  We consider the problem of designing a feedback controller for a
multivariable linear time-invariant system which regulates an arbitrary system
output to the solution of an equality-constrained convex optimization problem
despite unknown constant exogenous disturbances; we term this the linear-convex
optimal steady-state (OSS) control problem. We introduce the notion of an
optimality model, and show that the existence of an optimality model is
sufficient to reduce the OSS control problem to a stabilization problem. This
yields a constructive design framework for optimal steady-state control that
unifies and extends existing design methods in the literature. We illustrate
the approach via an application to optimal frequency control of power networks,
where our methodology recovers centralized and distributed controllers reported
in the recent literature.
