Approximation-Free Output-Feedback Control of Uncertain Nonlinear Systems Using Higher-Order Sliding Mode Observer

A novel output-feedback controller for uncertain single-input single-output (SISO) nonaffine nonlinear systems is proposed using high-order sliding mode (HOSM) observer, which is a robust exact finite-time convergent differentiator. The proposed controller utilizes (n + 1)th-order HOSM observer to cancel the uncertainty and disturbance where n is the relative degree of the controlled system. As a result, the control law has an extremely simple form of linear in the differentiator states. It is required no separate sliding-mode controller or universal approximators such as neural networks (NNs) or fuzzy logic systems (FLSs) that are adaptively tuned online. The proposed controller guarantees finite time stability of the output tracking error.