AC OPF-Based Methodology for Exploiting Flexibility Provision at TSO/DSO Interface via OLTC-Controlled Demand Reduction

Aimed to facilitate a safe massive integration of renewable energy sources in electric power systems, this paper explores an emerging demand reduction flexibility option which exploits the correlation between voltage and consumed power and is released upon the control of on-load tap changer (OLTC) transformers ratio at the interface between the transmission system operator (TSO) and distribution system operators (DSOs). Adopting a TSO view, the paper proposes a methodology for procuring the required amount of demand reduction to meet the active power balance needs on short term basis (i.e. up to tens of minutes). The core of the methodology integrates an AC optimal power flow (OPF), formulated as a mixed-integer nonlinear programing (MINLP) problem, tailored for this purpose. The interaction mode between the TSO and DSOs is discussed. The proposed methodology is illustrated on the Nordic32 system. The results obtained show the effectiveness of this promising flexibility option, which is able to reduce with up to 6 % the system load.