Voltage Distortion In Power System Research Articles

A Novel Method for Assessing the Contribution of Harmonic Sources to Voltage Distortion in Power Systems

This paper presents a method for evaluating the harmonic contributions of multiple harmonic sources to voltage distortion at the point of common coupling (PCC). The proposed method quantitatively represents harmonic contributions based on the equivalent voltage models of harmonic sources. The equivalent voltage models can be estimated using the recursive least square (RLS) algorithm and measured voltage and current at the PCC. The assessment of harmonic contribution heavily depends on the accuracy of equivalent model estimation. Many existing studies have assumed that the equivalent model parameters of harmonic sources are not changed. However, because harmonic source parameters and system operating conditions are not constant in real power systems, this assumption can lead large errors in harmonic contribution assessment. In this paper, we propose a new assessment method based on variable forgetting factor RLS and parameter change detection to solve the problem. The proposed method is also effective for evaluating comprehensive harmonic contributions as well as individual harmonic contributions. The case studies show that the proposed method is superior to the previous one even under parameter changing conditions.

Parameter Estimation of Single-Phase Rectifier-Based Loads: Analytical Approach

The recent rapid concentration increase of single-phase rectifier-based loads has led to the increasingly significant problem of current and voltage distortion in low-power electrical networks. To successfully perform a prediction of the current and voltage distortion in power systems due to such nonlinear loads, it is necessary to know the structure and model parameters of those power-electronics circuits. Generally speaking, since the structure of a typical single-phase rectifier-based load is rather known, the parameters of those loads remain to be determined. Concerning this matter, an algorithm for estimating the unknown parameters of a typical single-phase rectifier based load is presented in this paper. The algorithm is based on a general approach for determining analytically the waveform of the ac load current and the dc capacitor voltage within an arbitrary number of time periods. The described nonlinear load model along with the model parameters obtained by using the suggested estimation algorithm were verified by comparison against a laboratory-designed typical rectifier-based load. Excellent agreement between the estimated and measured load parameters, as well as between the measured and simulated current and voltage waveforms was found.

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.

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>

Measurement aspects of the voltage distortion compensation

AbstractA complete solution of the compensator controller, allowing to eliminate voltage distortion in power system is presented. The two‐step circuit identification procedure based on the interpolating “Fast Fourier Transformation “ (FFT) has been successfully used to damp the 3rd, 5th and 7th harmonic by 60 dB at selected buses. Interpolating, flat‐top and coherent sampling methods, when used to 10 bit A/D converted (noised) signals, have been compared and simulated. It is shown that the shortest signal record requested to perform step calculations is of only one voltage period when a modified windowed coherent sampling method is used. The proposed method is tolerant to the coherency mistuning, so easy to implement even if a very simple hardware frequency multiplier is used to generate the sampling signal. A background to the presented solutions is given, allowing easily to solve similar compensating problems with different constraints.