Advanced Single-Phase Non-Isolated Microinverter with Time-Sharing Maximum Power Point Tracking Control Strategy

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper introduces a time‑sharing MPPT control strategy implemented in a non‑isolated, single‑phase multi‑input microinverter, allowing one MPPT controller to sequentially optimise multiple PV modules under partial shading.
The paper has presented an innovative use of a single MPPT controller for multiple modules, reducing hardware cost and complexity. Simulation under complex dynamic shading scenarios; and experimental prototype have shown acceptable performance for this kind of converters
I see the paper has some novelty and the way its presented is relevent and enought to assess the proposed method.
Comments
in table 4, the Vo i think should be a different value .. please correct
Because this is an inverter, it is worth adding the sinwave experimental output after Fig 17 ... 
i think Fig 17 shows in the middle the DC voltagers not the output one so please correct it 

Author Response

Response to Reviewer 1

We would like to sincerely thank Reviewer 1 for the thoughtful and constructive feedback. We appreciate your time and effort in reviewing our work. Below, we address each comment in detail, and all corresponding changes have been clearly marked with yellow highlights in the revised manuscript.

Comment 1: In Table 4, the Vo should be a different value. Please correct.

Response:

Thank you for pointing this out. In the revised manuscript, we have corrected the label from “Vo” to “Voc (open-circuit voltage)” to accurately reflect the parameter being described which can be found in Page13 Section 4. The previously incorrect value carried over in error has now been updated to Voc = 23 V, consistent with the specifications in the PV module datasheet. We have also reviewed Table 4 for consistency and accuracy across all listed parameters.

 

Comment 2: Because this is an inverter, it is worth adding the sine-wave experimental output after Fig. 17. I think Fig. 17 shows in the middle the DC voltages, not the output one, so please correct it.

Response:

We appreciate this valuable suggestion. Figure 17 has been updated to explicitly clarify that the middle waveform corresponds to a DC-side voltage which can be found in Page 15 in the result Section. In addition, we have included a new figure labeled Figure 18 in Page 16 that shows the experimental sinusoidal AC output voltage (Vo) alongside the DC-link voltage (VCdc) for comparison. This enhancement ensures better clarity and fulfills the recommendation to show the inverter’s output behavior.

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript presented a non-isolated single-phase multi-input microinverter architecture integrated with a time-sharing distributed MPPT (TS-MPPT) control scheme. The approach allows sequential MPP tracking of multiple PV modules using a single MPPT control unit, thereby reducing system cost and complexity versus conventional distributed MPPT, where each PV module requires independent circuitry. The architecture incorporates a multi-input boost converter merged with a shared H-bridge inverter, with added active power decoupling functionality. Both simulation and experimental validation are presented, including fixed and dynamic irradiance conditions, fault scenarios, and thermal performance comparison of power devices (Si, SiC, GaN). Results suggest improved efficiency, reduced cost, scalability, and superior thermal management with GaN devices. I think many issues need to be addressed, for example:

While the paper claims novelty in combining multi-input topology with time-sharing MPPT, similar approaches using time-multiplexed control have been attempted in the past (e.g., Zhu et al. 2015). The authors must clarify how their proposed control goes beyond prior art, especially in scalability and efficiency. Explicit quantitative comparison with those earlier TS-MPPT techniques is needed.

The experimental section remains limited in scale. Only four modules under laboratory conditions were tested. This is reasonable for a proof-of-concept, but the scalability claim (e.g., to >10 modules or kW-scale PV systems) is not supported by empirical evidence. A stronger discussion of the challenges in scaling (switching stress, timing allocation, controller overhead) should be included.

More quantitative efficiency values (measured inverter efficiency under various loads and irradiance) are expected, rather than general qualitative statements.

The time-sharing nature introduces inevitable delays; however, the quantitative analysis of dynamic response time is not deeply provided (e.g., how long under rapidly fluctuating irradiance does the system lag compared to parallel DMPPT?).

The experimental validation focuses on step changes in irradiance, but more realistic test cases like fast-moving cloud conditions or random profiles would strengthen confidence.

GaN device thermal results are promising. However, the thermal analysis is superficial: Were heatsinks used? What ambient conditions? How is thermal cycling over extended operation considered? Were losses experimentally measured or only inferred from surface temperature imaging? These details need clarification.

The literature review is broad but slightly imbalanced toward older references (2012–2017). More recent works (2022–2024) on multi-port microinverters, wide-bandgap switch integration, and advanced GMPPT algorithms should be addressed.

Some figures (e.g., Fig. 8, Fig. 9, Fig. 12) contain overlapping labels and are difficult to interpret. Improve readability by resizing and clarifying legends.

The text is mostly clear but contains instances of spelling/grammatical errors (“sonds” instead of “seconds”; “dedcate” should be “dedicate”, etc.). So, I think language editing is recommended.

Many acronyms are overused (FPP, DPP, DMPPT, GMPPT, TS-MPPT). Suggest adding a clear Nomenclature table at the beginning.

Author Response

Response to Reviewer 2

We sincerely thank reviewer 2 for their thorough and constructive feedback, which has helped us significantly improve the clarity and robustness of our manuscript. Below are our detailed responses to each of the reviewer’s comments. All modifications in the revised manuscript are highlighted in yellow.

 

Comment 1: While the paper claims novelty in combining multi-input topology with time-sharing MPPT, similar approaches using time-multiplexed control have been attempted in the past (e.g., Zhu et al. 2015). The authors must clarify how their proposed control goes beyond prior art, especially in scalability and efficiency. Explicit quantitative comparison with those earlier TS-MPPT techniques is needed.

Response:

Thank you for this valuable observation. In response, we have revised the Discussion sections to more explicitly differentiate our proposed TS-MPPT control strategy from prior time-multiplexed methods. Specifically, our approach integrates a full power processing (FPP) mechanism combined with active power decoupling, which enables enhanced scalability, minimized hardware redundancy, and improved MPPT tracking performance under dynamic conditions. We have added an expanded comparison in Table 6 page 16 that includes a direct benchmark with earlier TS-MPPT strategies, including the method by Zhu et al. (2015) which is reference 21. The comparison covers key dimensions such as control complexity, number of MPPT units, utilization efficiency, scalability, thermal performance, and real-time tracking capability. These additions clarify the technical advancements introduced by our work and reinforce its practical applicability and novelty.

Comment 2: The experimental section remains limited in scale. Only four modules under laboratory conditions were tested. This is reasonable for a proof-of-concept, but the scalability claim (e.g., to >10 modules or kW-scale PV systems) is not supported by empirical evidence. A stronger discussion of the challenges in scaling (switching stress, timing allocation, controller overhead) should be included.

Response:

We thank the reviewer for this valuable observation. While our experimental setup involves only four PV modules, the proposed TS-MPPT architecture was developed with scalability in mind. In the revised manuscript ( Please see Section 4.2, page 16), we now include a focused paragraph addressing key scalability challenges when extending the system to >10 modules or kW-scale arrays. Specifically, we discuss switching stress, which may rise with more inputs, and how the use of GaN devices helps mitigate it. Also timing allocation, which becomes tighter with more modules, and how high-resolution timers ensure fair MPPT cycles. And lastly, controller overhead, which increases with sensing and computation demands, and how task optimization or field programmable gate array (FPGA) based solutions can address this. This addition provides a clearer and more grounded discussion of the system's scalability and limitations.

 

Comment 3: More quantitative efficiency values (measured inverter efficiency under various loads and irradiance) are expected, rather than general qualitative statements.

Response:

Thank you for this thoughtful comment. As the proposed system is designed to deliver regulated constant power to the load, dynamic load variation was not within the intended scope of this study. Our focus was on evaluating efficiency under varying irradiance levels, which better reflects real world PV fluctuations. These results have been added in Figure 9, 10,  and 12 (simulation base)  and Figure 16 and 17 (experimental base) in Section 4.2. In addition, we acknowledge that testing under different load conditions could offer further insights, and we plan to explore this in future work which is stated in section 4 page 16.

 

Comment 4: The time-sharing nature introduces inevitable delays; however, the quantitative analysis of dynamic response time is not deeply provided (e.g., how long under rapidly fluctuating irradiance does the system lag compared to parallel DMPPT?).

Response:

Thank you for this important observation. We agree that the dynamic response of TS-MPPT under fluctuating irradiance is a key evaluation point. In the revised manuscript Section 3.2, page 9, Figure 12a and 12b has been expanded to illustrate two dynamic irradiance scenarios with different fluctuation patterns. These figures show how the system responds to fast irradiance changes across PV1 to PV4. The response time is visible from the PV power and voltage recovery trajectories. We highlight the average response delay of about 0.01 s in TS-MPPT transitions as stated in page 9 Section 3.2, which remains within acceptable limits for most practical scenarios. A future study is planned to benchmark against parallel DMPPT under cloud shadow emulation.

Comment 5: The experimental validation focuses on step changes in irradiance, but more realistic test cases like fast-moving cloud conditions or random profiles would strengthen confidence.

Response:

We thank the reviewer for this valuable suggestion. We agree that testing under real world dynamic conditions such as fast moving clouds can provide additional validation. However, as this study is conducted in a controlled laboratory environment using a solar simulator, the scope is intentionally focused on validating the core functionality of the TS-MPPT strategy under emulated partial shading. Dynamic irradiance steps were deliberately introduced to mimic real world variations in a repeatable and measurable manner. Testing under outdoor conditions with natural cloud movement, while important, is beyond the current lab scale setup and is therefore reserved for future work. As noted in the revised results discussion section, future efforts will extend the evaluation to outdoor PV systems where stochastic irradiance events can be captured, allowing a more comprehensive validation of the controller’s real time tracking performance under fast-changing weather conditions.

 

Comment 6: GaN device thermal results are promising. However, the thermal analysis is superficial: Were heatsinks used? What ambient conditions? How is thermal cycling over extended operation considered? Were losses experimentally measured or only inferred from surface temperature imaging? These details need clarification.

Response:

We thank the reviewer for this insightful comment. As detailed on pages 13 and 14 (Figures 14 and 15), the thermal analysis was designed to provide a fair and focused comparison between Si, SiC, and GaN switches under identical operating conditions. No external heatsinks were used in this study, instead all devices were tested in a natural convection environment at an ambient temperature of 25 °C as added in page 14. This setup was intentionally chosen to isolate and highlight the intrinsic thermal behavior of each semiconductor technology without the influence of external cooling mechanisms. Our core objective was to assess the relative thermal efficiency of the devices themselves, rather than the performance of a full thermal management system. Surface temperatures were recorded using an HT-A1 infrared camera through designated observation windows, and losses were estimated using manufacturer datasheets in conjunction with the measured temperature profiles. While long-term thermal cycling and aging effects are critical for full system qualification, they are beyond the scope of this stage, which aims to validate the suitability of GaN for compact, high-power renewable energy systems. We believe that the presented thermal data sufficiently supports the rationale for selecting GaN devices in our microinverter design.

 

Comment 7: The literature review is broad but slightly imbalanced toward older references (2012–2017). More recent works (2022–2024) on multi-port microinverters, wide-bandgap switch integration, and advanced GMPPT algorithms should be addressed.

Response:

We appreciate the reviewer’s comment regarding the balance of references. While some foundational works from 2012 to 2017 are cited to provide necessary background and historical context, the manuscript includes a substantial number of recent publications from 2022 to 2024, ensuring the review remains current and relevant. These recent studies cover key advancements in the field, including multi-port and submodule microinverters (Ruchira et al., 2022 [1]; Alenezi & Hussain, 2024 [5]; Wang et al., 2018 [15]; Chu et al., 2020 [18]; Khan & Xiao, 2016 [19]), wide-bandgap switch integration, particularly with GaN-based devices (Alenezi & Hussain, 2024 [5]), and advanced GMPPT and DMPPT algorithms leveraging novel approaches such as evolutionary learning, hybrid DE-FFNN methods, and drone squadron optimization (Husain et al., 2023 [3]; Sameera et al., 2024 [7]; Ncir et al., 2023 [13]; Mazumdar et al., 2024 [24]). These references were carefully selected to reflect the current state of the art, ensuring both technical depth and temporal recency. Therefore, we believe the literature review is well-balanced and up-to-date. Nevertheless, we remain open to incorporating any additional recent references the reviewer may recommend to further strengthen the manuscript.

 

Comment 8: Some figures (e.g., Fig. 8, Fig. 9, Fig. 12) contain overlapping labels and are difficult to interpret. Improve readability by resizing and clarifying legends.

Response:

We thank the reviewer for this helpful comment. The affected figures (Fig. 8, Fig. 9, and Fig. 12) have been carefully revised to enhance clarity and visual readability. Specifically, axis labels, annotations, and legends were resized and repositioned to eliminate overlap. Legends have also been clarified and relocated outside the plotting area where appropriate for improved interpretation. Furthermore, all figures were redrawn at higher resolution to ensure sharpness in both digital and printed versions. These enhancements have been implemented in the revised manuscript to ensure better figure presentation and reader comprehension.

 

Comment 9: The text is mostly clear but contains instances of spelling/grammatical errors (“sonds” instead of “seconds”; “dedcate” should be “dedicate”, etc.). So, I think language editing is recommended.

Response:

We appreciate the reviewers careful reading. The entire manuscript has been thoroughly proofread, and all spelling and grammatical issues including those specifically mentioned have been corrected. In addition, the text was refined for consistency, clarity, and technical precision to meet publication standards. This increases the quality of our presentation.

 

Comment 10: Many acronyms are overused (FPP, DPP, DMPPT, GMPPT, TS-MPPT). Suggest adding a clear Nomenclature table at the beginning.

Response:

We thank the reviewer for this practical suggestion. A list of nomenclature table has been added immediately following the abstract to define all acronyms and key technical terms used throughout the paper which included FPP, DPP, DMPPT, GMPPT, TS-MPPT. This addition enhances our paper particularly for new readers unfamiliar with domain-specific terminology.

Reviewer 3 Report

Comments and Suggestions for Authors

Anees Alhasi et al well presented their research article entitled "An Advanced Single-Phase Non-Isolated Multi-Input Microinverter-Baseed MPPT Strategy for Optimizing PV System Performance". I recommend for the publication of the article in Energies. The following suggestions are recommended.

1. In line 53, the authors mentions the problems with multiple peaks including GMPP on the I-V and P-V curves. Recently, Abasi Abudulimu et. al has one publication "Bias‐Dependent Quantum Efficiency Reveals Recombination Pathways in Thin Film Solar Cells". Could you please address these issues in reference with the losses mentioned in the paper.
2. In line 54, and 80 the authors mentioned research by ref. #, rather than doing so I recommend to give credit to the first author et. al and write the reference number.

 

Author Response

Response to Reviewer 3

We sincerely thank reviewer 3 for their thorough and constructive feedback, which has helped us significantly improve the clarity and robustness of our manuscript. Below are our detailed responses to each of the reviewer’s comments. All modifications in the revised manuscript are highlighted in yellow.

 

Comment 1: In line 53, the authors mention the problems with multiple peaks including GMPP on the I-V and P-V curves. Recently, Abasi Abudulimu et al. published “Bias-Dependent Quantum Efficiency Reveals Recombination Pathways in Thin Film Solar Cells”. Could you please address these issues in reference with the losses mentioned in the paper?

Response:

We greatly appreciate this excellent suggestion, and we have addressed this which can be found in Page 1 of the Introduction Section. In response, we have expanded the discussion in line 53 to incorporate insights from the work of Abasi Abudulimu et al (2025). Their study utilized bias dependent quantum efficiency and drift-diffusion simulations to uncover the impact of front interface, bulk, and back-interface recombination on carrier collection in thin-film CdSeTe solar cells. These recombination dynamics can introduce power losses that lead to distortions and multiple local maxima in the P–V curve. By referencing this study, we emphasize the broader relevance of the multi peak phenomenon caused by recombination pathways not only due to external partial shading but also internal material level processes. This reinforces the importance of advanced MPPT strategies, such as the one proposed in our work, for reliably locating the global maximum power point (GMPP).

 

Comment 2: In line 54 and 80 the authors mentioned research by ref. #; rather than doing so I recommend giving credit to the first author et al. and writing the reference number.

Response:

Thank you for this suggestion. We appreciate this stylistic recommendation. In the revised manuscript, all instances of vague references such as “ref. #” have been replaced with the first author’s surname followed by “et al.” and the appropriate reference number in brackets. This enhances readability and properly credits the original authors. In line 54 Page 1 of the Introduction Section we have  replaced generic phrases “research by [13]” with author-credited citations in the form “Ncir et al. [13]” and line 80 to replace generic phrases “research by [23]” with author-credited citations in the form “Madeti [23]” as shown in page 2. This improves readability and properly attributes prior work while retaining the journal’s numerical referencing.

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

No any further comments.