Multilevel single phase isolated inverter with reduced number of switches

This paper proposes a cascaded single phase multilevel inverter using an off-the-shelf three-phase inverter and transformer. The concept is based on a cascaded connection of two inverter legs using a typical three phase inverter in such a way that the third leg is shared between the other two phases. The cascaded connection is achieved through an integrated series transformer with a typical three-phase transformer core. Utilization of a special transformer design has been previously proposed in the Custom Power Active Transformer. However, cascaded connection of inverter legs has not been previously investigated with such a concept. In this way, a three-leg inverter and a three-phase transformer are converted into an isolated multilevel single-phase inverter based on an unique configuration and modulation technique.Postprint (author's final draft

Synchronous frequency support of photovoltaic power plants with inertia emulation

©2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Grid stability is one of the main concerns in renewable energies. The lack of inertia and their low capability to provide frequency support has created the need for implementing new control strategies to solve this problem. In current networks, frequency and voltage support are performed through synchronous generators, which provide an inherent grid support due to the inertia presented in their mechanical rotors. Based on the same concept, renewable energies based on power converters have introduced synchronous controllers to emulate the dynamic behavior of synchronous generators and provide voltage and frequency support. However, most synchronous control strategies integrate their controllers as an add-on firmware embedded in each power converter, without presenting a coordinated synchronous performance when several converters operate in a PV power plant. The aggregation of several power converters operating with a coordinated synchronous response would be advantageous in these cases, since they can provide a harmonic response with an automatic power distribution when grid support is required. This paper presents a synchronous control strategy for photovoltaic power plants, which manages several power converters as an aggregated synchronous system.Peer ReviewedPostprint (author's final draft

Energy balancing with wide range of operation in the isolated multi-modular converter

The series-connection of modules in multilevel converters are prone to energy imbalances in the dc capacitor due to the differences between the power absorbed and consumed. In renewable energy applications where the primary source is directly connected to each module, energy imbalances can be even worse if the primary sources are affected by unpredictable weather conditions. Therefore, control strategies are required to compensate such energy imbalances, while maintaining the correct converter operation. Focusing our attention on a cascaded transformer multilevel inverter called Isolated MultiModular Converter, this paper introduces the combination of two control strategies aimed at providing a wide range of operation under imbalanced energy states. A general analytical model, including the regulation capability and differences with an existing strategy are presented to demonstrate the performance of the control proposed. The effectiveness of the proposal is validated through experimental results based on a three-phase multilevel prototype.This work was supported in part by the European Commission under Project FLEXITRANSTORE—H2020-LCE-2016-2017-SGS-774407 and Project INTERRFACE—H2020-LC-SC3-2018-ES-SCC-824330, and in part by the Spanish Ministry of Science under Project ENE2017-88889-C2-1-R.Peer ReviewedPostprint (published version

Model and control of the isolated multi-modular converter

Multi-modular converters have proven to be one of the most suitable topology to be used in high and power applications. The modularity of these configurations offer several advantages, such as: high quality voltage, redundancy and high efficiency. In these converters, the series connection of modules increase the number of voltage levels, but also the floating voltage of modules with respect the neutral point connection which may give rise to isolation issues at the DC side. Because of this, modules with two or more conversion stages are used to provide isolation and to prevent high floating voltages. However, increasing the number of conversion stages, increase also the losses and the implementation costs. In order to overcome these drawbacks, a new configuration of multi-modular converter is proposed in this paper. The proposed converter provides isolation with one conversion stage by means of using low frequency transformers in each module. The main principle behind this concept, the control structure and simulation results are presented to validate the proposed configuration.Peer ReviewedPostprint (author's final draft

Three-phase isolated multi-modular converter in renewable energy distribution systems

Multilevel converters are widely used in medium and high voltage applications. Their high performance, power quality, efficiency and smaller filters make them interesting for renewable energy distribution systems. In utility- scale photovoltaic plants, these topologies could provide multiple benefits since they are able to connect string of photovoltaic panels to independent modules. However, high floating voltages caused by high number of modules limit multilevel converters in medium and high voltage applications, since all of them are not suitable to provide isolation to each module. To offer a solution, this paper presents a novel multi-modular converter that provides multiple isolated modules connected in series through low frequency transformers to operate at medium voltage levels. This topology is able to achieve the power balancing between the connected modules and independently adjust the dc voltage of each module by means of controlling a circulating current which flows through the arms. Furthermore, the topology implemented in photovoltaic renewable energy systems and the control strategy required to regulate the circulating and the output current are presented. The main principle behind this concept and the performance of the converter are evaluated and validated through simulation and experimental results.Peer ReviewedPostprint (author's final draft

Surfactant Protein A Forms Extensive Lattice-Like Structures on 1,2-Dipalmitoylphosphatidylcholine/Rough-Lipopolysaccharide- Mixed Monolayers

Due to the inhalation of airborne particles containing bacterial lipopolysaccharide (LPS), these molecules might incorporate into the 1,2-dipalmitoylphosphatidylcholine (DPPC)-rich monolayer and interact with surfactant protein A (SP-A), the major surfactant protein component involved in host defense. In this study, epifluorescence microscopy combined with a surface balance was used to examine the interaction of SP-A with mixed monolayers of DPPC/rough LPS (Re-LPS). Binary monolayers of Re-LPS plus DPPC showed negative deviations from ideal behavior of the mean areas in the films consistent with partial miscibility and attractive interaction between the lipids. This interaction resulted in rearrangement and reduction of the size of DPPC-rich solid domains in DPPC/Re-LPS monolayers. The adsorption of SP-A to these monolayers caused expansion in the lipid molecular areas. SP-A interacted strongly with Re-LPS and promoted the formation of DPPC-rich solid domains. Fluorescently labeled Texas red-SP-A accumulated at the fluid-solid boundary regions and formed networks of interconnected filaments in the fluid phase of DPPC/Re-LPS monolayers in a Ca2+-independent manner. These lattice-like structures were also observed when TR-SP-A interacted with lipid A monolayers. These novel results deepen our understanding of the specific interaction of SP-A with the lipid A moiety of bacterial LPS

Enantioselective Palladium-Catalyzed [3C + 2C] and [4C + 3C] Intramolecular Cycloadditions of Alkylidenecyclopropanes

NOTICE: This is the peer reviewed version of the following article: Felipe Verdugo, Lara Villarino, Juan Durán, Moisés Gulías, José L. Mascareñas and Fernando López (2018), Enantioselective Palladium-Catalyzed [3C + 2C] and [4C + 3C] Intra-molecular Cycloadditions of Alkylidenecyclopropanes. ACS Catalysis, 2018, 8, 6100–6105 [DOI: 10.1021/acscatal.8b01296]. This article may be used for non-commercial purposes in accordance with American Chemical Society Terms and Conditions for self-archivingWe report a highly enantioselective [3C + 2C] intramolecular cycloaddition of alkylidenecyclopropanes (ACPs) and alkenes. The best results are obtained by using sterically demanding chiral phosphoramidite ligands derived from Vapol. Moreover, we also show that related, but less bulky, phosphoramidites can also lead to very effective [4C + 3C] cycloadditions when dienes, instead of alkenes, are used as reacting partners. The reactions provide a practical, simple, and selective access to optically active, synthetically appealing 5,5- and 5,7-bicyclic systemsThis work received financial support from the spanish MINECO grants (Nos. SAF2016-76689-R, CTQ2016-77047-P, CTQ2017-84767-P, FPU to L.V. and J.D.), Xunta de Galicia (Nos. ED431C 2017/19, 2015-CP082, and Centro Singular de Investigación de Galicia accreditation 2016-2019 ED431G/09), the ERDF and ERC (Adv. Grant No. 340055). The Orfeo-Cinqa network CTQ2016-81797-REDC, CONICYT-Becas Chile (Ph.D. grant to F.V.) and Sarah Walker (preliminary work) are also acknowledgedS

Pd-Catalyzed (3 + 2) Heterocycloadditions between Alkylidenecyclopropanes and Carbonyls: Straightforward Assembly of Highly Substituted Tetrahydrofurans

This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Catalysis, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acscatal.0c01827A Pd catalyst made from a Pd(0) source and a bulky biaryl phosphine ligand promotes highly efficient intramolecular (3 + 2) heterocycloadditions between alkylidenecyclopropanes (ACPs) and carbonyls. The annulations provide a straightforward access to fused polycyclic systems featuring β-methylene tetrahydrofuran moieties. DFT data support a pallada–ene process and shed light on the critical role of hemilabile interactions between the Pd center and the bulky biaryl phosphine. Significantly, these Pd(0) catalysts are also effective for promoting intermolecular formal cycloadditions between ACPs and trifluoromethyl ketones, thus providing for a direct entry to chiral tetrahydrofuran moieties (THFs) bearing trifluoromethyl–substituted carbonsThis work received financial support from the Spanish MINECO (SAF2016-76689-R, CTQ2017-84767-P), the Xunta de Galicia (ED431C 2017/19, 2015-CP082, Centro Singular de Investigación de Galicia accreditation 2019-2022, ED431G 2019/03, and a predoctoral Fellowship to E.d.C. and M.C.), CONICYT (grant to F.V.), and the ERDF, ERC (Adv. Grant 340055). The Orfeo–Cinqa network (CTQ2016-81797-REDC) is also acknowledgedS

The conservation status and distribution of Mediterranean saproxylic beetles

The Mediterranean Red List assessment is a review of the conservation status at regional level of approximately 6,000 species of animals and plants. This report summarizes the results for a key group of Mediterranean biodiversity: saproxylic beetles. Despite their key role in the ecosystem´s health and food chain, saproxylic beetles are still largely misunderstood and the current information gaps on these species´ population status, trends, and distribution are a reflection on how little we still know about them. The geographical scope followed for this assessment is the Mediterranean region according to the Mediterranean Basin Biodiversity Hotspot, with the exception of the Macaronesian islands, which have not been included in this study. All the obligate saproxylic beetles endemic or almost endemic to the Mediterranean region – 320 species and 1 subspecies – are included