Discontinuous PWM Strategy with Frequency Modulation for Vibration Reduction in Asynchronous Machines

Round 1

Reviewer 1 Report

The authors propose to reduce vibrations in asynchronous machines using a discontinuous PWN strategy with frequency modulation. In the introduction, the authors describe the various existing methods and highlight their advantages and disadvantages, based on numerous recent bibliographical references. This is followed by an analytical description of the sources of vibration generated in an induction motor. The third section describes the control method used to control a multi-level inverter. Analytical equations are used to theoretically describe the various waveforms obtained. The authors clearly show the effects of the parameters K and Am on the waveforms. A bench of measurements is used to demonstrate the effectiveness of their method by comparing it with traditional control methods. The results obtained show that the natural vibration of the motor is reduced by adjusting the choice of parameters K and Am. A conclusion summarises all the work and emphasises the importance of the choice of K on the performance of the control strategy and the reduction in THD. 

Author Response

Thank you very much for your review.

We have tried to improve the text and figures in the paper at the request of the editor and in response to comments from reviewers.

Reviewer 2 Report

"The manuscript presents a known control strategy (HIPWM-FMTC) for inverters that feed asynchronous motors. The aim of the paper is to tune the strategy with the aim of reducing motor vibration. The manuscript follows a development parallel to the paper, from the same authors: A. Ruiz-Gonzalez, J. -R. Heredia-Larrubia, M. J. Meco-Gutierrez and F. -M. Perez-Hidalgo, "Pulse-Width Modulation Technique with Harmonic Injection in the Modulating Wave and Discontinuous Frequency Modulation for the Carrier Wave for Multilevel Inverters: An Application to the Reduction of Acoustic Noise in Induction Motors," in IEEE Access, vol. 11, pp. 40579-40590, 2023, doi: 10.1109/ACCESS.2023.3269593 In the manuscript is not clear what is the novelty of this manuscript from the previous one. Therefore, the authors should make very clear what is the advance that this manuscript provides from [37]. In addition: This manuscript is an example of lumped references. This is a bad practice that should be avoided. Therefore, authors are encouraged to comment individually or suppress unneeded references. For example: References [9,10,11,12] or [16,17,18] are cited together in the second paragraph of page 3. This also happens with references [33,34,35,36,37,38] at the end of the first paragraph of section 3. Figure 1 should be commented prior to its appearance in the paper."

Author Response

Thank you for your comments which will help to improve the paper submitted for publication.

The difference between the article submitted for consideration for publication and the one published in IEEE Access lies in the application considered.  In the IEEE Access paper, the technique is adjusted to minimise the acoustic level because it is a limited variable in international standards (IEC 60034: specifying test methods for determining the sound power level of rotating electrical machines). This acoustic level is a subjective assessment that is modelled with a weighting curve (A) on the measured levels of pressure on a microphone, to approximate the RMS value to that of a healthy middle ear, and is linked to regulations on Health and Safety of operators and/or users of the installation.

However, the vibration level is related to the operational reliability and the lifetime of the machine. It is also regulated by international standards. Specifically, EN 60034-14 (Europe) dictates the maximum vibration level for electric motors. In this paper, a theoretical-practical study of a motor resonance frequencies has been carried out and it has been shown that, by adjusting the control variable (maintaining the frequency modulation order for all the techniques tested), it is possible to avoid activating them, reducing the level of vibrations measured with respect to other known techniques. The maximum switching frequencies of the carrier wave have been calculated for two frequency modulation orders: M=15 and M=11. In addition, it is shown graphically how the amplitude of each harmonic appearing in the line voltage at the output of the inverter can be adjusted to reduce the effects on the vibration level of the engine between maximum and minimum limits (harmonic 17 is shown). Information on other harmonics has not been included because we believe that they do not contribute anything to the understanding of the technique with respect to their use in reducing the vibrations produced by harmonics of temporal origin. The results in table 3 show how the THD value changes for each value of K, so it is evident that this occurs because the amplitudes of the different voltage harmonics produced change.

The proof that noise minimisation does not guarantee vibration minimisation is that, applying the same technique for the same motor, the control variable setting value for a frequency modulation order of 15 is K = 0.5 for noise minimisation (published in IEEE Access), and K=0.55 for the vibration level in the study presented in the paper submitted for publication. The control parameter has been adjusted to reduce vibrations to avoid resonance frequencies of the mechanical structure and the electrical harmonics for which the motor presents a high value of the coil harmonic factor (tooth harmonics). In addition to optimising the vibration level, the THD can be reduced compared to the other techniques with which it has been compared for some values of the control variable. Finally, the RMS voltage obtained using the same level of DC-LINK is slightly higher, so for the same transferred power, the current level will be lower for each IGBT.

The references have been updated and the lumped references have been removed.

And figure 1 has been annotated prior to its appearance in the paper.

Reviewer 3 Report

Dear authors

The paper presents a discontinuous PWM strategy with frequency modulation for vibration reduction in asynchronous machines. However, much work must be done to improve the paper's quality. The comments are: In general, all the figures are very bad.

1.     The abstract must be rewritten in a clear style.

2.     What are the contributions of this research?

3.     The literature review is weak and needs improvement.

4.     What information does Figure 6-b give us??!!

5.     All equations must be given a number (Eq. 5&6 for example). Also, put the reference you get from.

6.     Figure 1 and Figure 7-16 are so bad and unclear. Please redraw in a clear style. Also, the figures' captions must be rewritten.

7.     Some language errors are presented such as: (Please review all the manuscript carefully)

·         Abstract “The control strategy allows the electrical spectrum to be varied given a number of pulses per period by changing a parameter of the carrier wave, thereby avoiding natural mechanical resonance frequencies." Rewrite it is not clear.

Introduction “These harmonics produce vibrations and noises in the motors that can deteriorate it and reduce its life cycle [1, 2]. " replace with “……...deteriorate them and reduce their life cycle [1, 2]. "   

Moderate

Author Response

Thank you for your comments which will help to improve the paper submitted for publication.

 

1) The abstract has been rewritten in a clearer style.

2) In this work, a theoretical-practical study of the resonance frequencies of an engine has been carried out and it has been shown that, by adjusting the control variable of a discontinuous modulation technique, it is possible to avoid the activation of these resonance frequencies, and to reduce the vibration level measured with respect to other known techniques (maintaining the frequency modulation order for all the techniques tested). The maximum switching frequencies of the carrier wave for the proposed modulation technique have also been calculated for two different frequency modulation orders: M=15 and M=11, and used with one of them (M=15) to implement in a laboratory setup. In addition to optimising the vibration level, the THD can be reduced compared to the other techniques with which it has been compared for some values of the control variable. Finally, the RMS voltage obtained using the same level of DC-LINK is slightly higher, so for the same transferred power, the current level will be lower for each IGBT.

 

In addition, it is shown graphically how the amplitude of each harmonic appearing in the line voltage at the output of the inverter can be adjusted to reduce the effects on the vibration level of the engine between maximum and minimum limits (harmonic 17 is shown). Information on other harmonics has not been included because we believe that they do not contribute anything to the understanding of the technique with respect to their use in reducing the vibrations produced by harmonics of temporal origin. The results in table 3 show how the THD value changes for each value of K, so it is evident that this occurs because the amplitudes of the different voltage harmonics produced change.

3) The bibliographical references have been modified and updated.

4) Figure 6 has been changed.

5) All equations have an equation number assigned to them.

6) All figures have been modified except the vibration spectra because they are generated by the measuring equipment.

7) We have revised the English  of the paper.

Round 2

Reviewer 2 Report

The Authors have shown that the results of this manuscript aree different from their already published results.

However, the lumped reference problem remains in the cases:

[9, 10, 11] and [27, 28, 29].

Author Response

Thank you for your comments to improve the understanding of the paper.

references [9, 10, 11] and [27, 28, 29] have been separated, commented and highlighted in the text.

Reviewer 3 Report

Please add the contributions to the manuscript and fix Figure 5. 

Minor

Author Response

Thank you for your comments to improve the understanding of the paper.

As suggested, we have added the contributions of the paper in the section: 5. Conclusions. The changes to the text have been highlighted.

We have used the translation services suggested by the journal to improve the format and readability of the paper.

Figure 5 has been fixed.