Višefazni sustav za pretvorbu energije vjetra zasnovan na matričnom pretvarač

Abstract: This paper presents a new variable speed wind energy conversion systems (WECS). It is based on a six-phase asymmetrical squirrel cage induction generator (SCIG) and a matrix converter (MC) as power electronic interface between six-phase SCIG and electrical network. The analysis employs a rotor flux vector control algorithm and a scalar strategy modulated MC to control the generator. Characteristics of MC are used for maximizing the power tracking control when different wind speeds and delivering powers to the grid are simultaneously considered. The MC provides sinusoidal input and output voltages and a unity power factor, but causes an asymmetry in the generator. A current control strategy including the method of suppressing imbalance caused by this asymmetry is discussed. Some numerical simulations are carried out showing the effectiveness of the proposed WECS topology.U ovom radu prikazan je novi sustav za pretvorbu energije vjetra s promjenjivom brzinom. Zasnovan je na šestofaznom asimetričnom kaveznom generatoru i matričnom pretvaraču koji je sučelje između generatora i elektroenergetske mreže. U analizi se koristi vektorsko upravljanje tokom u rotoru i skalarna strategija moduliranog matričnog pretvarača za upravljanje generatorom. Karakteristike matričnog pretvarača koriste se za maksimiziranje slijeđenja snage u slučajevima kada se istovremeno promatraju različite brzine vjetra i snage koja se daje u mrežu. Matrični pretvarač daje sinusni ulazni i izlazni napon te jedinični faktor snage, ali uzrokuje asimetriju u generatoru. Razmotrena je strategija upravljanja strujom koja uključuje metodu za smanjivanje neravnoteže koju uzrokuje asimetrija. Provedene su numeričke simulacije koje pokazuju efektivnost predložene topologije sustava za pretvorbu energije vjetra

Optical properties of water under high pressure

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Distributed Photovoltaic Architecture for HVDC-bus Feeding with a Simple Evaluation of Optimal Tracking

International audienceThis contribution describes, compares, and analyses two structures and their operating modes dedicated to renewable energy production from photovoltaic (PV) sources. Between the two different technical approaches, photovoltaic sources placed in a distributed architecture supplying a high DC voltage HVDC bus points large advantages. Thus, after preliminary comparison of both solutions and concluding phases, this efficient solution finally constitutes the main original analysis presented in this contribution. The distributed PV structure is investigated, implemented and simulated in an original way under the OrCAD/Pspice software environment. The adaptation stage for maximum power transfer is modelled in detail. A method to calculate the optimal duty cycle for optimal use of PV panels power is proposed, tested and validated by the use of a marketed PV module datasheet

Simulation of different modes of heat transfer on a parabolic trough solar collector

The development of solar concentrator technology has just reached a very significant level. Using reflectors to concentrate the sun's rays on the absorber dramatically reduces the size of the absorber, reducing heat loss and increasing its efficiency at high temperatures. Another advantage of this system is that the reflectors are significantly less expensive, per unit area, than the flat collectors. To determine the performances of a cylindrical-parabolic concentrator, mathematical modeling of the heat balance on the absorber, the coolant, and the glass envelope was established using Matlab. The system of equations obtained is solved by the finite difference method. The results for a typical day are the variation in the temperature of the heat transfer fluid, the absorber tube, and the glass envelope. Thus, we examine the effect of the wind speed, flow rate on the temperature distribution of the coolant at the outlet. However, for a mass flow rate of the fluid of 0.1 kg / s, the outlet temperature of the fluid is 85 ° C with a thermal efficiency of 73%. Excluding the energy absorbed by the absorber tube is 75% of the solar intensity received on the reflector

A polaron approach to photorefractivity in Fe : LiNbO3

The thermally activated, incoherent hopping of small electron polarons generated by continuous illumination in iron-doped lithium niobate is simulated by a Marcus-Holstein model for which all the input parameters are known from literature. The results of the calculations are compared with a comprehensive set of data obtained from photorefractive, photogalvanic and photoconductive measurements under green light excitation on samples with different doping levels and stoichiometries in the temperature range between and room temperature. We show that the temperature and composition dependence of the photorefractive observables can be interpreted by a change in the abundance of the different hop types that a polaron performs before being captured by a deep Fe trap. Moreover, by a comparison between experimental and numerical data we obtain new insights on the initial photo-excitation part of the photorefractive process. In particular all results are consistent if a single value of the photogalvanic length is assumed for all the samples and all the temperatures. The photo-generation efficiency under green light excitation (somewhere denoted as quantum efficiency) is also estimated. It appears to decrease from 10%?15% at room temperature to about 5% at 150 K. This behavior is qualitatively interpreted in terms of a temperature-dependent re-trapping probability of the light-emitted particles from the initial Fe donor center

Energy and Climat Changes

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