DESIGN OF ADAPTIVE BLOCK BACKSTEPPING CONTROLLERS WITH PERTURBATIONS ESTIMATION FOR NONLINEAR STATE-DELAYED SYSTEMS IN SEMI-STRICT FEEDBACK FORM

This paper is an extended study of an existing block backstepping control scheme designed for a class of perturbed multi-input systems with multiple time-varying delays to solve regulation problems, where the time-varying delays must be linear with state variables. A new control scheme is proposed in this research where all the unknown multiple time-varying delay terms in the dynamic equations can be nonlinear state functions in non-strict feedback form, and the upper bounds of the time-delays as well as their derivatives need not to be known in advance. Another improvement is to further alleviate the problem of explosion of complexity, i.e., to reduce the number of time derivatives of virtual inputs that the designers have to compute in the design of controllers. This is done by utilizing an existent derivative estimation algorithm to estimate the perturbations in the designing of proposed controllers. Adaptive mechanisms are also embedded in the controllers so that the upper bounds of perturbations and perturbation estimation errors are not required to be known beforehand. The resultant controlled systems guarantee asymptotic stability in accordance with the Lyapunov stability theorem. Finally, a numerical example and a practical application are demonstrated to verify the merits and feasibility of the proposed control scheme.