Robust Output Regulation of Linear Systems with Structural Uncertainties

In this paper, we study the problem of robust regulation for a class of linear uncertain systems which admit the so-called Recursive Augmentation Structure. This structure is known to be quadratically stabilizable and is a rich class, including lower-triangular and upper-triangular structures (which correspond to the so-called back-stepping and forwarding in nonlinear control) as special cases. The results of this paper provide conditions on the Recursive Augmentation Structure under which robust regulation can be achieved. Our work differs from existing work on robust regulation for linear systems in the sense that we allow large uncertainties in the system. Our work is also expected to be useful in searching for possible new structures for regulation control of nonlinear systems.