Abstract: In this paper, a fuzzy adaptive output tracking controller is designed for a class of uncertain nonlinear systems to track a given sign. First, a time-varying parameter is introduced into the Gaussian membership functions of the rule antecedent, so that a new set of fuzzy rules with a time-varying parameter is given. This implies that the update motion of timevarying parameter changes not only the centers and widths of Gaussian membership functions, but also the output of the previous Mamdani fuzzy logic system, and thus a new fuzzy logic system with a timevarying parameter is synthesized. And then the modified fuzzy logic system can be used to approximate the unknown nonlinear term of the system, and the adaptive laws of timevarying parameter and the estimated values of the fuzzy approximate accuracy can be constructed, accordingly the fuzzy adaptive output tracking controller of the system can be synthesized. The advantage of the proposed method in this paper is that by the full use of existing limited number of fuzzy rules, the fuzzy adaptive output tracking controller can be synthesized with more fewer adaptive laws. Finally, the Duffing system′s simulation example demonstrates that the proposed method in this paper is feasible and effective.

Key words: fuzzy logic system; time-varying parameter; output tracking; adaptive control