Wide Area Measurement System Research Articles

Power system responses to geomagnetic disturbances recognized using phasor measurement recordings

Geomagnetically induced currents (GICs) flowing through transformers result in a DC bias, which poses a threat to safe and stable power grid operation. To evaluate the influence of geomagnetic storms on power systems, it is necessary to study actual power system responses. In this paper, the power system response is represented separately using current and reactive power measurements acquired using phasor measurement units (PMUs). On the basis of the data obtained from a wide-area measurement system, the power system responses to geomagnetic disturbances at Yangquan Substation, Shanxi, China were obtained. By employing the plane wave method, the data acquired during two mild magnetic storms at the Shisanling Geomagnetic Observatory were used to calculate the electric field and GIC at Yangquan Substation. The response variables and calculated GIC results agreed well, and the response variables were thus applied to assess the GIC level in the power system. The results show that the fluctuations in the PMU measurements were caused by GICs in the power system, laying the foundation for a significantly more detailed geomagnetic storm risk monitor.

Transient instability detection method based on multi-source trajectory information

Online monitoring of dynamic stability in wide-area power system is an important condition to reduce the negative impact of out-of-step oscillations. Research shows that during the oscillation of power system, the characteristics of the disturbed trajectory can reflect the instability of the system. Benefiting from the popularization and perfection of wide area measurement system, the transient instability criterion based on the disturbed trajectory analysis has made great progress in recent years. This paper summarizes the six common instability criteria based on the disturbed trajectory and explores the relationship between the criteria in the time sequence. According to the obtained relationship, a comprehensive strategy is constructed to integrate the criteria based on multi-source trajectory information. The multiple criteria are divided by the logic of early warning and judgment, in order to enhance the reliability of transient instability detection and save time for the calculation of the real-time islanding strategy. Simulation results using the IEEE 118 bus system show that the proposed strategy gives high reliability to the system in different scenarios.

VHDRA: A Vertical and Horizontal Intelligent Dataset Reduction Approach for Cyber-Physical Power Aware Intrusion Detection Systems

The Cypher Physical Power Systems (CPPS) became vital targets for intruders because of the large volume of high speed heterogeneous data provided from the Wide Area Measurement Systems (WAMS). The Nonnested Generalized Exemplars (NNGE) algorithm is one of the most accurate classification techniques that can work with such data of CPPS. However, NNGE algorithm tends to produce rules that test a large number of input features. This poses some problems for the large volume data and hinders the scalability of any detection system. In this paper, we introduce VHDRA, a Vertical and Horizontal Data Reduction Approach, to improve the classification accuracy and speed of the NNGE algorithm and reduce the computational resource consumption. VHDRA provides the following functionalities: (1) it vertically reduces the dataset features by selecting the most significant features and by reducing the NNGE’s hyperrectangles. (2) It horizontally reduces the size of data while preserving original key events and patterns within the datasets using an approach called STEM, State Tracking and Extraction Method. The experiments show that the overall performance of VHDRA using both the vertical and the horizontal reduction reduces the NNGE hyperrectangles by 29.06%, 37.34%, and 26.76% and improves the accuracy of the NNGE by 8.57%, 4.19%, and 3.78% using the Multi-, Binary, and Triple class datasets, respectively.

A Novel Multiobjective OPP for Power System Small Signal Stability Assessment Considering WAMS Uncertainties

In this paper, a multiobjective optimization method for the placement of phasor measurement units (PMUs) is proposed. The proposed method simultaneously considers different objectives including the power system small signal stability, the probability of system observability, and the total cost of PMUs. In the proposed optimal PMUs placement (OPP) model, wide area measurement system (WAMS) uncertainties and network configuration changes are also considered, while the variable cost of PMUs, based on the number of PMU channels is also observed. The elitist nondominated sorting genetic algorithm (NSGA-II) is used to obtain the Pareto optimal solutions and the best compromise final solution is selected by the decision maker on the basis of his priorities. Some simulation results on different test systems in different scenarios are presented and discussed. They confirmed that the proposed multiobjective model provides effective information for small signal stability assessment with minimum PMU cost in the presence of uncertainties.

A Priority-Based Synchronous Phasor Transmission Protocol Extension Method for the Active Distribution Network

With the advancement of active distribution network construction, to solve the shortcomings of the existing distribution network technology in distribution network perception and control, the relevant technologies of the Wide Area Measurement System (WAMS) in the transmission network have attracted more attention in terms of their usage in the distribution network. Micro Multifunction Phasor Measurement Unit (μMPMU), as an example, is being gradually utilized in the distribution network. However, the existing synchronous phasor transmission protocol is mainly designed for the transmission network, which requires an extension to meet the communication requirements to be directly used in the distribution network. In this work, the requirements of active distribution network communication are analyzed, and trade-offs between National Standard of the People’s Republic of China/Recommended (GB/T) 26865.2-2011 and International Electro technical Commission (IEC) 60870-5-101/104 protocol are compared. An extension method of the communication protocol is proposed, with the benefits of the prioritized transmission of important data, expanded remote control function of μMPMU, increased types of offline files, and reduced amount of network communication and data storage. The method is built upon the existing GB/T 26865.2-2011 protocol, and refers to the Application Service Data Unit (ASDU) of IEC 60870-5-101/104 to add an application extension frame. Application extension frames are used to transmit telemetry data, telesignalization, partial commands, and partial offline files. Finally, an experimental environment is set up, which includes a phasor measurement unit (PMU) Emulator, distribution network phasor data concentrator (PDC), and main station emulator to implement the standard GB/T 26865.2-2011 protocol and extension protocol. The feasibility and effectiveness of the method are confirmed by the superior performance of the extended protocol compared with the standard protocol.

Transient stability assessment and control system for power system

This paper addresses the issue of power system transient stability assessment and control (TSA&C) based on phase plane representation of the power angle and rotor speed. First, the relationship between transient stability–instability and concavity–convexity of the phase‐plane trajectory is found and proved based on the single machine infinite bus (SMIB) system, and a transient instability criterion is derived for real‐time instability detection. Second, with the aim that the phase‐plane trajectory swings back before the unstable equilibrium point (UEP) once instability is detected, near‐optimal control size of generator tripping to stabilize the system is determined based on the relationship between unbalanced power and the slope of the phase‐plane trajectory. Finally, the instability detection and control technique is extended to a multimachine power system based on SMIB equivalent transform. The proposed method is independent of the network structure and operation mode, which can be applied for real‐time emergency control based on wide area measurement system (WAMS). The simulations in the Institute of Electrical and Electronics Engineers (IEEE) 39‐bus system and the Sanhua Power Grid (in China) validate the accuracy and efficiency of the proposed method. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Current sensors based on GMR effect for smart grid applications

In the smart grid, wide-area current measurement system is of great importance to assist with the estimation of the power grid loss and the smart dispatching. However, the limited current sensing techniques have always been an obstacle to realizing such system. Recently, the development of giant magnetoresistance (GMR) based sensors has offered an effective solution to address this issue. The outstanding merits of compact size, high sensitivity and cost-effective price of GMR sensors have made them a perfect choice for widely distributed current measurement and data collection in smart grid. In this paper, with a design of flux guided structure for line current sensing, typical performance characteristics of optimized GMR design are illustrated. The validity of the structure is demonstrated with simulation and experiment. Based on the characteristics of GMR sensors, their prospects for application in smart grid are further discussed.

A Two-Level Hierarchical Controller to Enhance Stability and Dynamic Performance of Islanded Inverter-Based Microgrids With Static and Dynamic Loads

This paper proposes phasor measurement unit (PMU) supported two-level hierarchical controller to enhance stability and dynamic performance of islanded inverter-based microgrids with static and dynamic loads. The proposed hierarchical controller consists of a local decentralized controller for each inverter-interfaced distributed generation (IIDG) unit at the primary level helped by a multi-input multioutput centralized controller at the secondary level. The primary-level decentralized controller incorporates the addition of auxiliary control terms to the conventional droop controller. The auxiliary control terms are based on the total real and reactive power generation information acquired from wide area measurement system through PMUs and the desired power sharing of each IIDG unit. The secondary-level centralized controller, on the other hand, enhances the performance of each local decentralized controller by compensating the voltage and frequency deviations caused by the load disturbances. The performance of the proposed hierarchical controller has been demonstrated through eigenvalue analysis and time-domain simulation results carried out in MATLAB/SIMULINK environment. Further, in order to have a fair comparison, the performance of the proposed hierarchical controller, based on modal-based extended linear quadratic Gaussian (LQG) approach, has been compared with that of hierarchical controller based on state-based extended LQG approach. Simulation results revealed the capability of the proposed hierarchical controller to mitigate the unstable oscillations as well as to settle quickly at different operating points under the application of small-signal disturbances.

Enhancing WAMS Communication Network Against Delay Attacks

Smart grid is a typical cyber-physical system, which presents the dependence of power system operations on cyber infrastructure for control, monitoring, and protection purposes. The rapid deployment of synchrophasor measurements units (PMUs) supporting wide area measurement system (WAMS) in the smart grid transmission system has opened opportunities to enhance the grid operations through the introduction of WAMS applications. However, the increased deployment of synchrophasor technologies increases the effective attack surface available to attackers and exposes WAMS applications. Such applications have strict and stringent delay requirements, e.g., end-to-end delay as well as delay variation between measurements from different PMUs. In this paper, we present a mathematical model for constructing forwarding trees for PMUs’ measurements which satisfy the end-to-end delay as well as the delay variation requirements of WAMS applications at data concentrators. We illustrate that simple shortest path routing will result in larger fraction of data drop and that our method will achieve better delivery rate. We also validate our method against delay attacks using real-time co-simulation.

Event-Trigger Heterogeneous Nonlinear Filter for Wide-Area Measurement Systems in Power Grid

The development of distributed generation raises high requirement on accurate real-time state estimation with phasor measurement unit (PMU) for wide-area measurement systems (WAMSs). Although the particle filter is among the best in estimation performance, its computation burden is truly heavy toward smart sensors of current generation. Besides, the infrastructure for PMU data communication is confronted with the challenges of the amount of data boosted by the high sampling frequency of PMUs and booming grid size. This paper proposes an event-trigger heterogeneous nonlinear filter (ET-HNF) to solve these problems. A master–slave nonlinear filtering structure is designed for WAMS by taking full advantage of computation power both at generator node and estimation center. The local slave filter is established at generator node to perform the event-trigger strategy based on low computational unscented transformation. Moreover, a Monte Carlo-based filter served as the master, which improves estimation center’s filtering performance by cooperating with the center slave. Simulation results verify the feasibility and performance of ET-HNF using the standard IEEE 39-bus system with PMUs.

A Fast Recursive Algorithm For Spectrum Tracking in Power Grid Systems.

A major challenge for future wide area measurement systems is how to efficiently monitor and control the power system, which requires accurate and real-time tracking of the phase, frequency, and Power Factor (PF) of the system. The presence of inter and sub harmonics, especially in a distribution system caused by widely used non-linear power loads, rectifiers, and inverters, will distort estimation of phase/frequency and make it difficult to track the voltage, current and frequency variations. In this paper we present a new approach to identify and track the harmonics, sub-harmonics and inter-harmonics, as well as observe their impact on the power system. We propose a two-stage processing approach that consists of a subspace-based estimation method to detect and identify all harmonic components, followed by a low-complexity fast tracking algorithm to monitor frequency variations of voltage and current signals in real-time with great accuracy. The simulation results show that the proposed approach can provide highly reliable estimation and fast tracking of the harmonic components, while avoiding the impact of time variance.

An Augmented Prony Method for Power System Oscillation Analysis Using Synchrophasor Data

Intrinsic mode functions (IMFs) provide an intuitive representation of the oscillatory modes and are mainly calculated using Hilbert–Huang transform (HHT) methods. Those methods, however, suffer from the end effects, mode-mixing and Gibbs phenomena since they use an iterative procedure. This paper proposes an augmented Prony method for power system oscillation analysis using synchrophasor data obtained from a wide-area measurement system (WAMS). In the proposed method, in addition to the estimation of the modal information, IMFs are extracted using a new explicit mathematical formulation. Further, an indicator based on an energy and phase relationship of IMFs is proposed, which allows system operators to recognize the most effective generators/actuators on specific modes. The method is employed as an online oscillation-monitoring framework providing inputs for the so-called wide-area damping control (WADC) module. The efficacy of the proposed method is validated using three test cases, in which the IMFs calculation is simpler and more accurate if compared with other methods.

Research of a method for Synchronized Phasor Data transmission Based on IEC61850

At present, the communication services for the Wide Area Measurement system in intelligent substation don’t use the IEC-61850 system yet, which causes a lot of inconvenience and problems. In order to solve these problems, this paper proposes a method of Synchronized Phasor Data transmission based on IEC-61850. In this method, the communication services of Wide Area Measurement system are converted to IEC-61850 system, and find a way that can map the existing functions to the IEC-61850 system.Firstly, a method for high-speed data transmission and fast control is proposed.Then functional services that cannot be fully implemented by IEC-61850 services are expanded to fill the gaps in a prescribed way. Finally, from the perspective of unified substation information platform, the prospects of this scheme are analyzed.

Frequency mode identification using modified masking signal‐based empirical mode decomposition

A modified masking empirical mode decomposition (EMD) for effectively improving the mode separation capability of standard EMD while analysing power system signals with closely spaced modes of frequency is proposed here. A multi-frequency test signal resembling the dynamic power system signal and the actual data recorded by wide area measurement systems (WAMS) from Northern Grid, India, on 1 June 2010 due to generation loss are analysed by both the existing method and the proposed method. Various components of modal frequency extracted by masking signal base EMD are compared with extracted components by the proposed modified masking EMD. Further, the time–frequency representation of extracted modes by Hilbert spectral analysis is implemented to know mode behaviour with time reference. Simulation results prove that the EMD with proposed modification is capable of separating various modes of frequencies present in the WAMS signal.

A hybrid procedure to design a wide-area damping controller robust to permanent failure of the communication channels and power system operation uncertainties

One of the advantages of the Wide-Area Measurement Systems in Small-Signal Stability is the use of the Wide-Area Damping Controllers (WADCs) to improve the damping of the low-frequency oscillation modes of the power system. The WADC operation requires remote signals provided by Phasor Measurement Units and these signals are highly susceptible to failures or cyber-attacks that may compromise controller performance. This paper proposes a hybrid procedure to design a WADC robust to permanent failure of the communication channels and power system operation uncertainties. A set of possible operating conditions is linearized around their equilibrium points and it is used to construct the uncertainty model of the system with respect to a nominal condition. Different load levels are considered to build this set of possible operating conditions. In the first stage, a procedure based on the solution of the Riccati equation is used to design a WADC robust to power system operation uncertainties. In this stage, a nominal operating condition is defined and an uncertainty model is used to calculate automatically the matrices Q and R of the Riccati equation. After that, in the second stage, this resulting controller is used as an initial condition for a procedure based on Linear Matrix Inequalities to design a WADC robust to communication link failure and power system operation uncertainties. In this stage, the complete set of operating conditions are used during the control design. Time delays are considered in the central control design using a modified Padé approximation. Modal analysis and time-domain nonlinear simulations are carried out in the IEEE 39-bus and 68-bus power systems.

Situational awareness of coherency behavior of synchronous generators in a power system with utility-scale photovoltaics

The smart grid innovation targets at the problems of integrating large portion of intermittent generation resources such as utility-scale and rooftop photovoltaics (PVs), while ensuring both the security and reliability of the electric power grid operation during severe disturbances. To enhance the operators’ performance, the information processing of the large-scale widely interconnected electric power grid needs to be simplified and presented with situational awareness (SA) in a meaningful way, for timely response by the system operators in control centers. Coherency group identification separates the generators in the system into groups that feature similar behavior, which is a method for grid simplification. Meanwhile, wide area measurement systems (WAMS) using data from phasor measurement units (PMUs) provides a solution – enhanced situational awareness to power operation control centers addressing the concerns of capturing and transmitting dynamic data in near real-time. Based upon these technologies, a synchrophasor based identification of generator coherency groups and new visualizations for SA are proposed and developed for online application with using K-harmonic means clustering. Furthermore, a generator vulnerability index (GVI) and a corresponding power system vulnerability index (SVI) are proposed based on the dynamic coherency groups identified. These indices alert system operators on the coherency behavior of the synchronous generators in the system for variations of PV power and/or under severe system disturbances. Typical results are provided for four different disturbances including sudden PV power increase and decrease, unexpected bus faults on major tie-line (inter-area) transmission corridors. In summary, new algorithms, indices and visualization tools have been developed to enhance SA and provide actionable information to system operators in control centers in the presence of variable utility-scale PV power in a power system.

An on-line power/voltage stability index for multi-infeed HVDC systems

High-voltage direct current (HVDC) transmission is playing an increasingly important role in modern power systems, and the resulted power/voltage stability issue has raised widespread concern. This paper presents an on-line power/voltage stability index (PVSI) for multi-infeed HVDC (MIDC) systems. Different from the existing indices which are developed mainly for off-line and static analysis, the proposed PVSI can be applied in real time. Effects of system changes on stability assessment such as change of system states and control strategies are considered. Thus, helpful guidance can be provided for on-line HVDC stability and controls. The PVSI is originally deduced for single-infeed HVDC systems in an “AC way” by analyzing the power and voltage stability of both pure AC systems and HVDC systems. Moreover, its on-line application in practical MIDC systems is realized by building an equivalent single-infeed model, and utilizing nowadays measurement and communication infrastructures such as wide-area measurement system (WAMS). The effectiveness of the PVSI is verified through simulations in real-time digital simulator (RTDS).

Synchrophasors-Based Identification for Subsynchronous Oscillations in Power Systems

The wide-area measurement system (WAMS) provides the synchronized dynamic measurement for power systems; however, the effective monitoring of subsynchronous oscillations (SSO) with WAMS has not been achieved. To achieve SSO monitoring based on the synchrophasors provided by WAMS, a synchrophasors-based SSO identification technique was proposed in this paper. On the basis of existed synchrophasors, this technique can obtain the frequencies and amplitudes of both the fundamental and subsynchronous components of currents and voltages in SSOs effectively. In this technique, the impacts of both the fast Fourier transform synchrophasor algorithm and the sampling rate of synchrophasors on the spectrum of the subsynchronous component were taken into account. On one hand, the SSO frequency was obtained according to the spectrum of magnitudes of synchrophasors. On the other hand, a correction method for the spectrum of magnitudes of synchrophasors, in contrast to a constructed standard waveform that proportionally matches with the measured SSO, was applied to obtain the actual amplitudes of both the fundamental and subsynchronous components. Both the numerical simulation and the illustrations of two different actual SSO incidents were presented with comparisons to verify the correctness and feasibility of the proposed technique. This technique is of important practical value for mitigations of SSO in actual power systems.

MPTCP-H: A DDoS attack resilient transport protocol to secure wide area measurement systems

The penetration of distributed generators into the power distribution grid requires real-time control of the grid by monitoring the state of the power distribution grid. Such a large-scale monitoring cannot be performed by using traditional Supervisory Control and Data Acquisition (SCADA) systems due to its lack of the scalability. To address this issue, contemporary Wide Area Measurement Systems (WAMS) are deployed, which provide the dynamic snapshots of the power system. However, WAMS’s more open structure versus SCADA poses a risk of WAMS being vulnerable to cyberattacks. In particular, due to high responsiveness and availability requirements of WAMS applications, attacks i.e., Denial-of-Service (DoS) and Distributed DoS (DDoS) are of primary concern for WAMS.In this paper, we focus on internal DoS/DDoS attacks launched against the WAMS devices by exploiting the vulnerabilities. To counter such attacks, we propose a proactive and robust extension of the Multipath-TCP (MPTCP) transportation protocol, termed as MPTCP-H. The proposed extension mitigates the internal attacks by using a novel stream hopping mechanism, which periodically renews the subflows to hide the open port numbers of the connection. By doing so, MPTCP-H significantly increases the attacker’s cost for a successful attack without perturbing the WAMS data traffic. The experimental results show that the proposed MPTCP-H provides a significant DoS/DDoS attack mitigation for WAMS at the expense of reasonable overheads, i.e., additional latency and message.

PMU-WAMS research and application in Brazil

Wide area measurement system (WAMS), which is based on synchronization data from phasor measurement units (PMU) and EMS SCADA, is implemented to establish a system model that can handle certain functions such as realtime power system monitoring, oscillation mode analysis, accident analysis and decision-making assistance for emergency control. The Brazilian Interconnected Power System (BIPS) is a large system covering an extensive geographical region, which faces certain risks and challenges. It has several main transmission corridors associated with large power plants and interconnection between the northern and southeastern regions. Mismatch between the energy base and load pool also exists in Brazil as energy resources are not well-distributed; therefore, the use of large-capacity, long-distance transmission technique to transmit remote power is unescapable. On the other hand, there are many types of voltage levels and multiple entangled electromagnetic loops owing to historical reasons. Then, for insufficient power reservation and defective grid body in load pools, once the external power is cut, it’s easy to raise a blackout. The infrastructure is old and the power system operates close to the upper limit. All these represent risks and challenges to BIPS. Through WAMS technology research method in this project, the electrical power system function of monitoring, analysis, and control improved from the static state to the dynamic state. WAMS enhances data integration and real-time analysis capabilities, and can provide dispatchers with high quality real-time dynamic information and decision-making support information, enhance monitoring of auxiliary services in the electricity market, enable operators to improve the accuracy of power network analysis, thereby increasing power grid monitoring and operation, and improve the transmission capacity and reliability of the power grid operation [1].