Two-Stage Power Delivery Architecture Using Hybrid Converters for Data Centers and Telecommunication Systems
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsA two-stage power converter for data centers and telecommunication systems is proposed in this paper. The design and experimental validation are well given. Quite good work fulfilled, however still some points need to be fixed.
- In Figure 2, it is suggested the circuit should be clearly drawn, especially the connections for various lines. It should not be directly clipped from the windows.
- In Figure 4, the connections between the switch and the capacitor is not clearly given.
- The circuit parameters and the control parameters such as switching frequency should also be included in Tab. 1 and Tab. 2.
- What is the consideration of the authors to select the switch frequency of the converters? Could it be discussed in the paper?
- It is shown form Figure 14 and Figure 16 that the efficiency will be decreased dramatically with the improvement of the output current. Then in my opinion, the rated power of the designed converter should be close to the maximum point, which is about 50A. However, the authors claim the designed converter has the maximum output to 160A (in Abstract, last sentence). How you comment it?
- In Figure 13, all the title and unit of the vertical axis are missing.
Author Response
Comments 1: In Figure 2, it is suggested the circuit should be clearly drawn, especially the connections for various lines. It should not be directly clipped from the windows.
Response 1: Thank you for the suggestion. We believe the problem arose from the format of the figure. We have aligned some lines in the figures, extracted a better format of the image and included in the paper with a larger size. We hope, the image has sharper lines and it is now better to understand.
Comments 2: In Figure 4, the connections between the switch and the capacitor is not clearly given.
Response 2: Thank you for pointing it out. We have redrawn the pictures in Fig. 4.
Comments 3: The circuit parameters and the control parameters such as switching frequency should also be included in Tab. 1 and Tab. 2.
Response 3: Thank you for the suggestion. We have added the frequency information in the tables.
Comments 4: What is the consideration of the authors to select the switch frequency of the converters? Could it be discussed in the paper?
Response 4: The frequencies were selected based on the optimization of losses in each of the converters. As this paper is about the system design, we omitted the discussion about the loss analysis of each converter separately.
Comments 5: It is shown form Figure 14 and Figure 16 that the efficiency will be decreased dramatically with the improvement of the output current. Then in my opinion, the rated power of the designed converter should be close to the maximum point, which is about 50A. However, the authors claim the designed converter has the maximum output to 160A (in Abstract, last sentence). How you comment it?
Response 5: Thank you for pointing out the ambiguity that the authors did not intend. We have changed the language of the abstract as follows:
'In combination, the direct conversion from ~110 VAC to 1VDC achieves a peak efficiency of 84.1% at 50A and the setup has been tested with output currents up to 160A where the efficiency is 73.5%.'
The converters were designed separately. Hence, there is peak output power mismatch between the first and second stage. However, we wanted to demonstrate a full system instead of publishing about each stage separately. Hence, the overall performance may not be as attractive as it should be. However, there is no precedence from academia to demonstrate these two stages experiment together and report the performance. In future implementations, we will optimize both stages together to achieve a system level performance.
Comments 6: In Figure 13, all the title and unit of the vertical axis are missing.
Response 6: The authors would like to humbly point that the unit and the waveform titles are provided as legends.
Reviewer 2 Report
Comments and Suggestions for AuthorsDear Authors,
The following comments should be carefully checked to update the revised manuscript:
(1) The introduction part should be improved dramatically with more related references and previous research results.
(2) Figure 2 should be improved. The present form is not effective in showing its proposed circuits.
For example, the authors may separate the proposed circuits from the pictures of their prototypes.
Author Response
Comments 1: The introduction part should be improved dramatically with more related references and previous research results.
Response 1: The introduction has been rewritten. To author's knowledge, no publication has reported a combined two stage design for data center applications. If the reviewer can kindly suggest to point to some known publication which reported the two stages together, we will add it to the references.
Comments 2: Figure 2 should be improved. The present form is not effective in showing its proposed circuits. For example, the authors may separate the proposed circuits from the pictures of their prototypes.
Response 2: Thank you for the suggestions. We have removed the prototype pictures from FIg. 2.
Reviewer 3 Report
Comments and Suggestions for Authors- How do you start up the two-stage converter? The initial voltage of the flying capacitors is zero.
- Please compare the conventional two-stage converter with a high-frequency transformer and your proposed solution.
Author Response
Comments 1: How do you start up the two-stage converter? The initial voltage of the flying capacitors is zero.
Response 1: In the experiment, initially, we power up the driving circuits and the controllers of both the stages. After that, we increase the input AC voltage from 0 to 110VAC within 5ms. In this method, the flying capacitors of both the stages charged according to their respective input voltages. 5ms to increase the input AC seem a reasonable number to operate considering the practical considerations
Comments 2: The authors would like to humbly point out that the solutions with isolated converters never reported a full system solution. Previous Solutions with isolated stages were typically preceded by 110/220VAC to 400VDC PFC and then followed 400V VDC to 48VDC or 400VDC to 12VDC stage. Add no publication reported the two stages together. Hence a direct one to one combination is not possible. There are 48V to 1V isolated converters which can be compared with the non-isolated solution in the paper. However, the authors would like a view this paper as a full system solution.
Reviewer 4 Report
Comments and Suggestions for AuthorsThe article discusses a two-stage power supply system using hybrid converters, mainly in telecommunications applications. From the point of view of previously used converter systems, this is a new and interesting solution. Two conversion stages with new converter topologies are proposed, instead of a four-stage structure. New converters are also presented as solutions for the proposed two conversion stages.
A new AC-DC converter based on a switched capacitor (SC) has been proposed for the first stage and demonstrated for a voltage of 90 V-110 V AC to a 48-60 V DC intermediate bus with power factor correction. The second stage is also a hybrid SC-based converter with multiphase operation, suitable for supplying power to core voltages of ~1 V at high current density. Noteworthy is the new phase sequence for the second stage presented in the article to extend the output voltage range.
The research results obtained are also interesting. Individually, for the first stage, 96.1% peak efficiency was achieved for output currents in the range from 0 to 4.5 A, and for the second stage, 90.7% peak efficiency was achieved for a load range from 0 to 220 A at 1 V. The results for the measured peak power density are 73 W/in³ for the first stage and 2020 W/in³ for the second stage.
In total, for direct conversion from ~110 VAC to 1 VDC, a peak efficiency of 84.1% was achieved, while obtaining an output current of up to 160 A.
Figure 1(a) shows a traditional converter circuit, while Figure 1(b) shows the proposed innovative converter circuit. The article also includes photographs and components of the innovative converter circuits.
The principle of operation of the converters is described in an understandable way.
The two new converters presented are a new multi-level PFC converter with switched capacitors and a 6-level, multi-phase, hybrid converter (MPMIH) based on switched capacitors. The operation of the voltage-reducing PFC converter with output voltage and input current regulation mechanisms is discussed. During the design of the MP-MIH converter, a new phase sequence was proposed and verified experimentally for wider ranges of output voltage and current.
The selected theoretical and experimental waveforms presented confirm a high degree of consistency. The very high efficiency achieved is noteworthy.
Further research on this topic is worthwhile due to the energy efficiency aspect.
Notes to Authors:
- The authors' affiliations (employment, country, etc.) are missing.
- Enlarge Figures 11(a) and 11(b) – the graphs will be more legible.
- Enlarge Figures 14(a) and 14(b) – the graphs will be more legible.
- Enlarge Figures 15(a) and 15(b) – the curves will be more legible.
- Change the color from blue to black in the numbering of figures in the text, as well as chapters and subchapters.
Comments for author File: 
Comments.pdf
Author Response
Comments 1: The authors' affiliations (employment, country, etc.) are missing.
Response 1: Thank you for pointing it out. We have added the affiliations.
Comments 2: Enlarge Figures 11(a) and 11(b) – the graphs will be more legible.
Response 2: Thank you for the suggestions. We have enlarged them.
Comments 3: Enlarge Figures 14(a) and 14(b) – the graphs will be more legible.
Response 3: Thank you for the suggestions. We have enlarged them.
Comments 4: Enlarge Figures 15(a) and 15(b) – the curves will be more legible.
Response 4: Thank you for the suggestions. We have enlarged them.
Comments 5: Change the color from blue to black in the numbering of figures in the text, as well as chapters and subchapters.
Response 5: Thank you for the suggestions. We have edited the color.
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsDear Authors,
The revised manuscript has been properly updated following the reviewers' comments.
The following errors should be corrected before publication :
(1) Page 1 Line 7~9 : who are 1 and 2? Who is the corresponding author?
(2) Duplicate sentences :
- Page 11 Line 303 ~ Page 12 Line 315
- Page 13 Line 317 ~ 329
(3) Duplicate References :
- Reference 5 is missed and Reference 6 is duplicate.
Thank you for all your effort.
Author Response
Comments 1: Page 1 Line 7~9 : who are 1 and 2? Who is the corresponding author?
Response: Thank you for pointing it out. It has been fixed.
Comments 2: Duplicate sentences :
- Page 11 Line 303 ~ Page 12 Line 315
- Page 13 Line 317 ~ 329
Response: Thank you for pointing out. It is fixed now.
Comments 3: Duplicate References :
- Reference 5 is missed and Reference 6 is duplicate.
Response: Thank you for pointing out. It is fixed now.
