Fuzzy logic control of variable time delay systems with a stability safe guard

A closed loop control system incorporating fuzzy logic has been developed for a class of processes with unknown or variable time delay. A unique fuzzy logic controller structure with an efficient realization and a small rule base that can be easily implemented in existing industrial controllers has been proposed to compensate for the time delay without specifically taking into account the past inputs or requiring a predictive model. The fuzzy logic controller (FLC) consists of a rule base implementing a classical control strategy and an output membership adaptation mechanism to compensate for changes in the time delay. The FLC is applied to a tank temperature control problem and significant improvements in the system performance is observed in simulation. The FLC was also applied to plants with significant variations in parameters and the amount of delay. Robust performance was achieved through automatic online tuning. The stability of the FLC is investigated and a safe guard is established