Need for Enhanced Contingency-Dependent DER Aggregation Scheme for Transient Analysis in Modern Power Grid: A Case Study

The growing impact of distributed energy resources (DERs) on transmission operations has underscored the need for comprehensive modeling and simulation approaches in transient analysis. However, owing to their dispersed deployment, the DERs situated at varying locations "see" distinct grid conditions, potentially triggering individual protection and control responses during transmission-level contingencies. This requires modeling the DERs situated near fault locations with high fidelity, sometimes even individually, to accurately capture phenomena like voltage dips, while DERs beyond this boundary can be effectively aggregated. Consequently, there is a lack of investigation of the contingency-dependent DER behaviors in the literature. In this paper, we embark on the initial step in this direction, surpassing the conventional practice that typically aggregates a large number of DERs in distribution feeders using a single DER model at the point of common coupling. To that end, a hybrid EMT-phasor simulation platform for transmission-and-distribution systems is developed where the modified IEEE 39-bus system and the IEEE 33-node feeder with DERs represent the transmission and distribution systems, respectively. Then, the limitation of the commonly used single DER aggregated model for capturing the partial tripping of DERs and the need for an enhanced aggregation scheme is highlighted. Furthermore, the study proposes and demonstrates a preliminary contingency-dependent DER aggregation scheme utilizing hybrid time-domain simulation on the test system models. This pioneering endeavor leads to a promising trajectory for future research, which includes exploration into analytical and/or machine learning-based methodologies aimed at discerning the areas of interest where enhanced DER aggregation is needed.