Resilient Strategies Against Cyberattacks in Network Control Systems
Creators: Nazarzadeh Oghaz, Amin
Publisher: name: University of Alberta Library
Year: 2024

<p>Large scale modern control systems involve the interconnection of system components using a communication network. The presence of a network can make these systems vulnerable to cyber attacks, thus compromising overall<br>
system’s performance and stability. Cyber attacks in control systems has been a constant topic of research for over a decade, with concentration on three main issues; namely, attack detection, resiliency of the control system, and state estimation under cyber attacks. In this study, we address real-world challenges within this field and aim to enhance the current state of resiliency strategies in network control systems.</p>

<p>In the first part, we study input-to-state stability of nonlinear systems under DoS attack. More specifically, our goal is to obtain a relationship between ISS and DoS attack parameters. We propose a novel model-based dual-mode sampling approach which, depending on the attack intervals, intermittently switches between event-triggered and periodic sampling. We show that  the combined model-based state prediction, packetized data transmission, and event-triggered sampling can attenuate the effects of DoS attack on stability.</p>

<p>In the next part of this research, our interest is in the study of one of the most critical forms of deception attacks, known as zero-dynamics attacks \AM{(ZDAs)} in sampled-data systems. This type of attack excites the internal dynamics of the system resulting in unobservable, stealthy, deviation of the states when the internal system dynamics is non-minimum phase. In this part,<br>
our interest is in mitigating the effect of ZDAs in nonlinear sampled-data systems using the multi-rate approach. Our approach consists of analyzing the dissipativity property in the<br>
zero-dynamics part of the system and finding conditions on the sampling rate that neutralize the attack. We show that, under some mild conditions, using a multi-rate approach provides<br>
a secure nonlinear system against ZDAs by preserving the minimum-phase property.</p>

<p>Then, we consider the practical limitation of the network control system and design a secure<br>
control framework that takes advantage of the asynchronous sampling in event-triggered schemes and embeds a sense of sampling zeros dynamics into the triggering threshold. Therefore, the triggering instants happen in such a way that<br>
stabilize the zero-dynamics of the sampled-data system. In this way, the event-based controller not only addresses the stability problem and network limitation but also provides a solution<br>
to the unstable sampling zeros issue. Thus, aside from all the aforementioned benefits, our proposed method also serves as a self-defence mechanism that confronts ZDAs whenever the<br>
system is targeted by an adversary. </p>

<p>Finally, we propose a new method<br>
that aims to compensate for the performance loss observed with the previous approach. We develop a model-based event-triggered control setup consisting of a novel triggering condition with an inference-based control rule using a nonlinear model. The key point is to exploit<br>
the concept of asynchronous (nonuniform) sampling inherent in the event-triggered mechanism as the main solution. We employ the multiple Lyapunov<br>
functional method and determine conditions on the switching signal that produce the desired result. Finally, we analyze the stability of the overall<br>
system using Lyapunov theory and discover conditions on the event-triggered parameters and inference-based control law that satisfy the stability criteria and render the zero-dynamics minimum-phase. As a result, \AM{ZDA}s become ineffective and not a viable option to a malicious attacker.</p>