Small-Signal Modeling and Configuration Analysis of Grid-Forming Converter under 100% Renewable Electricity Systems

Round 1

Reviewer 1 Report

The paper is mostly well-written and organized. Here are some suggestions to improve it:

1. Consider finding a shorter term/acronym for '100% renewable electricity independent system' that can be defined once and repeated thereafter.

2. While the introduction is quite long, there aren't enough cited papers. The authors should make the introduction more dense and clear.

3. SCR should be defined the first time it is used, not after an entire section. SCR is used as the main parameter for the configuration method but there is insufficient background provided in terms of context and references.

4. There are formatting issues/random symbols present from page 12 onwards that need to be fixed. Also, lines 378-381 seem to be a mishmash of incomplete sentences that need to be revised.

5. Figures 14 and 15 are unreadable. Different types of signals are plotted on the same chart with no information on the axes.

6. Beyond the eigenvalue analysis, what is preventing the authors from recommending a fully grid-forming-control-based system? Please elaborate. 

The paper is well-written but proof-reading is required in some areas.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

The introduction gives a good overview of the issues and background.

The modeling section is clear and technically sound. 

The analysis results are informative.

The field test results help validate the approach. 

The conclusions summarize the main findings well. 

Please carefully proofread the paper to fix any minor grammar, spelling or style issues.

 

Thank you very much for your time and efforts.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 3 Report

This paper addresses the design and use of converters based on grid-forming and grid-following strategies in an energy recovery system. The authors note that grid-forming devices have the ability to maintain voltage and inertial response, allowing them to be successfully implemented in systems with high renewable energy content.

The article begins with a comparison of the operating principles and control methods of converters based on network formation and network following strategies. The authors construct a small-signal model and a detailed time-domain model and conduct a comparative analysis of the dynamic characteristics of network-forming and network-following converters. Further, the paper proposes a proportional configuration method for grid-forming converters in a grid-independent system based entirely on renewable energy sources. Using a small signal model, the authors discuss the impact of different proportions of grid-forming converters and control mode on the stability of a renewable energy system. In addition, the minimum required proportion of network-forming converters to ensure stable operation of the system is investigated. At the end of the article, the authors check the correctness of their proposed proportional configuration of grid-forming converters and the technical feasibility of independent operation of the system with 100% renewable energy.

Overall, the paper provides a useful study in the development and use of grid-forming converters and describes the application of such converters in high renewable energy systems. She also proposes a new method for proportional configuration of grid-forming converters and analyzes their impact on the stability of a renewable energy system.

Criticisms:

1. The structure of the article is broken. There is no discussion section. The author should add a “discussion” section before the conclusion. In which to note the positive and negative aspects of the study. I also recommend that the authors in this section explain how the objective function is formulated.

2. For scientific research of a technical nature, the “References” section must contain at least 40 sources; the authors have 19 sources. The author needs to refine the introduction section in more detail and describe the background of the study in more detail. I recommend that authors use the search engine mdpi.com or researchgate.net for this. As an example, I cite critically important articles on the topic of your research that must be included in your review.

  Ilyushin, Y.V.; Kapostey, E.I. Developing a Comprehensive Mathematical Model for Aluminum Production in a Soderberg Electrolyser. Energies 2023, 16, 6313. https://doi.org/10.3390/en16176313

Pershin, I.M.; Papush, E. G.; Kukharova, T.V.; Utkin, V.A. Modeling of Distributed Control System for Network of Mineral Water Wells. Water 2023, 15, 2289. https://doi.org/10.3390/w15122289

3. Figure 1. The outputs of the windings of each phase CA, Cb, CC are connected to each other through the corresponding capacitors. This action requires explanation.

4. Figure 2 (lower pictures). Negative feedback into the adder has an output. In the opposite direction from the adder. Denoted by the variables ud, uq, and Id, Iq What is it? Typo

5. Figure 3 (see note 4).

6. Variables in equations are not disclosed. The author must provide explanations for all variables used in the work.

7. 177. Is the triangle sign a Lapalasian or an average?

8. 187. Before w, did you lose the variable j?

9. Figure 15. The figure is difficult to read, I recommend enlarging the figure

 

Conclusion. The article is positive, but has some inaccuracies that make it difficult to understand. The author needs to correct these comments. Add recommended links. After correction, I am ready to recommend the article for publication.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 4 Report

This manuscript conducts the small-signal analysis in a 100% renewable system and proposes a method for calculating the minimum share of grid-forming converters, which is an interesting and emerging topic. Some concerns are as follows:

1. The 'grid-forming' in the title seems imprecise since the manuscript studies the hybrid grid-following/forming system.

2. The Nyquist diagram is based on the impedance, while the previous small signal modeling seems using state space method. Which stability analysis do you use in Section 2? If using impedance method, the authors should give the equation to draw the Nyquist plot.

3. There are much confusion in the first paragraph of 3.2. How does grid-following converter synchronize without an PLL? Please also check the language.

4. Could you give the parameters in Figure 5, since many conclusions are drawn in values?

5. Please only retain the critical eigenvalue locus in the zoomed-in plots of Figure 11 and 12.

6. How do you change the bandwidth of the voltage loop control? There should be a specific parameter.

7. What is the relationship of Section 4.4 and other analysis in the previous sections? Do you calculate the minimum share of grid-forming converters or study the parameter impact? If not, the authors may consider moving this part to the introduction.

Please carefully check the language, font size, and format.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

All comments have been eliminated

Reviewer 4 Report

The authors' replies are satisfying and have addressed the questions.