Online Optimization of LTI Systems Under Persistent Attacks: Stability, Tracking, and Robustness

TL;DR

This paper analyzes the stability of control systems with potential malicious attacks on control signals, demonstrating conditions under which stability can be maintained despite persistent switching attacks, using hybrid system theory.

Contribution

It introduces a stability analysis framework for LTI systems under persistent attacks, considering both static and gradient-flow controllers, with conditions for stability preservation.

Findings

Stability is maintained if attack frequency is sufficiently low.

A time-scale separation between plant and controllers is crucial.

Simulation confirms theoretical stability conditions.

Abstract

We study the stability properties of a control system composed of a dynamical plant and a feedback controller, the latter generating control signals that can be compromised by a malicious attacker. We consider two classes of feedback controllers: a static output-feedback controller, and a dynamical gradient-flow controller that seeks to steer the output of the plant towards the solution of a convex optimization problem. In both cases, we analyze the stability properties of the closed-loop system under a class of switching attacks that persistently modify the control inputs generated by the controllers. Our stability analysis leverages the framework of hybrid dynamical systems, Lyapunov-based arguments for switching systems with unstable modes, and singular perturbation theory. Our results reveal that, under a suitable time-scale separation between plant and controllers, the stability of the interconnected system can be preserved when the attack occurs with "sufficiently low frequency" in any bounded time interval. We present simulation results in a power-grid example that corroborate the technical findings.