International Journal of Information Technology, Control and Automation (IJITCA) Vol.2, No.2, April 2012 DOI:10.5121/ijitca.2012.2205 53        D. Elleuch, T. Damak University of Sfax, National Engineering School of Sfax (ENIS), Laboratory of Sciences and Techniques of Automatic control & computer engineering (Lab-STA), Tunisia B.P. 1173, 3038 Sfax-Tunisia dorsafelleuch@yahoo.fr tarak.damak@enis.rnu.tn ABSTRACT Control robustness is study for uncertain nonlinear systems transformed in semi strict feedback systems. An adaptive backstepping sliding mode control and an adaptive backstepping control robustness is considered. Robustness is studied when the unknown parameter are constants and varied. The simulation results prove that the sliding mode control is more robust than the backstepping control to tracking trajectory and to estimate the unknown parameter in two cases.. KEYWORDS adaptive backstepping control, adaptive backstepping sliding mode control, uncertain nonlinear system 1. INTRODUCTION The systems are made more complicated due to the technology development. Due to modeling nonlinear systems, an uncertainty term appears. Many conditions caused the uncertainty like the parameter variation, neglected term……………… To solve the tracking trajectory problem, many controllers are designed to uncertain nonlinear systems like sliding mode controller, backstepping controller, PID controller……….. The sliding mode technique is mostly applied to build a controller. The sliding mode controller is known as one of robust controller to reject perturbation and uncertainty. The sliding mode control problem is the chattering. Many solutions are proposed to eliminate its. In Literature ([1], [2], [3]), it was shown that the chattering phenomenon disappears with the higher order sliding mode control algorithms. The construction of the lyapunov function is complicated. The backstepping is a recursive method to build a lyapunov function. The backstepping technique is recently applied to construct an adaptive controller for some systems form like uncertain nonlinear systems, electrical machine. The backstepping control solves both the problem of stabilization and tracking trajectory of nonlinear systems [4]