Dissertations / Theses on the topic 'Unified Power Flow Controller (UPFC)'

Thesis (M.S.)--West Virginia University, 2000.
Title from document title page. Document formatted into pages; contains viii, 78 p. : ill. Includes abstract. Includes bibliographical references (p. 61-63).

The Unified Power Flow Controller (UPFC) is the versatile FACTS controller that can control up to three transmission system parameters individually or simultaneously in appropriate combinations. The work presented in this thesis is concentrated on the modelling and control of the UPFC. The overall aim is to provide effective tools for optimising the impact of the UPFC in the reinforcement of a transmission system. Existing modelling techniques for the UPFC together with the associated control strategies have been systematically reviewed. An exact power injection model is proposed which is based on the polar representation of the UPFC parameters and includes the reactive power capability of the shunt inverter. In addition, a steady-state model based on an ideal controlled voltage source has been developed using MATLAB/SIMULINK which provides a useful tool to analyse and develop the UPFC control system. The UPFC internal limits have been identified and accordingly, the feasible operating area of a transmission system incorporating a UPFC has been determined based on the UPFC maximum limits. The influence of both the series and shunt inverters on this controlled area has been analysed. The impact of a change in the system short circuit level on the UPFC operation and the size of the feasible area has also been investigated. Three modern controllers have been designed and tested for controlling the UPFC in a power flow mode for the series part and a voltage control mode for the shunt part. These controllers are: a fuzzy knowledge based controller, an artificial neural network based controller and a neuro-fuzzy based controller. For the former, the fuzzy rules are deduced from the relationship between the controlled power system parameters and the UPFC control variables. The second is a simple RBFNN controller which is constructed from a single neuron and trained on-line by a gradient descent algorithm. The third controller is designed using the adaptive capabilities of neural networks to estimate and tune the fuzzy rules. Computer simulation and experimental implementation of a UPFC using DS 1103 data acquisition board have been used to verify the proposed control strategies. In the experimental lab model, two 6-pulse inverters implementing the SPWM technique have been used to realise the UPFC system.

Neste trabalho são exploradas as potencialidades e efeitos de possíveis aplicações do UPFC (Unified Power Flow Controller) em redes elétricas. Este recente equipamento da família FACTS, apesar de mais complexo, apresenta rapidez e versatilidade de respostas que podem justificar sua aplicação em redes elétricas. São apresentados modelos matemáticos deste dispositivo, para regime permanente e transitório, utilizando transformações para coordenadas ortogonais. Com base nas respostas obtidas, durante as simulações das aplicações estudadas, pode-se constatar que a tensão série e seu posicionamento angular, introduzidos pelo UPFC, desempenham um importante papel no controle rápido e eficiente do fluxo de potência. Como contribuição deste trabalho, explorou-se a conexão do conversor shunt ao enrolamento terciário de autotransformadores, demonstrando a viabilidade do controle do fluxo de potência nestes equipamentos de transformação. O esquema proposto, instalado em transformadores em paralelo, eleva a disponibilidade de operação do UPFC, aumentando a flexibilidade operativa do sistema em implementações práticas. Através da formulação apresentada, o transformador de acoplamento shunt, convencionalmente utilizado pelo UPFC, apresenta dimensões reduzidas. Foi também examinada a possibilidade de limitação de correntes de curto-circuito, equilibrados ou não, com a ação dos controles do UPFC, particularmente, aprofundando a análise do seu desempenho mais eficiente diante de curtos monofásicos. Os resultados satisfatórios obtidos permitem considerar a viabilidade de limitação destas correntes como um subproduto interessante da atuação deste dispositivo FACTS.
In this thesis, the UPFC (Unified Power Flow Controller) various capabilities and effects for possible network applications, are studied. Although its structure is relatively more complex, when compared to the other FACTS controllers, its fast response and versatility can justify its application within the network. By utilising the orthogonal co-ordinates transform both the steady-state and transient mathematical models of the UPFC, are presented herein. Based on the results obtained and regarding the applications studied, it can be stated that the UPFC series voltage along with its phase angle play an important role for the fast and efficient control of the power flow. As a contribution of the present work, it has been proposed the connection of the shunt converter to the tertiary winding of autotransformers, demonstrating in this way the feasibility for controlling the power flow over such transforming assets. The proposed scheme, which regards two paralleled transformers, offers the UPFC a high operation availability increasing the system operative flexibility in actual implementations. By means of the proposed approach, the shunt coupling transformer, usually utilised in a classical UPFC configuration, presents a reduced size. Also, by utilising the UPFC control actions, it has been examined the possibility of short-circuit limitation over balanced and unbalanced circuits. Particularly, it has been analysed the UPFC most efficient performance towards line-to-ground faults. The satisfactory results obtained lead to consider the UPFC feasibility in limiting such currents; this, as an interesting by-product of this FACTS device action.

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Neste trabalho são apresentados quatro métodos de otimização bio-inspirados, Colônia de Abelhas Artificiais, Otimização por Enxame de Partículas, Algoritmo dos Vagalumes e um híbrido aqui denominado por Bee – PSO, que combina particularidades dos outros três. Estes métodos são utilizados no ajuste coordenado dos parâmetros dos controladores Proporcional-Integral e Suplementares de Amortecimento (Estabilizadores de Sistemas de Potência e o conjunto Unified Power Flow Controller – Power Oscillation Damping). O objetivo é inserir amortecimento adicional aos modos oscilatórios de baixa frequência e, consequentemente, garantir a estabilidade do sistema elétrico frente a pequenas perturbações. São considerados três cenários que englobam duas configurações de instalação dos controladores suplementares e duas condições de carregamento, uma fixa e outra variável. Uma formulação por injeções de corrente do dispositivo Unified Power Flow Controller é sugerida e incorporada ao Modelo de Sensibilidade de Corrente, utilizado para representar o sistema elétrico de potência. Análises estática e dinâmica foram realizadas nos sistemas teste Simétrico de Duas Áreas e New England para validar o modelo de injeções de corrente proposto para o Unified Power Flow Controller e determinar qual dos algoritmos apresentados é o mais eficiente no ajuste coordenado dos parâmetros dos controladores. Dos resultados obtidos foi possível concluir que a versão híbrida proposta neste trabalho possui desempenho superior na maioria dos cenários analisados, fornecendo soluções com amortecimento suficiente, mesmo quando pequenas variações no carregamento do sistema são consideradas.
In this work four bio-inspired optimization methods, Artificial Bee Colony, Particle Swarm Optimization, Firefly Algorithm, and a hybrid called Bee – PSO, which combines the characteristics of the other three are presented. These methods are used in the coordinated adjustment of the parameters of Proportional-Integral and Supplementary Damping Controllers (Power System Stabilizers and the Unified Power Flow Controller - Power Oscillation Damping). The goal is to insert additional damping into the low-frequency oscillatory modes and thus ensure the stability of the electrical system against minor disturbances. Three scenarios are considered that include two installation configurations of the supplementary controllers and two charging conditions, one fixed and one variable. A current injection formulation of the Unified Power Flow Controller is suggested and incorporated into the Current Sensitivity Model used to represent the electric power system. Static and dynamic analyzes were performed in the Two-Zone Symmetric and New England test systems to validate the proposed current injection model for the Unified Power Flow Controller and to determine which of the presented algorithms is the most efficient in the coordinated adjustment of the parameters of the controllers. From the results obtained it was possible to conclude that the hybrid version proposed in this work has superior performance in most scenarios analyzed, providing solutions with sufficient damping, even when small variations in system loading are considered.

Orientador: Percival Bueno de Araujo
Resumo: Neste trabalho são apresentados quatro métodos de otimização bio-inspirados, Colônia de Abelhas Artificiais, Otimização por Enxame de Partículas, Algoritmo dos Vagalumes e um híbrido aqui denominado por Bee – PSO, que combina particularidades dos outros três. Estes métodos são utilizados no ajuste coordenado dos parâmetros dos controladores Proporcional-Integral e Suplementares de Amortecimento (Estabilizadores de Sistemas de Potência e o conjunto Unified Power Flow Controller – Power Oscillation Damping). O objetivo é inserir amortecimento adicional aos modos oscilatórios de baixa frequência e, consequentemente, garantir a estabilidade do sistema elétrico frente a pequenas perturbações. São considerados três cenários que englobam duas configurações de instalação dos controladores suplementares e duas condições de carregamento, uma fixa e outra variável. Uma formulação por injeções de corrente do dispositivo Unified Power Flow Controller é sugerida e incorporada ao Modelo de Sensibilidade de Corrente, utilizado para representar o sistema elétrico de potência. Análises estática e dinâmica foram realizadas nos sistemas teste Simétrico de Duas Áreas e New England para validar o modelo de injeções de corrente proposto para o Unified Power Flow Controller e determinar qual dos algoritmos apresentados é o mais eficiente no ajuste coordenado dos parâmetros dos controladores. Dos resultados obtidos foi possível concluir que a versão híbrida proposta neste trabalho possui desempenho s... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: In this work four bio-inspired optimization methods, Artificial Bee Colony, Particle Swarm Optimization, Firefly Algorithm, and a hybrid called Bee – PSO, which combines the characteristics of the other three are presented. These methods are used in the coordinated adjustment of the parameters of Proportional-Integral and Supplementary Damping Controllers (Power System Stabilizers and the Unified Power Flow Controller - Power Oscillation Damping). The goal is to insert additional damping into the low-frequency oscillatory modes and thus ensure the stability of the electrical system against minor disturbances. Three scenarios are considered that include two installation configurations of the supplementary controllers and two charging conditions, one fixed and one variable. A current injection formulation of the Unified Power Flow Controller is suggested and incorporated into the Current Sensitivity Model used to represent the electric power system. Static and dynamic analyzes were performed in the Two-Zone Symmetric and New England test systems to validate the proposed current injection model for the Unified Power Flow Controller and to determine which of the presented algorithms is the most efficient in the coordinated adjustment of the parameters of the controllers. From the results obtained it was possible to conclude that the hybrid version proposed in this work has superior performance in most scenarios analyzed, providing solutions with sufficient damping, even when smal... (Complete abstract click electronic access below)
Doutor

In order to identify the weakest bus in a power system so that the Unified Power Flow Controller could be connected, an investigation of static and dynamic voltage stability is presented. Two stability indices, static and dynamic, have been proposed in the thesis. Multi-Input Multi-Output (MIMO) analysis has been used for the dynamic stability analysis. Results based on the Western System Coordinate Council (WSCC) 3-machine, 9-bus test system and IEEE 14 bus Reliability Test System (RTS) shows that these indices detect with the degree of accuracy the weakest bus, the weakest line and the voltage stability margin in the test system before suffering from voltage collapse. Recently, Flexible Alternating Current Transmission systems (FACTs) have become significant due to the need to strengthen existing power systems. The UPFC has been identified in literature as the most comprehensive and complex FACTs equipment that has emerged for the control and optimization of power flow in AC transmission systems. Significant research has been done on the UPFC. However, the extent of UPFC capability, connected to the weakest bus in maintaining the power flows under fault conditions, not only in the line where it is installed, but also in adjacent parallel lines, remains to be studied. In the literature, it has normally been assumed the UPFC is disconnected during a fault period. In this investigation it has been shown that fault conditions can affect the UPFC significantly, even if it occurred on far buses of the power system. This forms the main contribution presented in this thesis. The impact of UPFC in minimizing the disturbances in voltages, currents and power flows under fault conditions are investigated. The WSCC 3-machine, 9-bus test system is used to investigate the effect of an unsymmetrical fault type and position on the operation of UPFC controller in accordance to the G59 protection, stability and regulation. Results show that it is necessary to disconnect the UPFC controller from the power system during unsymmetrical fault conditions.
Libyan Government

In order to identify the weakest bus in a power system so that the Unified Power Flow Controller could be connected, an investigation of static and dynamic voltage stability is presented. Two stability indices, static and dynamic, have been proposed in the thesis. Multi-Input Multi-Output (MIMO) analysis has been used for the dynamic stability analysis. Results based on the Western System Coordinate Council (WSCC) 3-machine, 9-bus test system and IEEE 14 bus Reliability Test System (RTS) shows that these indices detect with the degree of accuracy the weakest bus, the weakest line and the voltage stability margin in the test system before suffering from voltage collapse. Recently, Flexible Alternating Current Transmission systems (FACTs) have become significant due to the need to strengthen existing power systems. The UPFC has been identified in literature as the most comprehensive and complex FACTs equipment that has emerged for the control and optimization of power flow in AC transmission systems. Significant research has been done on the UPFC. However, the extent of UPFC capability, connected to the weakest bus in maintaining the power flows under fault conditions, not only in the line where it is installed, but also in adjacent parallel lines, remains to be studied. In the literature, it has normally been assumed the UPFC is disconnected during a fault period. In this investigation it has been shown that fault conditions can affect the UPFC significantly, even if it occurred on far buses of the power system. This forms the main contribution presented in this thesis. The impact of UPFC in minimizing the disturbances in voltages, currents and power flows under fault conditions are investigated. The WSCC 3-machine, 9-bus test system is used to investigate the effect of an unsymmetrical fault type and position on the operation of UPFC controller in accordance to the G59 protection, stability and regulation. Results show that it is necessary to disconnect the UPFC controller from the power system during unsymmetrical fault conditions.

The Unified Power Flow Controller (UPFC) is an advanced Flexible AC Transmission System (FACTS) device that can be controlled to condition alternating voltage and alternating current simultaneously. In this project the use of a reverse connected UPFC topology has been investigated for the improvement of poor power quality at distribution voltage and power levels, namely voltage distortion due to voltage sags and current distortion due to non-linear loads. A three-phase, reverse connected UPFC model, based on two back-to-back connected two-level Voltage Sourced Converters (VSCs) has been modelled in software and tested. To validate the voltage conditioning part of the UPFC, and therefore one half of the software model, a hardware model using one three-phase two-level VSC was constructed and used to condition the load voltage. with a supply voltage distortion due to voltage sags. . With both the software and hardware models voltage sag magnitudes between 0% and 100% are considered. along with phase angle jumps between 00 and 400^ to determine the level of compensation power required from the DC voltage source energy storage. The emphasis on the control was to operate the system as fast as possible and therefore provide a degree of compensation to the fastest of unpredictable power quality disturbances. A preferred control technique was identified for each element of the RC-UPFC.

A single-phase, buck-boost based, dual-output AC-DC converter is studied in this thesis. The converter has two DC outputs with opposite polarities, which share the same ground with the input power line. The power stage performance, including the input filter, is studied and procedure to select power components is given. The circuit model is analyzed to develop appropriate control. Zerocrossing distortion of the source input current is addressed and a solution is proposed. Experimental results are satisfactory in that a high power factor line current results for steady-state operation.

This research introduces the unified power flow controller (UPFC) as a means to improve the overall performance of wind energy conversion system (WECS) through the development of an appropriate control algorithm. Also, application of the proposed UPFC control algorithm has been extended in this research to overcome some problems associated with the internal faults associated with WECS- voltage source converter (VSC), such as miss-fire, fire-through and dc-link faults.

Orientador: Percival Bueno de Araujo
Resumo: Este trabalho apresenta o Novel Bat Algorithm com uma nova técnica para realizar o ajuste coordenado dos parâmetros de controladores suplementares de amortecimento (Estabilizadores de Sistemas de Potência e do conjunto Generalized Unified Power Flow Controller – Power Oscillation Damping) em sistemas elétricos de potência multimáquinas. O objetivo principal é inserir amortecimento adicional aos modos oscilatórios de baixa frequência e, consequentemente, garantir a estabilidade do sistema elétrico frente a pequenas perturbações. Para representar o sistema elétrico de potência será utilizado o Modelo de Sensibilidade de Potência. Desse modo, todos os seus dispositivos e componentes foram modelados por injeções de potência. Análises estáticas e dinâmicas foram realizadas em dois sistemas teste, sendo: o Sistema Simétrico de Duas Áreas e o Sistema New England. A eficiência do dispositivo FACTS Generalized Unified Power Flow Controller atuando em conjunto com uma estrutura de controle baseada em controladores Proporcional – Integral foi criteriosamente avaliada para o controle de fluxos de potências ativa e reativa, para a melhoria do perfil de tensão do sistema elétrico e na redução das perdas no sistema de transmissão. O desempenho do Novel Bat Algorithm, no que concerne ao ajuste dos parâmetros dos controladores, foi comparado a outros quatro algoritmos bio-inspirados bastante difundidos na literatura: Particle Swarm Optimization, Bacterial Foragim Optimization, Bat Algorithm e... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: This work presents the Novel Bat Algorithm as a new technique for the to perform the coordinated tuning of the parameters of the supplementary damping controllers (Power Systems Stabilizers and Generalized Unified Power Flow Controller - Power Oscillation Damping) in multi-machine electric power systems. The main objective is to insert damping to low-frequency oscillations and thus ensure the stability of the electrical system against minor disturbances. The Power Sensitivity Model is used to represent the system. Thus, all devices and their components are modeled by power injection. Static and dynamic analyzes were performed in the two systems: the two-areas symmetric, and the New England. The performance of the proposed methodology (Novel Bat Algorithm), for tuning of the parameters of the controllers was compared to four other algorithms, presented in the literature: The Particle Swarm Optimization method, Bacterial Foraging Optimization method, Bat Algorithm method and a Genetic Algorithm with elitism. The results demonstrated that the Novel Bat Algorithm was more effective than the other techniques presented, generating robust solutions when variations on the scenarios of loads were considered, and therefore accredited it as a tool in the analysis of the study of small-signal stability.
Doutor

博士
長庚大學
電機工程學研究所
98
With increasing power system loading requirement, some transmission lines are running close to their full capacities. This increases operation flexibility and controllability for contingency outages and abnormal system conditions, respectively. Flexible Alternating Current Transmission System (FACTS) based on power electronics can offer an opportunity to enhance controllability, stability, and power transfer capability of power systems. Among all FACTS apparatuses, Unified Power Flow Controllers (UPFCs) seem to be the most comprehensive and can provide the greatest flexibility with multiple control functions. The aim of the dissertation is to develop the novel integrated UPFC controller including the primary and supplementary controller for enhancing power system stability. We will first utilize the Passivity-Based Control (PBC) for UPFC primary controller design. The proposed PBC primary control not only can provide rapid and precise regulation ability but also have lower designing complexity than that of PI control schemes. However, only using primary control could not suppress natural power oscillations under severe contingencies. To prevent instability and even improve the stability of the system, it is possible to add the supplementary control for damping of the post-fault power oscillation. A Lyapunov based recurrent neural network supplementary damping UPFC controller based on Network-Reduction Models (NRMs) is developed for improving transient stability of power systems. This controller can be treated as neural network approximations of Lyapunov control actions. However, employing NRMs requires the measurement of wide area signals fed into the supplementary controller. Therefore, this dissertation furthermore proposes an Energy Function based Forward Neural Network Supplementary Damping (EFFNNSD) UPFC controller based on Network-Preserving Models (NPMs). This approach merely requires the measurement of local bus signals. Since only local signals are employed, this control law is essentially decentralized with minimal control signal deployments. Finally, the novel integrated UPFC control system is obtained by combing a PBC primary control and an EFFNNSD control. The proposed ntegrated UPFC control system has been tested on a longitudinal two-area systemand a 10-machine 39-bus New-England system. Furthermore, the feasibility study of installing Static Synchronous Compensators (STATCOMs), that is, the shunt-side of UPFCs, is presented for enhancing voltage stability . A static/dynamic approach for allocating of STATCOMs and their capacity will also be investigated. After comprehensive simulation experiments, the proper strategy of installing STATCOMs for a longitudinal studied system will be proposed.

The focus of this research is on deriving small signal stability models for different Flexible AC Transmission Systems devices by introducing a simple systematic method that is applicable to any dynamic device. Two different small signal models for Unified Power Flow Controllers are introduced. One model is called the power control mode and the other model is the voltage control mode. The two models are compared from transient stability point of view to show the necessity of developing both models for UPFC. The thesis also shows how to derive the small signal stability model of Static Synchronous Compensator, as the shunt branch of UPFC. The small signal stability models of both devices are then validated to ensure the accuracy of the derived models. STATCOM and UPFC power control mode are validated against PSCAD. The UPFC voltage control mode is validated against nonlinear solution of system equations.

The transition of the power sector from vertically integrated utility (VIU) to deregulated system has resulted in reshaping of generation, transmission and distribution components. Some of the objectives of restructuring are to ensure a secure and reliable supply of electricity, encourage competition in all segments, sustain future economic and technological growth, etc. There are many challenges that arise in fulfilling these objectives. The thesis addresses some of them related to planning and operational aspects of real and reactive power, covering the following areas: Real power tracing, loss allocation and pricing Reactive power tracing, loss allocation and pricing Power system generation expansion planning Power transfer capability in interregional grids Voltage stability enhancement by improving reactive power margins In deregulated power systems, it has become important to identify the generation and transmission entities responsible in meeting loads. This is done by tracing the power flows through the transmission network. Power tracing is required to assess the extent of network usage by the participants, so as to allocate the transmission losses and charges. Many loss allocation methods are presented in the literature. The loss allocation method implemented in this thesis is a circuit based method. For obtaining the generators contribution towards meeting system loads and transmission losses, an approach of relative electrical distance (RED) between the generation and the load buses, is presented. The method is used to trace both real and reactive power flows. In the case of real power, the generators are the only sources and loads are the only sinks. However, reactive sources and sinks are distributed all along the transmission system. The reactive power sources considered are generators, switchable VAR sources (shunt capacitor banks) and line charging susceptances; and the reactive sinks are shunt reactors and reactive inductive loads. While tracing their flows the actual sources or sinks are to be identified which is obtained after adding reactive injections and absorptions at each bus. If the net value is absorbing, the bus is a reactive sink and if the net value is injecting, the bus is a reactive source. The transmission line charge susceptances contribution to the system’s reactive flows; and its aid extended in reducing the reactive generation at the generator buses is also discussed. A reactive power optimization technique is applied to optimally adjust the reactive controller settings of transformer taps, generator excitations and switched capacitors, so that the available reactive resources can be fully utilized. In the thesis, a methodology for evaluation of real and reactive power load and loss sharing proportions; and cost allocation towards transmission utilization is presented. Due to the ever growing increase in demands; on one hand the existing transmission networks are getting overloaded at some locations and on the other hand, the available generation is becoming insufficient to cater to the additional demand. To handle this problem, generation and transmission expansions become inevitable. Hence, additional public sector units or independent power producers and transmission providers are to be brought in. However in a restructured system, generally there is no central planning for new generation capacity or transmission additions. The reason being, these investments need huge capital and long period of commitment. While making a generation investment decision, expectations concerning future electricity demand, spot market prices, variations of regulatory policies, etc., are the major considerations. The locations, capacities and timing of new power plants are basically at the generation companies’ own discretion. Also, generation companies do not have any obligation to ensure sufficient supply of electricity to meet present and future requirements. Hence, it is a matter of concern as to how adequate generation capacity can be secured in the long run. Optimal siting and sizing of these new generation locations is also an issue of concern. In this thesis a new index called as ‘Tindex’ is proposed, which identifies prospective new generation expansion locations. The index is formulated based on the transmission network information, and it helps in identifying the most suitable new generation expansion locations. To implement this methodology each of the load bus is treated as a generation bus, one at a time, and the maximum generation capacity that can be installed at the location is computed from the approach. This method ensures minimum transmission expansion. Interconnected power systems help in exchanging power from one area to other areas at times of power deficiency in their own area. To enable this, their tieline capability to transfer power has to be sufficient, which is determined using total transfer capability (TTC) computation. TTC is an important index in power markets with large volume of interarea power exchanges and wheeling transactions taking place on an hourly basis. In the thesis, the total transfer capability (TTC) of interconnected tielines, under normal and contingency conditions is evaluated. The contingency cases evaluated are single line contingency, tieline contingency and generator outage. The most critical lines in each zone are identified using Fuzzy set theory. Unified power flow controller (UPFC), a flexible AC transmission system (FACTS) device is incorporated to improve the power transfers under contingency conditions. The best locations for UPFC placement are identified by analysing the power flow results obtained after considering the contingencies. For each of the normal and contingency cases, a base case and a limiting case are formed and the TTC is evaluated. Limiting case is formed by increasing the load in small steps till a point after which bus voltages or line loadings start to violate their stability constraints. To improve the system conditions in the limiting case, reactive power optimization and UPFC installation is carried out. The results reflect the improvement in system conditions and total transfer capability margins. Availability of sufficient generator reactive margins is very essential to ensure system’s voltage stability, without which even minor disturbances may lead to catastrophe. The amount of reactive power margin available in a system determines its proximity to voltage instability under normal and emergency conditions. One way of improving the reactive margin of a synchronous generator, is to reduce the real power generation within its MVA ratings. However this real power reduction will affect the real power contract agreements formed while power trading. The real power contracts are not disturbed and the reactive power margins are improved by optimally adjusting the other available reactive controllers, namely, generator exciter, transformer taps and shunt compensators. To have further control on the reactive flows, UPFC device is incorporated at appropriate locations. The thesis discusses how reactive margins are computed and subsequently improved using a reactive power optimization technique and UPFC. Case studies are carried out on typical sample 6bus, 8bus, 10bus, 16bus, 20bus, IEEE 30bus, IEEE 39bus systems, and reallife equivalents of Indian southern grid 24bus, 72bus, 87bus and 205bus systems to illustrate the proposed approaches.

With limited enhancement or expansion of the transmission infrastructure, the contemporary power systems are operating under more stressed conditions. It becomes important to fully utilize the existing transmission system to supply load demand as much as possible, thus eliminating or reducing the need for new transmission investment. Flexible AC Transmission System (FACTS) technology provides an alternative to fully utilize the existing transmission lines as well as new and upgraded lines, by controlling power and also enhancing the power transfer capability of transmission lines. However, the implementation of FACTS controllers in the transmission system has introduced new power system dynamics that must be addressed in the area of power system protection, such as rapid changes in line impedance, power angle, line currents, transients introduced by the occurrence of fault and associated control action of the FACTS controller. Therefore, the performance of the protection system must be carefully analyzed in the presence of FACTS controllers. The thesis aims at evaluating the performance of distance relays when different types of FACTS controllers, in particular Voltage Source Converter (VSC) based FACTS controllers, are incorporated at the midpoint of the transmission system to achieve voltage profile improvement and power transfer capability. The detailed models of these controllers and their control strategies are described. The presence of FACTS controllers in the loop affects both steady state and transient components of voltage and current signals. The rapid response of FACTS controllers to different power system configurations significantly affects the apparent impedance seen by distance relays. The apparent impedance seen by distance relays would be different from that of the system without FACTS controller. Due to this, the distance relay may malfunction, resulting in unreliable operation of the power system during faults. Furthermore, the effect of FACTS controllers on distance relay operation depends on the type of FACTS controller used, the application for which it has been installed and its location in the power system. The distance relay is evaluated for different loading conditions and for various fault conditions. Simulation studies are carried out using PSCAD/EMTDC based transient simulation package.

碩士
國立高雄應用科技大學
電機工程系
98
This thesis studies the detailed modeling and simulation of multi-pulse VSI based Unified Power Flow Controller (UPFC). The construction of multi-pulse inverter is investigated, and the output waveform characteristics and harmonic spectrum are analyzed. In addition, the PSCAD/EMTDC is used to build the detailed model of power circuit and controller of the three-level 24/48-pulse inverter based compensator, afterwards these compensators are connected with a 3-bus power system. As the result of simulation, these multi-pulse inverter based compensators could stabilize the system voltage and control the active and reactive power of transmission system.

碩士
國立聯合大學
電機工程學系碩士班
94
This thesis presents the design of intelligent controllers based on fuzzy neural networks (FNN) and recurrent fuzzy neural networks (RFNN) for the Unified Power Flow Controller (UPFC) to provide better control features in performing various power flow control functions during steady-state and transient operations of power systems. Two separate FNN (or RFNN) tuned PI con¬trollers or two direct FNN (or RFNN) controllers are respectively used for controlling the shunt and series converter modules of the UPFC. The principles and various structures of the fuzzy and recurrent fuzzy neural networks are investigated in full. Comprehensive simu¬lation studies carried out on commercial grade software packages are described and results of various power flow control examples showing the concerned power system parameters and the excellent control performance of the FNN and RFNN based UPFC are presented and discussed. Typical simulation results of the proposed controllers are compared with the conventional proportional plus integral (PI) controllers to demonstrate the superiority and effectiveness of the new FNN based control algorithm.

碩士
國立成功大學
電機工程學系
102
This thesis studies the dynamic-stability improvement of a multi-machine system connected with a large-scale offshore wind farm based on doubly-fed induction generator (DFIG) using a generalized unified power-flow controller (GUPFC). A two-area four-generator system model is employed as the studied multi-machine system. Two proportional-integral-derivative (PID) damping controllers and two fuzzy logic controllers (FLCs) of the proposed GUPFC are respectively designed to improve the stability of the studied multi-machine power system connected with the offshore wind farm under different operating conditions. A frequency-domain approach based on a linearized system model using eigenvalue analysis and a time-domain method based on nonlinear-model simulations subject to various disturbances are both performed to examine the effectiveness of the proposed GUPFC combined with the designed damping controllers. It can be concluded from the comparative simulation results that the proposed GUPFC joined with the designed FLCs demonstrates better damping performance for improving the stability of the studied multi-machine system subject to different disturbances than the designed PID damping controllers.