Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 157-163). Available also in a digital version from Dissertation Abstracts.

Master of Science / Department of Electrical and Computer Engineering / Shelli K. Starrett / This thesis introduces a Vehicle to Grid (V2G) system which coordinates the charging, and discharging among the Electric Vehicles (EVs) and two-test systems, to help with peak power shaving and voltage stability of the system. Allowing EVs to charge and discharge without any control may lead to voltage variations and disturbance to the grid, but if the charging and discharging of the EVs is done in a smart manner, they can help the power network. In this thesis, fuzzy logic controllers (FLC) are used to control the flow of power between the grid and the electric vehicles. The presented work in this thesis mainly focuses on the control architecture for a V2G station that allows for using EVs batteries to help the grid’s voltage stability. The designed controllers sustain the node voltage, and thus also achieve peak shaving. The proposed architectures are tested on 16 -generator and 6-generator test systems to examine the effectiveness of the proposed designs. Five fuzzy logic schemes are tested to illustrate the V2G system’s ability to influence system voltage stability. The major contributions of this thesis are as follows: 
 • FLC based control tool for V2G station present at a weak bus in the system. • Investigate the effect of the station location and voltage sensitivity. • Comparison of chargers providing real power versus reactive power. • Simulation of controller and system interactions in a daily load curve cycle. Keywords: State of Charge (SOC), Electric Vehicle (EV), Fuzzy Logic Controller (FLC), Vehicle to grid (V2G), and Power System Voltage Stability.

Orientador: Percival Bueno de Araujo / Co-orientador: Marcos Amorielle Furini / Banca: Anna Diva Plasencia Lotufo / Banca: André Luiz Silva Pereira / Resumo: O advento da energia elétrica e seu uso, ainda no final do século XIX, foram sem dúvida os grandes responsáveis pelo avanço tecnológico conquistado desde então. A oferta de energia para a população permitiu agregar maior conforto às pessoas e maior eficiência aos processos produtivos. Nos primórdios, os sistemas de energia eram compostos por unidades geradoras conectadas próximas aos consumidores. Essa proximidade era consequência direta do uso de transmissão em corrente contínua, o que naquela época inviabilizava a transmissão de energia elétrica através de longas distâncias. Com a invenção e utilização de máquinas de corrente alternada e transformadores, as características dos sistemas de energia passaram a ser de unidades geradoras cada vez mais distantes dos centros de consumo, sendo conectadas por longas linhas de transmissão de alta tensão. Pela metade do século XX, vislumbrou-se que a interligação de unidades geradoras, antes operando de maneira isolada, permitiria um melhor aproveitamento do potencial elétrico dos sistemas. Da mesma forma, a interligação dos consumidores permitiria maior confiabilidade no fornecimento de energia elétrica. Tais vantagens motivaram a interligação do sistema elétrico de potência. O que os visionários não poderiam imaginar era que a interconexão dos sistemas também traria novos problemas atrelados às oscilações de baixa frequência dos sistemas elétricos. Tais oscilações, em especial as relacionadas com os modos interárea, foram responsáveis por grandes blecautes ocorridos nos anos 1950 nos Estados Unidos e Canadá. Tornava-se evidente a necessidade de estudar e analisar tais oscilações, tal como o comportamento do sistema elétrico interligado como um todo quando submetido às contingências de grande e pequeno porte. Com as interligações os sistemas elétricos de potência se tornaram um dos mais complexos sistemas já desenvolvidos pelo homem. Tal ... / Abstract: The arising of electrical energy and its use in the end of 19th century are, for sure, one of the major responsible for the technology improvements conquered since then. The available of electrical energy for population also improved people's welfare and the production process efficiency. In the early days, electrical systems were composed by generator units connected close to consumers. This proximity was a straight consequence of DC (direct current) transmission, which one did not allow the transmission of power over large distances due to physical and economic constraints. With the development and use of AC (alternate current) machines and transformers, the electrical systems became composed of generator units far even more from consumer's centers, being connected to them by high voltage transmission lines. By the 1950's, it was noted that the interconnection of generators units, which was operating isolated from each other, would allow a better use of electric power system. From the same way, the interconnection of consumers allow more reliability in the electrical energy supply. Those advantages led to the interconnection of Electric Power Systems. What the visionaries could not imagine was that the interconnection would also bring to surface some new problems linked to the system's low frequency oscillations. Those oscillations, in special those related to the interarea mode, were responsible for big blackouts occurred in the 1950's in the USA and Canada. It was evident the necessity of study and analysis of those oscillations, also as the interconnected Power System behavior when under big and small contingencies. With the system's interconnection, Power Systems became one of the most complex systems already built by the man. Such complexity is extended for its analysis and study. Due to this, it was necessary create models to simplify the analysis without a loss in the results reliability. As regards to the study of small ... / Mestre

Made available in DSpace on 2014-06-11T19:22:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2013-11-29Bitstream added on 2014-06-13T20:09:47Z : No. of bitstreams: 1 000739791.pdf: 1468115 bytes, checksum: ad923e4b63aea183e8523102990d35de (MD5) / O advento da energia elétrica e seu uso, ainda no final do século XIX, foram sem dúvida os grandes responsáveis pelo avanço tecnológico conquistado desde então. A oferta de energia para a população permitiu agregar maior conforto às pessoas e maior eficiência aos processos produtivos. Nos primórdios, os sistemas de energia eram compostos por unidades geradoras conectadas próximas aos consumidores. Essa proximidade era consequência direta do uso de transmissão em corrente contínua, o que naquela época inviabilizava a transmissão de energia elétrica através de longas distâncias. Com a invenção e utilização de máquinas de corrente alternada e transformadores, as características dos sistemas de energia passaram a ser de unidades geradoras cada vez mais distantes dos centros de consumo, sendo conectadas por longas linhas de transmissão de alta tensão. Pela metade do século XX, vislumbrou-se que a interligação de unidades geradoras, antes operando de maneira isolada, permitiria um melhor aproveitamento do potencial elétrico dos sistemas. Da mesma forma, a interligação dos consumidores permitiria maior confiabilidade no fornecimento de energia elétrica. Tais vantagens motivaram a interligação do sistema elétrico de potência. O que os visionários não poderiam imaginar era que a interconexão dos sistemas também traria novos problemas atrelados às oscilações de baixa frequência dos sistemas elétricos. Tais oscilações, em especial as relacionadas com os modos interárea, foram responsáveis por grandes blecautes ocorridos nos anos 1950 nos Estados Unidos e Canadá. Tornava-se evidente a necessidade de estudar e analisar tais oscilações, tal como o comportamento do sistema elétrico interligado como um todo quando submetido às contingências de grande e pequeno porte. Com as interligações os sistemas elétricos de potência se tornaram um dos mais complexos sistemas já desenvolvidos pelo homem. Tal... / The arising of electrical energy and its use in the end of 19th century are, for sure, one of the major responsible for the technology improvements conquered since then. The available of electrical energy for population also improved people's welfare and the production process efficiency. In the early days, electrical systems were composed by generator units connected close to consumers. This proximity was a straight consequence of DC (direct current) transmission, which one did not allow the transmission of power over large distances due to physical and economic constraints. With the development and use of AC (alternate current) machines and transformers, the electrical systems became composed of generator units far even more from consumer’s centers, being connected to them by high voltage transmission lines. By the 1950’s, it was noted that the interconnection of generators units, which was operating isolated from each other, would allow a better use of electric power system. From the same way, the interconnection of consumers allow more reliability in the electrical energy supply. Those advantages led to the interconnection of Electric Power Systems. What the visionaries could not imagine was that the interconnection would also bring to surface some new problems linked to the system´s low frequency oscillations. Those oscillations, in special those related to the interarea mode, were responsible for big blackouts occurred in the 1950´s in the USA and Canada. It was evident the necessity of study and analysis of those oscillations, also as the interconnected Power System behavior when under big and small contingencies. With the system´s interconnection, Power Systems became one of the most complex systems already built by the man. Such complexity is extended for its analysis and study. Due to this, it was necessary create models to simplify the analysis without a loss in the results reliability. As regards to the study of small ...

Transient stability analysis is an important part of power planning and operation. For large power systems, such analysis is very time consuming and expensive. Therefore, an online transient stability assessment will be required as these large power systems are operated close to their maximum limits. In this thesis swallowtail catastrophe is used to determine the transient stability regions. The bifurcation set represents the transient stability region in terms of power system transient parameters bounded by the transient stability limits. The system modelling is generalized in such, that the analysis could handle either one or any number of critical machines. This generalized model is then tested on a three-machine as well as a seven-machine system. The results of the stability analysis done with the generalized method is compared with the time solution and the results were satisfactory. The transient stability regions determined are valid for any changes in loading conditions and fault location. This method is a good candidate for on-line assessment of transient stability of power systems. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

Contemporary power networks are gradually expanding incorporating new sources of electrical energy and power electronic based devices. The major stability issue in large interconnected power systems is the lightly damped interarea oscillations. In the light of growth of their incidents there are increased concerns about the effectiveness of current control devices and control systems in maintaining power system stability. This thesis presents a Wide Area Measurement System (WAMS) based control scheme to enhance power system stability. The control scheme has a hierarchical (two-level) structure comprising a Supplementary Wide-Area Controller (SWAC) built on top of existing Power System Stabilisers (PSSs). The SWAC's focus is on stabilising the critical interarea oscillations in the system while leaving local modes to be controlled entirely by local PSSs. Both control systems in the two levels work together to maintain system stability. The scheme relies on synchronised measurements supplied by Phasor Measurement Units (PMUs) through the WAMS and the only cost requirement is for the communication infrastructure which is already available, or it will be in the near future. A novel linear quadratic Gaussian (LQG) control design approach which targets the interarea modes directly is introduced in this thesis. Its features are demonstrated through a comparison with the conventional method commonly used in power system damping applications. The modal LQG approach offers simplicity and flexibility when targeting multiple interarea modes without affecting local modes and local controllers, thus making it highly suitable to hierarchical WAMS based control schemes. Applicability of the approach to large power systems is demonstrated using different scenarios of model order reduction. The design approach incorporates time delays experienced in the transmission of the SWAC's input/output signals. Issues regarding values of time delays and required level of detail in modelling time delays are thoroughly discussed. Three methods for selection of input/output signals for WAMS based damping controllers are presented and reviewed. The first method uses modal observability/controllability factors. The second method is based on the Sequential Orthogonalisation (SO) algorithm, a tool for the optimal placement of measurement devices. Its application is extended and generalised in this thesis to handle the problem of input/output signal selection. The third method combines clustering techniques and modal factor analysis. The clustering method uses advanced Principal Component Analysis (PCA) where its draw backs and limitations, in the context of power system dynamics' applications, are overcome. The methods for signal selection are compared using both small signal and transient stability analysis to determine the best optimal set of signals. Enhancement of power system stability is demonstrated by applying the proposed WAMS based control scheme on the New England test system. The multi-input multi-output (MIMO) WAMS based damping controller uses a reduced set of input/output signals and is designed using the modal LQG approach. Effectiveness of the control scheme is comprehensively assessed using both small signal and transient stability analysis for different case studies including small and large disturbances, changes in network topology and operating condition, variations in time delays, and failure of communication links.

Variations in the electricity consumption and production connected to the power system have to be balanced by active control. Hydropower is the most important balancing resource in the Nordic system, and will become even more important as the share of variable renewable energy sources increases. This thesis concerns balancing of active power, especially the real-time balancing called frequency control. The thesis starts in a description of the situation today, setting up models for the behaviour of hydropower units and the power system relevant to frequency control, and comparing the models with experiments on several hydropower units and on the response of the Nordic grid. It is found that backlash in the regulating mechanisms in hydropower units have a strong impact on the quality of the delivered frequency control. Then, an analysis of what can be done right now to improve frequency control and decrease its costs is made, discussing governor tuning, filters and strategies for allocation of frequency control reserves. The results show that grid frequency quality could be improved considerably by retuning of hydropower governors. However, clear technical requirements and incentives for good frequency control performance are needed. The last part of the thesis concerns the impact from increased electricity production from variable renewable energy sources. The induced balancing need in terms of energy storage volume and balancing power is quantified, and it is found that with large shares of wind power in the system, the energy storage need over the intra-week time horizon is drastically increased. Reduced system inertia due to higher shares of inverter connected production is identified as a problem for the frequency control of the system. A new, linear synthetic inertia concept is suggested to replace the lost inertia and damping. It is shown that continuously active, linear synthetic inertia can improve the frequency quality in normal operation and decrease wear and tear of hydropower units delivering frequency control.

No description available.

A new methodology is proposed to investigate the large-signal stability of interconnected power electronics systems. The approach consists of decoupling the system into a source subsystem and a load subsystem, and stability of the entire system can be analyzed based on investigating the feedback loop formed by the interconnected source/load system. The proposed methodology requires two stages: (1) since the source and the load are unknown nonlinear subsystems, system identification, which consists of isolating each subsystem into a series combination of a linear part and a nonlinear part, must be performed, and (2) stability analysis of the interconnected system is conducted thereafter based on a developed stability criterion suitable for the nonlinear interconnected-block-structure model. Applicability of the methodology is verified through stability analysis of PWM converters and a typical power electronics system. / Ph. D.

This thesis investigates the impacts of superconducting magnetic energy storage (SMES) unit on the power system first-swing stability by the impedance model of the SMES unit and EMTP simulations. The impedance model of the SMES unit is established in this thesis for study purpose. It has been concluded that SMES unit can greatly improve the power system first-swing stability. Based on the theoretical analysis and simulation results, the concept of the "Stability Protection Zone" of the SMES unit is proposed. Future work directions are discussed in the conclusion part. / Master of Science