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Publications

2019

Strategic bidding of virtual power plant in energy markets: A bi-level multi-objective approach

Authors
Shafiekhani, M; Badri, A; Shafie Khah, M; Catalao, JPS;

Publication
INTERNATIONAL JOURNAL OF ELECTRICAL POWER & ENERGY SYSTEMS

Abstract
This paper represents a model for finding the strategic bidding equilibrium of a virtual power plant in a joint energy and regulation market in the presence of rivals. A bi-level mathematical program with equilibrium constraints (MPEC) is represented for modeling the behavior of each producer. The upper level deals with profit maximization of each strategic unit and the lower level encompasses social welfare maximization. This is the first objective of the presented model. Power transfer distribution factors (PTDFs) are employed to model transmission constraints. The proposed bi-level problem is converted to a traceable mixed integer linear programming problem using duality theory and Karush-Kahn-Tucker (KKT) optimization conditions. Simultaneous solution of all MPECs forms an equilibrium problem with equilibrium constraints (EPEC). Solving the resulting EPEC using diagonalization algorithm and game theory, a market Nash equilibrium is obtained. Another goal is to solve the bi-level problem in a bi-objective way using the augmented epsilon constraint method, which maximizes the profit and minimizes the emissions of virtual power plant units. The proposed model is tested on a standard IEEE-24 bus system and the results indicate that, at the equilibrium point, the profit of a virtual power plant and GenCo will be less than in the initial state.

2019

A contextual family tree visualization design

Authors
Borges, J;

Publication
INFORMATION VISUALIZATION

Abstract
With the increase in availability of online national archives and software to manage genealogical records, genealogy studies are growing in popularity. While conducting research, genealogists communicate their findings either in written narratives or in genealogical charts. In that context, visualization methods can be very effective for promoting the understanding of the intricacies of a family tree and the relations among its individuals. Most of the software designed for genealogy provides a collection of standard charts to plot family trees, despite having limited analysis capabilities in general. In addition, most of the research in family tree visualization designs have been focused on methods to represent very large trees in a restricted space. Herein, we propose the contextual family tree, a new visualization design for family trees that represents individuals and their spouses with enhanced details about their families' context. The design was developed through an iterative prototype-evaluation design cycle. For illustrating the potential of our new visualization design, we used contextual family trees created from publicly available genealogical data communication files, showing that the design can be useful to provide a better understanding of the data and also for validating the consistency of the genealogical data.

2019

Simulation under Arbitrary Temporal Logic Constraints

Authors
Brunel, J; Chemouil, D; Cunha, A; Macedo, N;

Publication
ELECTRONIC PROCEEDINGS IN THEORETICAL COMPUTER SCIENCE

Abstract
Most model checkers provide a useful simulation mode, that allows users to explore the set of possible behaviours by interactively picking at each state which event to execute next. Traditionally this simulation mode cannot take into consideration additional temporal logic constraints, such as arbitrary fairness restrictions, substantially reducing its usability for debugging the modelled system behaviour. Similarly, when a specification is false, even if all its counter-examples combined also form a set of behaviours, most model checkers only present one of them to the user, providing little or no mechanism to explore alternatives. In this paper, we present a simple on-the-fly verification technique to allow the user to explore the behaviours that satisfy an arbitrary temporal logic specification, with an interactive process akin to simulation. This technique enables a unified interface for simulating the modelled system and exploring its counter-examples. The technique is formalised in the framework of state/event linear temporal logic and a proof of concept was implemented in an event-based variant of the Electrum framework.

2019

Seismic refraction traveltime tomography processing of apollo 14 and 16 active seismic experiment data

Authors
Moura, R; Almeida, F; Teixeira, L;

Publication
International Multidisciplinary Scientific GeoConference Surveying Geology and Mining Ecology Management, SGEM

Abstract
The American NASA Apollo missions to the lunar surface, between 1969 and 1972 greatly increased the knowledge of the Moon as well as that of our own Earth’s age and origins. Part of the scientific research used geophysical techniques to help define the structure of the Moon, both deep and also regarding the near surface. One such experimentation that was carried out, on both Apollo 14 and Apollo 16, as part of the Apollo Lunar Seismic Experiment Package (ALSEP), was the Active Seismic Experiment (ASE). The ASE comprised of three geophones, planted at approximately 45m apart along a longitudinal line, that recorded signals from small explosive charges deployed at specific distances in between the geophones, The analysis resulted in a set of traveltimes, from source to receiver, that were later interpreted using the intercept time method. Since then the data set results were accepted. The development of traveltime tomographic techniques in the early 1990’s allows for models to have a more realistic appearance with both lateral variations of seismic velocity as well as increasing velocities with a certain gradient in depth. This is opposed to the sharp sudden increases of compressional wave velocity typical of the intercept time method’s assumption. Herein we will present a discussion as well as the results of the reinterpretation of the Apollo 14 and 16 ASE refraction traveltimes using traveltime tomography techniques. © SGEM2019.

2019

Loss Mechanisms of Optical Waveguides Inscribed in Fused Silica by Femtosecond Laser Direct Writing

Authors
Amorim, VA; Maia, JM; Viveiros, D; Marques, PVS;

Publication
JOURNAL OF LIGHTWAVE TECHNOLOGY

Abstract
Optical waveguides directly written in fused silica using a femtosecond laser were characterized from 350 to 1750 nm to gain insight on the waveguide's loss mechanisms and their dependence on processing parameters, such as pulse energy, scan velocity, and annealing temperature. Two major loss mechanisms were identified. In the range of parameters tested, high pulse energy was seen to improve coupling losses at long wavelengths, while high scan velocity has a negative effect in both Rayleigh scattering and coupling losses at long wavelengths. Thermal annealing of the waveguides demonstrated an improvement of the Rayleigh scattering at a cost of higher coupling losses at long wavelengths. Wavelength independent Mie scattering was also observed, evolving negatively with pulse energy. A minimum Rayleigh scattering coefficient of approximate to 0.5 dB.cm(-1).mu m(4) (approximate to 0.08 dB.cm(-1).mu m(4) for thermally treated waveguides) together with a Mie scattering coefficient of approximate to 0.2-0.65 dB/cm are reported.

2019

Wind balancing costs in a power system with high wind penetration - Evidence from Portugal

Authors
Frade, PMS; Pereira, JP; Santana, JJE; Catalao, JPS;

Publication
ENERGY POLICY

Abstract
The growth of intermittent renewable power generation has been drawing attention to the design of balancing markets. Portugal is an interesting case study because wind generation already accounts for a high fraction of demand (23% in 2012-2016), but still there are no economic incentives for efficient wind forecasting (wind balancing costs are passed to end consumers). We analyze the evolution of the balancing market from 2012 to 2016. Using actual market data, we find wind balancing costs around 2 euros per MWh of generated energy. One main reason for these low costs is the existence of a robust transmission grid, which allows for the compensation of positive with negative wind imbalances across the system. Nevertheless, the results suggest that final consumers could save several million euros per year if wind generators were made responsible for the economic cost of their imbalances, in line with other European markets.

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