A self-tuning fuzzy PI controller

A robust self-tuning PI-type fuzzy logic controller (FLC) is presented. Dep ending on the process trend, the output scaling factor (SF) of the controll er is modified on-line by an updating factor (alpha). The value of alpha is determined from a rule-base defined on error (e) and change of error (de) of the controlled variable. The proposed self-tuning controller is designed using a very simple control rule-base and the most natural and unbiased me mbership functions (MFs) (symmetric triangles with equal base and 50% overl ap with neighboring MFs). The proposed scheme is tested for a wide variety of processes including a marginally stable system with different values of dead time. Performance comparison between the conventional PI-type and prop osed self-tuning FLCs is made in terms of several performance criteria such as peak overshoot, settling time, rise time, integral absolute error and i ntegral-of-time-multiplied absolute error, in addition to the responses due to step input and load disturbance. Results for various processes show tha t the proposed FLC outperforms its conventional counterpart in each case. ( C) 2000 Elsevier Science B.V. All rights reserved.