Design and Experimental Evaluation of an In-Wheel Flux-Switching Machine for Light Vehicle Application

Round 1

Reviewer 1 Report

This is the comments on the Manuscript Number: ID: machines-1835835;

Type: Article;

Title: Design and Experimental Evaluation of an In-Wheel Flux-Switching
Machine for Light Vehicle Application .

Authors: Gabriel Alves Mendonça, Diogo P. V. Galo, Luís C. M. Sales, Braz
J. Cardoso, Thales A. C. Maia.

Rate the Manuscript:

1. Significance to field and specialization of “Machines” journal:     good.

The paper contains the information about Restrictive regulations regarding emissions and fossil fuel
consumption place the electric vehicle as a strong candidate to replace the
conventional internal combustion engine vehicles.

The pure electric
powertrain technology and the charging infrastructure still are immature in
some regions around the globe. Improving existing technologies is one
alternative for the automotive industry, such as increasing combustion engine
efficiency with the aid of electrified powertrains. This paper presents the
design and experimental validation of an in-wheel flux-switching machine, in
which feasibility and technological challenges are discussed. The main goal
is to promote regenerative braking. Later, the energy can be used for fuel
handling and reforming performance enhancement, increasing efficiency and
reducing emissions. The electromagnetic design using the Maxwell-Fourier
method and a novel steady-state equivalent circuit are used for geometry
sensitivity analysis and optimization routine.

2. Scientific content:   good.

3. Originality: good.

4. Clarity and presentation:  acceptable.

5. Appropriateness for Journal: appropriate subject matter for the “Machines” .

6. Need for rapid publication: no.

Remarks:

1. Conclusions consistent with the evidence and arguments
   presented and they address the main question posed and practically similar to abstract:

2.     Must be: it has been established, shown, estimated, calculated, discovered, obtained, etc….

In this paper a flux-switching machine was designed and evaluated. Electromagnetic design was based on the Maxwell-Fourier analyses. The presented method allows the field distribution calculation in a structure with double salience with effectiveness. The calculated field distribution can also be used to estimate the magnetizing level on the core. The presented design was constrained by available space inside the wheel without mechanical modifications of the drum brake. The higher internal diameter, and low rotation speed limited the output power. However, the development and construction process helped to understand the ground base limitations of the application, which will lead to a better performance for upcoming designs. The expected performance was evaluated using the developed equivalent circuit and the machine model was validated using both the finite element method and experimental results. Simulation results showed that keeping the current constant on the field coils prevents field demagnetizing and, consequently, power reduction. This work was the first step towards a better understanding of the development of flux-switching machines for in-wheel application.

A more detailed assessment of the fabrication procedure and complete performance evaluation will be addressed in future papers?

3. The manuscript should be checked by native speaker for correct grammar and spelling.
4. Among 62 References – a lot of no crosref and selfcitations.

Comments for author File: Comments.pdf

Author Response

Revision and re-submission of the manuscript

Dear editor and reviewers, with this brief letter, we kindly address reviewers’ comments to our manuscript. Thank you for your valuable and insightful comments. We carefully reviewed the manuscript according to the comments. The suggestions, and questions lead the manuscript into a greatly improvement.

Many thanks and with all the best wishes,

The authors

The major modifications to the manuscript's

1. The duplicate words and redundant texts were cautiously removed from manuscript.

2. Grammar and spelling were carefully checked.

3. References have been replaced in the manuscript, as suggested by reviewers, in order to avoid self-citations.

4. Some paragraphs have been reformulated according to the authors' corrections.

5. All reviewers' comments were carefully replied.

Reviewer 1

We sincerely thank Reviewer 1 and appreciate his valuable comments and suggestions, which help us to strengthen the manuscript. Comments and suggestions have been carefully corrected.

1^st comment

1. Significance to field and specialization of “Machines” journal: good.

The paper contains the information about Restrictive regulations regarding emissions and fossil fuel consumption place the electric vehicle as a strong candidate to replace the conventional internal combustion engine vehicles. The pure electric powertrain technology and the charging infrastructure still are immature in some regions around the globe. Improving existing technologies is one alternative for the automotive industry, such as increasing combustion engine efficiency with the aid of electrified powertrains. This paper presents the design and experimental validation of an in-wheel flux-switching machine, in which feasibility and technological challenges are discussed. The main goal is to promote regenerative braking. Later, the energy can be used for fuel handling and reforming performance enhancement, increasing efficiency and reducing emissions. The electromagnetic design using the Maxwell-Fourier method and a novel steady-state equivalent circuit are used for geometry sensitivity analysis and optimization routine.

Response to 1^st comment

Thank you for your suggestion. The abstract has been rewritten highlighting the manuscript's scope according to the reviewer's suggestion.

2^nd to 5^th comment

2. Scientific content: good.

3. Originality: good.

4. Clarity and presentation: acceptable.

5. Appropriateness for Journal: appropriate subject matter for the “Machines”

Response to 2^nd to 5^th comment

We would like to gratefully thank the reviewer 1 for objective observations, excellent suggestions, and providing positive and specific comments about our research and the presented manuscript.

6^th comment

Conclusions consistent with the evidence and arguments presented and they address the main question posed and practically similar to abstract:

2. Must be: it has been established, shown, estimated,calculated, discovered, obtained, etc….

In this paper a flux-switching machine was designed and evaluated. Electromagnetic design was based on the

Maxwell-Fourier analyses. The presented method allows the field distribution calculation in a structure with double salience with effectiveness. The calculated field distribution can also be used to estimate the magnetizing level on the core.

The presented design was constrained by available space inside the wheel without mechanical modifications of the drum brake. The higher internal diameter, and low rotation speed limited the output power. However, the development and construction process helped to understand the ground base limitations of the application, which will lead to a better performance for upcoming designs.

The expected performance was evaluated using the developed equivalent circuit and the machine model was validated using both the finite element method and experimental results. Simulation results showed that keeping the current constant on the field coils prevents field demagnetizing and, consequently, power reduction.

This work was the first step towards a better understanding of the development of flux-switching machines for in-wheel application. A more detailed assessment of the fabrication procedure and complete performance evaluation will be addressed in future papers?

The manuscript should be checked by native speaker for correct grammar and spelling.

Among 62 References – a lot of no crosref and selfcitations.

Response to 6^th comment

Thank you for your suggestion. The conclusion has been rewritten highlighting the manuscript's contribution according to the reviewer's suggestion. The following modifications have been added:

- The electromagnetic design was calculated using the Maxwell-Fourier analyses.

- The calculated field distribution can also be used to evaluate the magnetizing level on the core.

- The machine output power is limited by the internal diameter and the low rotation speed.

- However, the development and construction process presented show the ground base limitations of the application, which can lead to a better performance for upcoming designs.

- The performance was evaluated using the developed equivalent circuit and the machine model was validated using both the finite element method and experimental results.

- It has been established that keeping the current constant on the field coils prevents field demagnetizing and, consequently, power reduction.

The last paragraph was removed since it doesn't add contribution to the conclusion section.

The manuscript was checked in order to correct grammar and spelling.

There four references that include self-citations:

[8] Maia, T.A.; Faria, O.A.; Barros, J.E.; Porto, M.P.; Cardoso Filho, B.J. Test and simulation of an electric generator driven by a micro-turbine. Electric Power Systems Research 2017, 147, 224–232.

[28] Guia, A.R.; Silva, R.A.; Pires, I.A.; Maia, T.A.C. In-Wheel Traction Motor: a Case Study for Formula SAE Electric. Anais do Congresso Brasileiro de Automática 2020 2020. https://doi.org/10.48011/asba.v2i1.1270.

[47] Mendonça, G.; Maia, T.; Filho, B.C. Magnetic Field Analytical Solution for Non-homogeneous Permeability in Retaining Sleeve of a High-Speed Permanent-Magnet Machine. Mathematical and Computational Applications 2018, 23, 72. https://doi.org/10.3390/mca23040072.

[48] Mendonça, G.A.; Maia, T.A.C.; de Jesus Cardoso Filho, B. IMPROVED SEMI-ANALYTICAL MAGNETIC FIELD SOLUTION FOR HIGH-SPEED PERMANENT-MAGNET MACHINES WITH PERMEABLE RETAINING SLEEVE INCLUDING DIFFUSION EFFECT. Progress In Electromagnetics Research B 2020, 88, 97–118. https://doi.org/10.2528/pierb20051904.

Reference [8] presents the development of an electrical machine with an OEM automotive turbocharger. The system was evaluated for power generation, but perfectly fits the turbo-generator discussion.

References [47] and [48] are extremely important for the reader which want to learn more about the mathematical aspect of Maxwell-Fourier analysis.

Reference [28] was removed without loss to the manuscript.

Author Response File: Author Response.pdf

Reviewer 2 Report

In this article, a conventional flux switching motor (FSM) without permanent magnets is proposed for use as an in-wheel motor for a light electric vehicle. Equivalent circuit equations are proposed for calculating the FSM characteristics. At the same time, the purpose and novelty of the article are unclear, since the output performances, weight, size and economic parameters of the considered motor are not calculated and compared with the main competitor (permanent magnet motor).

Comments to be addressed:

1) Information about the application in question is not complete: for which vehicle is it planned to apply the electric motor in question? Only the speed range shown in Fig. 8 is not enough. What are the required torque-speed diagrams in motoring and braking modes? What is the required constant power speed range (CPSR)? If the torque-speed diagrams are calculated from the thrust-velocity diagram of the vehicle, then it would be instructive to present the vehicle parameters needed for such conversion (vehicle mass, gear ratio, wheel radius, etc.).

2) Since the article is devoted to the design of an in-wheel motor, why is the design not considered a complete drive cycle, for example WLTP, or at least the operation of the motor at individual points (maximum torque, maximum speed) of the driving cycle?

3) Add the inverter circuit for the motor in question to the article. What power semiconductor modules are planned to be used? What strategy to flux weakening control is planned to be used?

4) It is not clear why the keywords contain "energy harvesting" and "regenerative braking". Justify it. It seems that these problems are practically not considered in the article.

5) What is the advantage of a more complex reluctance machine (FSM) in this application? Why cannot the simpler reluctance machines as a switched reluctance motor or a synchronous reluctance motor be used in this application?

6) In section 2, please mention the main disadvantages of SRM: very high torque ripple, noise and vibration and the need of the non-conventional inverter topology with a high current rating of the power semiconductor modules.

7) In section 2, why are induction motors not considered as a valuable alternative? Why do you not consider other types of similar flux modulation machines, for example, a claw pole machine (see, e.g. doi.org/10.3390/pr10030541) or a homopolar inductor machine (see, e.g. doi.org/10.3390/math10091581) for the use in the target application?

8) Why are formal multicriteria optimization techniques, such as differential evolution, not used in the motor design?

9) Authors should calculate the main characteristics of the FSM at the maximum torque (the rated load) and at maximum rotational speed (flux weakening region), such as efficiency, power factor, torque ripple, separate losses, inverter phase current at a given DC link voltage, weight and cost of the active materials and compare them with a state-of-art permanent magnet motor used in the application in question.

The reviewer believes that, in its current form, the practical impact and novelty of this article are unclear. I hope the authors will be able to substantially revise the article.

Author Response

Revision and re-submission of the manuscript

Dear editor and reviewers, with this brief letter, we kindly address reviewers’ comments to our manuscript. Thank you for your valuable and insightful comments. We carefully reviewed the manuscript according to the comments. The suggestions, and questions lead the manuscript into a greatly improvement.

Many thanks and with all the best wishes,

The authors

The major modifications to the manuscript's

1. The duplicate words and redundant texts were cautiously removed from manuscript.

2. Grammar and spelling were carefully checked.

3. References have been replaced in the manuscript, as suggested by reviewers, in order to avoid self-citations.

4. Some paragraphs have been reformulated according to the authors' corrections.

5. All reviewers' comments were carefully replied.

Reviewer 2

We sincerely thank Reviewer 2 and appreciate his valuable comments and suggestions, which help us to strengthen the manuscript. Comments and suggestions have been carefully corrected.

1^st comment

A) Information about the application in question is not complete: for which vehicle is it planned to apply the electric motor in question? Only the speed range shown in Fig. 8 is not enough.

B) What are the required torque-speed diagrams in motoring and braking modes? What is the required constant power speed range (CPSR)?

C) If the torque-speed diagrams are calculated from the thrust-velocity diagram of the vehicle, then it would be instructive to present the vehicle parameters needed for such conversion (vehicle mass, gear ratio, wheel radius, etc.).

Response to 1^st comment

Thank you for your suggestion and questions.

A) The electric motor is planned for a light vehicle application. We carefully reviewed the manuscript in order to clarify those statements.

Introduction

(line 69): (...)light-duty passenger vehicle [22].

[22] Commission, E. Commission Regulation (EU) 2017/1151 of 1 June 2017 supplementing Regulation (EC) No. 715/2007 of the European Parliament and of the Council on type-approval of motor vehicles with respect to emissions from light passenger and commercial vehicles (Euro 5 and Euro 6) and on access to vehicle repair and maintenance information, amending Directive 2007/46/EC of the European Parliament and of the Council, Commission Regulation (EC) No. 692/2008 and Commission Regulation (EU) No. 1230/2012 and repealing Commission Regulation (EC) No. 692/2008. Off. J. Eur. Union 2017, 175, 1–643.

Methodology

(line 174): (...) and performance for the light-duty ICE passenger vehicle, (…)

(line 187): (...) o retrofit a light ICE vehicle (…)

(line 198): In addition, for a 1,000kg ICE passenger car in the FTP 75 urban drive cycle, (…)

B) We are sorry about the misleading information. The machine was only developed for regenerative breaking operation. Motoring operation is not considered for the presented research. The project guidelines were based on a retrofit ICE vehicle which preserve the original battery and voltage levels at 12V. Thus, CPSR is only suitable when considering flux and field-oriented control.

The manuscript was reviewed in order to clarify this research goal.

C) We do agree with the reviewer comment. Unfortunately, we did not perform the torque-speed diagram since the proposal of this research is to design and validate the Maxwell-Fourier method with the aid of a novel steady-state equivalent circuit. We reviewed the manuscript in order to clarify the presented research goals and avoid confusion to future readers.

We also thank the reviewer considerations. We will consider using the proposed machine for motoring in the future works.

2^nd comment

Since the article is devoted to the design of an in-wheel motor, why is the design not considered a complete drive cycle, for example WLTP, or at least the operation of the motor at individual points (maximum torque, maximum speed) of the driving cycle?

Response to 2^nd comment

Thank you for your questions. The drive cycle was not considered since it depends on different parameters for regenerative breaking. The first one is the vehicle dynamics and mass transfer. If the machine is placed in the read or in the front axle, the amount of generated power will be different. The second one depends on storage capacity of the vehicle and its State-of-Charge. This scenario is completely feasible to be evaluated, however, the vehicle must be defined, as well its dynamic loads. Since the focus of this research is the design and validation of the machine, we considered only the constant load operation condition.

This discussion was added to the manuscript.

3^rd comment

Add the inverter circuit for the motor in question to the article. What power semiconductor modules are planned to be used? What strategy to flux weakening control is planned to be used?

Response to 3^rd comment

Thank you for your questions. The machine design is focused on cost reduction and simplicity during generative breaking. Only a passive diode rectifier was used. The output voltage is adjusted using an open-loop current adjust with the aid of a boost dc-dc converter. The information was reviewed in the manuscript.

4^th comment

It is not clear why the keywords contain "energy harvesting" and "regenerative braking". Justify it. It seems that these problems are practically not considered in the article.

Response to 4^th comment

Thank you for your questions. We are sorry about the confusion and our lack of attention during manuscript writing. The machine is designed to retrofit an internal combustion engine vehicle (ICE). During breaking, the energy is lost due to mechanical friction in the drum. Our research proposes the inclusion of a Flux Switching Machine inside the wheel. Thus, the parallel break strategy will partially recover break energy, while the mechanical break still operates.

The manuscript was carefully revised in order to add the information that the presented vehicle is an internal combustion engine, and the recovered energy will be used for fuel handling or to coexist with E-Flex systems.

5^th comment

What is the advantage of a more complex reluctance machine (FSM) in this application? Why cannot the simpler reluctance machines as a switched reluctance motor or a synchronous reluctance motor be used in this application?

Response to 5^th comment

Thank you for your questions. The proposed topology is adopted due to its great flexibility for both the stator and rotor structures. Besides, field-excited FSM offers controllable flux with a lower design cost. Also, FSM design is demonstrated to be a good candidate for hybrid EV, with the optimized result achieving a power density of 4.8~kW/kg. FSM also presents a robust structure and, with the adoption of a field winding, this topology can be operated using a simpler control circuit. The use of a FSM also eliminates the need to use an inverter.

The information was added to the manuscript.

6^th comment

In section 2, please mention the main disadvantages of SRM: very high torque ripple, noise and vibration and the need of the non-conventional inverter topology with a high current rating of the power semiconductor modules.

Response to 6^th comment

Thank you for your suggestion. The information was added to the manuscript.

7^th comment

In section 2, why are induction motors not considered as a valuable alternative? Why do you not consider other types of similar flux modulation machines, for example, a claw pole machine (see, e.g. doi.org/10.3390/pr10030541) or a homopolar inductor machine (see, e.g. doi.org/10.3390/math10091581) for the use in the target application?

Response to 7^th comment

Thank you for your question. The proposition of this work is not entirely to advocate on behalf of FSM. It was preliminary selected for its robust structure, which is an intrinsic characteristic for reluctance machines. Also, with the adoption of a field winding, this topology can be operated using a simpler control circuit. The generated voltage is close to a sine waveform and, for series connected field winding, the field inductance is constant.

On the other hand, this work is intended to present a novel design methodology using the developed steady state equivalent circuit, which was developed with the aid of Maxwell-Fourier method.

Thank you for your suggestion. The discussion was added to the manuscript, including the proposed references.

8^th comment

Why are formal multicriteria optimization techniques, such as differential evolution, not used in the motor design?

Response to 8^th comment

Thank you for your comment. The purpose of the presented discussion is to provide an overall guideline of the design optimization constraints. We also focused on defining a fast and accurate calculation method which can help on initial design stages, where the evaluated parameters have wide range of values. However, the choice of which optimization technique was not object of the analysis, and it can be evaluated in future works.

Thank you for your suggestion. The discussion was added to the manuscript.

9^th comment

Authors should calculate the main characteristics of the FSM at the maximum torque (the rated load) and at maximum rotational speed (flux weakening region), such as efficiency, power factor, torque ripple, separate losses, inverter phase current at a given DC link voltage, weight and cost of the active materials and compare them with a state-of-art permanent magnet motor used in the application in question.

Response to 9^th comment

Thank you for your suggestion. Performance characteristics of the designed and manufacture machine are briefly reported in the manuscript. We do agree that these characteristics are extremely important. However, the presented manuscript focused on design procedure. The performance characteristics will still be evaluated on future works, including temperature, flux, and power electronics dependence.

The discussion was added to the manuscript.

10^th comment

The reviewer believes that, in its current form, the practical impact and novelty of this article are unclear. I hope the authors will be able to substantially revise the article.

Response to 10^th comment

Thank you for your comment. After reviewer comments, we can clearly identify the flaws presented in the previous manuscript. We did our best in order to fulfill reviewer comments. Also, we have revised the manuscript in order to clarify the presented research contribution.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Thanks to the authors for the detailed answers. The paper may be published.