Analysis of Fault and Protection Strategy of a Converter Station in MMC-HVDC System

Round 1

Reviewer 1 Report

I appreciate the authors' efforts in revision. I suggest the following improvements.

1. Improve the starting of the conclusion to make the article more appealing.
2. To better integrate this work in the recent literature, authors should consider incorporating the following two recent references in the paper.

[1]  Z. Fu et al., "A Mutual-Inductance-Type Fault Current Limiter in MMC-HVDC Systems," in IEEE Transactions on Power Delivery, vol. 35, no. 5, pp. 2403-2413, Oct. 2020, doi: 10.1109/TPWRD.2020.2967837.

[2] M. Tahir, S. Hu, Z. Liang, and Y. Meng, “Unit Partition Resonance Analysis Strategy for Impedance Network in Modular Power Converters,” Front. Energy Res., vol. 10, 2022, doi: 10.3389/fenrg.2022.823938.

3. Please correct the caption of Figure 3.
4. There are still some grammatical errors, like in added part on line# 522. Please proofread are fix all language issues for better readability.

 

Comments for author File: Comments.pdf

Author Response

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Reviewer 2 Report

Thanks,

(1) Please the reviewer would want to see the screen shot of the “RT Lab Simulation Platform” and the results as obtained from the experiments; such as a screen shot from scope, etc;

(2) Please clarify the significance of reference [18] in the context of this paper:

“Chen, X.; Zhao, Y.; Yang, C.; Wang, Y.; Yang, Y. Investigation Analysis and Protection Strategy of Wenchang Pavilion in Peng- 608 cheng. Journal of landscape research 2020, 12, 74-79”

(3). Significant corrections required. For example, line 268 – 271; line 104, line 84-85, 87, etc

Author Response

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Reviewer 3 Report

Two minor suggestions:

1) In the introduction of Section I, short sentences should be used. Many commas should be changed to full stop. The authors can do some minor revision in this part.

2) The figure caption of Figure 3 appears twice in Line 272 and 273.

Author Response

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Reviewer 4 Report

The paper addresses an interesting idea to protect HVDC interfaces, but the paper is poorly written and very difficult to read:

1. There are grammatical errors, for example, line 111: "research, we proposeto set a certain".  Similarly, line 117: "the maincontributions of this". Please check carefully all the document to remove this type of errors.

2. Sometimes it is used "sub module", other times "submodule", please standardize.

3. The paper seems unfinished. For example, in line 270 it is stated the following: "Figure3 it is just a written equivalent circuit. The authors should include a clear caption." Is this comment from a previous reviewer? 

4. The procedure to obtain the mathematical model of Fig. 4 must be described.

5. Figure 5 presents a circuital model, not a mathematical one. This must be corrected.

6. It is required to introduce a flowchart of the protection strategy, so it is simpler to follow the protection algorithm.

Author Response

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Round 2

Reviewer 4 Report

This new version of the paper has a much better style than the previous one. Moreover, the algorithm is much more clear.

Author Response

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This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

This paper establishes the MMC mathematical model in a synchronous rotation coordinate system. After reading this paper, I'm not quite sure what is the theoretical and practical value of the proposed method. The authors did not explain the importance of the analysis clearly or give the outstanding improvement comparing with previous scheme. And the verified simulation is not very convincing. Also, obvious mistakes are shown in Fig.1 and Fig.5. The English description should also be improved.   

Author Response

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Reviewer 2 Report

Fault vulnerability and protection issues are major challenge in Grid connected inverters. The authors of this paper have presented a paper titled “Analysis of Fault and Protection Strategy of a Converter Station 2 in MMC-HVDC System”.

However, for this paper to be considered; the reviewer would want responses to the following concern:

• Please provide a clear description of the Test system used for the simulation studies; with all the parameters clearly indicated / Provided in the form of a Table.
• The literature materials included at the moment are based on the working principles and operations of the MMC. However, a detailed literature review focusing on previous works , which will provide a clear justification / necessity for this study; is also required.
• Please show clearly, how you work advances previous studies.
• Line 63-64: some conflicting statements…”.it lasts for a long time, generally adopting the circuit breaker failure and “lacking” good control strategy against the occurrence of failure and influence…”
• In Line 132, please provide clear justification why the half bridge sub-modules are commonly used; or provide a reference
• Please Figure 5 has another superimposed figure. Kindly amend this
• Please re-produce Figure 1; showing the path of current for “normal” operating condition and fault condition (each of failure of a submodule and the arm reactor). Ideally, this Figure should be in section 3, and thereafter provide clear narratives of the fault characteristics
• In line 137 – 144, please write the relevant mathematical expressions (for ease of comprehension)
• In line 154 – 170, please produce a Table showing the switching operations
• In line 391 to 423, please provides both mathematical expression/ relationship and also a Table showing the sequence of operation
• Clear reference needs to be made to all figures shown : for example line 368 : “As can be seen from the simulation results in the figure?” : the figure referred to needs to be clearly stated.
• The references made to “1_second” in line 368, not a representative of the Figures. The disturbance in your plots appears to happen after 7seconds following the start of the simulation.
• In line 152, reference also made to 1.5sec?
• Please double check typo : such as line 450 – 451: “because the hot standby sub-module only changes from the excused working state to the put into a working state”
• Line 452-473: Please produce a schematic of the converter bridge show the paths of fault current for the scenarios indicated (AC side fault and DC link fault). Thereafter produce a narrative linking this to how your proposed over-current protection strategy will isolate/clear the fault. The reviewer would also be interested in the simulation results.
• The reviewer is unsure about the significance of paper : ref [15] & [22] in this paper; which has been cited. Please clarify

Author Response

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Reviewer 3 Report

Comments and suggestions have been included in the attached file.  

Comments for author File: Comments.pdf

Author Response

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Round 2

Reviewer 2 Report

Thanks; however the reviewer would want the following clearly addressed.

1. The simulation parameters should be presented in the form of a Table, and where applicable; reference to be provided.
2. Sufficient literature review is required to present the current debates in the field, thereafter established the shortcomings of previous work, which necessitated this study. The literature materials provided at the moment only applies to the operation of the devices.
3. Previous protection strategies proposed in literature in the context of converter internal, faults should be explored
4. Figure 5 has two figures superimposed over each other;
5. Recall, DC side faults were not studied in this paper; therefore the first sentence in the conclusions that says “the possible faults in the MMC-HVDC systems” does not apply.

Author Response

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Round 3

Reviewer 2 Report

The authors are not able to provide sufficient justification that necessitated this paper. The literature review presented did not explore the current debates in the field which will help identify the current research gap. Generally, a detailed literature study is required focusing on previous works/ attempts made , which will provide a clear justification / necessity for this study. This is not evident in this paper.