A robust self-tuning scheme for PI- and PD-type fuzzy controllers

We propose a simple but robust model independent self-tuning scheme for fuzzy logic controllers (FLC's), Here, the output scaling factor (SF) is adjusted on-line by fuzzy rules according to the current trend of the controlled process. The rule-base for tuning the output SF is defined on error (e) and change of error (Delta e) of the controlled variable using the most natural and unbiased membership functions (MF's), The proposed self-tuning technique is applied to both PI- and PD-type FLC's to conduct simulation analysis for a wide range of different linear and nonlinear second-order processes including a marginally stable system where even the well known Ziegler-Nichols tuned conventional PI or PID controllers fail to provide an acceptable performance due to excessively large overshoot. Performances of the proposed self-tuning FLC's are compared,vith those of their corresponding conventional FLC's in terms of several performance measures such as peak overshoot, settling time, rise time, integral absolute error (IAE) and integral-of-time-multiplied absolute error (ITAE), in addition to the responses due to step set-point change and load disturbance and, in each case, the proposed scheme shows a remarkably improved performance over its conventional counterpart.