Contents I. Introduction
Over the past few years, the backstepping method [15] [16] [27] has become one of the most popular control approaches for a class of nonlinear systems, and many significant developments have been achieved. In [15], a systematic backstepping design of globally stable and asymptotically tracking adaptive controller was proposed for a class of nonlinear systems transformable to a parametric strict-feedback canonical form. In [16] and [17], the overparametrization problem was solved by elegantly introducing the concept of tuning function. In addition, the adaptive backstepping technique was further extended to parametric strict-feedback systems with unknown virtual control coefficients. With the introduction of a backstepping technique, almost disturbance decoupling for nonlinear systems with lower triangular form was addressed, respectively, in [14] [18] [28], and [35]. In [32], an observer-based adaptive controller was designed for single-input-single-output (SISO) nonlinear strict-feedback systems by backstepping technique. The backstepping-based design technique was extended to nonlinear delayed systems with strict-feedback structure in [8].
