Equivalent circuit modeling of grid-forming inverters in (sub)-transient time-frame
File(s)
Published version
Author(s)
Gupta, Ambuj
Chaudhuri, Balarko
O'Malley, Mark
Type
Journal Article
Abstract
The widely accepted definition of grid-forming (GFM) inverter states that it should behave as a (nearly) constant voltage source behind an impedance by maintaining a (nearly) constant internal voltage phasor in the sub-transient to transient time frame. Some system operators further mandate permissible ranges for this effective impedance. However, these specifications do not clearly define the location of the internal voltage source, and no systematic method exists to quantify its effective impedance for a black-box GFM model. To address this, we first compare the transient responses of an ideal voltage source and a GFM to show that an idealistic GFM maintains a (nearly) constant voltage across the filter capacitor, rather than at the inverter switches. Then we propose a systematic method to quantify the effective impedance of a GFM from its black-box model using frequency-domain admittance plots. Using standard PSCAD GFM models developed by NLR (formerly NREL), we demonstrate that the GFM’s equivalent impedance model captures the sub-transient response and static voltage stability limit accurately. Further, replacing the GFM with the proposed equivalent circuit model in the modified IEEE-39 bus system is shown to reproduce the small-signal stability characteristics with reasonable accuracy.
Date Issued
2027-01-01
Date Acceptance
2026-06-20
Citation
Electric Power Systems Research, 2027, 262, pp.1-9
ISSN
0378-7796
Publisher
Elsevier
Start Page
1
End Page
9
Journal / Book Title
Electric Power Systems Research
Volume
262
Copyright Statement
© 2026 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)
License URL
Identifier
https://www.sciencedirect.com/science/article/pii/S0378779626008199
Source
Power Systems Computation Conference (PSCC)
Subjects
Constant internal voltage
Definition
Equivalent impedance
Frequency-domain admittance spectra
Grid-forming
Publication Status
Published
Start Date
2026-06-08
Finish Date
2026-06-12
Coverage Spatial
Limassol, Cyprus
Date Publish Online
2026-06-26