Phasor Measurement Units Network Research Articles

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.

Intrusion Detection, Measurement Correction, and Attack Localization of PMU Networks

Accurate state estimation is essential for correct supervision of power grids. With the existence of cyber-attacks, state estimation may become inaccurate, which can eventually lead to wrong supervisory decision making. To detect cyber-attacks in power grids equipped with phasor measurement units (PMUs), a new intrusion detection system based on clustering approach, called PMU Intrusion Detection System (PMUIDS), is proposed in this article. After solving the optimal PMU placement in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> -1 contingency, several static state estimations are obtained by removing the measurements of one PMU in each time. The resulting state vectors are clustered in two steps: First, subtractive clustering is employed to obtain the number of clusters, which determines the number of integrity attacks; and second, fuzzy C-means clustering assigns the state vectors to the corresponding clusters, which determines the attacked PMUs. In addition, two theorems are proved, which indicate that the attacker cannot coordinate successful stealth attacks in cases that by removing attacked PMUs from state estimation, the power system still remains full observable. Furthermore, in the case of possible stealth attacks, the attacker cannot falsify the estimation of any arbitrary state variable. The hardware-in-the-loop results on a sample power system show that the proposed approach can detect integrity attacks, determine the number of attacks, obtain the correct state vector, and localize the attacks, even in case of multiple simultaneous attacks.

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.

Certificate Based Authentication Mechanism for PMU Communication Networks Based on IEC 61850-90-5

Smart grids are becoming increasingly popular thanks to their ability to operate with higher precision and smaller margins. Dynamic operation control in smart grids can be achieved with phasor measurement unit (PMU) based wide area monitoring and control systems. The data communication requirements for the PMU based applications are well addressed in the IEEE C37.118.2 and IEC 61850-90-5 standards. Due to the higher probability of cyberattacks and the scale of their impact, data security is a critical requirement in PMU communication networks. The IEC 61850-90-5 communication standard addresses this security concern and proposes the HMAC (hash based message authentication code) with key distribution center (KDC) scheme for achieving information authentication and integrity. However, these IEC 61850-90-5 security recommendations do not consider the mechanism for attacks such as man-in-the-middle (MITM) attacks during KDC key exchanges. MITM attacks can be easily implemented and may have a large impact on the grid operation. This paper proposed an explicit certificate-based authentication mechanism to mitigate MITM attacks in PMU communication networks. The proposed certificate-based authentication mechanisms were implemented in real-time using Python-based terminals to observe their performance with different signature algorithms.

Self-Healing Attack-Resilient PMU Network for Power System Operation

In this paper, we propose a self-healing phasor measurement unit (PMU) network that exploits the features of dynamic and programmable configuration in a software-defined networking infrastructure to achieve resiliency against cyber-attacks. After a cyber-attack, the configuration of network switches is changed to isolate the compromised PMUs/phasor data concentrators to prevent further propagation of the attack; meanwhile, the disconnected yet uncompromised PMUs will be reconnected to the network to “self-heal” and thus restore the observability of the power system. Specifically, we formulate an integer linear programming model to minimize the overhead of the self-healing process (e.g., the recovery latency), while considering the constraints of power system observability, hardware resources, and network topology. We also propose a heuristic algorithm to decrease the computational complexity. Case studies of a PMU network based on the IEEE 30-bus and 118-bus systems are used to validate the effectiveness of the self-healing mechanism.

Cost-Effective Upgrade of PMU Networks for Fault-Tolerant Sensing

This paper considers robust allocation of additional phasor measurement units (PMUs) into a PMU network in order to meet a data availability profile in the face of random communication interruptions and transmission line faul-sarailoo-2756030ts. Synchrophasor availability ( $\boldsymbol{SA}$ ) at a bus is the fraction of time the time-synchronized current/voltage phasors are correctly present for real-time usage. An algorithm that achieves the above objectives is developed. The algorithm switches between a placement step solved via integer programming and an $\boldsymbol{SA}$ evaluation step that uses a bus-centric stochastic model to efficiently determine the need for another placement step with a tightened constraint. The algorithm is shown to subsume the phasor observability and is equally applicable PMU network upgrade and creation. Scalability and computational efficiency of the algorithm are analyzed. The results of tests of the algorithm applied to the IEEE 118-bus system are reported, which are performed under a variety of availability specifications and random event arrival rates associated with communication interruptions, equipment faults, and their removals. Superior accuracy and fault tolerance in state estimation are achieved by PMU networks meeting more stringent ${\boldsymbol{SA}}$ .

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.

Sensitive Constrained Optimal PMU Allocation with Complete Observability for State Estimation Solution

In this paper, a sensitive constrained integer linear programming approach is formulated for the optimal allocation of Phasor Measurement Units (PMUs) in a power system network to obtain state estimation. In this approach, sensitive buses along with zero injection buses (ZIB) are considered for optimal allocation of PMUs in the network to generate state estimation solutions. Sensitive buses are evolved from the mean of bus voltages subjected to increase of load consistently up to 50%. Sensitive buses are ranked in order to place PMUs. Sensitive constrained optimal PMU allocation in case of single line and no line contingency are considered in observability analysis to ensure protection and control of power system from abnormal conditions. Modeling of ZIB constraints is included to minimize the number of PMU network allocations. This paper presents optimal allocation of PMU at sensitive buses with zero injection modeling, considering cost criteria and redundancy to increase the accuracy of state estimation solution without losing observability of the whole system. Simulations are carried out on IEEE 14, 30 and 57 bus systems and results obtained are compared with traditional and other state estimation methods available in the literature, to demonstrate the effectiveness of the proposed method.

Minimum Sparsity of Unobservable Power Network Attacks

Physical security of power networks under power injection attacks that alter generation and loads is studied. The system operator employs Phasor Measurement Units (PMUs) for detecting such attacks, while attackers devise attacks that are unobservable by such PMU networks. It is shown that, given the PMU locations, the solution to finding the sparsest unobservable attacks has a simple form with probability one, namely, $\kappa(G^M) + 1$, where $\kappa(G^M)$ is defined as the vulnerable vertex connectivity of an augmented graph. The constructive proof allows one to find the entire set of the sparsest unobservable attacks in polynomial time. Furthermore, a notion of the potential impact of unobservable attacks is introduced. With optimized PMU deployment, the sparsest unobservable attacks and their potential impact as functions of the number of PMUs are evaluated numerically for the IEEE 30, 57, 118 and 300-bus systems and the Polish 2383, 2737 and 3012-bus systems. It is observed that, as more PMUs are added, the maximum potential impact among all the sparsest unobservable attacks drops quickly until it reaches the minimum sparsity.

Performance comparison of IEC 61850-90-5 and IEEE C37.118.2 based wide area PMU communication networks

Dynamic operation and control of power system is being increasingly done with the help of phasor measurement unit (PMU) based wide area monitoring and control system. The data communication requirements for the PMU based applications are well addressed by IEEE C37.118.2 standard. However, IEC 61850 is now becoming a leading standard for power utility automation needs. A new part of IEC 61850, IEC 61850-90-5, specifying the IEEE C37.118.1 based synchrophasors data transfer according to IEC 61850, will lead to IEC 61850-90-5 based PMU communication networks. A novel IEC 61850-90-5 compliant communication model of PMU is proposed in this paper. We also present a comparative performance analysis of the PMU communication networks supporting the new synchrophasor standard for data transfer, i.e. IEC 61850-90-5, and the existing standard, i.e. IEEE C37.118.2, for end to end (ETE) delay requirements for a modified IEEE 30 bus test system.

A Probabilistic Risk Mitigation Model for Cyber-Attacks to PMU Networks

The power grid is becoming more dependent on information and communication technologies. Complex networks of advanced sensors such as phasor measurement units (PMUs) are used to collect real time data to improve the observability of the power system. Recent studies have shown that the power grid has significant cyber vulnerabilities which could increase when PMUs are used extensively. Therefore, recognizing and responding to vulnerabilities are critical to the security of the power grid. This paper proposes a risk mitigation model for optimal response to cyber-attacks to PMU networks. We model the optimal response action as a mixed integer linear programming (MILP) problem to prevent propagation of the cyber-attacks and maintain the observability of the power system.

Data-Availability-Constrained Placement of PMUs and Communication Links in a Power System

This paper presents a solution to placing a minimum number of phasor measurement units (PMUs) and communication links in a power system so that the steady-state availability of synchrophasor data at each bus meets a prescribed level. For this purpose, a Markov model suitable for the evaluation of synchrophasor availability is built. The model contains a set of binary decision variables representing actions or inactions to maintain PMUs or to utilize communication links. The decision variables are solved to minimize an expected cost for maintaining a PMU network and utilizing data links for synchrophasor inference, subject to a set of synchrophasor availability requirements at the buses. The new aspects of development in this paper concern first the selection of decision variables so that their solutions immediately imply whether a PMU should be placed at a bus and whether a communication link should be established between two buses and, second, the solution to PMU network placement in a large-scale electric network. In addition, permanent and random intermittent PMU outages are modeled. A five-bus power system is used to demonstrate the problem formulation, and placement results are presented. A method to treat a large power system as interconnected smaller power systems with common boundary buses is proposed to address the curse of dimensionality encountered. Each smaller power system formulates an independent optimal placement problem with constraints on matching boundary placement. The steps involved are illustrated through a 14-bus system. The complexity and optimality of a divided problem are compared to that of the original problem.

Minimum cost upgrade of phasor measurement unit networks for synchrophasor availability

SUMMARYThis paper considers the problem of placing additional phasor measurement units (PMUs) and communication links into a PMU network in a power system. The objective is for the synchrophasors (PMU outputs) across the power system to meet a prescribed availability profile with fewest new PMUs and links among them. Achieving a required synchrophasor availability profile is critical in supporting wide area monitoring, protection, and control in a power system. In our recently reported work, synchrophasor availability is solved from a controlled Markov chain where binary variables indicating placement decisions are embedded as stationary control variables. In this paper, the assumption that communication links are always available wherever needed is removed. Random interruptions in PMU communications are modeled in such a way that the reformulated placement problem remains Boolean‐convex, and the computational complexity with respect to the number of buses remains O(n2). The solution to placement of PMUs and communication links into the Institute of Electrical and Electronics Engineers (IEEE) 118‐bus test system is presented. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Voltage-stability protection and control using a wide-area network of phasor measurements

This paper presents a concept for local monitoring of the onset of voltage collapse, protective, and emergency control in the presence of voltage-sensitive loads. The onset of voltage collapse point is calculated based on the load characteristics and simulated voltage and current phasors measurements, which are provided by a network of phasor-measurement units. If the stability margin is small and the reactive-power reserves are nearly exhausted, then controls to steer the power system away from the critical point will be activated.

Voltage Stability Protection and Control Using a Wide Area Network of Phasor Measurements

This paper presents a concept for local monitoring of the onset of voltage collapse, protective, and emergency control in the presence of voltage-sensitive loads. The onset of voltage collapse point is calculated based on the load characteristics and simulated voltage and current phasors measurements, which are provided by a network of phasor-measurement units. If the stability margin is small and the reactive-power reserves are nearly exhausted, then controls to steer the power system away from the critical point will be activated.