Indirect adaptive fuzzy control for a class of MIMO nonlinear systems with unknown control direction

In this paper, an indirect adaptive fuzzy controller is developed for a class of uncertain MIMO nonlinear systems with unknown sign of the control gain matrix. Within this scheme,the fuzzy logic systems are used to approximate the plant's unknown nonlinear functions. The estimated gain matrix is decomposed into the product of one diagonal matrix and two orthogonal matrixes. In order to compensate the lumped errors,all parameter adaptive laws are adjusted by the time-varying dead-zone of the filtered tracking errors,which its size is adjusted adaptively with the estimated bounds on the approximation errors. The proposed scheme guarantees that all the signals in the resulting closed-loop system are bounded, and the tracking error converges to a small neighborhood of the origin. A simulation example is used to demonstrate the effectiveness of the proposed scheme.