  This paper presents a scheme to design a tracking controller for a class of
uncertain nonlinear systems using a robust feedback linearization approach. The
scheme is composed of two steps. In the first step, a linearized uncertainty
model for the corresponding uncertain nonlinear system is developed using a
robust feedback linearization approach. In this step, the standard feedback
linearization approach is used to linearize the nominal nonlinear dynamics of
the uncertain nonlinear system. The remaining nonlinear uncertainties are then
linearized at an arbitrary point using the mean value theorem. This approach
gives a multi-input multi-output (MIMO) linear uncertain system model with a
structured uncertainty representation. In the second step, a minimax linear
quadratic regulation (LQR) controller is designed for MIMO linearized uncertain
system model. In order to demonstrate the effectiveness of the proposed method,
it is applied to a velocity and altitude tracking control problem for an
air-breathing hypersonic flight vehicle.
