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Open AccessArticle
Peer-Review Record

Individual Phase Full-Power Testing Method for High-Power STATCOM

Electronics 2019, 8(7), 754; https://doi.org/10.3390/electronics8070754
Reviewer 1: Anonymous
Reviewer 2: Anonymous
Reviewer 3: Anonymous
Electronics 2019, 8(7), 754; https://doi.org/10.3390/electronics8070754
Received: 28 May 2019 / Revised: 27 June 2019 / Accepted: 29 June 2019 / Published: 4 July 2019
(This article belongs to the Special Issue Power Converters in Power Electronics)

Round 1

Reviewer 1 Report

This paper proposes a phase full-power testing method for High-power STATCOM. The abstract presents clearly the description of the work developed by the authors. This summary does not include the main conclusions and results obtained. The details of the proposed strategy are not indicated.

The introduction includes the state of the art of the problem studied. It would be advisable to increase the number of bibliographic references; as well as indicate the differences between the research works mentioned, showing some advantages and disadvantages among them. It may be advisable to develop a comparison between the techniques applied in each case. It is recommended that the authors clearly indicate their contribution to the study with respect to other researches develops and cited in the references. In the introduction it is indicated that there is an improvement of the system, as well as a more effective model, but the criteria are not developed in depth.

Sections 2 & 3 clearly show the basic principle of operation and theoretical concepts. the mathematical model and constraints are also shown. The mathematical equations allow us to understand the theory of control applied to the system. The analysis of the electrical system allows to understand the criteria and applied theory. The described application does not incorporate information of the harmonics nor of applied techniques for the suppression of harmonic currents. Diagram 4 does not provide much information to the reader.

Simulations have been carried out through the Matlab/Simulink software. It is necessary to incorporate more data and parameters in table 1 in order to reproduce the simulated model proposed by the authors. The impact of harmonic distortion is not appreciated. It would be very interesting to check the results of the simulation with experimental results in order to validate the model analyzed. Experimental results that support the results obtained are not presented.

In some cases, the conclusions shown in the document are shallow. The included text is more related to a discussion of the topic addressed than to the conclusions obtained according to the result shown in the tables and diagrams. Perhaps all this is due to the absence of experimental results. It would be advisable to indicate the contributions made by the authors to the topic addressed, because in recent years much has been written related to statcom systems.

Most of the bibliographical references are current. All of them have been published in this last decade. It would be advisable to carry out a search of more extensive academic work, all of them related to the topic addressed.

In short, in my opinion, the paper presented requires some chages. I hope that the comments provided serve to show a new approach to the document, providing more detailed theoretical explanations and some experimental results that can support the approach shown.

Author Response

Response to Reviewer 1 Comments

 

Point 1: This paper proposes a phase full-power testing method for High-power STATCOM. The abstract presents clearly the description of the work developed by the authors. This summary does not include the main conclusions and results obtained. The details of the proposed strategy are not indicated.

Response 1: In the revised version,we revised the abstract. From the aspects of structure and control, the main features of the proposed method are introduced, and the conclusions of the simulation and theoretical analysis are also reorganized.

 

Point 2: The introduction includes the state of the art of the problem studied. It would be advisable to increase the number of bibliographic references; as well as indicate the differences between the research works mentioned, showing some advantages and disadvantages among them. It may be advisable to develop a comparison between the techniques applied in each case. It is recommended that the authors clearly indicate their contribution to the study with respect to other researches develops and cited in the references. In the introduction it is indicated that there is an improvement of the system, as well as a more effective model, but the criteria are not developed in depth.

Response 2: Some related references were increased.The characteristics of each test method provided in the references were introduced and analyzed. Their advantages and disadvantages  were individually pointed out. In the last paragraph of the introduction, some expressions are revised so that the introduction corresponds exactly to the full text.

Point 3: Sections 2 & 3 clearly show the basic principle of operation and theoretical concepts. the mathematical model and constraints are also shown. The mathematical equations allow us to understand the theory of control applied to the system. The analysis of the electrical system allows to understand the criteria and applied theory. The described application does not incorporate information of the harmonics nor of applied techniques for the suppression of harmonic currents. Diagram 4 does not provide much information to the reader.

Response 3: The harmonics are not covered in this paper, because the focus of this method is to achieve the rated voltage and current operation while maintaining the active power balance of three phase converters. In fact, the basic principle of this method is relatively simple but the key difficulty lies in the three-phase active power balance under this special structure. Therefore, in this paper, only the fundamental characteristics which would affect the active power balance are analyzed and designed, where the harmonic issue was not considered.

Figure 4 is similar to Figure 3, but they have different emphasis. Figure 3 is to shows the alternative range of three-phase voltages and currents. Since there are many different options for C-phase voltage, the corresponding three-phase currents are also variable. So Figure 3 is just a rough representation of the voltage and current vector relationship. Figure 4 shows a specific example that conforms to the basic characteristics, and corresponds to Equation 5. It can better interpret Equation 5, and helps to facilitate the design of the latter control system.

Point 4: Simulations have been carried out through the Matlab/Simulink software. It is necessary to incorporate more data and parameters in table 1 in order to reproduce the simulated model proposed by the authors. The impact of harmonic distortion is not appreciated. It would be very interesting to check the results of the simulation with experimental results in order to validate the model analyzed. Experimental results that support the results obtained are not presented.

Response 4: In the table 1, we list more simulation parameters, including the number of submodules and DC capacitor parameters, as well as the control parameters. We given almost all the simulation parameters that can be set. Based on these parameters as well as the given control system block as Figure 5, it is easy for a reader to reproduce the simulation model and results. This simulation can prove the feasibility of the method to some extent. We also hope to verify this method by experiment, so we are building a scaled-down experimental platform. The construction and debugging would continue for 3-4 months, so we cannot complete the experiment and give the experiment results this time. We hope to get your understanding

The harmonic distortion does exist in this proposed testing system. In the simulation results, both the original voltage without filtering and the amplified C-phase current are given. The harmonic current is much smaller than the rated phase current, and it has almost no impact on the power test. So it is not considered during the full-power test.

Point 5: In some cases, the conclusions shown in the document are shallow. The included text is more related to a discussion of the topic addressed than to the conclusions obtained according to the result shown in the tables and diagrams. Perhaps all this is due to the absence of experimental results. It would be advisable to indicate the contributions made by the authors to the topic addressed, because in recent years much has been written related to statcom systems.

Response 5: We have revised the conclusions. The conclusion summarizes the principle and difficulties of the method, the main work of this paper and some key conclusions. Then the simulation results was introduced. Lastly, the characteristics of the proposed method and its application scope was indicated.

Point 6: Most of the bibliographical references are current. All of them have been published in this last decade. It would be advisable to carry out a search of more extensive academic work, all of them related to the topic addressed.

Response 6: We searched again for the relevant literature on the STATCOM test, and some representative reference are cited.

Point 7: In short, in my opinion, the paper presented requires some chages. I hope that the comments provided serve to show a new approach to the document, providing more detailed theoretical explanations and some experimental results that can support the approach shown.

Response 7: In the revised paper, we made many improvements according to the comments. More theoretical explanations are given in Sections 3, and the detailed simulation parameters are given for readers to reproduce the simulation model and verify this proposed method. Our experimental platform is under construction, so the experiments and their results are absent this time. We hope to get your understanding.

 


Author Response File: Author Response.pdf

Reviewer 2 Report

Very good paper on testing method of STATCOM converters, however some unclear parts were found in the manuscript.

In Fig. 3 iC is the longest among current vectors however the proposed testing method is based on assumption that this current has to be close to zero.

In Fig. 4 two names of "uC" are shown but only one vector "uC" can be presented

In Fig. 5 modulator blocks are referred as CSPWM however in the text CPSPWM name is used

The major part of the paper is devoted to the start-up procedure of the converter, in three figures dc voltages are shown, however the capacitance of dc-link capacitors are not given in the table 1. Number of submodules are also not presented however however the time durations shown in start-up waveforms are closly related to the capacitance and number of submodules. I recommend to comment the lack of this parameters or include them.  

Author Response

Response to Reviewer 2 Comments

 

 

Point 1: 
 Very good paper on testing method of STATCOM converters, however some unclear parts were found in the manuscript

Response 1: Thank you very much for your recognition of this paper. In the revised version, we have corrected the mentioned errors and other similar mistakes.

 

Point 2: 
 In Fig. 3 iC is the longest among current vectors however the proposed testing method is based on assumption that this current has to be close to zero.

Response 2:  In this proposed testing method, iC is actually very small . We redraw Figure 3 in the revised version and corrected the drawing error.

 

Point 3: 
In Fig. 4 two names of "uC" are shown but only one vector "uC" can be presented

Response 3: In the revised version, we redraw Figure 4 and removed the extra labels.

 

Point 4:  In Fig. 5 modulator blocks are referred as CSPWM however in the text CPSPWM name is used

Response 4: In the revised Figure 5, we corrected this error.

 

Point 5: The major part of the paper is devoted to the start-up procedure of the converter, in three figures dc voltages are shown, however the capacitance of dc-link capacitors are not given in the table 1. Number of submodules are also not presented however however the time durations shown in start-up waveforms are closly related to the capacitance and number of of submodules. I recommend to comment the lack of this parameters or include them.

Response 5:  In the revised version, both the number of submodules and the capacitance are given. In addition, the parameters of controllers are also given in Table 1. (In the simulation, the number of submodules in each phase is set as four to speed up simulation. Although it is much less than the actual number of STATCOM, it can also represent the MMC structure and then it is sufficient to verify the feasibility of the proposed method for MMC-STATCOM.) 

 

 

 


Author Response File: Author Response.pdf

Reviewer 3 Report

I do not agree with the sentence: "Since the phase relationship of A-phase voltage and current is definite ". I think that it is correct:"the phase relationship of uao (the voltage of the static converter) and current is definite (at steady state)". There is a displacement between the phase voltage uAo and uao). I tried to redraw figure 3. You can find the figure in the attached pdf document.

The losses in the three resistances Ra, Rb and Rc, at steady state, have to be compensated by the grid.

Please check all the symbols and subscripts. There is a lot of mess (for example: iA or ia, uAO or uAo

Line 21: none->no

Figure 1: R->RA, RB, RC

eq. 1: third eq. ib->ic

eq 2: I think that the second one is uCo=uAo-UAC

line 104: uAC first time

line 104: represent->represents

line 106: constraint->constraints

line 113: Iap->IaP (the same for Ibp)

line 124-128: the two sentences (1) and (2) are not clear. 

Figure 4: the figure is not correct because the sum of the three currents is not zero

line 148: Fig. 4-> Fig. 5

line 184: exceeds-> exceeded (the same for line 188)

line 188: "exit" is not clear

line 217: the->The

line 239; review the english of the sentence: "A novel full-power testing method is present for MMC-based STATCOM in this paper "

Comments for author File: Comments.pdf

Author Response

Response to Reviewer 3 Comments

 

 

Point 1: 
I do not agree with the sentence: "Since the phase relationship of A-phase voltage and current is definite ". I think that it is correct:"the phase relationship of uao (the voltage of the static converter) and current is definite (at steady state)". There is a displacement between the phase voltage uAo and uao). I tried to redraw figure 3. You can find the figure in the attached pdf document.

Response 1: Thanks for your reminder and patient guidance.In the vector diagram as Figure 3, our intention is to analyze  the relationship between the A-phase port voltage uAO (voltage difference between the port A and the internal neutral point O of STATCOM), the C-phase voltage uCO, the access line voltage uAC , and three phase currents. For the sake of brevity, this vector diagram does not involve the details among the internal voltages of each phase (port voltage, convector voltage and voltage drop across the impedance). The sentence in the original manuscript may be ambiguous, so we removed the description in the revised version. At the same time, the unsuitable C-phase current in the original  figure 3 was modified.


Point 2: The losses in the three resistances Ra, Rb and Rc, at steady state, have to be compensated by the grid.

Response 2:  The resistance loss and converter loss in each phase are actually compensated by the grid. In equation (4), the three phase active powers Pa, Pb, and Pc absorbed by each phase are to compensate for the aforementioned losses. These losses have been considered, but no detailed explanation was provided in the original manuscript. In the revised version, some explanations are added before equation (4) to illustrate these losses and active power balance of each phase.


Point 3: Please check all the symbols and subscripts. There is a lot of mess (for example: iA or ia, uAO or uAo)

Line 21: none->no

Figure 1: R->RA, RB, RC

eq. 1: third eq. ib->ic

eq 2: I think that the second one is uCo=uAo-UAC

line 104: uAC first time

line 104: represent->represents

line 106: constraint->constraints

line 113: Iap->IaP (the same for Ibp)

line 124-128: the two sentences (1) and (2) are not clear. 

Figure 4: the figure is not correct because the sum of the three currents is not zero

line 148: Fig. 4-> Fig. 5

line 184: exceeds-> exceeded (the same for line 188)

line 188: "exit" is not clear

line 217: the->The

line 239; review the english of the sentence: "A novel full-power testing method is present for MMC-based STATCOM in this paper "

Response 3:  These symbols mess and spelling mistakes have been modified, and then we recheck the paper and cleared some similar mistakes.

 

 

Point 4: eq 2: I think that the second one is uCo=uAo-UAC

Response 4:  Thank you for your reminder. You are right, I have corrected it in the modified version.

 

Point 5:line 124-128: the two sentences (1) and (2) are not clear. 

Response 5:  In the revised version, these two sentences are explained in more detail.

 

Point 6:Figure 4: the figure is not correct because the sum of the three currents is not zero

Response 6:  In the original manuscript, we focused on the phase relationship between the voltage and current of each phase, while neglected the amplitude relationship between there phases, resulting in the errors. In the revised version, Figure 4 has been modified .

 

 

 


Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have incorporated some of the recommendations made in the last report. Numerous references have been incorporated that improve the state-of-the-art. Although it would be advisable to indicate in the conclusions the novelty of the paper and the contribution of the authors to the topic addressed. It would be advisable to increase the number of bibliographical references.

Author Response

Response to Reviewer 1 Comments

 

Point 1: The authors have incorporated some of the recommendations made in the last report. Numerous references have been incorporated that improve the state-of-the-art. 

Response 1: Thank you for your affirmation and patient guidance.

  

Point 2: Although it would be advisable to indicate in the conclusions the novelty of the paper and the contribution of the authors to the topic addressed. 

Response 2: In the conclusions, we added a special paragraph to describe the difference between this proposed method and the existing similar methods, as well as its features and benefits, and then introduce the main content of this paper. So that readers can directly judge  the novelty and contribution of this article.


Point 3: It would be advisable to increase the number of bibliographical references.

Response 3: Based on your comments, we cited more bibliographical references. Some of them are in the introduction to show the typical structures and controls of STATCOM, and some are about the control system designed in this article, such as the control structure, modulation, and voltage balancing control. In the previous versions, we thought that these contents were common in the STATCOM, so they were not listed. In this revised version, we list special references on these contents to facilitate readers to understand the control details.

 

 


Author Response File: Author Response.pdf

Reviewer 3 Report

The authors improved the paper, according to the reviewers tips.

I thank the authors for the enhancements.

Some correcions:

line 193: Iadd represent an->Iadd represents an

line 298: that two-phase are in parallel ->hat two phases are in parallel


Author Response

Point 1: The authors improved the paper, according to the reviewers tips.

I thank the authors for the enhancements.

Response 1: Thank you for your affirmation and patient guidance.

Point 2: Some correcions:

 line 193: Iadd represent an->Iadd represents an

line 298: that two-phase are in parallel ->hat two phases are in parallel

Response 2: Thank you for your correction, these mistakes and some similar mistakes have been modified .


Author Response File: Author Response.pdf

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