Observer-based adaptive fuzzy output constrained control for MIMO nonlinear systems with unknown control directions

In this paper, an adaptive fuzzy output feedback control approach is proposed for a class of multi-inputand multi-output (MIMO) uncertain nonlinear systems with unmeasured states and unknown control directions. In the control design, by using fuzzy logic systems to approximate the unknown nonlinear functions, a fuzzy adaptive state observer is designed for state estimation as well as system identification, and a Nussbaum gain function is introduced into the control design to solve the unknown control direction problem. By applying the backstepping design techniques, a fuzzy adaptive output feedback control is constructed recursively. To address the problems of output constraint and " explosion of complexity", the barrier Lyapunov function method and dynamic surface control technique are employed, respectively. It is proved that the proposed control approach can guarantee the semi-globally uniform ultimate boundedness for all the signals and the tracking errors to a small neighborhoodof the origin. Simulation studies illustrate the effectiveness of the proposed approach. (C) 2015 Elsevier B.V. All rights reserved.