Thesis (DTech (Electrical Engineering))--Cape Peninsula University of Technology, 2016. / Electric power systems are being operated closer to their designed stability limits due to the constraints caused by the continuous increase in system loading, and the lack of new power stations and transmission network infrastructure to support this increase in system loading. This coupled with the practice of long distance bulk power transmission and cascading contingencies, makes system instability and consequently blackouts inevitable. In such scenarios, system instabilities like voltage instability becomes a serious threat to the secure operation of the power system, and voltage collapse (system-wide blackouts) are prone to occur. This is often compounded by the unavailability of real-time system measurements for situational awareness from the existing Supervisory Control and Data Acquisition (SCADA)/Energy Management System (EMS) platforms which are usually based on unsynchronized SCADA measurements with a slow reporting rate of 1 measurement every 2-10 seconds. This Doctoral thesis proposes non-iterative algorithms and methods of solution based on the IEEE C37.118 synchrophasor measurements from Phasor Measurement Units (PMUs) with a high reporting rate of up to 200 measurements every second (200 fps) for voltage stability assessment and automated wide area Centralised Protection/Control (CPC) against catastrophic voltage instabilities/blackouts in power systems. Extended formulations are proposed for the Optimal Placement of PMUs (OPP) in power systems with respect to voltage stability assessment. The impact of zero injection buses, critical buses, and PMU redundancy is considered in the formulation of the OPP problem solution. The extended formulations made use of Binary Integer programming (BIP) and Modal Participation Factors (MPFs) derived from the eigenvalues of the power flow Jacobian.

Orientador: Sergio Valdir Bajay / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-14T08:34:32Z (GMT). No. of bitstreams: 1 Sales_AlexandraLucio_M.pdf: 998470 bytes, checksum: 988d4fabf4b39a1195f5560161910d75 (MD5) Previous issue date: 2007 / Resumo Neste trabalho é feita uma análise do planejamento da expansão do parque gerador de energia elétrica do Brasil, a partir da caracterização do cenário atual do setor elétrico brasileiro. Procurou-se resgatar o histórico dos estudos de médio e de longo prazos, realizados desde a década de 1960 e que serviram de premissas para expansão do setor. O planejamento de sistemas hidrotérmicos de potência pode ser representado matematicamente por uma função objetivo, que, sujeito à certas restrições, sinalize uma operação ótima desses sistemas e suas necessidades de expansão. Diversos tipos de modelos computacionais podem ser utilizados como valiosas ferramentas de auxílio à tomada de decisão na solução deste problema. Este trabalho discute as principais estratégias de solução que vêm sendo aplicadas neste contexto. Em uma outra parte deste trabalho, foram analisadas diversas bases de dados, nacionais e internacionais, que disponibilizam informações a respeito de custos e de tendências tecnológicas para a geração de energia elétrica. A partir destas análises, foi feito um levantamento dos parâmetros que formam o custo unitário de geração, que permitiu a formulação de três cenários: "baixo", "referência" e "alto", que simulam, através de planilhas econômico-financeiras, condições de formação de baixos custos unitários de geração, custos mais prováveis e altos custos unitários de geração, respectivamente. Por fim, são analisados os resultados obtidos da planilha sob o aspecto da competitividade das tecnologias que complementam o parque hidráulico brasileiro. O estudo desenvolvido neste trabalho mostra a importância dos parâmetros econômico-financeiros e das políticas energéticas adotadas para o setor, dado que estes afetam diretamente o custo de geração e, conseqüentemente, os preços praticados no mercado de energia elétrica. / Abstract: An evaluation is carried out in this thesis about medium and long-term generation planning in the Brazilian electric power system, since the 1960's. Planning of hydrothermal power systems can be represented mathematically by an objective function, which, subject to certain constraints, indicates an optimal operation of these systems and their expansion needs. Several types of computer models can be used as valuable tools in the decisions making process involved in the solution of this problem. The main solution strategies which have been applied so far are discussed here. In another part of this thesis, several data basis, both national and international, providing information about electricity generation costs and technological trends, have been assessed. From these analysis, the main parameters that form the generation unit cost were identified, allowing the formulation of three scenarios - "low", "reference" and "high", which simulate, through economic-financial data sheets, low, more likely and high unit costs, respectively. The results obtained from the data sheets provide valuable insights about the competitive positions of the technologies that complement hydro power in Brazil. This thesis highlights the importance of economic-financial parameters and the public policies adopted for the power sector, since they affect directly generation unit cost and, consequently, the prices practiced in the electricity market. / Mestrado / Mestre em Planejamento de Sistemas Energéticos

With rapid depletion of fossil fuels and increasing environmental concerns, the trend to capture renewable energy, especially through wind energy resources, is increasing. The doubly fed induction generator (DFIG) is the most widely used generator for wind energy conversion because of its various advantages over other types of generators. In a DFIG, the rotor is fed through back to back converters via slip rings. The converters enable the generation control. This control property can be used to support reliable operation of a grid network system. Interarea oscillation has been a major factor in limiting power transfers in interconnected power systems. Poorly damped modes can trigger oscillatory instability, potentially leading to cascading blackouts in such systems. We consider a two-area system where DFIG based wind generation is integrated with conventional synchronous generators. A simple controller is proposed for the DFIG to improve damping of interarca oscillations. To support the proposition, case studies are conducted in Matlab/Simulink. The effectiveness of the proposed controller is then analyzed by eigenvalue analysis and verified with time domain simulation results. The results show that a properly tuned controller can increase the damping of dominant oscillatory mode by nearly 5% while improving the area transfer by about 200 MW of wind power. The results further show that with the proposed control strategy, damping of dominant oscillatory mode increased by more than 10%. / North Dakota State University. Graduate School / North Dakota State University. Department of Electrical and Computer Engineering

Thesis (M.Sc.(Engineering))--University of the Witwatersrand, Faculty of Engineering, 2000.

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Indiana University-Purdue University Indianapolis (IUPUI) / The inner structural characteristics of non-minimum phase DC-DC converters pose a severe limitation in direct regulation of voltage when addressed from a control perspective. This constraint is reflected by the presence of right half plane zeros or the unstable zero dynamics of the output voltage of these converters. The existing controllers make use of one-to-one correspondence between the voltage and current equilibriums of the non-minimum phase converters and exploit the property that when the average output of these converters is the inductor current, the system dynamics are stable and hence they indirectly regulate the voltage. As a result, the system performance is susceptible to circuit parameter and load variation and require additional controllers, which in turn increase the system complexity. In this thesis, a novel approach to this problem is proposed for second order non-minimum phase converters such as Boost and Buck-Boost Converter. Different solutions have been suggested to the problem based on whether the converter is modeled as a linear system or as a nonlinear system. For the converter modeled as a linear system, the non-minimum phase part of the system is decoupled and its transfer function is converted to minimum phase using a parallel compensator. Then the control action is achieved by using a simple proportional gain controller. This method accelerates the transient response of the converter, reduces the initial undershoot in the response, and considerably reduces the oscillations in the transient response. Simulation results demonstrate the effectiveness of the proposed approach. When the converter is modeled as a bilinear system, it preserves the stabilizing nonlinearities of the system. Hence, a more effective control approach is adopted by using Passivity properties. In this approach, the non-minimum phase converter system is viewed from an energy-based perspective and the property of passivity is used to achieve stable zero dynamics of the output voltage. A system is passive if its rate of energy storage is less than the supply rate i.e. the system dissipates more energy than stores. As a result, the energy storage function of the system is less than the supply rate function. Non-minimum phase systems are not passive, and passivation of non-minimum phase power converters is an attractive solution to the posed problem. Stability of non-minimum phase systems can also be investigated by defining the passivity indices. This research approaches the problem by characterizing the degree of passivity i.e. the amount of damping in the system, from passivity indices. Thus, the problem is viewed from a system level rather than from a circuit level description. This method uses feed-forward passivation to compensate for the shortage of passivity in the non-minimum phase converter and makes use of a parallel interconnection to the open-loop system to attain exponentially stable zero dynamics of the output voltage. Detailed analytical analysis regarding the control structure and passivation process is performed on a buck-boost converter. Simulation and experimental results carried out on the test bed validate the effectiveness of the proposed method.

No description available.

This research analyzes the linkage between power system disturbances and failures in relaying systems. The annual disturbance reports prepared by the North American Electric Reliability Council were examined. It has been found that relaying system failures plays very important role in power system cascading outages. The type of relaying system failures that are the most troublesome are the ones that have a potential to remain hidden until being exposed by some abnormal power system states to trigger relay misoperations. Each commonly used relaying scheme in transmission system is examined for any hidden failures that can lead to relay misoperations and multiple power system contingencies. Each hidden failure mode has a region, called region of vulnerability. Inside this region, some abnormal power system states can expose the hidden failure. The reach of the region depends largely on the settings of the relay in question. A method of computing the relative importance of each region of vulnerability, called vulnerability index, was proposed. The calculation of the index can be based on some measurements of power system performances. In this research, the stability measurements of the system following some contingencies that may occur in the region are chosen. With this approach, vulnerable relays can be identified. A preventive method was proposed so that the number of relay misoperations due to hidden failures and, ultimately, the number of power system disturbances can be reduced. / Ph. D.

This thesis investigates the use of real-time phasor measurements for voltage and transient stability monitoring and control. Taking advantage of the ability of a Phasor Measurement Unit (PMU) placed at a bus to sample at a fast rate the voltage and current phasors of that bus) various schemes for placing PMU's are considered and evaluated. These schemes include coherency based methods and pilot point placement techniques for system controllability. A novel scheme is proposed which places a minimal set of PMU's so as to make the system measurement model observable, and thereby linear. This placement scheme is derived from the topological observability theory. It concerns the building of a spanning measurement sub-graph across the system with actual or pseudo-measurement assigned to each of its branches. The minimal PMU set is found through a dual search algorithm which uses both a modified bisecting search and a simulated annealing-based method. The former fixes the number of PMU's while the latter look for a placement set that leads to an observable network. In order to accelerate the procedure, an initial PMU placement is provided by a graph-theoretic procedure which builds a spanning measurement sub-graph according to a depth-first search. From computer simulation results performed on various test systems, it appears that only one fourth of the system buses need to be provided with PMU's in order to make the system observable. In an effort to reduce the computing time of transient stability assessment, a dynamic equivalent is presented, which results from the elimination of the load buses provided with voltage--dependent loads. The elimination is performed through a new version of the Ward equivalencing method. In this approach, the equivalent current injections are expressed in terms of the retained bus angles and a sensitivity matrix. The non-linearity of the load flow model is accounted for through piecewise linear approximations by updating the sensitivity matrix whenever the operating point moves beyond the validity of the linearization. The expressions of the incremental changes in the generator electric power is derived. The study also investigates the possibility of using the telemetered data provided by the PMU's during pre-fault and post-fault operating conditions in conjunction with a. new version of the Extended Equal Area Criterion (EEAC) method. The latter is able to handle complex loads through the dynamic Ward equivalencing method. The performance of the approach is illustrated on three test systems which have been reduced to the internal generator nodes. / Ph. D.