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arxiv: 1906.09295 · v1 · pith:GEXYOSTYnew · submitted 2019-06-21 · 📡 eess.SY · cs.SY· eess.SP

Impact of Distributed Energy Resources on Frequency Regulation of the Bulk Power System

Mohammad Khatibi , Sara Ahmed This is my paper

Pith reviewed 2026-05-25 18:33 UTC · model grok-4.3

classification 📡 eess.SY cs.SYeess.SP
keywords distributed energy resourcesvirtual inertiafrequency regulationrate of change of frequencypower system stabilityinverter controlbulk power system
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The pith

Adding virtual inertia to inverter-based distributed energy resources increases stability margin and prevents relay tripping by improving frequency response in bulk power systems.

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

The paper examines how rising shares of distributed energy resources reduce overall system inertia because of their intermittent output and inverter interfaces, which leads to faster frequency swings, oscillations, and reverse power flows that limit further integration. It proposes a control method that emulates virtual inertia in those inverters so they inject synchronized active power during transients. This emulation is claimed to raise the stability margin, allow the system to track its nominal frequency, and slow the rate of change of frequency enough to keep protection relays from operating. The approach is demonstrated on a sample grid that includes generation, transmission, and distribution stages and is checked with real-time simulation hardware.

Core claim

Implementing virtual inertia through inverter controls on distributed energy resources increases the stability margin of the bulk system, enables tracking of the rated frequency, and supplies synchronized active power that improves the rate of change of frequency, thereby keeping protection relays from tripping.

What carries the argument

Virtual inertia emulation added to inverter-based DER controls, which supplies synchronized active power during frequency events.

If this is right

  • The stability margin of the bulk power system increases under the proposed control.
  • The system tracks its rated frequency more closely during transients.
  • Rate of change of frequency improves, reducing the likelihood of protection relay trips.
  • The control can be implemented on existing inverter-based resources in a sample grid with generation, transmission, and distribution.

Where Pith is reading between the lines

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

  • Higher shares of DERs could be integrated without immediate upgrades to synchronous generation.
  • Protection settings on the bulk system might eventually need revision if the new dynamics differ from those assumed in current relay design.
  • Performance on very large interconnected grids would require testing beyond the sample system used here.
  • The method could be combined with existing synchronous machines to manage overall system inertia more flexibly.

Load-bearing premise

Virtual inertia from DER inverters can sufficiently replicate the stabilizing behavior of synchronous generators without creating new instabilities or requiring changes to existing protection schemes.

What would settle it

A measurement on a real bulk power system showing that frequency nadir or rate of change of frequency still exceeds relay thresholds after the virtual inertia control is applied to a representative share of DER inverters.

Figures

Figures reproduced from arXiv: 1906.09295 by Mohammad Khatibi, Sara Ahmed.

Figure 1
Figure 1. Figure 1: Multiple time-frame frequency response in a power system following a frequency event. proportional integral (PI) controllers. The BES and PV unit are connected in parallel and form the DC link. III. IMPACT OF DER ON FREQUENCY Since the power electronic interfaces used in DGs has no rotating mass and damping, the inertial constant in the micro￾grid is reduced which results in an increase in the rate of chan… view at source ↗
Figure 2
Figure 2. Figure 2: T&D combined system with VSG technologies. SPWM VPV Inverter Lf Cf Transformer Grid IPV ig vg + _ VDC DC/DC DC/AC Load DC/DC PWM Ibatt Vbatt Vabc* PLL Power Cal. VSG Control PI PI PI PI abc dq iq id vq vd dd dq abc dq ig vg vg f Q θ Er dq abc P ig vg Vabc* PWM VDC Ibatt PI PI VDC Ref VPV MPPT IPV D [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: General schematic representation of the proposed VSG controller. first stage, primary frequency is implemented in the same way as a SG. In the second stage virtual inertia and damping are [PITH_FULL_IMAGE:figures/full_fig_p003_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: General schematic representation of the proposed VSG controller. added to complete the loop. The result is a reference angle that will be fed into park transform [30]. VSG control can be divided into two sections. First, the mechanical swing equation needs to be emulated and solved numerically. Then the results are used as a reference to control the voltage and current of the inverter. A. P-F control Mecha… view at source ↗
Figure 6
Figure 6. Figure 6: Frequency deviation of the proposed system under different value of Tj and 0.2 p.u. step load [PITH_FULL_IMAGE:figures/full_fig_p005_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: System frequency with no DER, with DER and no inertia em￾ulation and with DER and inertia emulation respectively at 200MW [PITH_FULL_IMAGE:figures/full_fig_p005_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: Effect of DER with VSG on BES frequency. VI. CONCLUSION DERs have multiple negative impacts on the bulk power systems which have been addressed in the paper. In between, lower or zero inertia is one of their major aspects that will affect the stability of the whole power grid and may lead into unwanted load shedding. The solution for adding inertia to DERs by mimicking synchronous generation behavior is in… view at source ↗
read the original abstract

The growing penetration of distributed energy resources (DERs) has increased the complexity of the power system due to their intermittent characteristics and lower inertial response, such as photovoltaic (PV) systems and wind turbines. This restructuring of the power system has a considerable effect on the transient response of the system resulting in inter-area oscillations, less synchronized coupling and power swings. Furthermore, the concept of being distributed itself and generating electricity from multiple locations in the power system makes the transient impact of DERs even worse by raising issues such as reverse power flows. This paper studies some impacts of the changing nature of power system which are limiting the large scale integration of DERs. In addition, a solution to increase the inertial response of the system is addressed by adding virtual inertia to the inverter based DERs in the power system. The proposed control results in increasing the stability margin and tracking the rated frequency of the system. The injected synchronized active power to the system will prevent the protection relays from tripping by improving the rate of change of frequency. The proposed system operation is implemented on a sample power grid comprising of generation, transmission and distribution and results are verified experimentally through the Opal-RT real-time simulation system.

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 / 1 minor

Summary. The manuscript examines the impacts of rising DER penetration (e.g., PV and wind) on bulk power system frequency regulation, highlighting reduced inertial response, inter-area oscillations, weaker synchronization, power swings, and reverse power flows. It proposes a virtual-inertia control strategy implemented on inverter-based DERs that is claimed to enlarge the stability margin, track rated frequency, and raise RoCoF sufficiently to keep protection relays from tripping. The method is demonstrated on an unspecified sample grid comprising generation, transmission, and distribution and is validated via Opal-RT real-time simulation.

Significance. If the stability-margin and RoCoF improvements can be shown to hold under reproducible conditions, the work would address a practically relevant barrier to high renewable penetration. The choice of real-time simulation for verification is a methodological strength that could support claims of practical relevance, provided the grid model, control parameters, and relay thresholds are fully documented.

major comments (3)
  1. [Abstract] Abstract (and throughout): the central claim that virtual inertia 'increases the stability margin' and 'prevents the protection relays from tripping by improving the rate of change of frequency' is presented without any analytical derivation, small-signal stability analysis, or explicit RoCoF threshold calculation; the manuscript therefore provides no evidence that the improvement is load-bearing rather than an artifact of the chosen simulation scenario.
  2. [Simulation results section] Simulation results section: the sample power grid, DER penetration levels, virtual-inertia control parameters (e.g., inertia constant, damping), and protection-relay trip settings are never specified; without these quantities the reported frequency-tracking and relay-prevention outcomes cannot be reproduced or generalized beyond the single Opal-RT run.
  3. [Proposed control description] Proposed control description: no block diagram, transfer-function, or differential-equation model of the virtual-inertia controller is supplied, so it is impossible to verify whether the added inertia mimics synchronous-machine behavior or introduces new oscillatory modes.
minor comments (1)
  1. [Abstract] The abstract states that DERs raise 'issues such as reverse power flows' but never returns to this topic when describing the virtual-inertia solution; a brief clarification of scope would improve readability.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for the constructive feedback on our manuscript. The comments highlight important areas for improving rigor, reproducibility, and clarity. We address each major comment below and will revise the manuscript accordingly.

read point-by-point responses

  1. Referee: [Abstract] Abstract (and throughout): the central claim that virtual inertia 'increases the stability margin' and 'prevents the protection relays from tripping by improving the rate of change of frequency' is presented without any analytical derivation, small-signal stability analysis, or explicit RoCoF threshold calculation; the manuscript therefore provides no evidence that the improvement is load-bearing rather than an artifact of the chosen simulation scenario.

    Authors: We agree that the manuscript relies on simulation evidence without accompanying analytical support such as small-signal analysis or explicit RoCoF calculations. The Opal-RT results demonstrate the frequency and RoCoF improvements, but this does not substitute for a derivation showing the effect is general. In revision we will add a small-signal stability analysis section comparing the system with and without virtual inertia to substantiate the stability-margin claims. revision: yes

  2. Referee: [Simulation results section] Simulation results section: the sample power grid, DER penetration levels, virtual-inertia control parameters (e.g., inertia constant, damping), and protection-relay trip settings are never specified; without these quantities the reported frequency-tracking and relay-prevention outcomes cannot be reproduced or generalized beyond the single Opal-RT run.

    Authors: We acknowledge that the manuscript does not provide the full set of parameters needed for reproducibility. The sample grid topology, exact DER penetration levels, virtual-inertia constants (inertia and damping), and relay trip thresholds are missing. We will include a dedicated section with the complete grid model, all numerical parameters, and relay settings in the revised manuscript. revision: yes

  3. Referee: [Proposed control description] Proposed control description: no block diagram, transfer-function, or differential-equation model of the virtual-inertia controller is supplied, so it is impossible to verify whether the added inertia mimics synchronous-machine behavior or introduces new oscillatory modes.

    Authors: The controller is described only in text. We agree a block diagram and mathematical model are required to allow verification of its inertial behavior and to check for introduced modes. In the revision we will add a block diagram together with the transfer-function or state-space representation of the virtual-inertia controller. revision: yes

Circularity Check

0 steps flagged

No circularity detected; paper presents simulation-based verification without analytical derivations or self-referential reductions.

full rationale

The manuscript describes DER impacts on frequency regulation and proposes virtual inertia via inverter controls, with results verified through Opal-RT simulation on a sample grid. No equations, derivations, fitted parameters presented as predictions, or self-citation chains appear in the abstract or described content. Central claims rest on simulation outcomes rather than any self-definitional, uniqueness-imported, or ansatz-smuggled steps. This is a standard non-finding for simulation-focused papers lacking load-bearing mathematical chains.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 1 invented entities

Review based on abstract only; full modeling assumptions, control derivations, and validation details unavailable. Virtual inertia is introduced as a control addition without external validation beyond the described simulation.

axioms (2)
  • domain assumption Inverter-based DERs can be controlled to emulate synchronous generator inertia through active power modulation.
    Invoked in the proposal to add virtual inertia; central to the solution but not derived in the abstract.
  • domain assumption The sample power grid model captures the relevant transient dynamics of real bulk systems with DERs.
    Used to verify results experimentally; if false, the simulation outcomes may not generalize.
invented entities (1)
  • virtual inertia no independent evidence
    purpose: To increase the inertial response of inverter-based DERs and improve frequency regulation.
    Postulated control addition to address low inertia; no independent evidence such as predicted measurable quantities outside the simulation is provided.

pith-pipeline@v0.9.0 · 5739 in / 1357 out tokens · 27672 ms · 2026-05-25T18:33:42.497494+00:00 · methodology

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