Comparison of Clustering Methods for Aggregation of Distribution Grid Flexibility at the Nodes of an adjusted REI equivalent

In this paper different clustering methods to aggregate distribution grid flexibilities at the nodes of an adjusted REI equivalent are compared with each other. The adjusted REI equivalent enables the flexibility exchange between transmission and distribution system operator considering multiple vertical interconnections between them. First, a literature review identifies clustering methods whose clustering is based on distance matrices. In addition, a purely topological clustering method is developed. Second, the clustering methods are compared with each other on the basis of two high voltage (HV) test grids with multiple interconnections to an extra high voltage (EHV) grid. The evaluation criterion is the replication accuracy of the vertical active and reactive power potential called Feasible Operation Region (FOR). The complete grid model is used as a reference scenario. A distance matrix relying on power transfer distribution factors (PTDFs) proves to be the most promising.