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Mapping Flexibility Region through Three-phase Distribution Optimal Power Flow at TSO-DSO Point of Interconnection

In the coming years, distributed energy resources (DERs) located at medium voltage (MV) and low voltage (LV) level will be employed as flexible resources to face the uncertainties and the operative problems introduced by renewable energy sources (RES) in power system management. Nevertheless, to unlock the potential of such resources, a coordinated operation between transmission (TSO) and distribution (DSO) system operators is needed. The methodology of flexibility region estimation well fits such need, since it allows to calculate active and reactive power that can be aggregated and released from the DSO to the TSO at the interface point, without violating any steady-state distribution grid constraint. This paper investigated the feasibility of implementing a flexibility region estimation routine based on formulation of an unbalanced three-phase optimal power flow (TOPF), suitable to deal also with LV resources and unbalanced distribution networks. The methodology is tested considering the detailed representation of a portion of an Italian distribution grid, comprising about six hundred MV/LV buses. The availability of both active and reactive flexibility resources has been considered.