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Measuring power system harmonics and interharmonics by an improved fast Fourier transform-based algorithm

IET GENERATION TRANSMISSION & DISTRIBUTION 2008年第2期2卷 192-201页

作者： Chang, G. W. Chen, C. I. Liu, Y. J. Wu, M. C. Natl Chung Cheng Univ Dept Elect Engn Chiayi 621 Taiwan

The fast Fourier transform (fft) has been widely used for the signal processing because of its computational efficiency. Because of the spectral leakage and picket-fence effects associated with the system fundamental frequency variation and improperly selected sampling time window, a direct application of the fft algorithm with a constant sampling rate may lead to inaccurate results for continuously measuring power system harmonics and interharmonics. An improved fft-based algorithm to measure harmonics and interharmonics accurately is proposed. In the proposed algorithm, a frequency-domain interpolation approach is adopted to determine the system fundamental frequency, and the interpolatory polynomial method is applied to reconstruct the sampled time-domain signal;it is followed by using the fft to calculate the actual harmonic components. Then, the frequency-domain interpolation is again applied to find the interharmonic components. The performance of the proposed algorithm is validated by testing the actual measured waveforms. Results are compared with those obtained by directly applying a typical fft algorithm and by the IEC grouping method. It shows that the solutions determined by the proposed algorithm are more accurate, and a reasonable computational efficiency is maintained.

关键词： power system measurement time-domain signal power system interharmonics interpolatory polynomial method polynomials power system harmonics fast Fourier transform-based algorithm fft algorithm picket-fence effects spectral leakage Power supply quality and harmonics frequency-domain interpolation approach Power system measurement and metering Interpolation and function approximation (numerical analysis) interpolation frequency-domain analysis Integral transforms in numerical analysis power system harmonics measurement fast Fourier transforms

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Dimension-reduction simulation of stochastic wind velocity fields by two continuous approaches

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WIND AND STRUCTURES 2019年第6期29卷 389-403页

作者： Liu, Zhangjun He, Chenggao Liu, Zenghui Lu, Hailin Wuhan Inst Technol Sch Civil Engn & Architecture Wuhan 430074 Hubei Peoples R China China Three Gorges Univ Coll Civil Engn & Architecture Yichang 443002 Peoples R China

In this study, two original spectral representations of stationary stochastic fields, say the continuous proper orthogonal decomposition (CPOD) and the frequency-wavenumber spectral representation (FWSR), are derived from the Fourier-Stietljes integral at first Meanwhile, the relations between the above two representations are discussed detailedly. However, the most widely used conventional Monte Carlo schemes associated with the two representations still leave two difficulties unsolved, say the high dimension of random variables and the incompleteness of probability with respect to the generated sample functions of the stochastic fields. In view of this, a dimension-reduction model involving merely one elementary random variable with the representative points set owing assigned probabilities is proposed, realizing the refined description of probability characteristics for the stochastic fields by generating just several hundred representative samples with assigned probabilities. In addition, for the purpose of overcoming the defects of simulation efficiency and accuracy in the FWSR, an improved scheme of non-uniform wavenumber intervals is suggested. Finally, the Fast Fourier Transform (fft) algorithm is adopted to further enhance the simulation efficiency of the horizontal stochastic wind velocity fields. Numerical examples fully reveal the validity and superiority of the proposed methods.

关键词： stochastic wind velocity field continuous proper orthogonal decomposition frequency-wavenumber spectral representation dimension reduction non-uniform wavenumber intervals fft algorithm

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New spectral decomposition based approach for flicker evaluation of electric arc furnaces

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IET GENERATION TRANSMISSION & DISTRIBUTION 2009年第4期3卷 393-411页

作者： Koese, N. Salor, Oe. TUBITAK Uzay Power Elect Grp TR-06531 Ankara Turkey METU Dept Elect & Elect Engn TR-06531 Ankara Turkey

A spectral decomposition-based approach is proposed to estimate the light flicker caused by electrical arc furnaces (EAFs) where the system frequency deviates significantly due to the EAF operation. Analytical expressions of the instantaneous light flicker sensation are obtained beginning from a voltage waveform and these expressions are used to obtain a flicker estimation method based on the IEC flickermeter. In the proposed method, the leakage effect of the fft algorithm due to fundamental frequency variation is reduced by employing a spectral amplitude correction around the fundamental frequency. The eye-brain weighting curve is realised comparing the voltage spectrum with the tabulated normalised IEC flickermeter responses for sinusoidal voltage fluctuations of the IEC standard. The proposed method is tested on both simulated data and field data obtained from three different EAF plants. The comparison with the digital realisation of the IEC flickermeter shows that the method gives satisfactory estimations of both the instantaneous flicker sensation and the short term flicker severity with low computational complexity. The method is especially useful for all other conditions such as disturbances and subsequent system transients where the system frequency deviates without the need for online sampling rate adjustment.

关键词： amplitude calibration Frequency variation Arc furnaces International Electrotechnical Commission voltage waveform Flicker spectral representation fft algorithm system frequency

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Analysis of circulant symmetric coupled strip lines

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JOURNAL OF ELECTROMAGNETIC WAVES AND APPLICATIONS 2002年第7期16卷 977-994页

作者： Cheldavi, A Amirhosseini, MK Iran Univ Sci & Technol Tehran 16844 Iran

In this paper a new kind of coupled transmission lines called circulant symmetric coupled microstrip structure and its application as an interconnect in high speed integrated circuits will be introduced. Also a simple method for frequency domain and transient analysis of this kind of coupled microstrip transmission lines is presented. First the capacitance ([C]) and inductance ([L]) matrices of the structure are derived. An special matrix is then defined to decompose the differential equations of the lines and diagonalize the [L] and [C] matrices (modal decomposition method). Finally the frequency domain solution is obtained and fft algorithm is used to find the time domain response of the line.

关键词： Multiconductor transmission-lines Time response Nonuniform Interconnections Simulation CENTROSYMMETRIC simulating TIME DOMAIN RESPONSE fft algorithm Nonuniform coupled transmission lines Frequency-domain analysis Strip Line Device Component Time response Transient analysis circulation superconducting microstrips

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Computer simulated holography and computer generated holograms

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AMERICAN JOURNAL OF PHYSICS 1996年第4期64卷 472-478页

作者： Trester, S LONG ISL UNIV DEPT PHYS CW POST CAMPUS BROOKVILLE NY 11548 USA

The success of calculating and displaying the Fraunhofer diffraction patterns for various apertures using the fast Fourier transform algorithm on an IBM compatible personal computer has been well documented in the recent literature. In this paper the technique is extended to the simulation of optical holography on the computer. Using this method, Fourier transform holograms are easily generated. Their. optically reconstructed images are compared to the ones reconstructed and displayed by the computer. These computer generated images allow for a quantitative verification of the holographic theory presented and can serve:as the basis of a tutorial on this subject suitable for advanced undergraduates. The calculations and graphics were accomplished using the MATHCAD(R) for WINDOWS(TM) software package. (C) 1996 American Association of Physics Teachers.

关键词： Computers Holograms Holography graphic images fft algorithm apertures

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Analysis of isolated self-excited induction generator feeding a rectifier load

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IEE PROCEEDINGS-GENERATION TRANSMISSION AND DISTRIBUTION 2002年第1期149卷 90-97页

作者： Kuo, SC Wang, L Natl Cheng Kung Univ Dept Elect Engn Tainan 70101 Taiwan

Both transient and steady-state performances of in isolated self-excited induction generator (SEIG) supplying a rectifier load are presented, A hybrid model based on abc and q-d induction machine models is employed to describe the dynamic equations of the studied system to improve simulation results. The stator voltage equations of the SEIG studied are described by a three-phase abc model which can be directly interfaced to the rectifier circuit. The rotor variables are properly transformed into q-d co-ordinates and the elements in the rotor inductance matrix are time-invariant. The controlled rectifiers, including both semi and full converters, are modelled by using three switching functions, which are designated to be tristate switches for each converter leg. Combining the SEIG model proposed with the rectifier model, the transient characteristics of the SEIG under various loading conditions are simulated and evaluated. The fft algorithm is used to analyse the voltage and current harmonic content Under steady-state conditions. Experimental results obtained from a laboratory 1.1 kW induction machine driven by a DC motor ire also performed to confirm the effectiveness of the proposed approach.

关键词： current harmonic content Asynchronous machines fft algorithm transient performances Power convertors and power supplies to apparatus AC-DC power convertors load (electric) machine theory voltage harmonic content loading conditions dynamic equations Linear algebra (numerical analysis) fast Fourier transforms steady-state performances stators matrix algebra asynchronous generators rotors Integral transforms in numerical analysis switching functions exciters abc induction machine models rectifier load stator voltage equations q-d induction machine models controlled rectifiers rotor inductance matrix 1.1 kW rectifying circuits isolated self-excited induction generator transient characteristics

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Low power receiver architectures for multi-carrier CDMA

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IEE PROCEEDINGS-CIRCUITS DEVICES AND SYSTEMS 2002年第4期149卷 227-233页

作者： McCormick, AC Grant, PM Thompson, JS Arslan, T Erdogan, AT Univ Edinburgh Dept Elect & Elect Engn Edinburgh EH9 3JL Midlothian Scotland

The implementation of multi-carrier code division multiple access (MC-CDMA) receivers in digital hardware is considered. A low power algorithm is proposed which treats the received signal as a block of symbols, rather than processing the symbols individually. This reduces power by holding one input to the multiplier circuits used in the multi-carrier combiner multiplication constant for a number of clock cycles. This produces a 50% reduction in power consumption for a multi-user detection combiner circuit. This algorithm is also extended to the fast Fourier transform (fft) block and allows an overall power drain reduction of 13% for the whole receiver. A software configurable version of the circuit, which allows a trade-off between power reduction and processing delay, is also described.

关键词： multi-user detection combiner circuit software reconfiguration fft algorithm multi-carrier CDMA multiplying circuits code division multiple access fast Fourier transforms digital hardware radio receivers multiplier circuit low-power electronics multiplication constant low-power receiver architecture

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Analysis and simulation of diffractive imaging field in thick film photoresist by using angular spectrum theory

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OPTICS COMMUNICATIONS 2005年第1-6期244卷 123-130页

作者： Tang, XG Gao, FH Guo, YK Du, JL Liu, SJ Gao, F Sichuan Univ Dept Phys Chengdu 610064 Peoples R China

The thick film photoresist lithography is a much more complicated process compared to the thin film photoresist lithography. In this paper, we have developed a new model for lithography of thick film photoresist by using the angular spectrum theory. The thick film photoresist is divided into many homogeneous layers, and the diffractive optical imaging distribution in photoresist is regarded as superposition of different spectrum plane waves. Propagation of each plane wave is determined by the optical transfer function, and the propagation direction, amplitude and phase are dominated by reflection and transmission between each interface of the sub-layers. The fast Fourier transform (fft) has been converted into a convolution calculation to keep the computation accurate and reduce computation cost. Numerical calculation results show that optical intensity in cross-sect of thick film resist is strongly affected by reflection, transmission on interface and variation of dielectric permittivity along direction of depth, and therefore these factors should be considered while analyzing diffractive imaging field in thick film photoresist. (C) 2004 Elsevier B.V. All rights reserved.

关键词： diffractive optics lithography angular spectrum theory optical transfer function thick film photoresist fft algorithm

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ADAPTIVE FILTER FOR 2-DIMENSIONAL GABOR TRANSFORMATION AND ITS IMPLEMENTATION

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IEE PROCEEDINGS-I COMMUNICATIONS SPEECH AND VISION 1993年第1期140卷 2-6页

作者： TEUNER, A HOSTICKA, BJ Fraunhofer Institute of Microelectronic Circuits and Systems Duisburg Germany

An adaptive filter that enables coefficient computation of the Gabor expansion while employing the least mean-squared algorithm for complex signals is described. A significant simplification of the filter structure and the use of fft algorithms contribute to a fast and efficient determination of the coefficients when compared with known algorithms for Gabor computation. Based on these results, we propose a hardware realisation using a CORDIC processor. Computer simulations indicate that sufficient precision and a fast convergence of the coefficients can be obtained.

关键词： ADAPTIVE FILTERS fft algorithm IMAGE COMPRESSION

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Efficient simulation of two-spatial dimensional turbulent wind fields based on the factorization of random functions

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JOURNAL OF WIND ENGINEERING AND INDUSTRIAL AERODYNAMICS 2024年 247卷

作者： Liu, Yun Wang, Hao Xu, Zidong Zhao, Kaiyong Southeast Univ Key Lab C &PC Struct Minist Educ Nanjing 211189 Peoples R China Southeast Univ Sch Civil Engn Nanjing 211189 Peoples R China

Refined modelling of turbulence in two-spatial dimensions is necessary for reliability assessment of large-size structures such as wind turbines. Stochastic wave-based spectral representation (SWSR) method is a widelyused tool. However, the correlation of turbulent components is usually neglected in it. Based on the SWSR, a multi-dimension (n-D) multi-variable (n-V) continuous temporal-spatial field model is thus proposed in this study. The low efficiency exist in this model, which are also unavoidable in others when simulating turbulence in multi-spatial dimensions. One reason is the large number of sample functions in the Monte Carlo (MC)-based method. The other is the n-D matrix-based Fast Fourier Transform (fft) algorithm in single sample generation. Therefore, an efficient method is given to improve efficiency in both two aspects. The former improvement is realized through defining multi-index dimension reduction (DR) expressions in the proposed model. The latter is based on the 1-D vector-based fft algorithm, the key to which are the decoupling of n-D matrices and factorization of multi-index DR expressions. A numerical simulation of a stochastic wind field in two-spatial dimensions is designed to demonstrate the validity of the proposed method. Results show its improvement of efficiency in both views of sample sets and single sample generation.

关键词： Turbulence simulation Stochastic wave Spectral representation method Dimension reduction fft algorithm

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