Disturbance Rejection by dynamic Output Feedback: A structural solution

Disturbance Rejection problem via dynamic Output Feedback (DROF) has received a lot of contributions. For the particular Disturbance Rejection problem via State Feedback (DRSF), there exist structural necessary and sufficient conditions for the existence of solutions, which rely on some particular structures of the infinite and finite zeros. One major advantage of a structural treatment is that it leads to new relations between geometric and algebraic approaches and brings more insight into the solvability requirements. As concerns DROF, some explicit structural conditions have been given by Commault, Dion and Benahcene. However some of their conditions are necessary, others are sufficient and, except for some particular situations, no necessary and sufficient condition is still available. We propose here new necessary and sufficient structural solutions to the DROF problem, with a natural extension to the DROF problem with internal stability.