Teaching with internet support : a case example

The evolution of Internet and all related technologies contributed, a lot, for the development of the e-learning. This paper discusses the advantages in using the new Technologies, namely the Internet, as an aid tool to teaching, and presents an example developed in the Degree of Industrial Electronics and Computer Engineering at University of Minho. It also discusses the motivations of the students on acquiring knowledge by an alternative method of teaching/learning.The authors are grateful to FCT (Fundação para a Ciência e a Tecnologia), projects funding POCTI/ESE/41170/2001 and POCTI/ESE/48242/2002

Rail power conditioner based on indirect AC/DC/AC modular multilevel converter using a three-phase V/V power transformer

This paper presents a rail power conditioner (RPC) system based on an indirect AC/DC/AC modular multilevel converter (MMC) where a V/V power transformer is used to feed the main catenary line and the locomotives. The proposed control strategy for this system has been introduced to guarantee a good compensating performance of negative sequence currents (NSCs) and harmonics on the public grid side. This control strategy has also the ability to achieve balanced and equal voltage between the MMC’s submodules (SMs) capacitors. Simulation results for this RPC based on an indirect MMC are presented in this paper to show the main advantages of using this topology. The results show how the proposed system is able to compensate NSCs and harmonics on the public grid side when the V/V power transformer feeds two unequal load sections.Fundação para a Ciência e Tecnologia (FCT)info:eu-repo/semantics/publishedVersio

Middleware Fault Tolerance Support for the BOSS Embedded Operating System

Critical embedded systems need a dependable operating system and application. Despite all efforts to prevent and remove faults in system development, residual software faults usually persist. Therefore, critical systems need some sort of fault tolerance to deal with these faults and also with hardware faults at operation time. This work proposes fault-tolerant support mechanisms for the BOSS embedded operating system, based on the application of proven fault tolerance strategies by middleware control software which transparently delivers the added functionality to the application software. Special attention is taken to complexity control and resource constraints, targeting the needs of the embedded market.Fundação para a Ciência e a Tecnologia (FCT

Application-level fault tolerance in real-time embedded systems

Critical real-time embedded systems need to make use of fault tolerance techniques to cope with operation time errors, either in hardware or software. Fault tolerance is usually applied by means of redundancy and diversity. Redundant hardware implies the establishment of a distributed system executing a set of fault tolerance strategies by software, and may also employ some form of diversity, by using different variants or versions for the same processing. This work proposes and evaluates a fault tolerance framework for supporting the development of dependable applications. This framework is build upon basic operating system services and middleware communications and brings flexible and transparent support for application threads. A case study involving radar filtering is described and the framework advantages and drawbacks are discussed.Fundação para a Ciência e a Tecnologia (FCT

Implementation of middleware fault tolerance support for real-time embedded applications

Critical real-time embedded systems need to apply fault tolerance strategies to deal with operation time errors, either in hardware or software. In this paper we present the ongoing work to provide application fault tolerance by means of implementing middleware transparent support over the BOSS embedded operating system. The middleware uses a publishersubscriber protocol and enables the execution of several fault tolerance strategies with minimum burden to the application level softwareFundação para a Ciência e a Tecnologia (FCT

Applying aspects to a real-time embedded operating system

The application of aspect-oriented programming (AOP) to the embedded operating system domain is still a very controversial topic, as this area demands high performance and small memory footprint. However, recent studies quantifying aspects overheads in AspectC++ show that the resource cost is very low. Therefore, operating system development may benefit with the modularization of crosscutting concerns and system specialization offered by AOP. This paper addresses our experience in applying aspects to synchronization (mutual exclusion) and logging in a real-time embedded operating system (BOSS). Furthermore, we present our ideas for future investigation in aspect-oriented implementations for fault tolerance, middleware customization and platform variability.(undefined

A personal computer based controller for an active power filter

This paper presents the development of controllers used in active power filters, applied to improve power quality in electrical systems. These active filters can be able to compensate for the following current or voltage related problems: short blackouts, current or voltage distortion due to harmonics, current or voltage unbalance in three-phase systems, flicker (subharmonics) and momentary over or under voltages. There are several causes for current and voltage distortion, namely, non linear loads, some types of voltage sources and thunderstorms. These problems cause instant and long term effects on the electrical equipment. The short term effects are imperfections, malfunctioning, interferences and degradation of the performance of devices or equipments. Effects in the long run are, basically, overheating and premature aging of the electric devices. The main goal of the work described in this paper is to develop an active power filter controller based on a personal computer and a standard multifunction data acquisition PCI bus card, due to its relative low cost, high processing capability, versatility and the numerous possibilities offered by such a computer-based system. Four different approaches were tested: using C++ on Microsoft Windows with the manufacturer’s device driver, using a new device driver for Windows, using Linux with real-time application interface; and using LabVIEW for Windows. Experimental and simulation results of the developed controllers are also presented

Aspect-oriented fault tolerance for real-time embedded systems

Real-time embedded systems for safety-critical applications have to introduce fault tolerance mechanisms in order to cope with hardware and software errors. Fault tolerance is usually applied by means of redundancy and diversity. Redundant hardware implies the establishment of a distributed system executing a set of fault tolerance strategies by software, and may also employ some form of diversity, by using different variants or versions for the same processing. This paper describes our approach to introduce fault tolerance in distributed embedded systems applications, using aspect-oriented programming (AOP). A real-time operating system sup-porting middleware thread communication was integrated to a fault tolerant framework. The introduction of fault tolerance in the system is performed by AOP at the application thread level. The advantages of this approach include higher modularization, less efforts for legacy systems evolution and better configurability for testing and product line development. This work has been tested and evaluated successfully in several fault tolerant configurations and presented no significant performance or memory footprint costs.Fundação para a Ciência e a Tecnologia (FCT

Optimizing the train-catenary electrical interface in AC railways through dynamic control reconfiguration

The power supply architecture of most AC electric railway vehicles is constituted by transformers and catenaries at increasingly high power levels. Inside the vehicles, the interface between the catenary and the DC-bus of the traction motors is based on a transformer and power electronics converters. A large part of these are AC-DC four quadrant converters that operate in parallel at relatively small switching frequencies. However, the use of the interleaving principle allows reaching a low harmonic distortion of the catenary current and imposing specific harmonic ranges in this current. Nevertheless, the current is not a pure sinusoidal wave and its harmonics can excite unwanted resonances due to the combined effect of the catenary distributed parameters, the substation equivalent impedance and the current frequency spectrum. This paper analyses this phenomenon and proposes a control strategy capable of minimizing the resonance effects in two different power supply architectures.The research has received funding from the FCT (Fundação para a Ciência e Tecnologia) under grant PD/BD/128051/2016. This work was partially supported by: FCT R&D Unit SYSTEC - POCI-01-0145-FEDER006933/SYSTEC funded by FEDER funds through COMPETE 2020 and by national funds through the FCT/MCTES, and co-funded by FEDER, in the scope of the PT2020 Partnership Agreement