Efficient detection for multifrequency dynamic phasor analysis

Analysis of harmonic and interharmonic phasors is a promising smart grid measurement and diagnostic tool. This creates the need to deal with multiple phasor components having different amplitudes, including interharmonics with unknown frequency locations. The Compressive Sensing Taylor-Fourier Multifrequency (CSTFM) algorithm provides very accurate results under demanding test conditions, but is computationally demanding. In this paper we present a novel frequency search criterion with significantly improved effectiveness, resulting in a very efficient revised CSTFM algorithm

Definition and assessment of reference values for PMU calibration in static and transient conditions

The calibration of Phasor Measurement Units (PMUs) consists of comparing Coordinated Universal Time (UTC) time-stamped phasors (synchrophasors) estimated by the PMU under test, against reference synchrophasors generated through a PMU calibrator. The IEEE Standard C37.118-2011 and its amendment (IEEE Std) describe compliance tests for static and dynamic conditions, and indicate the relative limits in terms of accuracy. In this context, the paper focuses on the definition and accuracy assessment of the reference synchrophasors in the test conditions dictated by the above IEEE Std. In the first part of the paper, we describe the characterization of a nonlinear least-squares (NL-LSQ) fitting algorithm used to determine the parameters of the reference synchrophasors. We analyse the uniqueness and robustness of the solution provided by the algorithm. We assess its accuracy within the whole range of static tests required by the IEEE Std. In the second part, we discuss the appropriateness of synchrophasor model to evaluate the PMU performance in step test conditions. We compare the proposed algorithm against two synchrophasor estimation algorithms. Finally, we propose a time domain process for the better evaluation of PMU performances in transient conditions

PMU-Based ROCOF Measurements: Uncertainty Limits and Metrological Significance in Power System Applications

In modern power systems, the Rate-of-Change-of-Frequency (ROCOF) may be largely employed in Wide Area Monitoring, Protection and Control (WAMPAC) applications. However, a standard approach towards ROCOF measurements is still missing. In this paper, we investigate the feasibility of Phasor Measurement Units (PMUs) deployment in ROCOF-based applications, with a specific focus on Under-Frequency Load-Shedding (UFLS). For this analysis, we select three state-of-the-art window-based synchrophasor estimation algorithms and compare different signal models, ROCOF estimation techniques and window lengths in datasets inspired by real-world acquisitions. In this sense, we are able to carry out a sensitivity analysis of the behavior of a PMU-based UFLS control scheme. Based on the proposed results, PMUs prove to be accurate ROCOF meters, as long as the harmonic and inter-harmonic distortion within the measurement pass-bandwidth is scarce. In the presence of transient events, the synchrophasor model looses its appropriateness as the signal energy spreads over the entire spectrum and cannot be approximated as a sequence of narrow-band components. Finally, we validate the actual feasibility of PMU-based UFLS in a real-time simulated scenario where we compare two different ROCOF estimation techniques with a frequency-based control scheme and we show their impact on the successful grid restoration.Comment: Manuscript IM-18-20133R. Accepted for publication on IEEE Transactions on Instrumentation and Measurement (acceptance date: 9 March 2019

Fast Iterative-Interpolated DFT Phasor Estimator Considering Out-of-band Interference

For interpolated discrete Fourier transform (IpDFT)-based phasor estimators, the out-of-band interference (OOBI) test is among the most challenging ones. The typical iterative-interpolated DFT (i-IpDFT) phasor estimator utilizes a two-step iterative framework to eliminate the effects of the negative frequency and OOBI. However, the speed of estimation is limited by the adopted frequency estimator and the redundant iterations. To this end, this article proposes a fast i-IpDFT (FiIpDFT) method for the phasor estimation of an OOBI contaminated signal, which utilizes the three-point IpDFT (I3pDFT) technique. The proposed method first applies a noniterative frequency, amplitude, and phase estimator to eliminate the negative frequency interference. Then, a straightforward formula and two-stop criterion are introduced to reduce the computational burden of the OOBI elimination process. The accuracy and effectiveness of the proposed FiIpDFT method are validated by simulations. These are designed, under steady and dynamic conditions, according to the requirements of the Standard IEC/IEEE 60255-118-1

Iterative-Interpolated DFT for Synchrophasor Estimation: A Single Algorithm for P- and M-Class Compliant PMUs

We present a single synchrophasor estimation (SE) algorithm that is simultaneously compliant with both P and M phasor measurement unit (PMU) performance classes. The method, called iterative-interpolated discrete Fourier transform (i-IpDFT), iteratively estimates and compensates the effects of the spectral interference produced by both a generic interfering tone, harmonic or interharmonic, and the negative image of the fundamental tone. We define the three-point i-IpDFT technique for cosine and Hanning window functions and we propose a procedure to select the i-IpDFT parameters. We assess the performance of the i-IpDFT with respect to all the operating conditions defined in the IEEE Std. C37.118 for P- and M-class PMUs. We demonstrate that the proposed SE method is simultaneously compliant with all the accuracy requirements of both PMU performance classes

Iterative-Interpolated DFT for Synchrophasor Estimation: A Single Algorithm for P- and M-Class Compliant PMUs

We present a single synchrophasor estimation (SE) algorithm that is simultaneously compliant with both P and M phasor measurement unit (PMU) performance classes. The method, called iterative-interpolated discrete Fourier transform (i-IpDFT), iteratively estimates and compensates the effects of the spectral interference produced by both a generic interfering tone, harmonic or interharmonic, and the negative image of the fundamental tone. We define the three-point i-IpDFT technique for cosine and Hanning window functions and we propose a procedure to select the i-IpDFT parameters. We assess the performance of the i-IpDFT with respect to all the operating conditions defined in the IEEE Std. C37.118 for P- and M-class PMUs. We demonstrate that the proposed SE method is simultaneously compliant with all the accuracy requirements of both PMU performance classes

Detección y análisis armónico en señales eléctricas usando sensado comprimido para evaluación de la calidad de energía

The measurement and analysis of harmonics are key parts of the evaluation of the quality of the energy; however, measuring the harmonics under the large-scale distributed measurement architecture faces the problem of obtaining measurements outside the sequence that brings latency into communication and data fusion. For this reason, this article proposes as a solution to the problems of measurement and improvement of the resolution of harmonic signals, the compressed sensing (SC) as a technique for the recovery and estimation of signals, a technique that reduces the length of harmonic sampling and complexity of the data procedure compared to other theories. For this, we use restoration algorithms such as least squares (LQ), Basic Pursuit (BP), Orthogonal Matching Pursuit (OMP), performing experiments on three signals with different degree of total harmonic distortion (THD), obtaining as results the error of reconstruction in each algorithm to find the minimum percentage of compression in the recovery of harmonic signals. Finally, the results of the experiment show the accuracy of the detection and the system response can be improved without the need to increase the sampling points, showing the variation of the error as a function of the percentage of compression.La medición y el análisis de armónicos son partes clave de la evaluación de la calidad de la energía; sin embargo, el medir armónicos bajo la arquitectura de medición distribuida a gran escala se enfrenta al problema de obtener mediciones fuera de secuencia que trae latencia en la comunicación y la fusión de datos. Por esta razón, en este artículo se propone como solución a los problemas de medición y mejora de la resolución de las señales armónicas el sensado comprimido (SC) como técnica para la recuperación y estimación de señales, técnica que permite disminuir la longitud de muestreo armónico y complejidad del procedimiento de datos en comparación con otras teorías. Para esto, se utilizan algoritmos de restauración como el least squares (LQ), Basic Pursuit (BP), Ortogonal Matching Pursuit (OMP), realizándose experimentos en tres señales con diferente grado de distorsión armónica total (THD), obteniendo como resultados el error de reconstrucción en cada algoritmo para encontrar el porcentaje mínimo de compresión en la recuperación de señales armónicas. Finalmente, los resultados del experimento muestran la precisión de detección y que la respuesta del sistema se puede mejorar sin la necesidad de aumentar los puntos de muestreo, mostrando la variación del error en función del porcentaje de compresión

Compressive Sensing of a Taylor-Fourier Multifrequency Model for Synchrophasor Estimation

Synchrophasor measurements, performed by phasor measurement units (PMUs), are becoming increasingly important for power system network monitoring. Synchrophasor standards define test signals for verification of PMU compliance, and set acceptance limits in each test condition for two performance classes (P and M). Several PMU algorithms have been proposed to deal with steady-state and dynamic operating conditions identified by the standard. Research and discussion arising from design, implementation, testing and characterization of PMUs evidenced that some disturbances, such as interharmonic interfering signals, can seriously degrade synchrophasor measurement accuracy. In this paper, a new Compressive Sensing (CS) approach is introduced and applied to synchrophasor measurements using a Taylor-Fourier multifrequency model (CSTFM). The aim is to exploit, in a joint method, the properties of CS and the Taylor- Fourier transform to identify the most relevant components of the signal, even under dynamic conditions, and to model them in the estimation procedure, thus limiting the impact of harmonic and interhamonic interferences. The CSTFM approach is verified using composite tests derived from the test conditions of the synchrophasor standard and simulation results are presented to show its potentialities