Online rule weighting of fuzzy PID controllers

In this study, a new weighting method is proposed for the fuzzy rules of the fuzzy PID controllers in an on-line manner. First, the transient phase of the unit response of the closed loop system is taken into consideration and the response is divided into certain regions which are assigned in accordance with the number of membership functions defined for the error input of the fuzzy logic controller. Secondly, the relative importance or influence of the fired fuzzy rules of the fuzzy logic controller are determined for each region and the meta-rules are derived for the adjustment of corresponding fuzzy rule weight values to obtain an efficient and appropriate control signal that will achieve a desired system response. For this purpose, two simple functions based on the absolute value of the normalized system error are used for the assignment of the rule weights by an adequate arrangement in accordance with the meta-rules derived. The effectiveness of the proposed self tuning method is demonstrated on various processes by simulations. The proposed new fuzzy rule weighting method improves the transient response in terms of overshoots, oscillations and settling time.