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arxiv: 2606.17565 · v1 · pith:TREIDWHQnew · submitted 2026-06-16 · 📡 eess.SY · cs.SY

Stability Analysis in Large-scale Centralized Bidirectional Inverter-based Stations Connected to Bulk Power Systems through AC and DC Connections

Qiang Fu , Wenjuan Du , Siqi Bu , Haifeng Wang This is my paper

Pith reviewed 2026-06-26 23:22 UTC · model grok-4.3

classification 📡 eess.SY cs.SY
keywords stability analysisbidirectional invertersAC and DC connectionssubsynchronous oscillationsconverter-driven stabilitylarge-scale stationspower flow direction
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The pith

DC connections reduce subsynchronous oscillation risks in large-scale bidirectional inverter stations compared to AC when line resistance is low.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

This paper studies how large numbers of bidirectional inverter-based stations connected to power grids can trigger converter-driven instability in the subsynchronous range. It compares AC and DC connection types by varying the number of controlled DC resources, power flow direction, and inverter control settings. AC links can drive instability as station count rises no matter the power direction, leading to a calculated maximum stable power level. DC links lower the risk provided DC resistance stays much smaller than AC reactance, and adjusting controls improves stability more effectively in the DC case. The work concludes DC is better suited for high-voltage transmission and checks the result across mixed AC-DC setups and different grid sizes.

Core claim

Large-scale IBSs can cause SSO instability through AC connections as the number of CDCRs grows regardless of power flow direction, while DC connections reduce the instability if DC line resistance is much less than AC line reactance; control-parameter tuning is more effective at raising the critical stability limit under DC, so the DC-IBS configuration is preferred for high-voltage transmission.

What carries the argument

Side-by-side examination of AC versus DC connection effects on stability, driven by changes in the number of CDCRs, power-flow direction, and inverter control parameters.

If this is right

  • AC-connected IBSs require an upper limit on power amplitude to stay stable.
  • DC connections lower instability risk for high-voltage transmission.
  • Tuning inverter control parameters raises the stability limit more effectively when the connection is DC.
  • The stability advantage of DC holds across varied network topologies and system scales.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Grid planners might favor DC links when adding many battery or storage resources to avoid repeated stability studies for each added unit.
  • The same resistance-versus-reactance condition could be checked in medium-voltage distribution networks that also use many inverters.
  • Real-world validation would need to confirm that AC and DC cases truly differ only in the line impedance and not in unmodeled control or protection details.

Load-bearing premise

The comparison treats the inverter models, control structures, and network parameters as identical except for the choice of AC or DC connection.

What would settle it

A test system in which increasing the number of CDCRs produces growing subsynchronous oscillations under AC connection but not under an otherwise identical DC connection with low line resistance.

Figures

Figures reproduced from arXiv: 2606.17565 by HaiFeng Wang, Qiang Fu, Siqi Bu, Wenjuan Du.

Figure 1
Figure 1. Figure 1: Configuration of the AC- and DC-IBSs [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Configuration of the CDCR-k. The constant power control used by the DC-DC converter of CDCR-k is shown in [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: DC voltage control loop of the bidirectional inverter of the SM-k. Based on the control loops illustrated in [PITH_FULL_IMAGE:figures/full_fig_p003_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Relationship between the different coordinates. x-y coordinates, whereas (3) is expressed in the d-q coordinates [PITH_FULL_IMAGE:figures/full_fig_p004_4.png] view at source ↗
read the original abstract

Massive controlled DC resources (CDCRs), such as battery energy storage systems, are connected to AC power systems through bidirectional inverters for power balance requirements. This study investigates converter-driven stability (CDS) issues in the sub-synchronous frequency range caused by large-scale bidirectional inverter-based stations (IBSs). The impacts of the AC and DC connections of IBSs on subsynchronous oscillations (SSOs) are compared by examining three factors: the number of CDCRs, power flow direction, and control parameters of the inverters. For AC connections, IBSs may induce instability as the number of CDCRs increases, regardless of the power flow direction. To maintain stability, the maximum power amplitude of the IBS is calculated. It is found that switching to DC connections can reduce these instability risks if the DC line resistance is much less than the AC line reactance. Moreover, the method of tuning control parameters is demonstrated to be more effective in improving power-related critical stability under DC connections. Therefore, The DC-IBS is preferred for high-voltage transmission. Finally, the conclusions are validated in power systems connected with both AC- and DC-IBSs under various network topologies and system scales.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 1 minor

Summary. The paper analyzes converter-driven stability (CDS) and subsynchronous oscillations (SSOs) in large-scale bidirectional inverter-based stations (IBSs) connected to bulk power systems. It claims that AC-connected IBSs become unstable as the number of controlled DC resources (CDCRs) increases, independent of power-flow direction, and derives a maximum power amplitude to preserve stability. It further claims that DC connections mitigate these risks provided DC line resistance is much smaller than AC line reactance, that control-parameter tuning is more effective for power-related stability margins under DC connections, and that DC-IBS configurations are therefore preferable for high-voltage transmission. These conclusions are stated to have been validated across multiple network topologies and system scales.

Significance. If the small-signal models and cross-connection comparisons are rigorously established, the results would supply concrete design guidance on connection type and parameter tuning for large-scale battery and similar resources, potentially reducing SSO risk in future high-voltage transmission planning.

major comments (2)
  1. [Abstract (modeling and comparison claims)] The central attribution of stability improvement to the connection type (DC vs. AC) rests on the unverified premise that the underlying inverter models, PLL, current-control loops, and network parameters are identical except for the replacement of line reactance by resistance. No derivation or cross-check confirming that the DC-IBS state-space or impedance model is obtained from the AC-IBS model solely by this substitution is referenced in the abstract or validation statements.
  2. [Abstract (stability-limit and tuning claims)] The reported maximum power amplitude for AC connections and the claim that parameter tuning is “more effective” under DC connections are presented without explicit small-signal equations, eigenvalue loci, or impedance-based margins that would allow independent verification of whether these quantities are derived from first principles or fitted to specific control gains.
minor comments (1)
  1. [Abstract] The sentence beginning “Therefore, The DC-IBS …” contains an erroneous capital “The.”

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive comments, which help clarify the presentation of our modeling approach and results. We respond to each major comment below and indicate planned revisions to strengthen the manuscript.

read point-by-point responses

  1. Referee: [Abstract (modeling and comparison claims)] The central attribution of stability improvement to the connection type (DC vs. AC) rests on the unverified premise that the underlying inverter models, PLL, current-control loops, and network parameters are identical except for the replacement of line reactance by resistance. No derivation or cross-check confirming that the DC-IBS state-space or impedance model is obtained from the AC-IBS model solely by this substitution is referenced in the abstract or validation statements.

    Authors: We agree that the abstract does not explicitly reference the model equivalence. Sections II and III of the manuscript derive the small-signal state-space models for the inverters, PLL, and current-control loops identically for both AC- and DC-IBSs. The sole difference is in the network impedance term: the AC case uses line reactance X in the admittance matrix, while the DC case substitutes the line resistance R (with no imaginary component). This direct substitution is shown by comparing the network equations in both configurations. We will revise the abstract to note this model equivalence and add an explicit cross-reference to Sections II–III in the validation statements. revision: yes

  2. Referee: [Abstract (stability-limit and tuning claims)] The reported maximum power amplitude for AC connections and the claim that parameter tuning is “more effective” under DC connections are presented without explicit small-signal equations, eigenvalue loci, or impedance-based margins that would allow independent verification of whether these quantities are derived from first principles or fitted to specific control gains.

    Authors: The maximum power amplitude is obtained analytically in Section IV from the condition that the real part of the critical eigenvalue remains negative as the number of CDCRs increases; this follows directly from the system state matrix without fitting. The claim that tuning is more effective under DC connections is supported by comparative eigenvalue loci and participation-factor analysis in the same section, showing larger stability-margin shifts for the same gain changes when R_dc ≪ X_ac. These derivations are from first principles. The abstract summarizes the outcomes; to improve verifiability we will add a brief clause indicating that both the power limit and tuning comparison are obtained via small-signal eigenvalue analysis. revision: partial

Circularity Check

0 steps flagged

No circularity detected; abstract contains no derivation chain or equations

full rationale

The provided abstract summarizes conclusions on AC vs. DC connections and parameter tuning but includes no equations, state-space models, impedance derivations, or self-citations. No load-bearing steps can be inspected for reduction to inputs by construction, fitted parameters renamed as predictions, or self-citation chains. The claims are presented as validated across topologies, making the derivation self-contained against external benchmarks with no evidence of circularity in the given text.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Only abstract available; no free parameters, axioms, or invented entities can be extracted or audited.

pith-pipeline@v0.9.1-grok · 5754 in / 1045 out tokens · 24799 ms · 2026-06-26T23:22:10.312000+00:00 · methodology

discussion (0)

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Reference graph

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