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Publications

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.

2019

Analyzing the Role of Microgrids to Mitigate the Effects of Forecasting Error of Renewable Distributed Generators

Authors
Lujano Rojas, JM; Dominguez Navarro, JA; Yusta, JM; Osorio, GJ; Santos, SF; Lotfi, M; Catalao, JPS;

Publication
2019 IEEE INTERNATIONAL CONFERENCE ON ENVIRONMENT AND ELECTRICAL ENGINEERING AND 2019 IEEE INDUSTRIAL AND COMMERCIAL POWER SYSTEMS EUROPE (EEEIC / I&CPS EUROPE)

Abstract
In this study, the operation of an energy system composed of a battery energy storage system (BESS) and a conventional generator to compensate the forecasting error of renewable power production has been analyzed. A scenario with low forecasting error and another with high forecasting error have been synthetically modeled and incorporated to a computational model of the energy system. The results obtained from a case study suggest that a low forecasting error could be compensated by a single BESS. However, a high forecasting error would require the installation of a controllable power source such as a conventional generator.

2019

Optimal Design of a Wide Area Measurement System Using Hybrid Wireless Sensors and Phasor Measurement Units

Authors
Bashian, A; Assili, M; Anvari Moghaddam, A; Catalao, JPS;

Publication
ELECTRONICS

Abstract
Real-time monitoring of the power system by phasor measurement units (PMUs) leads to the development of such devices in a wide area measurement system (WAMS). However, the power system observability cannot be obtained by employing only PMUs. The communication infrastructure (CI) is a significant part of the WAMS that has to be optimally designed and implemented to collect data from PMUs and deliver them to control centers. In this paper, a novel hybrid wireless sensor network is proposed for the connection of PMUs throughout the system to enable convenient and low-cost communication media. The problem of observability in the communication system is checked along with the optimal placement of PMUs in the power system to reach full observability. A hybrid wireless sensor network including plug-in powered sensor nodes (PPSNs) and energy harvesting sensor nodes (EHSNs) is utilized for increasing the reliability of the communication system. In the proposed co-optimal PMU-sensor placement problem, the main objective is to minimize the total cost of PMU placement and the related communication system, considering full observability of the power system and CI. To achieve better results, the zero-injection bus (ZIB) effect and system observability redundancy index (SORI) are considered as a constraint in the objective function. A binary-coded genetic algorithm is used for solving the proposed mixed-objective optimization problem subject to different technical operating constraints. The proposed method is examined on IEEE 13-bus and IEEE 37-bus test feeder systems. The results show the applicability and effectiveness of the proposed method compared with the conventional methods in this subject area.

2019

Successful Systems in Production Graduate Teaching

Authors
Shoker, A;

Publication
Proceedings of EduHPC 2019: Workshop on Education for High Performance Computing - Held in conjunction with SC 2019: The International Conference for High Performance Computing, Networking, Storage and Analysis

Abstract
This paper presents our experience in coordinating and teaching a novel graduate systems and computing course named 'Successful Systems in Production' (SSP). The course targets graduate students of different research interests in Computer Science. The course aims at giving a breadth knowledge on cutting-edge well-known systems in production, and exploring the potential synergies across different areas of research. Having its roots in Distributed Computing, SSP addresses those systems that overlap with other research areas like Computational Systems, Parallel Computing, Databases, Cloud Computing, Artificial Intelligence, Security, etc. SSP exhibits an agile topic selection model that fits several students' backgrounds in each academic year. The topics focus on the practical aspects of each selected system that is considered 'successful', i.e., based on its worldwide impact and technical significance. This is important for graduate students to acquire best practices in industry and academia, necessary to build practical computing systems. In the same vein, the assessment method includes a project that is based on one of the presented systems and also intersects with the student's own research plan. Based on our teaching experience and the excellent feedback of the students, we strongly recommend this graduate course to be taught at other universities. © 2019 IEEE.

2019

Long-Term Impact Evaluation of Advanced Under Frequency Load Shedding Schemes on Distribution Systems With DG Islanded Operation

Authors
Issicaba, D; da Rosa, MA; Resende, FO; Santos, B; Pecas Lopes, JAP;

Publication
IEEE TRANSACTIONS ON SMART GRID

Abstract
This paper presents a long-term impact evaluation algorithm to assess advanced under frequency load shedding (UFLS) schemes on distribution systems with intentional islanding of distributed generation (DG). The algorithm is based on a combined discrete-continuous simulation model which is utilized to verify the effect of the schemes on reliability indices such as the system average interruption frequency index, system average interruption duration index, and energy not supplied. Moreover, a polynomial neural network-based approach to advanced load shedding is implemented to support DG islanding in order to illustrate the applicability of the evaluation. Simulation results highlight the long-term effect of employing UFLS to support intentional islanding of DG using an actual network from the South of Brazil.

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