Sliding time windows assessment of storage systems capability for providing ancillary services to transmission and distribution grids

The continuous increase of Renewable Energy Sources (RESs) connected to distribution networks requires a careful review of the current regulatory framework to enable the provision of Ancillary Services (ASs) by these small-scale units. One of the envisaged options for coordinating Transmission System Operators (TSOs) and Distribution System Operators (DSOs) is the agreement and regulation of a scheduled power profile at the Primary Substation (PS). This means assigning the balancing responsibility to DSOs and, consequently, reducing the unpredictability of the power exchanges with the upstream transmission grid. The paper proposes a novel procedure for the management of Distributed Energy Storages (DESs) in order to provide ASs to both the DSO (local regulation of distribution network and congestion management) and the TSO (control of the power profile at the PS). The methodology, based on a sliding time window approach, evaluates the actual availability of each storage unit in providing ASs, assigns a scheduled profile and corrects it during the real-time operation. In addition, for each DES, the scheduled State of Charge (SoC) is restored in accordance with network constraints. Simulations on a realistic case study network are carried out considering randomly perturbed power profiles for both loads and generators. Benefits associated with storage coordination (power exchange management at the PS and support to DSO in voltage regulation and congestion resolution) are evaluated and discussed.