THE EFFECTS OF THE NUMBER OF RULES ON THE OUTPUT OF A FUZZY-LOGIC CONTROLLER EMPLOYED TO A PM D.C. MOTOR

This paper investigates the effects of the number of the rules in a fu zzy logic controller (FLC). In addition, a novel approach to form the linguistic fuzzy subsets and, fuzzy rule decision tables is also intro duced. The proposed method to form the fuzzy rule tables is ba.sed on the comparison of possible transient responses of the controlled syste m output and the reference set point. The relationship between the num ber of fuzzy rules and the controlled output signal for a permanent ma gnet direct current (pmdc) motor circuit is investigated using a three -dimensional output expression. Since the relationship between the inp ut and output is smooth, the effect of the number of the rules are neg ligible as long as they express a similar relationship. The sensitivit y of the FLC with respect to variations in the rule decision tables is also tested by changing the original decision table values in the ran ge of +/-30%. It is observed that these variations in the rule decisio n tables do not cause any instability in the proposed fuzzy logic cont roller. (C) 1998 Elsevier Science Ltd. All rights reserved.