Encontrados 26 documentos, a visualizar página 1 de 3
A cyclic time-dependent Markov process to model daily patterns in wind turbine ...
Scholz, Teresa; Lopes, Vitor V.; Estanqueiro, AnaWind energy is becoming a top contributor to the renewable energy mix, which raises potential reliability issues for the grid due to the fluctuating nature of its source. To achieve an adequate reserve commitment which mitigates wind integration costs as well as to promote market participation, it is necessary to provide models that can capture daily patterns in wind power production. This paper presents a cycl...
Impact of weather regimes on the wind power ramp forecast
Couto, A.; Costa, P.; Rodrigues, L.; Lopes, Vitor V.; Estanqueiro, AnaThe stochastic nature of wind and the continuous need to balance electric generation with demand poses serious challenges to the power system operators. The impact of large wind integration into the power system is mitigated by decreasing the uncertainty associated with wind forecasts. In particular, the forecast of severe wind power ramps is important due to its impact on the energy market and grid operation ...
Modelling and identification of the dominant phenomena in hydrogen fuel-cells b...
Lopes, Vitor V.; Rangel, C. M.; Novais, Augusto Q.This paper proposes the use of the distribution of relaxation times (DRT) for the analysis of the dynamic behavior of hydrogen fuel-cells. With this aim it presents a new method to compute the DRT directly from electrochemical impedance spectroscopy (EIS) data. The method is formulated as a nonconvex complex domain optimization problem where each EIS spectra is approximated by a general fractional-order Legen...
Assessing cell polarity reversal degradation phenomena in PEM fuel cells by ele...
Travassos, Maria Antónia; Lopes, Vitor V.; Silva, R. A.; Novais, Augusto Q.; Rangel, C. M.Electrochemical impedance spectroscopy (EIS) is identified as one of the most promising in-situ diagnostics tools available for assessing fuel cell ageing and degradation. In this work, the degradation phenomena caused by cell polarity reversal due to fuel starvation of an open cathode 16 membrane electrode assembly (MEA) – low power (PEM) fuel cell (15 W nominal power) – is reported using EIS as a base techni...
Electrochemical impedance spectroscopy modeling using the dis-tribution of rela...
Lopes, Vitor V.; Rangel, C. M.; Novais, Augusto Q.This paper proposes a new approach to determine the distribution of relaxation times (DRT) directly from the electro-chemical impedance spectroscopy (EIS) data, i.e. without the use of an equivalent electrical circuit model. The method uses a generalized fractional-order Laguerre basis to represent EIS where both the parameters of the basis and their co-efficients are estimated by solving a nonconvex minimizati...
Heuristic algorithm for the piecewise linear segmentation of multiple time-seri...
Lopes, Vitor V.; Ferro, Filipa; Carvalho, M. J.; Novais, Augusto Q.This paper presents a novel algorithm for the piecewise linear segmentation of multivariate time-series and proposes its application to the analysis of hot water thermal solar systems (TSS). The ISO 9459-5:2007 norm describes a non-intrusive dynamic test for the performance assessment of TSS. This allows to characterize the system heat losses and the thermal stratification properties, as well as to predict its ...
On the use of Markov chain models for the analysis of wind power time-series
Lopes, Vitor V.; Scholz, Teresa; Estanqueiro, Ana; Novais, Augusto Q.Wind energy is becoming a top contributor to the renewable energy mix, which raises potential reliability issues for the grid due to the fluctuating and intermittent nature of its source. This paper explores the use of Markov chain models for the analysis of wind power time-series. The proposed Markov chain model is based on a 2yr dataset collected from a wind turbine located in Portugal. The wind speed, direct...
Relaxation time distribution analysis of a polymer electrolyte fuel cell stack ...
Lopes, Vitor V.; Silva, R. A.; Novais, Augusto Q.; Rangel, C. M.Electrochemical impedance spectroscopy (EIS) is an analysis technique that is commonly used as a base diagnostics technique for the in-situ analysis of the kinetic and transport properties of proton exchange membrane (PEM) fuel cells. This work proposes to use the distribution of relaxation times (DRT) as a complementary analysis technique for the interpretation of EIS data. For this purpose, the DRT is deduced...
Assessing cell polarity reversal degradation phenomena in PEM Fuel Cells by ele...
Travassos, Maria Antónia; Lopes, Vitor V.; Novais, Augusto Q.; Rangel, C. M.The mechanisms of fuel cell degradation are multiple and not well understood. Irreversible changes in the kinetic and/or transport properties of the cell are fostered by thermal, chemical and mechanical issues which constrain stability, power and fuel cell lifetime. Within the in-situ diagnostics methods and tools available, in-situ electrochemical impedance spectroscopy (EIS) is within the most promising to be...
Novel data-driven methodologies for parameter estimation and interpretation of ...
Lopes, Vitor V.; Novais, Augusto Q.; Rangel, C. M.Fuel cell based power generation systems are expected to become more widespread in the near future. Stationary fuel cells may be used as an uninterruptible or back-up power supply, or to supply micro-grids. In particular, proton exchange membrane fuel cells (PEMFC) are an attractive technology due to its high energy density, rigid and simple structure, low operating temperature and fast start-up characteristics...
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