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Triggering Control Methods for Cyber-Physical Systems : : Security & Smart Grid Applications


This thesis contains work on control and monitoring of Cyber-Physical Systems (CPS) using triggering control techniques. Cyber-Physical Systems are remotely controlled and monitored physical systems which pervade our society today in the form of numerous important applications. However, their deployment poses numerous challenges due to their limited computing, communication, and control capabilities and/or environmental constraints. In the controls community, this latter fact has motivated a paradigm shift to a so-called self/event-triggered approach by means of which algorithms employ scarce resources for control only when needed. In this dissertation, we have studied two principal problems considering, respectively, a security and smart grid CPS applications where we develop novel triggering control techniques to solve these problems. In brief, these problems can be stated as (i) motivated by importance of ensuring security of CPS, to develop failure resilient triggering-based control methods, and (ii) motivated by emergence of smart grid application, to study robustness of event-based synchronization dynamics under switching topologies. In the following lines of this abstract, we shall provide a brief closer look on these problems and our developed solutions to them. In the first problem, we study the stability of remotely controlled and monitored single-input and multi-input controllable linear class of systems under power-constrained Pulse-Width Modulated (PWM) Denial-of-Service (DoS) signals. The effect of a DoS jamming signal is to corrupt the control and measurement channels, thus preventing the data to be received at its destination. Therefore, a power-constrained DoS signal is modeled as a series of on and off time-intervals, which restricts communications intermittently. In this work, we first assume that the DoS signal is partially known, i.e., a uniform lower-bound for the off time-intervals and the on-to-off transiting time-instants are known. Accordingly, we propose our resilient control and triggering strategies which are provably capable of beating partially known jamming signals of this class. Building on this, we then present our joint control and identification algorithms, JAMCOID FOR PERIODIC SIGNALS and JAMCOID,which are provably able to guarantee the system stability under unknown jamming signals. More precisely, JAMCOID FOR PERIODIC SIGNALS algorithm is able to partly identify a periodic DoS signal with known uniform lower bound for the off time-intervals, whereas JAMCOID algorithm is capable of dealing with power-constrained, but otherwise unknown, DoS signals whilst ensuring stability. The practicality of the proposed techniques is evaluated on a simulation example under partially known and unknown jamming scenarios. In the second problem, we study the robustness of an event-triggered synchronization dynamics for a network of identical nodes under various switching scenarios. We first consider an arbitrary switching scenario where, for a general class of isolated node dynamics we characterize sufficient conditions in terms of network topologies to maintain synchronization. In particular, we shall also demonstrate that for a specific class of skew-symmetric isolated node dynamics---which play important role in this class of synchronization problems--- the asymptotic synchronization is not achievable under arbitrary switching. We then considered two classes of constrained switching signals, namely uniform and average classes, i.e., Sdwell[tD], and Saverage[ta,N₀], respectively, where we characterize sufficient conditions in terms of the associated parameters, tD, ta and N₀ in order to ensure asymptotic synchronization. We shall wrap up our discussion by presenting relevant simulation studies

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