Design and Analysis of a Highly Reliable Permanent Magnet Synchronous Machine for Flywheel Energy Storage
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors
This paper aims to propose a permanent magnet synchronous machine (PMSM) design for flywheel energy storage systems (FESS), considering specific features to enhance its fault-tolerance capabilities / reliability. The following points are raised:
1. Introduction of the manuscript lacks depth, and the state of art is insufficiently showcased. Authors should provide additional references that clearly show the novelty and originality of their work. The introduction should also provide a more comprehensive discussion of existing works on the design of PMSM for FESS and high-speed(HS) FESS.
2. The flowchart of the article begins with the selection of the slot/pole count for an inner-rotor PMSM, considering auxiliary teeth in the stator structure to reduce short circuit (SC) currents. However, several choices lack sufficient reference support or analytical justification. In this sense, authors are asked to provide explanations for their selection criteria regarding the slot-pole combination, the shape and dimensions of the rotor magnetic barriers, etc.
3. Authors are asked to provide a detailed explanation for their choice of rotor speed, which appears to be lower than that of the latest trends of FESS. In this regard, PMSMs are preferred for HS-FESS due to their performance merits.
4. The resulting dimensions of the auxiliary tooth were obtained by considering a basic sweep analysis, and no further discussion was provided. Considering that the machine has fixed dimensions, and no optimization is carried out, the dimensioning of the auxiliary tooth is not generalizable. Also, the trade-off between SC current and torque capacity of the machine is not properly discussed. Authors are encouraged to provide information regarding SC current density as well: a larger auxiliary tooth can result in lower copper utilization, leading to an increase in current density for the same current magnitude. This could be addressed to better disclose the impact of adopting stator auxiliary teeth.
5. In this paper, high reliability is quantified only by the magnitude of SC current, but little evidence is provided to demonstrate this reliability increase when compared to other design alternatives. A numerical indicator should be devised or extracted from literature to disclose the “reliability” variation.
6. There are several pieces of information missing in the Experimental Validation section. The authors need to provide information about the experimental setup, including the specifics of the measuring devices and other relevant equipment.
7. In the Experimental Validation Section, only basic back-emf results are provided, which are not related to the PMSM reliability. Furthermore, authors do not link the experimental results with the discussion of the paper, other than stating that a good match is obtained between FE simulations and experimental testing. Considering that back-emf is a relatively simple variable, the bare minimum is to have a good match between FE simulation and experimental test in the back-emf, but this cannot be related to a good agreement in other performance metrics such as torque capacity, relevant inductances, cogging torque, efficiency, etc. Authors are then expected to better link the experimental results with the scope of the paper and strengthen this section.
8. The conclusion must be completely refocused, since several statements are already well-known from literature. it is well known that adopting a dual three-phase winding and auxiliary teeth in the stator structure contribute to enhance the fault-tolerance capability of a rotary electrical machine, so authors should showcase what the actual contribution of their work is. Also, it is stated that “a prototype was built and tested, which verifies the theoretical analysis and simulation results”, which is far from being true, and further discussion and results should be provided.
In summary, this version of the paper requires major changes to improve its technical quality, in order to reconsider if it genuinely contributes to advancing knowledge on the adoption of PMSM in FESS.
Comments on the Quality of English Language
Manuscript must be proofread, and grammar and redaction errors must be corrected, such as:
“High reliable”, used both in the article title and in other sections of the manuscript.
“vary between the different winding structures are different” in line 104.
Author Response
Comment 1:
Introduction of the manuscript lacks depth, and the state of art is insufficiently showcased. Authors should provide additional references that clearly show the novelty and originality of their work. The introduction should also provide a more comprehensive discussion of existing works on the design of PMSM for FESS and high-speed(HS) FESS.
Response:
Thank you very much for your comments! We agree with your comments. Your comments are valuable and helpful for improving the quality of this manuscript. We have provided additional references that clearly show the novelty and originality. Besides, PMSMs meet the requirements of flywheel energy storage system and are already used in the system. In [20], a high speed PMSM for magnetic suspended flywheel energy storage system was investigated. With a three-stage-rotor structure, the proposed machine retains the characteristics of common PMSMs, and has the advantages of easy manufacturing and assembling. The machine can provide considerable performance with a simple and solid structure, which is conducive to the increase of machine speed, as well as the increase of system power and stored energy. In [21], a cup winding PMSM was proposed for flywheel energy storage system. The machine can effectively improve the efficiency of the flywheel energy storage system and reduce the axial height of the flywheel. A new optimization strategy is proposed to optimize the efficiency and volume characteristics of the machine, and the results verify the correctness of the optimization method. (referred to Paragraph 2, Section 1)
Comment 2:
The flowchart of the article begins with the selection of the slot/pole count for an inner-rotor PMSM, considering auxiliary teeth in the stator structure to reduce short circuit (SC) currents. However, several choices lack sufficient reference support or analytical justification. In this sense, authors are asked to provide explanations for their selection criteria regarding the slot-pole combination, the shape and dimensions of the rotor magnetic barriers, etc.
Response:
Thank you very much for your comments! Your comments are valuable and helpful for improving the quality of this manuscript. Compared to the integer-slot distributed winding scheme, the fractional-slot concentrated winding scheme has a similar number of slot poles. Additionally, the winding factor of the fractional-slot concentrated winding scheme is generally higher, offering advantages such as increased reliability and higher power density. Considering the heat dissipation capacity of the machine, the number of slots should be appropriately large. As a result, the number of slots is selected to be 24. Besides, too many pole pairs can lead to significant eddy current losses. Finally, taking into account the winding factor, radial force, heat dissipation capacity, and overall losses, the 24-slot, 20-pole fractional-slot centralized winding scheme is adopted. Additionally, the magnetic barriers are designed on the rotor core to reduce magnetic flux leakage. Since the rotor without magnetic barriers is partially saturated, the region of partial saturation is designed with a magnetic barrier and is similar in size. In order to simplify the processing difficulty, the magnetic barrier is designed with a rectangular shape. (referred to Paragraph 2, Section 2)
Comment 3:
Authors are asked to provide a detailed explanation for their choice of rotor speed, which appears to be lower than that of the latest trends of FESS. In this regard, PMSMs are preferred for HS-FESS due to their performance merits.
Response:
Thank you very much for your comments! We agree with your comment. PMSMs are preferred for HS-FESS due to their performance merits. As all know, high-speed machines have extremely high requirements for the experimental platform, and the experimental testing of high-speed machines is dangerous. Considering the experimental conditions and safety factors, the rated speed of the PMSM proposed in the manuscript is determined to be 3500 rpm.
Comment 4:
The resulting dimensions of the auxiliary tooth were obtained by considering a basic sweep analysis, and no further discussion was provided. Considering that the machine has fixed dimensions, and no optimization is carried out, the dimensioning of the auxiliary tooth is not generalizable. Also, the trade-off between SC current and torque capacity of the machine is not properly discussed. Authors are encouraged to provide information regarding SC current density as well: a larger auxiliary tooth can result in lower copper utilization, leading to an increase in current density for the same current magnitude. This could be addressed to better disclose the impact of adopting stator auxiliary teeth.
Response:
Thank you very much for your comments. We agree with your comments. The dimensions of the auxiliary tooth are obtained by considering a basic sweep analysis, including length and width. Since the length of the auxiliary teeth has a huge influence on the self-inductance and mutual inductance of the PMSM, the length of the auxiliary teeth is determined first. However, the width of the auxiliary teeth is determined by considering the self-inductance and mutual inductance, short-circuit current and performance of the PMSM. Additionally, the short-circuit current and torque decrease approximately linearly with increasing width of the auxiliary teeth. However, the torque reduction shows slight fluctuations. Therefore, it is important to avoid a significant drop of the torque. Notably, when the width of the auxiliary teeth exceeds 4 mm, there is a marked decrease in torque. It is necessary to reduce the short-circuit current while reduce the impact on torque. Consequently, the width of the auxiliary teeth is selected to be 4 mm. Due to the design of the auxiliary teeth, the steady-state short-circuit current decreases from 123 A to 90 A, and the peak short-circuit current decreases from 234 A to 183 A, representing reductions of 27 % and 22 %, respectively. The adoption of the auxiliary teeth results in a decrease in average torque from 368 N·m to 354 N·m, accompanied by an increase in torque ripple from 2.6 % to 2.9 %. Additionally, in the auxiliary teeth design, the width of the stator teeth decreases as the size of auxiliary teeth increases, ensuring the groove area remains consistent. As a result, the slot fill rate and current density are kept constant. (referred to Paragraph 4 and 5, Section 3.2)
Comment 5:
In this paper, high reliability is quantified only by the magnitude of SC current, but little evidence is provided to demonstrate this reliability increase when compared to other design alternatives. A numerical indicator should be devised or extracted from literature to disclose the “reliability” variation.
Response:
Thank you very much for your comments! Your comments are valuable and helpful for improving the quality of this manuscript. Due to the design of the auxiliary teeth, the steady-state short-circuit current decreases from 123 A to 90 A, and the peak short-circuit current decreases from 234 A to 183 A, representing reductions of 27 % and 22 %, respectively. Reducing the short-circuit current effectively lowers the temperature and the risk of melting in the event of machine winding short circuit, thereby enhancing the reliability of the PMSM. Additionally, the degree of phase-to-phase coupling can serve as an indicator of the reliability of the PMSM. The degree of phase-to-phase coupling of the PMSM without auxiliary teeth is calculated as 23%. However, the phase-to-phase coupling for the PMSM with auxiliary teeth is only 12%, indicating a significant improvement in reliability. (referred to Paragraph 2, Section 4)
Comment 6:
There are several pieces of information missing in the Experimental Validation section. The authors need to provide information about the experimental setup, including the specifics of the measuring devices and other relevant equipment.
Response:
Thank you very much for your comment! The experimental platform is shown in Fig. R1, including the controller and machine.
Fig. R1. Experimental platform.
Comment 7:
In the Experimental Validation Section, only basic back-emf results are provided, which are not related to the PMSM reliability. Furthermore, authors do not link the experimental results with the discussion of the paper, other than stating that a good match is obtained between FE simulations and experimental testing. Considering that back-emf is a relatively simple variable, the bare minimum is to have a good match between FE simulation and experimental test in the back-emf, but this cannot be related to a good agreement in other performance metrics such as torque capacity, relevant inductances, cogging torque, efficiency, etc. Authors are then expected to better link the experimental results with the scope of the paper and strengthen this section.
Response:
Thank you very much for your comments! We have supplemented the experiment and compared the measured results with the simulation results. Since the experimental condition is limited, the short-circuit current test is not carried out. Besides, since the PMSM used in the experimental platform lacks a water-cooled sleeve, only low-load experiments can be conducted. The low-load experimental waveforms are measured and shown in Fig. R2. It is can be seen that the blue line represents the electrical angle of the PMSM at 0.3663 V/rad. The red line shows the bus current, the yellow line indicates the bus voltage and the green line corresponds to the phase A current. The electrical angle, bus current, bus voltage, and phase A current waveforms of the PMSM are measured. Under the steady-state conditions, the bus voltage is maintained at 600 V, the bus current is 15 A and the peak-to-peak fluctuation of the bus voltage is 5 V. The phase current shows distortion, with a large 3th harmonic content (referred to Paragraph 2, Section 5)
Fig. R2. Low-load experimental waveform.
Comment 8:
The conclusion must be completely refocused, since several statements are already well-known from literature. it is well known that adopting a dual three-phase winding and auxiliary teeth in the stator structure contribute to enhance the fault-tolerance capability of a rotary electrical machine, so authors should showcase what the actual contribution of their work is. Also, it is stated that “a prototype was built and tested, which verifies the theoretical analysis and simulation results”, which is far from being true, and further discussion and results should be provided.
Response:
Thank you very much for your comment! We agree with your comments. In this article, a high reliable PMSM has been proposed for flywheel energy storage system. The main contribution of the proposed PMSM was to enhance the reliability while ensuring the electromagnetic performance. A comparison and analysis were conducted between the conventional double-layer three-phase winding structure and the dual three-phase stator winding structure. The results indicate that the double redundant winding structure ensures fault-tolerant operation of the PMSM. Besides, the stator was designed with auxiliary teeth to reduce the short-circuit current. This reduction effectively lowers the temperature and mitigates the risk of melting during a winding short circuit, thereby enhancing the reliability. Moreover, the electromagnetic performance and mechanical stress were analyzed. A prototype was built and tested, and the measured and simulated back electromotive force coefficient were in good agreement, indicating the rationality of the prototype manufacturing and design. Due to limitations of the experimental platform, only low-load waveforms were measured. The bus voltage was maintained at 600 V, the bus current was 15 A, and the peak-to-peak fluctuation of the bus voltage was 5 V. The phase current exhibited distortion with significant 3th harmonic content. (referred to Paragraph 1, Section 6)
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsIn this article, a permanent magnet synchronous machine for a flywheel energy storage system is proposed. According to the authors, it is said to be highly reliable. The dual three-phase stator winding structure used is intended to suppress harmonics of the magnetomotive force and thus improve the reliability. In addition, the stator is equipped with auxiliary teeth to reduce the short-circuit current, which is also intended to improve the reliability of the PMSM.
Due to increasing climate change, the introduction of large-capacity energy storage technologies in the field of new energies is an important issue. Flywheel energy storage systems can play an important role in short-term storage due to their properties such as high energy storage density, high efficiency and long service life.
Unfortunately, the publication does not offer much added value compared to the state of the art and compared to other publications, as many topics are only examined and discussed very superficially, which is clearly not enough for a journal article. Specifically, I criticize the following points:
Introduction
· Flywheel mass storage systems are only used for short-term storage of electrical energy. This is not discussed at all.
· The large interturn short-circuit current is mainly described as a decisive parameter for reliability. However, there are no literature sources to show that this fault is actually a problem. What faults actually occur in flywheel energy storage systems? I think these are mainly mechanical problems.
· In addition, the harmonics of the magnetomotive force are described as a parameter to improve reliability. This statement is also not supported by any literature and is therefore baseless.
Machine Topology
· The current state of technology regarding auxiliary teeth is not discussed.
· No explanation is given as to why the 24/10 topology was chosen.
· All material data missing.
· The motor has a rated speed of 3500 rpm. How does this relate to fast rotating flywheel systems? What are the general requirements for these systems?
High Reliability Design
· What is the effect of a rotor step-skewing?
· Where do the results in Figures 3 to 5 come from? What does the simulation look like? What software was used? What boundary conditions were set? etc.
· Equations are missing, for example for calculating the winding factors or inductances.
· What slot fill factor was assumed?
Performance Analysis
· Where do the results in Figures 11 to 12 come from? What does the simulation look like? What software was used? What boundary conditions were set? etc.
· To what extent was the winding temperature taken into account?
Experimental Validation
· The experimental testing only includes the measurement of the EMF. That is not enough. What about the measurement of the inductances, the short-circuit currents, the torque? Where is the comparison between measurement and simulation?
Conclusion
· The discussion of the results is far too brief and superficial. The statement is made that the results show that the dual three-phase stator winding structure significantly improves reliability. This is not evident anywhere in the article.
In summary, it must unfortunately be stated that the article has serious flaws and additional experiments are required.
Author Response
Please refer to the pdf document as some pictures and equations can not be shown in the notes.
Comment 1:
Flywheel mass storage systems are only used for short-term storage of electrical energy. This is not discussed at all. The large interturn short-circuit current is mainly described as a decisive parameter for reliability. However, there are no literature sources to show that this fault is actually a problem. What faults actually occur in flywheel energy storage systems? I think these are mainly mechanical problems. In addition, the harmonics of the magnetomotive force are described as a parameter to improve reliability. This statement is also not supported by any literature and is therefore baseless.
Response:
Thank you very much for your comments! We agree with your comments. Flywheel energy storage systems are only used for short-term storage of electrical energy. Therefore, flywheel energy storage systems are well-suited for stabilizing grid load fluctuations and providing backup power. Flywheel energy storage systems can deliver power support for brief periods to maintain stable operation when the main power supply fails. The mainly faults of flywheel energy storage systems are mechanical problems. Besides, as the core component of flywheel energy storage systems, the main faults of the machine should be considered. We have discussed the main faults of PMSMs applied to flywheel energy storage systems. Since the magnetic field of the permanent magnet material cannot be eliminated, PMSM may continue to generate a strong magnetic field during a failure, causing equipment overheating or unsafe magnetic field interference. Reducing the short-circuit current can mitigate the impact on equipment and decrease the damage caused by failures. Additionally, there is a mistake in description of the magnetomotive force harmonics. The dual three-phase winding structure almost completely eliminates the second harmonic, resulting in a significant reduction in eddy loss for the PMSM. The double redundant winding structure ensures the fault-tolerant operation of the PMSM under a set of open-circuit winding faults. (referred to Paragraph 1, Section 1)
Comment 2:
The current state of technology regarding auxiliary teeth is not discussed. No explanation is given as to why the 24/10 topology was chosen. All material data missing. The motor has a rated speed of 3500 rpm. How does this relate to fast rotating flywheel systems? What are the general requirements for these systems?
Response:
Thank you very much for your comments! Your comments are valuable and helpful for improving the quality of this manuscript. Compared to the integer-slot distributed winding scheme, the fractional-slot concentrated winding scheme has a similar number of slot poles. Additionally, the winding factor of the fractional-slot concentrated winding scheme is generally higher, offering advantages such as increased reliability and higher power density. Considering the heat dissipation capacity of the machine, the number of slots should be appropriately large. As a result, the number of slots is selected to be 24. Besides, too many pole pairs can lead to significant eddy current losses. Finally, taking into account the winding factor, radial force, heat dissipation capacity, and overall losses, the 24-slot, 20-pole fractional-slot centralized winding scheme is adopted. All material data of the PMSM is listed in Table RI. As all know, high-speed machines have extremely high requirements for the experimental platform, and the experimental testing of high-speed machines is dangerous. Considering the experimental conditions and safety factors, the rated speed of the PMSM proposed in the manuscript is determined to be 3500 rpm. (referred to Paragraph 1 and 2, Table 1, Section 2)
TABLE RI
Material data of PMSM
|
Item |
Material |
|
Stator core |
B20AT1500 |
|
Rotor core |
B35AH230 |
|
Magnet |
N42UH |
Comment 3:
What is the effect of a rotor step-skewing? Where do the results in Figures 3 to 5 come from? What does the simulation look like? What software was used? What boundary conditions were set? etc. Equations are missing, for example for calculating the winding factors or inductances. What slot fill factor was assumed?
Response:
Thank you very much for your comments! Your comments are valuable and helpful for improving the quality of this manuscript. The results in Figures 3 and 4 are solved by finite-element analysis. The results in Figures 5 are derived by Fourier decomposition of the results in Figure 4. In addition, the results of Figures 3 to 5 are exported by finite-element software and plotted in Origin software. In finite-element analysis, a boundary condition with zero magnetic flux is set outside the PMSM model. The equations of the winding factors and inductances has been added to the manuscript. The slot fill factor is assumed to be 0.6. The winding coefficient kN can be expressed as
|
(R1) |
|
|
(R2) |
|
|
(R3) |
where Q is the number of the stator slots, p is the number of the rotor pole-pairs, q is the number of slots per pole per phase, α is the slot spacing angle. Therefore, the winding coefficient of the proposed PMSM is calculated as 0.933.
The self-inductance and mutual inductance can be expressed as
|
(R4) |
|
|
(R5) |
where θ is the mechanical angle of the PMSM, μ0 is the vacuum permeability, r is the radius of the effective air gap, l is the axial length of the PMSM, NA(θ) is the winding function. (referred to Paragraph 1, Equs. (1), (2) and (3), Section 2, Paragraph 1 and 2, Section 3.1, Paragraph 1, Equs. (4) and (5), Section 3.2)
Comment 4:
Where do the results in Figures 11 to 12 come from? What does the simulation look like? What software was used? What boundary conditions were set? etc. To what extent was the winding temperature taken into account?
Response:
Thank you very much for your comments! Your comments are valuable and helpful for improving the quality of this manuscript. The results in Figures 11 to 12 are solved by finite-element analysis. The results in Figures 11 (b) are derived by Fourier decomposition of the results in Figure 11 (a). In addition, the results of Figures 11 to 12 are exported by finite-element software and plotted in Origin software. In finite-element analysis, a boundary condition with zero magnetic flux is set outside the PMSM model. The temperature in the stator slot winding area can reach up to 128 degrees Celsius, as shown in Fig. R1.
Fig. R1. Radial temperature distribution.
Comment 5:
The experimental testing only includes the measurement of the EMF. That is not enough. What about the measurement of the inductances, the short-circuit currents, the torque? Where is the comparison between measurement and simulation?
Response:
Thank you very much for your comments! Your comments are valuable and helpful for improving the quality of this manuscript. We have supplemented the experiment and compared the measured results with the simulation results. Since the experimental condition is limited, the short-circuit current test is not carried out. Besides, since the PMSM used in the experimental platform lacks a water-cooled sleeve, only low-load experiments can be conducted. The low-load experimental waveforms are measured and shown in Fig. R2. It is can be seen that the blue line represents the electrical angle of the PMSM at 0.3663 V/rad. The red line shows the bus current, the yellow line indicates the bus voltage and the green line corresponds to the phase A current. The electrical angle, bus current, bus voltage, and phase A current waveforms of the PMSM are measured. Under the steady-state conditions, the bus voltage is maintained at 600 V, the bus current is 15 A and the peak-to-peak fluctuation of the bus voltage is 5 V. The phase current shows distortion, with a large 3th harmonic content (referred to Paragraph 2, Section 5)
Fig. R2. Low-load experimental waveform.
Comment 6:
The discussion of the results is far too brief and superficial. The statement is made that the results show that the dual three-phase stator winding structure significantly improves reliability. This is not evident anywhere in the article.
Response:
Thank you very much for your comments! Your comments are valuable and helpful for improving the quality of this manuscript. In this article, a high reliable PMSM has been proposed for flywheel energy storage system. The main contribution of the proposed PMSM was to enhance the reliability while ensuring the electromagnetic performance. A comparison and analysis were conducted between the conventional double-layer three-phase winding structure and the dual three-phase stator winding structure. The results indicate that the double redundant winding structure ensures fault-tolerant operation of the PMSM. Besides, the stator was designed with auxiliary teeth to reduce the short-circuit current. This reduction effectively lowers the temperature and mitigates the risk of melting during a winding short circuit, thereby enhancing the reliability. Moreover, the electromagnetic performance and mechanical stress were analyzed. A prototype was built and tested, and the measured and simulated back electromotive force coefficient were in good agreement, indicating the rationality of the prototype manufacturing and design. Due to limitations of the experimental platform, only low-load waveforms were measured. The bus voltage was maintained at 600 V, the bus current was 15 A, and the peak-to-peak fluctuation of the bus voltage was 5 V. The phase current exhibited distortion with significant 3th harmonic content. (referred to Paragraph 1, Section 6)
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe article concerns a very interesting topic, but it requires refinement. In my opinion, the following should be added:
1/. Winding diagrams and machine design dimensions with the type of machine and the determined winding coefficients
2/. Providing the method of determining MMF, inductance, currents, EMF, torques (FEM - what package ...)
3/. The waveforms from Figures 3 and 4 should be subjected to a reliable analysis due to their characteristic shapes
4/. It is necessary to compare model calculations with measurements and to formulate specific conclusions!!!
Due to the physical model of the machine that the authors have, this topic has great potential and may be interesting for many people.
The text should be subjected to linguistic correction.
Generally, the waveforms should be compared through harmonic analysis!!! This applies to all quantities and parameters (not only EMF).
I believe that in its current form the work is not suitable for publication.
Author Response
Comment 1:
Winding diagrams and machine design dimensions with the type of machine and the determined winding coefficients.
Response:
Thank you very much for your comments! Your comments are valuable and helpful for improving the quality of this manuscript. Winding connection diagram of the PMSM has been added to the manuscript, as shown in Fig. R1. It can be seen that a double-layer, dual three-phase winding structure is adopted in the stator. The design dimensions of the proposed PMSM have been added to the manuscript and listed in Table RI. Sine the numbers of the stator slots and rotor pole are 24 and 20 respectively, the winding coefficient can be calculated. The winding coefficient kN can be expressed as
|
(R1) |
|
|
(R2) |
|
|
(R3) |
where Q is the number of the stator slots, p is the number of the rotor pole-pairs, q is the number of slots per pole per phase, α is the slot spacing angle. Therefore, the winding coefficient of the proposed PMSM is calculated as 0.933. (referred to Paragraph 1and 2, Fig. 2, Table 1, Equs. (1), (2) and (3), Section 2)
Fig. R1. Winding connection.
TABLE RI
Design dimensions and structure parameters of proposed PMSM
|
Item |
Value |
|
Rotor speed /rpm |
3500 |
|
Direct current bus voltage /V |
750 |
|
Rated power /kW |
140 |
|
Stator slot number |
24 |
|
Rotor polo number |
20 |
|
Wingding coefficient |
0.933 |
|
Stator outer diameter /mm |
370 |
|
Stator inner diameter /mm |
270 |
|
Air gap length/mm |
0.9 |
|
Axial length/mm |
80 |
|
Permanent magnet thickness /mm |
4 |
|
Stator yoke thickness /mm |
9 |
Comment 2:
Providing the method of determining MMF, inductance, currents, EMF, torques.
Response:
Thank you very much for your comment! The simulation results of the MMF, inductance, currents, EMF, torques and so on of the proposed PMSM are solved by finite-element analysis. The relevant description has been added to the manuscript. (referred to Paragraph 2, Section 3.1)
Comment 3:
The waveforms from Figures 3 and 4 should be subjected to a reliable analysis due to their characteristic shapes.
Response:
Thank you very much for your comments! Your comments are valuable and helpful for improving the quality of this manuscript. The amplitude of the magnetomotive force remains consistent across each set of windings. The two sets of windings are completely independent. However, there exists a phase difference between each set of windings. The magnetomotive force distributions vary between the different winding structures are different, resulting in distinct harmonic content. Due to the double redundant winding structure of the dual three-phase winding, the fault-tolerant operation of the PMSM under a set of open-circuit winding faults can be ensured. As a result, the reliability of the PMSM is greatly improved. (referred to Paragraph 2, Section 3.1)
Comment 4:
It is necessary to compare model calculations with measurements and to formulate specific conclusions!!!
Response:
Thank you very much for your comment! We have supplemented the experiment and compared the measured results with the simulation results. The no-load back electromotive force waveform of the PMSM is measured and shown in Fig. R2 (a). It can be seen that the measured back electromotive force waveform appears predominantly sinusoidal. The peak of the back electromotive force is 455 V and the back electromotive force coefficient is 0.13 V/rpm. Fig. R2 (b) compares the experimental and simulated values of the no-load back electromotive force at various speeds. The simulated back electromotive force coefficient is 0.132 V/rpm, which closely matches the measured value, indicating the rationality of the prototype manufacturing and design. Since the PMSM used in the experimental platform lacks a water-cooled sleeve, only low-load experiments can be conducted. The low-load experimental waveforms are measured and shown in Fig. R3. It is can be seen that the blue line represents the electrical angle of the PMSM at 0.3663 V/rad. The red line shows the bus current, the yellow line indicates the bus voltage and the green line corresponds to the phase A current. The electrical angle, bus current, bus voltage, and phase A current waveforms of the PMSM are measured. Under the steady-state conditions, the bus voltage is maintained at 600 V, the bus current is 15 A and the peak-to-peak fluctuation of the bus voltage is 5 V. The phase current shows distortion, with a large 3th harmonic content (referred to Paragraph 1 and 2, Section 5)
|
|
(a) |
(b) |
Fig. R2. Comparison of experimental and simulated results. (a) Back electromotive force of prototype. (b) Comparison of back electromotive force coefficient.
Fig. R3. Low-load experimental waveform.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsEfforts were made to improve the previous version of the manuscript and several of my comments were addressed correctly. Nonetheless, the new version of the manuscript could better identify and discuss novelty, since only a few new references were added.
Comments on the Quality of English LanguageComments on the previous versions were correctly addressed
Author Response
Comment 1:
Efforts were made to improve the previous version of the manuscript and several of my comments were addressed correctly. Nonetheless, the new version of the manuscript could better identify and discuss novelty, since only a few new references were added.
Response:
Thank you very much for your comments! Your comments are valuable and helpful for improving the quality of this manuscript. We have discussed and summarized the innovations of this manuscript, including the dual three-phase stator winding structure and the design of the stator with auxiliary teeth. The double redundant winding structure ensures the fault-tolerant operation of the PMSM under a set of open-circuit winding faults. The stator is designed with auxiliary teeth to reduce the short-circuit current, thereby lowering temperature and mitigating the risk of melting during a winding short circuit. Due to the dual three-phase stator winding structure and auxiliary teeth, the reliability of the PMSM is significantly improved. Additionally, we have added more new references and related content to the manuscript. (referred to Paragraph 1, 2 and 4, Section 1)
Reviewer 2 Report
Comments and Suggestions for AuthorsThank you for the changes you have made, I can now accept your paper.
Author Response
Comment 1:
Thank you for the changes you have made, I can now accept your paper.
Response:
Thank you very much for your comments! We have tried our best to revise our manuscript according to your comments.
