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This book documents recent advances in the field of modeling, simulation, control, security and reliability of Cyber- Physical Systems (CPS) in power grids. The aim of this book is to help the reader gain insights into working of CPSs and understand their potential in transforming the power grids of tomorrow. This book will be useful for all those who are interested in design of cyber-physical systems, be they students or researchers in power systems, CPS modeling software developers, technical marketing professionals and business policy-makers.

Inhaltsverzeichnis

Frontmatter

Modeling and Simulation of Network Aspects for Distributed Cyber-Physical Energy Systems

Abstract
Electric power grids are presently being integrated with sensors that provide measurements at high rates and resolution. The abundance of sensor measurements, as well as the added complexity of applications trigger a demand for cyber-physical system (CPS) modeling and simulation for evaluating the characteristics of appropriate network fabrics, timing profiles and distributed application workflow of power applications. Although simulation aids in the pre-deployment decision making process, system models for complex CPS can quickly become impractical for the purposes of specialized evaluation of design aspects. Existing modeling techniques are inadequate for capturing the heterogeneous nature of CPS and tend to inherently couple orthogonal design concerns. To address this issue, we present an aspect-oriented modeling and simulation paradigm. The aspectoriented approach provides a separation between functional models and crosscutting modeling concerns such as network topology, latency profiles, security aspects, and quality of service (QoS) requirements. As a case study, we consider a three-area smart grid topology and demonstrate the aspect-oriented approach to modeling network and middleware behavior for a distributed state estimation application. We also explore how aspects leverage scalable co-simulation, fault modeling, and middleware-in-the loop simulation for complex smart grid models.
Ilge Akkaya, Yan Liu, Edward A. Lee

A Service-Oriented, Cyber-Physical Reference Model for Smart Grid

Abstract
This chapter presents a cyber-physical reference model for smart grid. Most of the early smart grid applications have been developed in an ad-hoc manner, without any underlying framework. The proposed reference model addresses this issue and enables the design of smart grid as a robust system that is extensible to the future. The proposed reference model is based on service-oriented computing paradigm and is compatible with the existing service-oriented technologies, used in enterprise computing, such as Web Services. However, it also extends these technologies for handling the hard real-time aspects of smart grid by introducing resource-aware service deployment and quality-of-service (QoS)-aware service monitoring phases. According to the proposed reference model, each smart grid scenario is characterized by three elements: (1) an application model that describes the smart grid applications to be supported by the system as a set of resource- and QoS-aware service descriptions, (2) a platform model that describes the smart grid platform as a set of computing nodes, communication links, sensors, actuators, and power system entities, and (3) a set of algorithms that enable resource-aware service deployment, QoS-aware service discovery, and QoS-aware service monitoring. This chapter also presents typical development steps of a smart grid application according to the proposed reference model. Moreover, this chapter identifies a number of technological requirements that can enable the development of smart grid applications according to the proposed reference model. Although the development of these required technologies is a topic of ongoing research, this chapter identifies some potential solution approaches, based on state-of-the-art techniques from realtime systems literature. The case study of a demand response application has been employed to explain the various aspects of the proposed smart grid reference model.
Muhammad Umer Tariq, Santiago Grijalva, Marilyn Wolf

Real Time Modeling and Simulation of Cyber-Power System

Abstract
Ongoing smart grid activities have resulted in proliferation of intelligent devices and associated Information and Communication Technologies (ICT) to enable enhanced system monitoring and control. Integration of ICT has led to an increase in the number of cyber assets and requires cyber-physical study for system analysis. In order to realize the vision of a smarter grid, it is necessary to understand the complex relationship between cyber and physical domains, and potential impacts on the power grid due to successful cyber-physical attacks. In order to understand this coupling, cyber physical test bed can help to model and simulate the smart grid with sufficient level of detail. In this chapter, an introduction to the smart electric grid and the challenges associated with the development of cyber-power test bed is presented. The integration of Real Time Digital Simulator (RTDS) and Network Simulator 3 (NS3) to realize a real time cyber-power test bed is discussed with the implementation of an example application.
Ceeman B. Vellaithurai, Saugata S. Biswas, Ren Liu, Anurag Srivastava

Cyber Physical Approach to HVDC Grid Control

Abstract
This chapter presents a cyber-physical approach to design of HVDC control system architectures and evolving HVDC grid operation and control modes. In addition, the chapter describes the communication system architectures needed for centralized and distributed operation and control of HVDC grids. Modeling and analysis methods suitable to analyze such systems using graph theoretic concepts, and also the design of distributed control systems utilizing a Multi-Agent approach and its dependence on the information graph theory. The chapter is concluded with a description of an application for distributed control of DC grids utilizing the concepts introduced. The application is presented both with regards to comparison with other design choices and analysis of performance and robustness of the algorithm versus communication metrics.
Lars Nordström, Davood Babazadeh

Smart Buildings in the Smart Grid: Contract-Based Design of an Integrated Energy Management System

Abstract
In a supply-following “smart” grid scenario, buildings can exploit remotely controllable thermostats and “smart” meters to communicate with energy providers, trade energy in real-time and offer frequency regulation services, by leveraging the flexibility in the energy consumption of their heating, ventilation and air conditioning (HVAC) systems. The realization of such a scenario is, however, strongly dependent on our ability to radically re-think the way both the grid and the building control algorithms are designed. In this work, we regard the grid as an integrated, distributed, cyber-physical system, and propose a compositional framework for the deployment of an optimal supply-following strategy. We use the concept of assume-guarantee contracts to formalize the requirements of the grid and the building subsystem as well as their interface. At the building level, such formalization leads to the development of an optimal control mechanism to determine the HVAC energy flexibility while maximizing the monetary incentive for it. At the grid level, it allows formulating a model predictive control scheme to optimally control the ancillary service power flow from buildings, while integrating constraints such as ramping rates of ancillary service providers, maximum available ancillary power, and load forecast information. Simulation results illustrate the effectiveness of the proposed design methodology and the improvements brought by the proposed control strategy with respect to the state of the art.
Mehdi Maasoumy, Pierluigi Nuzzo, Alberto Sangiovanni-Vincentelli

Decision-Support Tools for Renewables-Rich Power Systems: A Stochastic Futures

Abstract
The growing penetration of intermittent renewables (primarily wind and solar generation) in deregulated electric power systems is introducing significant challenges in forecasting generation and scheduling units. At the same time, the pervasive integration of cyber- tools in the control room provides unique opportunities for leveraging data sources like weather forecasts, computational resources, and visualization tools for real-time decision-making. Here, we introduce a framework and algorithm set for day-ahead generation scheduling, or unit commitment, that takes advantage of the close tie between cyber- and physical- resources in the electric power grid. First, we use a class of stochastic automata models known as influence models to forecast relevant spatio-temporal environmental parameters (wind speeds/direction, cloud cover), and in turn simulate probabilistic wind and solar generation futures across a wide area.  These models can be parameterized in real time to statistically match publicly-available ensemble forecast products, yet can be tailored to provide generation futures at appropriate spatial and temporal resolutions for scheduling.  The models also permit rapid selection of representative renewable-generation futures, and are able to capture local variability and spatial/temporal correlation in the generation profiles.   Second, a new method for unit scheduling for the day-ahead market, which uses the probabilistic wind/solar generation futures, is proposed and developed in a preliminary way. A novelty in this approach is a pre-selection step that can provide operators with situational awareness of critical (sensitive) units. The generation-scheduling and unit-commitment tools are demonstrated on a small-scale example, which is concerned with wind generation in the Columbia River Gorge of Washington State on a historical weather day.
Jiayi Jiang, Sandip Roy, Juhua Liu, Vaibhav Donde

Cyber Security of Smart Grid Communications: Risk Analysis and Experimental Testing

Abstract
The book chapter deals with the cyber security evaluation of active distribution grids characterized by a high level penetration of renewable Distributed Energy Resources (DER). This evolution of the energy infrastructure introduces significant changes in the control and communication functions needed for meeting the technical, security and quality requirements during the grid operation. The risk analysis and treatment of fully controllable smart grid energy infrastructures require effective evaluation tools and scalable security measures. The analysis focuses on a Voltage Control function in medium voltage grids addressing voltage stability of the power grid when a consistent amount of distributed renewable sources are connected. For this reason the chapter analyses the most relevant security scenarios of an ICT (Information and Communication Technology) architecture implementing this control application. The risk level resulting from the analysis are linked to security requirements and standard measures whose deployment in real scale infrastructures requires the security testing of application architectures. The chapter presents an experimental environment for the security testing and evaluation of voltage control communications. This includes the test bed set up, the test cases and the evaluation framework to be used for measuring the attack effects on substation-DER communications and verifying the mitigation capability of standard security measures.
Giovanna Dondossola, Roberta Terruggia

Reliable and Scalable Communication for the Power Grid

Abstract
Future smart power grids require constant data availability for actuation of control decisions. The job of ensuring the timely arrival of data falls onto the network that connects these intelligent devices. This network needs to be fault tolerant. When nodes, devices or communication links fail along a default route of a message from A to B, the underlying hardware and software layers should ensure that this message will actually be delivered as long as alternative routes exist. Existence and discovery of multi-route pathways is essential in ensuring delivery of critical data.
In this work, we present methods of developing network topologies of smart devices that enable multi-route discovery in an intelligent power grid. This is accomplished through the utilization of software overlays that (1) maintain a digital structure for the physical network and (2) identify new routes in the case of faults. The resulting cyber network structure is scalable, reliable and inexpensive to build by extending existing infrastructure.
Christopher Zimmer, Frank Mueller

Biologically Inspired Hierarchical Cyber-Physical Multi-agent Distributed Control Framework for Sustainable Smart Grids

Abstract
It is well known that information will play an important role in enhancing emerging power system operation.However, questions naturally arise as to when the increased data-dependence may be considered excessive. Two practical considerations emerge: 1) communications and computational overhead, in which redundant and irrelevant information acquisition and use results in heavy computational burden with limited performance return, and 2) increasing risks of cyber attack whereby indiscriminate cyber-dependence and -connectivity increases attack scope and impact. In this chapter, we present a hierarchical cyber-physical framework of power system operation based on flocking theory in the context of the smart grid stability problem. We study strategies to harness an appropriate degree of cyber technology by effectively leveraging physical couplings. Our formulation enables the identification of large-scale distributed control strategies for robust power grid operation. Furthermore, our formulation also enables a novel witness-based cyber-physical protocol whereby physical coherence is leveraged to probe and identify phasor measurement unit data corruption and estimate the true information values for attack mitigation.
Jin Wei, Deepa Kundur

Cyber-Physical Security Testbed for Substations in a Power Grid

Abstract
The physical system of the power grids relies on the cyber system for monitoring, control, and operation. As a result, the reliable operation of power grids is highly dependent on the associated cyber infrastructures. The integrated cyber and physical system of power grids creates a large and complex infrastructure. Due to the high penetration of Information and Communications Technology (ICT), Supervisory Control And Data Acquisition (SCADA) systems are highly interconnected with one another, resulting in higher vulnerability with respect to cyber intrusions. Recent reports indicate that cyber-attacks are increasingly likely for the critical infrastructures, e.g., control centers, nuclear power plants, and substations. These attacks may cause significant damages on the power grid. Cyber security research for the power grid is a high priority subject for the emerging smart grid environment.
Substations in the power grid are critical as they are installed with power system components such as transformers, busbars, circuit breakers, and Intelligent Electronic Devices (IEDs). Measurements from substations are used as input to Energy Management System (EMS) software applications, including state estimation and optimal power flow. These cyber and physical devices can be physically or electrically connected. For example, a protection and control unit of a transformer is connected to the user-interface via the substation local area network. Remote access to substation networks is a common way for maintenance of substation facilities. However, there are many potential cyber security issues including remote access connection. Simultaneous cyber intrusions to important substations may trigger multiple, cascaded sequences of events, leading to a blackout. As a result, it is crucial to enhance the cyber security of substations and analyze cyber and physical security as one integrated structure in order to enhance the resilience of power grids. The mitigation strategy is vital to cyber-physical security of substations in order to stop the attack, disconnect the intruder, and restore the power system to a normal state. Mitigation methods can be taken on the cyber (ICT) side and physical (power system) side. The key to cyber mitigation is to find anomaly activities or malicious behaviors, and disconnect or stop the intrusion.
A cyber-physical testbed is critical for the study of cyber-physical security of power systems. For reason of security by power companies, real measurements (e.g., voltages, currents and binary status) and ICT data (e.g., communication protocols, system logs, and security logs) are not available. A testbed is a good alternative to acquire realistic cyber (i.e., ICT data) and physical (i.e., power system measurements) system data for research and demonstration purposes. The cyberphysical testbed provides a realistic environment to study the interactions between a complex power system and the ICT system. It is important to study the causeeffect relationships of cyber intrusions, vulnerability and resilience of power systems, as well as the performance and reliability of applications in a realistic environment provided by a testbed.
Junho Hong, Ying Chen, Chen-Ching Liu, Manimaran Govindarasu

Cyber-Attacks in the Automatic Generation Control

Abstract
Power systems are traditionallymonitored and controlled by an IT infrastructure, referred to as Supervisory Control and Data Acquisition (SCADA) system. The cyber-physical interaction of power systems (physical) and SCADA systems (cyber) rises security issues, since the links between those systems are vulnerable to cyber-attacks that can potentially lead to catastrophic economical and societal effects. In this chapter we focus on a specific cyber-physical link, the Automatic Generation Control (AGC), which is an automatic frequency control loop closed over the SCADA system. We provide an impact analysis in case of a cyber-attack on the AGC signal. We first carry out a feasibility analysis based on reachability and optimal control theory, that provides an information regarding the existence of an attack pattern that can disturb the power system. We then deal with the problem of synthesizing an attack signal and treat it as a nonlinear control synthesis problem. Third, performance of our methodologies are illustrated by means of dynamic simulations on IEEE-118 bus network.
Maria Vrakopoulou, Peyman Mohajerin Esfahani, Kostas Margellos, John Lygeros, Göran Andersson

Intrusion Detection for CPS Real-Time Controllers

Abstract
Security in CPS-based real-time embedded systems controlling the power grid has been an afterthought, but it is becoming a critical issue as CPS systems are networked and inter-dependent. This work presents a set of mechanisms for timebased intrusion detection, i.e., the execution of unauthorized instructions in realtime CPS environments. The novelty is the utilization of information obtained by static timing analysis for intrusion detection. Real-time CPS systems are unique in that timing bounds on code sections are readily available since they are required for schedulability analysis.We demonstrate how micro-timings can be exploited for multiple granularity levels of application code to track execution progress. Through bounds checking of these micro-timings, we develop techniques to detect intrusions (1) in a self-checking manner by the application and (2) through the operating system scheduler, which are novel contributions to the real-time/embedded systems domain to the best of our knowledge.
Christopher Zimmer, Balasubramany Bhat, Frank Mueller, Sibin Mohan

Against Data Attacks on Smart Grid Operations: Attack Mechanisms and Security Measures

Abstract
This chapter provides a survey and some highlights of recent developments on cyber security issues related to smart grid operations. In particular, we present data attack models and attack mechanisms on system state estimation, generation dispatch, and market operations. Security measures via sensor protection and data authentication are discussed. Although presented in the context of a smart grid, the main ideas are applicable to general cyber physical systems.
Jinsub Kim, Lang Tong

Backmatter

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