In this thesis, controllers for power oscillation damping, transient stability improvement and power flow control by means of a Controlled Series Compensator (CSC) and and a Dynamic Power Flow Controller (DPFC) are proposed. These devices belong to the group of power system components referred to as Flexible AC Transmission System (FACTS) devices. The developed controllers use only quantities measured locally at the FACTS device as inputs, thereby avoiding the risk of interrupted communications associated with the use of remote signals for control. For power systems with one dominating, poorly damped inter-area power oscillation mode, it is shown that a simple generic system model can be used as a basis for damping- and power flow control design. The model for control of CSC includes two synchronous machine models representing the two grid areas participating in the oscillation and three reactance variables, representing the interconnecting transmission lines and the FACTS device. The model for control of DPFC is of the same type but it also includes the phase shift of the internal phase-shifting transformer of the DPFC. The key parameters of the generic grid models are adaptively set during the controller operation by estimation from the step responses in the FACTS line power to the changes in the line series reactance inserted by the FACTS device. The power oscillation damping controller is based on a time-discrete, non-linear approach which aims to damp the power oscillations and set the desired power flow on the FACTS line by means of two step changes in the line reactance separated in time by half an oscillation cycle. A verification of the proposed controllers was done by means of digital simulations using power system models of different complexities. The CSC and DPFC controllers were shown to significantly improve the small-signal- and transient stability in one four-machine system of a type commonly used to study inter-area oscillations. The CSC controller was also tested for 18 different contingencies in a 23-machine system, resulting in an improvement in both the system transient stability and the damping of the critical oscillation mode. / QC 20101112

Orientador: Percival Bueno de Araujo / Resumo: As perturbações ou variações de carga produzem oscilações eletromecânicas que devem ser amortecidas o mais rápido possível para garantir confiabilidade e estabilidade da rede. Neste trabalho apresenta-se uma análise do dispositivo FACTS Interline Power Flow Controller (IPFC) e o controlador Proporcional Integral (PI) no gerenciamento dos fluxos de potência e a influência dos Estabilizadores do Sistema de Potência (ESP) e do IPFC Power Oscillation Damping (POD) sobre a estabilidade do sistema elétrico de potência. Neste trabalho enfoca-se nos estudos de estabilidade a pequenas perturbações usando um Algoritmo Genético Adaptativo com Hiper-mutação (AGAH) para ajustar os parâmetros dos controladores suplementares de amortecimento, o Estabilizador de sistema de potência (ESPs) e o Power Oscillation Damping (POD) em forma coordenada. O AGAH tem como objetivo encontrar os parâmetros ótimos do controlador para melhorar o amortecimento fraco das oscilações de baixa frequência locais e inter-área. Neste trabalho representa-se o sistema de elétrico de potência com a inclusão do dispositivo Interline Power Flow Controller com o modelo de sensibilidade de corrente (MSC). Considera-se como sistema teste o sistema Simétrico de Duas Áreas e o sistema New England como o intuito de avaliar o algoritmo proposto. As simulações são feitas no ambiente do MatLab. Por fim, apresenta-se a comparação do algoritmo genético com o desempenho do algoritmo proposto. / Abstract: Small-magnitude disturbances happen to produce electro-mechanical oscillations which should be damped as quickly as possible to ensure reliability and stability of the network. This work presents an analysis of Interline Power Flow Controller (IPFC) FACTS device and PI controller to control and manage power flow and also how Power System Stabilizers and IPFC Power Oscillations Damping (POD) controller influence over an electric power system stability. This work focuses on small-signal stability studies using an Adaptive Genetic Algorithm with Hyper-mutation (AGAH) in order to tune controller parameters in a coordinated way ensuring proper damping. AGAH aims to find optimal controller parameters to enhance the poor damping of local and inter-area low frequency oscillations. This works represents the electric power system and Interline Power Flow Controller device by a current sensitivity model (CSM). This paper considers two areas 14 bus symmetrical power system and New England power system in order to assess proposed algorithm. Coding and Simulations take place in MatLab platform. AGAH and GA get compared by time convergence and performance. This paper shows AGAH is an interesting optimization technique which outweighs GA. / Mestre

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.

Power flow (PF) control can increase the utilization of the transmission system and connect lower cost generation with load. While PF controllers have demonstrated the ability to realize dynamic PF control for more than 25 years, PF control has been sparsely implemented. This research re-examines PF control in light of the recent development of fractionally-rated PF controllers and the incremental power flow (IPF) control concept. IPF control is the transfer of an incremental quantity of power from a specified source bus to specified destination bus along a specified path without influencing power flows on circuits outside of the path. The objectives of the research are to develop power system operation and planning methods compatible with IPF control, test the technical viability of IPF control, develop transmission planning frameworks leveraging PF and IPF control, develop power system operation and planning tools compatible with PF control, and quantify the impacts of PF and IPF control on multi-decade transmission planning. The results suggest that planning and operation of the power system are feasible with PF controllers and may lead to cost savings. The proposed planning frameworks may incent transmission investment and be compatible with the existing transmission planning process. If the results of the planning tool demonstration scale to the national level, the annual savings in electricity expenditures would be $13 billion per year (2010$). The proposed incremental packetized energy concept may facilitate a reduction in the environmental impact of energy consumption and lead to additional cost savings.