  This paper considers a distributed PI-controller for networked dynamical
systems. Sufficient conditions for when the controller is able to stabilize a
general linear system and eliminate static control errors are presented. The
proposed controller is applied to frequency control of power transmission
systems. Sufficient stability criteria are derived, and it is shown that the
controller parameters can always be chosen so that the frequencies in the
closed loop converge to nominal operational frequency. We show that the load
sharing property of the generators is maintained, i.e., the input power of the
generators is proportional to a controller parameter. The controller is
evaluated by simulation on the IEEE 30 bus test network, where its
effectiveness is demonstrated.
