Distributed Energy Storage Configuration Method for AC/DC Hybrid Distribution Network Based on Bi-Level Optimization

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1. General Assessment
The manuscript proposes a bi-level optimization framework for the siting, sizing, and operational scheduling of distributed energy storage systems (ESS) in AC/DC hybrid distribution networks. The topic is timely and relevant, especially given the rapid advancement of distributed PV, hybrid AC/DC architectures, and the role of ESS in voltage regulation and economic operation. The article is structured clearly and includes a well-developed mathematical formulation, case studies on a modified IEEE-33 system, and comparative experiments for different VSC control strategies.
However, despite the relevance and technical depth, the manuscript requires major revision. The work’s novelty is limited relative to recent literature on bi-level ESS optimization and AC/DC coordination; the mathematical formulation requires better justification; several assumptions are not sufficiently validated; and the experimental section would benefit from more comprehensive analysis and sensitivity studies.
The manuscript has potential but needs significant strengthening to reach MDPI publication standards.
2. Major Comments
1) Novelty and Positioning Relative to Existing Literature
While the authors propose a bi-level optimization framework, similar methodologies—combining ESS planning, AC/DC coordination, and VSC control—have been widely published in the last 5 years.
Examples include: AC/DC coordinated planning using convex relaxation, Bi-level ESS sizing with voltage constraints, AC/DC OPF models incorporating VSC control modes, and ESS planning under uncertainty
The manuscript should clearly articulate what methodological advance is introduced beyond Refs. [11–14]. Currently, the novelty appears incremental.
Required action: Strengthen the literature comparison, clearly state the innovation, and explicitly contrast your model with the closest existing works.
2) Validation and Robustness of the Bi-Level Model
The model is mathematically detailed, yet certain technical aspects remain insufficiently addressed:
- No convergence analysis or computational performance metrics for the improved PSO + Gurobi coordination.
- No justification for the chosen weighting coefficient μ in the upper-level objective.
- The convex relaxation section (SOCP) lacks validation that the relaxation remains tight in all tested scenarios.
Required action: Provide validation of relaxation tightness, convergence behavior, computational efficiency, and a rationale for parameter values.
3) Lack of Uncertainty Modelling
Voltage fluctuations in hybrid networks dominated by PV inherently involve uncertainties. However: PV variability is assumed deterministic;  
No scenarios (e.g., high/low PV output, ESS degradation, load forecast error) are included; The model does not address robustness or stochastic conditions.
Required action: Add uncertainty scenarios or provide justification for the deterministic assumption.
4) Experimental Analysis Requires Deepening
The IEEE-33 modified test system is standard, but the following issues weaken the analysis:
- No sensitivity analysis for the number of ESS units or power limits.
- Voltage deviation improvements are reported as percentages, but absolute values and profiles per bus are missing.
- Economic results are shown only per day; ESS lifecycle cost over 20 years should be included in the analysis narrative.
Required action: Enrich experiments with: sensitivity studies, per-bus voltage profiles, multi-day/seasonal scenarios and ESS lifecycle-level economic interpretation
5) Figures and Tables Require Clarity
Several figures (e.g., Figures 3–8) lack clear axis labels, units, or explanations. Three-dimensional voltage plots are difficult to interpret without scale or color mapping details.
Required action: Improve figure readability; add detailed captions; include units.

3. Minor Comments (Revised and Expanded)
- The manuscript type is not specified.
In the current submission, the authors have not indicated the Type of the Paper (e.g., Article, Review, Communication, Technical Note), which is mandatory in the MDPI template.
I have assumed that the work is intended to be an Article, given its methodological structure and experimental validation.
Required action: Please explicitly state the manuscript type on the first page, according to MDPI guidelines.
- English language quality and clarity
The manuscript contains numerous grammatical inaccuracies, run-on sentences, and inconsistent phrasing. Some technical explanations (especially in Sections 2.2–2.4 and the Results section) are difficult to follow due to language issues.
A full professional English proofreading is strongly recommended.
- Notation consistency and mathematical formatting
Several variables and symbols are introduced without formal definition or appear inconsistently across sections—for example, 𝑈𝑁; 𝑈𝑖,𝑡; 𝐼𝑖𝑗,𝑡; 𝑣𝑖𝑗,𝑡; 𝑙𝑖𝑗,𝑡.
Please provide a complete Nomenclature Table and ensure uniform notation in all equations.
- Units, parameter values, and assumptions
Some critical parameters (ESS cost coefficients, electricity prices, discount factor β, ESS life cycle, PV capacity assumptions) are provided without justification or external reference.
Add citations or explanations, especially for economic parameters.
- Figures and captions
Several figures (e.g., Figures 3–8) lack clear axis labels, units, or clarity in color mapping. The 3D voltage distribution plots are particularly difficult to interpret without a legend and scale.
Improve figure readability and expand captions to explain what each subplot represents.
- Formatting issues: Equation numbering is inconsistent (e.g., references to “Equations (26)–(31)” do not correspond to the visible numbering); The Highlights section exceeds typical MDPI length and should provide concise points (≤120 characters each); The Abstract is overly long and includes too much technical detail for MDPI standards.
- References
While the reference list is adequate, several citations rely heavily on regional or less widely indexed sources. To strengthen the scientific positioning, include more recent and high-impact references from journals such as IEEE Transactions on Power Systems, Applied Energy, Electric Power Systems Research, etc.
Review reference formatting for MDPI accuracy (DOI, title capitalization, consistency).
4. Recommendation 
Major Revision Required
The manuscript is relevant and technically promising but requires substantial improvements in clarity, novelty positioning, robustness of results, and compliance with MDPI formatting requirements.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

This work proposed a bi-level optimization model, the upper level of which minimizes ESS investment, line loss, main grid purchase costs, and overall bus voltage deviation for ESS allocation. The lower level, based on upper-level configurations, optimizes ESS operation under typical scenarios to reduce load standard deviation. Comments to the authors:

1) The connection between the upper level and the lower level is not clear. It can be explained in a better way in the revised paper.

2) Highlight the main contributions at the end of the Introduction section.

3) Explain the reason for using multiple objectives in this work.

4) Provide the computational times for each case studied in this paper.

5) Describe the figures 7 and 8 in the revised paper.

6) Provide the parameters used for PSO.

 

 

 

 

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

I have attached the manuscripts with highlights where I am concerned about 

• poor use of english, mainly idioms and informal terms which have no place in a technical journal
• use of acronyms without explanation
• use of phrases like 'domestic and foreign' have no place in an international journal

main points

• there is little justification of the values you have used in your modelling, you need to justify the values you are using from references. This includes why you have chosen particular buses for ESS, the coefficients for financial modelling and the sizes of PV and ESS
• it appears that the chinese system charges a levy for voltage deviation, but this needs explanation
• there is no consideration of using power flow analysis tools like IPSA, ERACS or digisilent as they use a similar iterative system
• The issue of investigating power flow, while charging and discharging  batteries means you have to consider whether the battery has capacity to contribute to the voltage changes needed. This is not addressed
• only voltage deviation is addressed, so you should specify this in the introduction, rather than the more comprehensive power quality.
• you have not discussed the financial consequences, except for the voltage deviation cost

 

Comments for author File: Comments.pdf

Comments on the Quality of English Language

Careful proofreading is needed as the use of the definite and indefinite article is not used correctly. There are too many informal phrases which should not be used in a technical journal

 

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have basically revised the manuscript. I have no additional questions or comments.