Dynamic equivalent model of active distribution networks providing frequency-related ancillary services to the transmission system

Nowadays, due to the large integration of converter-interfaced renewable energy sources (CI-RES), distribution networks progressively transform into active components of power systems, i.e., they transform into active distribution networks (ADN). In this new environment, ADN provide inertia and primary frequency response (PFR) as ancillary services (AS) to the transmission system. Under this new operational paradigm, conventional modeling approaches fail to simulate and analyze accurately the dynamic behavior of modern ADN under large frequency disturbances. Therefore, the scope of this paper is to formulate a new aggregated dynamic equivalent model for the representation of ADN in frequency stability studies. The proposed model receives as input the grid frequency and provides as output the active power variation of the examined ADN. The proposed model consists of several branches, allowing for the modeling and analysis of distinct frequency AS such as inertia and PFR. The performance of the proposed model is cross-validated using frequency responses, recorded during the system split event, occurred on the 8th of January 2021 in Continental Europe. Comparisons with conventional modeling approaches are also performed, highlighting the superior performance of the proposed aggregated equivalent.