Fault-Tolerant Control of Deterministic Input/Output Automata

This thesis deals with active fault-tolerant control of discrete event systems modeled by deterministic Input/Output (I/O) automata. Active fault-tolerant control realizes three operating modes -- nominal control, fault diagnosis and controller reconfiguration. A new fault-tolerant controller which autonomously ensures the fulfillment of the control aim, both, in the faultless and the faulty case is developed. The control aim is to steer the plant into a desired final state while guaranteeing the avoidance of illegal transitions.

Corresponding to the three operating modes, the proposed integrated fault-tolerant controller consists of a tracking controller, a diagnostic unit and a reconfiguration unit. As long as no fault is present, the tracking controller controls the plant in a feedback loop in order to guarantee the fulfillment of the control aim. At the same time the diagnostic unit detects whether a fault occurred. If a fault is detected, a novel active diagnosis method is used in order to identify the present fault as well as the current state of the faulty plant. The reconfiguration unit uses the diagnostic result provided by the diagnostic unit to reconfigure the tracking controller. As a main result, it is proved that the plant in the fault-tolerant control loop fulfills the control aim in the faultless as well as in the faulty case if the control loop is recoverable. The applicability of the fault-tolerant control method is demonstrated by means of a handling process at the Handling System HANS.