A Review of Torque Ripple Reduction Design Methods for Radial Flux PM Motors

Round 1

Reviewer 1 Report

This paper can be published as Review Paper. It will be better if more Experimental work mention.

Author Response

Dear reviewer:

 

Thank you for your comments to this paper that help us to improve it. We really appreciate all of them. In this letter, we expect that the ideas exposed in the paper have been clarified. The answers and the changes to the original version of this paper, according to your suggestions, are highlighted in yellow.

 

Reviewer Responses:

Reviewer #1:

Comment # 1: This paper can be published as Review Paper. It will be better if more Experimental work mention.

Answer to comment 1:

Thank you for your comment. We agree that more experimental work mention would be better. However, many of the found papers give only FEA results due to the cost of fabricating prototypes. Besides, the paper is pretty large already and adding experimental details would make it even larger, so instead we have added an advice for readers to encourage them to read the mentioned articles for details.

 

Author action:  The following are the changes we have introduced in the paper in an attempt to tell readers to go to the cited papers for experimental details.

Changes applied in Section 1 “Introduction” - Paragraph VII:

In every category, some application examples from research papers are presented and readers are encouraged to refer to those papers for mathematical and experimental details.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Dear Authors, your work proposes a review on torque ripple reduction in radial-flux PM machines. Generally, the paper is fluent, but, in my opinion, the following weaknesses can be detected:

1)      In the abstract the Authors state: “ Since control techniques have been reviewed and design methods don’t”. This fact is not true. You can find many review papers dealing with torque ripple suppression in PM machines, which have not been even cited in the paper, such as:

a.       Bianchi-Bolognani: “Design Techniques for Reducing the Cogging Torque in Surface-Mounted PM Motors” (IEEE Transactions On Industry Applications, vol. 38, no. 5, September/October 2002);

b.       D. G. Dorrell, M. -F. Hsieh, M. Popescu, L. Evans, D. A. Staton and V. Grout, "A Review of the Design Issues and Techniques for Radial-Flux Brushless Surface and Internal Rare-Earth Permanent-Magnet Motors," in IEEE Transactions on Industrial Electronics, vol. 58, no. 9, pp. 3741-3757, Sept. 2011.

c.       C. Bianchini, F. Immovilli, E. Lorenzani, A. Bellini and M. Davoli, "Review of Design Solutions for Internal Permanent-Magnet Machines Cogging Torque Reduction," in IEEE Transactions on Magnetics, vol. 48, no. 10, pp. 2685-2693, Oct. 2012.

d.       W. Fei and Z. Q. Zhu, "Comparison of Cogging Torque Reduction in Permanent Magnet Brushless Machines by Conventional and Herringbone Skewing Techniques," in IEEE Transactions on Energy Conversion, vol. 28, no. 3, pp. 664-674, Sept. 2013;

In order to be published, your review must contain some novelty in comparison with the ones already published (updated new techniques, a different perspective on the description of the reduction techniques, etc). Moreover, if the review has to cover all the PM machines, further effort should be devoted to the stator PM machines (flux-switching, flux-reversal and doubly-salient PM machines), which have not been adequately deepen (in these cases, the adopted minimization techniques can change significantly).

2)      The resolution of Fig. 1 must be improved. Moreover, for each technique reported in this figure, it can be useful to add the related reference.

3)      A critical discussion on the adoption of these techniques should be reported: why should one technique be more suitable than the others? Which factor is the most critical for this choice (the size, the complexity of the geometry, the application, etc…)?

4)      The techno-economical point of view should be also investigated, highlighting how the technical advantages of these techniques are related to the potential increases in overall manufacturing costs.

5) The list of references contains almost 100 papers, which is a good number. However, almost the whole list refers to only traditional PM motors, not including the new trends in PM machines (e.g., stator PM). 

Best Regards

 

Author Response

Dear reviewer:

 

Thank you for your comments to this paper that help us to improve it. We really appreciate all of them. In this letter, we expect that the ideas exposed in the paper have been clarified. The answers and the changes to the original version of this paper, according to your suggestions, are highlighted in yellow.

 

Reviewer Responses:

Reviewer #2:

Comment #1: Dear Authors, your work proposes a review on torque ripple reduction in radial-flux PM machines. Generally, the paper is fluent, but, in my opinion, the following weaknesses can be detected:

1)      In the abstract the Authors state: “ Since control techniques have been reviewed and design methods don’t”. This fact is not true. You can find many review papers dealing with torque ripple suppression in PM machines, which have not been even cited in the paper, such as:

1. Bianchi-Bolognani: “Design Techniques for Reducing the Cogging Torque in Surface-Mounted PM Motors” (IEEE Transactions On Industry Applications, vol. 38, no. 5, September/October 2002);
2. D. G. Dorrell, M. -F. Hsieh, M. Popescu, L. Evans, D. A. Staton and V. Grout, "A Review of the Design Issues and Techniques for Radial-Flux Brushless Surface and Internal Rare-Earth Permanent-Magnet Motors," in IEEE Transactions on Industrial Electronics, vol. 58, no. 9, pp. 3741-3757, Sept. 2011.
3. C. Bianchini, F. Immovilli, E. Lorenzani, A. Bellini and M. Davoli, "Review of Design Solutions for Internal Permanent-Magnet Machines Cogging Torque Reduction," in IEEE Transactions on Magnetics, vol. 48, no. 10, pp. 2685-2693, Oct. 2012.
4. W. Fei and Z. Q. Zhu, "Comparison of Cogging Torque Reduction in Permanent Magnet Brushless Machines by Conventional and Herringbone Skewing Techniques," in IEEE Transactions on Energy Conversion, vol. 28, no. 3, pp. 664-674, Sept. 2013;

In order to be published, your review must contain some novelty in comparison with the ones already published (updated new techniques, a different perspective on the description of the reduction techniques, etc). Moreover, if the review has to cover all the PM machines, further effort should be devoted to the stator PM machines (flux-switching, flux-reversal and doubly-salient PM machines), which have not been adequately deepen (in these cases, the adopted minimization techniques can change significantly).

Answer to comment 1:

Thank you for your comments. Although sometimes torque ripple and cogging torque are used as synonyms, they are not. Cogging torque is only one component of total torque ripple. Actually, a definition of cogging torque is given in all the mentioned papers just as we did in the introduction section. That said, papers “a”, “c“ and “d” are reviews of cogging torque reduction methods only while our paper covers that and other sources of torque variations. Paper “c” is a review of design issues where advice to design motors are given, it is not a review of techniques to reduce torque ripple, it only mentions the existence of torque ripple and some methods to reduce it but does not explain or give examples of them.

Some papers about stator PM machines have been included in Table 1 but not in the main text due to the small number of papers found about torque ripple reduction methods for them. For that reason and following your advice, a clarification has been inserted to state that the paper covers mainly rotor PM machines.

Author action:  The following are the changes we have introduced in the paper to make clear that the paper describes torque ripple reduction methods for surface PM machines only.

Changes applied in Section 2 “Torque Ripple Reduction Design Methods” - Paragraph I:

This section reviews various design methods to reduce torque ripple of rotor PM machines by different approaches and ¡Error! No se encuentra el origen de la referencia. summarizes some relevant information about them including a couple for stator PM machines.

Comment #2: The resolution of Fig. 1 must be improved. Moreover, for each technique reported in this figure, it can be useful to add the related reference.

Answer to comment 2:

Resolution of Fig. 1 has now been improved. The references for each group of techniques are given in their corresponding sections further in the paper for better display.

Comment #3: A critical discussion on the adoption of these techniques should be reported: why should one technique be more suitable than the others? Which factor is the most critical for this choice (the size, the complexity of the geometry, the application, etc…)?

Answer to comment 3:

The last paragraph of every presented method includes information about their advantages and disadvantages. It is not extensive so the paper does not get much larger than it already is but should be enough to give the readers an idea of what method would be better for their specific purposes.

Comment #4: The techno-economical point of view should be also investigated, highlighting how the technical advantages of these techniques are related to the potential increases in overall manufacturing costs.

Answer to comment 4:

The main objective of the paper is to introduce the design methods to reduce torque ripple and give their characteristics. However, some comments on the economic impact have been already made in some of the explained methods and in the discussion and conclusion sections, but a techno-economical analysis is a deep matter that could be worth its own paper.

Comment #5: The list of references contains almost 100 papers, which is a good number. However, almost the whole list refers to only traditional PM motors, not including the new trends in PM machines (e.g., stator PM)..

Answer to comment 5:

During the investigation few papers about torque ripple reduction in new PM motor types were found so they were referenced, and a couple included in Table 1 but not mentioned in section 2 due to the lack of information obtained. The action to address this issue is the same showed in the second part of the answer to comment 1.

Author Response File: Author Response.pdf

Reviewer 3 Report

1) The English language needs to be improved.

2) The Abstract is too general and mainly descriptive. In the Abstract the Authors should add some of the most important results obtained in this research (its exact values).

3) Radial flux PM motors should be properly described and the equations required for the calculation of its operating parameters should be presented. 

4) This paper lacks the necessary graphics and curves, these graphics and curves can often be very visual description of the problem.

6) The Conclusion section should be improved with the most important obtained results.

 

Author Response

Dear reviewer:

 

Thank you for your comments to this paper that help us to improve it. We really appreciate all of them. In this letter, we expect that the ideas exposed in the paper have been clarified. The answers and the changes to the original version of this paper, according to your suggestions, are highlighted in yellow.

 

Reviewer Responses:

Reviewer #3:

Comment #1: The English language needs to be improved.

Answer to comment 1:

Thank you very much for your comment, it has been very helpful.

The text has been checked using grammar software and by people who the native language is the English, so we hope this time the writing satisfies the requirements.

Comment #2: The Abstract is too general and mainly descriptive. In the Abstract the Authors should add some of the most important results obtained in this research (its exact values).

Answer to comment 2:

We agree with you, but in the information for authors section of the journal it is remarked that the extension of the abstract is limited to 200 words so we cannot get into deep details. However, the main results obtained are briefly described at the end of the abstract. Besides, this is a qualitative review paper, not quantitative. Therefore, there are no numerical values to report.

Comment #3: Radial flux PM motors should be properly described, and the equations required for the calculation of its operating parameters should be presented.

Answer to comment 3:

The main objective of the paper is to introduce the most found torque ripple reduction methods for radial flux PM machines. Hence, the focus is to describe those methods and briefly explain how they work assuming that the reader knows the basics about PM motors. Thus, giving detailed descriptions of the different topologies of radial flux PM motors. The design equations there included in the cited papers, so we consider it redundant to replicate this information in this paper so that it does not become too long (the complete design of PM motors is a somewhat complicated process). However, we have added some advice for readers to encourage them to read the mentioned articles for details.

 

Author action:  The following are the changes we have introduced in the paper to tell readers to refer to the cited papers for machine design details.

Changes applied in Section 1 “Introduction” - Paragraph VII:

In every category, some application examples from research papers are presented and readers are encouraged to refer to those papers for mathematical and experimental details.

Comment #4: This paper lacks the necessary graphics and curves, these graphics and curves can often be very visual description of the problem.

Answer to comment 4:

We agree with you and the paper was intended to have figures for every discussed method, but due to copyright issues we cannot include any figures from the cited papers or like them. All we can do is to tell readers to refer to the cited papers just like in the previous comment.

Comment #5: The Conclusion section should be improved with the most important obtained results..

Answer to comment 5:

Thank you by the comment, we agree that the conclusions must include the most important results. In this paper, to organize the conclusions we separate them in two sections: 3. Discussion and 4.  Conclusions. Two sections combined (Discussion and conclusions ) present the most important obtained results from the analysis done.

 

Author Response File: Author Response.pdf