Time-Optimal Current Control of Synchronous Motor Drives
Round 1
Reviewer 1 Report
1. The abstract is weak and the contribution is absent.
2. The literature has to be enriched by relevant works. I suggest the following researches:
doi.org/10.1080/21642583.2018.1547887, doi.org/10.1504/IJPEC.2013.057033
3. The contribution has to be stated clearly in the end of "Introduction" part.
4. Some abbreviations like TOC has to be extended when firstly mentioned.
5. The solution of x(t) does not obey to discretization techniques, where the controller will finally developed in discrete form at the real-time application.
6. The authors have to explain why Field Orientation has not be utilized in this application.
7. Figure (4) has to be indicated by labels to show its parts. Also, the hardware has to be explained.
8. The results have not addressed the real-time signals of currents, flux and speed.
9. In the abstract, the authors have mentioned the "PID" controller, which is not compared at all.
10. The results need to be reported in Tables.
11. The conclusion is descriptive and it lacks quantitative
Author Response
Thank you very much for the detailed and instructive review. We have made the requested changes as follows:
1. The abstract is weak and the contribution is absent.
• We have entirely rewritten the abstract and emphasized our contribution in the text.
2. The literature has to be enriched by relevant works. I suggest the following researches: doi.org/10.1080/21642583.2018.1547887, doi.org/10.1504/IJPEC.2013.057033
• We agree that the literature was too focused on the time optimal control without references to surrounding literature. We have now extended the introduction as well as the citation list.
3. The contribution has to be stated clearly in the end of "Introduction" part.
• We now explicitly list the contribution of our work.
4. Some abbreviations like TOC has to be extended when firstly mentioned.
• Thanks for spotting this mistake, we now define it in introduction.
5. The solution of x(t) does not obey to discretization techniques, where the controller will finally developed in discrete form at the real-time application.
• It is a very good point. The solution that we are evaluating is p_{0} which is substitution for t=0. However, it requires proper alignment of the continuous time with the discrete.
• We have added a new Section 3.3.1 to explain it.
6. The authors have to explain why Field Orientation has not be utilized in this application.
• The proposed controller is working in dq frame oriented with the rotor flux, hence it falls into the field orientation class.
• What has not been explained sufficiently well is that the proposed controller is a feed-forward controller that can be connected with any feedback control. We have now extended this description to make it more explicit.
7. Figure (4) has to be indicated by labels to show its parts. Also, the hardware has to be explained.
• We have added explanatory labels to objects on the image. Also we have added an image of the converter and the control board (all custom made).
8. The results have not addressed the real-time signals of currents, flux and speed.
• We have focused only on the transients since this is where the controller differs from each other. The transient lasts only a couple of sampling periods (typically under 20ms), hence the speed can be considered to be constant. Therefore, we provide it only in the form of a static number in Figure 8.
• All other real-time signals are displayed in Figure 8, except the flux which is only a a linear transformation of the current, hence we consider it redundant.
• We conjecture that figures 7 and 8 were too far away from each other that it was inconvenient to see the connection. We have restructured the document to bring the figures closer.
9. In the abstract, the authors have mentioned the "PID" controller, which is not compared at all.
• It is indeed a typo. The compared controller does not use the derivative part, hence it is a PI controller.
• We have corrected the abstract to acknowledge that.
10. The results need to be reported in Tables.
• Thank you for the suggestion. We have added the settling times to a new Table 2. The benefits are now much more clearly visible.
11. The conclusion is descriptive and it lacks quantitative
• We have improved the conclusion by including quantitative results and future work.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
My comments are listed below:
*Eq(2), move the dot (differentiation) on the symbol 'x'
*Sec 2.2: capitalize first letter 'T'ime-optimal
*Revise 'has from' above Eq(6).
*For Figure 8, the author may provide a summary table listing the key specifications achieved, eg, comparison of settling time under different approaches and how many percentage of TOC have improved.
*For the PI and Deadbeat controller, their mathematical forms should be provided. In addition, how do you justify the parameters of those compared controller have been tuned to be optimal?
*The authors should proofread the paper thoroughly and correct other writing errors.
Author Response
Thank you for providing us with a detailed and instructive review. We have addressed all points as follows:
- Eq(2), move the dot (differentiation) on the symbol 'x'
- Thanks for spotting the error. Corrected.
- Sec 2.2: capitalize first letter 'T'ime-optimal
- Thanks for spotting the error. Corrected.
- Revise 'has from' above Eq(6).
- Thanks for spotting the error. Corrected.
- For Figure 8, the author may provide a summary table listing the key specifications achieved, eg, comparison of settling time under different approaches and how many percentage of TOC have improved.
- Thanks for the suggestion. We have measured the settling times and listed them in Table 2. The TOC is 4 times faster at the highest speed.
- For the PI and Deadbeat controller, their mathematical forms should be provided. In addition, how do you justify the parameters of those compared controller have been tuned to be optimal?
- The DB controller has no parameters, hence it does not have to be tuned.
- The PI controller was tuned manually for best overall performance. Different tuning has local impact, however, it never changes the controller strategy since it is a pure feed-back controller. We have extended description of the tuning.
- The authors should proofread the paper thoroughly and correct other writing errors.
- We have done another round of proofreading.
We have uploaded a new version of the manuscript containing also changes requested by other reviewers.
Author Response File: Author Response.pdf
Reviewer 3 Report
In the article under review, the authors proposed a time-optimal control strategy for the current control of the synchronous motor. This strategy differs from the known ones by taking into account the stator resistance and the differences in stator inductances along the d and q axis. The studies were carried out both by methods of mathematical modeling and on an experimental setup with a 4.5 kW interior permanent magnet synchronous motor (IPMSM). Undoubtedly, the studies carried out by the authors are relevant. This is a theoretical study, the results of which can be useful to scientists and researchers, specialists in the field of synchronous electrical machines control.
In the Introduction and literature review, the prerequisites for conducting research are considered in sufficient detail, and the purpose of the paper is formulated. In the main parts of the paper, a mathematical description of the synchronous motor drive and a description of the strategy for time-optimal control with neglected stator resistance are presented. A strategy of time-optimal flux control considering stator resistance is developed. The results of simulations and experimental studies on a laboratory setup are presented.
However, during the review, I drew attention to the following shortcomings, the correction of which would improve the quality of the paper and I would also like to ask for clarification:
- I think that a description of the structure of the paper should be added to the Introduction.
- In what software did the authors perform simulations? This must be stated in the paper.
- Is there a practical application of the developments proposed by the authors? Please give a few examples.
- Do the authors of the paper have plans for further research? I propose to describe them at the end of the paper.
I would like to thank the authors for the quality research and congratulate the authors on a well-prepared article. I recommend this article for publication after minor revision.
Author Response
Thank you very much for providing us with detailed and instructive review. We have addressed all points and attach a new version that also reflects suggestions from other reviewers.- I think that a description of the structure of the paper should be added to the Introduction.
- We have added a structure description at the end of the Introduction.
- In what software did the authors perform simulations? This must be stated in the paper.
- All simulations were performed in Matlab. We now state it explicitly at the beginning of Section 4.
- Is there a practical application of the developments proposed by the authors? Please give a few examples.
- The key benefit is faster and more accurate torque tracking. We believe that it may be of great interest for servo drives in robotics or manipulation. We have extended the conclusion to mention that.
- Do the authors of the paper have plans for further research? I propose to describe them at the end of the paper.
- The proposed method can be used as a general feed-forward building block that can be combined with almost any existing controller. We believe that exploring such possibilities opens a lot of space for future research. This is now mentioned in conclusion.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors have addressed all my comments. No further comments are required. Thank you.
