Power Quality Enhancement in a Grid-Integrated Photovoltaic System Using Hybrid Techniques

Round 1

Reviewer 1 Report

Thank you for submitting your paper “Power Quality Enhancement in a Grid-Integrated Photovoltaic System Using Hybrid Techniques” to the Journal of Applied Sciences.

The paper draws attention to a significant subject. I have found the paper very interesting.

The article is well written and well structured as a scientific text; the literature review is comprehensive and up to date. However, several issues need to be addressed properly before the paper is being considered for publication.

My comments including major and minor concerns are given below:

• The title is too general; numerous studies have been done on this topic. The title should enhance the innovativeness of this study.
• I suggest reorganizing the abstract, highlighting the novelties introduced and the main numerical results obtained. It should contain answers to the following questions:
• What problem was studied and why is it important?
• What methods were used?
• What conclusions can be drawn from the results?
• What is the novelty of the work and where does it go beyond previous efforts in the literature?
• Other studies can be included, such as:
  • A literature review and statistical analysis of photovoltaic-wind hybrid renewable system research by considering the most relevant 550 articles: An upgradable matrix literature database, Journal of Cleaner Production, Volume 295, 2021, 126070, ISSN 0959-6526, https://doi.org/10.1016/j.jclepro.2021.126070.
  • A novel grid-connected solar PV-thermal/wind integrated system for simultaneous electricity and heat generation in single family buildings, Journal of Cleaner Production,

Volume 320, 2021, 128518, ISSN 0959-6526, https://doi.org/10.1016/j.jclepro.2021.128518.

• The methodology section should be improved considerably, which is my major concern. A flow chart can be useful to summarize the entire methodology. Furthermore, it is important to put in evidence the following points:
• The proposed methodology has numerous advantages, such as:
• The main novelties and objectives of the present work can be summarized as:
• All figures should be explained much more.
• Conclusions that are too summarized should be implemented.

Author Response

Dear Reviewer,

Thank you for taking the time to review our work.

We have addressed the suggested revisions throughout the body of the article.

REVIEWER

My comments including major and minor concerns are given below:

1. The title is too general; numerous studies have been done on this topic. The title should enhance the innovativeness of this study.

Answer:

Thank you for your useful comments. As per the reviewer’s comment, we have modified the research title which will show the innovativeness of this study.

2. I suggest reorganizing the abstract, highlighting the novelties introduced and the main numerical results obtained. It should contain answers to the following questions:

What problem was studied and why is it important?

What methods were used?

What conclusions can be drawn from the results?

What is the novelty of the work and where does it go beyond previous efforts in the literature?

Other studies can be included, such as:

A literature review and statistical analysis of photovoltaic-wind hybrid renewable system research by considering the most relevant 550 articles: An upgradable matrix literature database, Journal of Cleaner Production, Volume 295, 2021, 126070, ISSN 0959-6526, https://doi.org/10.1016/j.jclepro.2021.126070.

A novel grid-connected solar PV-thermal/wind integrated system for simultaneous electricity and heat generation in single family buildings, Journal of Cleaner Production, Volume 320, 2021, 128518, ISSN 0959-6526, https://doi.org/10.1016/j.jclepro.2021.128518.

Answer:

Thank you for your valuable comments. As per the reviewer’s comment, we have re-organized the abstract. Now the reader can easily understand the overview of the entire research from the abstract part.

3. The methodology section should be improved considerably, which is my major concern. A flow chart can be useful to summarize the entire methodology. Furthermore, it is important to put in evidence the following points: The proposed methodology has numerous advantages, such as:

Answer:

Thank you for your important comments. As per the reviewer’s comment, we have included a flowchart for the proposed method at section 6.3. Also, we have given the advantages for the proposed method at the beginning of section 6.

4. The main novelties and objectives of the present work can be summarized as:

Answer:

Thank you for your important comments. As per the reviewer’s comment, we have added the novelties and objectives at section 6.2.

5. All figures should be explained much more.

Answer:

Thank you for your important comments. As per the reviewer’s comment, we have given brief explanation for all the figures.

6. Conclusions that are too summarized should be implemented.

Answer:

Thank you for your useful comments. As per the reviewer’s comment, we have summarized the conclusion section.

Reviewer 2 Report

First of all authors please clean up the changes and resubmit the manuscript. Current presentation is chaotic and messy.

What is the hardware cost of the proposed method? Hardware overhead requirements for the three proposed approach need to be included for reader consideration.

Has author consider the non-ideality in actual hardware such as computation delay, comparator delay, etc.? 

Authors need to redraw the proposed approach BPSO, GWO and hybrid BPSO-GWO controller clearly in a successive and coherent diagram. The current format is very difficult to distinguish and compare the differences among these schemes proposed. Figure 4, Figure 5 captions need to be changed to reflect the exact scheme used. 

Author also need to allocate one paragraph to further discuss the most useful scheme, which is the hybrid BPSO-GWO scheme. How does the mix and match actually bring better results is unclear.

Author Response

Dear Reviewer,

Thank you for taking the time to review our work.

We have addressed the suggested revisions throughout the body of the article.

1. What is the hardware cost of the proposed method? Hardware overhead requirements for the three proposed approach need to be included for reader consideration.

Answer:

Thank you for the useful comment. We are in the consideration to proceed with TI- MSP430 launch pad kit, the experiment analysis for this research work in the future. The cost of the basic kit is about 30euros.

2. Has author consider the non-ideality in actual hardware such as computation delay, comparator delay, etc.? 

Answer:

Thank you for the useful comment. We have simulated grid connected PV systems under different load conditions. We have validated the proposed work by comparing it with the conventional methodologies at section 6.

3. Authors need to redraw the proposed approach BPSO, GWO and hybrid BPSO-GWO controller clearly in a successive and coherent diagram. The current format is very difficult to distinguish and compare the differences among these schemes proposed. Figure 4, Figure 5 captions need to be changed to reflect the exact scheme used. 

Answer:

Thank you for your useful comments. As per the reviewer’s comment, we have included the flowchart for the hybrid BPSO-GWO method at section 6.3. Also, we have changed the captions for the figure 4 and 5 (now changed to 5 and 6).

4. Author also need to allocate one paragraph to further discuss the most useful scheme, which is the hybrid BPSO-GWO scheme. How does the mix and match actually bring better results is unclear.

Answer:

Thank you for your important comments. As per the reviewer’s comment, we have included the flowchart and its advantages for the proposed method with clear explanation at the beginning of section 6

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Authors addressed the reviewers' suggestions

Author Response

Dear Reviewer, Thank you for your time and helpful suggestions that proved immensely valuable to me. As suggested, I've made spelling corrections and reformatted the document. Thank you once again. 

Author Response File: Author Response.pdf

Reviewer 2 Report

Previous manuscript were improved. I have no further comments except minor spell checking and pagination formatting.

Author Response

Dear Reviewer, Thank you for your time and helpful suggestions that proved immensely valuable to me. As suggested, I've made spelling corrections and reformatted the document.    Thank you once again

Author Response File: Author Response.pdf

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Thank you for submitting your paper “Power Quality Enhancement in Grid Integrated PV System Using Hybrid Techniques” to the Journal of Applied Sciences.

In my opinion, it is a valuable paper. Overall, the paper is well written but needs some improvements before publication.

The title should highlight the innovative aspect proposed by this study; in general it is preferable not to include acronyms in the title.

The novelty of this paper should be well described and emphasized in the abstract and conclusion. Please work on this and show us why this work is valuable.

The Abstract should contain answers to the following questions:

• What problem was studied and why is it important?
• What methods were used?
• What are the important results?
• What conclusions can be drawn from the results?
• What is the novelty of the work and where does it go beyond previous efforts in the literature?

Implement the state of the art.  The growing concern about environmental issues and the progressive depletion of fossil fuels has driven research towards renewable resources (A literature review and statistical analysis of photovoltaic-wind hybrid renewable system research by considering the most relevant 550 articles: An upgradable matrix literature database, Journal of Cleaner Production, https://doi.org/10.1016/j.jclepro.2021.126070).  PV modeling is now one of the most important steps in the process of PV power collection, due to its importance in calculating and finding PV system characteristics for any climate conditions (A model for direct-coupled PV systems with batteries depending on solar radiation, temperature and number of serial connected PV cells, Solar Energy, https://doi.org/10.1016/j.solener.2019.03.010).

As regards the methodology, it is important to put in evidence the following points:

• The proposed methodology has numerous advantages, such as:
• The main novelties and objectives of the present work can be summarized as:

All figures should be explained much more.

In figures 9 and 10 the setting can be shown in a table or described in the text.

Figure 11 improves the plotting of the x-axis.

I suggest implementing a discussion of the results obtained.

In general, I strongly suggest clearly explaining the significant findings and the real novelty of the work, implementing the conclusion part.

Please, add the Table of Nomenclature.

Author Response

Reviewer 1

Comments to the Author

1. The title should highlight the innovative aspect proposed by this study; in general, it is preferable not to include acronyms in the title.

Answer:

Thank you for important comments. As per the reviewer’s comment, we have removed the acronyms and made the proper title name.

2. The novelty of this paper should be well described and emphasized in the abstract and conclusion. Please work on this and show us why this work is valuable.

Answer:

Thank you for valuable comments. According to reviewer’s comment, we have described the novelty and how it achieves the better results in the abstract & conclusion part.

3. The Abstract should contain answers to the following questions:

• What problem was studied and why is it important?
• What methods were used?
• What are the important results?
• What conclusions can be drawn from the results?
• What is the novelty of the work and where does it go beyond previous efforts in the literature?

Answer:

Thank you for important comments. As per the reviewer’s comment, we have clearly elaborated the problem, methods, results, conclusion and novelty in the abstract part.

4. As regards the methodology, it is important to put in evidence the following points:

• The proposed methodology has numerous advantages, such as:
• The main novelties and objectives of the present work can be summarized as:

Answer:

Thank you for your important comments. Based on the reviewer comment, we have mentioned the advantages of the proposed method at the end of introduction part. Also we have explained the novelty in section 6.

5. All figures should be explained much more.

In figures 9 and 10 the setting can be shown in a table or described in the text.

Answer:

Thank you for your important comments. Based on the reviewer comment, we have added a table in the section 7. Also we have described the points about figure 9 and 10.

6. Figure 11 improves the plotting of the x-axis.

Answer:

Thank you for your important comments. According to the reviewer comment, we have changed the figure quality and x-axis of figure 11 which is illustrated in section 7.

7. Please, add the Table of Nomenclature.

Answer:

Thank you for your important comments. According to the reviewer comment, we have added the nomenclature table.

Author Response File: Author Response.docx

Reviewer 2 Report

Authors declare in the title that the paper aims to propose a "hybrid" method to improve power quality in PV systems, so I expected some "hybrid" circuitry or hybrid control approach.  On the othe rhand, the "hybrid" revealed to be just a combination of two collective search optimization algorithms, which is somehow misleading.

English language is really bad, and I had quite a hard time to understand some of the points. Also, symbols are not always clearly defined (e.g. Tr2 in Figure 1, most of the symbols in Figure 3 - I guess that SL3 is a Mosfet block, but which type?;  Ia, Ib and Ic - input currents? - and "Transfer function", Visq, and so on - in Fig. 4) while others are defined twice with different meanings (e.g. C1 and C2 in (4), (5) -defined as capacitances, while they have other meaning - and then in (8) and (9))

Also, it is not clear which is the fitness function defined in (21) in terms of... an average of i-th (undefined) fitness functions!

Anyway, the real problem is that it is not clear which is the objective function and the degrees of freedom of the optimization, how long it takes to reach its goals (and if such running times are compatible with a real time performance), and results are never truly compared with completely different techniques, even at the level of different algorithms, the only comparison with genetic algorithms / ANN being Table 3, which only shows different THD.

No clear references are provided for the PV array model, for the MPP definition, for the optimization algorithms, and also for the panel used in the study.

A seriously flawed set of specification is just provided - I can hardly believe that, e.g,  the diode saturation current  can be measured with an accuracy of 0.1 femtoAmpere, or that the series resistance can be measured with an accuracy of 10 microOhms.

This paper is far from being a piece of work worth publishing

Author Response

Comments to the Author

1. Authors declare in the title that the paper aims to propose a "hybrid" method to improve power quality in PV systems, so I expected some "hybrid" circuitry or hybrid control approach.  On the other hand, the "hybrid" revealed to be just a combination of two collective search optimization algorithms, which is somehow misleading

Answer:

Thank you for important comments. As per the reviewer’s comment, we have explained the concept about hybrid control approach and its advantages at the end of introduction part.

2. English language is really bad, and I had quite a hard time to understand some of the points. Also, symbols are not always clearly defined (e.g. Tr2 in Figure 1, most of the symbols in Figure 3 - I guess that SL3 is a Mosfet block, but which type?;  Ia, Ib and Ic - input currents? - and "Transfer function", Visq, and so on - in Fig. 4) while others are defined twice with different meanings (e.g. C1 and C2 in (4), (5) -defined as capacitances, while they have other meaning - and then in (8) and (9))

Answer:

Thank you for valuable comments. According to reviewer’s comment, we have made the proper changes in the English grammar. Also we have modified the symbols and explained the function of each symbol in figure 3 and 4. Furthermore, we have corrected the C1, C2 meanings in equation 8 & 9.

3. it is not clear which is the fitness function defined in (21) in terms of... an average of i-th (undefined) fitness functions!

Answer:

Thank you for important comments. As per the reviewer’s comment, we have clearly elaborated the fitness function and iteration conditions at the end of section 6.

4. Anyway, the real problem is that it is not clear which is the objective function and the degrees of freedom of the optimization, how long it takes to reach its goals (and if such running times are compatible with a real time performance), and results are never truly compared with completely different techniques, even at the level of different algorithms, the only comparison with genetic algorithms / ANN being Table 3, which only shows different THD.

Answer:

Thank you for your important comments. Based on the reviewer comment, we have mentioned the exact objectives and problems at the end of introduction part.  Also we have added the comparative analysis of PV power (figure 9) and explained in section 7.

5. No clear references are provided for the PV array model, for the MPP definition, for the optimization algorithms, and also for the panel used in the study..

Answer:

Thank you for your valuable comments. Based on the reviewer comment, we have added the suitable reference for the PV array model, MPP definition, Optimization algorithm and Panel study which are cited in the reference section.

Cited References:

[16] Ali, Mahmoud N., Karar Mahmoud, Matti Lehtonen, and Mohamed MF Darwish. "An efficient fuzzy-logic based variable-step incremental conductance MPPT method for grid-connected PV systems." Ieee Access 9 (2021): 26420-26430.

[17] Mohamed Hariri, Muhammad Hafeez, Mohd Khairunaz Mat Desa, Syafrudin Masri, and Muhammad Ammirrul Atiqi Mohd Zainuri. "Grid-Connected PV Generation System—Components and Challenges: A Review." Energies 13, no. 17 (2020): 4279.

[19] Abdulkadir, M., A. H. M. Yatim, and S. T. Yusuf. "An improved PSO-based MPPT control strategy for photovoltaic systems." International Journal of Photoenergy 2014 (2014).

[20] Almutairi, Abdulaziz, Ahmed G. Abo-Khalil, Khairy Sayed, and Naif Albagami. "MPPT for a PV grid-connected system to improve efficiency under partial shading conditions." Sustainability 12, no. 24 (2020): 10310.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Authors addressed the reviewers' suggestions

Author Response

Dear Reviewer, 

Thank you for valuable comments. According to reviewer’s comment, we have made the proper changes in the English grammar and have taken help from English editing team of MDPI journal. 

Author Response File: Author Response.pdf

Reviewer 2 Report

I regret to have not been able to explain myself clearly. I try to list here my comments, mostly still unanswered:

• Authors were asked to carefully check English language, which they did not do (I was still able to find sentences like "The random nature of the solar array generates by fluctuating the electric power", which is not an English sentence; many other examples can be still found in the text)
•  Authors were asked to comment about the reaction times of the method, and its capability to act in real time. I was not able to find a clear statement about this, but from fig. 8 it appears that reaction times are in the order of 50 ms. (2 periods and a half of 50 Hz). Is this compatible with grid needs?
• Authors were warned that using up to 6 decimals to define a parameter is not realistic. Yet, diode saturation current is still defined up to an accuracy of  10^-16 Amps
• Authors were asked to provide a comparison with other methods (not with just a different combination of their "component" methods.) As a matter of fact, they exclude Gauss-Newton search due to its need for function smoothness. Well, it comes with a price, since use of derivatives makes GN much faster, so at least a comparison with this algorithm was required to demonstrate that the proposed algorithm is prompt enough
• Authors were asked to be more careful about symbols, and I gave "C1" and "C2" as an example. These symbols are still called "capacitances" after eq. (3), thought they are dimensionless, and are still present with another meaning in eq. (8)
• I asked to clearly define the degrees of freedom, and the objective function. Authors added section 7 to define the objective function, but the statement they added cannot be considered a definition of an objective function
• Simulink schemes are still undefined (e.g. what is inside the "boost converter" block in Figure 5, and how it is linked to the scheme in fig. 4?

So, in my opinion this paper is not yet ready for publication

Author Response

Dear Reviewer,

With respect to the comments and quires raised by you, herewith I am answering for all the comments and quires with respect to the best of my knowledge.

1. Authors were asked to carefully check English language, which they did not do (I was still able to find sentences like "The random nature of the solar array generates by fluctuating the electric power", which is not an English sentence; many other examples can be still found in the text).

Answer:

Thank you for valuable comments. According to reviewer’s comment, we have made the proper changes in the English grammar and have taken help from English editing team of MDPI journal. Also we have corrected the above mentioned sentences, "The random nature of the solar array generates by fluctuating the electric power".

2. Authors were asked to comment about the reaction times of the method, and its capability to act in real time. I was not able to find a clear statement about this, but from fig. 8 it appears that reaction times are in the order of 50 ms. (2 periods and a half of 50 Hz). Is this compatible with grid needs?

Answer:

Thank you for important comments. As per the reviewer’s comment, we have extended the simulation timing from 1 sec to 10 sec. Also we have represented the figure 8 with extended reaction time. Now the system will be compatible for the grid requirements.

3. Authors were warned that using up to 6 decimals to define a parameter is not realistic. Yet, diode saturation current is still defined up to an accuracy of  10^-16 Amps

Answer:

Thank you for your important comments. Based on the reviewer comment, we have changed the diode saturation current up to 5 decimals which is feasible for the realistic calculation.

4. Authors were asked to provide a comparison with other methods (not with just a different combination of their "component" methods.) As a matter of fact, they exclude Gauss-Newton search due to its need for function smoothness. Well, it comes with a price, since use of derivatives makes GN much faster, so at least a comparison with this algorithm was required to demonstrate that the proposed algorithm is prompt enough.

Answer:

Thank you for valuable comments. According to reviewer’s comment, we have provided the comparison table (Table 2) with different existing methods which is explained in section 7.

Cited Reference:

[21] Ilyas, Mohd, Shamshad Ali, and Mumtaz Ahmad Khan. "Modeling and Simulation of 10 kW Grid Connected PV Generation System Using Matlab/Simulink." International Journal of Applied Engineering Research 13, no. 24 (2018): 16962-16970.

5. Authors were asked to be more careful about symbols, and I gave "C1" and "C2" as an example. These symbols are still called "capacitances" after eq. (3), thought they are dimensionless, and are still present with another meaning in eq. (8).

Answer:

Thank you for important comments. As per the reviewer’s comment, we have modified the variable name and its meaning (from C1, C2 into Q1, Q2) which is clearly explained at equation 8.

6. I asked to clearly define the degrees of freedom, and the objective function. Authors added section 7 to define the objective function, but the statement they added cannot be considered a definition of an objective function

Answer:

Thank you for valuable comments. According to reviewer’s comment, we have clearly explained the degree of freedom and objective functions. Also we have included the transient performance table (Table 3) which is described in section 7.

7. Simulink schemes are still undefined (e.g. what is inside the "boost converter" block in Figure 5, and how it is linked to the scheme in fig. 4?

Answer:

Thank you for important comments. As per the reviewer’s comment, we have described clearly about the boost converter and its working functions at the beginning of section 7. Also we have clarified in detail how the figure 4 is linked with figure 5 at section 6.3.

Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

I appreciated the effort from authors, but I am afraid I was not able to make my comments clear enough, so I don't think all of them were correctly implemented.

In order to cite just the most relevant ones:

1) The issue about capacitances and their physical dimensions is in Es. (3), and not (8). Symbols C1 and C2 ARE NOT FARADS!!! Also, I was not able to recover the used formula from ref. [16] (cited just before the equations, where the orginal source is supposed to be).

Authors are reuired to cite the source of equations, or to justify them

2) No comparison with newton-raphson based approaches is reported, and in addition, I guess results in ref. [16] were obtained using a different converter (authors claim they also propose a new 31-levels converter). So, is the comparison in fig. 11 meaningful?

3) Promptness of the approach in real implementations was not investigated. Authors simply extended the simulation from 1s to 10 s, which does not provide any info on the issue

4) The objective function is something like "power times duty-cicle", and the degree of freedom is the duty cicly. So, why authors used THD to justify the effectiveness of their approac? I was not able to understand this from the discussion.

5) I guess the 31-levels converter plays a major role in THD, but then, two motivations to improve results are present (converter and new hybrid approach), and they must be separatedly motivated.