Stability Condition Based Sliding Mode Modulators for Multilevel Power Converters

Sliding mode controllers for power converters usually employ hysteresis comparators to directly generate the power semiconductors switching states. This paper presents a new sliding mode modulator based on the direct implementation of the sliding mode stability condition, which for multilevel power converters shows advantages, as branch equalized switching frequencies and less distortion on the ac currents when operating near the rated converter power. The new sliding mode multilevel modulator is used to control a three-phase multilevel converter, operated as a reactive power compensator (STATCOM), implementing the stability condition in a digital signal processing system. The performance of this new sliding mode modulator is compared with a multilevel modulator based on hysteresis comparators. Simulation and experimental results are presented in order to highlight the system operation and control robustness.

Simula����o, em software adequado, da sintomatologia vibracional de avarias mec��nicas de m��quinas rotativas

Trabalho Final de Mestrado para obten����o do grau de Mestre em Engenharia Mec��nica na ��rea de Manuten����o e Produ����o

Est��gio na empresa SPECMAN para a pr��tica de t��cnicas de controlo da condi����o

Trabalho Final de Mestrado para obten����o do grau de Mestre em Engenharia Mec��nica

An��lise por ultra-sons no controlo de condi����o

Trabalho Final de Mestrado para obten����o do grau de Mestre em Engenharia Mec��nica

Metodologia para otimiza����o da manuten����o

Trabalho Final de Mestrado para obten����o do grau de Mestre em Engenharia da Manuten����o

An overview on how failure analysis contributes to flight safety in the Portuguese Air Force

Failure analysis has been, throughout the years, a fundamental tool used in the aerospace sector, supporting assessments performed by sustainment and design engineers mainly related to failure modes and material suitability. The predicted service life of aircrafts often exceeds 40 years, and the design assured life rarely accounts for all in service loads and in service environmental menaces that aging aircrafts must deal with throughout their service lives. From the most conservative safe-life conceptual design approaches to the most recent on-condition based design approaches, assessing the condition and predicting the failure modes of components and materials are essential for the development of adequate preventive and corrective maintenance actions as well as for the accomplishment and optimization of scheduled maintenance programs of aircrafts. Moreover, as the operational conditions of aircrafts may vary significantly from operator to operator (especially in military aircraft), it is necessary to access if the defined maintenance programs are adequate to guarantee the continuous reliability and safe usage of the aircrafts, preventing catastrophic failures which bear significant maintenance and repair costs, and that may lead to the loss of human lives. Thus being, failure analysis and material investigations performed as part of aircraft accidents and incidents investigations arise as powerful tools of the utmost importance for safety assurance and cost reduction within the aeronautical and aerospace sectors. The Portuguese Air Force (PRTAF) has operated different aircrafts throughout its long existence, and in some cases, has operated a particular type of aircraft for more than 30 years, gathering a great amount of expertise in: assessing failure modes of the aircrafts materials; conducting aircrafts accidents and incidents investigations (sometimes with the participation of the aircraft manufacturers and/or other operators); and in the development of design and repair solutions for in-service related problems. This paper addresses several studies to support the thesis that failure analysis plays a key role in flight safety improvement within the PRTAF. It presents a short summary of developed

Maintenance of fire sprinkler systems based on the dynamic assessment of its condition

Safety is one of the major concerns of process safety engineers in most industrial facilities all over the world. To this scope, some events play an important role once the effect of their consequences can be assumed as totally undesirable. One of these events refers to the occurrence of a fire. Such event can result in catastrophic consequences for life, equipment, and continuity of activities or even leading to environmental damage. A fire protection equipment with low reliability means that this equipment are often unavailable and thus the risk of a fire increases. Maintenance of fire protection equipment is very important because this kind of systems is mostly in a dormant mode, which gives uncertainty about their operability when demanded in a real situation of fire. This article outlines the importance of tests, inspection, and maintenance operations in the context of a fire sprinkler system and proposes a methodology based on international standards and supported by test/inspection reports to correct the frequency of these actions according to the level of degradation of the components and regarding safety purposes. �� 2015 American Institute of Chemical Engineers.

Modelos de risk based inspection e risk based inspection and maintenance aplicados a sistemas de produ����o de energias renov��veis

A utiliza����o de recursos energ��ticos renov��veis apresenta-se como um caminho vital para a humanidade alcan��ar um desenvolvimento sustent��vel. Nesta campanha, a energia e��lica surge como um dos principais vectores de orienta����o tendo evolu��do de forma quase exponencial nos ��ltimos anos. No entanto, apesar da sua relativa maturidade, esta tecnologia enfrenta ainda alguns problemas e desafios. N��o obstante a experi��ncia emp��rica da ind��stria e��lica, adquirida nos ��ltimos trinta anos e dos esfor��os para melhorar a fiabilidade operacional das turbinas, as taxas de falha ainda se apresentam elevadas. Face ��s correntes pr��ticas de Manuten����o das turbinas e parques e��licos e ��s caracter��sticas de falha, (por vezes catastr��ficas), existe a necessidade de optimizar as estrat��gias de manuten����o das turbinas e��licas e reduzir os custos durante o ciclo de vida, de modo a maximizar o retorno do investimento. Descreve-se neste trabalho o estado do conhecimento actual face ao objectivo pretendido, a recolha de dados reais da opera����o e Manuten����o, a aplicabilidade dos modelos escolhidos para obten����o da probabilidade de falha, e as consequ��ncias e avalia����o do risco. Assim, desenvolveu-se uma ferramenta de apoio �� decis��o, baseada em Modelos de RBI (Risk Based Inspection) e RBIM (Risk Based Inspection and Maintenance) aplicados a turbinas e��licas.

Low-cost vibration sensors: tendencies and applications in condition monitoring of machines and structures

Trabalho Final de Mestrado para obten����o do grau de Mestre em Engenharia Mec��nica

Programa de manuten����o de aeronaves das companhias de avia����o de baixo custo

Este trabalho aborda o Programa de Manuten����o de Aeronaves das companhias de avia����o de baixo custo, tendo como foco a an��lise e identifica����o dos requisitos legais e das metodologias de desenvolvimento de um Programa de Manuten����o de uma aeronave e a compara����o dos custos de manuten����o de companhias de baixo custo com as companhias regulares. A aplica����o eficaz de um programa de manuten����o, para al��m de reduzir os seus custos, tem um impacto positivo na seguran��a, economia da manuten����o e na fiabilidade de despacho. A metodologia utilizada foi a an��lise de informa����o de publica����es e artigos. Com base na revis��o de literaturas especializadas, fez-se uma selec����o dos diversos aspectos necess��rios para se obter um Programa de Manuten����o, o que permitiu construir o caso de estudo e efectuar a an��lise dos custos inerentes de manuten����o de um operador a��reo de baixo custo e de um operador a��reo regular. Os resultados da an��lise permitiram chegar a veracidade da hip��tese de que do ponto de vista de manuten����o �� igualmente seguro ou n��o seguro voar numa companhia de baixo custo e numa companhia regular, assim independentemente do tipo de companhia, ambas devem cumprir os requisitos para aprova����o do PMA imposto pela autoridade aeron��utica, para garantir a aeronavegabilidade das aeronaves, ou seja, a sua seguran��a para a condi����o de voo, sem p��r em causa o carimbo baixo custo ou regular da companhia.

Manuten����o preditiva e pr��-activa: filosofias alternativas ou complementares: estudo de caso

Trabalho Final de Mestrado para obten����o do grau de Mestre em Engenharia Mec��nica Ramo Manuten����o e Produ����o

Proposta de modelo de avalia����o do estado de conserva����o de equipamentos escolares

Disserta����o para obten����o de grau de Mestre em Engenharia Civil na ��rea de Especializa����o de Edifica����es

A gest��o de boas pr��ticas da manuten����o em equipamentos de anestesia

Mestrado em Gest��o e Avalia����o das Tecnologias em Sa��de

Diagn��stico de avarias em m��quinas rotativas utilizando a an��lise de ��rbitas

Trabalho Final de Mestrado para obten����o do grau de Mestre em Engenharia Mec��nica Perfil Manuten����o e Produ����o

Damage detection in structures using a transmissibility-based Mahalanobis distance

In this paper, a damage-detection approach using the Mahalanobis distance with structural forced dynamic response data, in the form of transmissibility, is proposed. Transmissibility, as a damage-sensitive feature, varies in accordance with the damage level. Besides, Mahalanobis distance can distinguish the damaged structural state condition from the undamaged one by condensing the baseline data. For comparison reasons, the Mahalanobis distance results using transmissibility are compared with those using frequency response functions. The experiment results reveal quite a significant capacity for damage detection, and the comparison between the use of transmissibility and frequency response functions shows that, in both cases, the different damage scenarios could be well detected. Copyright (c) 2015 John Wiley & Sons, Ltd.