  Active distribution networks (ADN) have grown considerably in recent years.
Distributed energy resources present in ADNs can provide flexibility to the
power system through TSO/DSO coordination, i.e., at the interface node (feeder)
between the transmission and distribution network. This paper addresses the
issue of calculating multi-period flexibility regions of the ADNs. Flexibility
regions are tightly dependent between periods and conditioned on the actual
deployment of such flexibilities in real-time. The existing state-of-the-art
has not provided a robust methodology for building multi-period flexible
regions. We present a new mathematical framework based on a non-iterative
formulation that considers the multi-period flexibility boundary points in a
single optimization problem. The proposed methodology is evaluated on IEEE
standard test networks and compared with the most widely used methods in the
literature.
