Phasor Measurement Units Performance Research Articles

A Robust Asynchrophasor in PMU Using Second-Order Kalman Filter

Phasor Measurement Units (PMUs) provide Global Positioning System (GPS) time-stamped synchronized measurements of voltage and current with the phase angle of the system at certain points along with the grid system. Those synchronized data measurements are extracted in the form of amplitude and phase from various locations of the power grid to monitor and control the power system condition. A PMU device is a crucial part of the power equipment in terms of the cost and operative point of view. However, such ongoing development and improvement to PMUs’ principal work are essential to the network operators to enhance the grid quality and the operating expenses. This paper introduces a proposed method that led to low-cost and less complex techniques to optimize the performance of PMU using Second-Order Kalman Filter. It is based on the Asyncrhophasor technique resulting in a phase error minimization when receiving the signal from an access point or from the main access point. The MATLAB model has been created to implement the proposed method in the presence of Gaussian and non-Gaussian. The results have shown the proposed method which is Second-Order Kalman Filter outperforms the existing model. The results were tested using Mean Square Error (MSE). The proposed Second-Order Kalman Filter method has been replaced with a synchronization unit into the PMU structure to clarify the significance of the proposed new PMU.

Phasor data concentrator placement in phasor measurement unit networks considering communication channel uncertainty and failure

AbstractOne challenge in Wide Area Measurement System is to design a reliable network which assures data availability. The availability of data in Phasor Measurement Unit (PMU) networks depends on two factors: 1‐Reliable data measurements which depend on performance of PMUs and transmission branches, 2‐Reliable data transmission which depends on the reliability of communication networks used to transfer data from PMUs to Phasor Data Concentrators (PDCs) and control centre. The reliability of data transmission can be improved by choosing proper locations for PDCs. In this paper, a novel approach for PDC placement is proposed based on two pre‐defined indices; observability reliability and Loss Of Data Expectation (LODE). In the proposed method, the probability of regional communication networks' failure and the uncertainty of failure data for all components are also included in the calculation of these two indices to achieve more realistic results. To handle uncertainty, fuzzy membership functions are obtained for repair time and failure rate of all components, and a fuzzy Monte Carlo method is presented to evaluate both indices for each possible PDCs' location. The minimum LODE is used to find the best locations for PDCs. The proposed method is investigated for three sample systems which prove the system efficacy.

Performance and comparison of different phasor calculation techniques for the power system monitoring

Day to day to electrical power demand increases very rapidly with linear and non-linear load demands. Especially the nonlinear loads are creating the harmonics in the current and voltage signals. The current and voltage signal values are measured with the phasor measurement unit (PMU) for the proper magnitude and phase angle calculation even in the presence of harmonic components in the signals. The performance of the PMU is depending upon the phasor calculation technique. Different technique/methods are available for the phasor calculation, from the method to method there is difference in the accuracy, phasor computation time and complexity. In this paper various techniques for phasor calculation are presented. For better performance of PMU, more accurate and less computation time for phasor calculation technique is required. But in real time, accuracy and speed both may not satisfied with single technique. Need to find a satisfactory technique, which satisfies the speed of phasor computation and accuracy. In this paper it is proposed that direct phasor estimation technique, which gives the better results in terms of accuracy and time and this method, satisfies the requirements for the dynamic monitoring of power system according to the IEEE std. C37.118.1-2011.

Closed-Form Expressions to Estimate the Mean and Variance of the Total Vector Error

The need for accurate measurements and for estimating the uncertainties associated with measures are two pillars for researchers and metrologists. This is particularly true in distribution networks due to a mass deployment of new intelligent electronic devices. Among such devices, phasor measurement units are key enablers for obtaining the full observability of the grid. The phasor measurement unit performance is mostly evaluated by means of the total vector error, which combines the error on amplitude, phase, and time. However, the total vector error is typically provided merely as a number, that could vary within an unknown interval. This may result into the phasor measurement unit incompliance with the final user expectancies. To this purpose, and with the aim of answering practical needs from the industrial world, this paper presents a closed-form expression that allows us to quantify, in a simple way, the confidence interval associated with the total vector error. The input required by the expression is the set of errors that typically affects the analog to digital converter of a phasor measurement unit. The obtained expression has been validated by means of the Monte Carlo method in a variety of realistic conditions. The results confirm the applicability and effectiveness of the proposed expression. It can be then easily implemented in all monitoring device algorithms, or directly by the manufacturer to characterize their devices, to solve the lack of knowledge that affects the total vector error computation.

End-to-End Remote Field Testing of Phasor Measurement Units Using Phasor Measurement Unit Performance Analyzer Test Suite

Phasor measurement unit (PMU) testing is desired to ensure the continued power system monitoring and the maneuvering precision of synchrophasor-based control. IEEE Std C37.118 and IEEE synchrophasor measurement test suite specification (TSS) clarify the different requirements for both steady-state and dynamic test scenarios with varied error ranges. Existing PMU testing requires taking PMUs out of service and test in the lab typically manually. This article presents an architecture for remote PMU testing utilizing the PMU performance analyzer (PPA) test suite, which can considerably reduce the cost while achieving the substation automation. The proposed field-programmable gate array (FPGA) programming method is demonstrated to meet the TSS requirements for signal source generators (SSG). The accuracy of the frequency and harmonic distortion factors by SSG using the proposed method are compared with the built-in signal generation module of the national instruments (NI) cRIO system. The steady-state and dynamic test results of remote PMU testing based on the proposed architecture are presented in this article. The satisfactory performance test results demonstrate the feasibility of the architecture.

Design and experimental validation of an FPGA-based PMU simultaneously compliant with P and M performance classes

Low-inertia grids are characterized by high shares of harmonic and inter-harmonic distortion, produced by the inverters that interface non-conventional generation assets to the electrical grid. These interfering tones largely compromise synchrophasor estimation and may jeopardize protection and control strategies based on Phasor Measurement Units (PMU). Indeed, the IEEE Std. C37.118 does not require resiliency against inter-harmonic tones for protection PMUs. In view of increasing synchrophasor technology reliability, the paper presents the design and the experimental validation of a PMU that is simultaneously compliant with both protection (P) and measurement (M) class of PMU performance defined in the IEEE Std. C37.118. The synchrophasor estimator is based on the interpolated DFT and iteratively estimates and compensates the effects of the spectral interference produced by a generic interfering tone and the negative image of the fundamental tone. The proposed hardware architecture is based on a Field Programmable Gate Array (FPGA).

Impact of inductive current transformers on synchrophasor measurement in presence of modulations

Instrument Transformers (ITs) are essential devices for all the measurement tasks, f.i. metering, protection and diagnostics, in electricity grids, since they scale voltage and current down to levels compatible with measuring instruments. At the input of Power Quality (PQ) instruments and Phasor Measurement Units (PMUs), inductive voltage and current transformers (VTs and CTs) are still the most used ITs, even if, their performance in presence of disturbances is not fully assessed. This paper analyses the impact of the inductive CTs on the measurement of fundamental synchrophasors, by a PMU, in presence of a particular class of disturbances, the undesired modulations on current signals. Experimental tests, on two different CTs, show that there are critical situations, where, even compensating CT systematic ratio and phase errors, 1) CT exceeds its accuracy class limit and 2) considering the sole contribution of CT, PMU performance stays very close to the error limits of the standards.

Characterization of uncertainty contributions in a high-accuracy PMU validation system

The effective deployment of Phasor Measurement Units (PMUs) in Distribution Networks (DNs) requires an enhancement in terms of estimation accuracy beyond the limits of IEEE Std C37.118.1 (IEEE Std), aiming at a Total Vector Error (TVE) in the order of 0.0x% in steady-state test conditions. As a consequence, a rigorous metrological characterization of PMU performance requires a validation system whose accuracy is at least one order of magnitude better than the one of the device under test, i.e. it requires a TVE in the order of 0.00x% in steady-state test conditions and 0.0x% in distorted or dynamic test conditions. In this paper, we consider the hardware and software architecture of a previously published PMU validation system specifically designed for PMUs operating in DNs. In this context, we evaluate the quality of the generated test waveforms, and we carry out a thorough metrological characterization of the uncertainty contributions due to generation, acquisition and synchronization stages. In this sense, the proposed analysis provides a rigorous methodology for the evaluation of such low uncertainty levels, and enables us to identify and discuss the most challenging aspects in the implementation of a high-accuracy PMU validation system.

Performance Criterion of Phasor Measurement Units for Distribution System State Estimation

A phasor measurement unit (PMU) is a device that can directly measure the phase angles of voltages and currents, with high accuracy, using accurate time signals. Hence, PMUs have originally been used to improve the accuracy of transmission system state estimation. The merit of PMUs, further, extends the scope of its application to distribution system state estimation (DSSE), which has recently been studied because of the growing needs for distribution system management due to high levels of distributed energy resources. More importantly, the scarcity of measuring sensors in distribution systems highlights the role of PMUs for the DSSE. However, the full deployment of PMUs in distribution systems is practically impossible because of the high installation costs and geographically large size of these systems. Therefore, this paper investigates the adequate and economic performance of PMUs to meet the DSSE requirement with respect to the estimation accuracy. The accuracy of different PMU performance classes and the accuracy of various measurement types are first defined. Different sets of measurements are then assigned to different meter locations in a testbed that is a three-phase unbalanced, asymmetric system. Various performance metrics for each case study are computed and compared from the numerical simulation results.

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.

Reliability analysis of a phaser measurement unit using a generalized fuzzy lambda-tau(GFLT) technique

Nowadays power consumption is increasing day-by-day. To fulfill failure free power requirement, planning and implementation of an effective and reliable power management system is essential. Phasor measurement unit(PMU) is one of the key device in wide area measurement and control systems. The reliable performance of PMU assures failure free power supply for any power system. So, the purpose of the present study is to analyse the reliability of a PMU used for controllability and observability of power systems utilizing available uncertain data. In this paper, a generalized fuzzy lambda-tau (GFLT) technique has been proposed for this purpose. In GFLT, system components' uncertain failure and repair rates are fuzzified using fuzzy numbers having different shapes such as triangular, normal, cauchy, sharp gamma and trapezoidal. To select a suitable fuzzy number for quantifying data uncertainty, system experts' opinion have been considered. The GFLT technique applies fault tree, lambda-tau method, fuzzified data using different membership functions, alpha-cut based fuzzy arithmetic operations to compute some important reliability indices. Furthermore, in this study ranking of critical components of the system using RAM-Index and sensitivity analysis have also been performed. The developed technique may be helpful to improve system performance significantly and can be applied to analyse fuzzy reliability of other engineering systems.

A Data Imputation Model in Phasor Measurement Units Based on Bagged Averaging of Multiple Linear Regression

Synchrophasor data from the phasor measurement unit (PMU) indicate the health of the electrical system. However, the PMU performance relies entirely on a supported communication network. The existing communication approaches do not guarantee the error-free channel for the PMU network. Meanwhile, the mean or median approaches are commonly used to impute the missing value. These methods, however, fail to recover some valuable frequency events. In this paper, we first proved the multiple linear regression features in many synchronized frequency data streams in the short-time window. Then, we proposed the Bagged Averaging of Multiple Linear Regression model, which handles and fulfills the missing values in synchronized frequency data measurement fast and efficiently. This technique was based on the ensemble learning by bootstrapping and averaging many multiple linear regressions to predict the missing values. Various experiments on the synchronized frequency measurement data from the Texas synchrophasor network have demonstrated the effectiveness of our proposed approach in recovering the missing frequency events. Our proposed approach guarantees the performance of real-time wide area monitoring system applications, such as frequency analysis or stability monitoring and trending.

Utilization of optical sensors for phasor measurement units

With the help of GPS signals for synchronization, increasingly ubiquitous phasor measurement units (PMUs) provide power grid operators unprecedented system monitoring and control opportunities. However, the performance of PMUs is limited by the inherent deficiencies in traditional transformers. To address these issues, an optical sensor is used in PMU for signal acquisition to replace the traditional transformers. This is the first time the utilization of an optical sensor in PMUs has ever been reported. The accuracy of frequency, angle, and amplitude are evaluated via experiments. The optical sensor based PMU can achieve the accuracy of 9.03×10−4Hz for frequency, 6.38×10−3rad for angle and 6.73×10−2V for amplitude with real power grid signal, demonstrating the practicability of optical sensors in future PMUs.

Definition of Accurate Reference Synchrophasors for Static and Dynamic Characterization of PMUs

The calibration of phasor measurement units (PMUs) consists of comparing coordinated universal time time-aligned phasors (synchrophasors) measured by the PMU under test, against reference synchrophasors generated through a PMU calibrator. The IEEE Standard C37.118–2011 and its latest amendment (IEEE Std) describe compliance tests for static and dynamic conditions, and indicate the relative limits in terms of accuracy. In this context, this paper focuses on the definition and accuracy assessment of the reference synchrophasors in the test conditions defined by the above IEEE Std. In the first part of this paper, we describe the characterization of a nonlinear least-squares fitting algorithm used to determine the parameters of these reference synchrophasors. For this analysis, we deploy the proposed algorithm in a PMU calibrator and characterize the algorithm performance within the actual hardware implementation for both static and dynamic test conditions. More specifically, we generate reference waveforms through a highly stable high-resolution digital-to-analog converter and evaluate how the algorithm parameters (observation interval length and sampling frequency) affect the solution accuracy. In the second part, we discuss on the appropriateness of the synchrophasor model in the evaluation of PMU performance under step test conditions. In this regard, we propose an alternative time-domain approach to assess the synchrophasor estimate during transient events.

Phasor Measurement Unit Test Under Interference Conditions

This paper investigates the performance of phasor measurement units (PMUs) under interference conditions, which can appear in a power system and are not tested by the C37.118.1 standard. Three PMUs from different vendors configured for the M-class requirements were used to test three possible interference condition scenarios. In the first scenario, noise is added to the PMU input signal. The test runs a sweep of signal-to-noise ratios and the accuracy versus the noise level is obtained. The second scenario injects multiple harmonics with the input to test the influence on accuracy. The last scenario focuses on instrument transformer saturation, which leads to a modified waveform injected in the PMU. This test goes through different levels of current transformer saturation and analyzes the effect of saturation on the accuracy of PMUs. The test results show PMU measurements will be degraded when the input signal is distorted by high noise or a saturated current waveform, but is not particularly affected by multiple harmonics. This information can be used when selecting a PMU to ensure that it will provide a reliable measurement for the intended use. It can also be used for developing more robust PMUs and applications resistant to degraded measurements.

Tool for testing of phasor measurement units: PMU performance analyser

Phasor measurement units (PMUs) are one of the key sensor technologies for real-time wide area monitoring to realise the smart power grid vision. Before deploying the PMUs, it is important to test and validate performance of this sensor to ensure high reliability and accuracy under different operating scenarios of the power system. However, PMU testing needs to be made simpler, easier, automated and cost-effective to encourage the PMU vendors and utilities to get their PMUs tested. This has been the driving motivation for the development of a new procedure and tool for testing PMUs in this study. The results and findings of PMU testing and analysis using a newly developed software application named ‘PMU Performance Analyzer' (PPA) have been discussed in this study. PPA can work with a real-time digital simulator and a phasor data concentrator to make the PMU testing simple, easy, mostly automated, less time-consuming, highly accurate and cost-effective.

Testing and Enhancement of the Dynamic Performance of a Phasor Measurement Unit

Phasor measurement units (PMUs) provide the basis for synchrophasor measurements, which are good data sources for capturing power system dynamic behavior. The recently published IEEE Standard C37.118.1-2011 characterizes the dynamic performance of synchrophasor measurements with two performance class filters: P-class and M-class. Practical implementation of a PMU to meet all dynamic requirements is a challenging task. Performance of an actual PMU with the proposed reference performance class filters is presented with a brief overview of the PMU performance evaluation process and the sources of errors in the test environment. Based on the test results, some inadequacies in the reference M-class filter algorithm provided in the standard are revealed, and several minor inconsistencies in the error limits imposed by the standard are highlighted. Finally, some modifications to the M-class reference filter and suggestions to rectify the minor issues in the new standard are proposed.

Calibration of Phasor Measurement Unit at NIST

This paper describes the basic operating principles of Phasor Measurement Units (PMUs) and their time requirements to estimate absolute phase angles. A National Institute of Standards and Technology (NIST) PMU calibration system that tests PMU performance necessary to meet the IEEE synchrophasor standard requirements is discussed. The calibration of voltage, current, and time measurements for the NIST PMU test system is described. The total vector error of the NIST PMU test system is estimated to be 0.05%. A comparison between the NIST PMU test system and a prototype commercial PMU calibrator was performed to assure traceability of relevant electrical measurements and time measurement.

Adaptive Phasor and Frequency-Tracking Schemes for Wide-Area Protection and Control

The steady-state performance of phasor measurement units (PMUs) is well standardized in the recently issued revised IEEE Std. C37.118. The Western Electricity Coordinating Council (WECC) has developed dynamic performance requirements for PMU filters as a means to guarantee better, uniform PMU response under dynamic conditions, such as power swings and changing harmonics. These have been endorsed by North American Synchrophasor Initiative (NASPI) for its wide-area monitoring infrastructure. The main purpose of this paper is to present a new framework for designing PMU filtering algorithms capable of meeting or exceeding the WECC/NASPI requirements, while achieving an optimum transient response time. To this end, an adaptive complex bandpass filter derived from the exponentially modulated filter bank theory has been devised. It is built from freely chosen low-pass filter prototypes that fulfill the WECC requirements. The static and dynamic performances of two specific schemes dedicated to control and monitoring with 4- and 7-cycle response-time, respectively, are ascertained under noisy waveforms and changing harmonics with system frequency varying from 40 to 80 Hz. The center-frequency adaptation approach is shown to be intrinsically superior to the frequency compensation scheme, especially under fast varying frequency and changing harmonics.

Synchronized Phasor and Frequency Measurement Under Transient Conditions

Synchronized phasor measurements are becoming an important element of wide area measurement systems used in advanced power system monitoring, protection, and control applications. The recently issued revised standard C37.118 for synchrophasors has facilitated interoperability of phasor measurement units (PMUs) from different manufacturers. This standard defines performance for compliance when the input signals are in steady state. The performance of PMUs under transient conditions is not considered by the standard at this time, although clearly PMUs will be subjected to inputs under transient conditions. This paper is an attempt to provide the authors' views on how one may approach the question of standardizing PMU response under transient conditions.