Iterative Quadrature Demodulation for Harmonic Synchrophasor Estimation

Power quality disruptions are triggered by variations in voltage magnitude and frequency.The widespread use of nonlinear loads exacerbates power quality issues.During normal operation, nonlinear loads are primarily responsible for power quality disturbances and harmonic distortions.In the event of faults, transient harmonics are generated in the power system, accompanied by voltage imbalances.These fluctuations alter voltage quality, induce harmonic distortions, and result in power losses within the system.This research endeavor aims to mitigate harmonic distortion through the application of harmonic filters with thyristor devices.Employing MATLAB modeling and simulation of power quality disturbances yields waveform and data, encompassing voltage and current.Various methods for harmonic reduction exist in the literature, all designed to enhance power quality.To curtail harmonic distortions, diverse control techniques such as active filters, passive filters, p-q methods, diode switches, and harmonic filters with thyristor devices are employed.This research delves deeper into elucidating the reduction of harmonic distortions.Results demonstrate that the use of harmonic filters and thyristor-based controls yields improved power quality by minimizing harmonics, in contrast to other techniques that exhibit higher Total Harmonics Distortion.Additionally, a simulation model is developed to address harmonic reduction during fault occurrences.

This paper presents the validation and characterization of a wavelet based decomposition method for the assessment of harmonic distortion in power systems, under stationary and non-stationary conditions. It uses Wavelet Packet Decomposition with Butterworth Infinite Impulse Response filters and a decomposition structure, which allows the measurement of both odd and even harmonics, up to the 63rd order, fully compliant with the requirements of the IEC 61000-4-7 standard. The method is shown to fulfil the IEC accuracy requirements for stationary harmonics, obtaining the same accuracy even under fluctuating conditions. Then, it is validated using simulated signals with real harmonic content. The proposed method is proven to be fully equivalent to Fourier analysis under stationary conditions, being often more accurate. Under non-stationary conditions, instead, it provides significantly higher accuracy, while the IEC strategy produces large errors. Lastly, the method is tested with real current and voltage signals, measured in conditions of high harmonic distortion. The proposed strategy provides a method with superior performance for fluctuating harmonics, but at the same time IEC compliant under stationary conditions.

The authors analyze interarea mode phenomena in stressed power systems, following large disturbances. It is shown that the interarea mode phenomenon could occur as a result of a nonlinear interaction of the natural modes of oscillation in the system. A technique for determining the interaction is developed and the machines participating in the interaction are identified. A procedure for predicting the onset of the interarea mode is presented. The technique was tested on two realistic sample test systems: a 50 generator system and a 126 generator system. The results of this analysis indicate that the procedure can detect the onset of the interarea mode phenomenon and also detect the machines which participate in the interacting natural modes of oscillation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Phasor measurement based on IEC 61850-9-2 and Kalman–Filtering

Yenilenebilir enerji kaynaklarının hızlı gelişimi, dağıtık üretim tesislerinin entegrasyonu ve dijitalleşmedeki ilerlemeler dünya genelindeki güç sistemlerinde karmaşık bir değişime neden olmaktadır. Güç sistemlerinin karmaşıklığı hem lisans hem de lisansüstü öğrencilerinin güç sistemleri ile ilgili çalışmalarını sıkıcı, zor ve zaman alıcı hale getirmektedir. Bununla birlikte, simülasyon araçlarının kullanılması, güç sistemleri çalışmalarıyla ilgili hesaplama işlemlerini büyük ölçüde basitleştirmiştir. Yalnızca güç sisteminin mevcut çalışma koşulları altında çalışmasını değil, aynı zamanda gelecekteki genişlemelerin planını ve tasarımını da değerlendirmek için güç akışı çalışmaları giderek daha gerekli hale gelmektedir. Bu makale, öğrencilerin güç sistemlerindeki karmaşık olayları daha iyi anlamalarına yardımcı olmak için gelişmiş görselleştirme teknikleri kullanan PowerWorld Simülatör ile güç akışı analizinin bir incelemesini sunmaktadır. Bu amaçla, Stevenson’ın 5 baralı güç sisteminin güç akışı analizi Newton-Raphson, Gauss-Seidel ve Hızlı Ayrık metotları ile incelenmiştir. Simülasyon sonuçları hem görsel olarak hem de tablo olarak verilmiştir. Sonuç olarak, PowerWorld Simülatör ile öğrencilerin geleneksel çözümlere ek olarak güç sistemi analiz problemlerini daha iyi anlayacağı görülmüştür.

With the advance of power electronics technology, power electronics devices have been widely used in industry, home appliances, office automation, etc. These devices may cause harmonies, which may result in voltage distortions, and device malfunctions. Thus the concerns with harmonics problems are growing. In this paper, we propose a new technique that makes use of a nonlinear programming technique to find out the optimal allocation and composition of passive filters. This technique is undertaken to remove harmonies and suppress voltage distortions in power systems in terms of the economy of the entire system when the harmonics generation sources are found. The proposed method makes the best use of the economy of passive filters, solves the resonance problem with the power system and finds the minimum number of allocations with the proper compositions. To verify the validity of the proposed method, we have carried out simulation studies using an IEEE 30-bus system.

Chaotic oscillation is an undesirable phenomenon in power system and it can destroy the stability of power system. The objective of this paper is to propose variable speed synergetic control to eliminate chattering phenomenon in sliding-mode control and avoid undesirable phenomena when suppressing chaotic oscillation in power system. The prominent advantage of proposed control scheme is that it can adjust convergence speed according to the system response thus avoiding undesirable phenomena in the control process. Simulation results show that our control scheme avoids undesirable phenomena in the control process and speeds up convergence rate.

36 - Electromagnetic Transients

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.

A method based on a Lure Lyapunov function is developed to analyse subsynchronous resonance (SSR) phenomena in power systems. An improved Lure Lyapunov function used to analyse the stability of a power system including the turbine-generator (T-G) shaft is presented first. Then, a standard Lure control model for a power system with a T-G shaft is obtained. The stability of such nonlinear systems at the equilibrium points is discussed in detail. The stable operation region of the system is discussed with the proposed method. The effectiveness of the proposed method is verified by a case study. This study has shown potential benefits and the validity of the Lyapunov direct method in the subsynchronous resonance analysis. Compared with the conventional analysis method, such as eigenvalue and frequency scanning techniques, the proposed method is based on the original nonlinear system. Error, that may be introduced by linearisation, is avoided completely. Moreover, the stable operation region of power systems can be obtained by the proposed method.

International audience

Electromagnetic transient study on flexible control processes of ferroresonance

Only qualitative aspects on the skin effect in conductors are properly described in the technical literature on power systems applications. Although the qualitative analysis is an important issue, it is not sufficient for a full approach and proper understanding of this electromagnetic phenomenon in power systems, more specifically in power transmission systems. The present work intends to provide a quantitative analysis of the skin effect on conductors based exclusively on the Maxwell Equations, whereby both physical and mathematical treatments of the phenomenon are properly analysed. This approach contrasts with the traditional one that uses a complex formulation based on both the differential Maxwell equations and potential concepts. Finally, a discussion on the application of the Poynting theorem on the external surface of the cylindrical conductor is presented in order to evaluate not only the resistance, but also the inductance as a function of the frequency, which is not properly discussed in the technical literature on power systems.

The increasing complexity of power systems and the need for analyses that ensure the safe and reliable operation of the system have led to the development and use of software tools that simulate system behaviour. In this context, Electromagnetic transient (EMT) studies are essential for understanding high-frequency phenomena in power systems, most often occurring during switching operations and atmospheric discharge.This paper discusses the application of SCAD/EMTDC, one of the leading software tools for EMT studies. It provides an example of modelling and energization of an overhead transmission line, with a focus on overvoltages and inrush currents that occur in the process. A detailed explanation of line modelling using the frequency-dependent model in PSCAD/EMTDC will be provided, as this level of detail is necessary for studies involving frequencies higher than the system’s fundamental frequency. Since switching overvoltages depend on the instantaneous voltage values in each phase, energization will be performed at different time instants within a single cycle to capture the worst-case overvoltage scenario. The simulation results will be analysed and compared with official technical recommendations for grid connection. Additionally, the study will provide insights into potential issues arising from switching operations and propose mitigation measures to reduce overvoltage stresses.

Real systems inevitably include some kind of nonlinearities. Power system is a typical nonlinear system with a huge scale. The steady state stability and the transient stability of power systems result from the intrinsic nonlinearities. Bifurcation theory tells us various kinds of nonlinear structure. In this article periodic orbits and chaotic behaviors detected from the view point of nonlinear system analysis are explained. Some engineering applications are also described.