Uma análise crítica e comparativa de experiências de ensino do empreendedorismo baseadas na abordagem de aprendizagem por projeto

Este artigo debruça-se sobre a aplicação da abordagem de aprendizagem por projeto no ensino do empreendedorismo ou da formação empresarial em cursos de engenharia. A literatura sobre o tema é ainda escassa e persiste um debate que se tem mostrado inconclusivo sobre determinadas questões fundamentais. Neste projeto de investigação estudaram-se diversas experiências educacionais que permitem tirar ilações sobre a abordagem da aprendizagem baseada em projeto utilizada em 6 unidades curriculares de diferentes cursos de engenharia da Universidade do Minho. O período de análise compreende os últimos 10 anos, remontando a 2006 quando estas experiências foram iniciadas. A estratégia de pesquisa foi essencialmente qualitativa, de natureza descritiva e exploratória, tendo-se seguido uma metodologia iminentemente etnográfica. O artigo descreve e explora a utilização desta abordagem educacional no ensino universitário e na área da gestão empresarial ou do empreendedorismo através de um conjunto de casos que se traduzem numa diversidade de situações muito interessante. É feita uma breve descrição de cada experiência, referindo particularmente o seu contexto e a sua evolução, assim como os resultados diretos e indiretos que lhe estão subjacentes. É importante compreender a motivação que esteve na origem da implementação e na adoção da abordagem da aprendizagem baseada em projetos, as dificuldades encontradas e as alterações realizadas.Fundação para a Ciência e Tecnologia, PEst- OE/EME/UI0252/2011Algoritmi (PEst2015-2020) UID/CEC/00319/201

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

New topology of a hybrid, three-phase, four-wire shunt active power filter

With a view to reducing harmonic content in electrical power systems, and, consequently, improving power quality level, filters and other harmonic compensation devices are widely used. In the category of filters, they can be distinguished into two classes that are related to the operating mode, active or passive, both widely known and applied in electrical power grids and in the most diverse industry sectors. In this sense, taking into account the use of compensating devices in four-wire electrical systems feeding single-phase, non-linear loads, this paper presents a new hybrid arrangement of harmonic compensation that incorporates both active and passive filtering, which performs all functions concerning the harmonic compensation of a four-leg shunt active power filter. In this hybrid arrangement, the harmonic filtering of positive and negative sequence components is performed by a three-leg shunt active power filter, while the filtering of zero-sequence harmonics is attributed to the electromagnetic zero-sequence suppressor. The results, which confirm the effectiveness of the proposed hybrid arrangement, are proven through simulations and experimental tests in different operating scenarios, revealing a substantial improvement in the system’s power factor, as well as a reduction in harmonic distortions.This research was funded by FCT—Fundação para a Ciência e Tecnologia grant number UIDB/00319/2020

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

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

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

Model predictive control of a single-phase five-level VIENNA rectifier

Power converters and control strategies are very vital for the increasing sustainability of the power grid targeting smart grids. In these circumstances, it is proposed a novel single-phase five-level (SP5L) VIENNA rectifier digitally controlled by a model predictive control (MPC) with fixed switching frequency, which can be useful for a variety of applications with a robust current tracking. The proposed SP5L VIENNA rectifier is an advancement of the classical three-level VIENNA rectifier, also contributing to preserve power quality, and exhibiting the advantage of operating with more voltage levels at the expense of few additional switching devices. The proposed topology is introduced and correlated with the classical solutions of active rectifiers. The operation principle is introduced and used to describe the MPC, which is given in detail, as well as the necessary modulation strategy. The results were obtained for a set of various operating conditions, both in terms of reference of current and grid-side voltage, as well as in steady-state and transient-state, proving the benefits of the proposed SP5L VIENNA rectifier and the accurate and precise use of the MPC to control the grid-side current.This work has been supported by FCT -Fundacao para a Ciencia 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 by the FCT Project DAIPESEV PTDC/EEI-EEE/30382/2017. Tiago Sousa is supported by the doctoral scholarship SFRH/BD/134353/2017 granted by FCT

Modeling, design, and experimental test of a zero‐sequence current electromagnetic suppressor

This paper presents the experimental investigation of an electromagnetic suppressor to minimize the circulation of zero‐sequence currents in three‐phase four‐wire distribution systems. The proposed zero‐sequence current electro- magnetic suppressor (ZSS) integrates two distinct electromagnetic devices, namely a zero‐sequence filter (ZSF) and a zero‐ sequence blocker (ZSB), connected in parallel and in series between the source and the load, respectively. In this paper are presented the theoretical modeling and analysis of each device, the mathematical concepts of harmonic compensation, and the procedures for the design and determination of the constructive details. The experimental results of the combined operation of the devices that integrate the ZSS demonstrate the feasibility of the proposed arrangement, by minimizing the flow of the zero‐sequence harmonic currents in the source side, enabling a significant reduction of the current in the neutral conductor, and also by improving the system power factor.This work has been supported by CNPq ‐ National Council for Scientific and Technological Development, by CAPES ‐ Coordinationfor the Improvement of Higher Education Personnel through the PDSE ‐ Doctoral Program Sandwich Abroad 7427‐12‐3, and by FCT ‐ Foundation for Science and Technology within the Project Scope: UID/CEC/00319/2019 and FCT within project PTDC/EEI‐EEE/28813/2017

Design and implementation of a real-time wireless sensor network

This paper describes the development of wireless sensor network prototype that gathers biometrical data and posture information from several wearable sensor networks and sends it in real-time to a personal computer where the information is monitored and stored. The wireless sensor network is based on a low power real-time MAC protocol that was designed and implemented in the MICAz platform. This paper also presents some analytical results and several experimental results regarding the behavior of the developed system.Fundação para a Ciência e a Tecnologia (FCT

Anxiety and Coping Stress Strategies in Researchers During COVID-19 Pandemic

Abstract The current COVID-19 pandemic has affected the whole world, leading to changes in one's personal and working life. Researchers have undergone extensive changes in their roles, mainly in the area of health care, with research into the virus now the priority. Aim: To assess the anxiety, depression, stress, fears, and coping strategies of Portuguese researchers during the COVID-19 pandemic. Participants and methods: A total of 243 researchers, with an average age of 37.9 ± 9.6, participated in an online questionnaire. The study was performed between 1 June 2021 and 11 August 2021. The questionnaire included depression, anxiety, and stress (DASS-21), fear of COVID-19 scale (FCV-19S), and coping inventory for stressful situations (CISS). Results: The findings suggest being female and younger seems to be related to more significant fears. Singles and younger researchers showed higher values of stress, depression, and anxiety. Research areas, such as medical and health sciences, presented higher levels in the DASS-21 depression and stress scale (p 0.70); CISS-21 emotional-oriented with DASS-21 stress (r = 0.683), DASS-21 depression (r = 0.622), and DASS-21 anxiety (r = 0.557); and emotional fear and cognitive fear (r = 0.652). Conclusion: The findings of this study support the growing concern for the psychological well-being of researchers and the need for intervention with more extensive and diverse studies