General Aspects, Islanding Detection, and Energy Management in Microgrids: A Review

Round 1

Reviewer 1 Report

This paper reviews three technical themes, i.e., the possible operating modes of MGs, islanding detection techniques (IDTs) and EMSs for MGs.

To this reviewer, the technical issues concerned are well known to engineers in the power engineering field; however, it provides a good reference for greenhands in MGs. Some suggestions are given below for the authors to consider.

1. The contents of section 1~6 should be simplified and properly combined with a general discussion section. since there are too basic and most of the information provided can be found in text books in the related courses.
2. Provide comprehensive comparison in performance of various IDTs papers reviewed, give a reasoning analysis on their advantages and drawbacks. What features require further improvement.
3. Provide comprehensive comparison in performance of various EMSs papers reviewed, give a reasoning analysis on their advantages and drawbacks. What features require further improvement.
4. Enhance the contents of MG challenges on operations of MGs, minimizing the operating cost, the efficiency and reliability improvement of MG operations.
5. Check the editorial issues and rearrangement the paper sections. Line 71, 2. Methodology, Line 89, 3. Methodology.?, Line 261, TIDT should be T_{IDT ?.}

Author Response

Reviewer #1:

 

Comment 1:

The contents of section 1~6 should be simplified and properly combined with a general discussion section. since there are too basic and most of the information provided can be found in text books in the related courses.

Response:

Thank you very much for your valuable comments. It helps us to present our work more clearly. Sections 1 to 5 have been combined with a general discussion in section 2, pages 1 to 9. Please refer to the revised manuscript.

 

Comment 2:

Provide comprehensive comparison in performance of various IDTs papers reviewed, give a reasoning analysis on their advantages and drawbacks. What features require further improvement.

Response:

As suggested, a comparison of various IDTs has been presented in Table 8, page 24. Please refer to the revised manuscript.

Table 8. Summary of various IDTs

IDT	Advantages	Disadvantages	Improvement
Passive technique	No impact on PQ; Detection speed is fast;	NDR is large; ED rate is higher than active technique;	An improved passive technique considering voltage/frequency behaviour of load and adaptively threshold can significantly reduce the NDR.
Active technique	NDR is small; ED rate is less;	Deteriorates PQ;	A modified reactive power control approach can detect ID with negligible NDR. This method does not deteriorate PQ.
Hybrid technique	NDR is very small; ED rate is low;	Slightly deteriorates PQ; Only effective for the complicated system;	A hybrid converter based ID can achieve zero-NDR and does not degrade PQ.
Remote technique	No NDR; No impact on PQ; ED can be eliminated;	Need a large amount of investment; Not economical for the small system;	Various devices like smart meters, phasor measurement unit can be applied for ID. This can significantly reduce the implementation time and cost making it practical and economically viable.
Intelligent technique	Easy implementation; No threshold  selection is required;	Need to train classifier; Parameter selection is difficult; Large computational burden;	Advanced digital signal processing methods combined with learning algorithm can be an effective tool for ID.

 

Comment 3:

Provide comprehensive comparison in performance of various EMSs papers reviewed, give a reasoning analysis on their advantages and drawbacks. What features require further improvement.

Response:

As suggested, a comparison of various IDTs has been presented in Table 13, page 41. Please refer to the revised manuscript.

Table 13. Comparison of various EMS techniques

EMS technique	Advantages	Disadvantages	Improvement
Conventional technique	High precision factor; Require less computational time;	Hard to implement for the large system; Limited space optimization;	Apply advanced mathematical techniques
Metaheuristic technique	Easy to implement; Capable of handling complex problems; Deals with numerous variables;	Relatively lower performance for determining global optimal solution; Premature convergence; Require long computational time;	Requires advanced heuristic strategies
Artificial  intelligence technique	Efficient performance for determining global optimal solution; Capable of handling complex problems;	Relatively hard to code	New deep leaning methods could improve the EMS
Stochastic and robust optimization technique	Capable of handling complex problems;	Computational time complexity is higher; Complex formulation;

 

Comment 4:

Enhance the contents of MG challenges on operations of MGs, minimizing the operating cost, the efficiency and reliability improvement of MG operations.

Response:

MG challenges have been modified according to reviewer’s comment in section 5, pages 42 to 44. Please refer to the revised manuscript.

 

Comment 5:

Check the editorial issues and rearrangement the paper sections. Line 71, 2. Methodology, Line 89, 3. Methodology.?, Line 261, TIDT should be TIDT ?.

Response:

As suggested by the reviewer, section headings 2 and 3 have been deleted and merge under the section “General aspects of MGs” in section 2, pages 2 to 4. The TIDT has been modified to T_IDT on page 12, line 306. Please refer to the revised manuscript.

 

 

 

List of changes

 

Many changes and corrections have been made to answer and clarify reviewers’ comments and suggestions. ALL THE CORRECTIONS ARE HIGHLIGHTED BY TRACK CHANGES in the revised manuscript. Please refer to the edited version.

Author Response File: Author Response.pdf

Reviewer 2 Report

Dear authors,
The article presented here is a very interesting take on the subject. After reading it, I find the material presented to be of very high quality. I would like to suggest a few minor corrections:
- figure captions should not end with a dot.
- Figures should be centred.
- Figure captions should be positioned equally, see Figure 1 (line 70) and Figure 2 (line 88).
- The table caption should not end with a dot.
- I suggest describing the variables in the formulae one under the other. This will be easier to read.
- I suggest checking what are the requirements for the length of the article. It seems to be too long. I suggest dividing it into two parts.

Author Response

Reviewer #2:

 

Comment 1:

Figure captions should not end with a dot. Figures should be centred. Figure captions should be positioned equally, see Figure 1 (line 70) and Figure 2 (line 88).

Response:

Thank you very much for appreciating our work. Figures and their captions have been positioned in the center. The dot at the end of the figure captions has been deleted. Please refer to the revised manuscript.

 

Comment 2:

The table caption should not end with a dot.

Response:

The dot at the end of the table captions has been deleted. Please refer to the revised manuscript.

 

Comment 3:

I suggest describing the variables in the formulae one under the other.

Response:

As suggested by the reviewer, variables have been described in the formula one under another, pages 11, 12, 14. Please refer to the revised manuscript.

 

Comment 4:

I suggest checking what are the requirements for the length of the article. It seems to be too long.

Response:

Sustainability has no restrictions on the length of manuscripts. Please find the below snapshot.

 

List of changes

 

Many changes and corrections have been made to answer and clarify reviewers’ comments and suggestions. ALL THE CORRECTIONS ARE HIGHLIGHTED BY TRACK CHANGES in the revised manuscript. Please refer to the edited version.

Author Response File: Author Response.pdf

Reviewer 3 Report

This is a comprehensive literature review on Islanding techniques and Energy management in microgrids. The authors have put effort in a thorough examination and classification of existing literature in this field. The general view is that given the scope covered by the authors, the paper could have been split into 2 separate papers giving more room for a more detailed technical comparison of the different methods discussed. Some minor comments to make the paper more understandable to readers are as follows:

1. Add a table of the numerous acronyms in the paper either at the front or back of the manuscript
2. Line 33: Figure
3. Line 45: Remove 'and' in line 45
4. Sections 2 and 3 have the same heading 'Methodology'. Please re-think the need for Section 2, details of the number of papers considered for review is not necessary given the references described and listed later on. Methodology can be better used to introduce how and why Island detection and Energy management have been classified this way in the rest of the paper
5. Line 118: What's meant by 'local generations'? You can explain in the context of figure 3 
6. Figure 3: Have you found other general layouts of the microgrid in the literature like the ring network etc?
7. Figure 8: DC/AC and AC/AC converters are connected to the main DC bus. Why is this?
8. It makes it more readable to write the full form of abbreviations for Section headings as in Section 6 for eg
9. There's a Subsection 4.2 below Section 6 in pg 7. Please check again the numberings of all sections and subsections
10. Line 213: Briefly describe the role of the intelligent bypass switch in Figure 5
11. Table 2: More value can be added if the authors can attempt to explain the difference in the Detection times mentioned  in various standards which vary by an order of magnitude here
12. Table 2: Has the relevance of the 'Quality factor' been explained?
13. Line 472: Replace 'those of' with 'the'
14. Line 663: The role of an external EMS in the Centralized EMS scheme can be explained here
15. Equation (9): Please reformat the equation, check if the subscripts and font size match those in the other equations. For eg, the font size in Eqns (10) and (11) look different
16. Line 826: 'constant' or 'stable'may be better alternatives to 'steadiness' of 'frequency and voltage'.
17. Line 1076: Has the 'greedy method' been reviewed or explained elsewhere before?
18. Section 8: This section is very general. Perhaps, more specific information on some patterns, similarities or areas to improve found after reviewing the different types of Island detection techniques and Energy management measures can be added. Other issues such as Power electronics need not be mentioned here as they don't seem to be the main focus
19. Line 1119: 'minimal NDR' may be a more realistic recommendation
20. Line 1150: What are these 'performance indices' mentioned? These could be listed here as a recap

Author Response

Reviewer #3:

 

Comment 1:

Add a table of the numerous acronyms in the paper either at the front or back of the manuscript

Response:

Thank you very much for the valuable comments. As suggested by the reviewer, a table of the numerous acronyms has been added at the back of the manuscript, pages 45 to 46. Please refer to the revised manuscript.

 

Comment 2:

Line 33: Figure

Response:

The word “Figur” has been modified to Figure in section 1, page 1, line 33. Please refer to the revised manuscript.

 

Comment 3:

Line 45: Remove 'and' in line 45

Response:

As suggested by the reviewer, the word “and” has been removed in section 1, page 1, line 45. Please refer to the revised manuscript.

 

Comment 4:

Sections 2 and 3 have the same heading 'Methodology'. Please re-think the need for Section 2, details of the number of papers considered for review is not necessary given the references described and listed later on. Methodology can be better used to introduce how and why Island detection and Energy management have been classified this way in the rest of the paper

Response:

As suggested by the reviewer 1, section headings 2 and 3 have been deleted and merge under the section “General aspects of MGs” in section 2, pages 2 to 4. Please refer to the revised manuscript.

 

Comment 5:

Line 118: What's meant by 'local generations'? You can explain in the context of figure 3.

Response:

Local generation means users’ own generation facility. If the loads are disconnected from the grid, users’ can provide electricity to the loads by their own generation capacity. Please refer to the revised manuscript in subsection 2.1.3, page 4, line 121. This can be co generator or onsite generators.

 

Comment 6:

Figure 3: Have you found other general layouts of the microgrid in the literature like the ring network etc?

Response:

In general, the MG layout is ring type network but it mostly operates as radial because of its simplicity, lower initial cost and ease of protection coordination.

 

Comment 7:

Figure 8: DC/AC and AC/AC converters are connected to the main DC bus. Why is this?

Response:

Extremely sorry for the mistake. The author has modified the figure 8, page 8. Please refer to the revised manuscript.

 

Comment 8:

It makes it more readable to write the full form of abbreviations for Section headings as in Section 6 for eg

Response:

Section headings have been written in full form. Please refer to the revised manuscript.

 

Comment 9:

There's a Subsection 4.2 below Section 6 in pg 7. Please check again the numberings of all sections and subsections

Response:

Subsection 4.2 has been modified to subsection 2.2.2 under section 2, page 5.  The numberings of all sections and subsections have been checked. Please refer to the revised manuscript.

 

Comment 10:

Line 213: Briefly describe the role of the intelligent bypass switch in Figure 5

Response:

The role of the intelligent bypass-directional switch has been described in subsection 2.2.2, page 5. Please refer to the revised manuscript.

 

Grid-tied MGs include a PCC and an intelligent bi-directional switch (Figure 5). The bi-directional switch manages the two-way connection of the MG to the main UG. The MG can take energy from the UG when it is demanded, as well as it can transfer surplus power to the UG.

 

Comment 11:

Table 2: More value can be added if the authors can attempt to explain the difference in the Detection times mentioned in various standards which vary by an order of magnitude here

Response:

Detection times and other parameters of table 2 have been explained in subsection 3.1, page 10. Please refer to the revised manuscript.

Table 2 lists the standards for ID as having their detection time, quality factor, frequency and voltage operating range. Rapid detection is a premise for MG to have sufficient time to operate the islanding approach, ensuring security and reliability. Islanding disconnection time is also imperative. The German VDE0126-1-1 has the strictest disconnection time limit below 0.2 s. Besides detection time, quality factor (Q_f) is also important. According to the IEEE929-2000 standard, Q_f can be represented as shown in equation (1). The selected Q_f of 2.5 corresponds to a power factor (PF) of 0.37. As PF increases, Q_f decreases. Therefore, the test requires that Q_f ≤2.5 equates to lines with uncorrected PFs from 0.37 to unity and appears to cover all reasonable distribution line configurations. With the Q_f zero, which is either capacitive or inductive loads to be zero, Japanese Standard recommends introducing a rotating machinery load when the MG is investigated for anti-islanding. The machinery load is supposed to behave to increase the Q_f. In addition to the Q_f, the voltage/frequency operation range also influences the ID capability. Australian standards AS4777.3-2005 and Japanese Standard require that frequency and voltage ranges be set by the manufacturer.

Comment 12:

Table 2: Has the relevance of the 'Quality factor' been explained?

Response:

The relevance of quality factor has been explained in subsection 3.1, page 10 and equation (4), page 11. Please refer to the revised manuscript.

 

Comment 13:

Line 472: Replace 'those of' with 'the'

Response:

As suggested by the reviewer, the phrase “those of” has been replace with “the” in subsection 3.2.1, page 18, line 521. Please refer to the revised manuscript.

 

Comment 14:

Line 663: The role of an external EMS in the Centralized EMS scheme can be explained here

Response:

External EMS has been removed from the figure 20. Please refer to the revised manuscript on page 26.

 

Comment 15:

Equation (9): Please reformat the equation, check if the subscripts and font size match those in the other equations. For eg, the font size in Eqns (10) and (11) look different

Response:

Equations 9, 10 and 11 have been reformatted.  Please refer to the revised manuscript on page 28.

 

Comment 16:

Line 826: 'constant' or 'stable'may be better alternatives to 'steadiness' of 'frequency and voltage'.

Response:

As suggested by the reviewer, the word “steadiness” has been replace with “constant” in subsection 4.3.2, page 30, line 884. Please refer to the revised manuscript.

 

 

Comment 17:

Line 1076: Has the 'greedy method' been reviewed or explained elsewhere before?

Response:

The greedy method has not reviewed in the study. Greedy method is not very popular for the energy management problem. This method is mostly used for sales man problem, shortest path identification, network configuration and so on.

 

Comment 18:

Section 8: This section is very general. Perhaps, more specific information on some patterns, similarities or areas to improve found after reviewing the different types of Island detection techniques and Energy management measures can be added. Other issues such as Power electronics need not be mentioned here as they don't seem to be the main focus

Response:

Section 8 has been modified with section 5. This section has been rewritten. Please refer to the revised manuscript on pages 42 to 44.

 

Comment 19:

Line 1119: 'minimal NDR' may be a more realistic recommendation

Response:

As suggested by the reviewer, the word “no NDR” has been replace with “minimal NDR'” in subsection 5.1, page 42, line 1219. Please refer to the revised manuscript.

 

Comment 20:

Line 1150: What are these 'performance indices' mentioned? These could be listed here as a recap

Response:

The performance indices have been mentioned as a recap in section 6, page 44, lines 1289. Please refer to the revised manuscript.

 

List of changes

 

Many changes and corrections have been made to answer and clarify reviewers’ comments and suggestions. ALL THE CORRECTIONS ARE HIGHLIGHTED BY TRACK CHANGES in the revised manuscript. Please refer to the edited version.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The quality of the revised paper has been improved.