No description available.

Thesis (Ed.M.)--Boston University

A problem of interest in the power industry is the mitigation of interarea and torsional oscillations. Interarea oscillations are due to the dynamics of interarea power transfer and often exhibit poor damping when the aggregate power transfer over a corridor is high relative to the transmission strength. These oscillations can severely restrict system operations and, in some cases, can lead to widespread system disturbances. Torsional oscillations are induced due to the interaction between transmission system disturbances and turbine-generator shaft systems. The high torsional stresses induced due to some of these disturbances reduce the life expectancy of the turbine-generators and, in severe cases, may cause shaft damage. <p>This thesis reports the development of novel control techniques for Flexible AC Transmission System (FACTS) devices for the purpose of damping power system interarea and torsional oscillations. In this context, investigations are conducted on a typical three-area power system incorporating FACTS devices. The Genetic Algorithm (GA) and fuzzy logic techniques are used for designing the FACTS controllers. Although attention is focused in the investigations of this thesis on the Unified Power Flow Controller (UPFC), studies are also conducted on two other FACTS devices, a three voltage-source converter Generalized Unified Power Flow Controller (GUPFC) and a voltage-source converter back-to-back HVdc link. <p>The results of the investigations conducted in this thesis show that the achieved control designs are effective in damping interarea oscillations as well as the high torsional torques induced in turbine-generator shafts due to clearing and high-speed reclosing of transmission system faults. The controller design procedures adopted in this thesis are general and can be applied to other FACTS devices incorporated in a power system. The results and discussion presented in this thesis should provide valuable information to electric power utilities engaged in planning and operating FACTS devices.

Interconnection of remotely power systems with large generation capacity and system load is progressively widespread due to the increase of the power exchanges between countries as well as regions within countries in many parts of the world. In the cases of long distance AC transmission, as in interconnected power systems, care has to be taken for maintaining synchronism as well as stable system voltages, particularly in conjunction with system faults and line switching. With series compensation, bulk AC power transmission over very long distances (1000 km and more) is in existence today. These long distance power transfers cause, however, the system low-frequency oscillations, typically within the range of 0.4 to 2 Hz, to become more lightly damped. For this reason, many power network operators and utilities are taking steps to add supplementary controls in their systems to provide extra system damping aiming to improve the system security by damping these undesirable oscillations. This thesis reports the results of time-domain simulation studies that are carried out to investigate the effectiveness of supplemental controls of a phase imbalance hybrid single-phase-Thyristor Controlled Series Capacitor (TCSC) compensation scheme and a static synchronous compensator in damping power system oscillations. In this context, studies are conducted on a typical large power system incorporating several series capacitor compensated transmission lines and large load centers with their reactive power support provided by static synchronous compensators (STATCOM). Several case studies investigating the effects of the location of the hybrid single-phase-TCSC compensation scheme, the degree of compensation provided by the scheme, the stabilizing signals of the supplemental controls, the fault clearing time, as well as the fault location on the damping of power system oscillations are documented. The results of the investigations conducted in this thesis demonstrate that the supplemental controls are very effective in damping power system oscillations resulting from clearing system faults. The time-domain simulation studies are conducted using the ElectroMagnetic Transients program Restructured Version (EMTP-RV).

A problem of interest in the power industry is the mitigation of interarea and torsional oscillations. Interarea oscillations are due to the dynamics of interarea power transfer and often exhibit poor damping when the aggregate power transfer over a corridor is high relative to the transmission strength. These oscillations can severely restrict system operations and, in some cases, can lead to widespread system disturbances. Torsional oscillations are induced due to the interaction between transmission system disturbances and turbine-generator shaft systems. The high torsional stresses induced due to some of these disturbances reduce the life expectancy of the turbine-generators and, in severe cases, may cause shaft damage. <p>This thesis reports the development of novel control techniques for Flexible AC Transmission System (FACTS) devices for the purpose of damping power system interarea and torsional oscillations. In this context, investigations are conducted on a typical three-area power system incorporating FACTS devices. The Genetic Algorithm (GA) and fuzzy logic techniques are used for designing the FACTS controllers. Although attention is focused in the investigations of this thesis on the Unified Power Flow Controller (UPFC), studies are also conducted on two other FACTS devices, a three voltage-source converter Generalized Unified Power Flow Controller (GUPFC) and a voltage-source converter back-to-back HVdc link. <p>The results of the investigations conducted in this thesis show that the achieved control designs are effective in damping interarea oscillations as well as the high torsional torques induced in turbine-generator shafts due to clearing and high-speed reclosing of transmission system faults. The controller design procedures adopted in this thesis are general and can be applied to other FACTS devices incorporated in a power system. The results and discussion presented in this thesis should provide valuable information to electric power utilities engaged in planning and operating FACTS devices.

The major goal of this paper is to study the problem of power dispatch for bilateral contract. The proposed problem was separated into two parts in this thesis. The first deals with the deregulated electricity market, where Generation Company and Distribution Company will be permitted to establish bilateral service contracts in the market. The Independent System Operator (ISO) has an overall responsibility to execute these bilateral contracts as far as the operating conditions permit. In this thesis, the problem of power dispatch for bilateral contract is formulated as minimization of deviations from transaction requests made by market participants. In addition, various constraints consisting of capacity coupling, spinning reserve capacity and transmission line constraints are explicitly taken into account. We also consider the impact of transmission congestion and environmental constraints. DC load flow and interior point (IP) methods were used in solving this problem. According to various simulations, the proposed method is reliable and helpful for ISO¡¦s power dispatch. Second part of the thesis deals with the flexible AC transmission system (FACTS) devices, such as thyristor controlled series compensators and thyristor controlled phase shifters, under transmission congestion. Evolutionary Programming, known to avoid local convergence and achieve nearly global optimum, was used to solve this combinatorial optimization problem. FACTS installation tried to solve or improve congestion in the transmission network for bilateral contracts. It could also provide planning tools for system expansion for operators¡¦ references.

The unified power controller (UPFC) is, the most comprehensive device emanated so far from the FACTS (Flexible AC Transmission Systems) initiative. Installation of UPFC to control power flow has become an emerging topic in today¡¦s power industry, especially the deregulated market. By the use of UPFC, a high-speed and low-cost power electronic device, the line flows can be controlled in such a way that thermal limits are kept, losses minimized, stability increased, and contractual requirements fulfilled without violating the economic generation dispatch. To coupe with control signals to attain various control capabilities, it can be used to control both the active and reactive powers and voltage magnitudes altogether. This thesis aims to study static UPFC models for power flow calculations. Basic operation of UPFC will be briefly reviewed. A new UPFC current-based model is proposed in this paper to improve existing power-based model by using the Norton Equivalent Theorem. The proposed model can be integrated with the ECI power flow model easily. The equivalent relationships between the new model and the traditional model will also be investigated. And the proposed current-based UPFC model will provide better convergent characteristics. The Evolutionary Programming (EP) method was also proposed in this research to solve the UPFC control parameters to attain a global optimum. EP is an artificial intelligence process including reproduction, mutation, competition, and selection. Being a stochastic method, EP can avoid the local convergence problem and provide a better opportunity to reach the global or near global optimum. Using the test cases of 5-bus and Taipower systems, the test results proves that the new UPFC new model can successfully control active power and reactive power, and voltage magnitudes simultaneously with an effective process and a feasible solution.

This thesis discusses the placement of conventional power flow controllers (namely the Fixed series capacitor (FSC), Phase Angle Regulating Transformer (PAR)) and Flexible AC Transmission System (FACTS) devices (namely the Thyristor Controlled Series Capacitor (TCSC), the Static Synchronous Series Compensator (SSSC), the Unified Power Flow Controllers (UPFC) and the Sen Transformer (ST)) in bulk power systems to minimize transmission losses in the entire system. This firstly resolves line overloading and improves the overall voltage profile of the entire system. Secondly the transmission losses are minimized and also help in reducing the generation, which results in additional dollar savings in terms of the fuel costs. The sizes of the FACTS devices used were small in order to keep the initial installation costs low for the utility. The reduced FACTS device ratings are mentioned as a benefit, but not included in the overall loss minimization calculations. Various types of FACTS devices were modeled and placed in the power system, and the economic benefits were discussed and compared for different power flow conditions. The FSC, PAR, and TCSC are the FACTS Devices commonly used in the electric utility industry. In addition to the previous devices, the SSSC and UPFC were also modeled in the popular PSS/E and PSAT software's. The Sen Transformer was modeled using an electromagnetic transient simulation program (PSCAD/EMTDC). A line stability index was used to find the optimum location for placing the FACTS device. This thesis also provides a quantified value for the overall losses with the different FACTS devices, which is not available in the previous research literature. The Sen Transformer is a new type of a FACTS device that was developed by a former Westinghouse engineer, Dr. Kalyan Sen in 2003. It is based on the same operating principle as a UPFC (i.e. provides independent active and reactive power control) but uses the proven transformer technology instead. The benefit of the SEN transformer is that it would cost approximately only 30% of the UPFC cost. This thesis studies the Sen Transformer for loss minimization. Since the Sen technology uses a mature transformer technology, its maintenance costs are going to be less and therefore the utilities would be more comfortable using such a device instead of UPFC. A 12 bus test system proposed by FACTS modeling working group was used for validating and testing the FACTS devices in this thesis. This test system is a composite model of Manitoba Hydro, North Dakota, Minnesota, and Chicago area subsystems. This test platform manifests number of operating problems, which the electric utilities typically face. This system has been used for congestion management, voltage support and stability improvement studies with the FACTS devices. The results show that compensating a short transmission line in this system is more effective in minimizing the overall losses and improving the voltage profile compared to a typical approach of compensating long lines. The results also show that the UPFC and Sen Transformer are the most effective in minimizing the overall losses with the Sen Transformer being the most cost effective solution.

The thesis begins with a brief introduction in which I set out a number of the major questions which I intend to consider. I indicate that the focus for discussion will be functional words. Two questions regarding functional words are asked. First, do they have descriptive content? Second, do they have evaluative content? After a brief discussion, I attempt to set out the significance of these two questions. I point out that both are potentially significant relative to recent controversies over how description is related to evaluation. I indicate, however, that my chief concern will not be with the prescriptivist/naturalist controversy; rather, my chief concern will be with attempting to discover the role played by functional words in both descriptive and evaluative contexts The purpose of the discussion will be to discover whether an analysis of functional words can shed any light on the nature of the fact/value relationship. After raising a number of subsidiary questions, which, it is hoped, will aid the reader in following the argument, I introduce some terminology of which the notion of an F-word is central. A definition of 'F-word' is provided in Chapter II. The 'definition' with which the notion is introduced is simply that an F-word is any word which is like functional words in relevant respects. [page ii of abstract missing] In Chapter IV the discussion turns to a detailed examination of a suggestion of Hare in The Language of Morals. I find it necessary to reconstruct his suggestion and find it contains three elements. Of these three elements I argue that Hare is correct in thinking that in F-inferences, a standard of evaluation is introduced by the use of an F-word. I then argue that Hare is incorrect in thinking that, as in inferences from pure descriptions to hypothetical imperatives, the standard of evaluation in F-inferences is introduced via the conclusion of the inference. Finally, I argue that Hare is incorrect in his view that both hypothetical imperatives and F-conclusions are analytic qua their imperative or evaluative content. I then point out that F-conclusions and hypothetical imperatives; are dissimilcir in this important respect, namely, that unlike hypothetical imperatives, evaluations entailed by F-descriptions are genuine evaluations. Chapter V is a summary of the conclusions which follow from the arguments of the first part of the thesis. I conclude that F-words do have both descriptive and evaluative content. Further, that their descriptive and evaluative content derive from the same source, namely, the fact that F-words identify objects by reference to their function. Because of this, the descriptive content of F-words cannot be separated off from their evaluative content and expressed in descriptive sentences which have no evaluative content. In this sense, F-words and F-descriptions cannot be eliminated. The chapter closes by asking whether there is a second sense in which F-words cannot be eliminated. I ask, 'Are F-words such that to eliminate them from one's descriptive vocabulary is to eliminate the possibility of using descriptive language?' The over all purpose of Part II is to answer the question posed at the conclusion of Part I. I begin that task with a two chapter examination of the relation between perception and goal directed behavior. The basis of the argument is the proposition that if the ability to engage in goal directed behavior is a necessary condition of perception, then the purposes or goals which guide human conduct will be reflected in the ways we identify things. The discussion in Chapter VI and VII revolves around three questions: (i) is perception a necessary feature of goal directed behavior? (ii) is perception itself a form of goal directed behavior? (iii) is there a necessary relation between perception and agency such that it is logically necessary that perceivers are agents? The first two questions are discussed in Chapter VI, the third in Chapter VII. The first question finds a positive answer. A thing which is incapable of perception is incapable, as a consequence, of goal directed behavior. The second question is answered negatively. I point out, however, that perception does exhibit a number of characteristics whose possession suggests that perception has much in common with goal directed behavior. Chapter VII considers the question 'Is there a logically necessary relation between perception and agency such that only agents are capable of perception?'. I argue that: (i) it is logically necessary that something be an agent if it is to be determined that it is a percipient thing; (ii) only if a percipient thing is an agent can it be determined what it is capabl of perceiving; (iii) there is convincing empirical evidence which demonstrates that perceptual skills are acquired in the context of goal directed behavior and further that this does have an important bearing on what someone does in fact perceive; but (iv) the kinds of arguments which attempt to show that percipient things logically must be agents are unconvincing. The next two chapters turn to a discussion of the relation between description and goal directed behavior. I argue that the use of descriptive language for communication is possible only to agents. Descriptive uses of language can be taught only if it is possible to establish publicly what the words in the language mean. A number of arguments are used to show that this is a genuine problem and one which cannot be overcome by non-agents. From this it is seen to follow that for communication to be possible, at least some of the objects about which communication takes place must be identified as objects of manipulation. I argue that it follows from this that for descriptive language users, a fundamental and non-eliminable way of identifying objects is as objects of manipulation. Chapter IX is devoted to an attempt to develop and illustrate the conclusions of Chapter VIII through the use of a model. In the course of the discussion, I show that an object of manipulation is an F-object. Chapter X is the concluding chapter of Part II. I conclude that to communicate using descriptive language f an individual must be able to identify at least some of the F-objects which those with whom he wishes to communicate are able to identify. I suggest that this constitutes a second sense in which F-words are not eliminable. Chapter XI comprises Part III of the thesis. Its purpose is to sum up in a brief way the conclusions of the previous two parts. It also suggests in a highly speculative way some possible implications of the position arrived at in the course of previous argument.

Erlangen, Nürnberg, Univ., Diss., 2007.