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Fault-tolerant generator telecontrol over a microgrid IP network
... It seems likely that the backbone for such an infrastructure will be the "utilities intranet": a data network which is common to the utilities but separate from the Internet, which is envisioned to allow for the eventual connection of all regional substations, equipment, and CCs throughout the grid [16,17]. Standard best-effort IP links cannot provide the required QoS and network availability requirements to ensure low-latency, low-jitter communications over multiple hops [2,18]. For a supply or generation utility degraded load following results in an inability to meet contractual power requirements, and in the worst-case it may result in the tripping of frequency protection devices and unintentional islanding should spinning reserves be unavailable. ...
... To satisfy the varying range of QoS and routing requirements that smart grid traffic requires [19], differentiated services (DIFFSERV) traffic prioritization and enhanced multicast user datagram protocol (UDP) concepts offered by IP version 6 (IPv6) could be leveraged [16][17][18][19][20]. However, such end-to-end QoS management across multiple control areas is still some way off becoming a practical reality. ...
... End-to-end QoS management is needed for distributed control and protection applications. For instance, the stability of the closed-loop while performing bilateral load following (with sampling rates Energies 2016, 9, 204 8 of 19 typically in the range 100-1000 ms) has been found to be highly dependent upon the latency (delay), variability in latency (jitter), and packet losses that the control network induces [2,18]. ...
In this paper, it is argued that some low-level aspects of the usual IEC 61850 mapping
to Ethernet are not well suited to microgrids due to their dynamic nature and geographical
distribution as compared to substations. It is proposed that the integration of IEEE time-sensitive
networking (TSN) concepts (which are currently implemented as audio video bridging (AVB)
technologies) within an IEC 61850 / Manufacturing Message Specification (MMS) framework provides a flexible and reconfigurable platform capable of overcoming such issues. A prototype test platform and bump-in-the-wire device for tunneling horizontal traffic through AVB are described. Experimental results are presented for sending IEC 61850 GOOSE (generic object oriented substation events) and SV (sampled values) messages through AVB tunnels. The obtained results verify that IEC 61850 event and sampled data may be reliably transported within the proposed framework with very
low latency, even over a congested network. It is argued that since AVB streams can be flexibly
configured from one or more central locations, and bandwidth reserved for their data ensuring
predictability of delivery, this gives a solution which seems significantly more reliable than a pure
MMS-based solution.
... Several previous works have considered the compensation of omitted samples and variable delays in networked systems, both wired and wireless. This work ranges from relatively simple first-order hold interpolators to be used in intelligent actuators (e.g., [22]) through to advanced techniques based upon H ∞ filtering of the data stream, application of adaptive sampling controls, and the use of buffering schemes within a robust control framework (e.g., [23,24]). In [23], the use of playback buffers in conjunction with information redundancy is suggested to overcome packet losses, packet disordering and variable latency of UDP/IP communication links in a closed loop. ...
... This work ranges from relatively simple first-order hold interpolators to be used in intelligent actuators (e.g., [22]) through to advanced techniques based upon H ∞ filtering of the data stream, application of adaptive sampling controls, and the use of buffering schemes within a robust control framework (e.g., [23,24]). In [23], the use of playback buffers in conjunction with information redundancy is suggested to overcome packet losses, packet disordering and variable latency of UDP/IP communication links in a closed loop. Buffer sizes should be selected to cover worst-case latencies of the links and in the absence of other methods can be estimated based upon gathered statistical data. ...
... They propose an augmented closed-loop DCS and develop an adaptive tracking controller to stabilize the resulting stochastic system. The implementation of such techniques can be non-trivial, and both [23] and [24]plus closely related methods-require a high-fidelity process model plus knowledge of the network characteristics such as delays and losses. The work in [23] requires the solution to a large non-convex optimization problem, obtained by sweeping the frequency parameter over a specified range using a given search granularity. ...
The use of wireless communications for real-time control applications poses several problems related to the comparatively low reliability of the communication channels. This paper is concerned with adaptive and predictive application-level strategies for ameliorating the effects of packet losses and burst errors in industrial sampled-data Distributed Control Systems (DCSs), which are implemented via one or more wireless and/or wired links and possibly spanning multiple hops. The paper describes an adaptive compensator that reconstructs the best estimates (in a least squares sense) of a sequence of one or more missing sensor node data packets in the controller node. At each sample time, the controller node calculates the current control, and a prediction of future controls to apply over a short time horizon; these controls are forwarded to the actuator node every sample
time step. A simple design method for a digital Proportional Integral Derivative (PID)-like adaptive controller is also described for use in the controller node. Together these mechanisms give robustness to packet losses around the control loop; in addition, the majority of the computational overhead resides in the controller node. An implementation of the proposed techniques is applied to a case study using a Hardware in the Loop (HIL) test facility, and favorable results (in terms of both performance and computational overheads)
are found when compared to an existing robust control method for a DCS experiencing artificially induced burst errors.
Microgrids are configured with hierarchal and higher-level monitoring and controlling systems, such as Supervisory Control and Data Acquisition, and equipped with advanced protection systems that need more measurements. For those control and protection systems to function properly, communication system should be deployed. Thus this chapter is targeted at discussing the communication requirements and the available communication media and protocols for application in the microgrids.
A suitable networked control scheme and its stability analysis framework have been developed for controlling inherent electromechanical oscillatory dynamics observed in power systems. It is assumed that the feedback signals are obtained at locations away from the controller/actuator and transmitted over a communication network with the help of phasor measurement units (PMUs). Within the generic framework of networked control system (NCS), the evolution of power system dynamics and associated control actions through a communication network have been modeled as a hybrid system. The data delivery rate has been modeled as a stochastic process. The closed-loop stability analysis framework has considered the limiting probability of data dropout in computing the stability margin. The contribution is in quantifying allowable data-dropout limit for a specified closed loop performance. The research findings are useful in specifying the requirement of communication infrastructure and protocol for operating future smart grids.
A smart grid is an energy distribution network that not only allows for the physical transfer of energy but also
supports ICT interfaces that enable real-time information exchange related to the scheduling, monitoring, control and protection of the interconnected energy generating, consuming and transmission equipment. To facilitate such a grid, the supporting ICT infrastructure must not only provide a wide variety of equipment interconnectivity options, but also support varying levels of flexibility (to support upgrades and re-configuration) and dependability (reliability/availability, security and timeliness). In this paper - Part I of a two-part work – a discussion of standards relevant to networking architectures for a micro grid is presented, and it is proposed that the integration of Audio Video Bridging (AVB) technology with IEC 61850 communication objects and procedures may provide a suitable reconfigurable platform capable of carrying the required information flows, even those which are time-critical. An outline for such a proposed networking infrastructure for micro grids employing AVB, along with some initial work describing a prototype implementation, is described in a companion work (Part II of the paper).
A smart grid is an energy distribution network that not only allows for the physical transfer of energy but also supports ICT interfaces that enable real-time information exchange related to the scheduling, monitoring, control and protection of the interconnected energy generating, consuming and transmission equipment. In Part I of this paper, a discussion of protocols and standards related to micro grids and small smart grids was presented, and it was suggested that the IEE Audio Video Bridging (AVB) protocols may be a good choice to support reconfigurable real-time information flows. In Part II of this paper, an outline for such a networking infrastructure based upon AVB protocols and IEC 61850 standards is described. Some initial work describing the development of a prototype implementation of the architecture, employing hardware-in-the-loop simulation, is also described. Initial tests involving Automatic Generation Control (AGC) are also reported in order to illustrate the suitability of the proposed test facility. The paper is concluded with a discussion of areas for future work.
Based on recent advances in control theory, we propose the notion of jitter margin for periodic control tasks. The jitter margin is defined as a function of the amount of constant delay in the control loop, and it describes how much additional time-varying delay can be tolerated before the loop goes unstable. Combined with scheduling theory, the jitter margin can be used to guarantee the stability and performance of the controller in the target system. It can also be used as a tool for assigning meaningful deadlines to control tasks. We discuss the need for best-case response-time analysis in this context, and propose a simple lower bound under EDF scheduling. Finally, a control- scheduling codesign procedure is given, where periods are assigned iteratively to yield the same relative performance degradation for each control task.
In a substation, a lot of distributed, safety related functions have to be performed. IEC 61850 is intended to replace all wires by serial communication. To achieve this goal IEC 61850 has to fulfill hard real-time criteria. Starting from the definition of these criteria the communication methods of IEC 61850 are investigated. The result shows the feasibility of these methods for interlocking and illustrates their usage. Some application rules are given.
With deregulation of the power generation sector, the necessity for an enhanced and open communication infrastructure to support an increasing variety of ancillary services is apparent. A duplex and distributed communication system seems to be the most suitable solution to meet and ensure good quality of these services. Parameters needed and additional limits introduced by this new communication topology must be investigated and defined. This paper focuses on the communication network requirements for a third party load frequency control service. Data communication models are proposed based on queuing theory. Simulation is performed to model the effects of certain types of signal delays on this ancillary service.
First, we review some previous work on networked control systems
(NCSs) and offer some improvements. Then, we summarize the fundamental
issues in NCSs and examine them with different underlying
network-scheduling protocols. We present NCS models with network-induced
delay and analyze their stability using stability regions and a hybrid
systems technique. Following that, we discuss methods to compensate
network-induced delay and present experimental results over a physical
network. Then, we model NCSs with packet dropout and multiple-packet
transmission as asynchronous dynamical systems and analyze their
stability. Finally, we present our conclusions
The continuing development and implementation of Synchrophasors throughout the world has given rise to multi-utility sharing of these synchronized measurements, new applications using these measurements, and the need for secure transmission of such. To this end, the IEC TC57 Working Group 10 has undertaken the task to identify the communication requirements for these synchronized measurements and to develop a communication profile to effectively meet the identified requirements. This paper starts by reviewing the identified requirements, including those defined in the North American SynchroPhasor Initiative Network (NASPINet) document, as well as a number of other “use” cases. A description of the resulting profile to meet these requirements is then presented. Of particular note is the use of existing IEC 61850 constructs, such as GOOSE and Sample Values and the XML-based configuration tools that already exist to populate such. The issue of transmitting large synchrophasor datasets will be discussed as well as the management of redundant messages by the subscriber. The paper will also review the complete security suite that is part of the profile including message authentication, data encryption, and key management among the various subscribers of the message. Operational needs in the larger network will be discussed. Finally, a comparison between the existing C37.118 communication profile and IEC 61850 90-5 will be presented.
A robust communication infrastructure is the touchstone of a smart grid that differentiates it from the conventional electrical grid by transforming it into an intelligent and adaptive energy delivery network. To cope with the rising penetration of renewable energy sources and expected widespread adoption of electric vehicles, the future smart grid needs to implement efficient monitoring and control technologies to improve its operational efficiency. However, the legacy communication infrastructures in the existing grid are quite insufficient, if not incapable of meeting the diverse communication requirements of the smart grid. Therefore, utilities from all over the world are now facing the key challenge of finding the most appropriate technology that can satisfy their future communication needs. In order to properly assess the vast landscape of available communication technologies, architectures and protocols, it is very important to acquire detailed knowledge about the current and prospective applications of the smart grid. With a view to addressing this critical issue, this paper offers an in depth review on the application characteristics and traffic requirements of several emerging smart grid applications and highlights some of the key research challenges present in this arena.
The smart power grid will extensively rely on networked control to increase eciency , reli- ability, and safety; to enable plug-and-play asset integration, such as in the case of distributed generation and alternative energy sources; to support market dynamics as well as reduce peak prices and stabilize costs when supply is limited. This paper reviews the major challenges in smart grid communication, and proposes Pow- erNet, a system of heterogeneous yet interoperable networks that provides adequate levels of real-time performance, reliability, and security, and that exploits current investments in software and hardware. Smart grid communication involves disparate designs and complex issues, and it can be eectiv ely evaluated through co-simulation. 1 Networked Smart Power Grid The smart power grid will consist of intelligent devices that use advanced communication methods, which in turn will improve situational awareness and enable networked control. Networked control will increase eciency , reliability, and safety; will enable plug-and-play asset integration, such as in the case of distributed generation and alternative energy sources; will support market dynamics as well as reduce peak prices and stabilize costs when supply is limited. Networked smart devices currently include smart meters at the customer site and phasor mea- surement units (syncronophasors) in the transmission and distribution grids. In the future, smart appliances will adjust their functions depending on instantaneous electricity cost, and a host of communicating devices will enable the feedback-loop networked control of the smart grid. In this paper, we will briey review the main objectives and technical challenges for the commu- nication infrastructure that will enable networked control of the smart grid; propose PowerNet, a communication framework for the smart power grid; and outline an evaluation methodology based on the co-simulation of the grid physics with the communication infrastructure.
In this chapter we present an overview of the development of today’s electric power industry, including the regulatory and historical evolution of the industry as well as the technical side of power generation. Included is enough thermodynamics to understand basic heat engines and how that all relates to modern steam-cycle, gas-turbine, combined-cycle, and cogeneration power plants. A first-cut at evaluating the most cost-effective combination of these various types of power plants in an electric utility system is also presented.
The future energy system has to satisfy a continuously growing demand for electricity and to reduce greenhouse gas emissions. Fulfilling such diverse needs requires the integration of renewable energy resources on a large scale. However, the existing information and communication infrastructure controlling the corresponding power grids and components is not directly designed to master the ever increasing complexity. An upcoming requirement is the need for the functional adaption of the control systems during operation. The main aim of this article is to discuss and analyze requirements as well as to introduce a standard-compliant concept for a reconfigurable software architecture used in intelligent electronic devices for distributed and renewable energy resources. A simulation case study shows the applicability of this approach. A secure adaptation of the functional structure and the corresponding algorithms in device controllers can substantially contribute to a more efficient energy system, while at the same time responding to future needs.
Distance concentration is the phenomenon that, in certain conditions, the contrast between the nearest and the farthest neighbouring
points vanishes as the data dimensionality increases. It affects high dimensional data processing, analysis, retrieval, and
indexing, which all rely on some notion of distance or dissimilarity. Previous work has characterised this phenomenon in the
limit of infinite dimensions. However, real data is finite dimensional, and hence the infinite-dimensional characterisation
is insufficient. Here we quantify the phenomenon more precisely, for the possibly high but finite dimensional case in a distribution-free
manner, by bounding the tails of the probability that distances become meaningless. As an application, we show how this can
be used to assess the concentration of a given distance function in some unknown data distribution solely on the basis of
an available data sample from it. This can be used to test and detect problematic cases more rigorously than it is currently
possible, and we demonstrate the working of this approach on both synthetic data and ten real-world data sets from different
domains.
KeywordsHigh dimensional data–Curse ofdimensionality–Distance concentration–Nearest neighbour–Chebyshev bound–Statistical test
This paper discusses the impact that communication will have on the electric power grid in the future. Recent efforts, such as UCA 2.0 and IEC 61850, are establishing a standard way for electric power substations, intelligent electronic devices, and other apparatus to communicate over data networks. These efforts pave the way to a future where protection and control of the electric power grid will migrate towards a common utility intranet. The intranet will almost certainly be based on Internet standards due to their widespread use, low cost, and easy migration path over time. A utility intranet, common to the utilities but separate from the Internet, will allow for the eventual connection of regional substations, equipment, and control centers throughout the grid. The transition will allow capabilities beyond what is currently available, but it requires a careful understanding of the implications for network capacity constraints, protocol selections, and quality-of-service technologies. This paper discusses the benefits of utility communication, the likely pitfalls in the use of Internet technology for protection and control systems, and technologies that can help to mitigate those pitfalls. This paper also introduces a model for the expected background traffic that will be present in a utility intranet. Experimental results illustrate the use of different communications protocols in representative power situations in the face of different levels of background traffic in the electric power and communication synchronizing simulator simulation environment.
The implementation of highly realistic real-time, massive, online, multi-time frame simulations is proposed as a means for building a common vision of smart grid functions among politicians, regulators, managers, operators, engineers, and technicians. These massive simulations will include hundreds of participants that play roles of reliability coordinators, transmission operators, distribution operators, power plant operators, and substation operators. These highly visible drills can demonstrate how the new smart grid systems, people, and processes can all work together economically and reliably. The industry, especially smart grid system designers, can get feedback from low cost, safe, and easily configurable simulations instead of waiting for expensive and hardwired deployments. Direct load control of millions of customer appliances is identified as a silver bullet to build self-healing and maximal flow smart grids that can accommodate large penetrations of intermittent wind and solar generation and rapid load growth due to plug-in electric vehicles. The paper recommends that up to 50% of load be controlled with minimal inconvenience to customers to potentially enhance angle, voltage, frequency, and thermal stability. An expert operator decision model is described with a view to helping system developers build operator-centered and friendly smart grid control systems.
Networked control systems (NCSs) have been one of the main research focuses in academia as well as in industry for many decades and have become a multidisciplinary area. With these growing research trends, it is important to consolidate the latest knowledge and information to keep up with the research needs. In this paper, the NCS and its different forms are introduced and discussed. The beginning of this paper discusses the history and evolution of NCSs. The next part of this paper focuses on different fields and research arenas such as networking technology, network delay, network resource allocation, scheduling, network security in real-time NCSs, integration of components on a network, fault tolerance, etc. A brief literature survey and possible future direction concerning each topic is included.
In this paper, quality of service (QoS) requirements of smart grid and other utility applications carried over an integrated Internet Protocol (IP) network are analyzed. The delay allowances for the traffic flows may vary from 8 to 10 ms for teleprotection applications to up to one second or more for interval measurements from smart meters. Networking product and service implementation and practices for network quality of service will need to support the large variation in delay and priority requirements of these applications. The paper offers four main contributions: 1) A survey of QoS requirements for smart grid applications; 2) a proposal for active use of extended differentiated services code points (DSCPs) beyond those used for traffic classification in typical networks, services, and product implementations; 3) an analysis of using the strict priority queue to support multiple mission critical and other high priority applications; and 4) a special discussion on support for traffic generated by the teleprotection application and for its QoS requirements.
Smart Grid: Technology and Applications
A play-back algorithm for networked control
- V Liberatore
MW Response of fossil-fueled steam units
- F P Demello