Flexibility aggregation via set projection for distribution grids with multiple interconnections

TL;DR

The paper addresses coordination between a Transmission System Operator (TSO) and Distribution System Operators (DSOs) in distribution grids connected at multiple interconnection points by computing high-dimensional Feasible Operational Regions ($\mathcal{P}_i$) through set projection of subgrid constraint sets. It uses a Taylor-series linearized AC power-flow model to obtain convex polyhedral representations $\mathcal{X}_i$, and projects onto coupling variables $z_i$ to produce $A_i z_i \le b_i$ FORs that can be readily communicated to the TSO. The method yields a 7-dimensional FOR for two interconnections, illustrating how voltage magnitudes $v_k$ and angle differences $\theta_k$ influence feasible exchanges and demonstrating how the aggregated FOR captures interconnection coupling beyond single-point abstractions. Comparisons with AC-OPF sampling indicate the linearized FOR closely tracks the true region while offering a compact polyhedral form, with some boundary infeasibilities due to linearization that warrant careful handling in practice. The work lays out a practical framework for multi-interconnection FLEX aggregation and points to future improvements in linear formulations and projection efficiency to generalize to more complex grid topologies.

Abstract

With the increasing number of flexible energy devices in distribution grids, coordination between Transmission System Operators (TSOs) and Distribution System Operators (DSOs) becomes critical for optimal system operation. One form of coordination is to solve the overall system operation problem in a hierarchical way, computing Feasible Operational Regions (FORs) for the interconnection between TSO/DSO. Most methods for computing FORs rely on the assumption of only one interconnection point between TSO and DSOs, which is often violated in practice. In this work, we propose a method for computing FORs in distribution grids with multiple interconnection points to the transmission grid. We test our method in a grid with two interconnecting points and analyze the properties of the resulting high-dimensional FOR from a power systems perspective.

Figures (7)

• Figure 1: CIGRE medium voltage European grid cigre.
• Figure 2: Comparison of FORs obtained with AC-OPF sampling and the proposed linearized set projection method for a single interconnection point.
• Figure 3: Projected views for active and reactive power of the 7D-FOR for the case with two interconnection points.
• Figure 4: Visualization of the relationship between active power flows $p_{1,2}$ and $p_{16,15}$ based on the 7D-FOR projection.
• Figure 5: Total active and reactive power requirements for the three cases of the two-interconnection scenario, compared to the single-interconnection case.