Showing papers by "Technical University of Madrid published in 1978"

Current-Source Double DC-Side Forced Commutated Inverter

Abstract: DC-side commutated inverters are very attractive due to their simplicity and efficient use of the commutation circuit. A new current-source commutated inverter of this type equally applicable to both single and multiphase bridge configurations is considered. Simultaneous turn-off of all bridge thyristors allows ample possibilities for programming the commutation sequence. The behavior of a threephase bridge is analized, and the optimum values of the commutation components are obtained. Guidelines for analysis under any commutation condition, as well as general programming rules and suggestions for snubber design are given. Results obtained in a 8-kVA variable speed drive prototype are shown and discussed.

INTERNAL QUANTUM EFFICIENCY OF BACK ILLUMINATED n+ pp+ SOLAR CELLS

Abstract: A theoretical analysis of the Internal Quantum Efficiency (I.Q.E.), taking into account the generation in the p+ layer of the back illuminated n+ pp+ solar cells has been carried out, and compared to that of the structure illuminated in the conventional way. Experimental cells have been made both by ion implantation and by alloying Al-Si to form the p+ layer. Very thin cells, here reported, present excellent values up to 90 % for the back illuminated to front illuminated I.Q.E. ratio.

Relationship between Hydrogen Metabolism and Nitrogen Fixation in Legumes

Abstract: The urgent need for conservation of energy throughout the world has created a renewed interest in biological N2 fixation. Increasing the extent and efficiency of biological N2 fixation hopefully will lead to a decreased demand for natural gas that is now being used extensively in the manufacture of nitrogen fertilizers. Loss of energy through H2 evolution from nodules of legumes has been known for twenty years, but realization that H2 evolution from a great majority of legumes represents a substantial proportion of the energy supplied to the nitrogenase system was not generally appreciated until recently (25,ll) . Legume cultivar-rhizobium strain combinations that efficiently utilize energy for metabolic processes might be expected to show increases in N2 fixation and plant growth. Several research and review papers concerning the role of H2 metabolism in nodulated legumes have been prepared in the last two years (25,26,ll) . It is the purpose of this paper to summarize the status of our present understanding of the relationship between H2 metabolism and N2 fixation in nodulated symbionts.

Numerical simulation of mixing layer vortices

Abstract: A simple model is proposed for the large spiral vortices observed in plane shear layers. An infinite, uniform vortex sheet is perturbed at one point and the resulting flow is studied numerically. A spiral structure appears that grows linearly for large values of time. The growth rates obtained agree with the observed values for the experimental layers within 25%.

Transcell, a novel approach for improving static photovoltaic concentration

Abstract: A two sided solar cell, called Transcell, is proposed to be used in proper Winston mirrors which permit double static concentration gain for a given acceptance angle. Theory and experiments show that the VOC x ISC is higher in the Transcell than in conventional or B.S.F. cells. A model of the series resistance is presented and applied for homogeneous and non homogeneous illumination beeing the calcul a ted results in good agreement with measurements. The geometric structure and dimensions are optimized for the Transcell, and their efficiency and open circuit voltage are calculated for several illumination conditions, showing that efficiencies of 11.2% can be obtained at ten AM2 suns.

A New Method of Exciting Axial Slots Cut on a Circular Cylinder

Abstract: A new method of exciting axial slots cut on a circular cylinder is presented. The interior volume of the cylinder is divided up into a number of wedge waveguides equal to the required number of slots along the circunference of the cylinder cross section. Each of these slots is thus excited independently by the corresponding wedge waveguide and its coupling can be controlled by changing its distances to the centerline of the waveguide curved wall. Theoretical expressions for the Value of the slot admittance in the wedge waveguide are given and compared with measurements on an X-band model. The new structure can be applied to microwave beacons and UHF broadcast transmitters requiring patterns which are more or less selective in the horizontal plane and narrow in the vertical plane.