Power quality studies in distribution systems involving spectral decomposition

Im Rahmen der Arbeit wurde eine Methode der Spannungsqualitätsanalyse vorgestellt, die zur Untersuchung von Oberschwingungen und Zwischenharmonischen in Verteilungsnetzen besonders geeignet ist. Der zunehmende Einsatz von elektronisch gesteuerten Geräten führt zur Beeinträchtigung der Energiequalität in elektrischen Netzen. Die resultierende Spannungs- und Stromverzerrung kann für empfindliche Einrichtungen gefährlich sein, besonders dann, wenn der Oberschwingungspegel nahe an den Störfestigkeitspegeln der angeschlossenen Betriebsmittel liegt oder diese überschreitet. Die in der Arbeit vorgestellte Methode findet die bezüglich Oberschwingungen und Zwischenharmonischen gefährdetsten Stellen in einem Verteilungssystem heraus. Somit wird eine Vorab-Analyse zur Ergreifung der notwendigen Maßnahmen ermöglicht. Zunächst wurde das Thema Spannungsqualität und ihr Zusammenhang mit der elektromagnetischen Verträglichkeit aus Sicht der Normen und Vorschriften erläutert. Darauf aufbauend wurde eine grundlegende Klassifikation der Spannungsqualitätsereignisse vorgestellt und analysiert. Es wurde festgestellt, dass die Spannungsqualität aus verschiedenen Gründen zunehmend überwacht werden muss - einerseits aufgrund verstärkter Resonanzgefahr durch wachsenden Anteil nichtlinearer Verbraucher bei gleichzeitig sinkenden Anteil ohmscher Lasten und andererseits, da der durch den veränderten Energiemarkt verstärkte Kostendruck die Evaluierung auch unter wirtschaftlichen Gesichtspunkten notwendig macht. Das Konzept eines entsprechend entwickelten Messsystems zur Beurteilung der Spannungsqualität in Verteilungsnetzen wurde vorgestellt. Der Einsatz der verwendeten Beurteilungsalgorithmen stand hierbei im Zentrum des Messsystems, deren flexibler Aufbau sowohl langzeitige Spannungsqualitätsmessungen aber auch Emissionsmessungen an einzelnen Geräten normgerecht ermöglicht. Im Weiteren wurden Modellierungsansätze für elektrische Betriebsmittel sowie sowohl lineare- als auch nicht-lineare Lasten für die Modellierung im FrequenzBereich vorgestellt. Dabei wurde verdeutlicht, dass das Zusammenwirken zwischen der Störquelle - nichtlinearer Last - und der Störsenke - dem Versorgungsnetz - sehr wesentlich für die Genauigkeit der Simulationen ist. Darauf aufbauend wurde eine messungsbasierte Methode vorgeschlagen, um die zu berücksichtigenden Nichtlinearitäten mit Hilfe einer Crossed-Frequency-Admittance-Matrix im Harmonischen-Bereich zu modellieren. Ein Beispiel illustriert detailliert dieses Verfahren, so dass alle Abhängigkeiten und Wechselwirkungen deutlich werden.  Um die in der Arbeit entwickelte Methode sinnvoll durchführen zu können, müssen im Voraus die sensitivsten Knoten in einem Verteilungsnetz gefunden werden. Deshalb wurde als Kern der entwickelten Methode ein Verfahren vorgeschlagen, das auf der internen Struktur des zu analysierenden Netzes basiert. Nachdem die mathematischen Grundlagen dieses spektralen Ansatzes vorgestellt wurden, wurde eine Beispielanalyse am realen Netz durchgeführt um die Eigenschaften dieser qualitativen Methode zu veranschaulichen. Die Untersuchungen zeigten, dass die Methode zur Beurteilung von Spannungsqualität in Verteilungsnetzen wirkungsvoll anwendbar ist und zu besserer Genauigkeit bei Simulationen führt. Durch die Filterungseigenschaft der Spektralanalyse wurde eine bessere Selektivität der Analyse erreicht als bei herkömmlichen Methoden der Spannungsqualitätsanalyse. Das ist besonders bei Verteilungsnetzen von Vorteil, bei denen ungünstige Verhältnisse bezüglich Spannungs– und Stromqualität, hervorgerufen durch niedrige Kurzschlussleistungen und eine Vielzahl von Störquellen in den Verteilungsnetzen, entstehen. &nbsp

Wavelet-Based Harmonic Magnitude Measurement in the Presence of Interharmonics

The increasing proliferation of power electronic converters, nonlinear loads, and distributed generation are leading to increased levels of harmonic and interharmonics in power networks. As a consequence, power quality (PQ) has become a critical performance indicator for power utilities and end-users. This study proposes a novel harmonic estimation method based on the real-time stationary discrete wavelet packet transform (RT-SDWPT). The proposed technique decomposes an input signal into frequency bands with harmonic information at cutoff frequencies and uses a compensation strategy to estimate root mean square (RMS) values of harmonics at every sampling period. The performance and effectiveness of the proposed method are assessed using real measurement data from field cases and experimental setup. The real measurements include challenging scenarios with harmonics, subharmonics, interharmonics, frequency deviation, and non-stationary PQ events. The proposed method outperforms the harmonic estimation provided by the discrete Fourier transform (DFT)-based approach and existing wavelet packet-based methods in terms of accuracy and speed

Frequency and fundamental signal measurement algorithms for distributed control and protection applications

Increasing penetration of distributed generation within electricity networks leads to the requirement for cheap, integrated, protection and control systems. To minimise cost, algorithms for the measurement of AC voltage and current waveforms can be implemented on a single microcontroller, which also carries out other protection and control tasks, including communication and data logging. This limits the frame rate of the major algorithms, although analogue to digital converters (ADCs) can be oversampled using peripheral control processors on suitable microcontrollers. Measurement algorithms also have to be tolerant of poor power quality, which may arise within grid-connected or islanded (e.g. emergency, battlefield or marine) power system scenarios. This study presents a 'Clarke-FLL hybrid' architecture, which combines a three-phase Clarke transformation measurement with a frequency-locked loop (FLL). This hybrid contains suitable algorithms for the measurement of frequency, amplitude and phase within dynamic three-phase AC power systems. The Clarke-FLL hybrid is shown to be robust and accurate, with harmonic content up to and above 28% total harmonic distortion (THD), and with the major algorithms executing at only 500 samples per second. This is achieved by careful optimisation and cascaded use of exact-time averaging techniques, which prove to be useful at all stages of the measurements: from DC bias removal through low-sample-rate Fourier analysis to sub-harmonic ripple removal. Platform-independent algorithms for three-phase nodal power flow analysis are benchmarked on three processors, including the Infineon TC1796 microcontroller, on which only 10% of the 2000 mus frame time is required, leaving the remainder free for other algorithms

DFT-based recursive group-harmonic energy distribution approach for power interharmonic identification

AbstractThe Discrete Fourier Transform (DFT) is still a widely used tool for analyzing and measuring both stationary and transient signals in power system harmonics. However, the misapplications of DFT can lead to incorrect results caused by some problems such as the aliasing effect, spectral leakage and picket-fence effect. The strategy of a DFT-based recursive Group-harmonic Energy Distribution (GED) algorithm is developed for system-wide harmonic/interharmonic evaluation in power systems. The proposed algorithm can restore individual dispersing spectral leakage energy caused by the DFT, and thus retrieve respective real harmonic/interharmonic value. Every distribution of energy minimizing iteration procedure for harmonic/interharmonic evaluation can be convergent fast, and therefore guarantee each harmonic/interharmonic magnitude and respective frequency approaches its actual value. Consequently, not only can high precision in integer harmonic measurement be retained, but also the interharmonics can be identified accurately, particularly under system frequency drift. A numerical example is presented to verify the proposed algorithm in terms of robust, fast and precise performance

An overview of measurement standards for power quality

Received: December 7th, 2020 ; Accepted: April 7th, 2021 ; Published: May 13th, 2021 ; Correspondence: [email protected] Quality (PQ) is a vital aspect of electrical power systems, which cannot be neglected anymore, as an ample PQ guarantees the essential compatibility between consumer equipment and the electricity network. The analysis of electrical parameters related to distributing electricity is recognized as a complex engineering problem. It remains a critical task to maintain and improve PQ in modern evolving networks as the overall system performance highly depends on it. Future smart grids will also require a further increase in PQ levels in terms of observability, affordability, data exchange, flexibility, and net metering, thus making the network much more complex as it will be featuring a large amount of variable renewable-based distributed generation. This will further require the need for the introduction of novel, efficient and intelligent monitoring, control, and communication systems with various demand manageable resources. In this paper, a review and comparisons have been made for different IEEE and IEC measurement standards that are used for PQ with a specific focus on harmonic distortion as it is one of the most important parameters in PQ and some guidelines have been suggested for future electricity networks

Harmonic Estimation Of Distorted Power Signals Using PSO – Adaline

In recent times, power system harmonics has got a great deal of interest by many Power system Engineers. It is primarily due to the fact that non-linear loads comprise an increasing portion of the total load for a typical industrial plant. This increase in proportion of non-linear load and due to increased use of semi-conductor based power processors by utility companies has detoriated the Power Quality. Harmonics are a mathematical way of describing distortion in voltage or current waveform. The term harmonic refers to a component of a waveform occurs at an integer multiple of the fundamental frequency. Several methods had been proposed, such as discrete Fourier transforms, least square error technique, Kalman filtering, adaptive notch filters etc; Unlike above techniques, which treat harmonic estimation as completely non-linear problem there are some other hybrid techniques like Genetic Algorithm (GA), LS-Adaline, LS-PSOPC which decompose the problem of harmonic estimation into linear and non-linear problem. The results of LS-PSOPC and LS-Adaline has most attractive features of compactness and fastness. . Our new proposed technique tries to reduce the pitfalls in the LS-PSOPC, LS-Adaline techniques. With new technique we tried to estimate the Amplitudes by Least square estimator, frequency of the signal by PSOPC and phases of the harmonics by Adaline technique using MATLAB program. Harmonic signals were estimated by using LS-PSOPC, PSOPC-Adaline. Errors in estimating the signal by both the techniques are calculated and compared with each other

Power Quality Issues in Distributed Generation

This book deals with several selected aspects of electric power quality issues typically faced during grid integration processes of contemporary renewable energy sources. In subsequent chapters of this book the reader will be familiarized with the issues related to voltage and current harmonics and inter-harmonics generation and elimination, harmonic emission of switch-mode rectifiers, reactive power flow control in power system with non-linear loads, modeling and simulation of power quality issues in power grid, advanced algorithms used for estimating harmonic components, and new methods of measurement and analysis of real time accessible power quality related data

Performance Improvement of Wide-Area-Monitoring-System (WAMS) and Applications Development

Wide area monitoring system (WAMS), as an application of situation awareness, provides essential information for power system monitoring, planning, operation, and control. To fully utilize WAMS in smart grid, it is important to investigate and improve its performance, and develop advanced applications based on the data from WAMS. In this dissertation, the work on improving the WAMS performance and developing advanced applications are introduced.To improve the performance of WAMS, the work includes investigation of the impacts of measurement error and the requirements of system based on WAMS, and the solutions. PMU is one of the main sensors for WAMS. The phasor and frequency estimation algorithms implemented highly influence the performance of PMUs, and therefore the WAMS. The algorithms of PMUs are reviewed in Chapter 2. To understand how the errors impact WAMS application, different applications are investigated in Chapter 3, and their requirements of accuracy are given. In chapter 4, the error model of PMUs are developed, regarding different parameters of input signals and PMU operation conditions. The factors influence of accuracy of PMUs are analyzed in Chapter 5, including both internal and external error sources. Specifically, the impacts of increase renewables are analyzed. Based on the analysis above, a novel PMU is developed in Chapter 6, including algorithm and realization. This PMU is able to provide high accurate and fast responding measurements during both steady and dynamic state. It is potential to improve the performance of WAMS. To improve the interoperability, the C37.118.2 based data communication protocol is curtailed and realized for single-phase distribution-level PMUs, which are presented in Chapter 7.WAMS-based applications are developed and introduced in Chapter 8-10. The first application is to use the spatial and temporal characterization of power system frequency for data authentication, location estimation and the detection of cyber-attack. The second application is to detect the GPS attack on the synchronized time interval. The third application is to detect the geomagnetically induced currents (GIC) resulted from GMD and EMP-E3. These applications, benefited from the novel PMU proposed in Chapter 6, can be used to enhance the security and robust of power system