The further result on global practical tracking for high-order uncertain nonlinear systems

This paper extends the unknown control coefficients with lower and upper constant bounds to the ones which may take arbitrarily large and /or small values. Since the existing methods are no longer applicable and the technical obstacles caused by the extensions are essential, new control design scheme should be exploited to the global practical tracking. By the approaches of Nussbaum-gain and adding a power integrator, the authors successfully propose the design scheme of the adaptive practical tracking controller for the systems. It is shown that the designed controller guarantees that all the closed-loop system states are bounded and the tracking error becomes prescribed arbitrarily small after a finite time.