Fuzzy almost disturbance decoupling for MIMO nonlinear uncertain systems based on high-gainobserver

The problem of disturbance decoupling with internal stability is investigated for a class of multi-input–multi-output (MIMO) nonlinear systems in strict-feedback form. The considered nonlinear system contains unknown nonlinear uncertainties and unmeasured states. Fuzzy logic systems are first utilized to approximate the unknown nonlinear uncertainties, and then a high-gain state observer is established to estimate the unmeasured states. Based on the backstepping design approach and combining with dynamic surface control (DSC) technique, a new fuzzy adaptive output feedback control scheme is constructed. It is proved that the proposed control scheme can not only achieve internal stability of the closed-loop system, but also diminish the effect of the disturbance on output in the sense of L2 gain. In addition, since DSC is introduced into the backstepping design, the proposed control scheme can overcome the problem of “explosion of complexity” inherent in the traditional backstepping design. Simulation results and comparisons with the previous methods are included to indicate that the proposed adaptive fuzzy control approach has a satisfactory control performance.