Coherency Identification for VSC Interfaced DERs Considering Network Topologies

Since a great share of renewables is integrated into the grids in the form of distributed energy resources (DERs) by Voltage Source Converters (VSCs), there is an increasing need to improve order-reduction techniques for analyzing grids due to the high order of VSCs. Coherency identification and equivalence is a method traditionally used for building reduced-order models of synchronous machines (SMs). With the electrification of power grids, there are researches focusing on the aggregation of VSCs. However, most of the existing researches assumed that all the VSCs are connected to one bus and only took control and filtering parameters into consideration. In this paper, certain network structures are also considered as control and filtering parameters in coherency identification. An order-reduced model for a distribution network with PQ-controlled VSCs integration considering network topologies is proposed. Kron reduction is conducted after coherency identification to simplify the model and intuitively show the relationship between the coherency of VSCs and the connection impedance. Finally, validations of the equivalent model are verified in a modified IEEE 33-bus distribution network model.