Phasor Measurement Unit Devices Research Articles

A Graph-Theoretic Approach for Optimal Phasor Measurement Units Placement Using Binary Firefly Algorithm

The pursuit of achieving total power network observability in smart grids using Phasor Measurement Units (PMUs) carries a significant promise of real-time Wide-Area Monitoring, Protection, and Control (WAMPAC). PMU applications eliminate periodical measurements, thereby increasing accuracy through a high sampling rate of the measured power systems quantities. The high costs of installation of PMUs for total power system observability presents a challenge in the implementation of PMUs. This is due to the expensive costs of PMU devices. This has led to a prominent optimal PMU placement (OPP) problem that researchers tirelessly aim to solve by ensuring a complete power network observability while using the least installed PMU devices possible. In this paper, a novel Binary Firefly Algorithm (BFA) based on the node degree centrality scores of each bus is proposed to minimize PMU installations. The BFA solves the OPP problem in consideration of the effect of Zero Injection Buses (ZIBs) under normal operation and single PMU outage (SPO). The robustness and efficiency of the proposed algorithm is tested on IEEE-approved test systems and visualized with a force-directed technique on an undirected power network graph. The proposed BFA yields the same but better optimal PMU numbers, obtained by existing meta-heuristic optimization techniques found in the literature for each of the IEEE test cases, as well as highlighting the cost–benefit of having a robust system against single PMU loss while considering the ZIB effect for an improved system measurement availability.

Ways of Using Phasor Measurements in Power System State Estimation

A review of publications on using data from phasor measurement units (PMU) in electric grid state estimation (SE) algorithms is presented. Ways of including phasor measurement data in the SE problem formulation are considered based on the weighted least squares method. The advantages and drawbacks of each of the presented approaches are analyzed. Much attention is paid to the prospects of simultaneously estimating telemetric information and PMU data, and performing SE based solely on the PMU data. The computational difficulties and other obstacles that arise in using phasor measurements in performing SE are analyzed, and various ways of solving existing problems in this field are presented. It is pointed out that the accuracy of data obtained from PMU devices differs essentially from that of data obtained from classic measurement instruments. This circumstance imposes certain specific features on selecting the weighting factors for phasor measurement data in solving the SE problem. The existing approaches to determining the weighting factors for phasor measurement data, in particular, by calculating them based on available statistical data, are reviewed.

Cyber-Attack and Reliability Monitoring of The Synchrophasor Smart Grid Network

The recent advancement of synchrophasor measurements technology in the conventional power grid can monitor and control the state variables of the network very accurately at a high sampling rate in real-time. The complete observability of system states can be achieved through the Phasor Measurement Unit (PMU). The inclusion of a zero injection bus (ZIB) optimized the total number of PMU requirements for complete observation of the synchrophasor network. The communication channels between measurement devices and control centers are highly vulnerable to cyber threats. Thus, an anomaly that occurs with PMU devices during a cyber-attack can affect the system’s reliability. Therefore, monitoring the reliability of the synchrophasor network has become essential for healthy power operation. Synchrophasor measurement technology can enhance wide-area surveillance and security functionality. However, the dependability of such technologies in the context of information network accessibility has yet to be investigated in a coherent model. Growing electric grid defence levels to mitigate the impact of cyber-attacks is essential. The cumulative effect of synchrophasor network observability and reliability is discussed in this paper by optimizing the number of PMUs deployed and the interruption load that occurs during an anomaly with PMU while taking ZIB into account.The backup PMU deployment modeling is also presented to secure the reliability and observability of the grid network during an anomaly occurs with PMU. The indices, Interrupted Load Probability Index (ILPI) and Expected Demand Not Supplied (EDNS), are used to evaluate the reliability of synchrophasor grid networks by integrating the state probability of PMU unavailability due to cyber intrusion.

Optimal PMU Allocation Strategy for Completely Observable Networks With Enhanced Transient Stability Characteristics

The installation of phasor measurement units (PMUs) in contemporary electrical networks provides enhanced monitoring and control capabilities of the entire system. However, the placement of additional PMU devices is constrained by the relatively high cost and complicated communication infrastructure. Consequently, optimizing the allocation of PMU units is required to achieve complete visibility of the power system operation while minimizing the associated cost. This paper presents a coherent approach for solving the optimal PMU placement (OPP) in order to reduce the total number of PMUs that is required to completely observe the network. Furthermore, the proposed formulation of the OPP allocation problem considers several objectives such as cost minimization, redundancy and efficiency maximization in addition to various constraints like incorporation of zero-injection buses, single PMU failure, single line outage and consideration of flow measurements. Moreover, a two-stage approach is proposed to ensure the numerical observability of the obtained PMU placement. The proposed framework relies on solving a mixed integer linear programming problem for the OPP placement problem based on conventional measurements. The rank of the gain matrix is thereafter computed to check if the solution is numerically observable. In contrast to reported studies in the literature, transient stability enhancement is augmented in the formulation of the optimization problem such that the redundancy of predetermined buses is guaranteed without increasing the total number of installed PMU units. A novel spectral cluster-based online coherency grouping is employed to identify buses which possess the ideal characteristics in terms of transient stability support.

Adaptive WADC scheme for damping inter‐area oscillation based on Jaya optimization algorithm in the presence of variable time latencies from WAMS data

The continual increase in the power network topological structure and long distances between load-generation sources lead to modern powers systems are operated near theirs stability margins. For this issue, reliable and secure operations of electric devices through inter-area oscillations remain an essential issue in the system dynamic stability. In the case of improper actions of controlling devices, the severe inter-area interactions may lead to wide-area instabilities and large blackouts. Using wide-area measurement system (WAMS), remote signals are transferred through communications links with different inherent time latencies. In the case of large time delays, the main controllers cannot work appropriately which leads to improper performance of damping controllers through severe inter-area fault event scenarios. For this issue, this paper presents an adaptive wide-area damping controller (AWADC) for damping inter-area oscillations in large power systems equipped with WAMS technology consisting of various time latencies. In this case, based on the IEEE C37.118.1 protocol, the generator buses are equipped with phasor measurement unit devices. Also, owing to the different communication links, the measured global signals (GSs) are involved within different time latencies. In this case, at each time window, considering time delay compensator (TDC) technology provided through Simevents discrete event tool, the overall time delay is evaluated and compensated. For identifying the best controlling GSs, considering two observability and controllability concepts, the system dynamic signals are evaluated which the best input decisioning signals and corresponding output controlling signals are provided. The proposed AWADC scheme consists of different compensating blocks which are adjusted through simple and well-known Jaya optimization algorithm (JOA) through online evaluations. The structure of the proposed AWADC controlling scheme is carried out on a modified 39-bus New England test system consisting of large synchronous generators whose damping performances are evaluated through severe fault events with the potential of unstable inter-area oscillations. Simulation results indicate the effectiveness of developed TDC and JOA techniques to provide proper controlling signals through the AWADC controller in the presence of different time latencies.

Novel Optimal PMU Placement Approach Based on the Network Parameters for Enhanced System Observability and Wide Area Damping Control Capability

The placement of phasor measurement units (PMUs) in modern power systems provides improved monitoring and control characteristics of the entire electrical network. Nevertheless, the installation of additional PMU devices is associated with relatively high cost and complicated communication infrastructure. As a result, the allocation of the PMU devices needs to be optimized to achieve complete observability of the system while minimizing the related cost. This paper proposes a new method for solving the optimal PMU placement (OPP) problem using integer linear programming (ILP) such that the global optimal solution is guaranteed. As opposed to the reported studies in the literature, the proposed method considers the network parameters such as the series impedances and the shunt admittances of the transmission lines and transformers impedances in the formulation of the OPP problem. These parameters are found to have a crucial impact on the observability of the entire network. A distinguishing feature of the proposed approach is that it decomposes the network into smaller subnetworks, with reduced dependence between them, thus making it scalable when applied to typical networks. In addition, the proposed method seeks to achieve the maximum measurement redundancy while considering the impact of failures among individual PMU devices (N-1 contingency), the PMU channel limitation and the pre-existing conventional measurements. Furthermore, the presented approach incorporates additional constraints which are associated with the control feedback signals of the supplementary damping controllers and thus enhance the small signal stability of the power grid. The effectiveness of the proposed method is tested using different standard IEEE systems as well as a large practical network.

A Security Mechanism for IEEE C37.118.2 PMU Communication

Phasor measurement units (PMUs) are widely used to monitor the operating conditions of a smart grid. The PMU communication network is, generally, a public wide area network, hence it is vulnerable to cyberattacks. At present, IEEE C37.118.2 is widely used as the communication standard for PMU communication. However, the IEEE C37.118.2 standard does not specify any security mechanism to protect the PMU data from cyberattacks. Deviation in the transmitted data of PMUs may lead to devastating consequences, such as blackouts in the grid. To mitigate cyberattacks on a PMU, this article proposes a security mechanism based on key distribution scheme that ensures integrity along with confidentiality. This mechanism involves addition of new security fields to IEEE C37.118.2 message structure. The introduction of security mechanism imposes additional computational complexity on resource constraint PMU devices and addition of new security fields in PMU message structure increases overall message size which in turn increases communication delays. In order to assess the additional computational complexity and increased communication delays, an experimental set up consisting of PMU simulators and network emulator is developed in this article. The developed PMU simulator generates IEEE C37.118.2 messages with proposed security mechanisms. Results validate the applicability of the proposed security mechanism in PMU networks without any repercussions.

PTP‐based time synchronisation of smart meter data for state estimation in power distribution networks

This paper develops a novel approach for distribution system monitoring and state estimation, where time synchronisation of smart-meter measurements is carried out via the Precision Time Protocol (PTP). The approach is based on the concept of a Modified Smart Meter (MSM), a distribution system monitoring instrument that enables accurate time synchronisation of smart meter data. The design, application, communication technique and protocols of the MSM are described in detail. The proposed MSM device features PTP-based time synchronisation of smart meter measurements, and the concept of unbundling is applied to collect measurements utilising the existing smart meter sensors. This is expected to reduce the overall implementation cost of an MSM-based distribution network monitoring system compared to a system based on Phasor Measurement Units (PMUs). The problem of requiring open sky access for GPS links can potentially be solved by means of PTP synchronisation. Three-phase state estimation simulations using the IEEE-13 and 123 bus unbalanced test networks are employed to demonstrate the applicability of the MSM, and its performance is compared to standard PMU devices. The results indicate that the MSM may represent a workable monitoring solution for MV and LV distribution networks, with an acceptable trade-off between cost and performance.

Power Grid Online Surveillance Through PMU-Embedded Convolutional Neural Networks

Power grid operation continuously undergoes state transitions caused by internal and external uncertainties, e.g., equipment failures and weather-driven faults, among others. This prompts an observation of different types of waveforms at the measurement points (substations) in power systems. Modern power systems utilize phasor measurement units (PMUs) and intelligent electronic devices embedded with PMU functionality to capture the corresponding peculiarities through synchrophasor measurements. However, existing PMU devices are equipped with only one synchrophasor estimation algorithm (SEA) and are, thus, not always robust to handle different types of signals across the network. This article proposes a PMU-embedded framework that ensures real-time grid surveillance and potentially enables adaptive selection of preinstalled SEAs in the PMU. Therefore, it ensures high-fidelity measurements at all times and irrespective of the input signals. Our proposed framework consists of: 1) a pseudocontinuous quadrature wavelet transform which generates the featured scalograms and 2) a convolutional neural network for event classification based on the extracted features in the scalograms. Our experiments demonstrate that the proposed framework achieves high classification accuracy on multiple types of prevailing events in power grids, through which an enhanced grid-scale situational awareness in real time can be realized.

A Synchrophasor Test Platform for Development and Assessment of Phasor Measurement Units

The development of platforms and methods for test and calibration of phasor measurement units (PMUs) has drawn attention from the power systems community, especially due to the wide range of specific tests that must be performed. Aiming at reducing labor-intensive processes and the complexity of such tests, this paper presents an automated platform for test, calibration, and performance assessment of PMUs following the IEEE Std C37.118.1. The platform is composed of signal-generation hardware and software running on a personal computer. The test signals are synthesized in software, allowing different waveform configurations for automated testing. Also, the software receives information from the PMU under test and compares it to reference data, displaying results and statistics in real time. Because most of the functions of the system are performed in software, easy inclusion of additional tests or migration to other signal-generation hardware platforms is possible. The resulting test system allows tracing the behavior of the hardware and corresponding embedded software used in the PMU architecture under test through thousands of measurements collected in just a few minutes. The simple and versatile low-cost system presented in this paper enables accurate, flexible, and versatile automated testing of PMU devices with real-time visualization of results.

General optimal substation coverage algorithm for phasor measurement unit placement in practical systems

The primary objective of the conventional optimal phasor measurement unit (PMU) placement problem is the minimisation of the number of PMU devices that, when placed in a power system, measure all bus voltages. However, due to advancements in the field of relay technology, digital relays can now act as PMUs. This has significantly reduced device costs. Moreover, although the goal is to observe all the buses, the devices themselves can only be placed in substations, whose upgrade costs are much higher than those of the devices. Considering these factors, the approach proposed here simultaneously optimises the number of substations where traditional PMUs and dual-use line relay PMUs can be placed. The general optimal substation coverage (GOSC) algorithm presented in this study is also able to incorporate practical requirements such as redundancy in the measurement of critical elements of the system, and estimation of the tap ratios of the transformers present. Simulation results indicate that the GOSC algorithm provides significant techno-economic benefits.

Advancing China?s Smart Grid: Phasor Measurement Units in a Wide-Area Management System

In developing a smart grid the measurement technology used plays a fundamental role for advanced power-system analysis and control. Phasor measurement units (PMUs), as part of a wide-area measurement system (WAMS), increasingly constitute the critical measurement infrastructures for transmission and generation systems. As of 2013, approximately 2,400 PMU sets had been deployed in power grids in China, covering all 500-kV substations in the country and a number of important power plants and 220/110-kV substations. In addition, more than 30 WAMS center stations are in service, providing important dynamic information about power system operation. Most of these PMU devices were deployed after 2006, when an article introducing the basic PMU/WAMS architectures and functions in China was published in IEEE Power & Energy Magazine. Here, we will briefly summarize recent and emerging developments in China?s PMU/WAMS communication and synchronization network and then present some major advanced applications and novel pilot projects utilizing synchrophasor measurement technology.

A Secure Wireless Spectrum Control, Error Correction Scheme in Synchrophasors

There is an immediate need to find solution on spectrum crunch for communication framework and how to defend against cyber-attacks while sustaining energy delivery function specifically carried by Phasor Measurement Units (PMUs) and Phasor Data concentrators (PDC) [Phadke, 2008]. The paper uses the concept of exploiting antenna directivity by assigning the same frequency to all three directions, and thus co-channel isolation will be increased, and eventually reducing the interference and increasing the channel capacity. The paper also discuss the error correction control, and security challenges that are required in existing TCP/IP networks for PMU and PDC devices.

A Framework for Phasor Measurement Placement in Hybrid State Estimation Via Gauss–Newton

In this paper, we study the placement of phasor measurement units (PMU) for enhancing hybrid state estimation via the traditional Gauss-Newton method, which uses measurements from both PMU devices and Supervisory Control and Data Acquisition (SCADA) systems. To compare the impact of PMU placements, we introduce a useful metric which accounts for three important requirements in power system state estimation: convergence, observability and performance (COP). Our COP metric can be used to evaluate the estimation performance and numerical stability of the state estimator, which is later used to optimize the PMU locations. In particular, we cast the optimal placement problem in a unified formulation as a semi-definite program (SDP) with integer variables and constraints that guarantee observability in case of measurements loss. Last but not least, we propose a relaxation scheme of the original integer-constrained SDP with randomization techniques, which closely approximates the optimum deployment. Simulations of the IEEE-30 and 118 systems corroborate our analysis, showing that the proposed scheme improves the convergence of the state estimator, while maintaining optimal asymptotic performance.

Optimal Integration of Disparate C37.118 PMUs in Wide-Area PSS With Electromagnetic Transients

The present paper investigates the effective application of phasor measurement units (PMUs) with different technologies and filtering dynamics to the design of wide-area power system stabilizer (WAPSS). Two frequency-adaptive PMU algorithms shown to exceed the C37.118 class-M requirements based on FIR- and Kalman-bandpass filtering are selected for study. Their sharp dynamic differences are characterized using accurate fourth-order transfer functions derived from step responses using system identification techniques. While FIR-based PMUs have no overshoot in their phase and amplitude step responses, the adaptive Kalman filter allows for better out-of-band interference rejection at the cost of a phase step response with overshoot and a higher computational burden. These PMUs are implemented in Simulink and then embedded in electro-magnetic transients (EMT) simulations to experiment the realistic WAPSS behavior with the discrete-time devices in the loop. It is shown that WAPSSs with optimized settings can improve the damping performance of EMT models of a test system and a simplified Hydro-Québec network including PMU filtering dynamics and transmission delays. However, WAPSSs based on EKF-PMUs yielded better performances, thanks to their shorter group delay compared with FIR-PMUs. PMU devices and algorithms meeting standard C37-118 can thus behave quite differently under stressed dynamics.

Optimal PMU Placement Based on Probabilistic Cost/Benefit Analysis

This letter proposes an analytic framework for achieving an optimal solution for phasor measurement unit (PMU) placement problem. The proposed technique is on the basis of the cost/benefit analysis while long-term economic aspects and existing technical issues are simultaneously accounted for. More deployment of PMU devices would result in more reliable and secure electricity services. The reduction of system risk cost is hence recognized as the benefit associated with the development of wide-area measurement system (WAMS). The optimal number and location of PMUs are determined such that adding more PMUs is no longer beneficial. Two systems are examined to demonstrate the performance of the proposed method.

The OpenPMU Platform for Open-Source Phasor Measurements

OpenPMU is an open platform for the development of phasor measurement unit (PMU) technology. A need has been identified for an open-source alternative to commercial PMU devices tailored to the needs of the university researcher and for enabling the development of new synchrophasor instruments from this foundation. OpenPMU achieves this through open-source hardware design specifications and software source code, allowing duplicates of the OpenPMU to be fabricated under open-source licenses. This paper presents the OpenPMU device based on the Labview development environment. The device is performance tested according to the IEEE C37.118.1 standard. Compatibility with the IEEE C37.118.2 messaging format is achieved through middleware which is readily adaptable to other PMU projects or applications. Improvements have been made to the original design to increase its flexibility. A new modularized architecture for the OpenPMU is presented using an open messaging format which the authors propose is adopted as a platform for PMU research.

Dynamic phasor and frequency estimator for phasor measurement units

Synchrophasors and frequency estimations play an increasingly important role in power systems. Discrete Fourier transform (DFT) may introduce errors into phasor and frequency estimations under dynamic conditions, such as power oscillation. A dynamic phasor and frequency estimator for phasor measurement units (PMUs) is proposed to improve accuracy by considering dynamic characteristics of power systems expressed as Taylor derivatives. Firstly, phasor estimations of sequence components of diffident data windows are attained via DFT. Secondly Taylor derivatives, expressed by adjacent phasors at different data windows, are employed to improve accuracy of estimations by reassigning estimations with the knowledge of dynamic characteristics. Finally, dynamic characteristics of positive sequence components are applied to estimate the fundamental frequency with less delay compared to a state-of-the-art algorithm, phasor-based synchronised frequency measurement (PSFM). To verify the performance, a set of digital dynamic tests and a power oscillation model using PSCAD/EMTDC are presented. The simulation results show that proposed algorithm can achieve highly accurate estimations of phasor and frequency over a wide range of dynamic conditions. Even though a minor increase in calculation burden is required, this technique provides accurate phasor and frequency estimations without changing the legacy structure of PMU devices. Additionally, it has been found that proposed algorithm really meets the needs of online applications.