Distortion In Power Systems Research Articles

Site Selection Strategy of Single-Frequency Tuned R-APF for Background Harmonic Voltage Damping in Power Systems

Series resonance between capacitance and line inductance may magnify background harmonic voltage and worsen the harmonic voltage distortion in power systems. To solve this problem, in this paper, the transmission line theory is used to set up the distributed parameter model of power system feeders, and analyze the harmonic voltage propagation caused by the background harmonic voltage in power systems. Then, a new strategy is proposed for the site selection of resistive active power filter to damp the background harmonic voltage in power systems. Experiments have been performed to verify the theoretical analysis and demonstrate the effectiveness of the proposed strategy.

Ensemble-Kalman-Filter-Based Power System Harmonic Estimation

The growing use of power-electronics-based components and nonlinear loads is increasing the presence of harmonics in power system signals. In this scenario, proper estimation of such harmonics is intended to maintain power quality and improved operation of the system. It is also desirable that the estimation technique should be computationally efficient while being accurate. From this viewpoint, this paper proposes a nonlinear state estimation technique based on ensemble Kalman filtering for estimation of harmonics, interharmonics, and subharmonics, all using a single framework and at a time, from distorted power system signal. The proposed technique is computationally efficient compared to conventional Kalman filtering leading to less computational cost and hardware requirement. It is observed from both simulation and experimental studies that the proposed ensemble Kalman filter (KF) approach to estimation of harmonics, interharmonics, and subharmonics in a distorted power system signal exhibits superior estimation performance in terms of tracking time and accuracy as compared to performances of some of the existing techniques such as recursive least square, recursive least mean square, and KF algorithms. The proposed technique is also found to be robust and gives accurate estimates even in the presence of amplitude variations in the measured signal.

Applications of Wavelet Transform for Analysis of Harmonic Distortion in Power Systems: A Review

Wavelet transform (WT) is one of the most useful digital signal processing tools for time-frequency analysis of power quality disturbances in power systems. This paper presents an extensive bibliographic review of applications of WTs in the measurement and analysis of harmonic distortion in power systems, discussing the performance of the different methods proposed in the technical literature.

BFO optimized RLS algorithm for power system harmonics estimation

In this paper a new estimation approach combining both Recursive Least Square (RLS) and Bacterial Foraging Optimization (BFO) is developed for accurate estimation of harmonics in distorted power system signals. The proposed RLS–BFO hybrid technique has been employed for estimating the fundamental as well as harmonic components present in power system voltage/current waveforms. The basic foraging strategy is made adaptive by using RLS that sequentially updates the unknown parameters of the signal. Simulation and experimental studies are included justifying the improvement in performance of this new estimation algorithm.

Estimating the Harmonic Contributions of Utility and Costumer in a distorted power system

This paper presents an improved method for determining the contribution of harmonic distortion generated by utility and customer at the Point of Common Coupling (PCC) in a distorted power system. For this purpose, first the magnitude and phase of voltage and current at the PCC in each frequency are estimated by adaptive Kalman filter. Then the parameters of Thevenin equivalent circuits of load and utility sides are estimated using the recursive least squares technique based on singular value decomposition (SVD). Finally, the contribution of utility and customer in harmonic distortion of the 3-phase voltage waveforms has been calculated by three approaches. A case study has been made to verify the accuracy of the proposed method. Also, the presented method has been used in a 13-bus IEEE standard distribution system. Presented simulation results show that the proposed method can accurately determine the harmonic contributions of utility and customer for measurements made at the PCC.

Harmonics estimation using KF-Adaline algorithm and elimination with hybrid active power filter in distorted power system signals

Harmonics estimation and its elimination for a signal distorted with additive noise is an interdisciplinary area of interest for many researchers. This paper presents Kalman filter – adaptive linear neural network (KF-Adaline) approach for harmonics estimation and hybrid active power filter (HAPF) with modified PWM control technique for its elimination in distorted power system signals. In the estimation process, the weight of the Adaline is updated using Kalman filter algorithm. Harmonics components are estimated from the updated weights of the Adaline. In order to mitigate these harmonics, HAPF with modified PWM control is proposed. The modified PWM control technique is based on comparing simultaneously a triangular high frequency carrier signal with a slow varying regulation signal and it is opposite. A laboratory prototype for HAPF with modified PWM technique is built for harmonics elimination in distorted power system signals. Simulation and experimental results are presented to verify the good behav...

New Algorithms for the Estimation of Distorted Time-varying Power System Signal Parameters in Noise

This article proposes an improved two-step augmented Gauss-Newton type algorithm for the estimation of distorted power system signals. The proposed algorithm is capable of accurately estimating the amplitude, phase, and frequency of the harmonics and interharmonics present in the power system signal in the presence of high additive white Gaussian noise. The estimation of all the parameters is divided into two steps. In the first step, the frequency of the signal is computed using an improved recursive Newton-type algorithm; in the second step, the amplitude and phase of the power system voltage or current are computed using a recursive Gauss-Newton-type algorithm. Further, to reduce the computational complexity of the standard Gauss-Newton algorithm, certain approximations are carried out, making the algorithm suitable for on-line applications. Also, a variable forgetting factor is used to improve the speed of convergence and accuracy of the algorithm. To demonstrate the robustness and accuracy in the estimation of the distorted fundamental and harmonic phasors using the proposed algorithm, the results obtained from computer simulations are presented.

Fuzzy Metrology-Sound Approach to the Identification of Sources Injecting Periodic Disturbances in Electric Networks

The identification of sources injecting periodic disturbances in electric systems is a critical point in the assessment of the electric power quality. The available methods, based on a deterministic approach, do not always provide correct results. Methods based on heuristic approaches, such as those based on a fuzzy inference system (FIS), provide better results but do not allow measurement uncertainty to be evaluated in a straightforward way. This paper applies a modified FIS to the identification of the sources producing periodic distortion in power systems. The method associates an index, provided together with its measurement uncertainty, to each load connected to a point of common coupling capable of assessing whether the load is injecting or suffering distortion and quantifying the severity of the injected or suffered distortion.

An overview of approaches for modelling uncertainty in harmonic load-flow

Harmonic distortion is a growing problem in all power systems (PS) around the world due to the increasing use of electronic power devices and nonlinear loads (NLL). Several methods have been developed for the computational analysis of PS harmonic load-flow (HLF). These approaches allow harmonic distortion to be estimated at each PS bus when NLLs (the harmonic sources) are distributed throughout a whole network. Some widely accepted deterministic formulations are used in HLF analysis; however, harmonic distortion in PS is a time-varying phenomenon because both linear loads (LL) and NLLs change non-predictably all the time. Moreover, network configuration also varies and such considerations make HLF calculation a mathematical problem which must be able to model the uncertainty associated with input data. Some approaches based on probability theory and others using fuzzy sets and possibility theories have been proposed for modeling such uncertainty. This paper was thus aimed at providing an overview regarding these approaches. The main HLF formulations within probabilistic and possibilistic frameworks have thus been introduced and some numerical comparisons have been made to clarify some concepts raised.

Bandpass Second-Degree Digital-Integrator-Based Power System Frequency Estimation Under Nonsinusoidal Conditions

A novel digital signal processing algorithm for online estimation of the fundamental frequency of the distorted power system signals is presented. The basic algorithm relies on the development of an efficient variance reduction algorithm; and design of a new stable bandpass infinite impulse response (IIR) second-degree digital integrator (SDDI) with reduced approximation error. Compared with the well-established technique such as the enhanced-phase-locked-loop (EPLL) system, the proposed algorithm provides the following: 1) higher degree of immunity and insensitivity to harmonics and noise and 2) faster response during step frequency change. Structural simplicity, wide range of application, controls over speed and accuracy, and parameter robustness are other salient features of the method. The only limitation as compared with the EPLL system is its slower transient response during step change in signal magnitude. Based on simulation studies, performances of the proposed algorithm at different operating conditions have been presented, and its accuracy and response time have been compared with the EPLL systems.

The effect of IEC grouping algorithms on frequency domain noise

In this paper, noise propagation through a two-stage nonlinear algorithm for measurement of harmonic distortion in power systems according to IEC 61000-4-7 is analyzed. Noise generated in the instrument’s input circuitry is considered as an aggregated noise source without detailed characterization of its origin. The first stage of the measurement algorithm is the discrete Fourier transform (DFT) of the input signal. Noise propagation through the DFT is analyzed by means of probability theory. The result of this analysis, the probability density function (pdf) of the DFT spectrum amplitudes, is used for characterization of the second stage of the measurement algorithm – the root-sum-square grouping of several spectrum components into a single harmonic distortion index. In this way, pdfs of the most common harmonic indices are derived and analyzed. The study presented reveals that noise generated in the input stage produces, besides the already known variance of the results, an offset in the harmonic distortion indices. Analysis of the resulting pdfs implies that an increase in the number of components in the grouping procedure increases the offset error, whereas the standard deviations are essentially independent of the number of components included in the group. The validity of the model derived has been tested with a prototype of a low-cost portable instrument for three-phase power quality measurements.

Design and implementation of a high accuracy sampling wattmeter under non-sinusoidal and off-nominal frequency conditions

Errors may creep in when measuring active power under non-sinusoidal and off-nominal frequency conditions by a conventional regularly spaced sampling digital wattmeter (RSSDW) due to the existence of higher order voltage and current harmonics, and asynchrony between the signal fundamental frequency and the sampling rate. This paper presents design and implementation of a modified regularly spaced sampling digital wattmeter, called M-RSSDW, immune to above mentioned drawbacks of the conventional RSSDW. The proposed method utilizes a modified/ first degree digital integrator design technique, suitable for the distorted power system signals. The harmful truncation errors of asynchronous sampling have been reduced using numerical compensation method. Compared with the well-established technique such as Liangs’ method, the proposed algorithm provides higher degree of immunity and insensitivity to harmonics and frequency deviation. Structural simplicity, wide range of application and reduced computational load are other salient features of the proposed method. Based on simulation studies, the performance and validity of the proposed algorithm at different operating conditions have been presented and its accuracy and response time have been compared with the Liangs’ approach.

Indices for Harmonic Distortion Monitoring of Power Distribution Systems

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Among the different power quality parameters, the voltage total harmonic distortion is important and is often studied. Different indices have previously been suggested to measure and monitor both the current and the voltage distortion in power systems, but the harmonic characterization of a power system can still not be performed in a satisfactory way. The state of the harmonic distortion is difficult to predict due to the variability and a large number of unknowns, such as detailed consumer and system characteristics. In this paper, a new index that describes the total harmonic distortion in the current measurements, i.e., the total rated distortion <formula formulatype="inline"><tex Notation="TeX">$(TRD)$</tex></formula>, is suggested to simplify and standardize the harmonic current measurements. Another index that represents the increase of the harmonic voltage distortion with <formula formulatype="inline"><tex Notation="TeX">$TRD$</tex></formula>, i.e., the equivalent harmonic impedance <formula formulatype="inline"><tex Notation="TeX">$z_{\rm eq}$</tex></formula>, is proposed as an efficient way of characterizing a particular site. It is analyzed when <formula formulatype="inline"><tex Notation="TeX">$z_{\rm eq}$</tex></formula> is increased or decreased with regard to the angle between the harmonic voltages and currents. Finally, extensive harmonic measurements of a real distribution system were performed to prove the usefulness of the proposed indices. </para>

Global method for time–frequency analysis of harmonic distortion in power systems using the wavelet packet transform

The paper proposes a method based on the use of the wavelet packet transform for the time–frequency analysis of harmonic distortion in power systems. The magnitude of harmonic and interharmonic groups, as defined in Standard IEC 61000-4-7, the magnitude of the subharmonic group, defined as an extension of the standard method, and the time evolution of odd harmonics in voltage and current waveforms can be simultaneously computed using different levels of the same wavelet decomposition tree applied to the samples of the input signal. The paper shows the performance of the method proposed in different measurement conditions and the comparison of the results with those obtained applying the standard method.

Comparison of Nonactive Powers for the Detection of Dominant Harmonic Sources in Power Systems

This paper deals with an innovative technique for the detection of disturbing loads in distorted power systems. The technique is a single-point strategy based on a comparison among different ldquononactiverdquo power quantities already proposed in the literature, which are measured at the same metering section. In this paper, the effectiveness of the strategy is discussed, which also considered the errors of the measurement transducers; the analysis is supported by simulation tests, which were carried out on both a simple single-phase system and an IEEE standard three-phase test power system. The latter was used by other authors as a benchmark system for the analysis of multipoint measurement techniques for harmonic pollution monitoring.

Measurement of IEC Groups and Subgroups Using Advanced Spectrum Estimation Methods

The International Electrotechnical Commission (IEC) standards characterize the waveform distortions in power systems with the amplitudes of harmonic and interharmonic groups and subgroups. These groups/subgroups utilize the waveform spectral components obtained from a fixed frequency-resolution discrete Fourier transform (DFT). Using the IEC standards allows for a compromise among the different goals, such as the needs for accuracy, simplification, and unification. In some cases, however, the power-system waveforms are characterized by spectral components that the DFT cannot capture with enough accuracy due to the fixed frequency resolution and/or the spectral leakage phenomenon. This paper investigates the possibility of a group/subgroup evaluation using the following advanced spectrum estimation methods: adaptive Prony, estimation of signal parameters via rotational invariance techniques, and root multiple-signal classification (MUSIC). These adaptive methods use variable lengths of time windows of analysis to ensure the best fit of the waveforms; they are not characterized by the fixed frequency resolution and do not suffer from the spectral leakage phenomenon. This paper also presents the results of the applications of these methods to three test waveforms, to current and voltage waveforms obtained from simulations of a real DC arc-furnace plant, and to waveforms measured at the point of common coupling of the low-voltage network supplying a high-performance laser printer.

Frequency Estimation of Distorted Power System Signals Using a Robust Algorithm

This paper proposes a robust algorithm based on an extended complex Kalman filter (ECKF) for improving frequency estimation of distorted power system signals. In general, abnormal data obtained from measurements may cause noises and disturbances of power systems as well as affect the accuracy of frequency estimation. For this reason, the proposed algorithm is employed to suppress the abnormalities from abnormal data of measurements for promoting the efficiency in frequency estimation. Moreover, not only can it perform the ECKF without changing any form of it, but it can also save the execution time. Results of frequency estimation for distorted signals using the proposed method are compared with the ECKF.

Intelligent Neural Network-Based Fast Power System Harmonic Detection

Nowadays, harmonic distortion in power systems is attracting significant attention. Traditional technical tools for harmonic distortion analysis using either fast Fourier transform or discrete Fourier transform are, however, susceptible to the presence of noise in the distorted signals. Harmonic detection by using Fourier transformation also requires input data for more than one cycle of the current waveform and requires time for the analysis in the next coming cycle. In this paper, an alternative method using neural network algorithm has achieved satisfactory results for fast and precise harmonic detection in noisy environments by providing only 1/2 cycle sampled values of distorted waveforms to neural network. Sensitivity considerations are conducted to determine the key factors affecting the performance efficiency of the proposed model to reach the lowest errors of testing patterns

Adaptive Prony method for waveform distortion detection in power systems

IEC Standards characterize the waveform distortions in power systems with the amplitudes of harmonic and interharmonic groupings (subgroups and groups) calculated by using the waveform spectral components obtained with a 5 Hz frequency resolution DFT. In some cases the power system waveforms are characterized by means of spectral signal components that the DFT with 5 Hz frequency resolution is unable to capture with sufficient accuracy. In this paper a new Prony method is proposed to calculate the harmonic and interharmonic subgroups. This method is based on an adaptive technique that acts with the aim of minimizing the mean square relative error of signal estimation.

A novel three‐phase time domain load modelling technique using instantaneous symmetrical components

AbstractThis paper presents a new time domain load modelling technique based on the method of Instantaneous Symmetrical Components (ISC) for three‐phase unbalanced and distorted power system loads. ISC is used here to obtain instantaneous symmetrical voltage and current components and these components are used in the calculation of the symmetrical component model parameters, resistance (R(0,1,2)), inductance (L(0,1,2)), capacitance (C(0,1,2)) and a harmonic instantaneous current source (j (t)), which are all connected in parallel. The results cover four cases of the system operation and the load parameters are found for each case, even in the presence of harmonic distortion. Consequently, it is shown that the developed method is a very powerful modelling technique to model time varying, unbalanced and distorted three‐phase loads, such as general loads: i.e. residential and commercial buildings. Copyright © 2004 John Wiley &amp; Sons, Ltd.