized measurements of phase angles which are essential in determining the transmission line reactance. This thesis provides the results of applying this model to estimate the Thevenin equivalent line reactance between McDonald Observatory in West Texas and The University of Texas at Austin. / text

The Estimation of Thevenin Equivalent Parameters is useful for System Monitoring and Protection. We studied a method for estimating the Thevenin equivalent circuits. We then studied two applications including voltage stability and fault location. A study of the concepts of Voltage Stability is done in the initial part of this thesis. A Six Bus Power System Model was simulated using MATLAB SIMULINK®. Subsequently, the Thevenin Parameters were calculated. The results were then used for two purposes, to calculate the Maximum Power that can be delivered and for Fault Location.

Transmission line is a crucial role in power transmission network which connects generating units to consumers. Some unpredicted failure events such as lightening or system faults can cause transmission line tripped, which may bring about a large interruption to the system and causes damage. When line outage happens, the power flow on the tripped line will be redistributed to the rest of lines in the system. It may cause risk of overload happens on other lines, and results in a cascading failure and system collapse. Reasonably, a single line outage will not affect all other lines in the system. Therefore, when a line outage happens, it is important for the system operator to have a preview of which lines will have serious impact and which lines will not, so that the operator can only focus on monitoring certain lines which will be seriously affected, rather than keeping monitoring the whole system. In this thesis, A Line Outage Distribution Factor (LODF) method is proposed and implemented in the IEEE 118 bus system to estimate active power flow redistribution after a line outage. After that, a definition of Thevenin electrical distance between two transmission lines is derived and applied to calculate electrical distances between the outage line and each line in the system. An exponential convergence tendency is found between maximum possible LODF predicted power flow variations and electrical distance, and an exponential regression method is applied to analyze this tendency. The contribution of this work is a rule has been found that starting from the outage line, the maximum possible active power flow variation on transmission lines exponentially decreases exponentially while the electrical distance increases. With only the information of system's normal operating condition and topological information, the maximum possible active power change on each lines caused by single line outage, and the margin of the impact of single line outage on power flow variations may propagate along electrical distance can be easily and quickly predicted. Ultimately, the goal of this work is to allow operators at the control center can concentrate on lines within a certain electrical distance instead of keeping monitoring the whole system when a line outage happens. / Master of Science

abstract: Two significant trends of recent power system evolution are: (1) increasing installa-tion of dynamic loads and distributed generation resources in distribution systems; (2) large-scale renewable energy integration at the transmission system level. A majority of these devices interface with power systems through power electronic converters. However, existing transient stability (TS) simulators are inadequate to represent the dynamic behavior of these devices accurately. On the other hand, simulating a large system using an electromagnetic transient (EMT) simulator is computationally impractical. EMT-TS hybrid simulation approach is an alternative to address these challenges. Furthermore, to thoroughly analyze the increased interactions among the transmission and distribution systems, an integrated modeling and simulation approach is essential. The thesis is divided into three parts. The first part focuses on an improved hybrid simulation approach and software development. Compared to the previous work, the pro-posed approach has three salient features: three-sequence TS simulation algorithm, three-phase/three-sequence network equivalencing and flexible switching of the serial and par-allel interaction protocols. The second part of the thesis concentrates on the applications of the hybrid simula-tion tool. The developed platform is first applied to conduct a detailed fault-induced de-layed voltage recovery (FIDVR) study on the Western Electricity Coordinating Council (WECC) system. This study uncovers that after a normally cleared single line to ground fault at the transmission system could cause air conditioner motors to stall in the distribu-tion systems, and the motor stalling could further propagate to an unfaulted phase under certain conditions. The developed tool is also applied to simulate power systems inter-faced with HVDC systems, including classical HVDC and the new generation voltage source converter (VSC)-HVDC system. The third part centers on the development of integrated transmission and distribution system simulation and an advanced hybrid simulation algorithm with a capability of switching from hybrid simulation mode to TS simulation. Firstly, a modeling framework suitable for integrated transmission and distribution systems is proposed. Secondly, a power flow algorithm and a diakoptics based dynamic simulation algorithm for the integrated transmission and distribution system are developed. Lastly, the EMT-TS hybrid simulation algorithm is combined with the diakoptics based dynamic simulation algorithm to realize flexible simulation mode switching to increase the simulation efficiency. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2016

<div>The high-frequency switching of transistors in power electronic (PE) converters is known to cause unintended common-mode (CM) current that flows through parasitically-coupled ground paths. One way to model these currents is to utilize time-domain simulations that capture switching dynamics and the corresponding parasitic response. Although potentially useful, the small time steps required can create a computational burden and limit the usefulness of the approach. In addition, access to internal hardware needed to characterize parasitic parameters is often limited.</div><div><br></div><div>In this thesis, frequency-domain Thevenin equivalent circuits (TECs) are derived to model the CM behavior of PE converters. To do so, periodic linear time-varying (PLTV) analysis is used to develop Thevenin-like models that account for switching behavior of PE circuits. Subsequently, it is shown that in many applications these PLTV TECs can be reduced to traditional linear time-invariant (LTI) forms. Methods to experimentally characterize LTI TEC parameters and couple multiple TECs together for system-level analysis are then established. Finally, the TEC approach is extended to model converters in which common- and differential-mode (CM/DM) behavior are strongly coupled. Simulation and experimental results are used to validate the proposed TEC techniques.</div>

[pt] O surgimento do fenômeno de estabilidade de tensão na operação dos sistemas elétricos motivou centenas de pesquisadores a desenvolverem métodos que permitam detectar a proximidade à instabilidade de tensão, com eficiência computacional, e tomar medidas acertadas para garantir a operação confiável e segura. Neste trabalho são analisados diferentes métodos que permitem transformar sistemas de grande porte em circuitos simples: o circuito equivalente entre geradores e cargas, baseado no cálculo de correntes de curto-circuito, na técnica de redução de rede pela eliminação de barras intermediárias e no equivalente de Thévenin. É analisada a utilização destes equivalentes na avaliação das condições de estabilidade de tensão com sistemas-testes de 3 e 4 barras. Através de diferentes testes verificou-se que o circuito equivalente entre geradores e cargas e a técnica de redução de rede não podem ser usados para o cálculo de índices de avaliação das condições de estabilidade de tensão, enquanto que, usando circuito equivalente de Thévenin encontrou-se um método que funciona corretamente para barra de carga terminal, barra não-terminal e barra de tensão controlada por gerador. / [en] The emergence of voltage stability phenomenon in the operation of power systems has motivated hundreds of researchers to develop methods to detect the proximity to voltage instability, with computational efficiency and to take all necessary and appropriate measures to ensure reliable and safe operation. In this work, different methods that allow transforming large systems into simple circuits were analyzed, such as the equivalent circuit between generators and loads, based on the calculation of short-circuit currents; the network reduction technique for eliminating intermediate buses; and the Thévenin equivalent. The application of these equivalents on voltage stability assessment of 3 and 4 bus testing systems were extensively tested. At the end, it was verified that that the equivalent circuit between the generator and load, and the network reduction technique, cannot be used for calculating the voltage stability conditions evaluation indexes. However, using Thévenin equivalent circuit, it was found a proper method, which works correctly for terminal buses, transit buses and voltage-controlled buses.

Hybrid powertrains represent the current trend on passenger cars. The purpose of thisreport is to create a basic model of a hybrid powertrain in Matlab/Simulinkenvironment and study their performance over certification driving cycle. Threecommonly used architectures are modeled and discussed in Simulink. Hence, the basiccomponents of a powertrain – battery, electric machine and combustion engine – arestudied and basic models are realized. A Thevenin equivalent circuit is used to simulatethe behavior of the battery, and the combustion engine is modeled after a Willansmodel. The electric machine model is based on a known efficiency map. Then, thearchitectures are created as well as their control strategies. The control strategies arecreated through state diagrams, and implemented into the Simulink model viaStateflow charts. A validation procedure is presented in order to study the consistencyof the models. / Hybrid drivlinor representerar en central personbilstrend. Syftet med rapporten är attpresentera en grundläggande modell för en hybrid drivlina i Matlab/Simulink. Trearkitekturer behandlas och har implementerats i Simulink. Sedan studeras degrundläggande komponenterna i ett drivaggregat (batteri, elmaskin ochförbränningsmotor). En Thevenin-ekvivalent krets används för att simulera batterietsbeteende. Förbränningsmotorn är modellerad efter en Willans-modell.Elmaskinmodellen är baserad på en känd verkningsgradsmapp. De tillhörandestyrstrategierna med hjälp av tillståndsdiagram. De implementeras i Simulinkmodellenmed hjälp av Stateflow-diagram. Ett valideringsförfarande presenteras ochvisar modellernas konsistens.

[pt] O fenômeno associado à estabilidade de tensão se caracteriza pela existência de valores máximos de potência ativa e reativa que podem ser transferidas a uma barra de carga, ou injetada na rede através dos geradores e compensadores síncronos. Sua relevância para o setor elétrico é constantemente reforçada pelo registro de ocorrências de colapsos de tensão em diversos países do mundo e, embora a instabilidade de tensão manifeste-se localmente, suas consequências se refletem na ampla deterioração do sistema. Impulsionado pelo crescente interesse a respeito dos métodos baseados em medições fasoriais sincronizadas para a detecção do máximo carregamento, este trabalho apresenta os principais modelos encontrados na literatura baseados em medições locais e no vasto monitoramento do sistema, com maior ênfase aos métodos de Corsi-Taranto e Circuito Acoplado de Porta-Simples Aprimorado (CAPS Aprimorado). Algumas contribuições são sugeridas ao modelo CAPS Aprimorado tendo em vista sua aplicação ao conjunto de barras de transferência e de geração. Explora-se a utilização dos equivalentes multi-portas como índice de avaliação das condições de estabilidade de tensão, comparando a identificação da barra crítica aos métodos da matriz D e dos autovalores e autovetores. São evidenciadas as principais limitações dos modelos mediante a um conjunto de análises estáticas e dinâmicas, considerando diferentes cenários de carregamento, a sensibilidade dos modelos ao ruído e a resposta dos métodos em face da atuação dos limitadores de sobre-excitação. / [en] The voltage stability phenomenon is characterized by the existence of a maximum active and reactive power that can be transferred to a load bus or injected into the network through the generators and synchronous compensators. Its relevance to the electric power sector is constantly reinforced by the record of occurrences of voltage collapses in several countries around the world. Although the voltage instability manifests itself locally, its consequences is reflected in the wide deterioration of the system. Driven by growing interest in methods based on synchronized phasor measurements for maximum loadability detection, this work presents the main models found in the literature based on local measurements and wide area monitoring, emphasizing the Corsi-Taranto method and Improved Coupled Single-Port Circuit (Improved CAPS). Some contributions are suggested to the Improved CAPS model considering its application to the set of transit and controlled buses. The use of the multi-port equivalents is explored as the evaluation index of voltage stability conditions, comparing the identification of the critical bus to the D matrix method and eigenvalues and eigenvalues method. The main limitations of the models are demonstrated through a static and dynamic studies, as well different loading scenarios, the sensitivity of the models to the noise and the response of the methods when the over-excitation limiters are considered.