Wrocław University of Science and Technology
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Parameter Estimation of Distorted Signals Using Prony Method
Get PDFModern frequency power converters generate a wide spectrum of harmonic components. Large converter systems can also generate noncharacteristic harmonics and interharmonics. Standard tools of harmonic analysis based on the Fourier transform assume that only harmonics are present and the periodicity intervals are fixed, while periodicity intervals in the presence of interharmonics are variable and very long. In the case of frequency converters the periods of the main component are unknown. The Prony method as applied for signal analysis in power frequency converter was tested in the paper. The method does not show the disadvantages of the traditional tools and allow exact estimation the frequencies of all or dominant components, even when the periodicity intervals are unknown. To investigate the appropriateness of the method several experiments were performed. For comparison, similar experiments were repeated using the FFT. The comparison proved the superiority of the Prony method
Location of Remote Harmonics in a Power System Using SVD
Get PDFThe SVD method for frequency location in the power system containing remote harmonics has been investigated in the paper. It has been shown, that the location of far distant harmonics creates the same problems of locating the frequencies as very closely spaced sinusoidal signals, and that the met hods developed for latter case are appropriate tools for the investigation of the power system containing harmonics differing significantly in their multiplicity. The proposed SVD method has been compared in its performance with the standard FFT technique and found superior to it
Properties of corona charged plasma vapour deposited PTFE film
Get PDFProperties characterising charge storage in submicron polytetrafluoroethylene (PTFE) layer deposited by evaporation in a radio-frequency (RF) plasma are described in this paper. X-ray diffraction (XRD) and scanning electron microscopy (SEM) investigations have shown that the method allows to deposit amorphous and uniform dielectric layers exhibiting resistivity at room temperature in the order of 10E14 Om. Electrical conductivity and thermo- stimulated discharge current (TSD) results were measured in the temperature range 300-450K while an isothermal discharge characteristic was examined at room temperature
Symmetrische Komponenten komplex erweiterter Zeitfunktionen und verallgemeinerter Zeiger
Get PDFErweitert man beliebige reelle Zeitfunktionen Komponenten etwa mit Hilfe der Hilbert-Transformation komplex, so lassen sich in Drehstromnetzen die symmetrischen Komponenten dieser komplex erweiterten Zeitfunktionen bilden. Sie sind ähnlich wie die Raumzeiaerkomponenten zur Analyse nichtstationärer Vorgänge in Drehstromnetzen geeignet, enthalten aber bei symmetrischen Netzen aktive Quellen nur im Mitsystem. Als Beispiel werden die Gleichungen einer Asynchronmaschine in die symmetrischen Komponenten transformiert. Berechnungsergebnisse von transienten Vorgängen bei Unterbrechung in einem Außenleiter werden gezeigt. Die Unterschiede der Analyse transienter Vorgänge mit symmetrischen Komponenten verallgemeineter Zeiger und mit Raumzeigern werden angegeben.------Symmetrical components of complex extended time functions and generalized phasors. Contents: Extending real time functions to compiex functions e.g. by means of the Hilbert transformation, in three-phase ac systems the symmetrical components of these complex extended time functions can be formed. Like the space-phasor components they are suitable to analyse transient processes in three-phase-ac systems, but with active sources only in the positive-sequence system if the three-phase system is balanced. By the way of example, the equations of an asynchronous machine are transformed to the symmetrical components. The calculation results of transient processes in case of one interrupted phase in the feeding system are presented. The differences between the analysis by symmetrical components of generalized phasors and by space phasors are shown
Piezoelectric PVDF cables
Get PDFPiezoelectrics belong to the group of electromagnetic smart materials and they fmd an increasingly wider range of applications in practice. The commonly used ceramic piezoelectrics have very good piezoelectric properties but their dimensions are limited by technological considerations. Their another drawback is their brittleness. Polymer piezoelectrics - among which polvinylidene fluoride (PVDF) is characterized by the best pr0pert.m - do not have such drawbacks. Most of research reports on the (echnology of moulding piezoelectrics from PVDF apply to thin films. Whereas in many applications, e.g. monitoring of large areas. picmlcctrics in the form of long lengths of a cable arc more suitable
Sygnały dyskretne w czasie, aliasing
Get PDFCelem ćwiczenia jest generacja sygnałów dyskretnych w czasie oraz ilustracja zjawiska aliasingu. Celem ćwiczenia jest także wprowadzenie do programowania w MATLABIE. Dzięki implementacji większości funkcji generacji i przetwarzania sygnałów oraz procedur graficznych studenci mogą skupić swój główny wysiłek na rozwiązywaniu problemu
Filtry cyfrowe
Get PDFCelem ćwiczenia jest poznanie wybranych metod projektowania filtrów cyfrowych SOI oraz NOI oraz przeprowadzenie filtracji symulowanych sygnałów dyskretnych
The effect of generation-recombination processes and of injection mechanism on current-voltage dependences in the metal-dielectric-metal system : I. Carrier generation
Get PDFA dielectric model in which electrons and holes are the charge carriers was studied. The space charge is formed by free electrons and holes as well as by trapped electrons. Carrier generation with two trapping states, in steady state and at constant voltage was considered in the assumed dielectric model. The considerations refer to the flat capacitor system. The charge injection mechanisms were described by the function of current density and field intensity at the electrodes. The effect of injection mechanisms in conditions of carrier generation on current-voltage relations was investigated
Analysis of nonstationary electric signals using the S-transform. Zastosowanie transformaty S do analizy sygnałów niestacjonarnych w elektrotechnice
Get PDFContemporary power systems, which contain a considerable number of non-linear loads, require advanced methods of spectral analysis for their investigation and control. Fourier-based spectral methods are useful in stationary signal analysis but is insufficient in the case of numerous real-life problems when signal contents changes in time. Nonstationary signals are usually analysed with STFT (Short-Time Fourier Transform). The method presented in this paper employs recently introduced S-transform which is an important development of STFT
Time-Frequency Representation for Non-Stationary Phenomena in Electrical Engineering
No full textThe paper introduces two-dimensional method of observation and diagnosis of non-stationary signals in electrical engineering. To investigate the methods several experiments were performed using simulated signals. First two-dimensional representations are obtained applying Wigner and Wigner-Ville Distribution . Then local frequency moments are calculated to achieve one-dimensional characteristics. It is shown that such characteristics preserve information about the nonstationarity in point of time, and can be used for calculation of the beginning and duration time of transient states