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Doubly-fed induction generators (DFIGs) are widely used in wind turbine systems. Traditionally, they rely on the grid voltage to operate. However, the increasing penetration of renewables necessitates wind turbines that can contribute to grid stability, and grid-forming control (GFM) has emerged as an attractive solution. Traditionally, the GFM control of DFIGs has been proposed as a single-loop control of the rotor flux magnitude and orientation, while double-loop schemes based on virtual impedance or virtual admittance have been scarcely investigated. This paper analyzes the operation and small-signal stability of a virtual-impedance-based dual-loop GFM control for DFIG. The small-signal impedance-model is derived and used to analyze the system stability in case of strong and weak grid connection. Electromagnetic transient simulations on a 1.5 MW wind turbine system are presented to validate the analysis.

Abstract Thermal energy storage (TES) will improve the efficiency and output of solar power plants. TES based on thermochemical cycles is an interesting option as thermochemical cycles can provide high energy storage densities and allow longer heat storage time. The use of multivalent solid oxide reduction–oxidation (REDOX) reactions for thermochemical heat storage is a promising option. Several concepts are feasible for coupling solar energy to the redox reaction. Among those a directly irradiated rotary kiln is one of the most interesting because it is able to provide high mass flow rates and high amounts of active material. A solar-heated rotary kiln was set-up and operated in the solar furnace of DLR for thermal reduction and oxidation of cobalt oxide. The redox material was fed into the reactor batch wise and reduced on-sun at temperatures of about 900 °C and re-oxidized off-sun in the same rotary kiln. Both steps were carried out in an air atmosphere. Thirty cycles were performed with one batch showing no evident degradation of the material. The results confirm that the rotary kiln is a feasible reactor set-up for the solar reduction of metal oxides and, hence, for thermochemical energy storage.

Thermokinetics of Biochar production.

The aim of the joint activity between CNR ITAE and University of Malta, funded in the framework of a bilateral agreement is the preliminary study of the possible application of thermally-activated technologies for the refrigeration of fish on-board of fishing vessels, with particular attention to the Mediterranean area. In such a context, the two partners, given their expertise in the adsorption and absorption cooling technologies, dedicated the first year of the joint project on several activities needed to define possible integration solutions on-board. The following report is then organized as follows: - Section 3 reports an analysis of the state-of-the-art concerning existing refrigeration systems currently employed in the fishing vessels' application as well as innovative activities recently performed on the possible integration of thermally-driven technologies for the refrigeration. - Section 4 focuses on the definition of possible integration between the waste heat recovered from the engines of the fishing vessel and the sorption technology for refrigeration. This analysis takes into account different possible applications, in terms of refrigeration temperatures as well as capacities. Furthermore, different possible waste heat streams at different temperature levels are investigated. - Section 5 identifies the typical working boundary conditions under which the fishing vessel operates, in terms of cooling demand, also considering different climatic zones (i.e. different geographical areas in which the vessel operates) and vessels' typology. - Section 6 investigates possible working pairs, both for adsorption and absorption technologies, which are promising for the given boundary conditions in Section 5. This activity is needed to set the operational limits that each technology and working pair cannot overcome. - Section 7 reports the calculations performed for each working pair and operating conditions, both taking into account thermodynamic constraints as well as analysing literature results on different prototypes realized and tested. - Section 8 introduces a dynamic model, implemented in TRNSYS environment, of an absorption refrigerator, which was validated and will be used in the following activities to investigate the defined schematics in Section 4. - Section 9 defines the Key Performance Indicators (KPIs) that will be used in the following activities to compare the achievable results of the different configurations.

Abstract This paper focuses on the study of an electricity market model, which evolves in T+1 stages, so that, at each stage, a continuum state of nature is possible. The decision-making framework of large consumers is considered: agents consume, they have the opportunity to produce, and the capability of signing contracts. Uncertainty on future possible stages leads to the problem being located in a filtered probability space. The aim is to reformulate the problem as a stochastic quasi-variational inequality, in order to obtain an existence result of equilibrium solutions.

Cereals, staple crops in human nutrition, are called to face manifold challenges to encounter the urgent demand of food along with a higher nutritional value ensuring the sustainability of the supply chain. In this view, research focuses on two main topics; firstly, the rise in productivity, balancing the growing demand of food, consistent with the availability of environmental resources. The second issue regards the urgency to properly cover the nutritional needs of the population which has become more sensitive to pathologies related to high-calorie eating habits and poor in valuable nutritional compounds. Faced with such important issues, it is desirable to adopt a full approach, based on projects aimed at satisfying multiple requests at once. The research here discussed concerns the development of three durum wheat genotypes in which novel properties have been combined both in the health-functional profile of the derived foods and in the milling characteristics of the grain. The project involves a group of durum wheat genotypes, in which the starch component has been modified in the amount of amylose, a polysaccharide that, together with amylopectin, constitutes the reserve starch. The high amylose genotypes are of interest due to the low glycemic profile and the prebiotic functionality of the derived foods depending on the increase in "resistant starch"; the amylose-free genotype is suitable for the design of highly digestible foods ideal for specific uses, such as nutrition for infants. These genotypes were, therefore, the subject of a further improvement breeding program focused on modifying the hardness of the seed associated with the efficiency and sustainability of grinding and the quality of the final products. In detail, three different genotypes of durum wheat have been selected:1) Soft Svevo /Sv SSIIa and 2) Soft Svevo/Sv SBEIIa combine a high amylose content with a softer kernel that results in increased resistant starch content and energy saving during the milling process. The third genotype, Soft Svevo/Sv Waxy, combines a softer kernel with free amylose starch following a novel starch digestibility profile suited for specific food categories. A marker-assisted selection based on HRM-genotyping has been performed to identify the homozygous mutants in the progenies of the three different crosses. Biochemical analyses such as the determination of total starch, resistant starch, starch damage, ?-glucan and arabinoxylan content are in progress and will be able to highlight the potential value of the selected genotypes.

The potential for global forest cover The restoration of forested land at a global scale could help capture atmospheric carbon and mitigate climate change. Bastin et al. used direct measurements of forest cover to generate a model of forest restoration potential across the globe (see the Perspective by Chazdon and Brancalion). Their spatially explicit maps show how much additional tree cover could exist outside of existing forests and agricultural and urban land. Ecosystems could support an additional 0.9 billion hectares of continuous forest. This would represent a greater than 25% increase in forested area, including more than 200 gigatonnes of additional carbon at maturity.Such a change has the potential to store an equivalent of 25% of the current atmospheric carbon pool. Science , this issue p. 76 ; see also p. 24

Artículos en revistas Numerical models of transmission-constrained electricity markets are used to inform regulatory decisions. How robust are their results? Three research groups used the same data set for the northwest Europe power market as input for their models. Under competitive conditions, the results coincide, but in the Cournot case, the predicted prices differed significantly. The Cournot equilibria are highly sensitive to assumptions about market design (whether timing of generation and transmission decisions is sequential or integrated) and expectations of generators regarding how their decisions affect transmission prices and fringe generation. These sensitivities are qualitatively similar to those predicted by a simple two-node model. info:eu-repo/semantics/publishedVersion