L.M. Ferreira

A Comparison Between Chronological and Probabilistic Methods to Estimate Wind Power Capacity Credit

In this paper, the issue of the capacity credit provided by wind energy conversion systems (WECS) is addressed. A chronological method of post-evaluation of the capacity credit is presented and compared with a pre-evaluation probabilistic method. The proposed chronological approach is based on the computation of the WECS capacity factor (ratio between average and total output) over some relevant time period. An appropriate choice of the time interval-for instance, the peak load hours-will lead to a closer approximation of the capacity credit. The comparison is illustrated with two case studies, concerning the Portuguese electric system. The analysis of the theoretical background of both methods and the results obtained allow the conclusion that chronological methods are best designed to assist system operators, whereas probabilistic methods, which are developed within the logic of the public system avoided resources, are a helping tool for system planners.

Optimal distribution network expansion planning under uncertainty by evolutionary decision convergence

We address the problem of distribution network expansion planning under uncertainty and present a new methodology capable of dealing with uncertainty in a realistic complex problem. Uncertainty is represented by a set of scenarios. A strategic objective problem is then formulated to fit the availability of reliable first stage information. An evolutionary algorithmic procedure is proposed to find a robust decision policy; by successive adjustments to the scenarios structure, convergence is achieved for the first stage decisions. A comprehensive example is presented to illustrate the convergence process and the robustness of the achieved decision.

Distributed Energy Resources Integration Challenges in Low-Voltage Networks: Voltage Control Limitations and Risk of Cascading

The integration of distributed energy resources (DER) in low-voltage networks is expected to increase significantly in the next few years. It is known that the large-scale integration of DER in conventional low-voltage (LV) networks poses many challenges such as voltage rise. To mitigate voltage rise caused by DER, utilities are defining simple voltage regulation strategies such as disconnecting DER when phase voltages rise above a defined threshold. In this paper, we model LV networks as three-phase unbalanced circuits and illustrate that such local regulation strategies may cause the cascading of the DER in a feeder. We then propose an optimal control approach to avoid cascading and optimize DER availability. Local control approaches are discussed in the context of global DER availability and their limitations are illustrated.

On spanning-tree recombination in evolutionary large-scale network problems - application to electrical distribution planning

We report the key algorithms involved in the recombination-based evolutionary software developed for planning electrical distribution networks. We focus on the dimensionality problem of large-scale networks and on the specificities of its search space. We report the difficulties in handling topology constraints and present both the geno-type and the operators to overcome such difficulties. The operators are designed to process meaningful topological information as geno-type substructures and turn the radiality and connectivity into genetic transmissible properties. First, a theoretical example is presented to illustrate important differences between other common approaches and the approach taken. Then, a real electrical industry application is presented to illustrate the ability of the approach to handle large-scale distribution-network problems.

An Artificial Neural Network Approach for Short-Term Electricity Prices Forecasting

This paper presents an artificial neural network approach for short-term electricity prices forecasting. In the new deregulated framework, producers and consumers require short-term price forecasting to derive their bidding strategies to the electricity market. Accurate forecasting tools are required for producers to maximize their profits and for consumers to maximize their utilities. A three-layered feedforward artificial neural network, trained by the Levenberg-Marquardt algorithm, is used for forecasting the next 168 hour electricity prices. We evaluate the accuracy of the price forecasting attained with the proposed approach, reporting the numerical results from a real-world case study based on an electricity market.

Preparation and characterization of polyethylene based graft copolymers. Applications in the immobilization of enzymes

Abstract In the last few years new copolymeric supports for the immobilization of biological compounds have been developed. The graft copolymer polyethylene-g.co-hydroxyethyl methacrylate, partially hydrolyzed, has shown to be a very promising support for this purpose. The more recent work in the preparation and characterization of this copolymer, as well as the immobilization of a lipase, is reported in this paper. Branches of poly(hydroxyethyl methacrylate) were grafted onto low density polyethylene by using gamma radiation. The influence of the presence and absence of air, as well as the monomer concentration on the yield of grafting were evaluated. The obtained copolymers were characterized by DSC and FTIR. The influence of the support properties on the synthesis biocatalytic activity was detected.

Profit-Based Short-Term Hydro Scheduling considering Head-Dependent Power Generation

This paper is on the problem of short-term hydro scheduling, particularly concerning head-dependent reservoirs under competitive environment. We propose a method, based on nonlinear programming, for optimizing power generation efficiency. The proposed method considers not only that the hydroelectric power generation is a function of the water discharge and of the head, but also that the maximum power generation is head-dependent. Numerical results based on a realistic cascaded hydro system illustrate the proficiency of the proposed method.

Dose determination by Monte Carlo — a useful tool in gamma radiation process

Abstract This paper presents results from absorbed dose calculations carried out using the Monte Carlo N-particles (MCNP) code in the Portuguese Gamma Irradiation Facility. The computer running time was chosen in such a way that the statistical errors were always less than 5%. Dose measurements using Amber Perspex and ceric-cerous dosimeters were performed in order to validate the calculations. Simulated and experimental data show good agreement even at positions with a high gradient dose. This fact indicates that the model is reliable. Consequently: (a) the code was used in a correct way; (b) source and geometry of the installation were well defined; and (c) dimension, composition and density of the product were correctly established. The amount of experimental work with dosimeters can thus be reduced. The results show that Monte Carlo simulations can be used as a predictive tool of dose measurements in an irradiation plant. However, some validation measurements must be performed.

Profit-Based Unit Commitment with Emission Limitations: A Multiobjective Approach

This paper is on the problem of profit-based unit commitment with emission limitations. We propose a multiobjective approach to handle the problem with conflicting profit and emission objectives. A trade-off curve between profit and emission in a way to aid decision-makers concerning emission allowance trading is obtained due to this multiobjective approach. Numerical results based on the standard IEEE 30-bus test system illustrate the proficiency of the proposed approach.

Monte Carlo studies of the irradiator geometry of the Portuguese Gamma Irradiation Facility

Abstract This paper describes a complete Monte Carlo study of the irradiator geometry of the Portuguese Gamma Irradiation Facility, using the MCNP code. In this work, eight different source rack configurations were simulated. Routine and non-routine irradiations have been studied. For routine irradiations, both the dose per source activity and the dose uniformity remain constant for all source configurations studied. For non-routine irradiations some dependence on source configuration has been found concerning the dose uniformity in the inner rows.