Synchronic modal equivalencing (SME) for structure-preserving dynamic equivalents

A novel framework for dynamic equivalencing of interconnected power systems that the authors recently introduced in the context of classical swing-equation models is extended in this paper to detailed models in structure-preserving, differential/algebraic-equation form. The system is partitioned into a study area and one or more external areas on the basis of synchrony, a generalization of slow-coherency that forms one leg of their framework. Retaining a detailed model for a single reference generator from each external area, the dynamics of the remaining external generators are then modally equivalenced in the style of selective modal analysis; this modal equivalencing is the other leg of their framework. The equivalenced external generators are thereby collectively replaced by a linear multi-port "admittance", which is easily represented using controlled current injectors at the buses of the replaced generators. The rest of the system model can be retained in its original nonlinear dynamic form. The approach is tested-with encouraging results-on the familiar third-order, 10-machine, 39-bus New England model, using an implementation in the EUROSTAG simulation package.