  In this paper, a robust nonlinear control scheme is proposed for a nonlinear
multi-input multi-output (MIMO) system subject to bounded time varying
uncertainty which satisfies a certain integral quadratic constraint condition.
The scheme develops a robust feedback linarization approach which uses standard
feedback linearization approach to linearize the nominal nonlinear dynamics of
the uncertain nonlinear system and linearizes the nonlinear time varying
uncertainties at an arbitrary point using the mean value theorem. This approach
transforms uncertain nonlinear MIMO systems into an equivalent MIMO linear
uncertain system model with unstructured uncertainty. Finally, a robust minimax
linear quadratic Gaussian (LQG) control design is proposed for the linearized
model. The scheme guarantees the internal stability of the closed loop system
and provides robust performance. In order to illustrate the effectiveness of
this approach, the proposed method is applied to a tracking control problem for
an air-breathing hypersonic flight vehicle (AHFV).
