Direct Power Control Scheme Based on Disturbance Rejection Principle for Three-Phase PWM AC/DC Converter under Different Input Voltage Conditions

Conventional direct power control (DPC) technique is a simple and efficient control strategy for three-phase PWM rectifier. However, its performance is deteriorated when the converter is supplied by unbalanced or distorted grid voltages. This paper describes the design and implementation of a new configuration of DPC based on disturbance rejection principle to achieve near-sinusoidal input current waveforms of the converter under different input voltage conditions. In the proposed DPC scheme, instantaneous active and reactive powers provided by harmonic component of input currents are directly controlled using a predefined switching table. In order to achieve full rejection of the effect of any disturbance on the quality of input currents, the reference of both controlled powers are directly given from the outside of the controller and are equal to zero. Moreover, prior knowledge of disturbance's nature, calculation of positive and negative sequences of unbalanced input voltages and content harmonic extraction are not required for the proposed DPC. Compared to the conventional DPC, the proposed one uses a PLL block to extract the fundamental of input currents and defining the position of the grid voltage vector in α-β plane without any passive filters. Finally, the simulation results have verified the validity of the proposed DPC and have proven an excellent performance under different input voltage conditions. Full disturbance rejection and good robustness towards supply voltage disturbances are the main advantages of the proposed DPC compared to the conventional one

Morphological characteristics and seed germination improvement of two ecotypes of Astragalus armatus Willd. subsp. armatus in Algeria

Astragalus armatus Willd. subsp. armatus is an endemic shrub of the Northern Africa. Its cultivation and domestication are very limited because of difficulty with seed germination and establishment. In this study, we investigated some plant morphological characteristics in real time and in situ (leaves, fruit and seeds) of different ecotypes of A. armatus, collected from two sites in Algeria (Arid Steppe of Aïn Naga and Condorcet Mountain), which elevation and climate data are very different. Moreover, the role played by the seed coat in seed dormancy of these two different populations was tested by the effects of the pretreatment and its duration on the performance of seed germination, by considering the final germination percentage (FGP) and the mean germination time (MGT). These parameters are estimated for 10 days in Petri dishes and stored in darkness at (25°C). Pre-sowing treatments included immersion in concentrated sulphuric acid for 30, 60 and 90 min, and immersion in hot water (100°C) for 10 min. Statistical analysis showed that the treatment and the ecotypes effects on both FGP and MGT were highly significant (p< 0.0001). Untreated seeds of both ecotypes of A. armatus failed to germinate (except for a few of Condorcet Mountain ecotypes). For both populations, the most effective treatment was immersion in sulphuric acid for 60 min for the ecotype of Arid Steppe of Aïn Naga, and only 30 min for Condorcet Mountain. An excellent germinative strength is characterized by a higher FGP and a reduced MGT. The morphological characteristic and seed germination could be attributed to intraspecific variations resulting from the natural selection of the same species

The recent progress on silver nanoparticles: Synthesis and electronic applications

Nanoscience enables researchers to develop new and cost-effective nanomaterials for energy, healthcare, and medical applications. Silver nanoparticles (Ag NPs) are currently increasingly synthesized for their superior physicochemical and electronic properties. Good knowledge of these characteristics allows the development of applications in all sensitive and essential fields in the service of humans and the environment. This review aims to summarize the Ag NPs synthesis methods, properties, applications, and future challenges. Generally, Ag NPs can be synthesized using physical, chemical, and biological routes. Due to the great and increasing demand for metal and metal oxide nanoparticles, researchers have invented a new, environmentally friendly, inexpensive synthetic method that replaces other methods with many defects. Studies of Ag NPs have increased after clear and substantial support from governments to develop nanotechnology. Ag NPs are the most widely due to their various potent properties. Thus, this comprehensive review discusses the different synthesis procedures and electronic applications of Ag NPs

Nurses' perceptions of aids and obstacles to the provision of optimal end of life care in ICU

Contains fulltext : 172380.pdf (publisher's version ) (Open Access

Analyse comparative des méthodes de calcul des pieux forés isolés à partir de l’essai SPT

La littérature géotechnique est assez riche en méthodes de calcul de la capacité portante des pieux isolés forés dans le sable à partir de l’essai de pénétration standard SPT. Ces méthodes ont été essentiellement développées à partir de l’analyse empirique des essais de chargement statique vertical des pieux. Les prévisions de ces méthodes sont souvent contradictoires et rares sont les études comparatives pour l’évaluation de la qualité de prévision de ces méthodes à partir des expériences de chargement des pieux. L’article se propose de contribuer à l’évaluation de quelques méthodes couramment utilisées en pratique, à travers une banque de données d’essais de pieux forés dans des sites sableux, en comparant les valeurs prédites de la charge verticale limite à celles interprétées de l’essai de chargement. Un classement de ces méthodes selon leur qualité de prévision a été proposé

Courbes P-Y des pieux isolés dans le sable. Détermination à partir de l’essai pressiométrique

L’analyse de la réponse d’un pieu isolé à un chargement horizontal est souvent menée en pratique à la base des méthodes du module de réaction, appelées aussi méthodes des courbes P-Y. Ces dernières ont connu un essor mondial considérable suite au développement d’importantes recherches expérimentales et numériques. L’article se propose de présenter une synthèse des résultats de l’interprétation des essais de chargement latéral en vraie grandeur des pieux isolés instrumentés dans des massifs sableux, en vue de la définition des paramètres des courbes P-Y, à savoir le module initial de réaction et la réaction latérale limite, à partir des caractéristiques pressiométriques du sable. L’étude montre clairement que ces deux paramètres varient en puissance avec la rigidité relative globale du système sol/pieu. A la base de cette formulation, une définition pratique des courbes P-Y hyperboliques dans le sable est proposée. L’application de la méthode proposée à des essais de chargement en vraie grandeur et en centrifugeuse montre une très bonne concordance entre les prévisions de la méthode, en termes de déplacements et moments de flexion, et les observations expérimentales

Effet de la proximité d'un talus sur un pieu court et rigide chargé horizontalement

L'influence de la proximité d'une pente sur le comportement d'un pieu court et rigide chargé horizontalement a été étudiée à l'aide d'essais sur modèles réduits centrifugés.L'étude des déplacements du pieu a montré que l'effet du talus n'est significatif que si le pieu se trouve en deçà d'une distance limite de la tête du talus.On montre qu'il est possible de prévoir le comportement d'un pieu implanté près d'un talus, en effectuant une correction adéquate des courbes P-Y correspondant à un sol horizontal

A Fuzzy-Logic-Based Controller for Three-Phase PWM Rectifier With Unity Power Factor Operation

In this paper, direct power control (DPC) of three-phase PWM rectifiers based on fuzzy logic controller is presented, without line voltage sensors. The control technique is built upon the ideas of the well known direct torque control (DTC) for induction motors. The instantaneous active and reactive powers, directly controlled by selecting the optimum state of the converter, are used as the PWM control variables instead of the phase line currents being used. The proposed fuzzy logic controller presents the advantage to be based on linguistic description and does not require a mathematical model of the system. The controller ensures a good regulation of the output voltage, and guarantees the power factor close to one. The simulation results show that the designed fuzzy controller has a good dynamic behavior, a good rejection of impact load disturbance, and is very robust