Abstract
Achieving carbon neutral power systems is pushing for higher penetration of distributed energy resources (DER) in existing distribution systems. Accordingly, sophisticated, yet, practical tools for the optimal operation and management of active distribution systems (ADS) are in high need. In response to this necessity, this paper presents a novel and scalable tool for ancillary services procurement by distribution system operators (DSOs). The developed tool takes into consideration the inter-temporal and variable nature of DER in an uncertainty-aware approach. This tool is also suited for real-world implementation with large ADS, as it adopts a sequential linearization approach. As such, it allows DSOs to procure flexibility optimally from DERs embedded in ADS in the day-ahead operation planning timeframe, where congestion and voltage issues are managed.

Abstract
This paper proposes a new decentralized framework for distribution system operators (DSO) to evaluate the network feasibility of the aggregators' bids and remunerate them in case of providing network support services. Compared to other state-of-the-art approaches, this framework is characterized as being more efficient in terms of communication and computational requirements, which is a great advantage for real world applications. The new framework includes a novel optimization model to decide if aggregators' bids should be curtailed or not to ensure network security and minimize DSO costs. To evaluate and compare the proposed DSO framework against the current one, we used the IEEE 69-bus network with three aggregators of distributed energy resources (DER) from the Iberian electricity market. Our experiments show that the proposed DSO framework ensures distribution network security, while the current framework in place in the Iberian Peninsula does not. In addition, we also studied three curtailment policies for the new DSO framework. The results show that minimizing curtailment costs is the most cost-effective policy for the DSO, compared to the other two policies focused on minimizing linear and squared curtailments.