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-input and 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 neighborhood of the origin. Simulation studies illustrate the effectiveness of the proposed approach.