Modal dynamic equivalent for electric power systems. I. Theory

The authors present the derivation of a second-order nonlinear dynamic equivalent for power systems based on modal analysis and on order reduction of the differential equations expressing the electromechanical behavior of the area being equivalenced. The equivalent is composed of a number of structures, easily represented in standard stability programs, known as modal generators, and defined for the retained modes of oscillation. The demonstrated order-reduction criterion demonstrated, is based on the rejection of the modes without significant electromechanical effect on the system external area response as seen from the interconnection buses.>