Planeamento Operacional de Curto Prazo de Sistemas de Energia Hidroeléctricos

Esta tese incide sobre o problema de planeamento operacional de curto prazo de sistemas de energia hidroeléctricos e os aspectos algorítmicos da sua solução. Recursos baseados em aproveitamentos hidroeléctricos com capacidades de armazenamento reduzidas são classificados como fio de água. Tipicamente, considera-se que estes recursos operam em condições estacionárias com altura de queda constante e ao nível máximo de água nos reservatórios, correspondendo, em regra e por projecto, ao ponto de operação óptimo. Contudo, é muitas vezes desejável alterar esta política, incorrendo-se, por isso, em variações da altura de queda. Devido ao reduzido volume de água nos reservatórios, a altura de queda pode variar rapidamente e a eficiência de operação torna-se sensível à altura de queda – efeito de variação da altura de queda. Assim, a potência gerada é função não só do caudal de água turbinado mas também da altura de queda. Este efeito não linear conjuntamente com a configuração hidráulica em cascata torna o problema complexo e de grande dimensão. Este estudo propõe e compara métodos de optimização baseados em programação dinâmica, linear e não linear em rede. Os resultados da simulação computacional mostram que a programação não linear em rede é o método de optimização mais apropriado.This thesis is on the problem of short-term operational planning of hydroelectric power systems and the algorithmic aspects of its solution. Resources based on hydroelectric power producers with small storage capacities are known as run-of-the-river. Typically, these resources are considered to operate under stationary conditions with constant head and at the maximum water level in the reservoirs, corresponding by design to the optimum operating point. However, it is often desirable to change this policy, thus incurring into head changes. Due to the reservoirs low volume, the head may change very fast and the operating efficiency becomes sensitive to the head – head change effect. Therefore, the power output is a function of the water discharge and also of the head. This nonlinear effect coupled with the cascaded hydro configuration tends to give to the problem complexity and huge dimension. This study proposes and compares optimization methods based on dynamic, linear and non-linear network programming. Numerical simulation results show that non-linear network programming is the most suitable optimization method

Novas Metodologias de Optimização em Sistemas de Energia Hidrotérmicos

Esta dissertação incide sobre o tema da optimização em sistemas de energia hidrotérmicos, evoluindo no contexto actual de reestruturação do sector eléctrico. Novas metodologias baseadas em optimização não linear e optimização multiobjectivo são propostas, respectivamente, para a exploração de recursos hídricos, tendo em consideração o efeito de queda, e para a exploração de recursos térmicos, tendo em consideração a restrição de emissões, concretizando assim contribuições originais para o progresso no conhecimento. Ainda, é desenvolvida uma ferramenta computacional, baseada em redes neuronais artificiais, para a previsão dos preços da energia eléctrica no apoio à decisão em ambiente competitivo. Os resultados obtidos em casos de estudo realísticos permitem concluir sobre o desempenho das novas metodologias de optimização propostas nesta dissertação

Modeling, control and simulation of full-power converter wind turbines equipped with permanent magnet synchronous generator

In this paper, two wind turbines equipped with a permanent magnet synchronous generator (PMSG) and respectively with a two-level or a multilevel converter are simulated in order to access the malfunction transient performance. Three different drive train mass models, respectively, one, two and three mass models, are considered in order to model the bending flexibility of the blades. Moreover, a fractional-order control strategy is studied comparatively to a classical integer-order control strategy. Computer simulations are carried out, and conclusions about the total harmonic distortion (THD) of the electric current injected into the electric grid are in favor of the fractional-order control strategy

Power converter topologies for wind energy conversion systems: Integrated modeling, control strategy and performance simulation

This paper presents new integrated model for variable-speed wind energy conversion systems, considering a more accurate dynamic of the wind turbine, rotor, generator, power converter and filter. Pulse width modulation by space vector modulation associated with sliding mode is used for controlling the power converters. Also, power factor control is introduced at the output of the power converters. Comprehensive performance simulation studies are carried out with matrix, two-level and multilevel power converter topologies in order to adequately assert the system performance. Conclusions are duly drawn

Transient analysis of variable-speed wind turbines at wind speed disturbances and a pitch control malfunction

As wind power generation undergoes rapid growth, new technical challenges emerge: dynamic stability and power quality. The influence of wind speed disturbances and a pitch control malfunction on the quality of the energy injected into the electric grid is studied for variable-speed wind turbines with different power-electronic converter topologies. Additionally, a new control strategy is proposed for the variable-speed operation of wind turbines with permanent magnet synchronous generators. The performance of disturbance attenuation and system robustness is ascertained. Simulation results are presented and conclusions are duly drawn. (C) 2010 Elsevier Ltd. All rights reserved

Fractional-order control and simulation of wind energy systems with PMSG/full-power converter topology

This paper presents a new integrated model for the simulation of wind energy systems. The proposed model is more realistic and accurate, considering a variable-speed wind turbine, two-mass rotor, permanent magnet synchronous generator (PMSG), different power converter topologies, and filters. Additionally, a new control strategy is proposed for the variable-speed operation of wind turbines with PMSG/full-power converter topology, based on fractional-order controllers. Comprehensive simulation studies are carried out with matrix and multilevel power converter topologies, in order to adequately assert the system performance in what regards the quality of the energy injected into the electric grid. Finally, conclusions are duly drawn

A Pitch Control Malfunction Analysis for Wind Turbines with Permanent Magnet Synchronous Generator and Full-power Converters: Proportional Integral Versus Fractional-order Controllers

A transient analysis for two full-power converter wind turbines equipped with a permanent magnet synchronous generator is studied in this article, taking into consideration, as a new contribution to earlier studies, a pitch control malfunction. The two full-power converters considered are, respectively, a two-level and a multi-level converter. Moreover, a novel control strategy based on fractional-order controllers for wind turbines is studied. Simulation results are presented; conclusions are in favor of the novel control strategy, improving the quality of the energy injected into the electric grid

Comparative study of power converter topologies and control strategies for the harmonic performance of variable-speed wind turbine generator systems

Power converters play a vital role in the integration of wind power into the electrical grid. Variable-speed wind turbine generator systems have a considerable interest of application for grid connection at constant frequency. In this paper, comprehensive simulation studies are carried out with three power converter topologies: matrix, two-level and multilevel. A fractional-order control strategy is studied for the variable-speed operation of wind turbine generator systems. The studies are in order to compare power converter topologies and control strategies. The studies reveal that the multilevel converter and the proposed fractional-order control strategy enable an improvement in the power quality, in comparison with the other power converters using a classical integer-order control strategy. (C) 2010 Elsevier Ltd. All rights reserved

Protection of wind energy systems against the indirect effects of lightning

This paper is concerned with the protection of wind energy systems against the indirect effects of lightning. As wind energy is gaining increasing importance throughout the world, lightning damages involving wind energy systems have come to be regarded with more attention. Nevertheless, there are still very few studies in Portugal regarding lightning protection of wind energy systems using models of the Electro-Magnetic Transients Program (EMTP). Hence, a new case study is presented in this paper, based on a wind turbine with an interconnecting transformer, considering that lightning strikes the soil near the tower at a distance such that galvanic coupling occurs through the grounding electrode. Computer simulations obtained by using EMTP-RV are presented and conclusions are duly drawn. (C) 2011 Elsevier Ltd. All rights reserved

Lightning Data Observed With Lightning Location System in Portugal

This paper presents an investigation into cloud-to-ground lightning activity over the continental territory of Portugal with data collected by the national Lightning Location System. The Lightning Location System in Portugal is first presented. Analyses about geographical, seasonal, and polarity distribution of cloud-to-ground lightning activity and cumulative probability of peak current are carried out. An overall ground flash density map is constructed from the database, which contains the information of more than five years and almost four million records. This map is compared with the thunderstorm days map, produced by the Portuguese Institute of Meteorology, and with the orographic map of Portugal. Finally, conclusions are duly drawn