Synchrophasor Estimation Research Articles

Performance evaluation of M-class synchrophasor estimation using enhanced band-pass FIR filter under a comprehensive integrated compliance test

Performance evaluation of M-class synchrophasor estimation using enhanced band-pass FIR filter under a comprehensive integrated compliance test

Goertzel based phasor and frequency measurement for low-cost PMUs

The need for low cost phasor measurement unit (PMU) devices in power system demands less complex measurement algorithms that can be implemented on inexpensive processing platforms. Unlike the widely used DFT, the Goertzel algorithm, having low complexity is not explored much for synchrophasor estimation. An efficient integration of zero crossing detection (ZCD) with Goertzel technique is presented in this work for the design of low cost synchrophasor devices. An extensive analysis has been done in the design of pre-filtering stage, selection of suitable window length, sampling rate, and other parameters to exploit the benefits of proposed algorithm. The metrological characterization of the proposed algorithm is delineated by showing the different test results following the IEEE synchrophasor standards. The proposed method exhibits the lowest computational time in comparison to the state-of-the-art methods with similar low computational complexity. Simulations and experimental results are obtained by using Raspberry Pi 3 model B+ board.

Enhanced IpD2FT-Based Synchrophasor Estimation for M Class PMUs Through Adaptive Narrowband Interferers Detection and Compensation

One of the most challenging problems in the design of next-generation Phasor Measurement Units (PMUs) is related to the need to minimize the impact of multiple harmonics and out-of-band interharmonics (OOBI) on the measurement of synchrophasors over short observation intervals. Most of the existing solutions aim at removing such narrowband disturbances before synchrophasor estimation. However, when data records are short, accurate OOBI filtering may be infeasible. The algorithm described in this paper tackles this problem through a prior estimation of the number and the frequency of the significant narrowband interferers emerging from the noise floor. This result is achieved using a non-parametric signal detector based on random matrix theory and hypothesis testing, followed by the application of the estimation of signal parameters via the rotational invariance technique (ESPRIT). Once the number and the frequency of the narrowband components are known, these parameters are used to augment the dimension of the frequency-domain linear system of equations employed by the Interpolated Dynamic Discrete Fourier Transform (IpD2FT) for synchrophasor estimation. The results of multiple simulations confirm not only that the proposed approach for narrowband components detection is robust and more accurate than other model-order estimation algorithms described in the scientific literature, but also that the synchrophasor estimation accuracy over two-cycle observation intervals is generally higher than using other for M Class PMUs algorithms when OOBIs or a mixture of OOBIs and harmonics are considered.

Computationally Efficient Synchrophasor Estimation: Delayed In-Quadrature Interpolated DFT

Computationally Efficient Synchrophasor Estimation: Delayed In-Quadrature Interpolated DFT

Implementation of Phasor Measurement Unit Based on Phase-Locked Loop Techniques: A Comprehensive Review

The dynamic monitoring, control, and protection of modern power systems in real time require time-stamped electrical measurements to accurately estimate the bus voltage phasors using the state estimation function under normal and abnormal conditions. These measurements can be acquired by time-synchronized devices, known as phasor measurement units (PMUs). PMUs can measure bus voltage and branch current phasors of a three-phase network, as well as the frequency and the rate of change of frequency (ROCOF), with high speed, accuracy and time stamping provided by global positioning system (GPS) at the coordinated universal time (UTC). Various phasor estimation algorithms have been proposed in the literature, while most of them are concentrated in the discrete Fourier transform (DFT) algorithm, where an integer number of samples multiple of the nominal frequency is required for the computations. In cases where the frequency of the power grid deviates from its nominal value, the raw application of the DFT approach can lead to large errors during phasor estimation. Another approach of the phasor estimation is based on the phase-locked loop (PLL) techniques, widely used in grid tie inverters. PLL techniques can track dynamically (continuous time) the estimated frequency to the time-variant frequency of the power grid. A brief introduction to the basic concepts of the synchrophasor definition is provided, while the main DFT methods for synchrophasor estimation according to recent literature are mentioned. PLL-based PMU techniques are reviewed for both steady-state and dynamic conditions according to IEEE standards. In conclusion, the performance of PLL-based PMU algorithms presented in this literature review is discussed.

Evaluation of the Fast Synchrophasors Estimation Algorithm Based on Physical Signals

The goal of this study is to evaluate the performance of the fast algorithm for synchrophasor estimation proposed on the basis of a physical system. The test system is represented by a physical model of a power system with four synchronous generators (15 and 5 kVA). Three synchronous machines represent steam turbine generators, while the fourth machine represents a hydro generator. The proposed method of accuracy assessment is based on comparison of the original and the recovered signals, using values of amplitude and phase angle. The experiments conducted in the study include three-phase faults, two-phase faults and single-phase faults at various buses of the test model. Functional dependencies of initial signal standard deviation from the recovered signal are obtained, as well as those for sampling rate and window width. Based on the results, the following requirements for measurement system and window width are formulated: sampling rate of analog-to-digital converter should be 10 kHz; and window width should start from 5 ms. In addition, the fast algorithm of synchrophasor estimation was tested on event recorder signals. The sampling rate of these signals was 2 kHz. Acceptable window width for event recorder signals is 8 ms. The algorithm was implemented using programming language Python 3 for the testing purposes. The proposed fast algorithm of synchrophasor estimation can be applied in methods for emergency control and equipment state monitoring with short time response.

A Multiple-Frequency-Taylor-Model based estimator for dynamic synchrophasor considering decaying DC component

When the grounding fault occurs in power systems, it might stimulate power oscillations and generate decaying dc component (DDC) in the fault currents. Both will cause a sharp drop in the phasor monitoring accuracy of phasor measurement units (PMUs) and even lead operational protection devices to malfunction. Thus, a multiple-frequency-Taylor-model (MFTM)-based dynamic synchrophasor estimator considering DDC (MFTDC) is proposed to overcome the adverse effect by modeling dynamic behavior and DDC. Firstly, several sub-phasors extended by the Taylor series are employed to form the dynamic fundamental component and DDC. Secondly, rough phasor estimations are obtained by DFT filters at multiple frequency bins to establish the MFTDC equation set. Then, all Taylor derivatives of MFTDC can be solved by the least square method. Finally, various IEEE standard P-class test and static/dynamic-state DDC test results of computer, PSCAD/EMTDC, and RTDS-generated signals verify that MFTDC is suitable for the protection applications of power systems. It can yield more accurate phasor estimations of PMUs than that of our previous work and shorten the convergence time to 20.3 ms or less, especially under the dynamic-state DDC scenarios.

A Novel Synchrophasor Estimation Based on Enhanced All-Phase DFT with Iterative Compensation and Its Implementation

Synchrophasor estimation was mostly used in transmission systems in the past, and it is difficult to directly apply an existing synchrophasor algorithm to a distribution system with a more complex structure and environment. A synchrophasor estimation algorithm with a high accuracy and fast response speed is required to complete the calculation of the phasor in the face of the complex and changeable power signal of a distribution network. Therefore, an enhanced all-phase discrete Fourier transform (e-apDFT) algorithm is proposed for a distribution system in this paper, and the algorithm is deployed in a phasor measurement unit (PMU) prototype based on digital signal processing (DSP). Aiming to solve the problem of the accuracy of the traditional apDFT being reduced when the response speed is fast due to the influence of a dense spectrum, the existing algorithm is improved through iteratively compensating the spectral interferences to the main bin produced by adjacent bins. The experimental results show that the e-apDFT algorithm still has a fast response speed and that its estimation accuracy is much better than that of the traditional apDFTs in the presence of adjacent harmonic components. The proposed algorithm also complies with the IEEE standards for P-class PMUs.

A Full-View Synchronized Measurement System for the Renewables, Controls, Loads, and Waveforms of Power-Electronics-Enabled Power Distribution Grids

With the rapid development of distributed renewables, DC transmission, and active loads, increasingly more power electronics are and will be introduced into distribution grids. This has led to an increasing need for a new synchronized measurement system that covers different scenarios and applications to improve the stability and reliability of power-electronics-enabled power grids. In this paper, a full-view synchronized measurement system (SYMS) for the renewables, controls, loads, and waveforms of power-electronics-enabled power distribution grids is established, and is composed of different types of synchronized measurement devices (SMDs) and a data center. A general design method for the synchrophasor estimation of SMDs in different scenarios is proposed by deducing phasor measurement error models. This is further applied in combination with the design of hardware and a communication protocol to develop SMDs for the measurement of the renewables, controls, loads, and waveforms of power-electronics-enabled power distribution grids. Then, a framework of the data center of the SYMS, as well as several potential applications based on real-time measurements, are presented and discussed. The SYMS is a comprehensive, shared, and open power system data platform for use by future researchers.

Distributed Intelligence for Online Situational Awareness in Power Grids

This paper presents a suite of analytics that are proposed to be embedded in next-generation smart sensors in electric power grids. The proposed analytics take the electrical signals as the input and unlock the full potential in signal processing and machine learning for real-time event detection and classification. Meanwhile, a robust synchrophasor estimation mechanism is housed within the proposed sensor technology that will be triggered following a detected event and guides on the adaptive selection of the best-fit (most accurate) synchrophasor estimation algorithms at all times. Embedding such analytics within the sensor and closer to where the waveforms are captured, the proposed distributed intelligence solution technology mitigates the potential risks to communication failures and latencies as well as malicious cyber threats. Our experiments demonstrate that the introduced scheme achieves improved quality of measurements with a promising event detection and classification accuracy, collectively resulting in enhanced online situational awareness in modern power grids.

Field PMU Test and Calibration Method– Part I: General Framework and Algorithms for PMU Calibrator

Laboratory testing of phasor measurement units (PMUs) guarantees their performance under laboratory conditions. However, many factors may cause PMU measurement problems in actual power systems, resulting in the malfunction of PMU-based applications. Therefore, field PMUs need to be tested and calibrated to ensure their performance and data quality. In this paper (Part I), a general framework for the field PMU test and calibration in different scenarios is proposed. This framework consists of a PMU calibrator and an analysis center, where the PMU calibrator provides the reference values for PMU error analysis. Two steps are implemented to ensure the calibrator accuracy for complex field signals: <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\textcircled{1}$</tex> by analyzing the frequency-domain probability distribution of random noise, a Fourier-transform-based signal denoising method is proposed to improve the anti-interference capability of the PMU calibrator; and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\textcircled{2}$</tex> a general synchrophasor estimation method based on complex bandpass filters is presented for accurate synchrophasor estimations in multiple scenarios. Simulation and experimental test results demonstrate that the PMU calibrator has a higher accuracy than that of other calibrator algorithms and is suitable for field PMU test. The analysis center for evaluating the performance of field PMUs and the applications of the proposed field PMU test system are provided in detail in Part II of the next-step research.

Real-Time B-Spline Interpolation for Harmonic Phasor Estimation in Power Systems

The fundamental component synchrophasors are widely used nowadays, based on the use of Phasor Measurement Units (PMU), in several applications in electrical power systems. For the advancement of monitoring technology, harmonic synchrophasor estimation is still a challenge. To make it possible, it is necessary to correctly estimate the harmonic phasor (magnitude and phase of each harmonic component), mainly in scenarios with frequency deviations and noise. In this context, the present paper proposes the use of B-Spline based interpolation as a preprocessing algorithm for the Discrete Fourier Transform (DFT). The performance is evaluated in terms of Total Vector Error (TVE) considering the tests proposed by the IEEE C37.118.1 and IEC 60255-118-1 standards and compared with four different harmonic phasor estimation methods, the HPE, SIFE, TFT and FT FIR. The proposed method can provide a TVE below 1% for all harmonic phasors, from the first to the fiftieth order, under significant frequency deviation. Also, for real time validation, the proposed method was implemented in an industrial computer as a software routine capable of processing the signals in real time. The signals are acquired by a commercial Merging Unit (MU) and the samples are published using the IEC 61850 Sampled Values (SV) protocol.

Dynamic Harmonic Phasor Estimator Considering Frequency Deviation

The fundamental frequency of power system may deviate from the nominal value due to various reasons, such as load variation, subsynchronous resonance and fault occurrence. The maximum frequency deviation considered by the latest IEEE standard is 5 Hz. This paper proposes a dynamic harmonic synchrophasor estimator, which can accurately estimate the dynamic harmonic parameters even if the frequency deviation reaches 5 Hz. Multiple discrete frequencies are generated at a fixed frequency interval on both sides of the nominal frequency, and multiple dynamic harmonic filters are generated offline based on those frequencies. The windowed interpolation discrete Fourier transform is adopted for online monitoring of the fundamental frequency. According to the detected frequency, a harmonic filter, which is generated with the discrete frequency that is closest to the detected frequency, can be selected to analyze the dynamic harmonic synchrophasor, frequency and rate of change of frequency. The performances of the proposed estimator are verified through tests under various frequency deviation conditions, and the test results show that the proposed estimator can accurately estimate the dynamic harmonic parameters when the frequency deviation is within 5 Hz.

A Dynamic Synchrophasor Estimation Algorithm Considering Out-of-Band Interference

The existence of out-of-band interference (OBI) signals in power systems will dramatically degrade the performance of synchrophasor estimation. In order to alleviate the influence of OBI, a hybrid phasor model is proposed, in which the OBI phasor and the dynamic fundamental phasor are expressed by Taylor series, respectively. Then, the rough fundamental frequency and OBI frequency estimation are achieved via the rough fundamental component and OBI component estimated from discrete Fourier transform (DFT). For attaining the accurate phasor, the proposed algorithm can invoke the corresponding coefficient matrices calculated off-line according to whether the power signal contains OBI or not. Finally, field data and computer-generated signals are used to assess the proposed algorithm performance. The results obtained indicate that the proposed algorithm can enhance phasor estimation performance by keeping maximum TVEs below 0.001% and 1% under frequency deviation and power modulation tests with OBI, respectively.

Dynamic Impedance Estimation: Challenges and Considerations

The objective of this paper was to examine the dynamic impedance estimation of electrical systems from online measurements. The paper makes several considerations and highlights the challenges to obtain a precise estimation. Transducer equalization and harmonic synchrophasor estimation (HSpE) are reviewed and discussed. The use of online and adaptive equalization for transducers proves to be a viable solution for improving voltage transducer’s (VT’s) and current transducer’s (CT’s) frequency response. Additionally, the use of oversampling algorithms can mitigate the effects of noise in the HSpE. Furthermore, methods for harmonic impedance estimation are discussed. The independent component analysis ICA-based dynamic impedance estimation is proposed and results presented, which yields excellent agreement. Finally, harmonic modeling and simulation of injected harmonic currents are used to observe resonances through the amplification and attenuations and, consequently, the opportunity to confirm the system self and transfer impedances of a test system. Dynamic impedance estimation will continue to be a great challenge for the power systems engineer as the system complexity increases with the massive insertion of power electronic inverters and the associated required filtering. Real-time signal processing will be an effective tool to determine the dynamic self or transfer impedance.

A SVD-Based Synchrophasor Estimator for P-Class PMUs With Improved Immune From Interharmonic Tones

The increasing use of renewable generation, power electronic devices, and nonlinear loads in power systems brings more severe interharmonic tones to the measurand, which can increase estimation errors of P-class PMUs, cause misoperation of protection relays, and even threaten the stability of the power systems. Therefore, the performance of the P-class synchrophasor estimator under interharmonic interference should be evaluated and new estimation schemes that can improve the operational robustness are needed for various protection and control applications. In this paper, a synchrophasor estimator design for P-class PMUs that introduces singular value decomposition to the least square algorithm based on the Taylor series is proposed. By constructing an optimization with proposed adjustable parameters, finite impulse response filters with high transition band attenuation are designed. Numerical and experimental tests verify the proposed dynamic synchrophasor estimator performance and show an effective improvement in rejecting interharmonic tones, especially when a short time window and light computational burden are required.

Three-Point Synchrophasor Estimator With Better Off-Nominal Frequency Leakage Reduction

Synchronous phasor measurements have long been an important tool in power flow modelling and network state estimation as well as in many other tasks that support power grid observability. Classic phasor estimation algorithms are often preferred over complex alternatives. They are based on a variant of the Discrete Fourier Transform (DFT) while relying on a sampling frequency locked to the system nominal frequency. The spectral leakage caused by the small off-nominal frequency excursions in such settings introduces errors that are handled by the estimation algorithms to a different extent. Well-known three-point averaging filter (3P) is a low-cost spectral leakage reduction technique in one of the simplest estimators based on a single-bin DFT. However, it only partially removes the oscillating components. When an independent standard-based frequency tracking is available, the errors can be further compensated with minimal cost. We propose a frequency-corrected three-point estimator (F3P) to eliminate the induced spurious spectrum progressively with the increasing sampling rate while building on the analytical expression of the remaining error. We show performance benefits of the F3P under finite sampling rates when compared to the baseline 3P and to the classical Interpolated DFT (IPDFT) in static conditions. The F3P removes most of the leakage without the need of data resampling. In less ideal conditions with additive 50-dB noise, up to a 10-fold reduction of the 3P error is achieved. The error ratio of the reference IPDFT over the F3P is approximately 1.4 under the same conditions and largely independent of the frequency excursion. The presented simulation results prove the algorithm's superior performance in most of the steady-state tests defined by the relevant Standard, whereas the dynamic performance can be brought to an acceptable level by the use of a single-cycle observation window, with the response times comparable to those of the IPDFT.

Fast and accurate dynamic synchrophasor estimator for protection applications

Fast and accurate dynamic synchrophasor estimator for protection applications

Harmonic Synchrophasors Measurement Algorithms With Embedded Compensation of Voltage Transformer Frequency Response

The widespread diffusion of nonlinear power electronics-based devices in distribution grids has raised the interest toward power quality monitoring. In this respect, the estimation of synchronized harmonic phasors would enable the employment of algorithms that allow identifying the sources of harmonic disturbances, which, until now, have only been tested through numerical simulations or implemented on small-scale. However, the impact of the uncertainty due to the employed voltage transformers (VTs) and to the other devices that compose the measurement chain has to be analyzed. In this framework, the present article proposes a class of harmonic synchrophasor estimation algorithms that allows compensating the frequency response function of the instrument transformer. The technique has been tested and validated under realistic conditions considering an inductive VT. Experimental results highlight its effectiveness, especially when taking into account its ease of implementation. The black-box approach allows abstracting from the operating principle of the VT.

A Novel Interpolated DFT Synchrophasor Estimation Algorithm With an Optimized Combined Cosine Self-Convolution Window

With the current power system being electronicized nowadays, synchrophasor estimation (SE) plays an increasingly critical role in the monitoring, analysis, and protection of the state of the power grid. One proposal has been brought to enhance the commonly used discrete Fourier transform (DFT) algorithm that has a large error due to the inherent spectral leakage and fence effect in asynchronous sampling by interpolations. This article proposes an SE algorithm based on an optimized combined cosine self-convolution (OCCSC) window. Using the sidelobe characteristics of the window functions as the evaluation index, an optimized combined cosine window is obtained by the accelerated particle swarm optimization (APSO) algorithm. The window function’s self-convolution is used to further expand its excellent characteristics. Based on these characteristics, combined with interpolated DFT, simulations and experimental verifications compared with other algorithms show the effectiveness of the proposed algorithm.