Two-stage Approach for the Provision of Time-Dependent Flexibility at TSO-DSO Interface

In this paper, a new methodology is presented for the provision of active and reactive power flexibility at the transmission and distribution system operator (TSO-DSO) interface. Its distinct feature is the effective integration of time-dependent flexibility resources, e.g., energy storage systems, thus moving a step closer to the accurate modeling of active distribution grids. The proposed methodology is part of the day-ahead analysis and is divided into two main stages. In the first stage, an iterative, optimization-based process is adopted to estimate the hourly flexibility areas at the TSO-DSO interface that maximize the daily flexibility capacity of the distribution grid. These areas can be used in the day-ahead scheduling of the electrical grid to determine the optimal power set-points at the TSO-DSO boundary nodes. The second stage is introduced to optimally coordinate the operation of the main network elements to meet the above set-points. The validity of the proposed methodology is demonstrated by performing simulations on a medium-voltage grid with radial configuration.