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Impact of Distributed Energy Resources on the Frequency Response of a Renewable Integrated Grid

Renewable energy sources, particularly distributed energy resources (DER), are playing an increasingly important role in the global energy landscape. However, in many power systems, DERs are connected to the same distribution feeder as loads, which can pose challenges in the event of a significant power outage. Specifically, activating the Under Frequency Load Shedding (UFLS) scheme can exacerbate frequency response by disconnecting DER-integrated feeders. To this end, a methodology is proposed in this study to assess the safe disconnection of DERs from a network in various DER penetration scenarios and under specific UFLS settings. The methodology is implemented on a modified version of the South Australian Test System (area 4) using the PSSE simulation platform. The results show that increasing DER integration decreases the allowable limit of DER disconnection to prevent blackout in the grid during an interconnection tripping event. Moreover, a negative linear correlation is observed between the maximum allowable disconnection level of DER and the level of DER penetration, as determined by linear regression analysis. From the relation, the safe operating zone of the DER integrated grid is defined to maintain frequency stability in the event of major power disturbance. This study can function as a useful asset during the grid planning stage for the secure integration of DER on the distribution feeders, taking frequency stability into consideration.