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The neutral-point-clamped (NPC) dual-active-bridge (DAB) converter with hybrid semiconductors (Si and SiC devices) is a promising topology for high-power energy storage systems. The triple-phase-shift (TPS) modulation can achieve high efficiency with zero-voltage switching (ZVS) by adjusting three phase shift angles. However, when applied to hybrid DAB topologies, switching and conduction losses are too high. In this paper, a hybrid modulation method using duty ratio and phase-shift is proposed to improve the efficiency of the hybrid NPC DAB converter. The Si and SiC devices on the primary NPC bridges work under different duty ratios with staggered switching instants so that the Si devices do not suffer from the high turn-off current, and the SiC devices benefit from less conduction time. The neutral current path is used to take over the negative current which flows through SiC body diodes under TPS. Switching and conduction losses under the proposed hybrid TPS modulation are compared. A 2-kW hardware prototype is built to verify the proposed hybrid modulation.

Distributed generation systems integrated into the modern electrical grid demand novel circuit architectures that can combine high efficiency and high power density together. The transformerless highly efficient and reliable inverter concept (HERIC) topologies are notable due to their mitigated leakage current concerns, constant common-mode voltage, and high efficiency. Nonetheless, the HERIC-based structures feature a maximum of three-level ac output voltage, forcing the conversion system to integrate large output filters to meet the grid codes. This article introduces a novel HERIC active-clamped converter with bidirectional power flow and full reactive power capabilities that can achieve five-level output voltage. This is accomplished by means of a phase-shifted pulsewidth modulation technique that effectively doubles the apparent switching frequency of the inverter and improves the quality of the injected ac power. Consequently, the topology can achieve higher power conversion efficiency, while using the same or a smaller output filter. To verify the feasibility of the proposed converter, a 2.5-kW SiC-based prototype was built and tested in the laboratory under different operation conditions.

Les excavacions del Centre d’Estudis Lacetans (CEL) als jaciments de Sant Miquel de Sorba i Castellvell d’Olius han permès obtenir noves dades sobre el període ibèric tardà al territori lacetà. Es tracta d’assentaments amb una ocupació intensa i renovada al llarg dels segles II-I aC, que han proporcionat abundant material arqueològic, el qual inclou interessants lots de ceràmiques importades o d’objectes considerats com a militaria. A partir d’aquí, es planteja una reflexió sobre la naturalesa d’aquests nuclis ibèrics tardans i la interpretació de la seva funció en relació amb la dinàmica d’implantació romana a la zona.

The unique advantages of modular multilevel converters (MMCs) have led to wide adoption of the converter topology in high voltage dc (HVDC) transmission systems, with great potential for use in medium voltage motor drive and dc grid applications. Inspired by the structure of the MMC, many extended converter topologies have been developed in the literature. These include, in addition to conventional parallel multiphase connection, a variety of series-connected topologies. Extended MMCs integrate the modular nature of cascaded SMs of the MMC but with different topology structure leading to substantially different operating principles. Given the growing number of such topologies, this paper provides a critical review of MMC derived topologies and summarizes individual advantages and disadvantages. The control schemes and application fields of these different topologies are analysed. This review facilitates the classification and understanding of extended MMCs and provides the necessary scaffold for the development of a general framework for new topologies and applications based on the MMC.

Within the project ‘Transdisciplinary and experimental study of firing structures in the western Mediterranean during Protohistory (1st millennium BC)’, the TRANSCOMB project is an experimental research programme conducted at the Ciutadella Ibèrica (Iberian Citadell) of Calafell Archaeological Site (Tarragona, Spain) (See Figure 1 and Figure 2). The main objective of the research is to deepen our knowledge of how Iron Age combustion structures worked and were used by protohistoric communities living in the western Mediterranean. Six hearths and one oven, made with mud and other materials, such as crushed pottery and pebbles, were built inside buildings and outdoors. Later, they were put to use employing diverse types of fuels, while measuring time and temperatures reached under different conditions. Diverse analyses are being applied to samples taken from the experimental combustion structures.

The modular multilevel converter (MMC) is currently one of the power converter topologies which has attracted more research and development worldwide. Its features, such as high quality of voltages and currents, high modularity and high voltage rating, have made the MMC a very good option for several applications including high-voltage dc (HVdc) transmission, static compensators (STATCOMs), and motor drives. However, its unique features such as the large number of submodules, floating capacitor voltages, and circulating currents require a dedicated control system able to manage the terminal variables, as well as the internal variables with high dynamical performance. In this paper, a review of the research and development achieved during the last years on MMCs is shown, focusing on the challenges and proposed solutions for this power converter still faces in terms of modeling, control, reliability, power topologies, and new applications.

The increasing importance of cascaded multilevel converters (CMCs), and the sub-category of modular multilevel converters (MMCs), is illustrated by their wide use in high voltage DC connections and in static compensators. Research is being undertaken into the use of these complex pieces of hardware and software for a variety of grid support services, on top of fundamental frequency power injection, requiring improved control for non-traditional duties. To validate these results, small-scale laboratory hardware prototypes are often required. Such systems have been built by many research teams around the globe and are also increasingly commercially available. Few publications go into detail on the construction options for prototype CMCs, and there is a lack of information on both design considerations and lessons learned from the build process, which will hinder research and the best application of these important units. This paper reviews options, gives key examples from leading research teams, and summarizes knowledge gained in the development of test rigs to clarify design considerations when constructing laboratory-scale CMCs.

The growing relevance of voltage source converters (VSCs), and the deep impact they have on the development and maintenance of the electrical grid, increase the necessity of further research on how to deal with nonideal grid conditions from the VSCs control. This paper is aimed to summarize the basic techniques and schemes that might be required for a grid-connected VSC to work under these conditions: grid synchronization schemes, sequence decomposition, current reference generation, and current controllers. At the same time, some alternative schemes that improves the basic ones are cited. Modelling and the two typical current controllers design and tuning under stationary and synchronous reference frames are also exhibited. Given the importance of the current control stage in the VSC behaviour, five control schemes, designed to track negative sequence currents, are shown and tested in simulation and experiments. According to the experiments, it is shown that the standard proportional-resonant controller achieves the best performance in negative sequence tracking due to the robustness of its non-ideal version, the improved implementation thanks to the delta operator, and the non-dependence on grid-synchronization schemes. Alternatively, one approach based on dual synchronous reference frame is also highlighted for easiness of implementation and good performance.

Hybrid modular multilevel converters (HMMC) address the DC-fault blocking limitations of the half-bridge submodules (HB-SMs) of the standard MMC by combining HB-SMs with full-bridge submodules (FB-SMs). In order to improve the overall conversion efficiency, this article proposes two low-loss configurations for the HMMC. The main improvement in the proposed HMMCs is achieved by the combination of low-loss unipolar and low-loss bipolar SMs in the same arm of the HMMC. It is shown that the simplest structure (LLH1) can reduce the SM losses (switching and conduction losses in an SM) by 30% compared to the HMMC at the cost of limited fault blocking capabilities. The fully controlled structure (LLH2) reduces SM losses by 10% compared to the HMMC, and 30% compared to the FBSM-based MMC. These results represent an increase of 20% over the typical HBSM-based MMC for a converter (LLH2) that can provide fault-blocking capabilities. Assessment of efficiency in both HMMCs is provided over a range of operating conditions both in inverter and rectifier mode from an 800-MVA HVDC system model.

Se presentan los resultados históricos derivados de la primera fase de la investigación sobre este importante yacimiento, realizada exclusivamente a partir de métodos no invasivos. Los datos recuperados a partir de la prospección pedestre y geofísica han permitido verificar la condición urbana del asentamiento, atestiguada tanto por sus dimensiones como por su complejidad estructural y la naturaleza de los materiales muebles recuperados, que sugieren actividades económicas especializadas y la coexistencia de distintos sectores sociales. La desaparición del asentamiento en torno a 200 a. C. confirma el profundo impacto de la conquista romana en los patrones de poblamiento del mundo ibérico septentrional.

This paper presents a new finite control set model predictive control strategy that, contrary to conventional approaches, achieves (i) zero steady-state error in the converter's AC current, and (ii) both fixed and lower harmonic spectrum, similar to that achieved by pulse width modulation based control schemes. These characteristics are attractive for medium and high voltage applications where high dv/dt is prohibitive and reduced switching losses are a must, or in applications that use passive filters and where a spread harmonic spectrum can cause resonances. The proposed strategy achieves dynamic results similar to those of conventional predictive control and a steady-state performance similar to that of a modulated control strategy. To do so, the strategy utilizes a modulated integral action to incorporate an input restriction into a conventional predictive control cost function. A grid-connected cascaded H-Bridge multilevel inverter is used to validate the strategy. Simulated and experimental results in both steady and transient states are presented to verify the proposed strategy's performance in the converter.

This paper proposes a simplified four-level (S4L) inverter based dynamic voltage restorer (DVR). In the proposed configuration, the dual buck stage can output full, two thirds, and one third of dc link voltage. Including the zero voltage provided by the two-level inverter, the output of the proposed inverter can be four levels. With the same switching frequency, the S4L inverter based DVR achieves better performance than the existing two-level and three-level inverters based DVRs. Moreover, compared with the existing four-level inverter based DVRs, it requires less active switches/diodes and only requires a single DC power source. The experimental results are provided for the validation of the proposed system.

En els darrers 25 anys, el Centre d’Estudis Lacetans està desenvolupant un projecte de recerca programada sobre l’estructura del poblament ibèric a la comarca del Solsonès. Això ha permès caracteritzar la seva evolució des de la primera edat del ferro fins al període ibèric tardà. Es constata que el segle III aC constitueix un moment àlgid, amb un elevat nivell de densitat i complexitat organitzativa. Tot apunta que en el territori lacetà es dona un panorama de forta fragmentació política, amb diverses entitats territorials que s’organitzen al voltant de nuclis de primer ordre, com els de Sorba, Castellvell o el Cogulló, sense evidències clares d’una centralització similar a la dels territoris costaners.

The circuit topology of a submodule (SM) in an modular multilevel converter (MMC) defines many of the functionalities of the complete power electronics conversion system and the specific applications that a specific MMC configuration can support. Most prominent among all applications for the MMC is its use in high-voltage direct current (HVDC) transmission systems and multiterminal dc grids. The aim of the paper is to provide a comprehensive review and classification of the many different SM circuit topologies that have been proposed for the MMC up to date. Using an 800-MVA, point-to-point MMC-based HVDC transmission system as a benchmark, the presented analysis identifies the limitations and drawbacks of certain SM configurations that limit their broader adoption as MMC SMs. A hybrid model of an MMC arm and appropriate implementations of voltage-balancing algorithms are used for detailed loss comparison of all SMs and to quantify differences among multiple SMs. The review also provides a comprehensive benchmark among all SM configurations, broad recommendations for the benefits and limitations of different SM topologies which can be further expanded based on the requirements of a specific application, and identifies future opportunities.

The idea to create the Experimental Camp of Protohistory (CEP) emerged in late 2009. It was set up in a field adjacent to the Iberian Culture settlement of Estinclells (Verdú, Urgell), an archaeological site with only one phase of occupation that offers an exceptional portrait of life in the third century BC. The aim of the camp is to concentrate the main lines of Protohistoric experimental research in a single space. These lines include construction, agriculture and processing products. A special emphasis is placed on production of olive oil, livestock and the manufacture of pottery.

The goal of this project is to reconstruct the operational sequence of manufacture of Iberian Iron Age pottery, from clay procurement to firing in a reconstructed kiln. Although pottery is the most characteristic artefact recovered on Iberian Iron Age excavations, most of its complex processes and production techniques remain poorly known. The first phase of this experiment began in 2007 with the construction of a scaled replica of the Iron Age Iberian kiln brought to light at the excavation of Alcalá de Júcar (Province of Albacete). This reconstruction employed materials and techniques identified on the archaeological dig, as well as ethnographic parallels. Some parallels were drawn from the Catalonian town of Verdú, the location of the experiment. This town has an uninterrupted 500 year tradition of ceramic production. The kiln comprised two chambers separated by a grate. Four sensors installed in the kiln recorded a maximum temperature of 600° C. This temperature is probably due to the fact that the kiln was empty during its initial firing. Replicas of Iberian Culture vessels thrown by potters from Verdú were fired in a second experiment. This revealed information regarding the general firing process of vertical updraught kilns in all its complexity, as well as the techniques of temperature control and oxidation and reduction processes, subjects to be examined in future research.

Modular and cascaded multilevel converters provide a functional solution for the integration of energy storage systems (ESSs). This paper develops a hybrid multilevel converter based on the modular multilevel converter (MMC) that can be functionally extended with partial embedded ESS as a fraction of the overall converter power rating. The configuration, which can operate as a typical DC-AC converter, enables multi-directional power flow between the DC- and AC-side of the converter, as well as the embedded energy storage elements. The use of a three-phase flying-capacitor submodule eliminates the second-order harmonic oscillations present in modular cascaded multilevel converters. Current, voltage and power control are discussed in the paper while simulation results illustrate the operation of the hybrid MMC as a DC-AC converter in a typical inverter application and the additional functions and control of the embedded ESS.

This paper presents the equivalence between two- and three-level converters for Vienna-type rectifiers, proposing a simple and fast space vector modulator built on this principle. The use of this duality permits the simple compliance of all topological constraints of this type of nonregenerative three-level rectifier, enabling as well the extension of its operating range by the use of simpler two-level overmodulation schemes. The proposed algorithm is further simplified by deriving its carrier-based equivalent implementation, exploiting the direct correspondence existent between the zero-sequence vectors of Vienna-type rectifiers and the zero state vectors of two-level converters. As a result, the proposed algorithm is also capable of controlling the rectifier neutral point voltage. This feature makes it attractive as well for neutral-point-clamped inverters, complementing previous carrier-based space vector modulators developed for these converters. A complete experimental evaluation using a 2 kW digital signal processor-field programmable gate array controlled Vienna-type rectifier is presented for verification purposes, asserting the excellent performance attained by the proposed carrier-based space vector modulator. [ABSTRACT FROM AUTHOR]

The nearest vectors to the reference vector are commonly used in space-vector modulation (SVM) strategies. The main advantages of these modulation strategies are the low switching frequencies of the devices, the good output voltage spectra, and the low electromagnetic interference. However, when these techniques are applied to the three-level neutral-point (NP)-clamped inverter, low-frequency oscillations appear in the NP voltage for some operating conditions. As a result, the value of the dc-link capacitors must be increased in order to attenuate such oscillations. In this paper, these amplitudes are quantified for two modulation strategies that use nearest vectors to the reference vector. Owing to the nondimensional variables used in the analysis, the information provided will help for the calculation of the dc-link capacitors in a given specific application. Simulated and experimental examples are presented. [ABSTRACT FROM AUTHOR]