Wrocław University of Science and Technology
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Analysis of non-stationary signals in power systems
Get PDFClassical techniques to estimate the spectrum of the multi-component signal are based on Fourier-based transformations. The frequency estimates obtained from their spectral peaks are affected by the window length and phase of signal component, thus presenting a large variance even in the absence of noise. We estimate the spectrum of the signals with the help of the Wigner-Ville distribution (WVD) and we obtain its time-frequency representation. For the same purpose the min-norm method (subspace method) is used. The accuracy and phase dependence of the tested methods were investigated and compared with the parameters of the frequency estimation via FFT. The proposed methods were also tested with nonstationary multiple-component signals occurring during the fault operation of inverter-fed drives and transmission lines
Advanced Spectrum Estimation Methods for Signal Analysis in Power Electronics
Get PDFModern frequency power converters generate a wide spectrum of harmonics components. Large converters systems can also generate non-characteristic 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. A novel approach to harmonic and interharmonic analysis, based on the subspace methods, is proposed. Min-norm harmonic retrieval method is an example of high-resolution eigenstructure-based methods. The Prony method as applied for signal analysis was also tested for this purpose. Both the high-resolution methods do not show the disadvantages of the traditional tools and allow exact estimation of the interharmonics frequencies. To investigate the methods several experiments were performed using simulated signals, current waveforms at the output of a simulated frequency converter and current waveforms at the output of an industrial frequency converter. For comparison, similar experiments were repeated using the FFT. The comparison proved the superiority of the new methods. However, their computation is much more complex than FFT
Application of Spectral Analysis to Detection of Space Charge Distribution in Solid Dielectrics
Get PDFThe paper deals with the signal processing of ultrasonic pulses to obtain information on space charge distribution is solid dielectrics. The linear theory based on the Fourier transform is applied to the study of ultrasonic wave propagation along the measuring path. Application of spectral method simplifies a signal analysis and enables description of the pulse and step responses accurately. The compiled computer procedures, which include FFT computer programs permit direct processing of measured signals that are stored in memory of oscilloscope
FPGA Implementation of DTC Control Method for the Induction Motor Drive
Get PDFThe high performance sensorless AC drives require a fast digital realization of many mathematical operations concerning control and estimators’ algorithms, which are time consuming. Therefore developing of custom-built digital interfaces as well as digital data processing blocks and sometimes even integration of ADC converters into one integrated circuit is necessary. Due to the fact that developing an ASIC chip is expensive and laborious, the FPGA based solution should rather be used on the design stage of the algorithm. In this paper the application of FPGA in high performance DTC induction motor drive is presented. Few issues concerning the implementation of IM drive control structures in FPGA are discussed. The use of CORDIC algorithm for some mathematical operations in the DTC method is described. Experimental test results of this drive control structure realised in FPGA are demonstrated
High resolution spectrum-estimation methods for signal analysis in power systems.
Get PDFThe spectrum-estimation methods based on the Fourier transform suffer from the major problem of resolution. The methods were developed and are mostly applied for periodic signals under the assumption that only harmonics are present and the periodicity intervals are fixed, while periodicity intervals in the presence of interharmonics are variable and very long. A novel approach to harmonic and interharmonic analysis based on the “subspace” methods is proposed. Min-norm and music harmonic retrieval methods are examples of high-resolution eigenstructure- based methods. Their resolution is theoretically independent of the signal-to-noise ratio (SNR). The Prony method as applied for parameter estimation of signal components was also tested in the paper. Both the high-resolution methods do not show the disadvantages of the traditional tools and allow exact estimation of the interharmonic frequencies. To investigate the methods, several experiments were carried out using simulated signals, current waveforms at the output of an industrial frequency converter, and current waveforms during out-of-step operation of a synchronous generator. For comparison, similar experiments were repeated using the fast Fourier transform (FFT). The comparison proved the superiority of the new methods
Parametric methods for time-frequency analysis of electric signals
Get PDFThe author presents a new approach to spectral analysis of electric signals and related problems encountered in power systems. This approach includes the use of high- resolution subspace spectrum estimation methods (such as MUSIC and ESPRIT) as replacement of widely used Fourier Transform-based techniques. The author proves that such approach can offer substantial advantages in parameter estimation accuracy, classification accuracy and many other aspects of power system analysis, especially when analyzing non- stationary waveforms. The problems treated in this work include theoretical analysis of the limitations of FFT-based analysis, problems in applications of Short Time Fourier Transform, description and characteristic properties of subspace frequency estimation methods - MUSIC and ESPRIT; estimation of the model order, theoretical development of time-varying spectrum, application of filter banks and advantages when applying to line spectra analysis, space-phasor for analysis of three-phase signals, power quality assessment using indices with practical application to waveforms from an arc furnace power supply, numerical analysis of performance of investigated methods and a novel approach to classification of power system events based on time-frequency representation and selection of "areas of interest" in time-frequency plane. The author concludes that the use of high-resolution methods significantly improves the accuracy of many parameter estimation techniques applied to power system analysis
Zespół elektrowni wiatrowych
Get PDFCelem niniejszej Pracy dyplomowej było modelowanie w środowisku programowym Matlabk-Simulink zespołu elektrowni wiatrowych. Ocena parametrów, stanów dynamicznych i statycznych pracy modelu
Hochauflösende Signalverarbeitungsmethoden in der Elektrotechnik
Get PDFModerne Frequenzumrichter erzeugen ein breites Spektrum von harmonischen Komponenten, in einigen Fällen nicht nur charakteristische Harmonische, aber auch eine ganze Menge von nichtcharakteristischen Harmonischen und Interharmonischen. Das kann wesentlich die Qualität der elektrischen Energie beeinträchtigen, die Verluste steigern und die Zuverlässigkeit des Energieversorgungssystems vermindern. Die Ermittlung von Stroms- und Spannungsparametern ist sehr wichtig für die Steuer- und Schutzeinrichtungen. Spektralanalyse von diskret abgetasteten Signalen basiert meistens auf der Fourier-Transformation. Es gibt aber verschiedene Ausführungsbegrenzungen der schnellen Fourier-Transformation. Fourieralgorithmen sind genau nur wenn das Abtastfenster ist gleich einer Periode oder mehreren Perioden der Grundschwingung. In Anwesenheit von Interharmonischen kann die Periode sehr lang sein. Die Begrenzungen werden auch lästig wenn man kurze Dateiaufnahmen analysiert. Viele alternative Methoden der Spektralanalyse sind in den letzten Jahrzehnten vorgeschlagen worden. Dazu zählen u.a. parametrische Methoden und Unterraummethoden. Die auf dem autoregressiven (AR) Model basierendes Gleichungssystem kann mit Hilfe von SVD-Technik (Singular Value Decomposition – Zerlegung nach den singulären Werten) gelöst werden. Das Prony Model ist speziell für Parameterermittlung von transienten Vorgängen geeignet, kann aber auch für periodische Vorgänge angewandt werden. Die Unterraummethoden (subspace methods), wie MUSIC (MUltiple SIgnal Classification) und MIN-NORM, auf der Theorie von Eigenwerten und Eigenvektoren. Alle obengenannten Methoden sind untersucht worden, mit der Anwendung von simulierten und reellen Signale
Analiza okresowych przebiegów odkształconych z zastosowaniem statystyk wyższych rzędów
Get PDFDuring recent years higher order statistics (HOS) have found a wide applicability in many diverse fields, e.g.: biomedicine, seismic data processing, harmonic retrieval and adaptive filtering. In power spectrum estimation, the signal under consideration is processed in such a way, that the distribution of power among its frequency is estimated and phase relations between the frequency components are suppressed. Higher order statistics known as cumulants, and their associated Fourier transforms, known as polyspectra, reveal not only amplitude information about a signal, but also phase information. If a non-Gaussian signal is received along with additive Gaussian noise, a transformation to higher order cumulant domain eliminates the noise. These are some methods for estimation of signal components, based on HOS. In the paper we apply the MUSIC method (Multiple Signal Classification) both for the correlation and the 4th order cumulant. When the investigated signal is distorted by a coloured noise the more exact results can be achieved by applying cumulants
Power system harmonics estimation using linear least squares method and SVD
Get PDFThe paper examines singular value decomposition (SVD) for the estimation of harmonics in signals in the presence of high noise. The proposed approach results in a linear least squares method. The methods developed for locating the frequencies as closely spaced sinusoidal signals are appropriate tools for the investigation of power system signals containing harmonics and interharmonics differing significantly in their multiplicity. The SVD approach is a numerical algorithm to calculate the linear least squares solution. The methods can also be applied for frequency estimation of heavy distorted periodical signals. To investigate the methods several experiments have been performed using simulated signals and the waveforms of a frequency converter current. For comparison, similar experiments have been repeated using the FFT with the same number of samples and sampling period. The comparison has proved the superiority of SVD for signals buried in the noise. However, the SVD computation is much more complex than FFT and requires more extensive mathematical manipulations