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Publicações

2016

Evaluation of Advanced Control for Li-ion Battery Balancing Systems Using Convex Optimization

Autores
Pinto, C; Barreras, JV; Schaltz, E; Araujo, RE;

Publicação
IEEE TRANSACTIONS ON SUSTAINABLE ENERGY

Abstract
Typically, the unique objective pursued in either active or passive balancing is equalization of single cell charge. However, a balancing circuit may offer more control features, like virtual equalization of single cell internal resistance or thermal balancing. Such control features for balancing systems are evaluated in this paper by means of convex optimization. More than one hundred cases in a pure EV application are evaluated. Balancing circuits' efficiency models are implemented and realistic cell-to-cell parameter distributions are considered based on experimental data. Different battery sizes and driving cycles are considered. Balancing circuit topology is taken into account by selecting a specific category of energy transfer: cell-to-heat, bypass, cell-to-pack, pack-to-cell, cell-to-cell shared, cell-to-cell distributed or cell-to-pack-to-cell. In general, better results in terms of energy losses, available capacity or temperature are obtained for the last three categories, even for moderate balancing currents. In particular, remarkable improvements are observed under conditions of high power demand with high variability, i.e., smaller battery sizes and more demanding driving cycles.

2016

MASCEM: Optimizing the performance of a multi-agent system

Autores
Santos, G; Pinto, T; Praca, I; Vale, Z;

Publicação
ENERGY

Abstract
The electricity market sector has suffered massive changes in the last few decades. The worldwide electricity market restructuring has been conducted to potentiate the increase in competitiveness and thus decrease electricity prices. However, the complexity in this sector has grown significantly as well, with the emergence of several new types of players, interacting in a constantly changing environment. Several electricity market simulators have been introduced in recent years with the purpose of supporting operators, regulators, and the involved players in understanding and dealing with this complex environment. This paper presents a new, enhanced version of MASCEM (Multi-Agent System for Competitive Electricity Markets), an electricity market simulator with over ten years of existence, which had to be restructured in order to be able to face the highly demanding requirements that the decision support in this field requires. This restructuring optimizes the performance of MASCEM, both in results and execution time.

2016

Setting the Maximum Import Net Transfer Capacity under Extreme RES Integration Scenarios

Autores
Matos, MA; Bessa, RJ; Goncalves, C; Cavalcante, L; Miranda, V; Machado, N; Marques, P; Matos, F;

Publicação
2016 INTERNATIONAL CONFERENCE ON PROBABILISTIC METHODS APPLIED TO POWER SYSTEMS (PMAPS)

Abstract
In order to reduce the curtailment of renewable generation in periods of low load, operators can limit the import net transfer capacity (NTC) of interconnections. This paper presents a probabilistic approach to support the operator in setting the maximum import NTC value in a way that the risk of curtailment remains below a pre-specified threshold. Main inputs are the probabilistic forecasts of wind power and solar PV generation, and special care is taken regarding the tails of the global margin distribution (all generation all loads and pumping), since the accepted thresholds are generally very low. Two techniques are used for this purpose: interpolation with exponential functions and nonparametric estimation of extreme conditional quantiles using extreme value theory. The methodology is applied to five representative days, where situations ranging from high maximum NTC values to NTC=0 are addressed. Comparison of the two techniques for modeling tails is also comprised.

2016

Determinants of knowledge-based entrepreneurship: an exploratory approach

Autores
Moutinho, R; Au Yong Oliveira, M; Coelho, A; Manso, JP;

Publicação
INTERNATIONAL ENTREPRENEURSHIP AND MANAGEMENT JOURNAL

Abstract
We intend to further the research related to the factors that determine successful entrepreneurial endeavours by academic researchers, and thus put forth an exploratory model of Knowledge-Based Entrepreneurship (KBE). Given the lack of extant adequate indicators, a new scale was developed based on the most frequently cited constructs in the literature. A sample of 1,401 researchers from Portuguese universities was administered a questionnaire and the data collected permitted a validation with regards to the psychometric properties of the questionnaire, to see its applicability to the study. The findings suggest that the absence of a patenting history or start-up portfolio act as significant barriers to academic entrepreneurship. However, when the institutional strategy is to increase patenting and spin-off activities, the university should begin investing in creating a networking environment capable of reinforcing the researchers' Social Capital. Observing the example of successful entrepreneurs motivates other researchers to consider the possibility of developing their own ventures. The Structural Equations Modelling (SEM) approach allowed for us to identify and measure the non-linear relationships that shape the core of KBE and influence the attainment of measurable outcomes aimed at encouraging entrepreneurship. A relatively high share of the variance of the dependent variables is explained by the model, ensuring their representativeness and contributing to the state-of-art of the knowledge in this research field.

2016

Optimal Bidding of a Group of Wind Farms in Day-Ahead Markets Through an External Agent

Autores
Guerrero Mestre, V; de la Nieta, AAS; Contreras, J; Catalao, JPS;

Publicação
IEEE TRANSACTIONS ON POWER SYSTEMS

Abstract
In deregulated electricity markets, producers offer their energy to the day-ahead market. As the subsidies for renewable producers are becoming lower and lower, they have to adapt to market prices. This paper models the energy trading in the day-ahead market for wind power producers. Different strategies are proposed for this purpose: 1) several wind farms offering their energy separately to the day-ahead market; 2) the same strategy as in 1) but compensating the imbalance among different wind farms; and 3) a joint offer involving several wind farms through an external agent in order to minimize the imbalances between the offer and the final power generation. The strategies are modeled with stochastic mixed integer linear programming and Conditional Value at Risk is used to consider the risk assessment. The expected profit including risk aversion is maximized for each wind power producer and for the set of wind power producers in the case of a joint offer. A comparison of the different cases is described in detail in a case study and relevant conclusions are provided.

2016

Design and Evaluation of Novel Textile Wearable Systems for the Surveillance of Vital Signals

Autores
Trindade, IG; da Silva, JM; Miguel, R; Pereira, M; Lucas, J; Oliveira, L; Valentim, B; Barreto, J; Silva, MS;

Publicação
SENSORS

Abstract
This article addresses the design, development, and evaluation of T-shirt prototypes that embed novel textile sensors for the capture of cardio and respiratory signals. The sensors are connected through textile interconnects to either an embedded custom-designed data acquisition and transmission unit or to snap fastener terminals for connection to external monitoring devices. The performance of the T-shirt prototype is evaluated in terms of signal-to-noise ratio amplitude and signal interference caused by baseline wander and motion artefacts, through laboratory tests with subjects in standing and walking conditions. Performance tests were also conducted in a hospital environment using a T-shirt prototype connected to a commercial three-channel Holter monitoring device. The textile sensors and interconnects were realized with the assistance of an industrial six-needle digital embroidery tool and their resistance to wear addressed with normalized tests of laundering and abrasion. The performance of these wearable systems is discussed, and pathways and methods for their optimization are highlighted.

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