Thermal Safety Assessment Method for Power Devices in Natural Air-Cooled Converters

Round 1

Reviewer 1 Report

Dear Authors,

your paper regarding selected problems in the area of thermal safety of the power semiconductor devices operating in natural air-cooled conditions includes new and interesting ideas. Please find my comments on your manuscript below.

1) p. 3, l. 104 - the uniformity of the temperature distribution depends on many factors, e.g. area, volume of the housing, used thermal interfaces, and distance between assembled power devices. I think it should be visualized to support the reader's understanding or the sentence should be rephrased.

2) Fig. 1 - Following the results of the investigations presented for the natural air-cooled semiconductor devices its junction-ambient thermal resistance is highly nonlinear due to the influence of temperature on the effectivity of convection. It is described in the recently published research e.g. doi.org/10.1109/TPEL.2020.2995414, doi.org/10.3390/en15103565. Please include this effect in Fig. 1 and the equation on at least comment on this issue.

3) p.4, l. 130 - Please state the thickness of the adhesive.

4) Please uniform: heat resistance or thermal resistance.

5) p. 6, l. 175 - following the paper doi.org/10.3390/en15103565, atmospheric pressure should be included within the listed factors influencing convective thermal resistance.

6) Please add the literature and brief information regarding convective thermal resistance. It isn't commonly used in power electronics research.

7) At the beginning of section 4, please make a short introduction regarding the concept of the whole section.

8) In equation 11, shouldn't it be considered power, not only current flowing through the device? The current does not include e.g. switching losses or the influence of temperature on on-state drain-source resistance.

9) Please state the used simulation program.

10) Please comment on how the fluctuations presented in Fig. 11 of the junction temperature influence the reliability.

11) Is it possible to present the results presented in Fig. 11 and 13 for a constant ambient temperature?

12) Over-temperature probability in Fig. 12 is not scaled in percentages, which is stated in this figure. 

13) Please state the used measurement instruments for experimental verification.

Author Response

Dear Reviewer:

Thanks for your comments concerning our manuscript entitled “Thermal Safety Assessment Method for Power Devices in Natural Air-Cooled Converters” (ID: 2945211). Those comments are very valuable and helpful for revising and improving our paper and our researches. Based on your comments, we have made extensive modification on the original manuscript again. Here, we attached revised manuscript, in the formats of PDF, for your approval. A revised manuscript with the correction sections red marked was attached as the supplemental material and for easy check or editing purpose.

If you have any questions, please contact us again without hesitate.

Author Response File: Author Response.docx

Reviewer 2 Report

Due to variations in ambient ventilation rate, the junction temperature of a power device in a natural air-cooled power converter might fluctuate at random. The majority of current thermal analysis methods fail to account for the unpredictability of airflow's effect on the heat dissipation capacity of these converters. To tackle this concern, the authors of this paper propose a thermal safety assessment procedure for power devices in natural air-cooled converters. It utilizes the equivalent thermal network model and the converter's historical operation temperature to extract convective thermal resistance samples of the converter enclosure. The time-frequency domain properties of convective thermal resistance are analyzed using Wavelet packet transform, while the random impact of airflow rate on device junction temperature is simulated using Monte Carlo simulation.Generally, it is a good paper.

Some comments for further improvement. 

1. insufficient literature review.The paper discussed and used thermal modeling methods. But the power devices have distinctive temperature distribution as mentioned:

"Distributed Thermal Modeling for Power Devices and Modules With Equivalent Heat Flow Path Extraction," in IEEE Journal of Emerging and Selected Topics in Power Electronics, vol. 11, no. 6, pp. 5863-5876, Dec. 2023.

"A 3-D thermal network model for the temperature monitoring of thermal grease as interface material", Microelectron. Rel., vol. 114, Nov. 2020.

Please discuss the impact of average junction temperature and the local temperature on the chip on the reliability discussed here.

2. Breadth of validation;can the authors make comparison between proposed thermal modeling and FEM? FEM can model the air cooling well as mentioned in many publications.

3.If it be possible to provide infrared figures for validation?

4.Air-cooled conditions are widely used but in practice we would design the converter with very large abundance. In this case, the impact of the environment might be very limited???

5. Please provide the time cost of the proposed method.

6. The main novelty is to adopt Monte Carlo Principles to discuss the worst case so that the reliability can be ensured. The writing should be improved.

In all, I think we are concerned with the temperature variation. But this paper discussed and focused on the limitation and probabilities of high junction temperature that exceed or approach the packaging-allowed limit. It would have practical meanings but would it show obvious advantages over FEM? It seems to be so but the authors are suggested to highlight this advantage of using the thermal network

Can be improved. 

Author Response

Dear Reviewer:

Thanks for your comments concerning our manuscript entitled “Thermal Safety Assessment Method for Power Devices in Natural Air-Cooled Converters” (ID: 2945211). Those comments are very valuable and helpful for revising and improving our paper and our researches. Based on your comments, we have made extensive modification on the original manuscript again. Here, we attached revised manuscript, in the formats of PDF, for your approval. A revised manuscript with the correction sections red marked was attached as the supplemental material and for easy check or editing purpose.

If you have any questions, please contact us again without hesitate.

Author Response File: Author Response.docx

Reviewer 3 Report

Dear Authors,

Since the research topic of this manuscript is related to the junction temperature estimation of a power device, I have reviewed the manuscript with interest. Here are my recommendations for the manuscript to be published in this journal.

(1) The Introduction part should be dramatically improved with more recent research results and related papers. Please clearly describe the originality and contribution of the manuscript compared with related reference papers.

(2) The Conclusion part should be also improved.

(3) Please rearrange the position of each equation number.

(4) How did you change or control the airflow rate in the experimental environment? I can see only a small electric fan in Figure 2.

(5) How did you measure the junction temperature variation of the device Q1 in the validation experiment as shown in Figure 13?

(6) At the end of '4. The Proposed Thermal Safety Assessment Method, you mentioned that "the proposed method can estimate and predict the over-temperature risk of devices in real time."

Since the proposed thermal safety assessment method requires a lot of calculations in real time, is it possible to use the present controller or microprocessor in the natural air-cooled converters?

Thank you for all your efforts to prepare the manuscript.

Author Response

Dear Reviewer:

Thanks for your comments concerning our manuscript entitled “Thermal Safety Assessment Method for Power Devices in Natural Air-Cooled Converters” (ID: 2945211). Those comments are very valuable and helpful for revising and improving our paper and our researches. Based on your comments, we have made extensive modification on the original manuscript again. Here, we attached revised manuscript, in the formats of PDF, for your approval. A revised manuscript with the correction sections red marked was attached as the supplemental material and for easy check or editing purpose.

If you have any questions, please contact us again without hesitate.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Dear Authors,

thank you for your responses. I recommend the publication of the paper in its current form.

Author Response

Dear Reviewer:

Thanks for your comments concerning our manuscript entitled “Thermal Safety Assessment Method for Power Devices in Natural Air-Cooled Converters” (ID: 2945211). Those comments are very valuable and helpful for revising and improving our paper and our researches. Based on your comments, we have made extensive modification on the original manuscript again. Here, we attached revised manuscript, in the formats of PDF, for your approval. A revised manuscript with the correction sections red marked was attached as the supplemental material and for easy check or editing purpose.

If you have any questions, please contact us again without hesitate.

Author Response File: Author Response.pdf

Reviewer 2 Report

Thanks for all the repsonses. I have no more comments.

The language is ok.

Author Response

Dear Reviewer:

Thanks for your comments concerning our manuscript entitled “Thermal Safety Assessment Method for Power Devices in Natural Air-Cooled Converters” (ID: 2945211). Those comments are very valuable and helpful for revising and improving our paper and our researches. Based on your comments, we have made extensive modification on the original manuscript again. Here, we attached revised manuscript, in the formats of PDF, for your approval. A revised manuscript with the correction sections red marked was attached as the supplemental material and for easy check or editing purpose.

If you have any questions, please contact us again without hesitate.

Author Response File: Author Response.pdf

Reviewer 3 Report

Dear Authors,

I confirm that all the recommendations have been updated in the revised manuscript.

Please try to update the recent References, which are related to linear and nonlinear thermal network models, especially nonlinear cases.

Thank you for all your effort.

Minor editing of English language required, especially for updated contents.

Author Response

Dear Reviewer:

Thanks for your comments concerning our manuscript entitled “Thermal Safety Assessment Method for Power Devices in Natural Air-Cooled Converters” (ID: 2945211). Those comments are very valuable and helpful for revising and improving our paper and our researches. Based on your comments, we have made extensive modification on the original manuscript again. Here, we attached revised manuscript, in the formats of PDF, for your approval. A revised manuscript with the correction sections red marked was attached as the supplemental material and for easy check or editing purpose.

If you have any questions, please contact us again without hesitate.

Author Response File: Author Response.pdf