Adaptive fuzzy output tracking control for a class of uncertain nonlinear systems

The universal approximation theorem of the fuzzy logic systems (FLS) is utilized to develop an adaptive control scheme for a class of nonlinear MIMO systems by the backstepping technique. The MIMO systems consist of some subsystems and each subsystem is able to be reputed as non-affine pure-feedback structure. The external disturbances appear in each equation of each subsystem and the disturbance coefficients are assumed to be unknown functions rather than constant one. The two main advantages of the developed scheme are that (1) it does not require a priori knowledge of the signs of the control gains and (2) only one parameter is needed to be adjusted online in controller design procedure for each subsystem. It is proven that, under the appropriate assumptions, the developed scheme can achieve that all the signals in the closed-loop system are bounded and the tracking errors converge to a small neighborhood around zero. Effectiveness of the developed scheme is illustrated by the simulation example.