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Capítulos en libros This paper proposes a simplified approach to design power system stabilizers (PSSs) aimed at damping low frequency inter-area oscillations when only limited information of the power system is available. The proposed method uses a simplified two-machine test system and a robust-PSS-design method based on eigenvalue sensitivities. The proposed approach has been used to evaluate the contribution of a number of PSSs installed in Spanish generators to the damping of 0.15 Hz inter-area mode of the European system. info:eu-repo/semantics/publishedVersion

The extensive abandonment of agricultural lands in the Mediterranean basin has led to large landscapes being dominated by early-successional species, characterized by high flammability and an increasing fire risk. This fact promotes fire occurrence and places ecosystems in a state of arrested succession. In this work, we assessed the effectiveness of several restoration actions in redirecting these ecosystems toward more resilient communities dominated by resprouting species. These actions included the mechanical clearing of early-successional species, the plantation of resprouting species, and the combination of both treatments. For 13 years, we assessed shifts in the successional trajectory and ecosystem flammability by changes in: species composition, species richness, ecosystem evenness, the natural colonization of resprouting species, total biomass and proportion of dead biomass. We observed that the plantation and clearing combination was a suitable strategy to promote resilience. Species richness increased as well as the presence of the resprouting species introduced by planting. The natural colonization of the resprouting species was also enhanced. These changes in the successional trajectory were accompanied by a possible reduction of fire risk by reducing dead fuel proportion. These findings are relevant for the management of Mediterranean basin areas, but also suggest new tools for redirecting systems in fire-prone areas worldwide.

The rotary regenerator (also called the heat wheel) is an important component of energy intensive sectors, which is used in many heat recovery systems. In this paper, a model-based analysis of a rotary regenerator is carried out with a major emphasis given to the development and implementation of mathematical models for the thermal analysis of the fluid and wheel matrix. The effect of heat conduction in the direction of the fluid flow is taken into account and the influence of variations in rotating speed of the wheel as well as other characteristics (ambient temperature, airflow and geometric size) on dynamic responses are analysed. The numerical results are compared with experimental measurements and with theoretical predications of energy efficiencies. (c) 2005 Elsevier B.V. All rights reserved.

Abstract Wood pellets were pyrolyzed using a microwave oven and different microwave power, apparatus set-up and microwave absorbers (none, Fe, and carbon). Pyrolysis was realized in a short time in the presence of Fe or carbon while it was incomplete if the absorber was not present. Furthermore when the absorber was present the shape of the pellets remained unaltered while if the absorber was not employed pellets were disaggregated. Three fractions were collected from each pyrolysis: a gas, a liquid also called bio-oil and a solid called bio-char. The bio-oil contained two phases and they were quantitatively characterized through a GC/MS-FID procedure using an internal standard according to a previously reported method. HPLC/MS, FTIR and 1 H NMR spectroscopy were also employed for characterization of these liquids. Cellulose pyrolysis products were present in the upper phase such as water, acetic acid, furans (such as furfural), carbohydrates and their derivatives. Compounds from pyrolysis of lignin such as phenols and veratric acid were present in the bottom phase. The microwave assisted pyrolysis showed the possibility to efficiently convert wood pellets in different products. The main economical important components may be separated and used as chemicals, natural drugs or pesticides, while the remaining components, the solid and the gas may be used for energy production (solid and bio-oil). Solid may be also used for carbon sequestration.

Artículos en revistas When facing any forecasting problem not only is accuracy on the predictions sought. Also, useful information about the underlying physics of the process and about the relevance of the forecasting variables is very much appreciated. In this paper, it is presented an automatic specification procedure for models that are based on additivity assumptions and piecewise linear regression. This procedure allows the analyst to gain insight about the problem by examining the automatically selected model, thus easily checking the validity of the forecast. Monte Carlo simulations have been run to ensure that the model selection procedure behaves correctly under weakly dependent data. Moreover, comparison over other well-known methodologies has been done to evaluate its accuracy performance, both in simulated data and in the context of short-term natural gas demand forecasting. Empirical results show that the accuracy of the proposed model is competitive against more complex methods such as neural networks. info:eu-repo/semantics/publishedVersion

Dual active bridge converters enable bidirectional power flow in buck and boost operating modes. This paper presents an advanced switching sequence and burst-mode strategy to balance conduction, switching, and magnetic losses under light, medium, and heavy loading conditions, leading to improved operating efficiency. The implementation of the switching sequence employs the natural state-plane trajectories of the converter and contributes to higher efficiency and the ability to perform burst mode. The proposed switching sequences improve the overall efficiency of the converter by enabling soft switching and adjusting the frequency to match the minimum RMS transformer current in the full operating range. Furthermore, it incorporates a fully controlled burst-mode switching sequence for light loading conditions to further extend the efficiency gains. As a result, maximum efficiency is obtained by taking advantage of all the possible switching structures of the converter. The analysis provides insight into the natural trajectories of the converter, which produce soft-switching transitions and enable the converter structures to achieve the target operating point directly. Simulation and experimental results are presented to validate the benefits of the switching sequence and illustrate the burst-mode operation.

Artículos en revistas To achieve an effective integration of the electric vehicle in the grid, not only technical issues must be solved, but also a new regulatory context and business models must be proposed. This paper proposes two electric vehicle integration business models; one resembles the mobile-phone business, while the other is more based on current practices in the electricity-supply business. Decomposition into three layers: physical, management, and business, is used to describe those business models. Furthermore, electric vehicle charging scenarios are presented to illustrate how the proposed business models fit in each of the potential situations. Finally, several practical study cases are presented. info:eu-repo/semantics/publishedVersion

Artículos en revistas South America is one of the most dynamic regions for the joint development of natural gas and electricity. Gas is abundant in the region, although unevenly distributed (see Figure 1), with significant new reserves projected in Brazil (in its Pre-Salt basins) and in Argentina (shale gas). Unconventional gas reserves in South America are estimated at 1,430 trillion ft3. info:eu-repo/semantics/publishedVersion