Reviewing System Strength Metrics in IBR-Dominated Power Systems: Definitions, Principles, and Classifications

Yue ZHU; Zitian QIU; Andreas HADJILEONIDAS; Yunjie GU; Tim GREEN

doi:10.13648/j.cnki.issn1674-0629.2025.07.006

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South Power Sys Technol ›› 2025, Vol. 19 ›› Issue (7) : 72-89. DOI: 10.13648/j.cnki.issn1674-0629.2025.07.006

Special Column on Boao New Power System International Forum

Reviewing System Strength Metrics in IBR-Dominated Power Systems: Definitions, Principles, and Classifications

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Abstract

Along with the growing integration of renewable energy resources, the new power systems, which are dominated by inverter-based resources （IBRs）, are facing critical challenges in both planning and operation stages. The conventionally used system strength metric, short-circuit ratio （SCR）, exhibits limitations in assessing connections of new IBRs due to their unique dynamic behaviour and control interactions. In this paper, the definition of system strength is reviewed. The underlying principles of conventional SCR and its variants are then discussed, with their constraints explained. To describe the system strength in a more comprehensive way, this paper further classifies system strength into three categories: quasi-static, small-signal, and large-signal. For each category, relevant metrics are introduced and their relative merits are discussed. Electromagnetic transient simulations are presented to illustrate key insights.

Key words

system strength / short-circuit ratio / inverter-based resource / quasi-static system strength / small-signal system strength / large-signal system strength

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Yue ZHU , Zitian QIU , Andreas HADJILEONIDAS , et al . Reviewing System Strength Metrics in IBR-Dominated Power Systems: Definitions, Principles, and Classifications[J]. Southern Power System Technology. 2025, 19(7): 72-89 https://doi.org/10.13648/j.cnki.issn1674-0629.2025.07.006

References

List( Publishing order | Descend order by publishing year | Descend order by cited within ) Chart analysis

[1]	BLAABJERG F， CHEN Z， KJAER S B.Power electronics as efficient interface in dispersed power generation systems［J］. IEEE Transactions on Power Electronics， 2004， 19（5）：1184 - 1194. Cited in this article [1]

[2]	GU Y， GREEN T C. Power system stability with a high penetration of inverter-based resources［J］. Proceedings of the IEEE， 2022（1）： 356 - 367. Cited in this article [1]

[3]	International Energy Agency （IEA）. Global energy review 2021［R/OL］. （2021）［2025 - 04 - 10］. https：//www.iea.org/reports/global-energy-review-2021/renewables. Cited in this article [1]

[4]	HATZIARGYRIOU N， MILANO F， AJJARAPU V， et al. Definition and classification of power system stability – Revisited & extended［J］. IEEE Transactions on Power Systems， 2021， 36（4）： 3271 - 3281. Cited in this article [1]

[5]	FRANKEN B， ANDERSSON G. Analysis of HVDC converters connected to weak AC systems［J］. IEEE Transactions on Power Systems， 1990， 5（1）： 235 - 242. Cited in this article [2]

[6]	GAVRILOVIC A. AC/DC system strength as indicated by short circuit ratios［C］//International Conference on AC and DC Power Transmission， May 5 - 6， 1991， London， UK. New York： IEEE， 1991： 27 - 32. Cited in this article [1]

[7]

DAMANIK

， SAKINCI

Ö C

， GRDENIĆ

， et al. Evaluation of the use of short-circuit ratio as a system strength indicator in converter-dominated power systems［C］//2022 IEEE PES Innovative Smart Grid Technologies Conference Europe （ISGT-Europe）， November 12 - 14， 2022， Novi Sad， Serbia. New York： IEEE， 2022： 1 - 5.

[8]	NIMPITIWAN N， HEYDT G T， AYYANAR R， et al. Fault current contribution from synchronous machine and inverter based distributed generators［J］. IEEE Transactions on Power Delivery， 2007， 22（1）： 634 - 641.

[9]	LIU Y， CHEN Z. Short circuit ratio analysis of multi-infeed HVDC system with a VSC-HVDC link［C］//IECON 2011 - 37th Annual Conference of the IEEE Industrial Electronics Society， April 24 - 25， Melbourne， Australia. New York：IEEE， 2011： 949 - 954.

[10]	North American Electric Reliability Corporation （NERC）. Integrating inverter-based resources into low short circuit strength systems： Reliability guideline［R］. USA， 2017［2025 - 04 - 10］. https：//www.nerc.com/comm/RSTC_Reliability_Guidelines.

[11]	YAMADA Y， TSUSAKA A， NANAHARA T， et al. A study on short-circuit-ratio for an inverter-based resource with power-voltage curves［J］. IEEE Transactions on Power Systems， 2024， 39（4）： 6076 - 6086. Cited in this article [2]

[12]	IEEE. IEEE guide for planning DC links terminating at AC locations having low short-circuit capacities： IEEE Standard 1204 - 1997 ［S］. New York： IEEE， 1997. Cited in this article [1]

[13]	GONZALEZ J W， WEINDL C， HEROLD G， et al. Feasibility of HVDC for very weak AC systems with SCR below 1.5［C］//Proceedings of the 12th International Power Electronics and Motion Control Conference， May 23 - 25， Portoroz， Slovenia. New York： IEEE， 2006： 1522 - 1527. Cited in this article [1]

[14]	BADRZADEH B， EMIN Z， GOYAL S， et al. System strength［J］. CIGRE Science & Engineering， 2021（N20）： 5 - 27. Cited in this article [2]

[15]	Australian Energy Market Operator （AEMO）. System strength in the NEM explained［R/OL］. Australia， 2020［2025 - 04 - 10］. https：//aemo.com.au/-/media/files/electricity/nem/system-strength-explained.pdf. Cited in this article [2]

[16]	Australian Energy Market Commission （AEMC）. National electricity amendment （managing power system fault levels） Rule 2017 ［S］.Australia： Australian Energy Market Commission （AEMC）， 2017. Cited in this article [2]

[17]	GORDON S， BELL K， HONG Q. Implications of reduced fault level and its relationship to system strength： a Scotland case study［C］//CIGRE Session 2022， August 28- September 2， 2022， Paris， France. Paris： CIGRE，2022 ： Paper C 4 - 10204_2022. Cited in this article [1]

[18]	National Grid ESO. Provision of short circuit level data［R/OL］. 2022［2025 - 04 - 10］. https：//www.nationalgrideso.com/document/238741/download. Cited in this article [1]

[19]	XIAO H， ZHANG Y， DUAN X， et al. Evaluating strength of hybrid multi-infeed HVDC systems for planning studies using hybrid multi-infeed interactive effective short-circuit ratio［J］. IEEE Transactions on Power Delivery， 2020， 8977（c）： 1 - 1. Cited in this article [5]

[20]	WU D， LI G， JAVADI M， et al. Assessing impact of renewable energy integration on system strength using site-dependent short circuit ratio［J］. IEEE Transactions on Sustainable Energy， 2018， 9（3）： 1072 - 1080. Cited in this article [3]

[21]	CIGRE. Connection of wind farms to weak AC networks［R/OL］. Paris： CIGRE， 2016［2025 - 04 - 10］. https：//e-cigre.org/publication/671-connection-of-wind-farms-to-weak-ac-networks. Cited in this article [3]

[22]	DIgSILENT. Short-circuit analysis［M］//PowerFactory technical reference documentation. Chapter 26. Cited in this article [3]

[23]	International Electrotechnical Commission. Short-circuit currents in three-phase AC systems - part 0： calculation of currents： IEC 60909 - 0 ［S］. London， IEC， 2016. Cited in this article [1]

[24]	DE METZ-NOBLAT B， DUMAS F， POULAIN C. Calculation of short-circuit currents［J］. Cahier Technique， 2005（158）： 124 - 135. Cited in this article [1]

[25]	North American Electric Reliability Corporation. Short-circuit modeling and system strength white paper［R/OL］. New York： North American Electric Reliability Corporation， 2018［2025 - 04 - 10］. Cited in this article [1]

[26]	LUND T， WU H， SOLTANI H， et al. Operating wind power plants under weak grid conditions considering voltage stability constraints［J］. IEEE Transactions on Power Electronics， 2022， 37（12）： 15482 - 15492. Cited in this article [2]

[27]	DONG W， XIN H， WU D， et al. Small signal stability analysis of multi-infeed power electronic systems based on grid strength assessment［J］. IEEE Transactions on Power Systems， 2019， 34（2）： 1393 - 1403. Cited in this article [2]

[28]	ZHU Y， GREEN T C， ZHOU X， et al. Impedance margin ratio： a new metric for small-signal system strength［J］. IEEE Transactions on Power Systems， 2024， 39（6）： 7291 - 7303. Cited in this article [4]

[29]	HENDERSON C， EGEA-ALVAREZ A， KNEUPPEL T， et al. Grid strength impedance metric： an alternative to SCR for evaluating system strength in converter dominated systems［J］. IEEE Transactions on Power Delivery， 2024， 39（1）： 386 - 396. Cited in this article [1]

[30]	XIAO Y， ZHANG X， ZHAN X， et al. Design-oriented small-signal stability assessment of grid-following inverter-based resources based on virtual dynamic short-circuit ratio［J］. IEEE Transactions on Industrial Electronics， 2019， 1（2）： 432 - 445. Cited in this article [2]

[31]	GE Energy Consulting， Midcontinent Independent System Operator （MISO）. Minnesota renewable energy integration and transmission study （final report）［R/OL］. 2014［2025 - 04 - 10］. http：//mn.gov/commerce-stat/pdfs/mrits-report-2014.pdf. Cited in this article [1]

[32]	ZHANG Y， HUANG S H F， SCHMALL J， et al. Evaluating system strength for large-scale wind plant integration［C］//2014 IEEE PES General Meeting， November 11 - 15， 2014， National Harbor， MD， USA. New York： IEEE， 2014： 1 - 5. Cited in this article [1]

[33]	GU Y， LI Y， ZHU Y， et al. Impedance-based whole-system modeling for a composite grid via embedding of frame dynamics［J］. IEEE Transactions on Power Systems， 2021， 33（2）：1231 - 1242. Cited in this article [1]

[34]	ZHU Y， GU Y， LI Y， et al. Impedance-based root-cause analysis： Comparative study of impedance models and calculation of eigenvalue sensitivity［J］. IEEE Transactions on Power Systems， 2022， 15（1）： 567 - 583. Cited in this article [1]

[35]	ZHANG F， XIN H， WU D， et al. Assessing strength of multi-infeed LCC-HVDC systems using generalized short-circuit ratio［J］. IEEE Transactions on Power Systems， 2019， 34（1）： 467 - 480. Cited in this article [1]

[36]	HADJILEONIDAS A， ZHU Y， GREEN T C. Admittance margin： A guideline for placement of grid-following and grid-forming inverters regarding small-signal stability［C］//IECON 2024， February 10 - 13， 2024， Chicago， IL， USA. New York： IEEE， 2024： 1 - 6. Cited in this article [1]

[37]	ZHU Y， GU Y， LI Y， et al. Participation analysis in impedance models： the grey-box approach for power system stability［J］. IEEE Transactions on Power Systems， 2022， 37（1）： 343 - 353. Cited in this article [1]

[38]	Simplus Grid Tool［CP/OL］. 2025［2025 - 04 - 10］. https：//github.com/Future-Power-Networks/Simplus-Grid-Tool/tree/2023Mar14_SmallSignalStrength. Cited in this article [1]

[39]	ZHU Y， GU Y， DÖHLER J S， et al. Hybrid data/model-driven whole-system admittance identification via single-point injections［EB/OL］. TechRxiv， 2025 - 03 - 28. Cited in this article [1]