Fully DC Aggregation Topology with Power Self-Balancing Capacitors for Offshore Wind Power Transmission: Simulation Study

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors propose a novel Input-Independent Output-Series (IIOS) DC converter topology using self-power-balancing capacitors and a hybrid control strategy called PFMT-PSMN. The goal is to balance power across submodules while minimizing switching frequency and maintaining soft-switching conditions (ZVS), which is crucial in offshore wind energy transmission systems.

Below are the strengths of the reviewed article:
- Innovative control strategy – PFMT-PSMN combines frequency modulation with phase-shift modulation, enhancing control flexibility.
- Reduction of switching losses – The use of zero-voltage switching (ZVS) across the power range helps minimize energy loss. 
- MATLAB/Simulink simulations – Demonstrate effective operation and voltage balancing performance under varied conditions.
- Simplified system architecture – Compared to dual-stage or bidirectional balancing methods, the proposed structure is simpler and potentially more efficient.
- Application relevance – Well aligned with the needs of offshore wind farms, where input power fluctuations are frequent.

Below are the weaknesses of the reviewed article:
1. Lack of comparison with existing solutions. The paper lacks a comprehensive performance comparison with established balancing techniques such as:
- Bidirectional Buck-Boost converters (e.g., Huang et al. 2021, [26]),
- Impedance-source networks (e.g., Liu et al. 2017, [25]),
- Resonant LC-based balancing units (e.g., Zhuang et al. 2021, [29]).
Suggestion: Include a comparative table with metrics such as loss, complexity, cost, and dynamic response.
2. Simulation-only validation. All results are based on MATLAB/Simulink simulations. In real-world systems: 
- Capacitors may exhibit non-linear behavior,
- EMI, thermal effects, and synchronization noise become significant.
Suggestion: Future work should include a laboratory prototype tested under dynamic loads and fault conditions.
3. Complexity of PFMT-PSMN control. While flexible, the proposed control method demands:
- Precise synchronization across all submodules,
- Real-time monitoring of multiple parameters (voltages, currents, gain).
Criticism: This may hinder industrial adoption, where simplicity and robustness are essential.
4. Insufficient consideration of real-world variability. In offshore wind farms, power inputs are highly nonuniform and stochastic. However:
- The simulations cover short time spans,
- Input conditions appear artificially stable.
Suggestion: Analyze performance under long-term, fluctuating wind profiles or during partial submodule failure.
5. No cost-benefit or implementation analysis. Although the paper claims the method is “cost-effective,” it lacks:
- Bill of materials or cost estimates,
- Analysis of transformer and capacitor requirements,
- Quantitative comparison with traditional designs.
Criticism: The economic feasibility of deploying power-balancing capacitors at scale remains unsubstantiated.

Summary
This paper presents a meaningful contribution to the development of modular DC converter systems for wind power integration, particularly with its control strategy and intrinsic power balancing approach. However, its practical relevance is limited by the lack of experimental data and techno-economic analysis.

Recommendations for Improvement
- Add experimental validation using a hardware prototype.
- Include a comparison table versus alternative balancing strategies.
- Analyze system sensitivity to synchronization errors and noise.
- Introduce basic implementation and cost feasibility analysis.

 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This paper focused on a topology-related method for self-balancing of the energy. In my opinion, the paper is good enough to be published.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

I have been doing H-bridge topology (different applications) for the most of my life.
Simulation of magnetic components is a problem, always. Because, same power converter could give different waveforms at different voltages and power levels. You should find reference to support this statement (you have enough good papers, already).
LC output makes this problem even larger (over voltages).
In simulation, it is easy to chose same capacitors capacitances. In real life different capacitances results in different output voltages. Problem is larger for the higher voltages. These problems is hard to simulate accordingly. Instead 400V and 400V you can get 350V and 450V which is not the same.
However, I like this topology and I think that It should be published. It seems innovative to me.
These things should be mentioned in paper. I suggest to put additional text near by figure 3.

In real life this figure looks different. vABn usually has oscillations following by changes in other waveforms. Figure 4 is important for the text but real life difference, should be mentioned because of leakage inductance and transformer model.

This id direct converter and it is sensitive to the lack of symmetry.
At figure 7 waveforms D1 and D2 should be explained. Voltage should be marked in Volts (V).

1. Title change
Fully DC Aggregation Topology with Power Self-Balancing Capacitors for Offshore Wind Power Transmission
should be
Fully DC Aggregation Topology with Power Self-Balancing Capacitors for Offshore Wind Power Transmission: Simulation Study

At the end you can mention that real time model design is underway. Maybe you have some results already which could confirm your approach.
I think this approach could be used for both on-shore and off-shore WECS (wind energy conversion systems) if not. explain.

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

This paper studies output power balancing problem in offshore wind DC aggregation systems caused by power fluctuations. A series-connected aggregation topology incorporating power self-balancing capacitors is given to enable energy equalization among the submodules. A PFMTPSMN hybrid control strategy is given to regulate the phase-shift duty cycle and switching frequency.

Generally, the paper is written in a clear manner. The problem is worthy of study. It is suggested to accept it after some revise.

1. What’s the problem with the series-connected DC aggregation topology?
2. The configuration and the dynamics of the wind farm are not shown in the paper. Please enhance it.
3. How to guarantee the power balance after fault? The steady-state balance is not difficult?
4. The research difficulty of “PFMT-PSMN control strategy” is to be explained more clearly.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Thank you for responding to my comments and incorporating them into the revised version of the reviewed article. I have no further critical comments.