Three-Stage Flexibility Provision Framework for Radial Distribution Systems Considering Uncertainties

Transmission system operators (TSOs) are procuring increasing services through distributed energy resources (DERs), many of which are distribution-level renewable energy sources (RESs). However, RES inherent uncertainties have negative impacts on distribution system operations, which is a critical problem when distribution system operators (DSOs) respond to the TSO's flexibility requirement. This raises the question of how the DSO can arrange flexible resources in each different time stage so that the DSO can offer the preset flexibility at as little economic loss as possible. In this context, a novel three-stage flexibility provision framework for radial distribution systems considering uncertainties is proposed. In the first stage, the DSO responds to the TSO's specific flexibility requirement by scheduling priced-based demand response (PBDR), battery energy storage systems (BESSs), and electric vehicles (EVs) on a day-ahead (DA) horizon. In the second stage, the BESS and EV scheduling are re-optimized to respond to the most recent intraday short-term predictions of RESs and loads. In the third stage, real-time frequency control is provided by BESSs and EVs to alleviate frequency variations and power imbalance at the TSO-DSO interface. The simulation results on a modified IEEE 33-bus system demonstrate the effectiveness of the proposed flexibility provision framework.