The regulator problem with robustness is solved for systems modelled by rational transfer matrices. A topology for possibly unstable plants is presented. A necessary and sufficient condition is derived for the existence of a proper controller which provides internal stability and output regulation throughout an open neighbourhood of the plant. A characterization of all such controllers is determined.
['Bruce A. Francis', 'M. Vidyasagar']
Brief paper: Algebraic and topological aspects of the regulator problem for lumped linear systems