Transient stability enhancement of multi-machine power systems: Synchronization via immersion of a pendular system

In this paper the problem of designing excitation controllers to improve the transient stability of multi-machine power systems is addressed adopting two new perspectives. First, instead of the standard formulation of stabilization of an equilibrium point, we aim here at the more realistic objective of keeping the difference between the generators rotor angles bounded and their speeds equal - which is called synchronization in the power literature - and translates into a problem of stabilization of a set. Second, we adopt the classical viewpoint of power systems as a set of coupled nonlinear pendula, and express our control objective as ensuring that some suitable defined pendula dynamics are (asymptotically) immersed into the power system dynamics. Our main contribution is the explicit computation of a control law for the two-machine system that achieves global synchronization. The same procedure is applicable to the n-machine case, for which the existence of a locally stabilizing solution is established.