Interval type-2 fuzzy PID controllers and an online self-tuning mechanism

In this study, the general structure of interval type-2 fuzzy pid (it2-fpid) controllers and a self-tuning mechanism for it2-fpid controller is presented. in this context, we will present and examine the controller structures of the type-1 fuzzy pid (t1-fpid) and it2-fpid controllers on a generic a symmetrical 3x3 rule base. then, an online self-tuning mechanism for it2-fpid controllers is presented. the presented self-tuning mechanism, which was firstly presented for t1-fpid, controllers, tunes the scaling factors of it2-fpid with respect to the current error value of the control system. a systematic design approach has been also presented for the self-tuning it2-fpid structure. the performance of the t1-fpid, it2-fpid and self-tuning it2-fpid structures has been investigated on a simulation study conducted on a nonlinear tank system. the results have shown that, since the proposed approach has more extra degree of freedom provided by its interval type-2 fuzzy sets and self-tuning mechanism, the self-tuning it2fpid resulted with a superior control performance in comparison with its type-1 and interval type-2 counterparts.