Assessment of the Steady-State Security Region for Integrated Medium-Voltage and Low-Voltage Active Distribution Networks

The security region (SR) of a distribution network (DN) is typically characterized as a connected set consisting of nodal active and reactive power injections that ensure the operational security of the DN, and is an important security metric. With extensive integration of distributed photovoltaic systems into low-voltage (LV) DNs, recent studies advocate that medium-voltage (MV) DN security assessment should entail LV security constraints. However, assessing the SR for an integrated MV and LV (IMLV) DN is concerned little in prior studies and is a challenging task at both modeling and solution levels. Firstly, to address the issue of inaccuracies in LV DN models, a pre designed outlier-immune two-sided conservative linear approximation method is designed to recover the LV DN model with satisfactory accuracy for the subsequent assessment. Then, an SR assessment model based on two-stage robust optimization is proposed that incorporates the constraints related to network equipment and uncertainties. To reduce computational time, a feasible inexact column-and-constraint generation (FI-C&CG) algorithm is further designed. Case studies on different scales of multi-phase DNs demonstrate the necessity of considering the interaction between the MV and LV DNs when assessing the SR, and showcase the superior computational performance of the FI C&CG algorithm compared to the regular C&CG.