A feasibility study of using MV and LV distributed energy resources flexibility in a TSO/DSO coordination perspective: the case study of Milan, Italy

The massive penetration of Renewable Energy Sources, preminently wind and photovoltaic power plants, and Distributed Energy Resources (DERs), such as Combined Heat and Power plants, Battery Energy Storage System, Electric Vehicles impose additional challenges in power system planning and operation. Pushing towards a low-carbon electricity system can increase potential issues such as congestion management, voltage control, controllability, observability, and generation-load forecasting. In this context, coordinated actions between Transmission System Operators (TSOs) and Distribution Systems Operators (DSOs) could be a valuable solution. For instance, through the DERs installed on the distribution network, the DSO could help the TSO to relieve a network contingency on the HV/HHV grid. This paper proposes a feasibility study of TSO-DSO coordination that allows using DERs to solve transmission network criticalities, both in operational and short- to medium-term time horizons, that does not involve the exchange of sensitive information between the two utilities. A straightforward algorithm is proposed for evaluating DERs available flexibility in terms of active and reactive power, and for estimating the aggregated capability curve at the point of common coupling, i.e., the flexibility available downstream a HV/MV substation. The proposed algorithm has been applied to Milan's case study using real data from Unareti, the local DSO, and Terna, the Italian TSO.