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arxiv: 2605.23041 · v1 · pith:VE2ZUH2Dnew · submitted 2026-05-21 · 📡 eess.SY · cs.SY

Holistic Grid-Forming Control to Enhance the Frequency Support from HVDC-Connected Offshore Wind Power Plants

Zhenghua XU , Dominic Gro{\ss} , George Alin Raducu , Behnam Nouri , Oscar Sabor\'io-Romano , Nicolaos A. Cutululis This is my paper

Pith reviewed 2026-05-25 05:27 UTC · model grok-4.3

classification 📡 eess.SY cs.SY
keywords grid-forming controlHVDCoffshore wind power plantfrequency supportinertial responsefrequency containment reserveconverter controlpower system stability
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0 comments X

The pith

Coordinating grid-forming controls across all AC and DC terminals of an HVDC-linked offshore wind plant improves frequency support without communication.

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

The paper develops a model of a typical HVDC-connected offshore wind power plant and proposes coordinated grid-forming controls at every terminal. An analytical tuning method identifies upper bounds on bandwidth at each terminal to achieve faster response to frequency events. Simulations compare the approach against other configurations and show quicker frequency support with less use of each converter's stored energy. A sympathetic reader would care because rising shares of power electronics reduce natural inertia, and this method lets existing HVDC assets contribute inertial response and frequency containment reserve more effectively.

Core claim

The central claim is that the proposed holistic grid-forming control coordinates the GFM implementations at all AC and DC terminals of the HVDC-OWPP system without requiring communication. By formulating controllers from the developed system model and applying analytical tuning that respects identified bandwidth upper bounds, the control achieves faster response and more effective frequency support while minimizing utilization of the inherent energy storage of each converter.

What carries the argument

Holistic grid-forming control that coordinates GFM at all AC and DC terminals without communication, using analytical bandwidth bounds derived from the system model.

If this is right

  • The OWPP can deliver inertial response and frequency containment reserve more rapidly than uncoordinated controls.
  • Converter energy storage is used less for the same level of frequency support.
  • No communication links are needed between terminals for the coordination to function.
  • The approach supports a design philosophy focused on coordinated converter control in power-electronics-dominated systems.

Where Pith is reading between the lines

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

  • Similar coordination might extend frequency support benefits to other multi-terminal HVDC configurations beyond offshore wind.
  • The minimized energy storage use could lower the sizing requirements for DC-link capacitors in future designs.
  • If the bandwidth bounds hold, operators could tune plants for tighter frequency limits without hardware additions.

Load-bearing premise

The system model developed for control design accurately represents the dynamics of the HVDC-OWPP at the relevant time scales, and the analytical upper bounds on bandwidth at each terminal remain valid under real operating conditions without communication.

What would settle it

A frequency disturbance test on the HVDC-OWPP model where the holistic control fails to produce a lower frequency nadir or slower rate of change of frequency than the best-performing individual-terminal GFM configuration.

Figures

Figures reproduced from arXiv: 2605.23041 by Behnam Nouri, Dominic Gro{\ss}, George Alin Raducu, Nicolaos A. Cutululis, Oscar Sabor\'io-Romano, Zhenghua Xu.

Figure 1
Figure 1. Figure 1: A typical point-to-point HVDC-OWPP system. (a) Single-line schematic diagram. (b) Equivalent circuit (three-phase systems are in bold). (c) Block [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Generic monopole MMC with half-bridge submodules [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 4
Figure 4. Figure 4: Generic type-4 WTG. B. OWPP A generic model of a type-4 WTG shown in [PITH_FULL_IMAGE:figures/full_fig_p004_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Controllers of the improved holistic GFM control. (a) Controller for the onshore and offshore MMCs ( [PITH_FULL_IMAGE:figures/full_fig_p005_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: Transient response of the HVDC-OWPP system under the improved holistic GFM control for an under-frequency event. [PITH_FULL_IMAGE:figures/full_fig_p006_6.png] view at source ↗
Figure 9
Figure 9. Figure 9: DC voltage control of the onshore or offshore MMC ( [PITH_FULL_IMAGE:figures/full_fig_p007_9.png] view at source ↗
Figure 8
Figure 8. Figure 8: Tuning by loop shaping (high-frequency range omitted for brevity). [PITH_FULL_IMAGE:figures/full_fig_p007_8.png] view at source ↗
Figure 11
Figure 11. Figure 11: Performance comparison among the proposed holistic GFM control [PITH_FULL_IMAGE:figures/full_fig_p009_11.png] view at source ↗
Figure 10
Figure 10. Figure 10: Simulation results of FCR and inertial response provision by the [PITH_FULL_IMAGE:figures/full_fig_p009_10.png] view at source ↗
read the original abstract

To address the frequency stability challenges posed by the rising penetration of power electronics in power systems, HVDC-connected offshore wind power plants (OWPPs) are increasingly expected to provide inertial response and frequency containment reserve (FCR). In this paper, an improved holistic grid-forming (GFM) control is proposed, aiming to enhance the frequency support by coordinating the GFM controls implemented at all AC and DC terminals of an HVDC-OWPP system, without requiring communication. Firstly, the model of a typical HVDC-OWPP system is developed for control design. Accordingly, the proposed controllers are formulated, followed by an analytical tuning method, where the upper bound of the bandwidth at each AC or DC terminal is identified. Finally, simulations are conducted to verify the functionality and compare the performance with that of representative control configurations. The results show that the proposed holistic GFM control achieves faster response and thus more effective frequency support, while the utilization of the inherent energy storage of each converter is minimized, thereby supporting a new design philosophy for converter control in converter-dominated systems.

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

3 major / 2 minor

Summary. The paper develops a system model for an HVDC-connected offshore wind power plant (OWPP), proposes a holistic grid-forming (GFM) control coordinating AC and DC terminals without communication, derives analytical upper bounds on bandwidth at each terminal for tuning, and presents simulations claiming faster frequency response with minimized converter energy storage use compared to representative configurations.

Significance. If the analytical tuning procedure and simulation results hold under realistic conditions, the work would offer a communication-free coordination method for frequency support from HVDC-OWPPs that leverages inherent converter energy storage more efficiently. The model-based bandwidth bounds represent a structured design approach, but the absence of explicit robustness validation against model mismatch limits the strength of the performance claims.

major comments (3)
  1. [Simulation results section] Simulation results section: The central claims of faster response and minimized energy storage utilization rest on simulations whose setup details (e.g., exact baselines, parameter values, disturbance types) are not fully specified, and no error bars, statistical measures, or Monte Carlo sweeps are reported to quantify improvement or confirm that the derived bandwidth upper bounds remain valid under plant deviations from the linearized model.
  2. [Analytical tuning method] Analytical tuning method (following controller formulation): The upper bounds on bandwidth at each terminal are derived directly from the developed HVDC-OWPP system model; however, no targeted robustness tests (e.g., against unmodeled dynamics, parameter drift, or nonlinear effects) are provided to demonstrate that these bounds do not induce instability or excess storage use when the real plant differs from the design model, which is load-bearing for the no-communication coordination claim.
  3. [System model section] System model section: The model is used both to formulate the holistic GFM controllers and to obtain the bandwidth bounds, yet the manuscript provides no explicit validation (e.g., comparison against detailed EMT simulations or measured data) that it accurately captures the relevant dynamics at the time scales of inertial response and FCR.
minor comments (2)
  1. [Abstract] The abstract states performance improvements without any quantitative metrics, error measures, or specific comparison cases, which reduces clarity on the magnitude of the claimed benefits.
  2. Notation for the bandwidth bounds and energy storage utilization metrics could be introduced more explicitly with cross-references to the equations defining them.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for the constructive comments and detailed review. We address each major comment point by point below, proposing revisions to enhance clarity and strengthen the claims where the concerns are valid.

read point-by-point responses

  1. Referee: [Simulation results section] Simulation results section: The central claims of faster response and minimized energy storage utilization rest on simulations whose setup details (e.g., exact baselines, parameter values, disturbance types) are not fully specified, and no error bars, statistical measures, or Monte Carlo sweeps are reported to quantify improvement or confirm that the derived bandwidth upper bounds remain valid under plant deviations from the linearized model.

    Authors: We agree that additional details on the simulation setup will improve reproducibility and support the claims. In the revised manuscript, we will add a table listing all system and controller parameters, explicitly define the baseline configurations (local GFM without coordination and uncoordinated DC-side GFM), and describe the disturbance (onshore load step of 0.2 pu). We will also include a sensitivity study with parameter variations to illustrate that the bandwidth bounds maintain performance under deviations from the nominal linearized model. revision: yes

  2. Referee: [Analytical tuning method] Analytical tuning method (following controller formulation): The upper bounds on bandwidth at each terminal are derived directly from the developed HVDC-OWPP system model; however, no targeted robustness tests (e.g., against unmodeled dynamics, parameter drift, or nonlinear effects) are provided to demonstrate that these bounds do not induce instability or excess storage use when the real plant differs from the design model, which is load-bearing for the no-communication coordination claim.

    Authors: The bandwidth upper bounds are derived to guarantee closed-loop stability margins from the linearized model. We will revise the tuning section to include a new robustness subsection with nonlinear simulations under parameter drift (e.g., ±15% variation in DC-link capacitance and AC line reactance) and unmodeled dynamics (e.g., added PLL effects). These tests will confirm that the coordinated control remains stable and does not increase energy storage utilization beyond the reported levels. revision: yes

  3. Referee: [System model section] System model section: The model is used both to formulate the holistic GFM controllers and to obtain the bandwidth bounds, yet the manuscript provides no explicit validation (e.g., comparison against detailed EMT simulations or measured data) that it accurately captures the relevant dynamics at the time scales of inertial response and FCR.

    Authors: The model uses standard averaged representations suitable for inertial and FCR timescales, consistent with established literature. We will update the system model section with a direct comparison of the proposed model against EMT simulation results for a frequency step disturbance, demonstrating agreement in active power and frequency trajectories over 0.5–10 s. This will explicitly validate the model's accuracy for the control design purposes. revision: yes

Circularity Check

0 steps flagged

Model-based derivation is self-contained with no circular reductions

full rationale

The paper first develops the HVDC-OWPP system model for control design, then formulates the holistic GFM controllers and derives analytical upper bounds on bandwidth from that model. Simulations are used only for verification and comparison. No equations or claims reduce by construction to fitted inputs, self-definitions, or load-bearing self-citations; the tuning procedure is independent of the target performance metrics it is later shown to achieve. This is standard model-driven control synthesis and scores as fully self-contained.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim depends on the accuracy of the developed system model and the validity of the analytical bandwidth tuning method; no free parameters or invented entities are identified from the abstract.

axioms (1)
  • domain assumption The model of a typical HVDC-OWPP system developed for control design captures the relevant dynamics for frequency support analysis.
    Stated as the first step before controller formulation and tuning.

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discussion (0)

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