Analysis and Control of Slotless Self-Bearing Motor

Round 1

Reviewer 1 Report

Dear Authors,

thank you for your work, here are some comments:

- In the abstract, you state that the forces are axial forces, however, from your paper, it becomes clear that you have designed a radial / axial force mb. Please correct.

- I did not understand the meaning of "proper minute distance", please maybe rephrase.

- The verdict "However, the AGBM has low power density and efficiency because of the axial flux motor principle." cannot be generalized. There are benefitial and non-benefitial arrangements.

- I did not understand the meaning of "This combination makes the motor size zooming out continuously", please maybe rephrase.

- please replace "energy loss." with "loss energy."

- In Fig.5, you give the currents for forces, torques, and combined force/torque. However, the current directions of 5)b and 5)c are identical while the force arrows, e.g. of d- c- phase are different in 5)b and 5)c. This seems to be wrong, please correct.

- Eqn.(11): parentheses missing!

- Please correct: "In order to the total force acting ON the rotor not be zero"

- Please take a look at (19). You are adding an angle (Phi0), another angular portion (pi/4 * z/lt), and a rational depending on the phase number. This does not make sense to me. Missing a factor 2pi for the middle term?

- (29): please use parenthesis in the numerator

- Fig. 15(a): please use a different scaling (-+0,5 or -+1)

- Fig. 20(a) and 20(b): the time scale does not fit your events. Are these consistent measurements?

General comments:

- I am not a control expert so I only briefly retraced your control value design. Generally: a lot of variable definitions are missing in that part.

- You do not consider saturation which becomes a major problem for your linear system. Please comment.

- In the abstract, you talk about "axial" forces, in the design chapters, you describe radial and axial forces, and in the experiment section, you only test radial forces. Also, your experiment seems to stabilize axial direction mechanically. This introduces a lot of doubts - please

a) properly describe the test setup

b) clearly state what you have tested - the sentence "and the SSBM could operate stably in all working conditions." is highly misleading.

- Please, in the beginning of the paper, describe what your intention is: You model the forces and torques based on the Lorentz forces, you deduct the control model and the control parameters, and you do some testing. Please let the user know about this and give some ideas WHY you are doing this.

Thank you!

Author Response

Dear Reviewer,

 

First of all, we would like to express our deep gratitude to you, who has spent a lot of time reading our paper and give us valuable advice. We also hope that we will receive your contribute in our future researches. Basing on your comments and questions, we have been tried our best to revise the manuscript. We would like to attach here the questions, our answers and revised manuscript.

Please see the attachment,

Yours faithfully,

Quang Dich Nguyen

Author Response File: Author Response.pdf

Reviewer 2 Report

Although the paper is technically sound, the authors need to cite more references.  Many researchers have been publishing slotless bearingless motor papers for a while, some using the type of control scheme considered in the present work.  More work needs to be done placing the paper the context of this previous work and explaining the novel aspects of this work.
1) The introduction makes it sound as if the present work is the first slotless bearingless motor.  Many papers have been written about this paper over a span of many years.  Some of these other works should be referenced.  For example, 10.1109/TIA.2015.2466683, 10.1109/TIE.2014.2311379
2) The rotating backiron design is also not very novel.  Thingap (www.thingap.com) has been marketing motors with this topology for a long time--just not bearingless ones.
3) The control scheme of the motor is also not very novel.  10.1109/IAS.2012.6374033 is an example of a similar DQ-based control scheme for motoring and suspension.

Author Response

Dear Reviewer,

 

First of all, we would like to express our deep gratitude to you, who has spent time reading our manuscript and give us some comments. Basing on your comments and questions, we have been tried our best to revise the paper. We would like to list here the questions and our answers.

Please see the attachment.

Yours faithfully,

Quang Dich Nguyen

Author Response File: Author Response.pdf

Reviewer 3 Report

This paper deals with the design and analysis of a slotless self-bearing motor based on the idea that electromagnetic forces from a proposed coil system generate both bearing forces and a traction torque. Main part of the paper is devoted to the derivation and explanation of expressions of forces and a torque generated by the motor with respect to particular current. Obtained findings are then used for the design of position control (using PID controller) and speed control (using PI controller). Pole placement method is employed to find controllers' coefficients after constructing transfer functions. The last part of the paper demonstrates several experimental results for a particular motor and various operating conditions.

The topic is interesting but the presentation is little bit confusing in certain parts of the paper. It should be improved mainly according to these points and questions:

1) Authors declare that "the paper presents improvement of control system". Please, specify the particular improvements with respect to previously published papers.

2) Derivation of magnetic forces and a torque is very complicated with many steps and modifications. In my opinion it is not possible to follow the derivation by a reader since there are some gaps in combining of various expressions and it seems that notation isn't fully consistent. This should be definitely improved.  

2) I suggest to include the list of variables.

3) Are equations in (31) really correct?

4) Variable psi is specified as the angular position of the rotor. However it vanishes in the end of section 2. Does it mean that bearing forces are not dependant on any rotor position variable?

5) How does it work with vertical (gravity) force?    

6) Please, explain the assumptions before formulating eq. (32) in more detail.

7) Equations of motion (35) includes certain undefined quantities, please, explain them.  

8) Formally - brackets are missing in several equations, e.g (25), (28), (40) etc.

9) How exactly can you choose s_0 parameter?

10) What are the exact values of PID and PI controllers' coefficients used in experiments and were the results sensitive to the choice of these values?

11) Please, use the space between value and its quantity in the course of typesetting.

12) There are some typos that should be corrected.

13) It would be very valuable to include also some results of numerical simulations in order to show the verified behaviour of the proposed system and the controller.      

 

Author Response

Dear Reviewer,

 

First of all, we would like to express our deep gratitude to you, who has spent a lot of time reading our paper and give us valuable advice. We also hope that we will receive your contribute in our future researches. Basing on your comments and questions, we have been tried our best to revise the manuscript. We would like to list here the questions and our answers.

Please see the attachment,

Yours faithfully,

Quang Dich Nguyen

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Dear authors,

thank you for introducing significant corrections. I still am not convinced that a reader will actually go through the detailed analytical modelling of the torque and force calculation, as, e.g. for the non-parallel wire branches. I therefore have not reviewed all calculation steps in detail, please carry your own responsibility for the correct calculation. I strongly recommend a second check for correctness.

The same holds true for the long modelling part of the control, however, a reader who is new to the topic of magnetic bearings may find helpful approaches on how to deal with certain steps.

Author Response

Dear Reviewer,

 

First of all, we would like to express our deep gratitude to you, who have spent much of your time reading our paper and give us valuable advice. We also hope that we will receive your contribution in our future researches. Basing on your comments and questions, we have been trying our best to revise the paper. We would like to attach here the questions and our answers.

Please see the attachment.

Yours faithfully,

Quang Dich, Nguyen

Author Response File: Author Response.pdf

Reviewer 2 Report

No changes were made the the paper in response to this reviewer's comments.  Explanations of novelty that differentiate the present paper from previous work should be in the paper, not in the response to the reviewer.  Since there were no changes to the paper in response to the previous round of comments, this reviewer's assessment is unchanged.

1) The introduction makes it sound as if the present work is the first slotless bearingless motor.  Many papers have been written about this paper over a span of many years.  Some of these other works should be referenced.  For example, 10.1109/TIA.2015.2466683, 10.1109/TIE.2014.2311379 [Suggest that the authors add additional references for other slotless bearingless motors to help differentiate their approach.]
2) The rotating backiron design is also not very novel.  Thingap (www.thingap.com) has been marketing motors with this topology for a long time--just not bearingless ones. [Suggest that the authors put text in paper explaining novelty vs. these previous motors]
3) The control scheme of the motor is also not very novel.  10.1109/IAS.2012.6374033 is an example of a similar DQ-based control scheme for motoring and suspension. [Suggest that the authors put text in the paper explaining how the controller is novel vs. other slotless bearingless controllers.  Although the motor structure has differences than other bearingless motors, the control approach looks very similar to other bearingless PM motors].

Author Response

Dear Reviewer,

 

First of all, we would like to express our deep gratitude to you, who have spent much of your time reading our paper and give us valuable advice. We also hope that we will receive your contribution in our future researches. Basing on your comments and questions, we have been trying our best to revise the paper. We would like to attach here the questions and our answers.

Please see the attachment

Yours faithfully,

Quang Dich, Nguyen

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors have partly improved their manuscript according to reviewers' comments and suggestions. There are still some points that should be addressed:

1) Please, explain in the introduction why is the proposed control approach better than previously published control approaches? Refer to appropriate papers in order to compare your approach with other authors.

2) Why is the only one denominator equal to "6n" and others are equal to "3n" in equation (31)?

3) I still suggest to include the simulation results for sake of demonstration that your model is correct.   

Author Response

Dear Reviewer,

 

First of all, we would like to express our deep gratitude to you, who have spent much of your time reading our paper and give us valuable advice. We also hope that we will receive your contribution in our future researches. Basing on your comments and questions, we have been trying our best to revise the paper. We would like to attacted here the questions and our answers.

Please see the attachment

Yours faithfully,

Quang Dich, Nguyen

Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

The revised version adequately addresses this reviewer's comments.