  The ongoing integration of controllable distributed energy resources (DER)
makes distribution networks capable of aggregating flexible power and providing
flexibility services at both transmission and distribution levels. The
aggregated flexibility of an active distribution network (ADN) can be
represented as its feasible operating area in the P-Q space. The limits of this
area are pivotal for arranging flexibility markets and coordinating
transmission and distribution system operators (TSOs and DSOs). However,
motivated by the current technical limitations of distribution networks (e.g.,
protection schemes), existing literature on ADN flexibility and TSO-DSO
coordination mostly focuses on radial networks, overlooking the potential
benefits of network reconfiguration. This paper, using a realistic meshed
distribution system from the UK and the exact ACOPF model for flexibility
estimation, demonstrates that network reconfiguration can increase the limits
of ADN aggregated flexibility and improve the economic efficiency of
flexibility markets.
