1,721,008 research outputs found
Non recursive multi-harmonic least squares fitting for grid frequency estimation
No full textA new method to approximate the least squares multi-harmonic fitting is proposed. The basic idea is to expand in Taylor’s series the derivative on ω of the least squares cost function around a central value, so reducing the frequency estimation to a calculation of a root of a polynomial. In this way the method provides a frequency estimation in a closed form avoiding the recursion that is necessary in the classical approach. The results show that the proposed algorithm reaches the Cramer–Rao bound in a narrow range of frequency around a pre-estimation. Increasing the approximation orders of the Taylor’s expansion the range of maximum accuracy widens. This method is particularly suitable in grid frequency estimation due its low variability. The proposed algorithm, preserving the accuracy, requires an execution time up to 8 times lower compared to a single iteration of the classical recursive approach
Wavelets and Hilbert Transform for detection of short disturbances in electrical power networks
No full textIn electrical energy power network, disturbances can cause problems in electronic devices therefore their monitoring is fundamental to properly design the protection and compensation devices. In this paper we address the problem of disturbances’ detection by using two different signal processing methods: Wavelets and Hilbert Transform (HT). Methods were tested under different conditions of noise and harmonic distortion (THD) showing the Hilbert Transform can be used as a valid approach for this type of phenomena
Sistema neurale per la previsione del carico elettrico di stazioni di telecomunicazione
No full textSi descrive un sistema interconnesso di reti neuronali pr la previsione del carico di stazioni per telecomunicazion
Orthonormal Gas-chromatography sets of Extra Virgin Olive Oil
No full textStarting from gas-chromatograms of extra virgin olive oil samples, choosing the most significant peaks, authors try to define a standard ortho-normal base to be deposited for quality valuation
Methods for detection of sub-harmonics in power systems
No full textWith a wide range of power electronics-related applications
in power systems, harmonic currents are increasing at
an alarming rate which has greatly deteriorated the power
quality in electrical power networks. Moreover, some of
electronic controlled equipments used in power systems,
such as cycloconverters, produce sub-harmonics, a type of
waveform distortion, which can severely degrade the power
system performance. Therefore, they must be closely monitored.
Moreover, Fast Fourier Transform cannot accurately
analyze waveforms containing sub-harmonics because the
synchronization of the sampling procedure to subharmonics
is practically infeasible. The detection of subharmonics
requires a different approach from that used for
harmonics analysis. In most analysis methods the voltage
waveform is expected to be a pure sinusoid with a given
frequency and amplitude. Standard tools of harmonic
analysis based on the Fourier transform assume that only
harmonics are present in the investigated signal and the
periodicity intervals are fixed, while periodicity intervals in
the presence of interharmonics and sub-harmonics can be
variable and very long. Two novel approaches to analyze
non-stationary signals are shown in this paper. The first is
the “Root-Music” harmonic retrieval method that is an
example of high-resolution eigenstructure-based method,
the second is a numerical method based on moving average
Orthonormal Gas Chromatography Sets Of Extra Virgin Olive Oil,
No full textStarting from gas-chromatograms of samples of extra virgin olive oil, choosing most significant peaks, authors try to
define a standard ortho-normal base be deposited for quality valuatio
Evaluation Software for Fuel Cells Performance Tests
No full textA software to evaluate the performances of fuel cells. has been developed The software, initially developed for Molten. Carbonate Fuel Cells, allows to realize some measurement tests. on it, satisfying flexibility characteristics particularly appreciated. by qualified developer and researcher. The software allows to. verify both single cells and whole stack by the control of voltage. waveform versus time or current. Moreover it can be used also. for other kind of fuel cells
Comparison between DFT, Adpative Window DFT and EDFT for Power Quality Frequency Spectrum Analysis
No full textSpectral leakage and picket-fence effects associated with the system fundamental frequency variation and improperly selected sampling time window prevents a direct application of the DFT algorithm with a constant sampling rate. In particular it’s very difficult to detect low level interharmoincs and subharmonics. In this paper we compare two methods, proposed in literature, evaluating the detection capability and accuracy in frequency spectrum estimation. Several tests in different condition has been effected for the comparison
Comparison between DFT, Adpative Window DFT and EDFT for Power Quality Frequency Spectrum Analysis
No full textSpectral leakage and picket-fence effects associated with the system fundamental frequency variation and improperly selected sampling time window prevents a direct application of the DFT algorithm with a constant sampling rate. In particular it’s very difficult to detect low level interharmoincs and subharmonics. In this paper we compare two methods, proposed in literature, evaluating the detection capability and accuracy in frequency spectrum estimation. Several tests in different condition has been effected for the comparison
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