Adaptive dynamic surface control design for uncertain nonlinear strict-feedback systems with unknown control direction and disturbances

This paper investigates the adaptive tracking control problem for a class of uncertain single-input and single-output strict-feedback nonlinear systems with unknown control direction and disturbances. Dynamic surface control is utilized to handle the problem of 'explosion of complexity' occurred in the conventional backstepping design. In order to escape analytic calculation, a first-order filter is used to generate the command signals and their derivatives. Moreover, Nussbaum function is employed to handle the problem of the unknown control coefficient. New controllers and adaptive laws are designed by combining the compensation tracking error and the prediction error that exist between the system state and the serial-parallel estimation model. It is proved that all the variables in the closed-loop system are bounded and the tracking error is driven to the origin with a small neighborhood. Finally, the simulation results are presented to verify the effectiveness of the proposed approach.