Robust Control with Rejection of Harmonic Disturbances

This paper considers a finite-time output feedback control problem for a class of uncertain systems subject to harmonic disturbances of known frequencies. The controller is required to minimize a quadratic cost functional subject to the given uncertainties and harmonic disturbances. The main result gives a necessary and sufficient condition for the existence of a suitable controller. The condition is given terms of a pair of Riccati differential equations which arise in a corresponding H∞control problem.