The demand for electrical energy in industrialised countries continues to increase steadily. As a result of this growing demand for electrical energy, there is a need for optimisation of the power system in terms of transmission and control. One option could possibly be an increase in transmission facilities to handle the increase in growth; however factors such as environmental issues as well as the possible cost incurred could hamper this particular approach. An alternative resides in loading the existing transmission network beyond its present operating region but below its thermal limit, which would ensure no degradation of the system. For this approach to be realised, improved control of the flow of power in an interconnected network would be advantageous so as to prevent unwanted loop flows and inadvertent overloading of certain lines. This approach can be made possible by the use of Flexible AC Transmission Systems (FACTS) technology. The concept of FACTS incorporates power-electronic compensation devices that can be typically used in an ac power system to enhance the system's power transfer and controllability. There exists a number of FACTS devices, where each device can be utilised differently to achieve the broad objective. One such device is the Thyristor Controlled Series Capacitor (TCSC). The TCSC is a class of FACTS device that makes it possible to alter the net impedance of a particular transmission line in an effort to force the flow of power along a "contract path". This thesis identifies, in the published literature, a set of strategies for the scheduling of power flow by use of variable compensation; such strategies are then considered in more detail in the analysis of the thesis. Firstly, a detailed dynamic model of a TCSC is developed together with its various controls and associated circuitry within the power systems simulation package PSCAD. In addition to this, a power flow controller scheme is then implemented, which exhibits the functionality of the power flow controller strategies reviewed in the literature. In order to test the validity and operation of the TCSC model as well as the analysis of the power flow controller scheme, a single-machine infinite bus (SMIB) study system model is developed and used as part of the investigation. This thesis, firstly, presents a theoretical analysis of two particular modes of power flow control in an interconnected ac transmission system. Secondly it confirms the results of an analytical study in previously published work with the implementation of the two control modes, and further extends the scope of the previous study by examining the impact of the power flow controller's design on the small-signal and transient stability characteristics of the study system. The key findings of this extended investigation are that the power flow controller's mode of operation has an important influence on both small-signal and transient stability characteristics of a power system: in partiCUlar, it is shown that one mode can be detrimental while the other beneficial to both system damping and first swing stability. Finally, the thesis applies the understanding of the power flow controller's operation obtained from the SMIB study system to the problem of inter-area mode oscillations on a well-known, two-area, multi-:generator study system. Real-time simulator results are presented to exhibit the effect of the power flow controller modes and controller design on the oscillatory characteristics of the two-area study system. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2005

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This thesis describes a novel harmonic domain approach for assessing the steady state performance of Flexible AC Transmission System (FACTS) devices. Existing harmonic analysis techniques are reviewed and used as the basis for a novel iterative harmonic domain model for PWM FACTS devices. The unified Newton formulation adopted uses a combination of positive frequency real valued harmonic and three-phase fundamental frequency power-flow mismatches to characterise a PWM converter system. A dc side mismatch formulation is employed in order to reduce the solution size, something only possible because of the hard switched nature of PWM converters. This computationally efficient formulation permits the study of generalised systems containing multiple FACTS devices. This modular PWM converter block is applied to series, shunt and multi-converter FACTS topologies, with a variety of basic control schemes. Using a three-phase power-flow initialisation and a fixed harmonic Jacobian provides robust convergence to a solution consistent with time domain simulation. By including the power-flow variables in the full harmonic solution the model avoids unnecessary assumptions regarding a fixed (or linearised) operating point, fully modelling system imbalance and the associated non-characteristic harmonics. The capability of the proposed technique is illustrated by considering a range of harmonic interaction mechanisms, both within and between FACTS devices. In particular, the impact of transmission network modelling and operating point variation is investigated with reference to ac and dc side harmonic interaction. The minor role harmonic distortion and over-modulation play in the PWM switching process is finally considered with reference to the associated reduction in system linearity.

The analysis and characterization of the steady-state security of a bulk-power electric system is investigated in a region-wise or set-theoretic framework. The study is divided into three parts: a detailed examination of the theoretical aspects of general security regions; a formulation and analysis of the problem of characterizing a set of secure operating points by a simple, explicit function; and an investigation into the secure loadability of a power system. Based on the results of the theoretical study, general approximate relations expressing dependent load flow variables in terms of the nodal injections are derived. Their degree of accuracy and extent of validity are investigated through analytical and simulation-based analyses. The general problem of characterizing subsets of a security region by simple, explicit functions is formulated as an optimization problem. For the case where the subsets are expressed by ellipsoids, two algorithms are developed and tested. The problem is then extended to include embedding the largest ellipsoid of a £ixed orientation inside a security region. The application of explicit security sets to the problem of predictive security assessment is studied in detail. A number of explicit security subsets overlapping along the predicted daily trajectory is used to define a "security corridor". This predicted corridor has the property that as long as the actual trajectory stays within it, very little computation is needed to assess the system security. The secure loadability of a power system is first studied in the demand space by considering the orthogonal projection of security sets into that space. It is then studied in the voltage space in the context of existence of a secure load flow solution to a given loading condition. Properties of the set of secure voltage solutions are explored by enclosing it with a linear set. Furthermore, it is shown that, under favorable conditions, one can easily characterize a subset of the set / L'analyse et la caracterisation de la securite en regime permanent pour un reseau et transmission ont ete etudiees dans le contexte de la theorie des ensembles. L'etude est divisee en trois parties: un examen detaille: des aspects theoriques des regions de securite generale; la formulation et l'analyse de probleme de la caracterisation d'un ensemble de points de fonctionnement par une fonction simple, sous forme explicite, et l'etude de la capacite de charge d'un reseau. Une analyse theorique a permis de deriver des relations approximative generales, exprimant les variables dependantes de l'ecoulement de puissance en terme des injections de noeud. Le degre de precision de ces approximations ainsi que leurs limites d'application sont determinees a l'aide de simulations et d'analyses theoriques. Le probleme general de la caracterisation des sous-ensembles d'une region de securite par des fonctions simples et sous forme explicite est formule comme probleme d'optimisation. Dans le cas ou les sous-ensembles sont exprimes par des ellipsoides, deux algorithmes sont developpes et verifies. Le probleme est alors elargi de facon a inclure le plus grand ellipsoide d'orientation fixe a l'interieur d'une region de securite. L'application d'ensembles de securite au prob1eme de l'evaluation preventive est etudiee en detail. On utilise un certain nombre d'ensembles de securite se recoupant long de la trajectoire journaliere prevue de facon a definir un corridor de securite. Ce corridor prevu possede la propriete qu'aussi longtemps que la trajectoire y est confinee, un minimum de calculs est requis pour evaluer la securite du systeme. Le chargement securitaire d'un reseau est en premier lieu etudie en considerant la projection orthogonale des ensembles de securite sur cet espace. Il est ensuite etudie dans l'espace des tensions, dans le contexte de l'existence d'une solution pour une charge donnee. Les proprietes de l'ensemble des solutions securitaires sont explorees en l'enchas

Thesis (Ph. D.)--University of Wyoming, 2005. / Title from PDF title page (viewed on Oct. 16, 2007). Includes bibliographical references (p. 117-120).

Thesis (Ph. D.)--University of Adelaide, 1992. / Includes bibliographical references (leaves 329-349).

Thesis (Ph. D.)--Missouri University of Science and Technology, 2008. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed August 21, 2008) Includes bibliographical references.

Thesis (Ph. D.)--Missouri University of Science and Technology, 2009. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed February 18, 2009) Includes bibliographical references.