Review Reports

Round 1

Reviewer 1 Report

The authors compare the smart inverter control schemes based on their communication types and voltage control types. However, the reviewer hardly finds technical contributions compared with previous works.

For example, any quantitative comparison between each type is not presented. Dividing voltage control models into Centralized/Distributed/Local/Decentralized groups is no new. Muhammad Y. already reviewed grid connected PV inverters based on their modulation techniques[1]. It would be better if the authors presented a summarized table to compare each scheme.

Minor comment: There are some single-sentence paragraphs in the manuscript. They should be modified.

 

Muhammad Y.A.K, "A Comprehensive Review on Grid Connected Photovoltaic Inverters, Their Modulation Techniques, and Control Strategies," MDPI energies, 2020.

Author Response

1. Minor comment: There are some single-sentence paragraphs in the manuscript. They should be modified.- Could You clarify the note and indicate where it is in the article?
2. Muhammad Y. already reviewed grid connected PV inverters based on their modulation techniques[1]. It would be better if the authors presented a summarized table to compare each scheme.- Thanks for the recommendation to You. I read the article. I would like to mention that the article has been written for almost a year but has not yet been published. Our article is distinguished by the fact that more sources are used to review the literature.

         A point-by-point response letter is in the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript proposes to present a review considering the subject “Voltage and Reactive Power Algorithms in Low Voltage Networks”, aiming to contribute to the state of knowledge existing in the literature, differentiating itself by presenting a review of the main types of controllers used in PV systems.

Regarding the topic chosen for the work, despite being intensively studied in the literature, with operational and technological advances being incorporated into equipment due to new government regulations and standards, the subject still has good archival potential if the proposal is treated properly.

The work was based on a collection of 125 references to develop the review, in which only about 25% have a year of publication equal to or less than 2016. No occurrences of self-citation were found. Thus, the quantity and quality of the references used, most of them from periodicals, can be considered adequate. However, the reviewer noted the lack of some references and suggests the inclusion and treatment of the following works, involving articles that bring aspects of the use of repetitive controllers (cited as scarce in the literature) and interesting alternatives for comparing controllers.

1. Liu, T. Caldognetto, S. Buso, "Review and Comparison of Grid-Tied Inverter Controllers in Microgrids," IEEE Trans. Power Electron., vol. 35, no 7, July 2020
2. A. Ramos, R. C. Castello, "Comparison of Different Repetitive Control Architectures: Synthesis and
   Comparison. Application to VSI Converters," MDPI Electronics, vol. 446, 2018

The article presents adequate writing, generally lacking relevant aspects of revision regarding grammar and language use. However, the strategy adopted by the authors to deal with the issues, considering notes by lists, without the use of tables conventionally used in review works, in some circumstances can make it difficult to understand and cover the statements, since the analysis condition does not is established.

As, for example, in the list of advantages in section 2.2, item 1 states that communication would not be required, while item 3 points out that concerning the centralized method less communication would be required. Correct aspects, but that need better clarification so that the statements do not become ambiguous.

“1. No communication is required, and reactive power output depends only on locally measured data [27].

3. Less communication is required compared to the centralized method, as information needs to be exchanged only with the secondary substation [1]”;

In this sense, the reviewer suggests that the authors try to adopt some tables and/or figures to facilitate the foundation, explanation, and comparison of the conditions and situations being compared.

Regarding the structure of section 2, this presents an adequate survey of the “Voltage and Reactive Power Algorithms in Low Voltage Networks”. However, the generality of the presentation could be improved by indicating in which sector the algorithms could be worked (primary, secondary, tertiary, etc.).

With respect to section 2.3 of Hybrid methods, these were described through a single paragraph in the section, there is no pointed reference or in-depth discussion carried out. Being a review article, this subject should be better dealt with.

Regarding section 3, Controllers for Distribution Network PV Systems, pointed out as a differential to other review works in the literature, the section presents a survey of the types of controllers used, considering the classification and reference of works that employ them.

However, it considers the union of characteristics from different works, which are not necessarily evaluating the same conditions, if the condition is not clearly established, the understanding may not be generalized.

The discussions that converge on the advantages and disadvantages, bring only inherent and known characteristics of the type of generic controller addressed, despite linking and quoting works properly, with the exception of the first section (linear controllers) it does not evolve into in-depth discussions related to the operational impact on the system due to controller usage, or what type of quantities or architectures are applied to each controller, application level, and other important aspects from the controller's point of view: acceptable steady-state error, transient response, control bandwidth, and phase delays, implementation complexity, computational burden.

The reviewer would like to mention some aspects to collaborate with the improvement of the work.

- On the Introduction, page 3 (line 117): "demand response" appears twice.

- In the introduction, there is a reference to the phrase “The present study aims to find the optimum voltage and reactive power control”. However, the work does not present and does not apply an optimization methodology to achieve this goal.

- In section 2.2 - the terminologies adopted to describe the methods in section 2.2 could be aligned with the designations made in the introduction of section 2 [ constant power factor (PF) mode, PF-active power, (PF-watt) mode, voltage -reactive power (volt-var) mode, and voltage-active power (volt-watt) mode].

- Figure 5 - it would be interesting to include the units in the chart shown on the right.

- Figure 6. b - shouldn't the graph on the right side vary? include comments

Author Response

1. However, the generality of the presentation could be improved by indicating in which sector the algorithms could be worked (primary, secondary, tertiary, etc.).- If I have understood Your note correctly, the information is given in lines 144-152.

      A point-by-point response letter is in the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

The article discusses about the effect of growing distributed resources on voltage profile in low voltage networks. Authors initially discussed current methods to maintain voltage profile in limits. Those methods are difficult to control distributed resources. Later, authors talked about different controllers that can be used in PV system to maintain voltage.

Please see the comments below:

1. Authors included background discussion on distributed energy resources in abstract. Abstract needs to be brief in abstract. Third paragraph will be sufficient with edits. Please revise the abstract.
2. Authors in the lines between 69-75 discussed about the characteristics of European LV distribution network. This characteristics apply to all distribution networks around the globe.
3. Please summarize the article contributions at the end of introduction section.
4. Authors discussed the different controller strategies for PV inverters to maintain voltage under limits. PV control system might include more than one loop and choice of controller can't be chosen solely based on controlling voltage. To comply with interconnection standards, control becomes more complex.
5. Authors need to first discuss state-of-the-art controllers used in inverters. 
6. Later they can compare the current research against state-of-the-art controllers.

Author Response

1. Authors included background discussion on distributed energy resources in abstract. Abstract needs to be brief in abstract. Third paragraph will be sufficient with edits. Please revise the abstract.- Could You clarify the note?

      A point-by-point response letter is in the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Please see the attached file.

Comments for author File: Comments.pdf

Author Response

Dear, Reviewer
Thank you for the positive feedback.

Reviewer 2 Report

The authors provided answers to all comments listed in the review process, incorporating some of the answers in the revised version in order to improve the manuscript.

Considering the answers to the questions provided by the authors, despite agreeing with all the reviewer's comments, some were not actually added to the manuscript (items 2, 7, and 8 of the authors' comments to the reviewer), with the justification that the scope of the review would already be big or because the work is still in development.

Among these, there is item 8 which deals with the controllers' discussions, an aspect highlighted as a differential contribution in the review proposal, that is, no review implemented in section 3 was found. Thus, the reservation pointed out in the first review process remains in the revised version, being important to adjust the emphasis given to this contribution.

Other aspects that could be reviewed:

 - In section 2.3, include some references to support the statements.

- In table 1, it would be important to include the set of references that support the statements in one of the columns of the table.

Author Response

Dear Reviewer,

Thanks for your valuable suggestions. I tried to incorporate your suggestions into the article when updating it. I hope I understood correctly.

Red highlights the parts of the article that have been modified (lines 442, 475, 476-477).

 

Author Response File: Author Response.doc