This thesis investigates the design of damping controllers to alleviate the problem of low frequency electro-mechanical oscillations in power systems. The operating point and network parameters of power systems are continually changing, resulting in changes in system dynamics. The conventional controller design methodology has therefore come under increasing scrutiny for its lack of considerations for robustness. The thesis first outlines the conventional design of a power system stabilizer (PSS) and then applies two robust techniques (Hoo and Quantitative Feedback Theory, QFT) to the design problem. The single machine infinite bus (SMIB) model is used to illustrate the procedure for all three design techniques. The final design is undertaken to illustrate the more important problem of robust multi-machine PSS design using QFT. The design requires linearised models of the multi-machine system. A brief discussion is given on how these can be obtained. An introduction to decentralized control design in QFT is included to support the multi-machine design. Chapter three proceeds through the design steps required to generate a conventional PSS. The technique is shown to be simple for a given set of operating conditions. The controller is shown to be adequately robust over the given set of operating conditions albeit not by design. Chapter four introduces a design technique that directly addresses robustness issues during the controller design. For a restricted range of operating conditions the designed controller demonstrates the desired robustness and performance characteristics. The inherent difficulties with Hoo in PSS design become more apparent as the operating range is extended. Chapter five introduces the second robust controller design technique. QFT is shown to be more adept at dealing with increased operating ranges and changing specifications in the single-machine infinite-bus case. The controller is easy to generate and performs well over the entire range of operating conditions. QFT is also applied to the controller design for a four-machine study system. The design is a marginally more complex than in the single machine case but is still easily accomplished. This thesis confirms previous attempts at solving the design problem using the methods outlined above. The performance of all controllers is assessed for small and large disturbances using non-linear time domain simulations with models developed using PSCAD/EMTDC and MATLAB. / Thesis (M.Sc.)-University of Natal,Durban, 2002.

Poorly damped oscillations that occur between the generators in large interconnected power systems often limit the amount of power that can be transmitted through a transmission corridor and are a threat to secure system operation. Coordinated insertion and removal of capacitors in series with a transmission line is one of the approaches that has been known for many years to be capable of enhancing the damping of power system oscillations. Unfortunately however, this approach historically relied on the operation of mechanical circuit breakers which were too slow and unreliable for the high-speed and repetitive operation that such an application demands. Recently-emerged, high-speed power-electronic-based switching devices are finding increasing use in modem power systems in the so-called Flexible AC Transmission Systems (F ACTS) concept. One particular FACTS impedance controller, namely the inverter-based series compensator, can rapidly alter the magnitude of capacitive compensating reactance in series with the line to make it practically feasible to enhance the damping of power system oscillations via dynamically-controlled series compensation. This thesis identifies, in the literature, an insightful approach to the design of an idealised controllable series compensator (CSC) damping scheme; such an approach has been considered in the analyses of the thesis. Three mathematical models of a single-machine infinite bus (SMIB) system are developed and are subsequently used in the initial design and analysis of a CSC damping controller carried out in the thesis. The simple SMIB system case study is used to identify and investigate the factors that have a significant impact on the performance of a CSC damping controller before studying the more complex issue of inter-area mode damping using a CSC. This thesis successfully confirms the results of a previous analytical study in which an idealised representation of the CSC was used, and extends the scope of that previous study by also considering a detailed representation of one particular type of CSC: the inverter-based series compensator. The two key findings of this extended investigation are that the inverter-based form of controllable series compensator can successfully be used to damp power oscillations and that, where the damping of oscillations is the particular focus of study, an idealised representation of the inverterbased CSC is suitable for the analyses. In the case of the inter-area mode damping problem, the selection of an appropriate input signal to the CSC damping controller is a key issue, since the oscillations that are to be damped involve a number of participating generators. This thesis examines the suitability of a few candidate input signals that have been proposed in the literature using the conceptually simpler SMIB system analytical models that have been developed. Finally, the thesis applies the understanding of CSC damping controller design gained from the SMIB study to the problem of inter-area mode damping on a four-generator study system. Time-domain simulation results are presented to demonstrate the impact of the controlled inverter-based series compensator on the damping of the inter-area mode of this system. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2000.

Voltage unbalance performance of a power line depends on a few parameters that are not necessarily constant at any given instance. The random nature of a power system raises questions around the ability of a system planner to allocate equitable share of the power quality parameters, like voltage unbalance, at design stage. Even a more interesting question is whether applying current methods will guarantee that emissions will be under the set limits. The presence of single or dual phase feeders on such a line will result in a more dynamic voltage unbalance. The first part of this research is a study on deterministic method of voltage unbalance allocation presented by the IEC. The IEC 61000-13-3 report is a comprehensive guideline and the best place to start when looking to develop an emissions standard for voltage unbalance. This dissertation presents a method that can be used to set planning levels for unbalance emission at various voltage levels in order to avoid high voltage unbalance at the end user. The method depends on the agreed power of the customer, the power of the unbalanced load, and the system characteristics. The method works well for short feeders with roughly the same negative sequence impedance and equal short circuit levels. In South Africa, however, there are radial feeders that span over 100km. Hence on such a feeder, there can be ratios of 1:10 between sending end and the last customer on the line. Preliminary research revealed that IEC 61000-6-3, a report on allocation of harmonics, has a method applicable to long feeders. This method was investigated extensively and applied to voltage unbalance allocation. At the core of the method is the assumption that feeders have an even distribution of load. To illustrate the application of this method an example is given. The second part of the study explores a stochastic method of voltage unbalance allocation. In this study the possibility of random connection is considered. A Monte Carlo study is presented. The impact of various parameters are analysed and the findings reveal that phase allocation has the most influence on emission. The results show that the method of random connection of loads can be applied in special conditions only i.e. were sizes of loads do not differ greatly and the number of required connections are low. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2011.

No description available.

A low-cost power router (PR), capable of dynamic, independent control of active- and reactive-power flows on meshed grids is presented. The operating principle, detailed schematics, and various possible implementations of the proposed power router are discussed. Various operating modes are identified and a control algorithm has been proposed and verified through simulations. Small-signal and frequency-domain models of the power router from basic time-domain equations are developed. A three-tier protection system based on the fail-normal switch to avoid single point-of-failure is presented. The operation of proposed protection system in isolating the converter and the grid in the event of faults is verified through simulation. An analytical method to evaluate the stability of a system with multiple power routers is proposed. Necessary conditions for the PR-controller design to ensure stable operation of a system with multiple power routers is proposed. These necessary conditions are verified through simulation studies. Potential applications of proposed power router in distribution system and the associated challenges in implementation are presented. The functionality and advantages of the proposed power router are experimentally demonstrated at 13 kV, 1 MVA. The proposed power router can result in a low cost power routing solution that can reduce electric grid congestion and efficient implementation of RPS mandates.

Embedded generation (EG) provides many benefits in terms of reduction of system technical losses and increased load carrying capacity. In this study the sustainable EG carrying capacity permutations in a medium voltage distribution system, will be determined. Using these results, the financial investment recovery potential of EG will be studied and the impact on the cost recovery by the Utility as a result of compensating the EG at the current system marginal price, will be analysed. The study was done to show what capitalisation can be done on a medium voltage distribution system, by the owners of EG plant receiving revenue from the Utility, at the system margin price with the anticipated inflationary increases. The study will also cover the effect on the revenue stream of the Utility as a result of voltage changes caused by the EGs to the loads being supplied. The electrical system used in the study consisted of a radial system with distributed load and generation. The distributed loads were modelled using the average load capacity supplied by the Utility in medium voltage system. The average volume of sales lost as a result of non-technical losses was included in the load model so that the overall accuracy of the revenue effect by EG on the Utility, could be increased. The amount of capitalisation that is achievable by the owners of the EG was tested against various practical permutation scenarios, including variation of location, system impedance (different X/R ratios), time of operation and changing load volume and type. The extent of successful penetration of EG into the distribution system was found to be between 20% and 60% of the load carrying capacity of the system. The simulated results revealed “bathtub curve” behaviour for the cost of energy losses and this reconciled with the theoretical analysis of other studies done in this area. Lower volume penetration of EG results in higher investment potential of up to ten million rand per MW with a 5% MARR per year. This is very low when compared to the levelised cost of the expensive renewable energy technologies that are currently available in the market. With higher penetration of EG on low impedance systems, the gross contribution of the Utility is negatively affected which would introduce instability in the SMP yearly increases. / M. Sc. Eng. University of KwaZulu-Natal, Durban 2013.

Due to its unique features such as controllable power factor, controllable bi-directional power flow, and rapid dynamic response, Voltage Source Converters (VSCs) have been widely used in various industrial applications such as distributed generation systems, power distribution systems, uninterruptible power supplies (UPS), AC motor drives, etc. To optimize the performance of the VSC, many control algorithms have been proposed. This thesis investigates development of the nonlinear control for the VSC in two applications: power factor control and active power filtering. A detailed description of the dynamic model of the VSC system is presented in different reference frames. A linearization-based control scheme is introduced for power factor regulation and verified by switched simulation and real-time experiment on a test stand which has been constructed at the Applied Nonlinear Control Lab (ANCL), University of Alberta. In addition, an internal model-based control scheme is introduced to perform active power filtering. This algorithm is verified by simulation. / Controls

Bibliography: leaves 238-248 / xxix, 248 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This thesis is concerned with the design and coordination of linear, fixed parameter controllers for the purpose of enhancing the dynamic performance of a multimachine power system. The studies are based on linear control theory and involve state space analysis, modal analysis, eigenanalysis and conventional frequency response techniques. The emphasis is on the small-signal performance of the system / Thesis (Ph.D.)--University of Adelaide, Dept. of Electrical and Electronic Engineering, 1997?

Η παρούσα διπλωματική εργασία παρουσιάζει τα Ευφυή Συστήματα ελέγχου και τις εφαρμογές τους στον έλεγχο συστημάτων ηλεκτρικής ενέργειας. Τα διάφορα είδη Σταθεροποιητών Συστημάτων Ισχύος (ΣΣΙ) παρουσιάζονται επίσης. Τα ηλεκτρικά συστήματα είναι δυναμικά συστήματα και υποβάλλονται συνεχώς σε διαταραχές. Είναι σημαντικό οι διαταραχές αυτές να μην οδηγούν το σύστημα σε αστάθεια. Για αυτόν το λόγο, πρόσθετα σήματα που προέρχονται από την απόκλιση ταχύτητας, την απόκλιση διέγερσης και την ροπή επιτάχυνσης εισάγονται στους ρυθμιστές τάσης. Η συσκευή που παρέχει αυτά τα σήματα αναφέρεται ως Σταθεροποιητής Συστημάτων Ισχύος. Η χρήση των Σταθεροποιητών Συστημάτων Ισχύος είναι πολύ συχνή στη λειτουργία των μεγάλων συστημάτων ηλεκτρικής ενέργειας. Οι συμβατικοί Σταθεροποιητές Συστημάτων Ισχύος που χρησιμοποιούν την αντιστάθμιση προήγησης-καθυστέρησης φάσης, όπου οι ρυθμίσεις κέρδους σχεδιάζονται για τις συγκεκριμένες συνθήκες λειτουργίας, δίνουν φτωχές επίδοσεις υπό τις διαφορετικές συνθήκες φόρτισης. Επομένως, είναι πολύ δύσκολο να σχεδιαστεί ένας σταθεροποιητής που θα μπορούσε να επιτύχει καλές επιδόσεις σε διάφορες συνθήκες λειτουργίας των συστημάτων ηλεκτρικής ενέργειας. Σε μία προσπάθεια να καλυφθεί ένα ευρύ φάσμα των συνθηκών λειτουργίας,τα Ευφυή Συστήματα ελέγχου έχουν προταθεί ως πιθανή λύση για να υπερνικηθεί αυτό το πρόβλημα. Σε αυτήν την εργασία, μια συστηματική προσέγγιση στο σχέδιο ελέγχου Ασαφούς λογικής προτείνεται. Παρουσιάζεται η μελέτη του Σταθεροποιητή Συστημάτων Ισχύος Ασαφούς λογικής για την αύξηση της ευστάθειας ενός συστήματος μιας μηχανής συνδεδεμένης σε άπειρο ζυγό. Προκειμένου να ολοκληρωθεί η αύξηση της ευστάθειας, η απόκλιση ταχύτητας και η επιτάχυνση του ρότορα της σύγχρονης γεννήτριας λαμβάνονται ως είσοδοι στον ελεγκτή ασαφούς λογικής. Αυτές οι μεταβλητές έχουν σημαντική επίδραση στην απόσβεση των μηχανικών ταλαντώσεων των αξόνων των γεννητριών. Τα σήματα ευστάθειας υπολογίστηκαν χρησιμοποιώντας την ασαφή συνάρτηση συμμετοχής ανάλογα με αυτές τις μεταβλητές. Το Simulink/Μatlab χρησιμοποιήθηκε στην εφαρμογή της μελέτης. Η απόδοση του συστήματος με το Σταθεροποιητή Συστημάτων Ισχύος Ασαφούς λογικής συγκρίνεται με το σύστημα με το συμβατικό Σταθεροποιητή Συστημάτων Ισχύος καθώς και με το σύστημα χωρίς Σταθεροποιητή Συστημάτων Ισχύος. / In this thesis the different types of intelligent control systems and the various techniques used in power system stabilizers are considered. The power system is a dynamic system and it is constantly being subjected to disturbances. It is important that these disturbances do not drive the system to unstable conditions. For this purpose, additional signals derived from speed deviation, excitation deviation and accelerating power are injected into voltage regulators. The device to provide these signals is referred as power system stabilizer. The use of power system stabilizers has become very common in operation of large electric power systems. The conventional PSS which uses lead-lag compensation, where gain settings designed for specific operating conditions, is giving poor performance under different loading conditions. Therefore, it is very difficult to design a stabilizer that could present good performance in all operating points of electric power systems. In an attempt to cover a wide range of operating conditions, intelligent control systems have been suggested as a possible solution to overcome this problem. Inittialy in this thesis, an introduction of power system control and the different types of stabilizers is briefly described. Afterwards, the system modeling and power system stabilizer model is presented. Finally, a systematic approach to fuzzy logic control design is proposed. The study of fuzzy logic power system stabilizer for stability enhancement of a single machine infinite bus system is presented. In order to accomplish the stability enhancement, speed deviation and acceleration of the rotor synchronous generator are taken as the inputs to the fuzzy logic controller. These variables take significant effects on damping the generator shaft mechanical oscillations. The stabilizing signals were computed using the fuzzy membership function depending on these variables. Simulink Block Design and Matlab is utilized in implementing the study. The performance of the system with fuzzy logic based power system stabilizer is compared with the system having conventional power system stabilizer and system without power system stabilizer.

As novas tecnologias FACTS aplicadas ao sistema de transmissão, com base em eletrônica de potência, podem também ser úteis à distribuição. Para tal é preciso conduzir um procedimento de consolidação da utilização e do desempenho destas, para sua aplicação sem riscos. Neste trabalho, dois aspectos serão contemplados. O primeiro se refere à aplicação do dispositivo FACTS atuando como um capacitor série. Em se tendo controle de módulo e da fase da tensão inserida em série com a linha pode-se fazê-la comportar-se como uma queda em uma reatância série capacitiva ou indutiva. O controle dessa reatância série (aumentando/diminuindo) permitirá a aplicação do conceito de compensação série em qualquer ponto do sistema de distribuição, provendo benefícios de um controle contínuo da tensão e também do controle do fluxo de carga no sistema independente da corrente. O segundo aspecto refere-se ao uso dos dispositivos na conexão de alimentadores controlando a potência ativa entre eles. Para esta operação outro dispositivo UPFC, com conceito similar ao descrito acima, entretanto atuando na fase da tensão entre 2 barras, comporta-se como um transformador defasador com variação contínua de ?taps?, podendo controlar a potência ativa entre os alimentadores. A aplicação destas tecnologias propiciarão vários benefícios para a expansão da distribuição tais como, flexibilização do uso da rede, interligação de alimentadores permitindo manobras de blocos de energia sem ?pisca?, ajuste contínuo do suporte de reativos durante a operação, controle dinâmico do fluxo de potência. O objetivo deste trabalho é estudar a aplicabilidade da tecnologia FACTS e estender este conceito para aplicação em sistemas de distribuição e conduzir simulações digitais em redes de distribuição (15kV) identificando o desempenho e os benefícios atingidos. O programa de simulação utilizado é o ATP (Alternative Transients Program). / The new FACTS technologies applied to the transmission system, based on power electronics, can also be useful to the distribution. For that, it is necessary to drive a procedure to consolidate the use and the performance for their application without risks. In this work two aspects will be approached. The first refers to the application of a FACTS device acting as series compensator. This device will be able to control the voltage in module and phase in order to act as a voltage drop in a serie reactance with capacitive or inductive features. The control of this series reactance (increasing/ decreasing) will allow the application of series compensation concept to any point of the distribution system, providing the benefits of continuous control of the voltage added to the load flow control in the system independent of the current. The second aspect refers to its use in the connection of two feeders controlling the active power between them. For this operation other device, UPFC, with similar concept as described previously, acts mainly in the phase of the injected voltage in the line, performing as a phase-shift with continuous taps variation and is able to control the active power flow between feeders. The application of this technology will provide several benefits for the distribution expansion, such as, a greater flexibility in the use of the network, connection of feeders without load flow interruption, continuous adjust of reactive power during the operation and dynamic control of power flow. The purpose of this work is to study the applicability of the FACTS technology, to extend this concept for the application in the distribution system by using digital simulations in distribution network up to 15kV identifying the performance and the reached benefits.