Improved Sensor Fault-Tolerant Control Technique Applied to Three-Phase Induction Motor Drive

An improved fault-tolerant control (FTC) method using mathematical functions is applied to the induction motor drive (IMD) against current sensors and speed encoder failures, which occur when the sensor is disconnected or completely damaged. The IMD with two current sensors and an encoder is speed controlled based on the field-oriented control (FOC) technique in regular operation. In this paper, an FTC unit is implemented in the FOC controller to detect and solve the sensor fault to increase the reliability of the speed control process. The measured stator currents and the feedback speed signal are integrated into the diagnosis algorithms to create a sensor fault-tolerant control function. Three diagnosis functions operating in a defined sequence are proposed for determining the health status of current and speed sensors. The FTC function performs isolation and replaces the faulty sensor signals with the proper estimated signals; then, the IMD will operate in the corresponding sensorless mode. Simulations will be performed to verify the accuracy and reliability of the proposed method under various sensor faults

Interaction rupture-flambage, le cas du splitting de tube métallique (approche expérimentale et numérique)

Lorsqu on découpe un feuillard à l aide d un outil, ou lorsqu on découpe un tube selon son axe, au fur et à mesure que l on propage la fissure qui traduit la découpe il arrive que des ondulations de flambage perturbent les deux bords libres générés par la propagation de la fissure. Cette étude vise à analyser les origines de ces ondulations. Nous avons mené une campagne expérimentale, dans laquelle des tubes en acier inox avec différentes géométries (rayon/épaisseur) sont découpés selon une génératrice. Une instrumentation adéquate, couplant des mesures ponctuelles, à l aide de jauges de déformation, et une méthode champ par corrélation d image, nous a permis de correctement mettre en exergue la phénoménologie, en particulier les cinématiques induites à l échelle géométrique de la fissure (front de fissure) ainsi qu à l échelle du tube, avec les longueurs d onde de flambage observées à l aval de la fissure. La modélisation numérique menée en non linéaire géométrique (flambage), matériau (déchirure ductile), et conditions aux limites (contact) est aussi abordée à l aide du code de calcul Abaqus/Standard. Pour la gestion de la propagation de la fissure, deux modèles de rupture sont proposés. Le premier modèle dit zone cohésive est développé et implanté dans le code Abaqus via la subroutine UEL. Pour la deuxième modélisation, nous avons utilisé le modèle dit d endommagement ductile du code Abaqus. La modélisation via des éléments massifs ou des éléments coques volumiques ainsi que l utilisation de ces modèles de rupture permettent de corroborer les observations expérimentales. Ces travaux montrent que l augmentation de la charge inhérente au déplacement de l outil de découpe , induit une extension dans la direction circonférentielle et donc une striction dans la direction radiale amenant finalement la rupture. Lors de la rupture, un sillage plastique apparait, relativement large, près et parallèle aux bords de la fissure. Confiné par les autres parties du tube qui restent élastiques, des contraintes de compression axiale résiduelles apparaissent dans ce sillage plastique, à l aval de la fissure, leur intensité est suffisante pour produire les ondulations des bords libres qui traduisent un flambage local. Les contraintes résiduelles liées à l opération de découpe induisent donc le flambage.When one uses a tool to cut a sheet metal, or a tube according to his axis, as one propagates the crack which translates cutting it arrives that undulations of buckling disturb the two free edges generated by the propagation of the crack. This study aims at analyzing the origins of this behavior. We conducted an experimental campaign, in which stainless steel tubes with various geometries (radius/thickness) are cut out according to a generator. An adequate instrumentation, coupling of specific measurements, using strain gauges, and a field method, by digital image correlation, allowed us accurately to put forward phenomenology, in particular the kinematics at the scale of the crack (ahead of crack tip) and at the level of tube, with the wavelengths of buckling observed at the downstream of the crack tip. The numerical modeling taking into account nonlinearities of material (ductile tear), geometry (buckling) and boundary conditions (contact) is also approached using the code Abaqus/Standard. For the management of the crack propagation, two rupture models are proposed. The first model called cohesive zone is developed and implemented in the Abaqus code via the user routine UEL. For the second modeling, we used the model called ductile damage model in the Abaqus code. Modeling via solid elements or shell continuum elements as well as the use of these rupture models make it possible to corroborate the experimental observations. These studies show that the increase of the load inherent in the displacement of the tool of cutting induced a circumferential extension of the tube that leads to a local necking in the radial direction bringing the rupture finally. During the failure, a plastic wake appears, relatively wide, close and parallel to crack lips. Constrained by other parts of the tube which remain elastic, sufficient axial residual compressive stresses produced in this plastic wake produce the undulations which represents a local buckling. The residual stresses related to the operation of cutting thus induce buckling.VILLEURBANNE-DOC'INSA-Bib. elec. (692669901) / SudocSudocFranceF

Lignin and Cellulose Extraction from Vietnam’s Rice Straw Using Ultrasound-Assisted Alkaline Treatment Method

The process of cellulose and lignin extraction from Vietnam’s rice straw without paraffin pretreatment was proposed to improve economic efficiency and reduce environmental pollution. Treatment of the rice straw with ultrasonic irradiation for 30 min increased yields of lignin separation from 72.8% to 84.7%. In addition, the extraction time was reduced from 2.5 h to 1.5 h when combined with ultrasonic irradiation for the same extraction yields. Results from modern analytical methods of FT-IR, SEM, EDX, TG-DTA, and GC-MS indicated that lignin obtained by ultrasound-assisted alkaline treatment method had a high purity and showed a higher molecular weight than that of lignin extracted from rice straw without ultrasonic irradiation. The lignin and cellulose which were extracted from rice straw showed higher thermal stability with 5% degradation at a temperature of over 230°C. The ultrasonic-assisted alkaline extraction method was recommended for lignin and cellulose extraction from Vietnam’s rice straw

Contract Farming as a Determinant of Promoting Tea Marketing Channel for Small Producers in Phu Tho Province

Making contracts between farmers and firms (contract farming, for short) plays an important role in establishing access to the agricultural markets for the small producers, especially in the developing and less developed countries. It is argued that contract farming provides farmers with the assured sale of their crops and agro-business firms with a steady supply of agricultural products required by the market. This paper focuses on analyzing benefits of tea producers through signing contract with firms. By using relevant research methods of verifying studying areas, making Participatory Rural Appraisal (PRA), and surveying farmers, the paper finds that although contract farmers receive lower fresh tea price in compared with the price received by non-contract farmers, they would have higher price stability and are provided with market guarantee mechanism. These benefits are really important in context of globalization and market liberalization with the demand for high quality and high value products. It is highly recommended that small farmers therefore should participate in the coordination model between farmers and firms in the process of tea production and marketing in Phu Tho Province, Vietnam.Peer reviewe

Particle swarm optimization-based stator resistance observer for speed sensorless induction motor drive

This paper presents a different technique for the online stator resistance estimation using a particle swarm optimization (PSO) based algorithm for rotor flux oriented control schemes of induction motor drives without a rotor speed sensor. First, a conventional proportional-integral controller-based stator resistance estimation technique is used for a speed sensorless control scheme with two different model reference adaptive system (MRAS) concepts. Finally, a novel method for the stator resistance estimation based on the PSO algorithm is presented for the two MRAS-type observers. Simulation results in the Matlab/Simulink environment show good adaptability of the proposed estimation model while the stator resistance is varied to 200% of the nominal value. The results also confirm more accurate stator resistance and rotor speed estimation in comparison with the conventional technique