  This article presents an exciting finding for the power industry: the
parameters of secondary frequency control based on integral or proportional
integral control can be tuned to achieve economic operation and frequency
regulation simultaneously. We show that if the power imbalance is represented
by frequency deviation, an iterative dual decomposition based economic dispatch
solving is equivalent to integral control. An iterative method of multipliers
based economic dispatch is equivalent to proportional integral control.
Similarly, if the controller parameters of the secondary frequency controls are
chosen based on generator cost functions, these secondary frequency controllers
achieve both economic operation and frequency regulation simultaneously.
