  A high-gain extended observer is designed for a class of nonlinear uncertain
systems. This observer has the ability of estimating system uncertainty, and it
can be used to estimate the derivatives of signal up to order n. The controller
based on this extended observer can make the tracking error and its derivatives
converge to zero rapidly even when uncertainties and disturbances exist. The
result of simulation indicates that this method has satisfactory control
performance for nonlinear uncertain systems.
