Optimal Hybrid Pulse Width Modulation for Three-Phase Inverters in Electric Propulsion Ships

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Comments for Authors:

1.     After the title of chapter 2, first the text with a reference to Figure 1.

2.     Figure 1 – please explain the presence of chokes in the DC circuit? They will damage the AFE Rectifier.

3.     Line 150 – should it be 2.1.1. instead of 2.1.1 (?)

4.     Line 159, 161 and 165 – formula (1) is not an “Equation”, but an inequality.

5.     Figure 3 – generally no explanation of what S(x,x,x) is. What does angle alpha mean?

6.     Line 172 – how do the Authors define "modulation index"?

7.     Lines 214, 215, 239 and 240 – what does "Vsn" mean?

8.     Where are formulas (2) and (3)?

9.     Figure 6 – axis descriptions are a bit difficult to read.

10. Figure 7 – not all variables are defined.

11. Figure 11 – no units for "Time". Why is it a capital letter and a lower case letter for phase-a (line 225 – Phase A, line 411 – phase A )? Different fonts in axis descriptions etc.

12. Figure 11, 12 and 13 – no interpretation of the harmonic spectrum. No unit for "Time".

13. Figure 14 – no description of the X axis.

14. Figure 15 – no units for "Time".

15. Figure 16 – no units for "Time" and for “RPM”.

16. Line 436 – instead of "table below" "Table 2"?

17. Line 472 – how were individual input and output powers measured?

18. Figure 18 – what does "load angle" mean?

19. Table 3 – the reason for the difference in losses should be explained in more detail (applies to the last two columns).

Author Response

This is a late reply, but we have revised the content to reflect the reviewer's opinion as much as possible.
The reviewers' valuable comments made my paper more valuable.
We will also reflect the opinions of reviewers in the development of inverters for small electric propulsion ships, which we are carrying out as future research.
Please check the attached file for revised comments.
I ask for your continued interest in my research.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This paper deals proposes an optimal hybrid pulse width modulation for 3-PH inverters applied to electric propulsion ships. The introduction is sufficienlty well written with an adequate number of references. All the references are recent. Section 2 describes the well known conventional pulse width modulation strategy for 3-PH inverters. Section 3 proposes th hybrid pulse width modulation strategy. Fig. 6 is not clear. Under what conditions are the measures taken? Swtiching frequency? What kind of power devices are used? etc...
Section 4 shows the experimental results. In my opinion, if the application is electric propulsion ships a model using 150Vbus and 2.2 kW motor is not representative of the real application. High power applications such as electric propulsion ships feature very high power switching devices. These devices require high dead time, etc... How do you plan to model these situations?
Poor experimental results and the lack of novelty are the main problem of this paper.

Author Response

This is a late reply, but we have revised the content to reflect the reviewer's opinion as much as possible.
The reviewers' valuable comments made my paper more valuable.
We will also reflect the opinions of reviewers in the development of inverters for small electric propulsion ships, which we are carrying out as future research.
Please check the attached file for revised comments.
I ask for your continued interest in my research.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Congratulations on your paper!

I have only one recommandation. In Conclusion section you argued that the proposed HPWM method is superior to existing methods. It would be great if you mention 2 or 3 characteristics that suport your statement, in order to highlight your findings.

Author Response

This is a late reply, but we have revised the content to reflect the reviewer's opinion as much as possible.
The reviewers' valuable comments made my paper more valuable.
We will also reflect the opinions of reviewers in the development of inverters for small electric propulsion ships, which we are carrying out as future research.
Please check the attached file for revised comments.
I ask for your continued interest in my research.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

The contribution of this paper is good at a hybrid pulse-width modulation method for optimal inverter operation. Compared to the conventional PWM techniques, the proposed control strategy is a simple proposal to achieve harmonic improvement and loss reduction. However, there are some questions about this paper. Please address the following concerns.

(1)  From Fig. 7 to Fig. 9, the block diagram needs three-phase current references and a high modulation index (0.8) reference. Is there any limitation for the lowest modulation index of the proposed HPWM method?

(2) In Fig. 17(a), the output current THD increases significantly when the modulation index is 0.8. In Fig. 17(b), the total losses are similar when the modulation index is between 0.6 and 0.8. Please give more explanations about these two situations.

(3) In Table II, the authors mention that the proposed HPWM method has the highest average efficiency. I suggest the authors provide more experimental results to demonstrate the efficiency performance for low-speed (<500 rpm) and high-speed (>1500 rpm) conditions. 

Author Response

답변이 늦었지만 리뷰어의 의견을 최대한 반영하여 내용을 수정했습니다.
심사위원님들의 소중한 코멘트가 제 논문을 더욱 가치 있게 만들어 주었습니다.
또한 향후 연구로 진행하고 있는 소형 전기추진 선박용 인버터 개발에도 심사위원들의 의견을 반영하도록 하겠습니다.
수정된 의견은 첨부파일을 확인해주세요.
제 연구에 지속적인 관심을 부탁드립니다.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Referring to my 2nd question, of course I agree with the explanations regarding the purpose of using the filter. However, wouldn't it be better to use a C-L-C filter instead of L-C? This solution would eliminate the risk of overvoltages. The currently presented filter topology may cause overvoltages during switching "AFE Rectifier" transistors, due to the presence of chokes on the AC side and directly on the DC side.

Author Response

I think the reviewer's opinion can help me make up for my shortcomings.
Because the content is centered on analysis of the inverter's operation, I think I missed something.

Since the design and testing of a 100kw-class inverter is in progress in the future, we will take this into consideration and compare when conducting experiments in this area.

If you are interested, please continue to comment on my paper.

Reviewer 2 Report

Comments and Suggestions for Authors

Thanks to the authors for the reply to my questions. I think is better to wait for the readiness of the new 100kW converter to plan the pubblication of this paper. I think for now the paper is not suitable to be published due to poor experimental results and for the lack of novelty.

Comments on the Quality of English Language

English language is fine, in my opinion.

Author Response

I approached the reviewer's opinions carefully, and revised and changed the paper to reflect them as much as possible. However, the content may not be perfect and we plan to conduct more experiments.

This part was tested under rated conditions, and the proposed method shows sufficiently improved performance. Please check the paper carefully again.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

Thanks for the authors' effort to answer the questions. I think this manuscript has been significantly improved.

Author Response

In the paper, the proposed method also reflects modifications made under the 100kW rating conditions. Please confirm.

I ask for your continued interest in my research in the future.