Coherency on electrical power systems

This paper proposes a new methodology to study coherency in power systems. The methodology is supported by a theoretical background and does not require the solution of the differential equations. The concept of weak coherency is defined as the coherency between a reduced gradient system associated to the power system equations. Many information can be derived from the weak coherency concept. One that is straightforward is the location of the unstable equilibrium points in the state space which can be very useful to improve transient stability analysis through direct methods.