The energy transition is transforming electricity distribution networks, leading to increased congestion due to the rapid integration of decentralized renewable energy sources (RES) and electrification of demand. In this context, real-time congestion management (RTCM) is becoming essential. Aggregators, parties that coordinate distributed energy resources (DERs), are recognized as key enablers of RTCM due to their ability to dynamically shift load and respond to local grid conditions. However, current institutional and operational frameworks often fail to support their effective participation.

This thesis investigates how aggregator-based flexibility can be effectively activated and utilized for RTCM in distribution networks. Combining a literature review with expert interviews, the study identifies key design uncertainties, behavioural dynamics, and institutional barriers that currently hinder aggregator participation. These insights are synthesized into a functional coordination framework, outlining six core system functions required for effective RTCM, such as real-time communication, technical validation, transparent activation logic, and feedback mechanisms.

In parallel, a cost benchmark model is developed to estimate the financial bandwidth within which real-time activation strategies must operate. The model uses historical market data from aFRR and curtailment to evaluate the cost-effectiveness of flexibility deployment. Applied to the Dordtsche Kil region in the Netherlands, the simulation reveals that targeted real-time activation can significantly reduce average activation costs, but introduces exposure to price volatility.

The findings underscore that real-time flexibility deployment is not only a technical challenge but also an institutional and behavioural one. Key barriers identified include limited access to real-time grid data, the role of Balance Responsible Parties (BRPs), and lack of predictable compensation. These barriers foster risk-averse strategies among aggregators, reducing participation in existing mechanisms.

The study concludes that RTCM requires more than price signals or market access: it demands a robust system architecture that aligns technical feasibility with institutional rules and behavioural incentives. The proposed framework and benchmark model provide DSOs and policymakers with actionable tools to design and evaluate RTCM mechanisms. Recommendations include piloting the coordination framework in congested areas, investing in digital infrastructure (e.g., APIs and dashboards), and addressing BRP-related constraints through policy reforms.

Ultimately, this research contributes to the academic and societal discourse by proposing a structured, interdisciplinary approach to enabling aggregator-based flexibility in real-time distribution grid operations, thus supporting a more reliable, cost-efficient, and sustainable energy system.