A modified robust self-tuning controller for Hammerstein nonlinear systems with asymmetric deadzone input nonlinearity

Abstract

This article presents a novel adaptive control method for a class of uncertain discrete-time Hammerstein nonlinear systems with asymmetric deadzone input nonlinearity and bounded external disturbance. Based on the parameterization model of Hammerstein systems, the unknown parameters are updated by a robust recursive least squares algorithm with a deadzone weighted factor. Then, by introducing an estimate of the unmodeled dynamics as a feedback, the deadzone compensating control law is derived without an adaptive deadzone inverse. Theoretical results show that all the signals in the closed-loop system are bounded and the output tracking error is convergent with a relatively small residue. To show the usefulness of the developed results, simulation examples including an electro-hydraulic servo system and a DC motor subjected to a nonlinear friction are studied.