I. Introduction
The continuous integration of distributed energy resources (DER) [1], specially renewable energy resources (RES), at the distribution grid level will lead to the development of new models and methodologies to deal with the uncertainty of these resources [2]. Hence, traditional methodologies for operation and management of the distribution grid must be replaced by new active management methodologies, by which distribution system operators (DSOs) can contract/control power generation/consumption (flexibility) from DER to solve congestion/voltage problems in the distribution network [3].