Improvements in the sensor recovery mechanism for a multisensor control scheme

This paper deals with a multisensor scheme based on set theoretic principles, whereby different invariant sets that characterize healthy and faulty functioning of system components are computed offline. Such sets allow to partition the ensemble of sensors into `healthy', `faulty' and `under recovery' subclasses. Fault detection and isolation consists of online set-membership verifications with low computational complexity. Sensors that are deemed healthy are utilized in the computation of the feedback control law, while sensors that are deemed `faulty' or `under recovery' are prevented from participating in the feedback control action. The main focus of this paper is on the reintegration of `under recovery' sensors, that is to say, the transition of sensors from the `under recovery' to the `healthy' sensor subclass. This transition, in contrast to all other possible transitions, is particularly difficult to evaluate since it involves set membership conditions based on unmeasurable quantities. This difficulty is circumvented by resorting to necessary and sufficient conditions for the recognition of recovery, which are based exclusively upon measurable quantities. The interplay between the necessary conditions and the sufficient conditions, together with the particular system structure and fault detection mechanism, allows to obtain further important improvements in the recovery procedure in terms of transient times and sensitivity to the topology of the invariant sets.