A Method to Determine the Existence of Genuine Interharmonics (original) (raw)

Detection Methods of Interharmonics Parameters Based on DFT Filter Banks

There are a large number of interharmonics in electric power system. But if FFT algorithm is directly used for interharmonic analysis, it exists spectrum leakage and hurdle effect. This paper presents using multi-sample rate digital signal processing technology to realize narrowb and low-pass filter, on this basis, using the DFT filter banks to detect interharmonic frequency and amplitude. The simulation results show, the new algorithm has high detection precision. Keywords DFT filter bank; interharmonics; multi-sample rate

Real-time interharmonics detection and measurement based on FFT algorithm

2009 Applied Electronics, 2009

The modern power systems are supplying an increasing number of non-linear loads like: double conversion systems, arc furnaces, arc discharging, high power Cycloconverter (CCV) etc. These loads are harmonics and interharmonics sources. Therefore, it is important to measure interharmonics accurately. The Fast Fourier Transform (FFT) is used for signal processing because of its computational efficiency. Most power quality meters and digital relays adopt FFT-Based algorithm to characterize harmonics of the measured signals. The International Electrotechnical Commission (IEC) standards on power quality have defined the terminology, limits and measurements guidelines for interharmonics. This paper shows effects on windowing in the interharmonics detection based on IEC technique. Simulations and experimental results based on the Real-time platforms are discussed.

A Weighting Method to Identify Interharmonics Based On Calculating the Bandwidth in Group-Harmonic

2013

Power converters produce a vast range of harmonics, subharmonics and interharmonics. Harmonics analyzing tools based on the Fast Fourier Transform (FFT) assume that only harmonics are present and the periodicity intervals are fixed, while these periodicity intervals are variable and long in the presence of interharmonics. Using FFT may lead to invalid and undesired results due to the above mentioned issues. They can also lead to problems such as frequency blending, spectral leakage and the picket-fence effect. In this paper, the group-harmonic weighting (GHW) approach has been presented to identify the interharmonics in a power system. Afterwards, a modified GHW has been introduced to calculate the proper bandwidth for analyzing the various values of interharmonics. Modifying this method leads to more precise results in the FFT of a waveform containing inter harmonics especially in power systems with a fundamental frequency drift or frequency interference. Numerical simulations have been performed to prove the efficiency of the presented algorithm in interharmonics detection and to increase the accuracy of the FFT and the GWH methods.

Interharmonics: Theory and Modeling

IEEE Transactions on Power Delivery, 2000

Some of the most remarkable issues related to interharmonic theory and modeling are presented. Starting from the basic definitions and concepts, attention is first devoted to interharmonic sources. Then, the interharmonic assessment is considered with particular attention to the problem of the frequency resolution and of the computational burden associated with the analysis of periodic steady-state waveforms. Finally, modeling of different kinds of interharmonic sources and the extension of the classical models developed for power system harmonic analysis to include interharmonics are discussed. Numerical results for the issues presented are given with references to case studies constituted by popular schemes of adjustable speed drives.

Prony’S Method Used for Testing Harmonics and Interharmonics in Electrical Power Systems

Metrology and Measurement Systems, 2012

The article presents an application of Prony’s method with some known components in the analysis of electric power quality. Modifications of the Prony algorithm broaden the scope of method application. Modification of the filter of known components enables more accurate analysis of the parameters of unknown components and components with known or assumed frequencies. This article presents a comparison of the results of analyses conducted with the proposed algorithm for simulated and real signals and the results obtained by means of a commercial electric power quality testing device, operating in class A and using the Fourier transform. The proposed method enables to estimate the levels of the harmonic components, the frequency of the fundamental signal and real parameters of the interharmonic components, which are grouped and averaged in the contemporary monitoring equipment. Knowledge of the individual parameters of the interharmonics has considerable diagnostic importance while re...

Interharmonics: Theory and Modeling IEEE Task Force on Harmonics Modeling and Simulation

2000

Some of the most remarkable issues related to inter- harmonic theory and modeling are presented. Starting from the basic definitions and concepts, attention is first devoted to interhar- monic sources. Then, the interharmonic assessment is considered with particular attention to the problem of the frequency resolu- tion and of the computational burden associated with the analysis of periodic steady-state waveforms.

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

IET Generation, Transmission & Distribution, 2008

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.

Estimating Interharmonics by Using Sliding-Window ESPRIT

IEEE Transactions on Power Delivery, 2000

A method is proposed for estimating interharmonic frequencies in power system voltage and current signals. The method is based on a spectrum-estimation method known as "estimation of signal parameters via rotational invariance techniques" (ESPRIT). To allow for a more reliable spectral estimation and to cover nonstationarity in the signal, a sliding-window version of ESPRIT is introduced. This paper describes the basic ESPRIT method as well as sliding-window ESPRIT. The paper discusses the application of the method to one synthetic signal and three measurement signals. It is shown that the method allows for very accurate frequency estimation of interharmonic components. The limitations of the methods, such as line splitting and spurious components, can be overcome by using the coherent information obtained from the sliding-window method. A number of remaining issues are also discussed in this paper.

Metrological Aspects of Inter -Harmonic Identification and Grouping in Electrical Power Systems

The main purpose of this paper is to present some metrological aspects of identification and grouping of harmonics and interharmonics and calculation of total harmonic. The Virtual Instrument for identification of distorted signal spectrum is described and the demonstration may take place at the presentation of the paper at the oral or poster session. We define the total harmonic and interharmonic distortion coefficient and analyse its sensitivity to variation in fundamental and interharmonic frequency and sensitivity to incompleteness of samples for five different cases: rectangular window, triangular, Hanning, Hamming and Blackman windows. The virtual test signal was selected arbitrarily. This signal was processed first by the virtual harmonic analyser, in such a way that all components were identified without any errors, and then the signal was analysed according to the requirements specified in IEC 61000-30-4 draft standard, in which also Harmonic Groups (HG) and Interharmonic G...

A PC-based instrument for harmonics and interharmonics measurement in power supply systems

Measurement, 2004

Growing interest on power quality has led international working groups to define new standards for testing and measurement techniques to apply to power systems. Special attention has been paid to harmonic and interharmonic measurements. Here, the authors introduce a PC-based instrument capable of synchronising sampling frequency with fundamental frequency in order to perform on-line voltage or current distortion analysis. The instrument has been developed in accordance with currently available standards and international documents