Wide Area Control Research Articles

Controls for Smart Grids: Architectures and Applications

Control is and will continue to be a key discipline for realizing the objectives of smart grid initiatives. Research in control science and engineering is not limited to one or a few application concepts but is pervasive across the smart grid ecosystem. The principal contribution of this paper is to review, from a system-architectural perspective, how control enables smart grid applications. Application “templates” are presented for direct load control, automated demand response, microgrid optimization, control for distribution grids, wide-area control, and market-centric control. Technological developments, including in power electronics, that are enabling smart grid control research and applications are also itemized and two cross-cutting needs/opportunities for future research discussed. We conclude with a summary of a recent status report on the progress that has been made in the United States, noting also the challenges to further progress, in renewable generation, energy efficiency, and carbon reduction.

A Survey of Distributed Optimization and Control Algorithms for Electric Power Systems

Historically, centrally computed algorithms have been the primary means of power system optimization and control. With increasing penetrations of distributed energy resources requiring optimization and control of power systems with many controllable devices, distributed algorithms have been the subject of significant research interest. This paper surveys the literature of distributed algorithms with applications to optimization and control of power systems. In particular, this paper reviews distributed algorithms for offline solution of optimal power flow (OPF) problems as well as online algorithms for real-time solution of OPF, optimal frequency control, optimal voltage control, and optimal wide-area control problems.

Improving actionable observability of large distribution networks for transmission operators to support improved system control, fault detection and mitigation

The widespread introduction of phasor measurement unit (PMUs) in transmission networks is well understood and has improved visibility enhancing grid stability and avoiding low probability events such as blackouts. For many transmission system operators, there is little-to-no visibility of the real-time state of distribution networks beyond the grid supply points. With the increased penetration of distributed energy resources on low- and medium-voltage networks of the state, and thus behaviour, of the distribution network cannot be assumed to follow historical patterns. The future transition to distribution system operator concept requires better visibility, especially around grid supply points, for deploying wide-area control strategies and active network management schemes. This implies active sharing of data between transmission and distribution monitoring systems. There are a number of challenges in extending the use of PMUs to distribution networks. Many of the lessons and best practises at transmission do not translate to the operation of distribution networks, as an exponential increase in network complexity makes it infeasible to perform complex analysis of the complete network model in real time. This paper presents a methodology for addressing the problems faced in deploying microPMUs at the distribution level.

Optimal PMU placement considering state estimation uncertainty and voltage controllability

The development of monitoring technologies in smart grid is undergoing an essential transition from periodical magnitude-based measurement by supervisory control and data acquisition (SCADA) to real-time phasor measurement unit (PMU)-based wide area monitoring and control. The implementation of PMUs can substantially facilitate grid-wide state estimation and operation control, which is dependent on an effective PMU placement strategy. In this study, the optimal PMU placement (OPP) problem is investigated with respect to zonal voltage controllability and voltage magnitude estimation in cooperation with SCADA. In particular, the OPP is formulated as a multi-objective minimal Ncut partitioning problem, in which various operating scenarios are represented by probabilistic load flows to achieve a general solution for planning purpose. Spectral clustering is employed to efficiently find the optimal clustering boundaries, which indicate the resulting placement layout. The proposed placement scheme is tested on New England 39-bus and IEEE 118-bus systems. Simulation results demonstrate the effectiveness of the proposed approach.

Transmission Control Protocol Global Synchronization Problem in Wide Area Monitoring and Control Systems

The electrical power network is a significant element of the critical infrastructure in modern society. Nowadays, wide area monitoring and control systems (WAMC) are becoming increasingly an important topic that motivates several researchers to improve, develop, and find the problems that hinder progress toward WAMC systems. WAMC is used to monitor and control the power network so the power network can be adapt to failures in automatic way. In this work, verification of the extent found a problem in transmission control protocol (TCP) which is called global synchronization and its impact on utilizing the buffer of the routers. A simulation models had been belt of WAMC system using OMNeT++ to study the performance of TCP in two queuing algorithms for measuring transmission of phasor measurement units and to test if global synchronization problem occurs. Three scenarios were used to test the survival of this problem on the system. It is found that the problem of global synchronization occurred in two scenarios which in turn causes low utilization for a buffer of routers. Index Terms: Global Synchronization, Phasor Measurement Units, Power Network, Transmission Control Protocol, Wide Area Monitoring and Control Systems

Wide‐area voltage control system of flexible AC transmission system devices to prevent voltage collapse

Hydro-Québec has identified wide-area control system as a key initiative able to significantly increase the voltage stability of its grid. In this context, an innovative project for wide-area and local voltage control of shunt compensators was initiated. Its main objective is to implement a closed-loop control system on Hydro-Québec's network to optimise the reactive power support from the dynamic shunt compensators. The outcome of this project is the ‘global and local control of compensators’ (GLCCs) system which is based on synchrophasor technology and intelligent electronics devices. Applied to each shunt compensator of Hydro-Québec's network, this robust voltage control system measures voltage variations in the load area and adjusts the operation set point of each shunt compensator accordingly, thus avoiding voltage collapse resulting from extreme contingencies. The GLCC control solution was intensively tested in simulation using PSSE software. Moreover, a pilot project was commissioned on a test bench replica of the system and also tested in real time using Hydro-Québec's Hypersim digital simulator. Field tests of the GLCC were conducted on a −230/ + 660 MVars static vars compensator. The results of this pilot project were deemed conclusive and the deployment of the new voltage control system has been initiated by Hydro-Québec.

Robust Wide Area Controller Design with DFIG-Fractional Order PID for Inter-Area Oscillations Damping

Robust Wide Area Controller Design with DFIG-Fractional Order PID for Inter-Area Oscillations Damping

Analysis and prediction of vulnerability in smart power transmission system: A geometrical approach

The paper proposes a novel methodology to analyze and measure the impact of line tripping on grid vulnerability which may lead to cascade failure in smart power transmission system. The key contributions are analysis of current flow path and identification of critical line from normal to perturbed grid with the knowledge of grid topology. To achieve this two performance indices i.e. power flow index and vulnerability index have been defined on the bases of geometry of current flow path. A power flow index is defined to analyze impact of topological changes on current flow path and identify underloaded and overloaded lines. Probability of the critical line and the location of vulnerability center are identified by the vulnerability index. Analytically defined performance indices are applied analyzed and validate using the benchmark IEEE 30 bus power system. The critical line identified by proposed indices is also verified with the probabilistic framework. The proposed methodology allows to focus attention on the power grid vulnerable areas and can help the control system operator to investigate the changes in power flow on transmission lines and initiate the necessary corrective action. The methodology proposed in this paper can be used in security assessment and centralized monitoring of power flow in future smart grid wide area monitoring protection and control system.

The Impact of Time Synchronization Deviation on the Performance of Synchrophasor Measurements and Wide Area Damping Control

The phasor measurement unit (PMU) provides synchrophasor measurements for wide area dynamic security monitoring and control. Synchronism of measurements is the essential feature of PMU, whose precision directly affects the accuracy and reliability of phasor measurements. In this paper, the impacts of time synchronization deviation (TSD) on PMU measurements and wide area damping control are analyzed, respectively. Both PMUs in substations and in power plants are included in the analysis. And for each kind of PMU, the impact is elaborated systematically under steady and dynamic states. Furthermore, by studying the TSD's impact on the input signal of a wide area power system stabilizer, the influence of TSD on the effect of wide area damping control based on these two kinds of PMUs is presented. Finally, the validity of theoretical analysis is confirmed through a series of hardware-in-the-loop experiments and simulation results.

Input-Output Properties of the Swing Dynamics for Power Transmission Networks with HVDC Modulation

There is a growing need for wide-area evaluation and control of fast dynamics in the bulk power transmission network, and at the same time new technologies are coming to fruition that enable such control. Analyzing disruptions and designing wide-area controls crucially requires understanding input-output properties of the power network’s swing dynamics. In this article, we study input-output properties of the classical swing dynamics model - specifically, the finite zeros of input-output channels in the model - from a graph theory perspective. Because deployed controls for high-voltage direct-current (HVDC) lines are known to impact transients/oscillation across a wide area, we also enrich the model to represent modulated (controlled) HVDC, and analyze the zeros of the enriched model. The analyses demonstrate that the graph topology of the power network, the location of the input-output channel, and the type of control used on the HVDC line, primarily determine whether or not the dynamics is minimum phase.

Testing and validation of wide‐area control of STATCOM using real‐time digital simulator with hybrid HIL–SIL configuration

This study presents a novel interfacing setup for testing and validating wide-area monitoring and control (WAMC) techniques used in smart grids. The main purpose of this study is to provide a realistic approach for conducting WAMC studies. In here, a wide-area controller (WAC) for a flexible AC transmission system (FACTS) device is implemented. The measurements for the WAC are collected using phasor measurements units (PMUs). Three main segments are being interfaced in this study. First, the real-power grid, the local area controller of the actual FACTS device, and the PMUs are simulated using real-time digital simulator. This simulation represents the central simulation and is interfaced with the WAC, which is realised using a MATLAB-based program. This interface represents a novel software-in-the-loop (SIL) scheme. On the other hand, an actual FACTS device is designed and interfaced to the central simulation via hardware-in-the-loop (HIL) scheme. This SIL and HIL combination makes the experimental testbed more realistic and closer to the industrial standard. Various tests are conducted to examine the performance of the developed testbed.

Conformance Testing and Analysis of Synchrophasor Communication Message Structures and Formats for Wide Area Measurement Systems in Smart Grids

The renewed quest for situational awareness in power systems has brought about the use of digital signal processing of power system measurements, and the transmission of such data to control centres via communication networks. At the control centres, power system stability algorithms are executed to provide monitoring, protection, and control in order to prevent blackouts. This can be achieved by upgrading the existing Supervisory Control and Data Acquisition (SCADA) systems through the deployment of newly proposed power system synchrophasor-based applications for Wide Area Monitoring, Protection, and Control (WAMPAC). However, this can only be done when there is a complete understanding of the methods and technologies associated with the communication network, message structure, and formats required. This paper presents an analysis of the IEEE C37.118 synchrophasor message framework, message formats, and data communication of synchrophasor measurements from Phasor Measurement Units (PMUs) for WAMPAC schemes in smart grids. A newly designed lab-scale testbed is implemented and used in the practical experimentation relating to this paper. Synchrophasor measurements from the PMUs are captured using a network protocol analyzer software-Wireshark, and the compliance of the synchrophasor message structures and formats captured was compared to the specifications defined in the IEEE C37.118 synchrophasor standard.

A WACS exploiting generator Excitation Boosters for power system transient stability enhancement

Excitation Boosters (EB) are designed to improve transient stability of synchronous generators equipped with bus fed static excitation systems. They can be controlled using either local or remote signals following a disturbance. This paper explores how critical clearing times (CCT) can be improved by EBs controlled using remote signals. Particularly, Pseudo Center of Inertia (PCOI) and Dominant Interarea Path (DIP) signals derived from Phasor Measurement Units (PMU) within a Wide Area Control System (WACS) are used. Prototype controllers are tested by means of a Real Time (RT) Hardware-in-the-Loop (HIL) experimental setup.

Smart Grids

The papers in this special section focus on the topic of smart grids. Smart Grids are an essential component of future energy systems, which are characterized by distributed, volatile energy production (solar, wind) and entirely new components (electric vehicles) and operation concepts (virtual power plants). Smart Grids are also a prominent example of Cyber Physical Systems, as they combine wide-area control, computation, and communications. While traditional automation of the power grid makes use of wireline communications (copper, fiber), Smart Grids require wide-area coverage with flexible, cost-efficient, but also very reliable communications networks. Therefore, wireless communication technologies will play an increasingly important role in future deployment scenarios. The investigated options range from cellular networks over satellite systems to wireless mesh networks. Also, the ongoing discussion of future 5G systems is driven by the requirements of Smart Grids as one major use case. Particular challenges for wireless communication options include availability, real-time capabilities for incident mitigation, and resilience. The performance evaluation of Smart Grids calls for new methods, such as the interdisciplinary hybrid simulation of energy and communication networks.

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.

A delay-aware cyber-physical architecture for wide-area control of power systems

In this paper we address the problem of wide-area control of power systems using Synchrophasor measurements in the presence of network delays. We propose a novel cyber-physical architecture that uses an arbitrated network control systems approach for mitigating the destabilizing effects of delays in power systems. The approach consists of: (1) utilization of Synchrophasor measurements from distributed measurements across different buses in the power network, (2) estimation of delays that control messages experience, (3) a delay-aware control design that explicitly accommodates the delays and judiciously utilizes estimated system states when needed, and (4) a switching control strategy that aborts the computation of control signals when delays exceed a certain threshold to improve resource utilization. While the control gains are determined using a centralized power system model and state feedback, it is shown that the delay-aware aspects of the proposed architecture allow both distributed measurements and distributed implementation of the control law. The results are illustrated using a 50-bus, 14-generator, 4-area power system model. The results clearly demonstrate that the proposed controller recovers the ideal system performance (such as deviations in frequency<3mHz) even in the presence of large intra-area and inter-area delays with a small amount of additional control effort. Using the proposed overrun strategy, the results also confirm that about 30% drops can be accommodated with the proposed arbitrated network control systems approach.

Intelligent Controller Based Wide-Area Control in Power System

A new strategy based on Takagi–Sugeno fuzzy controller is proposed in this paper for wide-area power system. In this strategy, the proposed fuzzy controller is optimized by a new hybrid metaheuristic algorithm and hyperplane clustering algorithm to partition the fuzzy space of the given input–output data. A global signal from the centralized controller is employed in wide area control (WAC) scheme to damp out the inter-area mode as well as local mode of oscillations. To demonstrate the capability of proposed strategy, three case studies have been used in this paper. The obtained results demonstrate the validity of proposed strategy through comparison with other techniques in this problem.

Game-Theoretic Multi-Agent Control and Network Cost Allocation Under Communication Constraints

Multi-agent networked linear dynamic systems have attracted the attention of researchers in power systems, intelligent transportation, and industrial automation. The agents might cooperatively optimize a global performance objective, resulting in social optimization, or try to satisfy their own selfish objectives using a noncooperative differential game. However, in these solutions, large volumes of data must be sent from system states to possibly distant control inputs, thus resulting in high cost of the underlying communication network. To enable economically viable communication, a game-theoretic framework is proposed under the communication cost , or sparsity , constraint, given by the number of communicating state/control input pairs. As this constraint tightens, the system transitions from dense to sparse communication, providing the tradeoff between dynamic system performance and information exchange. Moreover, using the proposed sparsity-constrained distributed social optimization and noncooperative game algorithms, we develop a method to allocate the costs of the communication infrastructure fairly and according to the agents’ diverse needs for feedback and cooperation. Numerical results illustrate utilization of the proposed algorithms to enable and ensure economic fairness of wide-area control among power companies.

A Wide-Area Damping Controller Considering Network Input and Output Delays and Packet Drop

This paper presents the development of a novel synchrophasor measurement-based wide-area centralized damping controller to improve the stability of a power system in presence of time-varying delay and packet dropout in the communication network. Two different strategies have been adopted to deal with the input and the output delays. In the first strategy, the system output delay has been compensated by predicting the dynamics of the signals. In the second strategy, a wide-area controller, based on delay-range-dependent stability criteria, has been designed for the time-varying delays in the input signals. The network induced delays and the maximum amount of the consecutive packet dropout are assumed to be bounded. The controller parameters are optimally obtained using a trace minimization of certain matrix variables by formulating Linear Matrix Inequalities problem. The system has been identified by applying Prediction-Error-Minimization methodology, and proposing a new type of probing test input-signal. A new methodology has been proposed to obtain the feedback channel latency in real time. The proposed methodology has been simulated on New England 39-bus test system and also validated on a hardware testbed consisting of physical Phasor Measurement Units connected, in feedback loop, to a Real-Time Digital Simulator.

A method exploiting direct communication between phasor measurement units for power system wide-area protection and control algorithms

Synchrophasor measurements from Phasor Measurement Units (PMUs) are the primary sensors used to deploy Wide-Area Monitoring, Protection and Control (WAMPAC) systems. PMUs stream out synchrophasor measurements through the IEEE C37.118.2 protocol using TCP/IP or UDP/IP. The proposed method establishes a direct communication between two PMUs, thus eliminating the requirement of an intermediate phasor data concentrator, data mediator and/or protocol parser and thereby ensuring minimum communication latency without considering communication link delays. This method allows utilizing synchrophasor measurements internally in a PMU to deploy custom protection and control algorithms. These algorithms are deployed using protection logic equations which are supported by all the PMU vendors. Moreover, this method reduces overall equipment cost as the algorithms execute internally in a PMU and therefore does not require any additional controller for their deployment. The proposed method can be utilized for fast prototyping of wide-area measurements based protection and control applications. The proposed method is tested by coupling commercial PMUs as Hardware-in-the-Loop (HIL) with Opal-RT’s eMEGAsim Real-Time Simulator (RTS). As illustrative example, anti-islanding protection application is deployed using proposed method and its performance is assessed. The essential points in the method are:•Bypassing intermediate phasor data concentrator or protocol parsers as the synchrophasors are communicated directly between the PMUs (minimizes communication delays).•Wide Area Protection and Control Algorithm is deployed using logic equations in the client PMU, therefore eliminating the requirement for an external hardware controller (cost curtailment)•Effortless means to exploit PMU measurements in an environment familiar to protection engineers.