| 1. |
- Stankovic, M. S., et al.
(författare)
-
Distributed Offset Correction for Time Synchronization in Networks with Random Delays
- 2018
-
Ingår i: 2018 European Control Conference, ECC 2018. - : Institute of Electrical and Electronics Engineers Inc.. - 9783952426982 ; , s. 2212-2217
-
Konferensbidrag (refereegranskat)abstract
- A new distributed asynchronous offset correction algorithm for time synchronization in networks with random communication delays, communication dropouts, and measurement noise is proposed. The algorithm is based on a specially constructed error function which includes delay compensation and unboundedly-increasing-time compensation parameters. Convergence of the algorithm in the mean square sense and w.p.l is proved. A modification of the algorithm based on consensus on the delay compensation parameter is also proposed, offering better performance in practice. Illustrative simulation results are presented.
|
|
| 2. |
- Iwaki, Takuya, 1986-, et al.
(författare)
-
Multi-loop periodic event-triggered actuation : applications to PID, cascade, and decoupling control
- 2022
-
Ingår i: International Journal of Control. - : Informa UK Limited. - 0020-7179 .- 1366-5820. ; , s. 1-16
-
Tidskriftsartikel (refereegranskat)abstract
- This paper studies periodic event-triggered actuation applied to PID, cascade, and decoupling control. We propose an event-triggered output feedback controller, in which the control command is actuated only when it exceeds its previous value by a certain threshold. An exponential stability condition is derived in the form of LMIs using a Lyapunov–Krasovskii functional based on Wirtinger's inequality. It is shown that an observer-based controller can reject an unknown step disturbance. Using this result, we propose a way to tune the event threshold subject to a given stability margin. We apply the proposed framework to PID, cascade, and decoupling control to illustrate how the event thresholds can be tuned in practice. Numerical examples show for these three control architectures how controller–actuator communication can be reduced without performance degradation.
|
|
| 3. |
- Teixeira, Andre, et al.
(författare)
-
Networked Control Systems under Cyber Attacks with Applications to Power Networks
- 2010
-
Ingår i: 2010 AMERICAN CONTROL CONFERENCE. - : IEEE. - 9781424474271 ; , s. 3690-3696
-
Konferensbidrag (refereegranskat)abstract
- Networked control systems under certain cyber attacks are analyzed. The communication network of these control systems make them vulnerable to attacks from malicious outsiders. Our work deals with two types of attacks: attacks on the network nodes and attacks on the communication between the nodes. We propose a distributed scheme to detect and isolate the attacks using observers. Furthermore, we discuss how to reduce the number of observer nodes while maintaining the coverage of the entire network. The results are applied to two classes of networked control systems: a network running the consensus protocol and a power network defined by the linearized swing equation. Sufficient conditions for the existence of the proposed attack detection scheme are provided for the first class of systems. For the second class, we provide a necessary condition for the existence of the proposed detection scheme.
|
|
| 4. |
- Aminian, Behdad, et al.
(författare)
-
GISOO : A virtual testbed for wireless cyber-physical systems
- 2013
-
Ingår i: Industrial Electronics Society, IECON 2013 - 39th Annual Conference of the IEEE. - : IEEE. - 9781479902248 ; , s. 5588-5593
-
Konferensbidrag (refereegranskat)abstract
- The increasing demand for wireless cyber-physical systems requires correct design, implementation and validation of computation, communication and control methods. Traditional simulation tools, which focus on either computation, communication or control, are insufficient when the three aspects interact. Efforts to extend the traditional tools to cover multiple domains, e.g., from simulating only control aspects to simulating both control and communication, often rely on simplistic models of a small subset of possible communication solutions. We introduce GISOO, a virtual testbed for simulation of wireless cyber-physical systems that integrates two state-of-the art simulators, Simulink and COOJA. GISOO enables users to evaluate actual embedded code for the wireless nodes in realistic cyber-physical experiments, observing the effects of both the control and communication components. In this way, a wide range of communication solutions can be evaluated without developing abstract models of their control-relevant aspects, and changes made to the networking code in simulations is guaranteed to be translated into production code without errors. A double-tank laboratory experimental setup controlled over a multi-hop relay wireless network is used to validate GISOO and demonstrate its features.
|
|
| 5. |
- Bemporad, Alberto, et al.
(författare)
-
Hybrid Model Predictive Control Based on Wireless Sensor Feedback : an experimental study
- 2007
-
Ingår i: Proceedings of the 46<sup>th</sup> IEEE Conference on Decision and Control. - New Orleans, Louisiana, USA. : IEEE. - 9781424414970 ; , s. 5062-5067
-
Konferensbidrag (refereegranskat)abstract
- This paper presents the design and the experimental validation of model predictive control (MPC) of a hybrid dynamical process based on measurements collected by a wireless sensor network. The proposed setup is the prototype of an industrial application in which a remote station controls the process via wireless network links. The experimental platform is a laboratory process consisting of four infrared lamps, controlled in pairs by two on/off switches, and of a transport belt, where moving parts equipped with wireless sensors are heated by the lamps. By approximating the stationary heat spatial distribution as a piecewise affine function of the position along the belt, the resulting plant model is a hybrid dynamical system. The control architecture is based on the reference governor approach: the process is actuated by a local controller, while a hybrid MPC algorithm running on a remote base station sends optimal belt velocity set-points and lamp on/off commands over a network link exploiting the information received through the wireless network. A discrete-time hybrid model of the process is used for the hybrid MPC algorithm and for the state estimator.
|
|
| 6. |
- Dimarogonas, Dimos V., et al.
(författare)
-
Distributed Event-Triggered Control for Multi-Agent Systems
- 2012
-
Ingår i: IEEE Transactions on Automatic Control. - 0018-9286 .- 1558-2523. ; 57:5, s. 1291-1297
-
Tidskriftsartikel (refereegranskat)abstract
- Event-driven strategies for multi-agent systems are motivated by the future use of embedded microprocessors with limited resources that will gather information and actuate the individual agent controller updates. The controller updates considered here are event-driven, depending on the ratio of a certain measurement error with respect to the norm of a function of the state, and are applied to a first order agreement problem. A centralized formulation is considered first and then its distributed counterpart, in which agents require knowledge only of their neighbors' states for the controller implementation. The results are then extended to a self-triggered setup, where each agent computes its next update time at the previous one, without having to keep track of the state error that triggers the actuation between two consecutive update instants. The results are illustrated through simulation examples.
|
|
| 7. |
- Ramesh, Chithrupa, et al.
(författare)
-
Design of State-Based Schedulers for a Network of Control Loops
- 2013
-
Ingår i: IEEE Transactions on Automatic Control. - 0018-9286 .- 1558-2523. ; 58:8, s. 1962-1975
-
Tidskriftsartikel (refereegranskat)abstract
- For a closed-loop system with a contention-based multiple access network on its sensor link, the medium access controller (MAC) may discard some packets when the traffic on the link is high. We use a local state-based scheduler to select a few critical data packets to send to the MAC. In this paper, we analyze the impact of such a scheduler on the closed-loop system in the presence of traffic, and show that there is a dual effect with state-based scheduling. In general, this makes the optimal scheduler and controller hard to find. However, by removing past controls from the scheduling criterion, we find that certainty equivalence holds. This condition is related to the classical result of Bar-Shalom and Tse, and it leads to the design of an innovations-based scheduler with a certainty equivalent controller. However, this controller is not an equivalent design for the optimal controller, in the sense of Witsenhausen. The computation of the estimate can be simplified by introducing a symmetry constraint on the scheduler. Based on these findings, we propose a dual predictor architecture for the closed-loop system, which ensures separation between scheduler, observer and controller. We present an example of this architecture, which illustrates a network-aware event-triggering mechanism.
|
|
| 8. |
- Teixeira, André, et al.
(författare)
-
Cyber-Secure and Resilient Architectures for Industrial Control Systems
- 2015
-
Ingår i: Smart Grid Security: Innovative Solutions for a Modernized Grid. - : Elsevier. - 9780128023549 ; , s. 149-183
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- In this chapter, we survey cyber security solutions for control and monitoring systems that are used to manage the Smart Grid. We start with a short review of the history and use of Industrial Control Systems (ICSs) and Supervisory Control and Data Acquisition (SCADA) systems, and how cyber security in control systems has recently become a major concern, in the wake of the Stuxnet and other recently discovered malware. We follow up with surveying information technology and control-centric security tools that can be used to improve the resilience of industrial control systems. Feedback control loops are core components in the Smart Grid, as they enable the maximal utilization of the physical infrastructure and its resources. As the number of control loops in the Smart Grid increases, the cyber security challenges faced by ICSs become increasingly important within the Smart Grid's context. To highlight such novel challenges, we give an overview of the envisioned control loops in future Smart Grids, and discuss the potential impact of cyber threats targeting critical Smart Grid functionalities. As a case study, false-data injection attacks on power transmission networks are considered. The level of resilience to such attacks is assessed through a control-centric risk assessment methodology, which is also used for allocating the deployment of more modern and secure equipment. The chapter ends with a discussion of future research challenges in the area.
|
|
| 9. |
- Teixeira, André, et al.
(författare)
-
Quantifying Cyber-Security for Networked Control Systems
- 2013
-
Ingår i: Control of Cyber-Physical Systems. - Switzerland : Springer International Publishing. - 0170-8643. - 9783319011585 ; , s. 123-142
-
Bokkapitel (refereegranskat)abstract
- In this paper we consider a typical architecture for a networked control system under false-data injection attacks. Under a previously proposed adversary modeling framework, various formulations for quantifying cyber-security of control systems are proposed and formulated as constrained optimization problems. These formulations capture trade-offs in terms of attack impact on the control performance, attack detectability, and adversarial resources. The formulations are then discussed and related to system theoretic concepts, followed by numerical examples illustrating the various trade-offs for a quadruple-tank process.
|
|
| 10. |
- Teixeira, André, et al.
(författare)
-
Voltage control for interconnected microgrids under adversarial actions
- 2015
-
Ingår i: IEEE International Conference on Emerging Technologies and Factory Automation, ETFA. - : IEEE conference proceedings. - 9781467379298 ; , s. 1-8
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we study the impact of adversarial actions on voltage control schemes in interconnected microgrids. Each microgrid is abstracted as a power inverter that can be controlled to regulate its voltage magnitude and phase-angle independently. Moreover, each power inverter is modeled as a single integrator, whose input is given by a voltage droop-control policy that is computed based on voltage magnitude and reactive power injection measurements. Under mild assumptions, we then establish important properties of the nominal linearized closed-loop system, such as stability, positivity, and diagonal dominance. These properties play an important role when characterizing the potential impact of different attack scenarios. In particular, we discuss two attack scenarios where the adversary corrupts measurement data and reference signals received by the voltage droop controllers. The potential impact of instances of each scenario is analyzed using control-theoretic tools, which may be used to develop methodologies for identifying high-risk attack scenarios, as is illustrated by numerical examples.
|
|
