Disturbance observer-based adaptive fuzzy control for pure-feedback systems with deferred output constraints

In this paper, the concentration is on a tracking control issue for a class of deferred time-varying output-constrained pure-feedback systems subject to unknown external disturbance. In the control scheme design procedure, the nonlinearities are approximated by fuzzy logic systems. To obtain a virtual term, the mean value theorem is applied to separate the non-affine component of pure-feedback systems. A fuzzy compensation disturbance observer is proposed to further weaken the impact of disturbances on the system. An auxiliary system is designed to ensure that the compensation term is related to the error between the ideal and actual signals. The shifting function and the fractional barrier function are combined to achieve deferred constraints on the system output. The proposed strategy can be used to determine the boundary parameters of the barrier function immediately and to avoid the need for prior knowledge of initial conditions. Two simulations are performed to confirm the validity of the presented strategy.