FFTと連続ウェーブレット変換法を用いた同期位相計測に基づく電力システムのモード検出とダンピング推定

The thesis carries out the estimation of damping as well as the frequencymode of inter area oscillations in the range of 0.1 to 1.0 Hz. This belongs underthe topic of angle stability management of power systems. Previously some otherstudies had been conducted in this area at which most of them employed themethods such as the least squares, Yule-Walker, autoregressive (AR),autoregressive moving average (ARMA), the Kalman filter and the subspacemethod. Another research also had been conducted which based on Fast FourierTransform (FFT) analysis individually, the damping ratio and frequencyoscillation were estimated from eigenvalue of the matrix associated to a SingleMachine Infinite Bus (SMIB) model. An output-only-based simplified oscillationmodel was developed to estimate the characteristic of inter-area power oscillationbased on extracted oscillation data. However, this previous method did notexplain how to calculate damping ratio without considering any simplified model.Furthermore, the behavior of the signal during certain time of analysis could notbe described.This thesis promotes a novel approach in analyzing PMU data based onFast Fourier Transform (FFT) and Continuous Wavelet Transform (CWT)algorithm. Then proceed by demodulating the slicing signal at a particular peakand ridge of the signal using a decrement technique. The approach applied in thisthesis can be classified into the non-parametric approach, where it works directlyon the data. The damping calculation method in this thesis emphasized on theaccurate and robust damping estimations which was proved by attempting thesimulation towards various level of signal to noise ratio (SNR).To verify the outcome of this method a synthesized signal contains ofthree ringdown modes representing a real signal from PMU was analyzed. Theresults were compared to the given parameters and it was clearly shown that thismethod gave the result within an acceptable range of error. Additionally, theacceptability of this method was also verified by comparing to the result ofeigenvalue-based calculation on a standard power system model. The simulationindicated the results of the two approaches fitted each other means this FFT-CWTis workable to assess the damping ratio of a small signal oscillation in powersystem. The advantage of this method is no prior data of the system required;hence this approach is very applicable in the power system where gathering datafrom the network is not attainable.This thesis also elaborated the application of wide area signal recorded byPMU, refined by the FFT-CWT method, for controlling the oscillation damping ofpower system. The simulation showed the application of wide area signal as aninput to the damping controller has a great prospective to countermeasure the interarea oscillation in the system.九州工業大学博士学位論文 学位記番号:工博甲第413号 学位授与年月日:平成28年3月25日1. INTRODUCTION|2. SYNCHROPHASOR MEASUREMENT AND THE METHOD OF ANALYSIS|3. FAST FOURIER TRANSFORM AND CONTINUOUS WAVELET TRANSFORM APPROACH|4. APPLICATION OF THE APPROACH FOR MODE AND DAMPING CALCULATION|5. WIDE AREA SIGNAL DAMPING CONTROLLER|6. CONCLUSION AND FUTURE WORK九州工業大学平成27年

Wide-area monitoring and control of future smart grids

Application of wide-area monitoring and control for future smart grids with substantial wind penetration and advanced network control options through FACTS and HVDC (both point-to-point and multi-terminal) is the subject matter of this thesis. For wide-area monitoring, a novel technique is proposed to characterize the system dynamic response in near real-time in terms of not only damping and frequency but also mode-shape, the latter being critical for corrective control action. Real-time simulation in Opal-RT is carried out to illustrate the effectiveness and practical feasibility of the proposed approach. Potential problem with wide-area closed-loop continuous control using FACTS devices due to continuously time-varying latency is addressed through the proposed modification of the traditional phasor POD concept introduced by ABB. Adverse impact of limited bandwidth availability due to networked communication is established and a solution using an observer at the PMU location has been demonstrated. Impact of wind penetration on the system dynamic performance has been analyzed along with effectiveness of damping control through proper coordination of wind farms and HVDC links. For multi-terminal HVDC (MTDC) grids the critical issue of autonomous power sharing among the converter stations following a contingency (e.g. converter outage) is addressed. Use of a power-voltage droop in the DC link voltage control loops using remote voltage feedback is shown to yield proper distribution of power mismatch according to the converter ratings while use of local voltages turns out to be unsatisfactory. A novel scheme for adapting the droop coefficients to share the burden according to the available headroom of each converter station is also studied. The effectiveness of the proposed approaches is illustrated through detailed frequency domain analysis and extensive time-domain simulation results on different test systems

A wide area system for power transmission security enhancement using a process systems approach

Imperial Users onl

Adaptive Parameter Estimation of Power System Dynamic Models Using Modal Information

Knowledge of the parameter values of the dynamic generator models is of paramount importance for creating accurate models for power system dynamics studies. Traditionally, power systems consists of a relatively limited numbers of large power stations and the values of generator parameters were provided by manufacturers and validated by utilities. Recently however, with the increasing penetration of distributed generation, the accuracy of these models and parameters cannot be guaranteed. This thesis addresses the above concerns by developing a methodology to estimate the parameter values of a power system dynamic model online, employing dynamic system modes, i.e. modal frequencies and damping. The dynamic modes are extracted from real-time measurements. The aim of the proposed methodology is to minimise the differences between the observed and modelled modes of oscillation. It should be emphasised that the proposed methodology does not aim to develop the dynamic model itself but rather modify its parameter using WAMS measurements. The developed methodology is general and can be used to identify any generator parameters., However, thesis concentrates on the estimation of generator inertia constants. The results suggest that the proposed methodology can estimate inertias and replicate the dynamic behaviour of the power system accurately, through the inclusion of pseudo-measurements in the optimisation process. The pseudo-measurements not only improves the accuracy of the parameter estimation but also the robustness of it. Observability, a problem when there are fewer numbers of measurements than the numbers of parameters to be estimated, has also been successfully tackled. It has been shown that the damping measurements do not influence the accuracy and robustness of generator inertia estimation significantly

キャンパスWAMSによる改良されたヒルベルトホーン変換を用いた電力系統動揺特性解析

九州工業大学博士学位論文 学位記番号:工博甲第390号 学位授与年月日:平成27年3月25日Chapter1. Introduction||Chapter2. Wide-Area Measurement System Using Synchrophasors Technology||Chapter3. On-line Oscillation Characteristics Monitoring Algorithm Analysis||Chapter4. The Enhanced HHT Method||Chapter5. The Developed Oscillation Monitoring System||Chapter6. ConclusionsThis dissertation presents a complete oscillation monitoring system based on real-time wide-area measurements from PMUs. This oscillation monitoring system employs the enhanced Hilbert-Huang transform (HHT) to analyze power system oscillation characteristics and estimate the damping of oscillatory modes from ambient data. This new oscillation system can give an indication of the damping of transient oscillations that will follow a disturbance, once it occurs. The application is based on a system identification procedure that is carried out in real-time. This research studies various low frequency oscillation analysis algorithms. It mainly introduces the concept, character and implementation process of FFT, WLT and HHT method. According to the characteristics of low frequency oscillation signal we can get advantage and disadvantage of these algorithms. It is important to remember that power system is actually a high-order time-varying nonlinear system. Only under certain circumstances can it be simplified to linear or time-invariant systems. Although ambient condition is reasonably molded as a linear system, for system response following some events, nonlinearities play an important role in the measured data. HHT is a new type of nonlinear and non-stationary signal processing method. Compared with other methods, HHT has absolute advantage of analyzing low frequency oscillation signal because the power system responses following system disturbances contain both linear and nonlinear phenomena. Nevertheless, the traditional methods, whether FFT or WLT, etc. the signals are approximately processed as linear signal when analysis non-linear and non-stationary signals. This feature is the main advantage of HHT algorithm, which is also widely used by the reasons. Secondly, HHT method is adaptive, which means that can be adaptive extracted from the signal decomposed by EMD itself. It is based on an adaptive basis, and the frequency is defined through the Hilbert transform. Consequently, the "base" of Fourier transform is the trigonometric functions, the "base" of wavelet transform requires pre-selected. Therefore, HHT has completely adaptability. Third, it is suitable for analysis mutation signal. Due to the Heisenberg uncertainty principle constraint, many traditional algorithms must be satisfied the product of frequency window by time window is constant. This property makes these algorithms cannot achieve high precision both in time domain and frequency domain at the same time. Nevertheless, there is no uncertainty principle limitation on time or frequency resolution from the convolution pairs based on a priori bases. For these reasons, it can be said applying HHT method to dealing with power system oscillation signal is a good choice. However, it is still have some issues need to be resolved carefully. To ensure accurate monitoring of system dynamics with noise-polluted WAMS measurements, serval key signal-processing techniques are implemented to improve HHT method in this research: Data pre-treatment processing, the boundary end effect problem caused by the Empirical mode decomposition(EMD) algorithm and the boundary end effect problem caused by Hilbert transform based on Auto-Regressive and Moving Average Model (ARMA). There are six methods: a). polynomial extension method, b). slope method extension method, c). parallel extension method, d). extreme point symmetric extension method, e). mirror method f). Boundary local characteristic scale extension methods are used to inhibit the boundary end effects, which results in a serious distortion in the EMD sifting process. Furthermore, an integrated scheme for the monitoring and detection of low-frequency oscillations has been developed based on HHT algorithm for oscillation analysis in CampusWAMS projects. By analyzing the real-time synchro-phasors, the proposed scheme is competent to identify the characteristics of the low-frequency oscillations in real-time. Third, this dissertation presents an estimation algorithm method based on enhanced HHT for the parameters of a low frequency oscillation signal in power system. In the end, the developed scheme is tested with simulated signals and measurements from CampusWAMS. An oscillation monitoring system based on real-time wide-area measurements from PMUs is established. It can determine the center rage frequency of the concerned mode automatically and accurately, which is then be used to determine the parameter of the extraction. The extracted mode frequency, damping and mode shape can be detected by this oscillation monitoring system. The results have convincingly demonstrated the validity and practicability of the developed scheme

Power System Dynamics Enhancement Through Phase Unbalanced and Adaptive Control Schemes in Series FACTS devices

This thesis presents novel series compensation schemes and adaptive control techniques to enhance power system dynamics through damping Subsynchronous Resonance (SSR) and low-frequency power oscillations: local and inter-area oscillations. Series capacitive compensation of transmission lines is used to improve power transfer capability of the transmission line and is economical compared to the addition of new lines. However, one of the impeding factors for the increased utilization of series capacitive compensation is the potential risk of SSR, where electrical energy is exchanged with turbine-generator shaft systems in a growing manner which can result in shaft damage. Furthermore, the fixed capacitor does not provide controllable reactance and does not aid in the low-frequency oscillations damping. The Flexible AC Transmission System (FACTS) controllers have the flexibility of controlling both real and reactive power which could provide an excellent capability for improving power system dynamics. Several studies have investigated the potential of using this capability in mitigating the low-frequency (electromechanical) as well as the subsynchronous resonance (SSR) oscillations. However, the practical implementations of FACTS devices are very limited due to their high cost. To address this issue, this thesis proposes a new series capacitive compensation concept capable of enhancing power system dynamics. The idea behind the concept is a series capacitive compensation which provides balanced compensation at the power frequency while it provides phase unbalance at other frequencies of oscillations. The compensation scheme is a combination of a single-phase Thyristor Controlled Series Capacitor (TCSC) or Static Synchronous Series Compensator (SSSC) and a fixed series capacitors in series in one phase of the compensated transmission line and fixed capacitors on the other two phases. The proposed scheme is economical compared to a full three-phase FACTS counterpart and improves reliability of the device by reducing number of switching components. The phase unbalance during transients reduces the coupling strength between the mechanical and the electrical system at asynchronous oscillations, thus suppressing the build-up of torsional stresses on the generator shaft systems. The SSR oscillations damping capability of the schemes is validated through detailed time-domain electromagnetic transient simulation studies on the IEEE first and second benchmark models. Furthermore, as the proposed schemes provide controllable reactance through TCSC or SSSC, the supplementary controllers can be implemented to damp low-frequency power oscillations as well. The low-frequency damping capability of the schemes is validated through detail time-domain electromagnetic transient simulation studies on two machines systems connected to a very large system and a three-area, six-machine power system. The simulation studies are carried out using commercially available electromagnetic transient simulation tools (EMTP-RV and PSCAD/EMTDC). An adaptive controller consisting of a robust on-line identifier, namely a robust Recursive Least Square (RLS), and a Pole-Shift (PS) controller is also proposed to provide optimal damping over a wide range of power system operations. The proposed identifier penalizes large estimated errors and smooth-out the change in parameters during large power system disturbances. The PS control is ideal for its robustness and stability conditions. The combination results in a computationally efficient estimator and a controller suitable for optimal control over wider range of operations of a non-linear system such as power system. The most important aspect of the controller is that it can be designed with an approximate linearized model of the complete power system, and does not need to be re-tuned after it is commissioned. The damping capability of such controller is demonstrated through detail studies on a three-area test system and on an IEEE 12-bus test system. Finally, the adaptive control algorithm is developed on a Digital Signal Processing Board, and the performance is experimentally tested using hardware-in-the-loop studies. For this purpose, a Real Time Digital Simulator (RTDS) is used, which is capable of simulating power system in real-time at 50 µs simulation time step. The RTDS facilitates the performance evaluation of a controller just like testing on a real power system. The experimental results match closely with the simulation results; which demonstrated the practical applicability of the adaptive controller in power systems. The proposed controller is computationally efficient and simple to implement in DSP hardware

Estimation of oscillations and frequency responses of power systems via optimal vector fitting

Orientador: Prof. Dr. Gustavo Henrique da Costa OliveiraCoorientador: Prof. Dr. Rôman KuiavaTese (doutorado) - Universidade Federal do Paraná, Setor de Tecnologia, Programa de Pós-Graduação em Engenharia Elétrica. Defesa : Curitiba, 19/06/2019Inclui referências: p. 123-129Área de concentração: Sistemas de EnergiaResumo: A identificacao de sistemas esta presente em diversas areas da engenharia onde um modelo matematico preciso e exigido. Diferentes tipos de algoritmos de estimacao tem sido usados para identificar sistemas lineares invariantes no tempo. Contudo, o caso particular que considera a utilizacao dos chamados metodos iterativos Vector Fitting (VF) tem atraido atencao significativa da comunidade cientifica, especialmente durante as ultimas duas decadas. Neste contexto, esta tese aborda o problema de formulacao de algoritmos VF para ambos os dominios, do tempo e da frequencia. No dominio do tempo, algoritmos VF sao aqui desenvolvidos dentro de um contexto ringdown, de modo que dinamicas oscilatorias (assim como dinamicas puramente exponenciais) de sistemas de potencia possam ser efetivamente estimadas atraves de conjuntos de dados transitorios extraidos desses sistemas. Neste sentido, tambem e apresentada uma abordagem multisinal para estimar simultaneamente multiplos sinais transitorios possivelmente distribuidos em diferentes localizacoes do sistema de potencia que esta sendo modelado. Por outro lado, no ambito do dominio da frequencia, esta tese apresenta um metodo VF que pode ser aplicado na estimacao de modelos formados por bases de funcoes racionais (BFRs) definidas tanto no tempo continuo como no tempo discreto. Em ambos os contextos do tempo e da frequencia, formulacoes VF alternativas baseadas em variaveis instrumentais (VI) sao tambem vastamente investigadas neste trabalho. Solucoes convergidas fornecidas por essas formulacoes VF baseadas em VI sao provadamente otimos locais de suas funcoes objetivo nao-lineares correspondentes, sendo essa importante propriedade de otimalidade local independente da natureza do ruido que corrompe os dados de estimacao. Exemplos numericos apresentados neste trabalho focam em dados de resposta em frequencia extraidos de transformadores de potencia e de potencial indutivo reais assim como em conjuntos de dados transitorios extraidos do sistema de potencia interconectado Brasileiro e do sistema de interconexao leste norte americano. Palavras-chave: identificacao de sistemas. vector fitting. analise ringdown. estimacao de respostas em frequencia. variaveis instrumentaisAbstract: System identification appears in several areas of engineering where a accurate mathematical model is required. Many different types of estimating algorithms have been used for identifying linear time-invariant systems. Nonetheless, the particular case of using the so-called iterative Vector Fitting (VF) algorithms has been drawing significant attention from scientific community, especially during the last two decades. In this context, this thesis addresses the problem of formulating VF algorithms for both time- and frequencydomain system identification. When it comes to time-domain, VF algorithms are here developed within a ringdown context, so that oscillatory (as well as purely exponential) dynamics of power systems can be effectively estimated through transient (ringdown) data sets extracted from these systems. In this sense, it is also presented a multi-signal approach for simultaneously estimating multiple transient signals possibly distributed over different locations of the power system under modeling. On the other hand, when it comes to frequency-domain, this thesis presents a unifying VF method which can be similarly applied for estimating models formed either by continuous- or discrete-time rational basis functions (RBFs). In both time- and frequency-domain contexts, alternative VF formulations based on instrumental variables (IV) are also intensively investigated throughout this thesis. Converged solutions provided by these IV-based VF formulations are proved to be local optimums of their corresponding nonlinear objective functions, being this important optimality property independent on the nature of the noise that corrupts estimation data. Numerical examples presented in this work focus on frequency response data extracted from actual power and potential transformers as well as on transient data sets extracted from the Brazilian Interconnected Power (BIP) system and from the North American Eastern Interconnection (NAEI) system. Keywords: system identification. vector fitting. ringdown analysis. frequency response estimation. instrumental variables

Visualization And Mining Of Phasor Data From Optimally Placed Synchrophasors In A Smart-Grid

Synchrophasors, or also known as Phasor Measurement Units (PMUs), are the state- of-the-art measurement sensor that gather key sensor parameters such as voltage, frequency (f), current (i), and phase angle (ϕ) to monitor the state of an electric grid. The significant feature of a synchrophasor is in its ability to provide real-time streaming data from smart grid. The sampling rate of PMUs ranges from 30 samples to a maximum of 120 samples per second. With such large date-rate, the operations of the power-grid is known with high granularity. However, utilities face certain challenges with synchrophasor measurements. One of the common challenge with synchrophasor is the selection of location to place them in the grid. A synchrophasor placed on a bus is capable of measuring currents, voltages, phasor and frequency information on the entire transmission line incident to that bus. Furthermore, neighboring buses also become observable (i.e. adjacent bus voltage equations are solvable) using Ohm’s law, Kirchhoff’s Voltage Law (KVL) and Kirchhoff’s Current Law (KCL). Thus, it is not necessary to place PMUs on every single bus of the power-grid. Synchrophasors are expensive units and depending on vendor type, the number of measurement channels and features, the cost per unit can increase. There are several optimal solutions proposed to minimize the cost function to place the synchrophasors. Studies often ignored other metrics such as reliability, and security. This can jeopardize the reliability of the power-grid. Thus, this thesis work focus on a multi-objective problem that include reliability, cost, energy, and distance. This research proposes a criteria called as Optimal Redundancy Criterion (ORC) based on Linear Programming (LP) methods to find an optimal solution for the placement problem. Although, synchrophasors provide real-time information about the grid, the system operators need to identify, classify and analyze fault or anomalies in the power-grid. Such detection of the faults will improve the situational awareness of the power-grid. This research addresses such challenges by developing data mining algorithms for effective visualization and control of data. The secondary goal is accomplished by implementing a Density-Based Spatial Clustering of Applications with Noise (DBSCAN) algorithm to IEEE test system and phasor data from openPDC framework. The scalability and decision making process for large scale utility test systems using DBSCAN is also investigated

Vulnerability Assessment and Privacy-preserving Computations in Smart Grid

Modern advances in sensor, computing, and communication technologies enable various smart grid applications which highlight the vulnerability that requires novel approaches to the field of cybersecurity. While substantial numbers of technologies have been adopted to protect cyber attacks in smart grid, there lacks a comprehensive review of the implementations, impacts, and solutions of cyber attacks specific to the smart grid.In this dissertation, we are motivated to evaluate the security requirements for the smart grid which include three main properties: confidentiality, integrity, and availability. First, we review the cyber-physical security of the synchrophasor network, which highlights all three aspects of security issues. Taking the synchrophasor network as an example, we give an overview of how to attack a smart grid network. We test three types of attacks and show the impact of each attack consisting of denial-of-service attack, sniffing attack, and false data injection attack.Next, we discuss how to protect against each attack. For protecting availability, we examine possible defense strategies for the associated vulnerabilities.For protecting data integrity, a small-scale prototype of secure synchrophasor network is presented with different cryptosystems. Besides, a deep learning based time-series anomaly detector is proposed to detect injected measurement. Our approach observes both data measurements and network traffic features to jointly learn system states and can detect attacks when state vector estimator fails.For protecting data confidentiality, we propose privacy-preserving algorithms for two important smart grid applications. 1) A distributed privacy-preserving quadratic optimization algorithm to solve Security Constrained Optimal Power Flow (SCOPF) problem. The SCOPF problem is decomposed into small subproblems using the Alternating Direction Method of Multipliers (ADMM) and gradient projection algorithms. 2) We use Paillier cryptosystem to secure the computation of the power system dynamic simulation. The IEEE 3-Machine 9-Bus System is used to implement and demonstrate the proposed scheme. The security and performance analysis of our implementations demonstrate that our algorithms can prevent chosen-ciphertext attacks at a reasonable cost