Extensions, simplifications, and tests of synchronic modal equivalencing (SME)

Synchronic modal equivalencing (SME) is aimed at structure-preserving dynamic equivalencing of large power system models. SME is motivated by the slow-coherency method for system partitioning and aggregation, but its formulation and associated computational algorithms are more general in some important respects. Ideal synchrony of a group of generators requires the motion of each generator in the group to be a linear combination of the motions of a fixed set of basis generators in the group, when some subset of the system modes (not necessarily the slowest) is excited. SME keeps intact the dynamic models of all the generators in a synchronic study group and of all the basis generators external to this group. The model of each remaining generator is replaced by a simple nondynamic linear circuit containing a dependent current source driven by the motions of the basis generators. The remainder of the network can be left unmodified. Previous numerical tests of SME have been limited to relatively small and simple models. This paper makes the transition to a detailed, intermediate-sized model, while also introducing certain extensions and simplifications that open the door to experiments with much larger models. A recommended SME procedure is specified in the gaper, and illustrated with tests performed using the simulation package EUROSTAG and a model loosely based on the France-Spain power system. The unreduced model has 23 generators, 83 buses, and 476 state variables; the model is reduced in a structure-preserving way to 10 generators and 255 state variables, with very good results.