Power System Harmonic Analysis Research Articles

An approach to power system harmonic analysis based on triple-line interpolation discrete Fourier transform

An approach to power system harmonic analysis based on triple-line interpolation discrete Fourier transform

Power system harmonic analysis with real geomagnetically induced current from the 2003 halloween storm

It is well understood that geomagnetically induced currents (GICs) flow through the grounded neutrals of wye-connected transformers, generating harmonic currents that flow along frequency-dependent transmission lines. Harmonic currents affect protection systems and cause harmonic voltage drops that disturb power system voltage stability. In the literature, GICs are modelled as dc-currents for harmonic analysis. However, GICs are multi-frequency currents having both positive and negative polarities. Therefore, a representative harmonic analysis of power systems is only possible when GICs are modelled as multi-frequency AC currents. In this paper, the authors subjected a multi-machine power system model to real GICs from the 2003 halloween storm. Representative time intervals within the storm were selected, and a harmonic analysis of transmission line and generator stator currents was carried out. The results showed that the harmonic spectrum of currents fluctuated with a real GIC instead of reaching a steady state with a DC model for GIC. Moreover, harmonics induced on generator windings increase the risk of dynamic voltage and power system instability. The results confirm the susceptibility of power system generators to GICs and validate the use of synthetic GIC for modelling the effect of power system stability.

An impedance matrix model of DFIG for harmonic power flow analysis considering DC-link dynamics

The doubly-fed induction generator (DFIG) has been increasingly used in modern power systems for interfacing wind energies.Because of the nonlinear characteristics of the DFIG, it is important to properly model the DFIG when conducting harmonic analysis in power systems. This is especially important for low-order harmonics that are routinely encountered by present power systems. Therefore, this paper presents a model of DFIG for harmonic power flow analysis. The harmonic model of the back-to-back converters, i.e., the combined rotor-side converter (RSC) and grid-side converter (GSC) unit, is first established through mathematical derivations, and the result shows that it can be represented by a coupled impedance matrix, which includes the harmonic coupling between the RSC and the GSC and coupling between different harmonics. The studies also show that the coupling between different harmonics is negligible; thus, a simplified 2 × 2 impedance matrix can be practically used with confidence. After integrating with the induction generator model, a full harmonic model of DFIG can be obtained through circuit analyses. The correctness of the developed model has been verified using EMT simulations and lab experiments. The new model fills in a gap in the modeling of renewable energies for harmonic power flow analysis.

Fast-Decaying Sine Ramp Windows for Signals With Limited Frequency Resolution

Windowing digital signals is essential to digital signal processing. The matter is a complicated one, and choosing a window function is always a tradeoff between certain undesired effects on one hand and important benefits on the other. In this article, a new window class of windows called sine ramp windows is presented, which is very fast decaying with regard to the frequency resolution. These new windows improve the attenuation of far-distant spectral leakage while maintaining an acceptable minimal signal duration, which is beneficial, e.g., in the harmonic analysis of power systems in transient conditions. This window class is then extensively benchmarked against the state of science using common figures of merit proving its advantages, which are then shown in two application examples.

Power system harmonic analysis of a pulse DC sintering system

Pulse DC Sintering System (PDCS) produces metallic and nonmetallic samples in a cheap and efficient way in a short time. Some PDCS systems possess thyristor-based rectifiers to control their output power. This results in PDCS systems creating power system harmonics. The harmonic content of an PDCS system varies during sample manufacturing process since the PDCS container resistance is temperature dependent. In this study, power system harmonics of a PDCS system is examined for the first time in literature. A power analyzer device is used to measure and record the supply side current, voltage and power of the PDCS system as a function of time. Besides, an infrared temperature meter module is a used to measure PDCS container temperature and record it with respect to time during sample production. Total harmonic distortion is found to be decreasing with container temperature increasing.

Harmonic Estimation Algorithm based on ESPRIT and Linear Neural Network in Power System

In this paper, the drawbacks of current harmonic frequency estimation algorithm in power system are pointed out. In order to improve the detection accuracy and reduce the computational complexity, a new harmonic estimation algorithm for power system is proposed by combining the ESPRIT algorithm with linear neural network. Theoretic analysis and simulation experiments indicated that the new algorithm has super resolution characteristics, ideally suited for harmonic analysis in power system.

Interfacing transient stability and extended harmonic domain for dynamic harmonic analysis of power systems

This study presents a novel methodology for steady and dynamic states harmonic analysis of power systems. It employs a decomposition framework so that harmonic-producing devices are considered as separate subsystems which are solved via the extended harmonic domain (EHD) technique. The EHD is inherently a frequency domain dependent solution method that provides dynamic harmonic indices based on operational matrices. The remaining system is modelled and resolved via commonly used harmonic analysis methods while transient stability (TS) is conducted (at fundamental frequency) to account for dynamic behaviour of generators and controllers. Interfacing of EHD and TS solutions is performed via an iterative scheme. As for steady-state initialisation, an efficient and robust algorithm is proposed in this study. The proposed method is implemented in an existing software package and applied to IEEE 9-bus test system. A thorough comparison of the proposed method with the PSCAD/EMTDC software tool is also presented.

Harmonic Analysis in Power System using ZSI and Comparison with Conventional Inverter Techniques

Harmonics can appear due to non uniform condition or non-linearity in system. Harmonics out-turn distortion, losses and finally reduction in quality and efficiency. Distortion triggered by harmonic meters in term of % of THD (total harmonic distortion) which tie-up with distortion factor (unity for pure sine wave). Using MATLAB a circuit is sketch, for analyzing different harmonic effect in different fault condition, faults condition (with suitable parameter) imposed on system. By using ZS (Impedance source), VS (Voltage source) and CS (Current source) type inverters in design system contrast or similarity between results is analyzed.

A comparative study of modelling AC electric arc by one-dimensional interpolation for power system harmonics analysis

Electric arc is a discharge phenomenon caused by particular electrical events and arc produced facilities in power system, for example the occurrence of short-circuit fault in feeders and the use of electric arc furnace for steel-making. All of these electric arcs have a highly nonlinear nature and can be considered as a significant source of power quality problems. To investigate the impacts of the electric arcs on power quality studies the development of the electric arc models for simulation analysis is became necessary. This paper thus presents the use of different one-dimensional interpolation methods for modelling the alternating current electric arc. The performances of different methods are compared by simulation results that are derived from the modelling of an alternating current electric arc furnace load and a low-frequency fluorescent tube.

An Improved Method for Power Harmonic Analysis Based on Blackman Window and Phase Difference Correction

It is difficult to make the realization of synchronous sampling and the whole cycle truncation when we use the fast Fourier transform (FFT) for power system harmonic analysis .Once the FFT is used, the spectral leakage caused by it will affect the accuracy. Using Blackman window weighted to the harmonic signal, combined with the spectrum analysis of phase, An improved method for power harmonic analysis based on Blackman window and phase shifted difference correction is presented in this paper. The calculation equation of multiple fundamental harmonic signal frequency, amplitude and initial phase angle is derived and the conventional spectral phase correction method is improved. The simulation results show that the calculation accuracy using Blackman window phase correction signal harmonic analysis is improved significantly compared to Hanning window interpolation, Blackman window interpolation and Hanning window phase difference. The algorithm is simple, and has high precision and versatility, which can be applied to high-precision power metering and power quality analysis.

The multi-core parallel algorithms of wavelet/wavelet packet transforms and their applications in power system harmonic analysis and data compression

SUMMARY The multi-core technology can not only provide the computation in parallel but also avoid the redundancy costs by the communication and maintenance of multi-machine network structure. This paper uses the multi-core technology to achieve the parallelism of wavelet and wavelet packet transforms, so that the computation speed is increasing and the time is shortening in the practical applications. The parallel algorithms of wavelet and wavelet packet transforms, respectively, on the basis of POSIX thread and OpenMP are proposed and realized. The parallel results can meet the requirements by comparing parallel algorithms with the serial algorithms of single-layer and multi-layer transforms. For OpenMP, the paper takes the guidance statements to parallelize the loops of serial programs. In addition, the paper proposes one kind of nesting and non-nesting parallel means of wavelet packet transform and compares the parallel results with the serial programs. The experimental results show that the speedup is increasing with the amount of data and finally closing to 2. It is shown that the proposed parallel algorithms can improve the transform speed significantly. These parallel algorithms are applied in the harmonic analysis and data compression of power system, and a parallel strategy for compression with bitmap is proposed. The results show that the parallel algorithms of wavelet and wavelet packet transforms can improve the analysis and compression speed significantly. Copyright © 2014 John Wiley & Sons, Ltd.

Resolution Enhancement by Compressive Sensing in Power Quality and Phasor Measurement

Measurement in power systems and, particularly, in smart grids and smart microgrids is often concerned with harmonic analysis of voltage and current waveforms. The use of Fourier-based algorithms is widespread, and the limits following from the fundamental time-versus-frequency tradeoff that relates observation time to frequency resolution are well understood. This paper presents the application of an algorithm based on the principles of compressive sensing that can achieve an order-of-magnitude resolution improvement without significantly extending total observation time. For harmonic analysis in power systems, this means that accurate results can be obtained using shorter observation intervals, which allow to effectively track changes and reduce the effect of transients on measurements. The application of the algorithm to harmonics and interharmonics, as well as to phasor measurement, is considered and analyzed.

A Simple Method for Power System Harmonic Analysis

With the increasing use of non-linear electrical loads in power system, the harmonic pollution has become a severe problem. In this paper, we proposed a simple method for power system harmonic analysis. Cascaded adaptive comb filter is designed specifically to suppress the electric harmonic pollution. And a high-precision but easily implemented frequency estimation algorithm is presented based on least square estimation method. So the electric signal frequency fluctuation can be real-time tracked, and coefficients of the comb filters can be adaptively updated with this algorithm.

Harmonic analysis of power systems including thyristor-controlled series capacitor (TCSC) and its interaction with the transmission line

The increase of nonlinear devices in power systems leads us to consider their adverse effects on the waveform distortion, and consequently, the effects and propagation of this harmonic distortion over the whole power system. This paper presents the analysis of the adverse impact caused by the harmonic distortion generated by the thyristor-controlled series capacitor (TCSC) and its interaction with the transmission line. The analysis is carried out on the frequency domain, where total harmonic distortion, apparent power, active power, reactive power, distortion power and power losses are presented under different TCSC operation condition. The analysis of a four-node radial power system exhibiting harmonic distortion because of the TCSC operation is presented.

Analysis for Power System Transient Harmonics Based on Wavelet Packet Transform

In this paper, the principles of wavelet transform and wavelet packet transform were presented. The wavelet packet transform had good characteristics of uniform frequency decomposition, and thus transient harmonic analysis method was proposed based on wavelet packet transform. Finally, transient interharmonic, time varying harmonic and transient oscillation signals in power systems were simulated with Matlab emulator. The perfect results of simulation show that the presented method can accurately detect the transient harmonics, which provides support for harmonic analysis in power systems.

EMD Analysis of Power Harmonics

It can obtain intrinsic mode function (IMF) of signal wave with empirical mode decomposition (EMD) in harmonic analysis of power system. Harmonic frequency, amplitude and duration can be obtained through analysis of IMFs. Through EMD analysis on distortion waveform of single-phase AC inverter output as an example, combined with applied scene of distorted voltage, cause of distortion waveform can be deduced. The result shows that EMD analysis on non-stationary signals is of good performance, and a new substitute method of FFT transform in harmonic analysis.

Fast Harmonic Estimation of Stationary and Time-Varying Signals Using EA-AWNN

Field measurement of harmonic distortion is a fundamental requirement for monitoring, analysis, and/or control of power system harmonics. Fast and accurate estimation of time-varying harmonics is a key to realize many objectives of the smarter and cleaner grid such as harmonic source identification, improved active filter control for mitigation of harmonics, and smart meters for harmonic pollution metering. This paper presents a fast and accurate approach for real-time estimation of moderate time-varying harmonics of voltage/current signals. The proposed method is based on estimation of signal parameters via rotational invariance technique (ESPRIT)-assisted adaptive wavelet neural network (AWNN). The AWNN provides quick estimates (twice every fundamental cycle with only half-cycle data as input) of the dominant harmonics, whereas the ESPRIT complements it to handle time-varying signals with higher accuracy. The salient features of the proposed method are validated on the simulated and experimental signals of stationary and time-varying nature.

10-Point DFT and its Application in Power System Harmonic Analysis

In this paper, an efficient algorithm for computing 10-point DFT, radix-10 FFT algorithm for computing 10M-point DFT and N=L×10M-point DFT are presented. FFT is often employed in power systems harmonics analysis even though it is not accurate due to spectral leakage and barrier effect. When N=L×10M-point DFTs are used to analyze harmonics in power systems, comparing to N=2M-point DFTs, very accurate harmonic parameters can be obtained. The simulation results in MATLAB show that the methods are feasible and effective to enhance analysis accuracy.

The Harmonic Analysis of Power System

This document mainly analyses the sources of harmonic and harmonic hazards in power system. The article mainly from a few key links of power system which are electric power capacitor, power transformer, electric motors, relay protection to illustrate harmonic hazards and described harmonic treatment methods.

Harmonic Phasor Analysis Based on Improved FFT Algorithm

An approach for power system harmonic phasor analysis under asynchronous sampling is proposed in this paper. It is based on smoothing sampled data by windowing the signal with the four-term fifth derivative Nuttall (FFDN) window, and then calculating harmonic phasors in the frequency domain with an improved fast Fourier transform (IFFT) algorithm. The applicable rectification formulas of the IFFT are obtained by using the polynomial curve fitting, dramatically reducing the computation load. The FFDN window can effectively inhibit the spectral leakage and the picket fence effect can be modified by the IFFT algorithm under asynchronous sampling, and the overall algorithm can easily be implemented in embedded systems. The effectiveness of the proposed method was analyzed by means of simulations and practical experiments for multifrequency signals with the fluctuation of the fundamental frequency and with the presence of white noise and interharmonics.