A Software-based Low-Jitter Servo Clock for Inexpensive Phasor Measurement Units

This paper presents the design and the implementation of a servo-clock (SC) for low-cost Phasor Measurement Units (PMUs). The SC relies on a classic Proportional Integral (PI) controller, which has been properly tuned to minimize the synchronization error due to the local oscillator triggering the on-board timer. The SC has been implemented into a PMU prototype developed within the OpenPMU project using a BeagleBone Black (BBB) board. The distinctive feature of the proposed solution is its ability to track an input Pulse-Per-Second (PPS) reference with good long-term stability and with no need for specific on-board synchronization circuitry. Indeed, the SC implementation relies only on one co-processor for real-time application and requires just an input PPS signal that could be distributed from a single substation clock

Smart Power Grid Synchronization With Fault Tolerant Nonlinear Estimation

Effective real-time state estimation is essential for smart grid synchronization, as electricity demand continues to grow, and renewable energy resources increase their penetration into the grid. In order to provide a more reliable state estimation technique to address the problem of bad data in the PMU-based power synchronization, this paper presents a novel nonlinear estimation framework to dynamically track frequency, voltage magnitudes and phase angles. Instead of directly analyzing in abc coordinate frame, symmetrical component transformation is employed to separate the positive, negative, and zero sequence networks. Then, Clarke\u27s transformation is used to transform the sequence networks into the αβ stationary coordinate frame, which leads to system model formulation. A novel fault tolerant extended Kalman filter based real-time estimation framework is proposed for smart grid synchronization with noisy bad data measurements. Computer simulation studies have demonstrated that the proposed fault tolerant extended Kalman filter (FTEKF) provides more accurate voltage synchronization results than the extended Kalman filter (EKF). The proposed approach has been implemented with dSPACE DS1103 and National Instruments CompactRIO hardware platforms. Computer simulation and hardware instrumentation results have shown the potential applications of FTEKF in smart grid synchronization

Development and application of synchronized wide-area power grid measurement

Phasor measurement units (PMUs) provide an innovative technology for real-time monitoring of the operational state of entire power systems and significantly improve power grid dynamic observability. This dissertation focuses on development and application of synchronized power grid measurements. The contributions of this dissertation are as followed:First, a novel method for successive approximation register analog to digital converter control in PMUs is developed to compensate for the sampling time error caused by the division remainder between the desirable sampling rate and the oscillator frequency. A variable sampling interval control method is presented by interlacing two integers under a proposed criterion. The frequency of the onboard oscillator is monitored in using the PPS from GPS.Second, the prevalence of GPS signal loss (GSL) on PMUs is first investigated using real PMU data. The correlation between GSL and time, spatial location, solar activity are explored via comprehensive statistical analysis. Furthermore, the impact of GSL on phasor measurement accuracy has been studied via experiments. Several potential solutions to mitigate the impact of GSL on PMUs are discussed and compared.Third, PMU integrated the novel sensors are presented. First, two innovative designs for non-contact PMUs presented. Compared with conventional synchrophasors, non-contact PMUs are more flexible and have lower costs. Moreover, to address nonlinear issues in conventional CT and PT, an optical sensor is used for signal acquisition in PMU. This is the first time the utilization of an optical sensor in PMUs has ever been reported.Fourth, the development of power grid phasor measurement function on an Android based mobile device is developed. The proposed device has the advantages of flexibility, easy installation, lower cost, data visualization and built-in communication channels, compared with conventional PMUs.Fifth, an identification method combining a wavelet-based signature extraction and artificial neural network based machine learning, is presented to identify the location of unsourced measurements. Experiments at multiple geographic scales are performed to validate the effectiveness of the proposed method using ambient frequency measurements. Identification accuracy is presented and the factors that affect identification performance are discussed

An Accurate Offline Phasor Estimation Technique For Fault Location In Series Compensated Lines

In series compensated transmission lines, current and voltage signals measured by the line protection system include considerable sub-synchronous frequency components (SSFCs) which are not sufficiently damped within a typical fault clearing time of line protection system. This does not allow accurate phasor estimation and thereby phasor-based fault location. This paper presents an accurate algorithm which effectively filters out the unwanted frequency components and noise to perform accurate phasor estimation for fault location in series compensated transmission lines. Phasor estimation of a theoretical signal is first evaluated using the proposed method, Direct-Prony analysis and 4-cycle discrete Fourier transform algorithm. Then, various fault locations of a 500 kV series compensated transmission line simulated in PSCAD/EMTDC are used to comprehensively evaluate the performance of the proposed technique. It is shown that the proposed method can effectively attenuate SSFCs and other unwanted frequency components in current and voltage signals allowing accurate phasor estimation

A Phase-Angle Tracking Method for Synchronization of Single- and Three-Phase Grid-Connected Converters

This thesis proposes a phase-angle tracking method, i.e., based on discrete Fourier transform for synchronization of three-phase and single-phase power-electronic converters under distorted and variable-frequency conditions. The proposed methods are designed based on fixed sampling rate and, thus, they can simply be employed for control applications. For three-phase applications, first, analytical analysis are presented to determine the errors associated with the phasor estimation using standard full-cycle discrete Fourier transform in a variable-frequency environment. Then, a robust phase-angle estimation technique is proposed, which is based on a combination of estimated positive and negative sequences, tracked frequency, and two proposed compensation coefficients. The proposed method has one cycle transient response and is immune to harmonics, noises, voltage imbalances, and grid frequency variations. An effective approximation technique is proposed to simplify the computation of the compensation coefficients. The effectiveness of the proposed method is verified through a comprehensive set of simulations in Matlab software. Simulation results show the robust and accurate performance of the proposed method in various abnormal operating conditions. For single-phase applications, an accurate phasor-estimation method is proposed to track the phase-angle of fundamental frequency component of voltage or current signals. This method can be used in three-phase applications as well. The proposed method is based on a fixed sampling frequency and, thus, it can simply be integrated in control applications of the grid-connected converters. Full-cycle discrete Fourier transform (DFT) is adopted as a base for phasor estimation. Two procedures are taken to effectiveness reduce the phasor estimation error using DFT during o - nominal frequency operation. First, adaptive window length (AWL) is applied to match the window-length of the DFT with respect to the input signal frequency. As AWL can partially reduce the error if sampling rate is not high, phasor compensation is employed to compensate the remaining error in the estimated phasor. Both procedures require system frequency, thus, an effective frequency-estimation technique is proposed to obtain fast and accurate performance. The proposed method has one cycle transient response and is immune to harmonics, noises, and grid frequency variations. The effectiveness of the proposed method is verified through a comprehensive set of simulations in Matlab and hardware implementation test using real-time digital signal processor data acquisition system

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

Fault location and forewarning on transmission systems using travelling wave transients

University of Technology, Sydney. Faculty of Engineering.This thesis examines the main circuit modelling fundamentals and fault location techniques that may be applied to electricity transmission networks. Using a statistical comparison, it then investigates both impedance and travelling wave based fault location methods. This appears to be a novel comparison as no publications have been identified which draw conclusions on the accuracy of these fault location techniques. This work subsequently led TransGrid to install a new commercial travelling wave fault location system on the New South Wales 330kV transmission network. Following the commissioning of this system, there was an ongoing process to store data that was being observed by the travelling wave recorders. This data was later cross- referenced to determine the fault location, and the waveform interpreted to identify the source of the travelling wave transient. However, this analysis has revealed that the theoretical accuracy of this travelling wave system was not as good as previously expected from publication. The source of the degradation was tracked down and found to centre on the frequency response of the coupling transducers used by most conventional travelling wave recording hardware. These errors are not currently considered in publication but can result in several kilometres of uncertainty in a fault location calculation. Hence, it can be concluded that the use of conventional substation current transducers can introduce additional uncertainty into travelling wave fault location calculations. The source and nature of this uncertainty has subsequently led to the development of a novel unsynchronised fault location algorithm based on the continuous wavelet transform. This new technique also uses an assessment of waveform polarity to distinguish between signals generated by solid or incipient line faults. Several unusual events have also been observed which have led to a number of new developments in fault location and forewarning. These include specific requirements for impedance algorithms during unearthed inter-circuit faults on double circuit lines. Similarly, this thesis presents the development of a new method to forewarn of faults within oil impregnated current transformers. This has been based on the high frequency transients observed by the travelling wave system prior to the failure of a 330kV current transformer. This thesis also identifies significant potential for travelling wave techniques to forewarn of developing insulator faults on overhead circuits