The Effects of the Number of Rules on the Output of a Fuzzy Logic Controller Employed to a PM D.C. Motor

Abstract

This paper investigates the effects of the number of the rules in a fuzzy logic controller (FLC). In addition, a novel approach to form the linguistic fuzzy subsets and fuzzy rule decision tables is also introduced. The proposed method to form the fuzzy rule tables is based on the comparison of possible transient responses of the controlled system output and the reference set point. The relationship between the number of fuzzy rules and the controlled output signal for a permanent magnet direct current (pmdc) motor circuit is investigated using a three-dimensional output expression. Since the relationship between the input and output is smooth, the effect of the number of the rules are negligible as long as they express a similar relationship. The sensitivity of the FLC with respect to variations in the rule decision tables is also tested by changing the original decision table values in the range of ±30%. It is observed that these variations in the rule decision tables do not cause any instability in the proposed fuzzy logic controller. © 1998 Elsevier Science Ltd. All rights reserved.