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Axo: Masking delay faults in real-time control systems

Type of publication Peer-reviewed
Publikationsform Proceedings (peer-reviewed)
Author Mohiuddin Maaz, Saab Wajeb, Bliudze Simon, Le Boudec Jean-Yves,
Project Integration of Intermittent Widespread Energy Sources in Distribution Networks: Scalable and Reliable Real Time Control of Power Flows
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Proceedings (peer-reviewed)

Title of proceedings IECON 2016 - 42nd Annual Conference of the IEEE Industrial Electronics Society
Place Florence, Italy
DOI 10.1109/iecon.2016.7793512

Open Access


We consider real-time control systems that consist of a controller that computes and sends setpoints to be implemented in physical processes through process agents. We focus on systems that use commercial off-the-shelf hardware and software components. Setpoints of these systems have strict real-time constraints: Implementing a setpoint after its deadline, or not receiving setpoints within a deadline, can cause failure. In this paper, we address delay faults: faults that cause setpoints to violate their real-time constraints. We present Axo, a fault-tolerance protocol that guarantees safety and improves availability for a class of such systems that exhibit two main properties: the setpoints must have a known validity horizon, and process agents must be capable of handling duplicate setpoints. To reason about delay faults, and consequently design Axo, we present an abstraction of a controller; the abstraction applies to a wide range of real-time control systems. We prove guarantees of safety and availability. Finally, we present an implementation of Axo and the results of the tests performed with Commelec, a real-time control system for electric grids.