Modeling and enhanced control of hybrid full bridge–half bridge MMCs for HVDC grid studies

Modular multilevel converters (MMCs) are expected to play an important role in future high voltage direct current (HVDC) grids. Moreover, advanced MMC topologies may include various submodule (SM) types. In this sense, the modeling of MMCs is paramount for HVDC grid studies. Detailed models of MMCs are cumbersome for electromagnetic transient (EMT) programs due to the high number of components and large simulation times. For this reason, simplified models that reduce the computation times while reproducing the dynamics of the MMCs are needed. However, up to now, the models already developed do not consider hybrid MMCs, which consist of different types of SMs. In this paper, a procedure to simulate MMCs having different SM topologies is proposed. First, the structure of hybrid MMCs and the modeling method is presented. Next, an enhanced procedure to compute the number of SMs to be inserted that takes into account the different behavior of full-bridge SMs (FB-SMs) and half-bridge submodules (HB-SMs) is proposed in order to improve the steady-state and dynamic response of hybrid MMCs. Finally, the MMC model and its control are validated by means of detailed PSCAD simulations for both steady-state and transients conditions (AC and DC faults)

Finite element formulation to study thermal stresses in nanoencapsulated phase change materials for energy storage

Nanoencapsulated phase change materials (nePCMs) – which are composed of a core with a phase change material and of a shell that envelopes the core – are currently under research for heat storage applications. Mechanically, one problem encountered in the synthesis of nePCMs is the failure of the shell due to thermal stresses during heating/cooling cycles. Thus, a compromise between shell and core volumes must be found to guarantee both mechanical reliability and heat storage capacity. At present, this compromise is commonly achieved by trial and error experiments or by using simple analytical solutions. On this ground, the current work presents a thermodynamically consistent and three-dimensional finite element (FE) formulation considering both solid and liquid phases to study thermal stresses in nePCMs. Despite the fact that there are several phase change FE formulations in the literature, the main novelty of the present work is its monolithic coupling – no staggered approaches are required – between thermal and mechanical fields. Then, the FE formulation is implemented in a computational code and it is validated against one-dimensional analytical solutions. Finally, the FE model is used to perform a thermal stress analysis for different nePCM geometries and materials to predict their mechanical failure by using Rankine’s criterion

Calzadina segurai gen. nov., sp. nov. (Mollusca: Gastropoda) from the Albian of Cabanes de l'Arc (la Plana Alta, Maestrat basin, NE Spain)

Es descriu un tàxon nou, Calzadina segurai. El nou gasteròpode prové de l’Albià de Cabanes de l’Arc(la Plana Alta), de la conca sedimentària del Maestrat. Es fa la segona cita de l’escleractini Angelismiliamagnei Reig, 1995. Calzadina segurai gen. nov., sp. nov. (Mollusca: Gastropoda) from the Albian of Cabanesde l’Arc (la Plana Alta, Maestrat basin, NE Spain).A new taxon, Calzadina segurai is described. The new species comes from the Albian of Cabanes del’Arc (la Plana Alta, NE Spain), in the Maestrat basin. The scleractinian Angelismilia magnei Reig 1995is recorded here for the second time.Key words: Gastropoda, Euomphalidae, taxonomy, new genus, new species, Albian, Maestrat Basi

Retail trade. Internationalisation of retail trade

Analysis of 4 case studies : Cocoa Sampaka, Fiesta Party, Raffel Pagès, GAE

Comerç minorista. La internacionalització del comerç detallista

Anàlisi de 4 casos d'èxit: Cacao Sampaka, Party Fiesta, Raffel Pagès, GAE

Ares del Maestrat a finals del segle XIX: estructura de la riquesa i classes socials

Segones Jornades de Foment de la Investigació de la FCHS (Any 1996-1997