Counterintuitive VSM Behavior under CVR Incorporating Distribution System

TL;DR

This paper investigates how conservation voltage reduction (CVR) unexpectedly decreases voltage stability margin (VSM) by increasing effective impedance, supported by co-simulation results on IEEE systems and theoretical analysis.

Contribution

It provides a novel theoretical explanation for the counterintuitive VSM reduction under CVR and validates it through extensive T&D co-simulation results.

Findings

VSM decreases under CVR conditions.

Effective impedance increases with CVR, reducing stability margin.

Results confirmed on IEEE 9-bus and 123-bus systems.

Abstract

This paper analyses the impact of conservation by voltage reduction (CVR) on voltage stability margin (VSM) considering transmission and distribution (T&D) systems. VSM is determined by P-V curve analysis using PSSE and GridLAB-D solvers to co-simulate the T&D systems under CVR and No CVR conditions. ZIP loads with profile [ZIP] = [0.4 0.3 0.3] are used to model the load. The paper discusses the counterintuitive result: under CVR, the VSM is reduced. Theoretical justification for the reduced VSM under CVR is the increase in the effective impedance between generation and load and this is proved using an extended 2-bus system. The paper shares T&D co-simulation results with IEEE 9-bus transmission system and a larger 123-bus distribution system and with distributed generation (DG) in unity power factor (UPF) and volt-VAR control (VVC) mode.