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( 2006) João Peças Lopes ; F. Kanellos ; N. Hatziargyriou ; Carlos Moreira ; André Guimarães Madureira ; Fernanda Resende ; X. Wu ; N. Jayawarna ; Y. Zhang ; N. Jenkins

Under normal operating conditions, a MicroGrid (MG) is interconnected with the Medium Voltage (MV) network. However, planned or unplanned events like maintenance or faults in the MV network, respectively, may lead to MG islanding. In order to deal with islanded operation and even black start following a general blackout, an emergency operation mode must be envisaged. Two possible control strategies were investigated and are described in this paper in order to operate a MG under emergency mode. A sequence of actions for a well succeeded black start procedure, involving microgeneration units, has also been identified contributing for an increase in distribution network reliability.

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Optimal design of work-in-process buffers

( 2006) Manuel Matos ; José António Pereira de Faria ; Eusébio Nunes

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Defining Control Strategies for MicroGrids Islanded Operation

( 2006) Carlos Moreira ; André Guimarães Madureira ; João Peças Lopes

This paper describes and evaluates the feasibility of control strategies to be adopted for the operation of a microgrid when it becomes isolated. Normally, the microgrid operates in interconnected mode with the medium voltage network; however, scheduled or forced isolation can take place. In such conditions, the microgrid must have the ability to operate stably and autonomously. An evaluation of the need of storage devices and load shedding strategies is included in this paper.

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Optimum Generation Control in Wind Parks when Carrying out System Operator Requests

( 2006) João Peças Lopes ; Rogério Almeida ; Edgardo Castronuovo

This paper proposes an optimized dispatch control strategy for active and reactive powers delivered by a doubly fed induction generator in a wind park. In this control approach, wind turbines are supposed to operate over a deloaded maximum power extraction curve and will respond to a supervisory wind farm control after a request from a system operator for adjusting the outputs of the wind park. The definition of the active and reactive powers operating points, for each wind turbine, is defined from an optimization algorithm that uses the primal-dual predictor corrector interior point method. The control strategy used at the wind generator level exploits a combination of pitch control and control of the static converters to adjust the rotor speed for the required operation points. A small wind park is used to illustrate the effectiveness of the developed approach.

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Integrated framework for energy loss allocation in electric distribution systems under liberalised energy markets

( 2006) Paulo Oliveira de Jesus ; Teresa Ponce Leão

This paper discusses an integrated framework for cost allocation of energy losses of electric distribution systems under liberalised energy markets. As key contribution is developed an allocation strategy based upon Locational and Uniform Incremental Prices. The locational incremental prices send efficient economical signals to distributed generators with incentives for loss minimisation and uniform incremental pricing are applied to consumers avoiding non-discriminatory access to the network due to the consumer's geographical localisation. Proposed methodology has been tested and compared with different loss allocation procedures reported in literature under the scope of the social welfare theory in order to assess its impact in the market equilibrium.

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Valuation of switchable tariff for wind energy

( 2006) ; Gerard Sheblé ; João Peças Lopes ; Manuel Matos

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Application of Monte Carlo simulation to generating system well-being analysis considering renewable sources

( 2007) Vladimiro Miranda ; Manuel João Aguiar ; Manuel Matos ; João Peças Lopes ; Armando Leite da Silva ; Luiz Antônio Manso ; Warlley S. Sales ; Leonidas Resende

This paper presents an application of Monte Carlo chronological simulation to evaluate the reserve requirements of generating systems, considering renewable energy sources. The idea is to investigate the behavior of reliability indices, including those from the well-being analysis, when the major portion of the energy sources is renewable. Renewable in this work comprises hydroelectric, mini-hydroelectric, and wind power sources. Case studies on a configuration of the Portuguese Generating System are presented and discussed. Copyright#2006 JohnWiley & Sons, Ltd.

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Network Cost Loss Allocation Methods Evaluation under the Perspective of the Social Welfare Theory

( 2007) Teresa Ponce Leão ; Paulo Manuel De Oliveira-De Jesus ; Hussein Khodr

Different ex-post methodologies have been proposed to allocate network losses. Under day-ahead pool-based electricity markets, the implementation of these procedures implies an access-pricing framework based on half-hour or hourly locational prices. Since every allocation procedure modifies the locational prices in a different way, the initial market equilibrium point is altered as a result of the price elasticity of demand. This implies that some form of cross-subsidy appears among market agents, affecting economic variables as social welfare and network remuneration. This paper aims to contribute to the regulatory assessment by means of an analysis based on the social welfare theory in order to ensure a non-discriminatory access to the network. A base scenario is obtained through an optimal power flow study with the purpose of simulating an efficient energy market, and four allocation philosophies have been considered: incremental, roll-in-embedded, tracing based and cir

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An Improved Fuzzy Inference System for Voltage/VAR Control

( 2007) Vladimiro Miranda ; André Moreira ; Jorge Correia Pereira

This paper describes the concept of a voltage/VAR controller based on an interaction of fuzzy Mamdani controllers, with the main objective of keeping voltages at all busbars inside an admissible band while avoiding line flows to exceed admissible limits. Estimation of sensitivities via fuzzy clustering of load profiles is proposed. A complex rule base interacts with a Newton-Raphson power flow routine in iterative steps until a terminating criterion is met, following a basic min-max approach. Tests to the method reveal it as one order of magnitude faster than a competing simulated annealing routine.

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A Multiple Scenario Security Constrained Reactive Power Planning Tool Using EPSO

( 2007) Hrvoje Keko ; Alvaro Duque ; Vladimiro Miranda

Evolutionary Particle Swarm Optimization (EPSO) is a robust optimization algorithm belonging to evolutionary methods. EPSO borrows the movement rules from Particle Swarm Optimization (PSO) and uses it as a recombination operator that evolves under selection. This paper presents a reactive power planning approach taking advantage of EPSO robustness, in a model that considers simultaneously multiple contingencies and multiple load levels. Results for selected problems are summarized including a trade-off analysis of results.

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Un Modelo de Planificación y Control Orientado a la Adaptación Económica de Sistemas de Distribución de Energía Eléctrica

( 2007) Vladimiro Miranda ; Gustavo Schweickardt

(in Spanish) This paper describes a method to evaluate the dynamic adaptation of a Power Distribution system in terms of its planning for a given time span of tarif control. The model requires two stages: a multiple criteria planning based on Fuzzy Dynamic Programming taking risk as a criterion and on Hierarquical Analytical Processes, and a decision phase of system adaptation control based on Decision Making within the Hierarquical Analytical Process analysis. The result is a Vector of Dynamic Adaptation of the system associated to the succession of unbalances that happen during system evolution, so that the system may remain as much as possible dynamically and economically adapted.

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A fuzzy dynamic programming approach for evaluation of expansion distribution cost in uncertainty environments

( 2007) Vladimiro Miranda ; Gustavo Schweickardt

This paper presents a new Fuzzy Dynamic Programming model that calculates the optimum solution of problems with uncertainties in data defined by fuzzy sets. The result includes the determination of an Intrinsic Risk Threshold of the solution. Extrinsic Risk Thresholds may also be set by a Decision Maker, in order to obtain more robust solutions. The technique is applied to the calculation of Distribution System expansion costs to serve the objectives of a Regulatory Authority (Regulator) in fixing levels of efficiency, targets and penalties to a regulated market.

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Strategies for power systems expansion planning in a competitive electrical market

( 2007) A. M. Andreoni ; João Tomé Saraiva ; T. J. Strada ; A. Garcia-Agreda

A new methodology is presented for decision making in long-term expansion planning. Power system expansion planning involves an intrinsic uncertainty on data and parameters, a fact often worsened by the new rules of deregulated electrical markets. The proposed proceduremodels both the uncertainty in load forecasting and the experience of the planning expert who uses fuzzy sets theory and fuzzy dynamic programming in themodel algorithm to find an optimal expansion alternative.This procedure was tested in a realistic model system and the results obtained were arranged in an expansion planning ranking list according to their membership in the decision set.

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