Feasibility and flexibility regions estimation at TSO-DSO interconnection node using grid structure optimization

Major integration of renewable energy has raised the requirement of frequency and voltage control ancillary services. This necessitates to utilize distributed energy resources for grid flexibility solutions. Aggregated DERs' flexibility at TSO-DSO node, identified by flexibility operating regions, can provide these services to the grid. Estimating the actual shape of the flexibility region for both slow and fast response systems, is important for real-time applications. However, correct estimation of this region is challenging due to its dependence on various factors, its non-convex shape, and high computational requirements. Proposed novel methodology named 'Grid Structure Optimization' can estimate the actual shape of the flexibility region for both slow and fast response systems without any prior shape approximation. The proposed approach is tested on modified IEEE 9 and 33 bus systems considering impacts of Q/P ratio, market dispatch point, cost and type of market. Results highlight the efficacy of this approach for real-time applications as the shape of the region completely avoids the possibility of infeasible points in the region. The results also indicate that the cost willingness is a factor of nonconvexity on the feasibility region. Furthermore, the proposed approach is demonstrated to identify DER's flexibility for contingency-based frequency control ancillary services. (c) 2022 Elsevier Ltd. All rights reserved.