Real-time Wide Area Research Articles

Wide-area voltage stability assessment using loading margin sensitivity for increasing linear load levels and wind power penetration

Increase in integration of fluctuating and unpredictable renewable energy to the power grid, raise the complexity of real-time assessment of voltage stability. A precise measurement-dependent real-time wide area loading-margin-sensitivity study is a novel solution to this problem. This is a challenging task for a wind farm integrated WAMS-based large power system with GPS-aided PMU technology. The study here shows the computation of a real-time sensitivity index while increasing static load levels linearly. The index will be utilized for identifying the weakest buses for load shedding and provides situational awareness to the grid operator for load voltage control to avoid any power outages. Moreover, it assists in determining the fittest bus for load adjustment during scheduled maintenance and the auxiliary bus for instant load increment decisions based on demand. This study also investigates the effects of increasing DFIG-based wind energy penetration to determine the best wind-power penetration level. The proposed analysis was found to be accurate for voltage assessment on the WSCC three-machine nine-bus network and the New England sixteen-machine sixty-eight bus large power networks. An experimental study, to validate the results, is performed using a three-phase industrial category load on the SEL-based hardware test-bed using actual PMU recordings.

Randomized singular value decomposition based Real-time Wide Area Voltage Stability (WAVS) Assessment

Phasor Measurement Units (PMUs) are the advanced measuring devices which provide time-stamped measurements of voltage magnitudes as well as phase angles in Wide Area Monitoring Systems. These synchrophasors are exploited in this paper to develop a model-free voltage stability assessment method using randomized singular value decomposition (rSVD). Stage-1 of the proposal carries out an off-line study to (a) identify voltage weak buses to equip them with PMUs and (b) estimate the voltage stability monitor’s threshold based on the largest singular value (LSV). Stage-2 proposes a temporal change detection technique to identify and isolate the disturbance samples from steady state measurement window to maintain linearity of PMU data matrix. Finally, Stage-3 proposes the use of rSVD technique in an online environment to assess the WAVS. This technique performs SVD of low dimensional PMU data matrix to make the approach computationally lighter. The performance of the proposed scheme is demonstrated on the IEEE 14-bus system and the IEEE 118-bus system. The viability of the real-time implementation of the proposed scheme is also verified by way of its Real-Time Digital Simulation on the IEEE 14-bus system.

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.

Smart5Grid Solutions for enhanced TSO grid observability and manageability in massive RES penetration environment.

This article presents the latency minimisation potential provided by the Smart5Grid Open Experimentation Platform (OEP) developed by the Horizon 2020 Smart5Grid Research and Innovation (R&I) project. It discusses the OEP performance and provides experimental data to substantiate its contribution to improving observability and manageability of distributed renewable generation in power grids. That experimental proof is delivered by two pilots running on the OEP: Demo 1 Millisecond Level Precise Distribution Generation Control, and Demo 2 Real-time Wide Area Monitoring (WAM) pilot of 5G virtual Phasor Data Concentrator v(PDC) capabilities for WAM of end-to-end electricity grids. This work reports two Network Applications (NetApps) created to support both demos and provides experimental evidence that the OEP offers latency of comparable measure to well-established wire-bound communications in addition to availability and reliability on top of by-design flexibility, scalability and modularity, which are especially relevant to power systems with high shares of Distributed Renewable Energy Recourses (DRERs).The software and methods used for the OEP development and experimental testbeds applied to measure its latency performance in both tailored pilot demos are explained at length. The test results are presented and interpreted with a view to discussing potential contributions of the presented 5G-enabled solutions for power grid smartification in conditions of high rollout of distributed renewable generation. All pilot demos generate openly accessible data, except where specific security restrictions are applicable.

Smart5Grid Solutions for enhanced TSO grid observability and manageability in massive RES penetration environment

Background This article elaborates on Horizon 2020 Smart5Grid Research and Innovation (R&I) project and reports the Smart5Grid Open Experimentation Platform (OEP), including its Open Service Repository (OSR), Verification and Validation (V&V), NetApp Controller (NAC), and Multi-access Edge Computing Orchestrator (MECO), as key results of this project. It then translates those results into energy vertical implications of the Smart5Grid for Transmission System Operators (TSOs), focusing on two particular Use Cases (UCs): UC3 Millisecond Level Precise Distribution Generation Control and UC4 Real-time Wide Area Monitoring pilot demonstrator of 5G virtual PDC capabilities for WAM of end-to-end electricity grids. More specifically, this work exhibits UC3 and UC4 NetApps developed as one of the key project deliverables. All use cases generate openly accessible data, except where specific security restrictions are applicable. Methods The Smart5Grid development methodology is based on the concept of Network Applications (NetApps). Their main mission is to hide the complexity of a 5G telco network for energy application developers in a way that empowers them to develop a NetApp without having to deal with the underlying network. A Virtual Infrastructure Manager (VIM) such as OpenStack or Kubernetes hosts every unit that composes a NetApp. The VIM provides monitoring data to a Network Function Vurtualisation Manager and Orchestrator (NFV MANO) framework, which airs information to the NAC that employs analysis algorithms to propose the optimal Virtual Network Function (VNF) and NetApp placing. A Slice Manager (SM) reserves resources for all these capabilities. Results The Smart5Grid architecture represents the main result that this work delineates in the context of its enhanced 5G telecommunication provider (telco) capabilities for transmission and distribution grids to face and manage more efficiently high Renewable Energy Sources (RES) penetration in a decarbonisation context.

Risk-Constrained Minimization of Combined Event Detection and Decision Time for Online Transient Stability Assessment

This paper addresses the problem of `quickest possible' online transient stability assessment, by minimizing the decision time of combined event detection that might lead to a system split and unstable generator group prediction, from real-time wide area power system measurements. More importantly it does so by respecting predefined probabilistic error constraints for the prediction. The statistical theory of optimal detection is applied, firstly to choose the detection threshold and secondly to select a flexible assessment time, after using probabilistic neural networks to provide a temporal representation of the data. On simulated wide area measurements from the interconnected New England test system and New York power system this approach is between two and three times faster on average than strategies based on fixed assessment times, despite having comparable error rates.

Power systems wide-area voltage stability assessment considering dissimilar load variations and credible contingencies

This paper reveals that the existing techniques have some deficiencies in the proper estimation of voltage stability margin (VSM) when applied to a power system with different load change scenarios. The problem gets worse when credible contingencies occur. This paper proposes a real-time wide-area approach to estimate VSM of power systems with different possible load change scenarios under normal and contingency operating conditions. The new method is based on an artificial neural network (ANN) whose inputs are bus voltage phasors captured by phasor measurement units (PMUs) and rates of change of active power loads. A new input feature is also accommodated to overcome the inability of trained ANN in prediction of VSM under N−1 and N−2 contingencies. With a new algorithm, the number of contingencies is reduced for the effective training of ANN. Robustness of the proposed technique is assured through adding a random noise to input variables. To deal with systems with a limited number of PMUs, a search algorithm is accomplished to identify the optimal placement of PMUs. The proposed method is examined on the IEEE 6-bus and the New England 39-bus test system. Results show that the VSM could be predicted with less than 1% error.

Real-Time Wide-Area Disturbance Monitoring and Protection Methodology for EHV Transmission lines

This paper presents a real-time wide-area disturbance monitoring and protection (RWADMP) methodology for the backup protection of EHV transmission lines in smart grids (SG). The proposed methodology employs harmonic phasors (1st, 2nd, and 3rd order) of 3-Φ current signals estimated using multi-phasor measurement unit (MPMU) for fault detection, classification, and discrimination of faulty line accurately. Further, the stressed condition such as load encroachment is discriminated from fault. The phasors which were estimated at MPMU are communicated to phasor data concentrator (PDC) at system protection center. MPMU is realized in hardware using NI cRIO, current sensor and GPS module in conjunction with LabVIEW software. Performance of the proposed methodology has been validated on the scale down laboratory models of 400 kV EHV transmission systems such as two-generator two-bus and two-generator three-bus systems. The experimental results show the efficacy of the proposed methodology in improving the overall reliability of the protection system. Also, the proposed methodology is less sensitive to the different fault conditions like fault resistance (FR) and fault distance (FD). Further, the user-friendly LabVIEW monitoring system enhances the visualization of the power system state in PDC. Also, it helps the grid operator to take appropriate action in case of system stressed condition and avoids the mal-operation of the protective devices.

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.

Hybrid Transient Energy Function-Based Real-Time Optimal Wide-Area Damping Controller

This paper presents a real-time wide-area damping controller design based on a hybrid intelligent and direct method to improve the power system transient stability. The algorithm applied as a nonlinear optimal wide-area damping controller monitors the oscillations in the system and optimally augments the local excitation system of the synchronous generators. First, energy functions and Prony analysis techniques are used to identify these local or interarea oscillations and develop stability or damping performance index at a given time. Second, artificial neural networks are deployed to learn the dynamics of the system and energy functions based on supervised learning to construct an optimal control design. Then, using online reinforcement learning the quadratic objective function based on the stability index is estimated and optimized forward-in-time. Results on the IEEE 68-bus in Power System Toolbox and HYPERSIM real-time simulator show better transient and damping response when compared to conventional schemes and local power system stabilizers.

Co‐simulation platform for integrated real‐time power system emulation and wide area communication

Phasor measurement units (PMUs) are increasingly being deployed in electric power systems in an attempt to improve grid reliability and make the grid smarter through real-time wide area situational awareness, monitoring, protection and control applications. PMU-based applications require communication networks in the transmission of synchrophasor measurements from the substations to the control centres. However, the quality-of-service of these synchrophasor measurements are not guaranteed when transmitted over a global wide area network especially in the presence of non-deterministic communication network conditions. This study presents the design, development, and integration of an IEEE Std. C37.118-based co-simulation platform comprising of power system hardware-in-the-loop simulations using the real-time digital simulator interfaced to a communication network. The impact of adverse communication network conditions such as latency, packet losses, and corruption on the exchange of data using the co-simulation platform and their impact on a centralised wide area monitoring, protection, and control (WAMPAC) system was investigated with software-in-the-loop simulations. Moreover, the maximum allowable adverse communication conditions are quantified with respect to the WAMPAC applications during emergency conditions.

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.

Research and Engineering Practice of Wide area Protection and Control Systems

Wide area protection (WAP) system is a control and protection system based on power grid information through network communication. WAP can determine fault location and clear fault selectively and quickly, then analysis the effect of power system stability after fault components disconnection and take appropriate control measures. WAP consists of master and slave station. With wide area information, WAP can solve the setting and matching difficulty of protective relaying, and can shorter the delay time of back-up protection. WAP also can improve the level of power system security and stability operation, and coordinate protective relaying and stability control. Obtain real-time wide area information reliably and accurately is the key point to build WAP. The reliability of network, synchronization accuracy, and the efficiency of communication protocols are key technologies of WAP. Full use of wide area information to get smarter, more reliable and more adaptable control strategy that coordinated protective relaying and stability control is the core contents of WAP. This paper summarizes the theory and engineering problems countered in the process of WAP research and application, and introduces the solutions or ideas. This paper brings out several urgent problems to be solved in order to promote WAP technology, and gives outlook of key issues in the implementation WAP at smart substation.

Performance Assessment of Communication Network in WAMS

Wide Area Measurement Systems (WAMS) based on Synchronized Measurement Technology (SMT) is getting considerable attention worldwide from the power system engineers in last few years. The fast and synchronized measurements facilitate the real time Wide Area Monitoring and Control (WAMC) of the power system. The backbone of WAMS is high performance communication infrastructure. Network designer has vast variety of architecture, protocol and communication medium. The medium should be selected in such a manner that it provides guaranteed bandwidth for the utilities. In this paper, we have simulated Phasor Measurement Unit (PMUs) data traffic in OPNET, and then created scenarios with different routing protocols. The performance of WAMS has also been analyzed in presence of varying background traffic and main link failure. Simulation results have been pursued in such a way that under worst situation the ‘end to end delay’ is within an acceptable range.

Laboratory-Based Smart Power System, Part II: Control, Monitoring, and Protection

Wide area monitoring (WAM), wide area protection (WAP), and wide area control (WAC) systems will enhance the future of smart grid operation in terms of reliability and security. In part I of this paper, a proposed architecture for a hybrid ac/dc smart grid hardware test-bed system was presented. Design details of the various components and their connectivity in the overall system architecture were identified. In part II of the paper, the focus is on the design of monitoring, control, and protection systems and their integrated real-time operation. Various control scenarios for system startup and continuous operation are examined. We have developed a control system based on wide area measurements. The advanced measurement system based on synchrophasors was also implemented using DAQs real-time synchronous data. The developed system features a wide variety of capabilities such as online system parameters calculation and online voltage stability monitoring. These are implemented as an experimental case to enhance wide area monitoring systems. Moreover, the protection system was designed inside of the real-time software environment to monitor the real-time wide area data, and make a comprehensive and reliable coordination for the whole system. Ideas related to the interaction of a dc microgrid involving sustainable energy sources with the main ac grid have been also implemented and presented. The implemented system is explicit and achievable in any research laboratory and for real-time real-world smart grid applications.

Wide Area RTK: A satellite navigation system based on precise real‐time ionospheric modelling

The Wide Area Real Time Kinematic (WARTK) is an augmentation system concept for multi‐frequency users based on precise real‐time ionospheric modeling. It is able to provide a high accuracy and integrity GNSS positioning service over continental areas using the infrastructure of a network of permanent ground monitor stations, such as the European Geostationary Navigation Overlay Service (EGNOS) network of Ranging and Integrity Monitoring Stations (RIMS) in Europe. In this way, it allows an additional benefit to be obtained from these reference stations, that is, the network has the potential to support two independent systems: a satellite‐based augmentation system, such as EGNOS, and a high‐precision positioning service, based on WARTK. Indeed, thanks to the accuracy of the ionospheric corrections provided, WARTK users have available in real‐time an extra constraint per satellite between the carrier phase ambiguities, which helps solve them quickly. Once such ambiguities have been solved, the GNSS user obtains navigation accurate to within 20 cm at the 95th percentile (about 10 cm RMS). Moreover, this precise positioning is achieved in a few minutes (with two frequency signals) or in a single epoch, after initial convergence of the tropospheric delay (with three frequency signals), even up to hundreds of kilometers away from the nearest reference station. While previous WARTK research has been devoted to implementing the concept and assessing its feasibility, considering in particular the accuracy achievable, the work reported in this paper focused on consolidating the results by analyzing a large and representative data set, and on deeper analysis of the integrity issue. It was carried out in the context of the Multi‐constellation Regional System (MRS) project, within the European Space Agency GNSS Evolution Programme, with the aim of designing a high accuracy service for GPS and/or Galileo. Three months of actual data, from more than 25 permanent GPS stations in Europe, have been processed (some of them as a roving user), for high‐, mid‐ and low‐solar cycle conditions (in 2002, 2004 and 2006 respectively). In addition, several ionospheric storms occurred during the selected periods, withDstvalues reaching up to −150 nT. Results based on these data show that user domain integrity was maintained for baselines of up to 400 km. At the 95th percentile, the daily horizontal and vertical position errors were 20 and 30 cm, respectively, and the corresponding protection levels were about 1 and 2 m. The convergence time was around 5 minutes with actual GPS constellation data. The benefits of using a multi‐constellation system were also studied, with simulated GPS and three‐frequency Galileo data, showing that it is possible to reduce the convergence time to a few seconds.

Adapting a Main-Stream Internet Switch Architecture for Multihop Real-Time Industrial Networks

As real-time industrial control systems scale up, single real-time local area network (LAN) is no longer sufficient; instead, we need real-time switches to merge many real-time LANs into real-time wide area networks (WANs). However, nowadays commercially-off-the-shelf WAN switches are designed for best-effort Internet traffic rather than real-time traffic. To address this problem, we propose a real-time crossbar switch design that minimally modifies, and even simplifies the de facto industrial standard switch design of iSLIP. Specifically, we change the iSLIP request-grant-accept negotiation to deterministic grant. The switch runs periodically with an M cell-time clock-period. Every input port runs per-flow queueing, and every output port deterministically grants input port per-flow queues according to its own M cell-time clock-period schedule. The schedules are created offline. We prove that the global scheduling can be reduced to a preemptive open shop scheduling problem; as long as every input/output needs to send/fetch no more than M cells per M cell-time clock-period, all outputs schedules do not conflict; and the scheduling algorithm takes O(N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> ) time (N is the number of input/output ports). Such design serves real-time periodic/aperiodic traffic in a time-division multiple-access (TDMA) fashion. This simplifies analysis, provides isolation, and results in a close-form end-to-end delay bound. We implemented the proposed real-time switch using Xilinx field programmable gate arrays (FPGAs), and built a distributed control test bed upon the switched networks. Using the test bed, we carried out experiments to compare the implemented real-time switches and iSLIP switches. The results prove the necessity of using real-time switches for real-time industrial control.

Wide area real time kinematic decimetre positioning with multiple carrier GNSS signals

This paper presents the technical basis for wide area real time decimetre positioning services using multiple carrier signals transmitted by future GNSS such as modernized GPS and Compass systems. The first step is to form two ionosphere-reduced extra-widelanes (EWL) that have the minimal total noise levels in cycles, considering the effects of the ionospheric and tropospheric delays, orbital error, and phase noise terms in various observational environments. The proposed three carrier ambiguity resolution approach can determine the integer ambiguities of the selected EWL signals with geometry-free and geometry-based estimations respectively over the distances of typically hundreds of kilometres. With two ambiguity-fixed EWL signals, the kinematic positioning solutions can be achieved in decimetre level accuracy. A semi-simulation method is employed to generate three frequency Compass data to demonstrate the above expected performance for decimetre positioning services. Both theoretical and experimental results have demonstrated the overall 3D root mean square accuracy of better than 15 cm obtained through with a phase smoothing process over 120 epochs. The dominating error factor in this positioning result is the residual tropospheric biases, which would become less correlated as the baselines grow beyond hundreds of kilometres. With respect to dual-frequency based precise point positioning and wide area differential positioning solutions, a major advantage of using the third frequency signals is the convergence time being shorten from tens of minutes to a few minutes. In addition, due to the instant ambiguity resolution capability, phase breaks or cycle slips no longer affect the continuity of the solutions. This reliable decimetre positioning capability introduces a significant improvement to safety-of-life, liability-critical and professional applications.

Real Time Wide Area Voltage Stability Index in the Korean Metropolitan Area

Through the development of phasor measurement units (PMU), various aspects of power system dynamic behavior could be monitored and diagnosed. Monitoring dynamic voltage stability has become one of the achievements we can obtain from PMUs. It is very important to select the most appropriate method for the Korea Electric Power Corporation (KEPCO) system since there are many voltage stability indices. In this paper, we propose an advanced WAVI (Wide Area Voltage Stability) that is well suited for the purposes of monitoring the dynamic voltage stability of KEPCO’s PMU installation plan. The salient features of the proposed index are: i) it uses only PMU measurements without coupling with EMS data; ii) it is computationally unburdened and can be applied to real-time situations. The proposed index is applied to the KEPCO test system and the results show that it successfully predicts voltage instability through comparative studies.

Measurements get together

This article deals with the synchronized measurement technology that has the potential of becoming the backbone for real-time monitoring system. The secure and reliable operation of modern power systems is an increasingly challenging task due to the ever-increasing demand for electricity, the growing number of interconnections, penetration of variable renewable energy sources, and deregulated energy market conditions. Power companies in different parts of the world are therefore feeling the need for a real-time wide area monitoring, protection, and control (WAMPAC) system. Synchronized measurement technology (SMT) has the potential of becoming the backbone of this system. The major advantages of using SMT are that 1) the measurements from widely dispersed locations can be synchronized with respect to a Global Positioning System (GPS) clock, 2) voltage phase angles can be measured directly, which was so far technically infeasible, and 3) the accuracy and speed of energy management system (EMS) applications increases manifold.