Finite-state transition models for path planning, packet screening and control of networked industrial control systems



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This research project investigates the use of finite-state transition representations for path planning, cyber security, and closed-loop control of networked industrial control systems. In particular, we consider systems consisting of physical components that are controlled by networked digital devices, such as programmable logic controllers (PLCs). The physical components are typically described in continuous time using differential equations, while the communication and control components operate in discrete time. Such combinations of continuous and discrete elements are called "hybrid systems." Although there is a substantial body of literature for analyzing either continuous or discrete systems, the techniques applicable to one are generally not compatible with the other, making analysis and control of hybrid systems a challenging task. The approach taken here is to approximate the continuous dynamics by finitestate, discrete-time transition models. These can be naturally integrated with the digital control and communication infrastructure, and the resulting unified finite-state transition models can be analyzed using powerful algorithmic tools. In this work, the tasks of interest are 1) planning open-loop set-point changes of the system state, 2) detecting and neutralizing harmful control actions, and 3) implementing closed-loop control for uncertainty and disturbance rejection.

We first extend existing methods for finite-state transition modeling to include multiple equilibrium points with both stable and unstable points. This extension is demonstrated on the classic inverted pendulum on a cart (IPC). We show the path planning and closed-loop control capabilities by swinging up the IPC to its unstable, upward-pointing position and stabilizing it there. Finally, we extend the current state-of-the-art in cyber security for networked industrial control systems, by using the finite-state transition model to create a state-aware packet monitoring system to interpret control inputs in the context of the current system configuration.



Packet screening, Packet sniffing, FSTS, Networked industrial control systems