Uma intervenção de ensino em estatística no ensino profissional através de investigações estatísticas

Alguns estudos realizados em Portugal (e não só) têm mostrado que o ensino da Estatística nas escolas assume um carácter técnico e teórico (Fernandes, Carvalho & Ribeiro, 2007; Fernandes, Sousa & Ribeiro, 2004), não incluindo tarefas abertas, o uso de Tecnologias de Informação e Comunicação ou o trabalho de grupo, que constituem orientações actuais para o ensino da Estatística. No presente estudo relatamos uma experiência de ensino em Estatística, envolvendo uma turma do Curso Profissional de Técnico de Gestão de Equipamentos Informáticos, do 10º ano, e em que os alunos, trabalhando em pequenos grupos, desenvolveram investigações estatísticas sobre problemáticas seleccionadas com a ajuda da folha de cálculo. Em termos de resultados da intervenção de ensino, verificou-se que todos os alunos concluíram a unidade de Estatística e manifestaram uma opinião positiva sobre a intervenção realizada, valorizando quer a estratégia usada quer o uso da folha de cálculo. O interesse e a importância destes resultados é ainda maior se tivermos presente que estes alunos, em geral, têm um percurso escolar menos sucedido na escola

A bidirectional multilevel DC-DC converter applied to a bipolar DC grid: analysis of operation under fault conditions

Recently, DC grids have been an important subject of research due to their attractive features comparing with AC grids. The characteristic advantages of DC grids are not only related with the integration of native DC technologies, as renewable energy sources (RES) and energy storage systems (ESS), but also with the reduced number of power converters. Relatively to the configurations of DC grids, in this paper, it is presented a bipolar DC grid, where an innovative bidirectional multilevel DC-DC converter is considered under a fault-tolerance analysis. This converter can be used to interface with several technologies, but, in the scope of this paper, it is considered the application of an electric vehicle (EV) battery charger. Taking into account that some failures can occur, namely in the DC-DC converter and in the bipolar DC grid, the operation of the DC-DC converter within the bipolar DC grid can be harmful. Therefore, this paper also presents a fault-tolerance analysis of the DC-DC converter when facing the occurrence of failures in itself and in the bipolar DC grid, namely for different scenarios of failure in the DC-link wires. Besides, the control strategy for the DC-DC converter is described in detail for distinct scenarios of operation, both in steady-state and transient-state.This work has been supported by FCT – Fundação para a Ciência e Tecnologia within the R&D Units Project Scope: UIDB/00319/2020. This work has been supported by the FCT Project newERA4GRIDs PTDC/EEI-EEE/30283/2017 and the FCT Project DAIPESEV PTDC/EEI-EEE/30382/2017

Experimental validation of a bidirectional multilevel dc–dc power converter for electric vehicle battery charging operating under normal and fault conditions

This paper presents a bidirectional multilevel dc–dc power converter for electric vehicle (EV) battery charging. The operating principle of the power converter was presented, analyzed, and experimentally validated under normal and fault conditions. The topology under study was integrated into a bipolar dc grid through the split dc-link of the bidirectional multilevel dc–dc power converter. Considering the failures that can occur in the bipolar dc grid, i.e., in each wire of the bipolar dc grid (positive, negative, and neutral), it was experimentally verified that the dc–dc power converter ensures that the EV battery-charging process continues, regardless of the occurrence or absence of open-circuit failures. In light of this fact, the proposed control algorithms and the presented topology were validated through a set of considerable simulation and experimental results, analyzing the distinct states of the power semiconductors, which compose the bidirectional multilevel dc–dc power converter, for distinct conditions of operation. The developed laboratory prototype of the bidirectional multilevel dc–dc power converter for EV battery charging, which was implemented to obtain the experimental results, is described in detail in this paper. The experimental validation was carried out for the main different fault conditions in the bipolar dc grid in terms of open-circuit failures and, moreover, considering the steady-state and transient-state operations of the dc–dc power converter. The experimental analysis demonstrated that even in the presence of failures in the positive, negative, or neutral wires of the bipolar dc grid, the bidirectional multilevel dc–dc power converter guarantees the correct EV battery-charging operation.This work has been supported by FCT–Fundação para a Ciência e Tecnologia within the R&D Units Project Scope: UIDB/00319/2020. This work has been supported by the MEGASOLAR Project POCI-01-0247-FEDER-047220

Fault analysis of a non-isolated three-level DC-DC converter integrated in a bipolar DC power grid

DC power grids present significant advantages over AC power grids, namely higher stability and controllability, and the absence of harmonic currents and reactive power. Moreover, DC grids facilitate the interface with renewable energy sources (RES) and energy storage systems (ESS). DC grids can be either unipolar or bipolar, where the latter consists of three wires and provides higher flexibility, reliability and transmission capacity. However, failures in bipolar DC grids (especially in the power semiconductors) can occur. The consequences of these failures can result in increased costs, depending on the damage, e.g., if it occurs a wire of the DC grid or in the connected power converter. Thus, in this paper is presented a fault analysis of a non-isolated three-level DC-DC converter used to interface solar photovoltaic (PV) panels into a bipolar DC power grid. The fault analysis is conceived through computational simulations, where can be observed the performance of the presented DC-DC converter under fault conditions in each wire of the bipolar DC grid. The simulation results demonstrate the DC-DC converter operating in two different situations: steady-state and transient-state. The control strategy applied in normal and fault conditions, as well as the different operation modes, are explained in detail.This work has been supported by FCT – Fundação para a Ciência e Tecnologia within the R&D Units Project Scope: UIDB/00319/2020. This work has been supported by the FCT Project newERA4GRIDs PTDC/EEI-EEE/30283/2017

A multilevel bidirectional Four-Port DC-DC converter to create a DC-Grid in Solid-State transformers with hybrid AC/DC grids

Smart grids are incessantly contemplating new challenges about power electronics technologies, and this paper focuses on the application of solid-state transformers (SSTs) and the forthcoming perspective of hybrid AC/DC grids. In such perspective, a multilevel bidirectional four-port (MB4P) DC-DC converter is proposed to be integrated in a three-phase SST. It interfaces the SST through three independently ports, corresponding to the three-phases, and the other port is used to create a DC grid. The proposed MB4P DC-DC converter has as main features a multilevel operation with seven voltage levels as function of the voltages on both DC sides, as well as the interleaved operation, where the controlled variables have a ripple with a frequency six times higher than the switching frequency. Furthermore, it can operate in buck or boost modes, and with current or voltage control. Besides the voltage and current control, specific attention is given to the proposed PWM. The advanced attributes of the MB4P DC-DC converter are proven by computer simulations and by analytical description, both exploring steady-state and transient-state distinctive requirements.FCT -Fundação para a Ciência e a Tecnologia(DAIPESEV PTDC/EEI-EEE/30382/2017

Hydrothermal processing of hardwoods and agro-industrial residues :evaluation of xylo-oligosaccharides production

Autohydrolysis was used as a pre-treatment method for the selective hydrolysis of hemicelluloses of four lignocellulosic materials: eucalypt wood chips (EWC), corn cobs (CC), wheat straw (WS) and brewery’s spent grain (BSG), and the process was optimized towards the production of xylo-oligosaccharides (XOS). The effects of temperature, both at isothermal (150-190ºC), and non-isothermal (up to 240ºC) conditions, and liquid-to-solid ratio (LSR), 8 or 10 g/g, on the composition of both the liquid and solid phases were studied. The operational conditions leading to the maximal recovery of XOS for each raw material were established and discussed based on the severity factor (log R0). The higher yields obtained were in the range of 43–65% of the feedstock (arabino)xylan, with the highest value attained for CC for log R0 =3.75. Under the optimised conditions for XOS production, glucan was only slightly solubilised, enabling an enrichment of the solid phase (up to 67% of glucan for EWC). Delignification was also not extensive reaching utmost 18%, in the case of CC. cosmetic industries

A single-phase current-source converter combined with a hybrid converter for interfacing an electric vehicle and a renewable energy source

This paper presents a single-phase current-source converter (CSC) combined with a hybrid converter on the dc-link, allowing to interface an electric vehicle (EV) and a renewable energy source (RES). Therefore, the interface with the power grid is only performed through the CSC, which also permits the operation as shunt active power filter (SAPF), allowing to compensate power quality problems related with current and low power factor in the electrical installation. The whole system is composed by two main power stages, namely, the CSC that is responsible for compensating the current harmonics and low power factor, as well as operating as a grid-tied inverter or as an active rectifier, and the hybrid converter that is responsible for interfacing the dc-link of the CSC with the converters for the EV and the RES interfaces. As demonstrated along the paper, the CSC, combined with the hybrid converter on the dc-link, allows the operation as SAPF, as well as the operation in bidirectional mode, specifically for the EV operation, and also for injecting power from the RES. In the paper, the power electronics structure is described and the principle of operation is introduced, supported by the description of the control algorithms. The validation results show the proper operation of the CSC, combined with the hybrid converter on the dc-link, for the main conditions of operation, namely exchanging power with the power grid in bidirectional mode and operating as a SAPF.This work has been supported by FCT – Fundação para a Ciência e Tecnologia with-in the Project Scope: UIDB/00319/2020. This work has been supported by the FCT Project newERA4GRIDs PTDC/EEI-EEE/30283/2017 and the FCT Project DAIPESEV PTDC/EEI-EEE/30382/2017

TSFEL: Time Series Feature Extraction Library

POCI-01-0247-FEDER-038436Time series feature extraction is one of the preliminary steps of conventional machine learning pipelines. Quite often, this process ends being a time consuming and complex task as data scientists must consider a combination between a multitude of domain knowledge factors and coding implementation. We present in this paper a Python package entitled Time Series Feature Extraction Library (TSFEL), which computes over 60 different features extracted across temporal, statistical and spectral domains. User customisation is achieved using either an online interface or a conventional Python package for more flexibility and integration into real deployment scenarios. TSFEL is designed to support the process of fast exploratory data analysis and feature extraction on time series with computational cost evaluation.publishersversionpublishe

Riparian Ecological Infrastructures: Potential for Biodiversity-Related Ecosystem Services in Mediterranean Human-Dominated Landscapes

Riparian Ecological Infrastructures are networks of natural and semi-natural riparian areas located in human-dominated landscapes, crucial in supporting processes that directly or indirectly benefit humans or enhance social welfare. In this study, we developed a novel multimetric index, termed Habitat Ecological Infrastructure’s Diversity Index (HEIDI), to quantify the potential of Riparian Ecological Infrastructures in supporting biodiversity, and related ecosystem services, in three managed landscapes: Intensive Agriculture, Extensive Agriculture, and Forest Production. Metrics describing the structure, composition, and management of riparian vegetation and associated habitats were used to derive the potential of Riparian Ecological Infrastructures in supporting three distinct biological dispersal groups: short-range dispersers (ants), medium-range dispersers (pollinators), and long-range dispersers (birds, bats, and non-flying small mammals). The composition of floristic resources, assessed by identifying trees and shrubs at the species and genus level, and herbaceous plants at the family level, was used as a proxy to evaluate the potential of Riparian Ecological Infrastructures in promoting seed dispersal and pollination ecosystem services provided by the three biological communities. Our research evidenced that Riparian Ecological Infrastructures located in the Forest Production and Intensive Agriculture landscapes exhibited the highest and lowest potential for biodiversity-related ecosystem services, respectively. The Forest Production landscape revealed higher suitability of forage resources for short- and medium-range dispersers and a higher landscape coverage by Riparian Ecological Infrastructures, resulting in more potential to create ecological corridors and to provide ecosystem services. The Riparian Ecological Infrastructures located in the Extensive Agriculture landscape seemed to be particularly relevant for supporting long-ranges dispersers, despite providing less habitat for the biological communities. Land-use systems in the proximity of Riparian Ecological Infrastructures should be sustainably managed to promote riparian vegetation composition and structural quality, as well as the riparian width, safeguarding biodiversity, and the sustainable provision of biodiversity-related ecosystem servicesinfo:eu-repo/semantics/publishedVersio

Experimental validation of a current-source converter with reduced dc-link operating as shunt active power filter

Nowadays, the majority of electronic equipment behaves as nonlinear loads, introducing power quality problems into the power grid, namely, current harmonics and low power factor. These problems contribute to reduce the efficiency of the power grid and can cause malfunctioning of sensitive loads connected to the power grid. Therefore, it is important to develop power electronics solutions capable to mitigate these power quality problems. In this context, this paper presents a novel single-phase shunt active power filter (SAPF) based on a current-source converter, where the key differencing factor, when compared with the conventional approach, is the reduced dc-link. As the proposed topology requires a reduced dc-link, it represents a relevant advantage, requiring a less bulky inductance in the dc-link, reducing the losses, cost, and volume. The proposed SAPF with reduced dc-link is introduced in detail along the paper, and a comprehensive comparison with the conventional SAPF is established based on computer simulations. Besides, an experimental validation is carried out with a developed laboratory prototype, validating the main advantages of the proposed SAPF with reduced dc-link.This work has been supported by FCT – Fundação para a Ciência e Tecnologia with-in the Project Scope: UIDB/00319/2020. This work has been supported by the FCT Project newERA4GRIDs PTDC/EEI-EEE/30283/2017 and the FCT Project QUALITY4POWER PTDC/EEI-EEE/28813/2017, and by. Mr. Luis A. M. Barros is supported by the doctoral scholarship PD/BD/143006/2018 granted by the Portuguese FCT foundation