Flexibility Aggregation at Multiple Vertical Interconnections of Active Distribution Networks

This paper presents a methodology for aggregating feasible operation regions (FORs) across multiple vertical interconnections crossing various active distribution networks (ADNs). This enables TSO-DSO coordination for efficient use of flexibility even without detailed network information (e.g. network topologies). The determined FOR of a distribution network could be convex or non-convex. Non-convexity occurs when the distribution networks are operated in stressed conditions due to the quadratic characteristic of power losses, the nonlinear mapping between voltage phasors, power injections and operational constraints. During aggregation of FORs from different distribution networks there could be discrepancies when the input FORs are non-convex or a mix of convex and nonconvex FORs. The key novelty of this paper is a method which uses a decomposition-based Minkowski addition technique that can handle both convex and non-convex FORs as input, such that the aggregated FOR is a close estimation. The proposed method is tested on a modified CIGRE MV distribution network with higher penetration of distributed energy resources (DERs). The proposed methodology finds the exact aggregated FOR for exclusively convex input FORs. If the input FORs are non-convex, the proposed method splits the detected non-convex FOR into convex sub regions. The convex sub regions are aggregated and their hulls are used in the Minkowski summation, which results in a aggregated FOR.