Impedance Modeling Based Method for Sub/Supsynchronous Oscillation Analysis of D-PMSG Wind Farm
Round 1
Reviewer 1 Report
Dear Authors,
thank you for submitting your work for possible publication in Applied Sciences.
Your manuscript deals with an important issue, namely sub-synchronous oscillation of D-PMSG used, as reported, in wind farms. Over the last years, a few works have been reported in the literature regarding this issue, and as a result your manuscript comes within the scope to respond to this issue.
Your manuscript is well written and structured. The current state-of-the-art is clearly introduced and the motivation to carry out this research work as well. The reported results are relevant. Please find below my feedback to take into consideration for a second review round process:
1) please rewrite equation (5), a part is missing. Same problem with equation (8).
2) Same problem with equation (13), equations (17) and (18).
3) Please correct at row 221 "grid-connected".
4) At row 223, "simulation experiment" is not clear. Please provide further details.
5) Equation (20) and (22).
Author Response
Dear Editors and Reviewers:
Thank you for your letter and for the reviewers’ comments concerning our manuscript entitled “Impedance Modeling Based Method for sub/sup-Synchronous Oscillation Analysis of D-PMSG Wind Farm” (ID: applsci-550980). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are marked in red or blue in "Track Changes" of the paper.
The main corrections in the paper and the responds to the reviewer’s comments are as flowing:
Point 1: please rewrite equation (5), a part is missing. Same problem with equation (8).
Response 1: We apologize for the display error of equation (5), since we have used the equation editor "Mathtype". And the problem is the "Black Dot" won't display if the viewer's PC doesn't have this software. And we have made corrections as follows:
Vqv[f] =-jVp (5)
The previous version used a "Black Dot" between "j" and " Vp" to represent multiplication. Same problems with other equations.
Point 2: Same problem with equation (13), equations (17) and (18).
Response 2: We are very sorry for the impact on your viewing, and we have made corrections.
Point 3: Please correct at row 221 "grid-connected".
Response 3: We are very sorry for our negligence of the inaccurate description. And we have made correction according to the Reviewer’s comments.
Point 4: At row 223, "simulation experiment" is not clear. Please provide further details.
Response 4: We are very sorry for our inaccurate description of the simulation. And we have provided more details of circuit diagram and parameters. To be noticed that Appendix A provides the converter's parameters.
Point 5: Equation (20) and (22).
Response 5: We feel sorry and these two equations were also changed.
The revised full manuscript is updated in the attachment. And we hope that your valuable suggestions have been answered.
Sincere regards~
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Dear authors,
Here some questions:
1. You wrote, “Compared to DFIG, PMSG doesn’t need gearbox and uses full power converters”. However, gear can reduce the generator size in the case of PMSG as well. If it is so, please, mention it and maybe change the paper title.
2. You claim that you described a new type of SSO. Have engineers encountered with this new kind of problems? If no, which features of existing wind farms prevent these oscillations? If yes, how did they deal with them?
3. Every abbreviation should be deciphered at its first use. For example, PLL.
Then, maybe I’ll ask other questions.
Author Response
Dear Editors and Reviewers:
Thank you for your letter and for the reviewers’ comments concerning our manuscript entitled “Impedance Modeling Based Method for sub/sup-Synchronous Oscillation Analysis of D-PMSG Wind Farm” (ID: applsci-550980). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are marked in red or blue, clear to see in "Track Changes" of the paper.
The main corrections in the paper and the responds to the reviewer’s comments are as flowing:
Point 1:
You wrote, “Compared to DFIG, PMSG doesn’t need gearbox and uses full power converters”. However, gear can reduce the generator size in the case of PMSG as well. If it is so, please, mention it and maybe change the paper title.
Response 1:
Response: We apologize for the inaccurate description in the article. The statement, “Compared to DFIG, PMSG doesn’t need gearbox and uses full power converters”, is an introduction to indicate that the main type of wind turbine we concerned in this paper is D-PMSG, not DFIG. For practical applications, we understand that not all PMSGs have no gearboxes. Therefore, we have re-written this part according to the Reviewer’s suggestion.
Point 2:
You claim that you described a new type of SSO. Have engineers encountered with this new kind of problems? If no, which features of existing wind farms prevent these oscillations? If yes, how did they deal with them?
Response 2:
This comment includes two questions: First, have engineers encountered with this new kind of problems? Second, what countermeasures do we have to deal with this problem?
Response: First, this new type of SSO has already happened in Xinjiang, China, in July, 2015[12,13], which has already described in the introduction. The main involved dynamic components of this type of SSO is D-PMSG based wind farm, which has no relation with series compensation and HVDC. This is also the main reason why this paper mainly discusses the SSO of PMSG. Second, After the accident, the engineers eliminated the oscillation mainly by adjusting the parameters of the controller or cutting off some the generators. The core idea of this way is to avoid unstable oscillation modes by changing the operation condition of the power system. In addition, SSO can be suppressed by applying the additional device such as STATCOM.
Point 3:
Every abbreviation should be deciphered at its first use. For example, PLL.
Response 3
We are very sorry for our negligence of the inaccurate description of the abbreviation. We have made correction according to the Reviewer’s comments.
The revised full manuscript is updated in the attachment. And we hope that your valuable suggestions have been answered.
Sincere regards~
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Dear Authors,
thank you very much for taking into consideration my remarks for a second review round process.
After reading carefully your revised manuscript, it matches my expectation.
The reported work is relevant and brings a new contribution in this field.
Thank you for submitting your work in Applied Sciences.
Reviewer 2 Report
Dear authors,
you have corrected all my remarks.
The paper is interesting and can be published.
