Smart Grids and Sustainability in the Age of PMSG-Dominated Renewable Energy Generation

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper is very interesting; the following corrections are necessary:

1. The internal lettering in many figures is excessively large, for example in Figures 1 and 2. It is recommended to adjust the font size so that it is proportional to the typography used in the body text of the article.

2. In the results figures, both the axis numbers and the axis labels are too small, which affects readability. Their size should be increased to facilitate interpretation of the data.

3. The results are plotted using very thin lines, which makes the signals difficult to distinguish. It is recommended to increase the line thickness to improve the clarity of the presented results.

4. The technical contribution of the article needs to be stated more clearly in the abstract and introduction, explicitly highlighting the original contribution in comparison with previous studies.

5. The system model employed is highly simplified for drawing broad conclusions about resilience in next-generation grids. At least one additional scenario with demand variability or multiple PMSG units should be included to improve representativeness.

6. The resilience assessment relies solely on instantaneous electrical metrics. It is recommended to justify this choice or incorporate additional indicators that strengthen the validity of the analysis.

7. The interaction among the VSG, BESS, and STATCOM controllers requires deeper explanation, describing the mechanisms that enable the combined performance improvement and the conditions under which such synergy may not occur.

8. The parameters and capabilities of the BESS are not presented in sufficient detail. A table with the values used in the simulations should be included to allow correct interpretation of the dynamic behavior.

9. A sensitivity analysis of the control parameters is missing and is necessary to evaluate robustness. Including it, at least for one representative scenario, is recommended.

10. The discussion should incorporate a more critical perspective, identifying limitations of the proposed approach and potential trade-offs, such as cost, complexity, or maintenance issues of the hybrid system.

11. The cybersecurity section is disconnected from the numerical results. It would be useful to link it to concrete scenarios involving PMSG-based systems or to include at least a preliminary analysis in the simulations.

12. The conclusions present broad recommendations without considering economic, regulatory, or technological constraints. It is recommended to moderate the scope of these statements or support them with additional evidence.

Author Response

Response to Reviewer

We sincerely thank the reviewer for the careful evaluation of our manuscript and for the constructive and insightful comments. The suggestions have significantly contributed to improving the clarity, technical depth, and overall quality of the paper. All comments have been carefully considered, and the manuscript has been revised accordingly. Our point-by-point responses are provided below.

Comment 1

The internal lettering in many figures is excessively large, for example in Figures 1 and 2.

Response:
The font sizes of the internal lettering in Figures 1 and 2 have been corrected and scaled proportionally to the typography of the main text. This adjustment ensures visual consistency and improves overall readability.

Comment 2

In the results figures, both the axis numbers and the axis labels are too small.

Response:
The resolution and formatting of all result figures have been improved. The axis labels and numerical ticks have been enlarged to enhance readability and facilitate correct interpretation of the results.

Comment 3

The results are plotted using very thin lines, which makes the signals difficult to distinguish.

Response:
The line thickness in all result figures has been increased. This modification improves signal visibility and allows for clearer distinction between different control strategies.

Comment 4

The technical contribution of the article needs to be stated more clearly in the abstract and introduction.

Response:
The Abstract has been rewritten to explicitly emphasize the original technical contributions of the paper. Additionally, a new paragraph has been added at the end of the Introduction to clearly position the proposed work with respect to existing studies and to highlight its novelty.

Comment 5

The system model employed is highly simplified for drawing broad conclusions about resilience.

Response:
An additional dynamic scenario has been incorporated into the study, involving three PMSG units with heterogeneous inertia constants operating under variable load conditions. The Abstract, Discussion, and Conclusions sections have been revised accordingly to reflect the extended scope and improved representativeness of the analysis.

Comment 6

The resilience assessment relies solely on instantaneous electrical metrics.

Response:
This methodological choice has now been explicitly justified in the manuscript. The Discussion section has been expanded to explain why instantaneous electrical metrics are appropriate for converter-dominated systems, and to outline future research directions that will include complementary resilience indicators.

Comment 7

The interaction among the VSG, BESS, and STATCOM controllers requires deeper explanation.

Response:
The Discussion section has been substantially expanded to provide a clearer explanation of the interaction mechanisms between the VSG, BESS, and STATCOM controllers. The synergistic effects, coordination requirements, and operating conditions under which such synergy may be reduced are now discussed in detail.

Comment 8

The parameters and capabilities of the BESS are not presented in sufficient detail.

Response:
A dedicated table summarizing the BESS parameters and operational limits has been added to the Case Study and Simulation Analysis section. This addition allows for transparent interpretation of the dynamic behavior of the system.

Comment 9

A sensitivity analysis of the control parameters is missing and is necessary to evaluate robustness.

Response:
A sensitivity analysis of the key VSG control parameters has been performed and added at the end of the Case Study and Simulation Analysis section. The analysis includes both a quantitative discussion and a summary table for a representative scenario.

Comment 10

The discussion should incorporate a more critical perspective, identifying limitations and potential trade-offs.

Response:
The Discussion section has been expanded to explicitly address the limitations and trade-offs of the proposed hybrid control approach, including implementation complexity, cost considerations, scalability, and maintenance aspects.

Comment 11

The cybersecurity section is disconnected from the numerical results.

Response:
A new cyber-physical disturbance scenario has been developed and included in the simulations. The Abstract, Discussion, and Conclusions sections have been revised to explicitly link cybersecurity aspects with numerical results, demonstrating their impact on system resilience.

Comment 12

The conclusions present broad recommendations without considering economic, regulatory, or technological constraints.

Response:
The Conclusions section has been revised to moderate the scope of the recommendations. Economic, regulatory, and technological constraints are now explicitly acknowledged, and the findings are presented as simulation-based insights rather than immediate deployment recommendations.

Final remark

We once again thank the reviewer for the constructive and insightful comments. The feedback was instrumental in strengthening the manuscript and improving its scientific clarity, technical rigor, and overall contribution.

Reviewer 2 Report

Comments and Suggestions for Authors Section 5. At the entry to the section, a number of “weak points” of PMSG generators are indicated (inertia, limited reactive tension, presence of power electronics). How does the VSG-algorithm itself address these skin problems, and which of them lose their normal symptoms when VSG is frozen?   What is the structure of the VSG outlined by the conceptual scheme, what does it indicate a specific implementation from the literature? What considerations are included in this structure (ideal shading, absence of locks, linearity)?     Regarding Figure 2, it is not clear whether the presented VSG structure is a generalized conceptual diagram or corresponds to a specific implementation from the literature. The authors are encouraged to clarify the assumptions underlying this figure (e.g., ideal measurements, neglect of delays, linearized models).   The results indicate the “best balanced results” for VSG+BESS+STATCOM. To what extent are the results sensitive to the choice of treatment parameters (inertia, damping, flow exchange) and how their variation is analyzed?   First, the 7 th chapter repeatedly emphasize the superiority of the combined VSG+BESS+STATCOM strategy. Nevertheless, all results are derived from a single-generator, fixed-load test system, which significantly limits the generality of the findings. Real power systems are characterized by multiple inverter-based sources, diverse operating conditions, inter-area interactions, and stochastic demand. Without demonstrating that the observed advantages persist under such conditions, the conclusions appear premature and insufficiently justified.     The topic is relevant and the simulation results are promising; however, the conclusions currently overstate the applicability and policy implications of the findings. Significant clarification, additional analysis, and a more restrained interpretation of results are required before the manuscript can be considered for publication.              

Author Response

Response to Reviewer

We sincerely thank the reviewer for the detailed and technically insightful comments. The remarks have helped us to clarify key methodological assumptions, strengthen the interpretation of the results, and moderate the scope of the conclusions. All concerns have been carefully addressed, as detailed below.

Comment

Section 5. At the entry to the section, a number of “weak points” of PMSG generators are indicated (inertia, limited reactive tension, presence of power electronics). How does the VSG algorithm itself address these problems, and which of them lose their normal symptoms when VSG is frozen?

Response:
This point has now been explicitly clarified in Section 5. The VSG algorithm directly addresses the three fundamental weaknesses of PMSG-based systems as follows:

• Lack of inertia:
  The VSG introduces a virtual swing equation that emulates the electromechanical dynamics of a synchronous generator. This synthetic inertia enables temporary energy exchange during power imbalance, smoothing frequency deviations.

• Limited reactive voltage control:
  A voltage–reactive power control loop analogous to excitation control is implemented within the VSG structure, allowing active voltage regulation and improved reactive power support.

• Decoupling due to power electronics:
  The VSG transforms the inverter from a grid-following current source into a grid-forming voltage source, mitigating the negative effects of converter decoupling.

When the VSG control is frozen and the inverter reverts to PLL-based grid-following operation, these benefits disappear: synthetic inertia vanishes, voltage regulation becomes indirect and limited, and the converter again depends on external grid strength. This behavior is now explicitly described in the revised manuscript.

Comment

What is the structure of the VSG outlined by the conceptual scheme? Does it indicate a specific implementation from the literature? What considerations are included in this structure (ideal sensing, absence of limiters, linearity)?

Response:
The VSG structure presented in Section 5 and illustrated in Figure 2 has been clarified as a generalized conceptual control framework, not a direct reproduction of a specific implementation from the literature.

The figure represents a commonly accepted abstraction of VSG dynamics used for comparative and benchmarking studies. The following assumptions underlying this structure are now explicitly stated in the manuscript:

• Ideal measurement signals without noise;

• Neglect of communication delays and latency;

• Linearized system behavior without saturation or dead zones;

• No active current, voltage, or power limiters in the nominal operating range;

• Ideal PWM modulation without switching harmonics;

• Balanced three-phase system without asymmetries.

These assumptions are consistent with standard reduced-order VSG models used to isolate intrinsic control behavior and enable fair comparison among different control strategies under identical conditions.

Comment

Regarding Figure 2, it is not clear whether the presented VSG structure is conceptual or corresponds to a specific implementation. The authors are encouraged to clarify the assumptions.

Response:
This ambiguity has been resolved. Figure 2 is now explicitly described as a conceptual abstraction of the VSG inertia and damping loop, illustrating the transformation of the swing equation into inverter control signals. The figure does not represent a hardware-specific or proprietary implementation but rather a generalized model used to support comparative analysis.

A dedicated paragraph has been added to clarify the modeling assumptions and the scope of applicability of the presented structure.

Comment

The results indicate the “best balanced results” for VSG+BESS+STATCOM. To what extent are the results sensitive to the choice of control parameters, and how is this variation analyzed?

Response:
A sensitivity analysis has been added to address this concern. The analysis focuses on the most influential VSG control parameters, namely the virtual inertia constant and the damping coefficient, evaluated for the representative VSG+BESS+STATCOM configuration.

The results demonstrate that:

• Higher inertia and damping values improve frequency stability and resilience index (RI) but slow down transient response;

• Lower values lead to faster dynamics but increased oscillations and reduced damping;

• An intermediate parameter set provides the best compromise between stability and responsiveness.

The results are summarized in a new table and discussed in detail, confirming that while the absolute values of the metrics vary with parameter selection, the qualitative performance ranking of the control strategies remains consistent within realistic parameter ranges.

Comment

Chapter 7 emphasizes the superiority of VSG+BESS+STATCOM, but results are derived from a single-generator, fixed-load system. This limits generality and makes the conclusions premature.

Response:
We fully agree with this observation and have revised the manuscript accordingly. To extend the scope beyond a single-generator case, an additional multi-PMSG dynamic scenario has been introduced, involving three generators with heterogeneous inertia constants operating under variable load conditions.

Furthermore, the Discussion and Conclusions sections have been substantially revised to clearly acknowledge the limitations of the simplified test system. The conclusions are now framed as simulation-based proof-of-concept findings, rather than generalized claims applicable to all power system configurations.

Comment

The conclusions overstate applicability and policy implications. A more restrained interpretation is required.

Response:
The Conclusions section has been rewritten to moderate the scope of the claims. Economic, regulatory, and technological constraints are now explicitly acknowledged, and policy-related statements have been reformulated as long-term perspectives rather than direct recommendations.

The manuscript now clearly states that further validation under large-scale, stochastic, and multi-area conditions is required before drawing broader system-level or policy conclusions.

Final remark

We sincerely thank the reviewer for the constructive and technically rigorous comments. The feedback has been instrumental in clarifying modeling assumptions, strengthening the analytical depth, and ensuring a more balanced and realistic interpretation of the results.

Reviewer 3 Report

Comments and Suggestions for Authors

In the article titled “Smart grids and sustainability in the age of PMSG-dominated renewable energy generation”, the authors address an important and timely topic related to the integration of PMSG-based renewable energy sources and grid resilience. The manuscript provides a broad overview of modern control strategies and presents simulation-based comparisons that may be useful for readers interested in smart grid operations. The article can be accepted after the authors address the following comments.

• The authors are encouraged to more clearly highlight the main contribution and novelty of the study in comparison with existing literature.
• The simulation model needs to add additional details regarding system parameters, control settings, and network configuration to improve clarity and reproducibility.
• The results related to the PLL-based control strategy should be further discussed to better align the observations with established physical interpretations.
• The authors are suggested to include a brief discussion on model limitations or possible validation approaches to strengthen the overall presentation.

Author Response

Response to Reviewer

We thank the reviewer for the positive assessment of the manuscript and for recognizing the relevance and timeliness of the topic. The constructive comments have been carefully considered and have helped to further improve the clarity, transparency, and positioning of the study. Our responses are provided below.

Comment 1

The authors are encouraged to more clearly highlight the main contribution and novelty of the study in comparison with existing literature.

Response:
The main contributions and novelty of the study have been clarified and strengthened. The Abstract has been revised to explicitly emphasize the originality of the unified analytical and simulation framework, which enables a consistent quantitative comparison of multiple control strategies within a single modeling environment. In addition, a dedicated paragraph has been added at the end of the Introduction to clearly distinguish the proposed approach from existing literature, particularly highlighting the joint assessment of synthetic, natural, and cyber-physical resilience in PMSG-dominated smart grids.

Comment 2

The simulation model needs to add additional details regarding system parameters, control settings, and network configuration to improve clarity and reproducibility.

Response:
Additional technical details have been incorporated to improve transparency and reproducibility. A dedicated table summarizing the BESS parameters has been added to the Case Study and Simulation Analysis section. Furthermore, key control settings, system assumptions, and network simplifications are now explicitly described, including control gains, inertia and damping parameters, sampling times, and modeling assumptions. These additions provide a clearer description of the simulated system configuration.

Comment 3

The results related to the PLL-based control strategy should be further discussed to better align the observations with established physical interpretations.

Response:
The Discussion section has been expanded to provide a clearer physical interpretation of the PLL-based control results. The revised text now explicitly explains that PLL-based grid-following control does not contribute synthetic inertia or voltage stiffness, which accounts for its observed limitations under dynamic load changes. The discussion aligns the simulation observations with well-established physical behavior of converter-dominated, grid-following inverters reported in the literature.

Comment 4

The authors are suggested to include a brief discussion on model limitations or possible validation approaches to strengthen the overall presentation.

Response:
A dedicated discussion of model limitations has been added to the Discussion and Conclusions sections. The manuscript now explicitly acknowledges the simplified nature of the test system, reduced-order modeling assumptions, and the absence of hardware validation. Possible validation pathways, including hardware-in-the-loop (HIL) testing, real-time digital simulation, and experimental microgrid setups, are suggested as future research directions.

Final remark

We thank the reviewer for the constructive feedback and for acknowledging the potential relevance of the presented results. The comments have contributed to improving the clarity, reproducibility, and balanced interpretation of the manuscript.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Thank you very much for the initial corrections. The following revisions are necessary to improve the quality of the paper:

1. Include at the beginning of the simulation section a brief paragraph explicitly stating the idealized assumptions of the model (absence of saturation effects, ideal converters, no harmonics, perfect communications) and discuss how these simplifications may influence the validity of the results when extrapolated to real power systems.

2. Add a comparative table that summarizes, in a single view, the main advantages and limitations of each evaluated control strategy (PLL, VSG, VSG+BESS, VSG+STATCOM, and VSG+BESS+STATCOM), focusing on frequency stability, voltage support, implementation complexity, and infrastructure requirements.

3. Provide a clearer justification for the numerical values selected for the VSG parameters (virtual inertia and damping coefficient), indicating whether they are derived from the literature, standard design criteria, or empirical tuning procedures.

4. Incorporate a brief discussion on the scalability of the proposed scheme, explaining how the conclusions might change if, instead of one or three PMSG units, a microgrid with a larger number of distributed generators were considered.

5. Add a clarification regarding the relationship between the rated power of the PMSG and the maximum power assigned to the BESS, indicating whether this ratio is representative of real applications and how system performance would be affected by a larger or smaller storage capacity.

6. In the resilience index section, explain in greater detail the physical meaning of each term composing the index and justify why the selected combination is appropriate to jointly evaluate frequency, active power, and reactive power performance.

7. Introduce a qualitative comment on the relative cost and complexity of each solution, stating that the VSG+BESS+STATCOM architecture implies significantly higher investment and integration effort compared to PLL or pure VSG schemes.

8. In the cybersecurity part, more clearly specify whether the delay and false data injection scenarios represent moderate or realistic conditions according to the literature, in order to better contextualize the magnitude of their impact on system resilience.

9. Adjust the conclusions to explicitly state that the results correspond to a simulation-level validation and that, as immediate future work, an experimental implementation in a laboratory environment or on a small-scale test bench is required.

Author Response

Dear Reviewer 1,
Thank you for your thorough second-round review of our manuscript (cleantechnol-3854961) and for the constructive comments that helped us further improve the clarity, transparency, and practical relevance of the paper. Below we provide a point-by-point response, and we indicate where each revision has been incorporated in the revised manuscript.

Comment 1

Include at the beginning of the simulation section a brief paragraph explicitly stating the idealized assumptions of the model (absence of saturation effects, ideal converters, no harmonics, perfect communications) and discuss how these simplifications may influence the validity of the results when extrapolated to real power systems.

Response:
We thank the reviewer for this valuable suggestion. We have added a dedicated introductory paragraph at the beginning of Section 6 (Case Study and Simulation Analysis) explicitly listing the key idealized assumptions (ideal converters/no harmonics, no saturation/nonlinearities, balanced operation, ideal sensing/communication, and neglected parasitic dynamics). We also added an explicit discussion on how these assumptions may limit direct extrapolation to real systems and stated that future work will extend the framework with non-ideal converter models and experimental/HIL validation.

Comment 2

Add a comparative table that summarizes, in a single view, the main advantages and limitations of each evaluated control strategy (PLL, VSG, VSG+BESS, VSG+STATCOM, and VSG+BESS+STATCOM), focusing on frequency stability, voltage support, implementation complexity, and infrastructure requirements.

Response:
We fully agree that such a summary improves readability. Accordingly, we introduced Table 3 (“Comparative summary of the evaluated control strategies”) at the end of Section 6, just before the Discussion. The table provides a qualitative comparison across the requested criteria (frequency stability, voltage support, implementation complexity, infrastructure requirements) and also lists the main advantages and limitations observed in the simulations for each strategy.

Comment 3

Provide a clearer justification for the numerical values selected for the VSG parameters (virtual inertia and damping coefficient), indicating whether they are derived from the literature, standard design criteria, or empirical tuning procedures.

Response:
We thank the reviewer for this important remark. To improve transparency and reproducibility, we expanded the explanation in Section 5.1 (Virtual Synchronous Generators – VSG). The revised text clarifies that the nominal values (e.g., H = 0.5 s, D = 1.0 p.u.) were selected within literature-reported ranges for grid-forming/VSM-type controllers and were subsequently fine-tuned through empirical tuning to achieve a well-damped transient response (reduced overshoot and settling time) under the disturbances defined in Section 6. We also added the typical ranges used for context and included a short sensitivity/tuning rationale.

Comment 4

Incorporate a brief discussion on the scalability of the proposed scheme, explaining how the conclusions might change if, instead of one or three PMSG units, a microgrid with a larger number of distributed generators were considered.

Response:
We appreciate this insightful suggestion. We have added a new paragraph at the end of Section 7 (Discussion) addressing scalability. The added text explains how the conclusions conceptually extend to microgrids with many distributed units, highlights the growing importance of inter-unit coupling, secondary/tertiary coordination, and communication effects as the number of devices increases, and clarifies that the current results should be interpreted primarily as representative of local/cluster dynamics in a controlled simulation setting.

Comment 5

Add a clarification regarding the relationship between the rated power of the PMSG and the maximum power assigned to the BESS, indicating whether this ratio is representative of real applications and how system performance would be affected by a larger or smaller storage capacity.

Response:
We thank the reviewer for this valuable observation. We added a clarifying paragraph in Section 6 describing the selected BESS-to-PMSG power ratio (and its motivation as a practical, medium-scale design choice used for short-term support rather than long-duration energy shifting). The text also explains the expected impact of increasing/decreasing storage capacity on frequency deviations, RoCoF, and RI, while acknowledging the associated cost, converter sizing, and control complexity trade-offs.

Comment 6

In the resilience index section, explain in greater detail the physical meaning of each term composing the index and justify why the selected combination is appropriate to jointly evaluate frequency, active power, and reactive power performance.

Response:
We thank the reviewer for this insightful comment. The Resilience Index (RI) subsection has been revised to provide clearer physical interpretation of each component (frequency RMSE as a proxy for inertial/synchronization stability, active-power deviation as energy balancing capability, reactive-power deviation as voltage/reactive support capability). We also strengthened the justification for combining these metrics into a single normalized indicator and clarified the role of weighting factors.

Comment 7

Introduce a qualitative comment on the relative cost and complexity of each solution, stating that the VSG+BESS+STATCOM architecture implies significantly higher investment and integration effort compared to PLL or pure VSG schemes.

Response:
We thank the reviewer for this constructive suggestion. We added a qualitative cost/complexity discussion in Section 7 (Discussion). The new text explicitly notes that while VSG+BESS+STATCOM provides the best composite technical performance, it also entails substantially higher investment, integration effort, and maintenance burden compared to PLL and standalone VSG, and that the preferred architecture depends on application criticality and economic constraints.

Comment 8

In the cybersecurity part, more clearly specify whether the delay and false data injection scenarios represent moderate or realistic conditions according to the literature, in order to better contextualize the magnitude of their impact on system resilience.

Response:
We thank the reviewer for this valuable remark. We expanded the Cybersecurity Analysis subsection to better contextualize the modeled cyber-physical disturbances. The revised text states that the simulated communication delays (e.g., 50–150 ms range) and the FDI perturbation magnitude correspond to moderate, literature-supported, realistic conditions for smart-grid communication/control networks and explains that these scenarios were selected to represent credible disturbances rather than catastrophic failures.

Comment 9

Adjust the conclusions to explicitly state that the results correspond to a simulation-level validation and that, as immediate future work, an experimental implementation in a laboratory environment or on a small-scale test bench is required.

Response:
We thank the reviewer for this important observation. The Conclusion section has been revised to explicitly state that the presented findings constitute simulation-level validation within a unified analytical framework. We also added a clear future-work statement indicating that laboratory-scale testing and/or hardware-in-the-loop (HIL) implementation is the immediate next step to evaluate unmodeled effects (nonlinearities, measurement/communication imperfections, converter dynamics) and to bridge simulation insights with experimental validation.

 

We sincerely thank the reviewer for the time, expertise, and careful attention devoted to the evaluation of our manuscript. The reviewer’s insightful, detailed, and constructive comments significantly contributed to improving the clarity, technical rigor, and overall quality of the paper. We believe that the revised version has been substantially strengthened thanks to these valuable recommendations.

Reviewer 2 Report

Comments and Suggestions for Authors

I recommend this article for publication.

Author Response

We sincerely thank the reviewer for the positive evaluation of our manuscript and for recommending it for publication. We greatly appreciate the time and effort devoted to the review and are pleased that the quality and contribution of the work were found to be satisfactory.