9 research outputs found

    More-stable EPLL

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    The enhanced phase-locked loop (EPLL) is one of the most famous PLLs in single-phase applications and a versatile tool for different signal processing applications, especially for the grid synchronization of power converters. Recently, it has been proved that the EPLL has a quite narrow stable zone (compared to its unstable zone) in the positive parameter space from a small-signal point of view. This zone will be even more narrow if maintaining a minimum stability margin is required. This article aims to modify the EPLL structure to improve its stability margin, and at the same time, make it unconditionally stable in the positive parameter space from a small-signal point of view.Peer ReviewedPostprint (author's final draft

    A PLL-based multirate structure for time-varying power systems harmonic/interharmonic estimation

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    This paper describes a phase-locked-loop (PLL)-based power systems harmonic estimation algorithm, which uses an analysis filter bank and multirate processing. The filter bank is composed of bandpass filters. The initial center frequency of each filter is purposely chosen to be equal to harmonic frequencies. However, an adaptation strategy makes it possible to track time-varying frequencies as well as interharmonic components. A downsampler device follows the filtering stage, reducing the computational burden, especially because undersampling operations are performed. Finally, the last stage is composed of a PLL estimator which provides estimates for amplitude, phase, and frequency of the input signal. The proposed method improves the accuracy, computational effort, and convergence time of the previous harmonic estimator based on cascade PLL configuration

    Impact of prominent synchrophasor estimation algorithms on power system stability assessment

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    The electricity network is a critical infrastructure and its reliability is of paramount importance for the functionality of many critical systems in the modern society. Power system stability is one of the imperative aspects that impacts the reliability of electrical networks, hence power system stability needs to be observed in real-time for secure and reliable operation of the power grids. Conventionally, supervisory control and data acquisition (SCADA) based wide-area monitoring systems (WAMS) have been used for this purpose, however, they are predominantly designed to detect static changes in steady-state stability. In contrast, modern wide-area power networks pose significant challenges such as presence of power electronic switching loads and inductive motor loads, asynchronous distributed generation and dynamic fluctuations in demand and supply. Synchrophasor based WAMS is the next generation WAMS technology and offers great advantages over traditional SCADA systems such as precise time synchronisation, universally accepted standardisation and extremely fast and robust phasor estimation. A strategically placed network of phasor measurement units (PMUs) enables full visibility of the entire power network. Time synchronised PMU data can then be transferred to a phasor data centre (PDC) using efficient communication algorithms where multi facet analysis, including realtime stability assessment, could be performed. Despite significant benefits of the synchrophasor technology, several factors have hindered the widespread adoption ofthe synchrophasor technology. This research addresses such contemporary issues. The first phase of this research details an empirical study of existing synchrophasor estimation algorithms (SEAs) and considers the need for a benchmark in terms of robustness. Synchrophasor research is heavily populated with studies presenting diverse SEAs. Interestingly, not many studies have attempted to develop a robust SEA based on the mathematical technique proposed in the original Institute of Electrical and Electronics Engineers (IEEE) standardisation (i.e. IEEE std. C37.118.1-2011), the quadrature demodulation (QD) technique. Therefore, a verifiable benchmark algorithm is not currently available. This research presents comprehensive synchrophasor estimation models developed based on the QD technique and is then presented as the benchmark SEA. Proposed models are tested against all compliance requirements stipulated in the latest IEEE standardisation. Furthermore, a detailed comparison of prominent synchrophasor models is conducted against the proposed benchmark models, to understand the impact of the SEAs on the overall phasor estimation. Results establish a clear link between the accuracy/latency of the phasor estimation and the accompanying synchrophasor algorithm. The second phase of this research involves testing and comparison of synchrophasor models on hardware platforms. Even though development of SEA has been a prominent research area, only a few of these studies have been verified and validated with field tested results. This is a significant barrier to the advent of improved SEAs beyond academic literature, especially in industrial applications. A laboratory scale, hardware based synchrophasor test platform is proposed where any synchrophasor algorithm can be tested for any test condition or fault signal. Key highlights of this section include; global position system (GPS) time synchronisation of synchrophasors and a sinusoidal pulse width modulation (SPWM) technique based scalable input system capable of generating measurement conditions emulating any fault condition. Results establish the superiority of the proposed benchmark algorithm and identify key implementation issues in hardware implementation of some of the prominent synchrophasor models. The final phase of this research develops a synchrophasor based WAMS by using a bottom-up approach to evaluate real-time stability of wide-area networks under practical power network fault conditions. As part of this research the analyses and the impact of SEAs on the overall stability assessment has been evaluated. Development and testing of PMUs, and stability studies are historically conducted in two disjointed silos. As a result, stability analysis is often conducted based on the assumption that the PMU data delivered to the PDC are accurate and instantaneous. On the other hand, SEAs are tested against the compliance criteria listed in the IEEE standardisation which do not involve any practical power network faults. This study attempts to dive into this unexplored territory. Performance in realtime voltage and frequency stability of prominent SEAs is evaluated by employing a strategically placed PMU network on two standard power networks simulation models. The IEEE 9-bus system and New England 39-bus system are considered and consists synchronous generation sources, dynamic load centres and transmission links. By modelling practical transient fault conditions such as short circuit faults, loss of generation and addition of load centres, the real-time voltage and frequency stability have been studied. A modified highest Lyapunov exponent (HLE) based real-time stability assessment algorithm (RSAA) is proposed to suit implementation in practical power networks. Despite the full compliance against the IEEE standardisation, tested algorithms produce significantly different outcomes in the stability assessment that may directly impact on the subsequent activation of protection systems and overall network stability. Results of this study point to interesting findings and establishes a clear link between the reliability and the performance of the underlining SEA. In conclusion, key findings of this research contribute to two prominent areas within the synchrophasor research; SEA development and testing, and real-time stability assessment. This research has established a strong link between these disjointed research fields, thereby enabling future advancements synchrophasor based stability monitoring and control systems

    Mitigation of Power System Oscillation in a DFIG-Wind Integrated Grid: A Review

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    The continuous rise in demand for power supply has made researchers and power system engineers seek alternatives through renewable energy sources to complement the power supply in the power system grid. Wind energy conversion system (WECS) which is the means of harnessing power generation through wind is reportedly one of the most widely installed renewable alternative sources globally. Integrating WECS into the conventional power system grid results in a complex power system grid. Thus, during a disturbance or a fault period on the grid, if proper control measures are not put in place, power system instability due to power system oscillations arises. One such control measure is the damping controller which is coupled to the generating plant through its excitation system. Damping controllers help to dampen power system oscillations, but due to the dynamic nature of the power system and uncertainties inherent in a wind-integrated power grid system, fixed damping controller parameters cannot effectively dampen power system oscillations. Hence, damping controller design becomes an optimization problem. This research reviews damping controller design in a wind-integrated system using optimization techniques

    Power Quality in Electrified Transportation Systems

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    "Power Quality in Electrified Transportation Systems" has covered interesting horizontal topics over diversified transportation technologies, ranging from railways to electric vehicles and ships. Although the attention is chiefly focused on typical railway issues such as harmonics, resonances and reactive power flow compensation, the integration of electric vehicles plays a significant role. The book is completed by some additional significant contributions, focusing on the interpretation of Power Quality phenomena propagation in railways using the fundamentals of electromagnetic theory and on electric ships in the light of the latest standardization efforts

    Methoden zur Analyse der Spannungsqualität im Frequenzbereich bis 500 kHz

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    Die Ankopplung von Geräten an das elektrische Energienetz erfolgt zunehmend mittels leistungselektronischer Baugruppen. Dies führt zu einer Degradation der Spannungsqualität und zu Leistungsflüssen oberhalb der Grundschwingung. Bisher können diese Effekte nicht ausreichend genau gemessen werden. In dieser Arbeit wird ein Messsystem entwickelt, das die Messung spektraler Spannungsqualität, harmonischer Leistungen und der Netzfrequenz mit höherer Genauigkeit und Zeitauflösung ermöglicht. Mit einem Laborprototypen wird die Leistungsfähigkeit durch Messungen am Netz gezeigt.Devices are increasingly being connected to the electrical power grid by means of power electronic assemblies. This causes a degradation in power quality and power flows above the fundamental frequency. Until now, those effects cannot be measured with sufficient accuracy. In this thesis, a novel measurement system is developed that allows the measurement of spectral power quality, harmonic power flows and power system frequency with higher accuracy and time resolution. A laboratory prototype is used to demonstrate its performance through measurements on the grid

    Power Quality

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    Electrical power is becoming one of the most dominant factors in our society. Power generation, transmission, distribution and usage are undergoing signifi cant changes that will aff ect the electrical quality and performance needs of our 21st century industry. One major aspect of electrical power is its quality and stability – or so called Power Quality. The view on Power Quality did change over the past few years. It seems that Power Quality is becoming a more important term in the academic world dealing with electrical power, and it is becoming more visible in all areas of commerce and industry, because of the ever increasing industry automation using sensitive electrical equipment on one hand and due to the dramatic change of our global electrical infrastructure on the other. For the past century, grid stability was maintained with a limited amount of major generators that have a large amount of rotational inertia. And the rate of change of phase angle is slow. Unfortunately, this does not work anymore with renewable energy sources adding their share to the grid like wind turbines or PV modules. Although the basic idea to use renewable energies is great and will be our path into the next century, it comes with a curse for the power grid as power fl ow stability will suff er. It is not only the source side that is about to change. We have also seen signifi cant changes on the load side as well. Industry is using machines and electrical products such as AC drives or PLCs that are sensitive to the slightest change of power quality, and we at home use more and more electrical products with switching power supplies or starting to plug in our electric cars to charge batt eries. In addition, many of us have begun installing our own distributed generation systems on our rooft ops using the latest solar panels. So we did look for a way to address this severe impact on our distribution network. To match supply and demand, we are about to create a new, intelligent and self-healing electric power infrastructure. The Smart Grid. The basic idea is to maintain the necessary balance between generators and loads on a grid. In other words, to make sure we have a good grid balance at all times. But the key question that you should ask yourself is: Does it also improve Power Quality? Probably not! Further on, the way how Power Quality is measured is going to be changed. Traditionally, each country had its own Power Quality standards and defi ned its own power quality instrument requirements. But more and more international harmonization efforts can be seen. Such as IEC 61000-4-30, which is an excellent standard that ensures that all compliant power quality instruments, regardless of manufacturer, will produce of measurement instruments so that they can also be used in volume applications and even directly embedded into sensitive loads. But work still has to be done. We still use Power Quality standards that have been writt en decades ago and don’t match today’s technology any more, such as fl icker standards that use parameters that have been defi ned by the behavior of 60-watt incandescent light bulbs, which are becoming extinct. Almost all experts are in agreement - although we will see an improvement in metering and control of the power fl ow, Power Quality will suff er. This book will give an overview of how power quality might impact our lives today and tomorrow, introduce new ways to monitor power quality and inform us about interesting possibilities to mitigate power quality problems. Regardless of any enhancements of the power grid, “Power Quality is just compatibility” like my good old friend and teacher Alex McEachern used to say. Power Quality will always remain an economic compromise between supply and load. The power available on the grid must be suffi ciently clean for the loads to operate correctly, and the loads must be suffi ciently strong to tolerate normal disturbances on the grid

    The LANDSAT Tutorial Workbook: Basics of Satellite Remote Sensing

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    Most of the subject matter of a full training course in applying remote sensing is presented in a self-teaching mode in this how-to manual which combines a review of basics, a survey of systems, and a treatment of the principles and mechanics of image analysis by computers, with a laboratory approach for learning to utilize the data through practical experiences. All relevant image products are included
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