A Novel Quasi-Single-Stage High-Efficiency and High-Power-Factor AC/DC Converter^†

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript presents a quasi-single-stage AC/DC converter integrating a boost PFC stage and an LLC resonant converter with magnetically integrated inductors. The work is relevant and experimentally validated; however, several important issues should be addressed before publication:

 

Clarification of Novelty: The manuscript claims a novel topology, but similar quasi-single-stage boost–LLC converters already exist. The authors should clearly highlight – what differentiates this work from existing topologies, whether the main contribution lies in topology, control, or magnetic integration

Lack of Comparison with State-of-the-Art: A quantitative comparison with recent literature is missing. The authors should include a table comparing – efficiency, power factor, THD, component count,  power density

Insufficient Loss Analysis: The manuscript reports overall efficiency but does not provide a breakdown of losses (switching, conduction, magnetic). This analysis is important to support the claimed high efficiency.

Burst Mode Analysis: The burst-mode operation is introduced to regulate bus voltage under light load, but, its effect on PF and THD is not sufficiently quantified,  EMI implications are not discussed

Magnetic Integration Validation: The integrated magnetic design is well analyzed theoretically, but, no comparison with conventional discrete inductors is provided, no thermal or core loss analysis is included

Control Strategy Description: The control method lacks sufficient detail. The authors should provide: stability analysis (e.g., Bode plots or control loop explanation), implementation details for reproducibility

Presentation Improvements: improve figure clarity and labeling, simplify or better explain complex equations and ensure consistent notation throughout the manuscript

Author Response

Comments 1: [Clarification of Novelty: The manuscript claims a novel topology, but similar quasi-single-stage boost–LLC converters already exist. The authors should clearly highlight – what differentiates this work from existing topologies, whether the main contribution lies in topology, control, or magnetic integration.]
Response 1: We thank the reviewer for this constructive suggestion. We have revised the Introduction to more explicitly clarify the novelty of this work. The primary contributions have been redefined to emphasize the synergy of our proposed topology, digital control, and magnetic integration. By comparing these aspects with existing literature, the revised text now clearly distinguishes our work in terms of improved light-load regulation and higher power density.

Comments 2: [Lack of Comparison with State-of-the-Art: A quantitative comparison with recent literature is missing. The authors should include a table comparing – efficiency, power factor, THD, component count,  power density.]
Response 2: We thank the reviewer for this valuable suggestion. To provide a comprehensive benchmark of the proposed converter, we have added a quantitative comparison table (Table 6) in the revised manuscript, positioned just before the Conclusion section. This table compares our work with recent state-of-the-art integrated topologies across several key metrics, including efficiency, power factor, THD, switch count, and magnetic integration. The comparison highlights the advantages of our design in terms of component reduction and enhanced regulation capability while maintaining competitive electrical performance.

Comments 3: [Insufficient Loss Analysis: The manuscript reports overall efficiency but does not provide a breakdown of losses (switching, conduction, magnetic). This analysis is important to support the claimed high efficiency.]
Response 3: We fully agree that a detailed loss analysis is necessary to support the reported efficiency. We have added a rigorous textual loss breakdown immediately following the efficiency results in Table 4 for the 400 W load condition. Instead of a general estimation, the provided analysis is derived from analytical modeling and simulation-based extraction of switching losses. By quantifying the specific contributions of the integrated magnetic components (13.4 W) and the semiconductor devices (20.1 W), we have provided a solid theoretical foundation that aligns with the experimental 91.85% peak efficiency. We believe this detailed breakdown sufficiently clarifies the loss distribution and justifies the claimed high efficiency.

Comments 4: [Burst Mode Analysis: The burst-mode operation is introduced to regulate bus voltage under light load, but, its effect on PF and THD is not sufficiently quantified,  EMI implications are not discussed.]
Response 4: We thank the reviewer for this insightful comment. We have addressed these concerns by expanding the discussion in Section 4.2.3 (Burst Mode Analysis):

1. PF and THD Quantification: We have clarified the power quality performance during burst-mode operation. Based on the experimental trends, the converter maintains a high power factor (above 0.99) and a THD below 5.0% even under light-load conditions, which satisfies the harmonic requirements of IEC 61000-3-2. This confirms that the zero-crossing-triggered strategy effectively minimizes the impact of intermittent conduction on power quality.

2. EMI Considerations: A discussion on EMI implications has been added. The burst-mode transitions are specifically synchronized with the line voltage zero-crossings to avoid large switching transients at peak voltages. Additionally, we highlight that the integrated magnetic structure provides inherent filtering, which helps suppress high-frequency EMI during burst-mode operation.

Comments 5: [Magnetic Integration Validation: The integrated magnetic design is well analyzed theoretically, but, no comparison with conventional discrete inductors is provided, no thermal or core loss analysis is included.]
Response 5: We have addressed these concerns by adding a concluding discussion to Section 3.4:

1. Comparison with Discrete Components: We explicitly highlighted that the integrated EI-core reduces total volume and enhances material utilization through magnetic flux cancellation, compared to discrete implementations.

2. Loss and Thermal Analysis: While detailed FEA is omitted, we have cited established analytical models that provide proven methodologies for evaluating core losses and thermal behavior in similar integrated structures.

3. Experimental Validation: We clarified that the prototype maintained stable thermal equilibrium during full-load testing, empirically confirming the design's reliability.

Comments 6: [Control Strategy Description: The control method lacks sufficient detail. The authors should provide: stability analysis (e.g., Bode plots or control loop explanation), implementation details for reproducibility.]
Response 6: We have revised Section 4.1 to provide a more rigorous description of the control loop architecture and its stability. Specifically, we have detailed the closed-loop feedback path—from output voltage sampling to PI-based frequency modulation—and provided a theoretical stability analysis. By highlighting that the DCM operation eliminates the RHP zero, we justify the system's inherent stability and robust phase margin without the need for complex compensation. These additions provide the necessary details for understanding and reproducing the control strategy.

Comments 7: [Presentation Improvements: improve figure clarity and labeling, simplify or better explain complex equations and ensure consistent notation throughout the manuscript.]
Response 7: We sincerely thank the reviewer for the constructive suggestions. We have carefully revised the manuscript to improve its overall presentation:

1. Consistent Notation: We have standardized all variable notations throughout the text, figures, and equations .

2. Equation Clarification: We have added brief physical interpretations for the key mathematical models in Section 3 to make the theoretical derivations easier to follow.

3. Figure Enhancements: All figures have been updated to ensure high legibility and correct labeling. Furthermore, the figure captions have been rewritten to be more descriptive and precise.

We believe these revisions have significantly improved the readability of the manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

The paper proposes a novel Quasi-single stage high performance AC/DC converter. The proposed AC/DC converter integrates a boost PFC stage with a half-bridge LLC resonant converter using magnetically integrated differential-mode coupled inductors. the proposed work aims at increasing AC/DC converter efficiency while decreasing components count. the work is novel and the paper is well written with nice hardware experiments to validate the design. however, some minor modifications are needed: 

• the authors should consider adding more explanation for equations as the paper locks condensed with equations.
• you need to add a comparison table with recent papers from literature. 
• add clear explanation for all figures inside text.
• the plagiarism percent is too high especially from another paper published previously by authors.
• please justify the assumption of ideal components in the analysis.
• revise figure captions to be more descriptive. 

 

Author Response

Comments 1: [the authors should consider adding more explanation for equations as the paper locks condensed with equations.]
Response 1: We have added concise physical explanations and transition sentences for key equations (e.g., Eqs. 1, 3, 6, 9, and 14) to clarify the derivation logic and the physical meanings of the variables. This ensures a better connection between the mathematical framework and the circuit behavior.

Comments 2: [you need to add a comparison table with recent papers from literature.]
Response 2: We sincerely thank the reviewer for this suggestion. A comprehensive comparison table (Table 6) has been added to Section 5 to evaluate our work against state-of-the-art topologies (2021–2025). The comparison highlights three key advantages of the proposed converter:

• Topological Simplicity: The structure is optimized with only three active switches, significantly reducing cost and control complexity compared to [27] and [28].

• High Power Factor: By integrating differential-mode coupled inductors, the proposed design achieves a superior power factor, outperforming the QSS charger in [28].

• Wide Regulation Range: The introduced Burst Mode effectively suppresses DC-link voltage spikes under light-load conditions, ensuring stable regulation across the entire load range.

We believe this addition provides a clearer positioning of our research within the current literature.

Comments 3: [add clear explanation for all figures inside text.]
Response 3: We sincerely thank the reviewer for this suggestion. The manuscript has been revised to provide more precise and academic descriptions for key figures, ensuring a better link between the graphical results and the theoretical analysis:

• Figure 5 & 7(b): Added analysis of current slopes and the $180^\circ$ phase-shift for the interleaved boost operation. The description of Mode 2 (Figure 7b) was refined to detail the single-phase conduction path and energy storage state.

• Figures 8 & 9: Inserted textual analysis following the PF and THD derivations. These additions discuss how the coupling coefficient $k$ and voltage gain $m$ influence the input performance, providing clearer design guidelines.

• Figures 14 & 15: Corrected the references to distinguish between the control topology (Fig. 14) and dynamic waveforms (Fig. 15). We also expanded the explanation of the zero-crossing synchronization logic in burst mode for EMI mitigation.

We believe these enhancements significantly clarify the logical flow of the paper.

Comments 4: [the plagiarism percent is too high especially from another paper published previously by authors.]
Response 4: We sincerely apologize for the high similarity index in the initial submission. This was partly due to the fact that the current manuscript is an extensive expansion of our previous preliminary work, where maintaining consistency in technical descriptions and fundamental modeling was necessary. However, we fully respect the reviewer’s concern. We have thoroughly rewritten the highlighted sections, particularly in the operational principle analysis and experimental descriptions, to ensure the uniqueness and originality of this submission. We hope these revisions meet the journal's standards.

Comments 5: [please justify the assumption of ideal components in the analysis.]
Response 5: We appreciate the reviewer’s valuable comment. In the revised manuscript, we have added justifications for the ideal component assumptions in Sections 2.2, 3.1, and the Conclusion.

The assumption is primarily based on the following considerations:

1. Focus on Core Mechanism: To clearly illustrate the novel topological features and the ripple-reduction mechanism of the integrated inductors, secondary non-ideal factors (such as semiconductor voltage drops and ESR) were neglected. This is a common practice in power electronics to obtain analytical closed-form solutions that provide intuitive design insights.

2. Experimental Validation: As demonstrated in the experimental section, the measured efficiency (91.9%) and the high alignment between the theoretical and experimental waveforms confirm that these parasitic effects do not significantly deviate the converter’s performance from the predicted model.

We believe these simplifications maintain a proper balance between mathematical clarity and practical accuracy for the steady-state analysis.

Comments 6: [revise figure captions to be more descriptive.]
Response 6: We have thoroughly revised the captions of all figures in the manuscript to ensure they are more descriptive and accurately reflect the experimental or theoretical results presented. The repetitive phrasing has been removed to improve the clarity and uniqueness of each figure's description.

Reviewer 3 Report

Comments and Suggestions for Authors

The work is devoted to the development of the topology of the AC/DC converter with improving its robustness to harmonic components and power factor. There are a number of comments and suggestions on the work.

1) Abstract and keywords. The abbreviations EMI, PFC, and LLC are used. It is necessary to eliminate their use in this part of the work.

2) Introduction. "In most quasi-single-stage designs, a boost-type PFC stage is integrated with a soft-switching LLC." The abbreviation LLC is used for the first time. It is necessary to decipher where it is used for the first time. This applies to a number of other abbreviations.

3) Introduction. There are abbreviations that are introduced but are either not used further or are used no more than twice. Why overload the work with redundant abbreviations? It is necessary to eliminate abbreviations that are not justified. This applies not only to the introduction.

4) In section 2.1, there is no reference to Figure 1 in the text preceding it. This needs to be corrected.

5) In section 3.1, the numbers of Figures 7-11 need to be corrected.

6) Section 3.2. What is plotted on the O-x and O-y axes in Figures 15 and 16? It should be explicitly shown.

7) Section 3.3. "The dynamic operating waveforms of the burst mode are illustrated in FIGURE. 18 and FIGURE. 19". The figures should be written in uppercase letters.

8) Why write the same thing twice?

• "The detailed parameters and the photograph of the prototype are given in Table 2 and Figure 24, respectively."
• "The physical experimental prototype built to verify the proposed topology and control strategy is shown in Figure 24."

 

Author Response

Comments 1: [Abstract and keywords. The abbreviations EMI, PFC, and LLC are used. It is necessary to eliminate their use in this part of the work.]
Response 1: Thank you for pointing this out. We agree with this comment. Therefore, we have replaced the abbreviations EMI, PFC, and LLC with their full names in the Abstract and Keywords sections to ensure the manuscript meets formal academic standards.These changes can be found on Page 1, in the Abstract and Keywords section.

Comments 2: [Introduction. "In most quasi-single-stage designs, a boost-type PFC stage is integrated with a soft-switching LLC." The abbreviation LLC is used for the first time. It is necessary to decipher where it is used for the first time. This applies to a number of other abbreviations.]
Response 2: 

Thank you for this suggestion. We have conducted a thorough check of the entire manuscript and defined all technical abbreviations at their first appearance in the main text.

The specific revisions are as follows:

1.For PFC and LLC: In the first paragraph of the Introduction, we have provided the full names "power factor correction (PFC)" and "inductor-inductor-capacitor (LLC) resonant converter".

2.For EMI: In the fifth paragraph of the Introduction, we have added the full name "electromagnetic interference (EMI)".

3.For PF: In the third section, "Analysis and Design of AC/DC Converter", specifically below Equation (9), we have added the full name "power factor (PF)".

Comments 3: [Introduction. There are abbreviations that are introduced but are either not used further or are used no more than twice. Why overload the work with redundant abbreviations? It is necessary to eliminate abbreviations that are not justified. This applies not only to the introduction.]
Response 3: Thank you for this constructive suggestion. We agree that redundant abbreviations can clutter the text and hinder readability. Following your advice, we have thoroughly reviewed the manuscript and removed abbreviations that were either redundant or used only a few times. These terms have been replaced with their full technical names to ensure clarity.

The specific revisions are as follows:

1.In the Introduction: The abbreviation "PSU" in the first paragraph, and "PFM" and "IAPWM" in the fourth paragraph have been removed.

2.In Section 3: The abbreviation "FHA" has been removed from the first paragraph of Section 3.2 ("LLC Resonant Converter") and the third paragraph of Section 3.5.3 ("Parameters of LLC Resonant Converter").

3.In Section 4: In Section 4.2.2 ("Soft-Switching Performance"), the redundant abbreviations for "ZVS" and "ZCS" have been eliminated.

Comments 4: [In section 2.1, there is no reference to Figure 1 in the text preceding it. This needs to be corrected.]
Response 4: Thank you for this correction. We have added a formal reference to Figure 1 at the very beginning of Section 2.1 to ensure that all figures are properly introduced in the text before they appear.

Comments 5: [In section 3.1, the numbers of Figures 7-11 need to be corrected.]
Response 5: 

Thank you for pointing out this formatting error. The issue was caused by a LaTeX coding error where the subfigures were incorrectly assigned independent main figure numbers (Figures 7–10) before the main caption (Figure 11).

We have corrected the code. Now, the four working modes are properly combined into a single figure (Figure 7), with subfigures correctly labeled as (a), (b), (c), and (d). Consequently, all subsequent figure numbers and their corresponding cross-references in the text of Section 3.1 and the rest of the manuscript have been updated to ensure complete accuracy.

Comments 6: [Section 3.2. What is plotted on the O-x and O-y axes in Figures 15 and 16? It should be explicitly shown.]
Response 6: Thank you for this suggestion. We have updated the figures to explicitly show the physical quantities and units on the O-x and O-y axes.The specific revisions are as follows:For Figures 11 and 12: (Formerly Figures 15 and 16 before renumbering). The horizontal and vertical coordinate labels have been added to ensure the parameters being analyzed are clearly identified.

Comments 7: [Section 3.3. "The dynamic operating waveforms of the burst mode are illustrated in FIGURE. 18 and FIGURE. 19". The figures should be written in uppercase letters.]
Response 7: Thank you for pointing out this inconsistency. We have corrected the reference format for Figure 14 and Figure 15 (formerly Figures 18 and 19) to ensure they follow the standardized capitalization and style required by the journal. Additionally, we have verified that all figure references throughout the manuscript now adhere to this unified format.

Comments 8: [

Why write the same thing twice?

• "The detailed parameters and the photograph of the prototype are given in Table 2 and Figure 24, respectively."
• "The physical experimental prototype built to verify the proposed topology and control strategy is shown in Figure 24."

]
Response 8: Thank you for this suggestion. We agree that the previous description was redundant. We have combined these two sentences into one concise statement to improve the flow and readability of the manuscript.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The author made the required modification, hence, the manuscript is now suitable for publication.