James J. Nutaro

Integrated Hybrid-Simulation of Electric Power and Communications Systems

The modern power grid is strongly integrated with its communication network. While a power system primarily consists of elements that are modeled by continuous equations, a communication system has discrete event dynamics. We model the integrated operation of these two systems with a hybrid modeling and simulation technique. Systematically combining continuous and discrete event system models is necessary for correctly simulating critical system behaviors. This paper discusses an approach based on the discrete event system specification (DEVS) that characterizes the interaction of the two systems formally to preserve simulation correctness. We demonstrate the implementation of our integrated hybrid simulation technique with detailed generator and network models in a wide-area cooperative automatic load-control scenario.

The Impact of Market Clearing Time and Price Signal Delay on the Stability of Electric Power Markets

We generalize a model, proposed by Alvarado, of the electric power market by including the effects of control and communication. To simulate realistic markets, our model issues control signals only at given times and those signals are delayed during transmission. These two effects transform Alvarados continuous system into a hybrid system, with consequential effects. The stability analysis of the new system reveals two important properties. First, there is an upper limit on the market clearing time and the delay of the price signal beyond which the system becomes unstable. Second, there is a counter-intuitive relationship between the market clearing time and price signal delay: when the market clearing time is relatively long, delaying the price signal can improve the markets stability while reducing the communication delay can destabilize the market. This counter-intuitive effect shows that the full impact of information technology on power markets can be significant and difficult to anticipate. Therefore, as markets are designed and regulated, careful attention should be paid to the effects of information technology on the markets dynamic behavior.

On constructing optimistic simulation algorithms for the discrete event system specification

This article describes a Time Warp simulation algorithm for discrete event models that are described in terms of the Discrete Event System Specification (DEVS). The article shows how the total state transition and total output function of a DEVS atomic model can be transformed into an event processing procedure for a logical process. A specific Time Warp algorithm is constructed around this logical process, and it is shown that the algorithm correctly simulates a DEVS coupled model that consists entirely of interacting atomic models. The simulation algorithm is presented abstractly; it is intended to provide a basis for implementing efficient and scalable parallel algorithms that correctly simulate DEVS models.

Integrated modeling of the electric grid, communications, and control

Purpose – This paper aims to address a central concern in modeling and simulating electric grids and the information infrastructure that monitors and controls them. The paper discusses the need for and methods to construct simulation models that include important interactions between the physical and computational elements of a large power system.Design/methodology/approach – The paper offers a particular approach to modeling and simulation of hybrid systems as an enabling technology for analysis (via simulation) of modern electric power grids. The approach, based on the discrete event system specification, integrates existing simulation tools into a unified simulation scheme. The paper demonstrates this approach with an integrated information and electric grid model of a distributed, automatic frequency maintenance activity.Findings – Power grid modernization efforts need powerful modeling and simulation tools for hybrid systems.Research limitations/implications – The main limitation of this approach is ...

Designing power system simulators for the smart grid: Combining controls, communications, and electro-mechanical dynamics

Open source software has a leading role in research on simulation technology for electrical power systems. Research simulators demonstrate new features for which there is nascent but growing demand not yet provided for by commercial simulators. Of particular interest is the inclusion of models of software-intensive and communication-intensive controls in simulations of power system transients. This paper describes two features of the ORNL power system simulator that help it meet this need. First is its use of discrete event simulation for all aspects of the model: control, communication, and electro-mechanical dynamics. Second is an interoperability interface that enables the ORNL power system simulator to be integrated with existing, discrete event simulators of digital communication systems. The paper concludes with a brief discussion of how these aspects of the ORNL power system simulator might be inserted into production-grade simulation tools.

The split system approach to managing time in simulations of hybrid systems having continuous and discrete event components

The efficient and accurate management of time in simulations of hybrid models is an outstanding engineering problem. General a priori knowledge about the dynamic behavior of the hybrid system (i.e. essentially continuous, essentially discrete, or ‘truly hybrid’) facilitates this task. Indeed, for essentially discrete and essentially continuous systems, existing software packages can be conveniently used to perform quite sophisticated and satisfactory simulations. The situation is different for ‘truly hybrid’ systems, for which direct application of existing software packages results in a lengthy design process, cumbersome software assemblies, inaccurate results, or some combination of these independent of the designer’s a priori knowledge about the system’s structure and behavior. The main goal of this paper is to provide a methodology whereby simulation designers can use a priori knowledge about the hybrid model’s structure to build a straightforward, efficient, and accurate simulator with existing software packages. The proposed methodology is based on a formal decomposition and re-articulation of the hybrid system; this is the main theoretical result of the paper. To set the result in the right perspective, we briefly review the essentially continuous and essentially discrete approaches, which are illustrated with typical examples. Then we present our new, split system approach, first in a general formal context, then in three more specific guises that reflect the viewpoints of three main communities of hybrid system researchers and practitioners. For each of these variants we indicate an implementation path. Our approach is illustrated with an archetypal problem of power grid control.

DEVS-Based Dynamic Model Reconfiguration and Simulation Control in the Enhanced DoDAF Design Process

The combination of DoDAF operational views, which capture the requirements of an architecture, and System views, which provide its technical attributes, forms the basis for semi-automated construction of simulation models. In this paper, we describe an enhanced Model-View-Controller paradigm that works in tandem with the DEVS M&S framework. We also employ the recently introduced DoDAF extensions that incorporate new operational views to allow DoDAF specifications to be written in the Discrete Event System Specification (DEVS) formalism and, in the process, refine these new extensions. This paper describes a DEVS-based network modeling and simulation environment with dynamic reconfiguration and simulation control. The DEVS modeling and simulation framework with its separation of model, experimental frame, and simulator facilitates the development of a simulation framework supporting run-time simulation tuning. We present a layered simulation architecture that provides the capability to control and reconfigure simulation on-the-fly and steer it toward the desired performance parameters. The rapid feedback cycle supported by “real-time” intervention allows experimentation with parameters and structures and results in effective model configuration that is difficult to achieve when turnaround requires hours or days. We explore the area of system reconfiguration further by providing enhanced capabilities to control the parameters for system design and performance evaluation with respect to Net-Ready Key Performance Parameters (NR-KPP) and the way in which the refined DoDAF extensions can expedite the development of Key Interface Profile (KIP) for any DoDAF architecture. We demonstrate the enhanced capabilities with an example of the development of a simulation environment for the Systems Capable of Planned Expansion (SCOPE) command.

A discrete event method for wave simulation

This article describes a discrete event interpretation of the finite difference time domain (FDTD) and digital wave guide network (DWN) wave simulation schemes. The discrete event method is formalized using the discrete event system specification (DEVS). The scheme is shown to have errors that are proportional to the resolution of the spatial grid. A numerical example demonstrates the relative efficiency of the scheme with respect to FDTD and DWN schemes. The potential for the discrete event scheme to reduce numerical dispersion and attenuation errors is discussed.

Interfacing Power System and ICT Simulators: Challenges, State-of-the-Art, and Case Studies

With the transition toward a smart grid, the power system has become strongly intertwined with the information and communication technology (ICT) infrastructure. The interdependency of both domains requires a combined analysis of physical and ICT processes, but simulating these together is a major challenge due to the fundamentally different modeling and simulation concepts. After outlining these challenges, such as time synchronization and event handling, this paper presents an overview of state-of-the-art solutions to interface power system and ICT simulators. Due to their prominence in recent research, a special focus is set on co-simulation approaches and their challenges and potentials. Further, two case studies analyzing the impact of ICT on applications in power system operation illustrate the necessity of a holistic approach and show the capabilities of state-of-the-art co-simulation platforms.

The Activity-tracking paradigm in discrete-event modeling and simulation: The case of spatially continuous distributed systems

From a modeling and simulation perspective, studying dynamic systems consists of focusing on changes in states. According to the precision of state changes, generic algorithms can be developed to track the activity of sub-systems. This paper aims at describing and applying this more natural and intuitive way to describe and implement dynamic systems. Activity is defined mathematically. A generic application case of diffusion is experimented with to compare the efficiency of quantized state methods using this new approach with traditional methods which do not focus computations on active areas. Our goal is to demonstrate that the concept of activity can estimate the computational effort required by a quantized state method. Specifically, when properly designed, a discrete-event simulator for such a method achieves a reduction in the number of state transitions that more than compensates for the overhead it imposes.