Aggregated distribution grid flexibilities in subtransmission grid operational management

Abstract

Aggregated flexibilities or PQ-capabilities (active and reactive power capabilities) are termed in literature as Feasible Operating Regions (FORs). The FORs from underlying active distribution grids can effectively contribute to the operational management at the HV grid level. The HV buses are allocated aggregated FORs from the underlying MV grids, which are inherently nonlinear and non-convex. Therefore, two approaches are proposed in the paper to apply the FOR constraints in the HV grid operational management. First, a mixed integer linear programming (MILP) based optimization approach for alleviating the HV grid constraint violations is proposed, which addresses the non-convexity of the FOR using piecewise segmentation. Furthermore, the MILP method is enhanced to consider the influence of the HV bus voltage on the underlying MV grid flexibilities resulting in a three dimensional PQ(V)-FOR. Second, a convexification approach is proposed, which uses a convex approximation of the non-convex 3D PQ(V)-FOR shape for implementation in a linear optimization method. Results reveal a robust utilization of the distribution flexibilities to maintain grid security and reliability at the HV grid level. Comparisons present increased computation times for the MILP method which are significantly improved using the convexification based approach.

Figures (16)

• Figure 1: Schematic diagram representing aggregated FOR utilization for mitigating steady state HV grid problems.
• Figure 2: Linearization parameters for a schematic FOR segment
• Figure 3: A 3D PQ(V)-FOR depicted in discrete FOR slices, from a representative adaptation of the Cigré MV grid
• Figure 4: A piecewise segmentation of the 3D PQ(V)-FOR
• Figure 5: A convex representation of the 3D PQ(V)-FOR using triangulated segmentation of the convex envelope