Stabilization and voltage regulation of electric power systems with (P,Q) load buses preserved

The mathematical model for the power networks we are considering consists of the electromechanical dynamic equations at generation buses and the nonlinear algebraic active and reactive power equations at (P,Q) load buses. The resulting nonlinear model is treated as such; no resort to linearization around operating points is taken. The control strategy we propose is, in fact, meant for true emergency situations when large variations in reactive power demand and structural changes in the network occur. We stress, however, that the resulting nonlinear controls coincide around stable operating points with linear controls designed on the basis of linearizations around those points.