Wyniki wyszukiwania - Biblioteka Nauki

1

Voltage-current equations of power electronic matrix converters in frequency domain

100%

Sobczyk T. J.

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tom Vol. 51, nr 1

105-114

EN

The paper presents an analysis of voltages and currents in the matrix converter, which directly (without any intermediate DC link) transforms the N-phase system with frequency f1 to the M-phase system with frequency f2. Relations between input and output voltages and currents have been investigated in the frequency domain, using the symmetrical component approach. For a chosen control strategy of switching of converter semiconductor elements, the Fourier spectra of input and output voltages and currents have been determined and relations between them have been found. It has been proved that the voltages and currents on both sides of the converter are symmetrical, which is the main result of the paper.

PL

W pracy jest przedstawiona analiza napięć i prądów przekształtnika macierzowego, którego celem jest bezpośrednie (bez pośrednictwa prądu stałego) przekształcanie N-fazowego układu napięć i prądów o częstotliwości f1 w układ M-fazowy o częstotliwości f2. Aby opisać związki między napięciami i prądami na wejściu i wyjściu przekształtnika, przeprowadzono analizę w dziedzinie częstotliwości, używając do opisu wielofazowych składowych symetrycznych. Dla wybranej strategii przełączania półprzewodnikowych elementów przekształtnika dokonano analizy widm Fouriera napięć i prądów na wejściu i wyjściu oraz podano związki pomiędzy nimi. Najważniejszym rezultatem pracy jest wykazanie, że przy tej strategii sterowania napięcia i prądy po obu stronach zachowują symetrię.

2

Analysis of the single stage cycloidal gearbox with lobe defects. Fault diagnosis attempts using coherence function and Morris minimum-bandwidth wavelets

84%

Król R.

Archive of Mechanical Engineering

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2023

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tom LXX, nr 3

409--431

EN

In this article, the frequency characteristics of the forces and torques in the various cycloidal gearbox designs were investigated. The aim of the article is the search for frequency patterns that could be used in the formulation of a fault diagnosis methodology. Numerical analysis was performed in the cycloidal gearbox without defects as well as in cycloidal gearboxes with lobe defects or with removed lobes. The results of the numerical analysis were obtained in the multibody dynamics model of the cycloidal gearbox, implemented in Fortran and using the 2nd-order Runge-Kutta method for the integration of the motion equations. The used model is planar and uses Hunt and Crossley’s nonlinear contact modelling algorithm, which was modified using the Heaviside function and backlash to fit cycloidal gearbox model convergence demands. In the analysis of fault diagnosis methods, the coherence function and Morris minimum-bandwidth wavelets were used. It is difficult to find a unique pattern in the results to use in the fault diagnosis because of the random characteristics of the torques at the input and output shafts. Based on obtained results, a promising, low-vibration cycloidal gearbox design with removed 7 lobes of the single wheel was studied using the FFT algorithm.

3

The fractional Fourier transform as a biomedical signal and image processing tool: A review

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Gómez-Echavarría A. , Ugarte J. P. , Tobón C.

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tom Vol. 40, no. 3

1081--1093

EN

This work presents a literature review of the fractional Fourier transform (FrFT) investiga-tions and applications in the biomedical field. The FrFT is a time-frequency analysis tool that has been used for signal and image processing due to its capability in capturing the nonstationary characteristics of real signals. Most biomedical signals are an example of such non-stationarity. Thus, the FrFT-based solutions can be formulated, aiming to enhance the health technology. As the literature review indicates, common applications of the FrFT involves signal detection, filtering and features extraction. Establishing adequate solutions for these tasks requires a proper fractional order estimation and implementing the suitable numeric approach for the discrete FrFT calculation. Since most of the reports barely describe the methodology on this regard, it is important that future works include detailed information about the implementation criteria of the FrFT. Although the applications in biomedical sciences are not yet among the most frequent FrFT fields of action, the growing interest of the scientific community in the FrFT, supports its practical usefulness for developing new biomedical tools.

4

Advanced time-frequency representation in voice signal analysis

67%

Mika D. , Józwik J.

Advances in Science and Technology. Research Journal

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2018

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tom Vol. 12, no 1

251--259

EN

The most commonly used time-frequency representation of the analysis in voice signal is spectrogram. This representation belongs in general to Cohen’s class, the class of time-frequency energy distributions. From the standpoint of properties of the resolution, spectrogram representation is not optimal. In Cohen class representations are known which have a better resolution properties. All of them are created by smoothing the Wigner-Ville’a distribution characterized by the best resolution, however, the biggest harmful interference. The used smoothing functions decide about a compromise between the properties of resolution and eliminating harmful interference term. Another class of time-frequency energy distributions is the affine class of distributions. From the point of view of readability of analysis of the best properties are known so called Redistribution of energy caused by the use of a general methodology referred to as reassignment to any time-frequency representation. Reassigned distributions efficiently combine a reduction of the interference terms provided by a well adapted smoothing kernel and an increased concentration of the signal components.