Investigation of Relevant Distribution System Representation with DG for Voltage Stability Margin Assessment

TL;DR

This paper investigates how unbalanced distribution systems with high DER integration affect voltage stability margins, emphasizing the need for detailed modeling and co-simulation to accurately assess system stability.

Contribution

It demonstrates the impact of net-load unbalance and DER proliferation on voltage stability margin using T&D co-simulation with detailed distribution system modeling.

Findings

Higher unbalance reduces voltage stability margin.

DER proliferation in various phases affects system stability.

Volt/VAR control influences voltage stability margin.

Abstract

This paper emphasizes the importance of including the unbalance in the distribution networks for stability studies in power systems. The paper aims to: discuss the various simulation methods for power system analysis; highlight the need for modeling unbalanced distribution system for accurate load margin assessment; demonstrate the influence of net-load unbalance (NLU) on voltage stability margin (VSM). We also share a T&D co-simulation interface with commercial power system solvers. The distribution system is evolving rapidly with high proliferation of distributed energy resources (DERs); these are not guaranteed to proliferate in a balanced manner and uncertainty resulting due to these DERs is well acknowledged. These uncertainties cannot be captured or visualized without representing the distribution system in detail along with the transmission system. We show the impact of proliferation of DERs in various 3-phase proportions on voltage stability margin through T&D co-simulation. We also study the impact of volt/VAR control on voltage stability margin. This analysis is only possible by representing the distribution system in detail through T&D co-simulation. Higher percentage of net-load unbalance (NLU) in distribution system aggravates the stability margin of the distribution system which can further negatively impact the overall stability margin of the system.