AC Fault Ride-Through Strategy of a Transformerless Soft Normally Open Point

Round 1

Reviewer 1 Report

Following are the comments for the authors.

1. The novelty and contribution of the work should be highlighted in the introduction section as well as the conclusions section.

2. It is suggested to thoroughly go through the paper and remove the grammatical/typo errors.

3. How are the gains of PR controller determined?

4. How are the positive, negative and zero sequence components of current determined? How does the dynamic response of the algorithm affect the system operation?

5. What are the challenges in the practical implementation of the proposed scheme?

 

Author Response

Point 1: The novelty and contribution of the work should be highlighted in the introduction section as well as the conclusions section.

Response 1: Thanks very much for your valuable suggestion. We have added the novelty and contribution of this paper in the introduction and conclusions sections, and the modified content is marked in red.

Point 2: It is suggested to thoroughly go through the paper and remove the grammatical/typo errors.

Response 2: Thanks very much for your valuable suggestion. We have thoroughly gone through the paper and removed the grammatical/typo errors.

Point 3: How are the gains of PR controller determined?

Response 3: Thanks very much for your valuable suggestion. The parameter selection method of PR controller has been added in Section 5.1, and the modified content is marked in red.

Point 4: How are the positive, negative and zero sequence components of current determined? How does the dynamic response of the algorithm affect the system operation?

Response 4: Thanks very much for your valuable suggestion. The control strategy for the positive, negative and zero sequence components of current is shown in Fig. 6. The positive and negative sequence components are controlled by the well-known PI controller, and the zero-sequence current is controlled by the PR controller proposed in this paper. The positive-sequence current is controlled to control the active power and reactive power. The negative-sequence current is always controlled to zero, which ensures that the converter will not be locked due to over-current. The zero-sequence current is controlled to zero, which isolates the fault influence between the supply areas connected by the SNOP.

Point 5: What are the challenges in the practical implementation of the proposed scheme?

Response 5: Thanks very much for your valuable suggestion. The proposed scheme in this paper not only needs to increase the zero-sequence control strategy, but also has requirement on the topology of MMC. The bridge arm of MMC is required to output (0.87k-0.5)N negative levels. If the MMC in the project meets the above conditions, it has the conditions for practical application.

Author Response File: Author Response.docx

Reviewer 2 Report

The following comments are suggested to improve the quality of paper.

1. Add a clear novelty statement in the introduction section.

2. Improve literature review with relevant recent publications. The cited articles are very old. Identify the research gap. 

3. Optimization needs to be demonstrated clearly.

4. Tuning of controller parameters has not been described with sufficient details. 

5. Methodology needs more clarification like a flow chart, etc. 

6. The presented results should be compared with existing work in the literature. 

7. The methodology can be tested for different type of faults to assess the robustness of the controller. 

Author Response

Point 1: Add a clear novelty statement in the introduction section.

Response 1: Thanks very much for your valuable suggestion. We have added the novelty and contribution of this paper in the introduction section, and the modified content is marked in red.

Point 2: Improve literature review with relevant recent publications. The cited articles are very old. Identify the research gap.

Response 2: Thanks very much for your valuable suggestion. We have changed 19 cited articles with relevant recent publications, and the modified content is marked in red.

Point 3: Optimization needs to be demonstrated clearly.

Response 3: Thanks very much for your valuable suggestion. In Section 5, the demonstration of the optimization is improved, and relevant statements have been changed.

Point 4: Tuning of controller parameters has not been described with sufficient details.

Response 4: Thanks very much for your valuable suggestion. The parameter selection method of PR controller has been added in Section 5.1, and the modified content is marked in red.

Point 5: Methodology needs more clarification like a flow chart, etc.

Response 5: Thanks very much for your valuable suggestion. In Section 5, a flow chat to describe the methodology is added.

Point 6: The presented results should be compared with existing work in the literature.

Response 6: Thanks very much for your valuable suggestion. Traditional SNOP generally contains transformers, and this paper is the first one about the control and regulation of zero-sequence component without transformers.

Point 7: The methodology can be tested for different type of faults to assess the robustness of the controller.

Response 7: Thanks very much for your valuable suggestion. In Section 6.3, a two-phase grounding fault scene is added and presented to further supplement the robustness of the controller. In fact, the single-phase grounding faults, two-phase faults and two-phase grounding faults all have been tested.

Round 2

Reviewer 2 Report

Thank you.

In my opinion, introduction coupled with literature review is still very shallow. Better not to give lumped references. 

A final proofreading is required. 

 

 

Author Response

Point 1: In my opinion, introduction coupled with literature review is still very shallow. Better not to give lumped references.

Response 1: Thanks very much for your valuable suggestion. The literature review has been modified in the Introduction Section.

Point 2: A final proofreading is required.

Response 2: Thanks very much for your valuable suggestion. We have thoroughly gone through the paper and removed some grammatical/typo errors.

Author Response File: Author Response.docx