Uncertainty-Aware TSO-DSO Coordination Methodology for Transmission Voltages Control

This paper proposes a new coordination methodology between the Transmission System Operator (TSO) and Distribution System Operators (DSOs), which enables the optimal usage by the TSO of reactive power flexibility from active distribution systems (ADSs), as an additional option to control voltages in the transmission system. The proposed methodology addresses day-ahead operation planning in three successive steps: 1) the quantification by DSOs of the reactive power flexibility range and associated cost at the interfaces with the TSO, 2) voltage control at TSO level through reactive power dispatch, including reactive power flexibility offered by the DSOs, and 3) optimal re-dispatch of flexible resources by DSOs to maintain the committed active/reactive power schedule at their TSO-DSO interface without breaching operation constraints of the ADSs. The methodology goes beyond the state-of-the-art by considering renewable generation uncertainties for both TSO and DSO, N-1 security for TSO, and temporal inter-links of emerging flexible resources, such as flexible loads (FL) and energy storage systems (ESS), for DSO. The proposed methodology solves stochastic multi-period AC security-constrained optimal power flow (S-MPSCOPF) for TSO and stochastic multi-period AC optimal power flow (S-MP-OPF) for DSO, both problems being formulated as non-linear programs (NLPs). The usefulness of the proposed methodology is demonstrated on a 60-bus transmission system that contains five interfaces to 34-bus ADSs.