Generalized output regulation for linear systems

One of the most important problems in linear multivariable control theory is that of controlling a given plant in order to have its output track (or reject) a reference (or disturbance) signal produced by some external generator, called the exosystem. The disturbance or reference contains only the frequency components of the exosystem. This is called the output regulation problem. We generalize the problem framework in several directions. One is to model disturbances and references by an exosystem that is not, unlike the traditional approach, autonomous but is driven. Another direction is to incorporate the derivative information in the problem formulation. Consequently, we formulate two classes of generalized exact and almost output regulation problems. We provide solvability conditions and the solutions to these problems. Finally, and most importantly, we show that if solvability conditions for regulation are not satisfied, one can design a regulator to achieve "best" tracking (or rejection) of reference (or disturbance) signal is any desired induced norm sense.