Ahmad T. Al-Hammouri

A co-simulation platform for actuator networks

Actuator networks will enable an unprecedented degree of distributed control of physical environments, and further progress will critically depend on the availability of a simulation platform that can capture both the physical and the communication dynamics.

Co-simulation Tools for Networked Control Systems

In this paper, we argue that simulation of Networked Control Systems (NCSs) needs to be carried out through co-simulation, which requires the joint and simultaneous simulation of both physical and communication networks dynamics. Co-simulation enables construction of synthetic large-scale networks and workloads, replay of collected traces, and obtaining a complete snapshot of both the network behavior and the physical systems states. Therefore, co-simulation provides in-depth understanding of the interaction between communication networks and physical systems dynamics. In this paper, we overview three co-simulation tools that we have developed for NCS co-simulation. The first two tools are extensions to ns-2 called Agent/Plant and NSCSPlant ; the third tool integrates Modelica and ns-2 . For each tool, we present demonstrative case studies that highlight its capabilities.

Decentralized and dynamic bandwidth allocation in networked control systems

In this paper, we propose a bandwidth allocation scheme for networked control systems that have their control loops closed over a geographically distributed network. We first formulate the bandwidth allocation as a convex optimization problem. We then present an allocation scheme that solves this optimization problem in a fully distributed manner. In addition to being fully distributed, the proposed scheme is asynchronous, scalable, dynamic and flexible. We further discuss mechanisms to enhance the performance of the allocation scheme. We present analytical and simulation results

Virtualization of synchronized phasor measurement units within real-time simulators for smart grid applications

Synchronized phasor measurement units (PMUs) provide GPS-time tagged, high-sampling rate, positive-sequence voltage and current phasors. When placed in high-voltage substations in power networks, PMUs can provide real-time information that is necessary for the development of Smart Transmission Grids software applications whose main objective is to improve the power systems monitoring, control and protection. The development of these applications, particularly for use within control centers for on-line purposes, is limited by the availability of and access to real-time PMU data and other information. One attractive approach for application development is the use of real-time simulators to which PMUs can be interfaced as hardware-in-the-loop (HIL) devices to harvest PMU data. However, this approach has technical and economical limitations, which can be tackled by the virtualization of PMU devices. This article describes the development of an entirely software-based synchronized phasor measurement unit for use within real-time simulators to emulate a large number of real-life PMUs, which in turn can be used for creating new phasor-based applications.

Compliant control and software agents for Internet robotics

This paper describes the architectural principles of a distributed agent-based platform for the remote supervision of robotic manipulation tasks. The main contributions are that real-time constraints can be encapsulated within the local robotic controller through methods of compliant control, and that such a low-level API (application program interface) is the foundation for distributed applications that are evolvable, survivable, and can guarantee stability and compliance even in the presence of failures and lack of QoS (quality of service) provisioning. We discuss our experience with a prototype implementation and outline future research directions.

A platform for wide area monitoring and control system ICT analysis and development

PMU-based Wide Area Monitoring and Control (WAMC) system is introduced to improve the monitoring of power grid across large geographic areas and control the grid using more efficient and smart applications. The performance of WAMC applications in real power system scenarios and impact of their supporting Information and Communication Technology (ICT) on the data quality can be quantified and analyzed by pseudo-real co-simulation test beds. The purpose of this study is to propose and develop a WAMC testing platform to facilitate the real-time simulation of dynamic power grid, the ICT infrastructure that overlays the grid and WAMS applications. The platform consists of OPNET, a powerful communication network emulator, connected to a real-time power system simulator through virtualized PMU device. The end point stations such as Phasor Data Concentrator or PMU-based applications are also linked to the platform through OPNETs real-simulation gateway called SITL (System-In-The-Loop). To assess the performance of the platform architecture, a case study has been performed with five PMUs which collect the data from a power model and deliver to PMU-based mode-estimation application over a typical communication network. In this study, the results explicitly intend to quantify the effect of network protocols on data delay.

A co-simulation platform for medium/low voltage monitoring and control applications

The increasing demand for electricity and the penetration of renewable energy resources into the electrical grid are triggering the electric power system to undergo changes and complex modifications at high, medium and low voltage levels. There are large and complex projects like Smart Grid Gotland that are developing solutions to deal with these challenges. However, there are several scenarios that could be more practical to be first studied at the simulation level. Therefore, the purpose of this study is to propose and develop a co-simulation platform that allows performing real-time monitoring and control tests and simulations for MV/LV grids. This platform combines both electrical and information and communication technology (ICT) infrastructure simulations. It consists of a real-time power system simulator (Opal-RT) connected to a communication network emulator (OPNET) through an automatic meter reading interface that is based on commercial off-the-shelf (COTS) and low cost devices like Raspberry Pi and Arduino boards. The platform allows the analysis of realistic MV/LV grids and communication networks and will facilitate the simulation and comparison of low voltage control strategies for real-time test scenarios that could be more complicated to test in the reality due to cost and complexity aspects (i.e. high power losses on the low voltage grid).

Fast Flux Watch: A mechanism for online detection of fast flux networks

Fast flux networks represent a special type of botnets that are used to provide highly available web services to a backend server, which usually hosts malicious content. Detection of fast flux networks continues to be a challenging issue because of the similar behavior between these networks and other legitimate infrastructures, such as CDNs and server farms. This paper proposes Fast Flux Watch (FF-Watch), a mechanism for online detection of fast flux agents. FF-Watch is envisioned to exist as a software agent at leaf routers that connect stub networks to the Internet. The core mechanism of FF-Watch is based on the inherent feature of fast flux networks: flux agents within stub networks take the role of relaying client requests to point-of-sale websites of spam campaigns. The main idea of FF-Watch is to correlate incoming TCP connection requests to flux agents within a stub network with outgoing TCP connection requests from the same agents to the point-of-sale website. Theoretical and traffic trace driven analysis shows that the proposed mechanism can be utilized to efficiently detect fast flux agents within a stub network.

To concentrate or not to concentrate: Performance analysis of ICT system with data concentrations for Wide-area Monitoring and Control Systems

Timely and synchronized phasor data at high resolutions holds great promise for more responsible and advanced power grid operations. It is expected that combined effort of developing new application paradigms and the supporting Information and Communication Technology (ICT) will enable the miracle of “Smart Grid” at the transmission level. This paper addresses the design of the supporting ICT system for Wide Area Monitoring and Control applications from the performance perspective. The major contribution that distinguishes this paper from previous research efforts in the same area is that this study quantifies the end-to-end data delay with consideration of different levels of data concentrations. The analysis performed in this paper is not limited to the delay caused by individual ICT components but also provides means to view and analyze the delay of the entire supporting ICT system. Moreover, the quantified delay results drawn in this paper will potentially provide valuable input to the discussion on the coming standards for synchronized phasor measurements.

Complete stability region characterization for PI-AQM

This paper describes a method for finding the stability regions of the PI and PIP controllers for TCP AQM with delays. The method is applied on several representative examples, showing that stable controllers can exhibit widely different performance. Thus, the results highlight the importance of optimizing the design of PI AQM. Furthermore, the paper shows that the previously proposed PIP controller can be unstable in the presence of delays even for the control parameters given in the literature.