A new concept of an aggregate model for tertiary control coordination of regional voltages

A theoretical formulation of a discrete process representing regulation of steady-state voltages over midterm horizons is introduced. The main interest is in regulating critical steady-state voltages in response to significant load and generation variations under the assumption that the system is transiently stable. The practical motivation for this work comes from the need to study coordination of different electrically connected regions of the French power network. The discrete process representing a sequence of steady-state voltages over a midterm horizon is only system input (load and control) driven, since the natural response is assumed to be stable and instantaneous. The fact that only controls drive the process leads to many interesting results in postulating an aggregate model for coordinating very-large-scale power systems. It is shown in a theoretically rigorous way that the natural coordinating variables are reactive power flows among the regions.