Showing papers by "Raymond H. Kwong published in 2016"

Detection and prevention of actuator enablement attacks in supervisory control systems

Abstract: The deployment of control systems with network-connected components nowadays has made feedback control systems vulnerable to attacks over the network. This paper considers the problem of intrusion detection and prevention in supervisory control systems, where the attacker has the ability to enable vulnerable actuator events that are disabled by the supervisor. We present a mathematical model for the system under such actuator enablement attacks and propose a defense strategy that detects attacks online and disables all controllable events after an attack is detected. We develop an algorithm for verifying whether the system can prevent damage from attacks with the proposed defense strategy, where damage is modeled as the reachability of a pre-defined set of “unsafe” states. The technical condition of interest that is necessary and sufficient in this context is characterized; it is termed “AE-safe controllability”. Finally, we illustrate the methodology with a traffic system example.

Adaptive cooperative output tracking control for input and output constrained multiagent systems with actuator faults

Abstract: In this work, we present a novel adaptive fault tolerant cooperative output tracking control scheme for a class of high-order nonlinear multiagent systems with a time-varying active leader, subject to constraints on the control input and agents' output. Each follower node has distinct nonlinear dynamics with both parametric and nonparametric uncertainties. Both multiplicative and additive actuator faults are considered. We show that under the proposed scheme, exponential convergence of the cooperative output tracking error into a small set around zero is guaranteed, while the constraint requirements on the system output will not be violated during operation, despite the presence of actuator faults and system uncertainties. State vectors of the agents and all other closed loop signals are shown to be bounded. An illustrative example is presented to further demonstrate the effectiveness of the proposed cooperative output tracking control scheme.

Optimized decentralized control of large scale systems

Abstract: This paper presents a new optimal decentralized controller design method for solving the tracking and disturbance rejection problems for the class of large scale LTI systems, using only low order decentralized controllers. In particular, the class of large scale systems considered in this paper is described by the LTI model M2y + M1y + M0y = Bu + Eω, where y is the output, u is the input, ω is an unknown constant disturbance, where e = y − yref is the tracking error in the system and yref is a constant given signal. To illustrate the type of results which can be obtained using the new optimal decentralized control design method, the control of a large flexible space structure is studied and compared with the standard centralized LQR-Observer controller. In this case it is shown that the new decentralized controller obtained is orders of magnitude lower in dimension than the standard centralized LQR-Observer controller. The proposed controller also has the property that if a sensor/actuator failure occurs, the resulting system has certain fail-safe properties. The proposed optimal controller also has the property that it is strongly robust as compared to the standard centralized LQR-Observer controller. In particular, the proposed controller can have the property of being some 5 orders of magnitude more robust than the standard LQR-Observer controller. An illustration of the new decentralized controller design method is applied to a large flexible space structure (LFSS) system with 5 inputs and 5 outputs and of order 24.

Optimal decentralized control of large scale systems

Abstract: This paper presents a new optimized decentralized controller design method for solving the tracking and disturbance rejection problems for large-scale linear time-invariant systems, using only low-order decentralized controllers. To illustrate the type of results which can be obtained using the new optimized decentralized control design method, the control of a large flexible space structure is studied and compared with the standard centralized LQR-observer controller. The order of the resultant decentralized controller is much smaller than that of the standard centralized LQR-observer controller. The proposed controller also has certain fail-safe properties and, in addition, it can be five orders of magnitude more robust than the standard LQR-observer controller based on their real stability radii. The new decentralized controller design method is applied to a large flexible space structure system with 5 inputs and 5 outputs and of order 24.