Analysis of overload and sensorless control capability of PM-assisted synchronous reluctance machines

Synchronous reluctance machines are a valid alternative to induction motors for industrial applications requiring variable speed regulation. To mitigate the well-known downside of their lower power factor, permanent-magnetassisted topologies are adopted. Both high-strength rare-earth magnets and low cost ferrite magnets can be used in such machines. Their design and optimization procedures have been discussed in related literature. This paper compares synchronous reluctance machines assisted with NdFeB and ferrite magnets, focusing on torque overload capability and feasibility of saliencybased position estimation algorithms. Three prototypes were realized and tested. They all have the stator of a commercial induction motor, and three custom synchronous reluctance rotors with same laminations: one has no magnets, the other two have NdFeB and ferrite magnets respectively, designed to give the same torque at rated current. Results from simulations and experiments are presented, focusing on torque and demagnetization limits in the over-current loading range. Moreover, the feasibility of saliency-based sensorless methods is investigated, both at high and low current loads. The results of the paper suggest that the ferrite-assisted solution is the candidate solution for replacing induction motors in variable speed applications

Metodologia de avaliacao de germoplasma de Lycopersicon visando resistencia ao virus de vira-cabeca do tomateiro.

Verificou-se, previamente, que a inoculacao mecanica do virus de vira-cabeca nas folhas primarias de feijao 'Manteiga', nao completamente expandidas, resultou em maior numero de lesoes locais em condicoes de estufa (18-40oC) do que em camara de crescimento (18-25oC). Com base na concentracao do virus, avaliada pelo numero de lesoes em feijao 'Manteiga', constatou-se que as melhores hospedeiras para multiplicacao do virus foram N. rustica e fumo 'TNN', seguidas de tomate 'Santa Cruz'. Outrossim, a concentracao do virus, nessas hospedeiras, foi mais alta em camara de crescimento do que em estufa. Em ambas condicoes, o pico de concentracao do virus ocorreu entre 10 e 15 dias. A melhor diluicao do inoculo foi a de 1:5. Mudas de tomate 'Angela I-5.100', inoculadas nos estadios de (a) 1-2 folhas (14 dias apos o semeio - DAS), (b) 3-4 folhas (19 DAS) ou (c) 5-6 folhas (24 DAS) apresentaram maior percentagem de infeccao, maior reducao de tamanho e maior severidade dos sintomas em (a) e (b) do que em (c)

Impact of PWM Voltage Waveforms in High-Speed Drives: A Survey on High-Frequency Motor Models and Partial Discharge Phenomenon

The insulation system’s dielectric of the electric motor is very often subjected to severe electrical stress generated by the high dv/dt seen at the machine’s terminals. The electrical stress and high reflected wave transient overvoltage are even more evident in case of high-speed machines fed by high-frequency (HF) converters featuring very fast wide-bandgap devices. They are promoting the occurrence of partial discharges and consequently accelerate ageing. As this is serious issue and the main cause of the drive failure, it is important to analyse and characterise the surges at the motor terminals. Several HF models of motors have been proposed in the literature for this purpose. This article presents a survey on HF motor models, which is crucial in understanding and studying the most critical parameter identification and overvoltage mitigation techniques. Moreover, it offers a comparison of the models’ main features as well as a comparison with the experimental voltage waveform at motor terminals. A general overview of the partial discharge (PD) phenomenon is also provided, as it is favoured by HF operation and together with HF motor modelling provides key insights to the insulation ageing issue. In particular, an analysis of the effects of PWM waveform affecting insulation is given, as well as useful methods for developing strategies for the inspection and maintenance of winding insulation

Microsatellite markers for Caesalpinia echinata Lam. (Brazilwood), a tree that named a country.

Made available in DSpace on 2018-06-07T01:00:04Z (GMT). No. of bitstreams: 1 ID290951.pdf: 141717 bytes, checksum: 2de15d866e43b11e1c7eb0ec541abeed (MD5) Previous issue date: 2008-02-1

Dados preliminares de um levantamento de viroses de plantas cultivadas na região de Tomé-Açú e Belém, PA.

Resumos do 13º Congresso da Sociedade Brasileira de Fitopatologia, 1980, Rio de Janeiro

Reduced fronto-striatal volume in attention-deficit/hyperactivity disorder in two cohorts across the lifespan

Attention-Deficit/Hyperactivity Disorder (ADHD) has been associated with altered brain anatomy in neuroimaging studies. However, small and heterogeneous study samples, and the use of region-of-interest and tissue-specific analyses have limited the consistency and replicability of these effects. We used a data-driven multivariate approach to investigate neuroanatomical features associated with ADHD in two independent cohorts: the Dutch NeuroIMAGE cohort (n = 890, 17.2 years) and the Brazilian IMpACT cohort (n = 180, 44.2 years). Using independent component analysis of whole-brain morphometry images, 375 neuroanatomical components were assessed for association with ADHD. In both discovery (corrected-p = 0.0085) and replication (p = 0.032) cohorts, ADHD was associated with reduced volume in frontal lobes, striatum, and their interconnecting white-matter. Current results provide further evidence for the role of the fronto-striatal circuit in ADHD in children, and for the first time show its relevance to ADHD in adults. The fact that the cohorts are from different continents and comprise different age ranges highlights the robustness of the findings