Fault-Tolerant Controller Applied to a Wind System Using a Doubly Fed Induction Generator

Round 1

Reviewer 1 Report

1.      There is too little summary of existing research in the research status section of the manuscript, and there is no comparison to illustrate the advantages of the manuscript compared to existing research.

2.      The innovation of the manuscript is not enough. In Chapter 4 of the manuscript, the innovative work done by the author is not clearly stated in the control system design. The positive sequence and negative sequence control proposed in the manuscript is not clearly reflected in the controller design. After deriving the formula, the manuscript should add a control block diagram about the proposed control. Secondly, the simulation results are insufficient, and the waveforms in the manuscript do not reflect the advantages of the proposed control compared to existing controls. It is recommended to add a comparison with existing controls and explain the reason why the current amplitude and frequency in the simulated waveform in Figure 8 are significantly different before and after fault cleared.

3.      The simulation analysis cannot reasonably support the conclusions of the manuscript. For example, in the simulation analysis, the conclusion that positive sequence control maximizes the capture of wind energy and controls the DC bus voltage was not clearly reflected. The second controller is designed in negative sequence to cancel the generator's negative torque produced by the negative sequence currents and cancels out the negative sequence reactive power flow by the stator winding, but there is a lack of well explanation in the simulation analysis.

1.      It should be pay attention to the specifications of the regular and italic fonts in the formula. For example, the formats of T_tb, n_gb in formula (1) and C_p in formula (2) are different from those in the following parameter description. There are many similar issues that need to be carefully checked and modified.

2.      In formula (10), Lsr is incorrectly written as Lsrm. The equations in formula (18) and formula (33) should be left aligned uniformly.

3.      It should be pay attention to the punctuation standards. For example the semicolons at the end of line 222 and the end of line 235 missing a period. Missing colon at the end of line 257. The page numbers in reference 10 from 0 to 0, some of the charts in the manuscript are not formatted properly.

4.      Figures 7 and Figures 9 are repeated. There is an error in the legend in Figure 12 and the actual value and reference value was reversed.

Author Response

Revisor 1.

Dear Reviewer,

We appreciate your valuable time reviewing our article. We have taken all your comments into account and adjusted the article. Below we show both your comments and our reply. Besides, it has been attached the new version of the manuscript.

Comment 1:

There is too little summary of existing research in the research status section of the manuscript, and there is no comparison to illustrate the advantages of the manuscript compared to existing research.

Reply:

The authors thank the reviewer for suggested references which have helped to update our References list with related and important results on the topic. Three of them were included in the Introduction section. In addition, the introduction section was improved.

Comment 2, which was divided in two sections a and b:

1. The innovation of the manuscript is not enough. In Chapter 4 of the manuscript, the innovative work done by the author is not clearly stated in the control system design. The positive sequence and negative sequence control proposed in the manuscript is not clearly reflected in the controller design. After deriving the formula, the manuscript should add a control block diagram about the proposed control.

Reply:

Section 4 of the manuscript has been significantly improved considering your valuable recommendations. A block diagram of the proposed control system was also added at the end of the same section.

1. Secondly, the simulation results are insufficient, and the waveforms in the manuscript do not reflect the advantages of the proposed control compared to existing controls. It is recommended to add a comparison with existing controls and explain the reason why the current amplitude and frequency in the simulated waveform in Figure 8 are significantly different before and after fault cleared.

Reply:

Subsection 6.1 Performance of the wind system controller under a phase-to-ground fault in the utility grid was divided into two subsubsections: 6.1 Performance of a non-tolerant controller in a ph-to.gr fault and  6.2 Performance of the tolerant fault controller proposed in a ph-to-gr fault. In this way, you can verify clearly the contrast between the non-tolerant fault controller and the fault-tolerant controller

In the new version the Figure you were referring to is now the Figure 9.

explain the reason why the current amplitude and frequency in the simulated waveform in Figure 8 are significantly different before and after the fault cleared.

              The difference in both frequency and amplitude of the stator currents before and after clearing the fault is due to a transient process. For the rotor currents, it is difficult to distinguish the transient process due to very low frequencies compared to the fault´s duration.

3. The simulation analysis cannot reasonably support the conclusions of the manuscript. For example, in the simulation analysis, the conclusion that positive sequence control maximizes the capture of wind energy and controls the DC bus voltage was not clearly reflected. The second controller is designed in negative sequence to cancel the generator's negative torque produced by the negative sequence currents and cancels out the negative sequence reactive power flow by the stator winding, but there is a lack of well explanation in the simulation analysis.

Reply:

      Section 6 “Simulation Results” was significantly improved, and section 8 “Conclusions” was rewritten considering your comments.

Comments on the Quality of English Language

1. It should be pay attention to the specifications of the regular and italic fonts in the formula. For example, the formats of T_tb, n_gb in formula (1) and C_p in formula (2) are different from those in the following parameter description. There are many similar issues that need to be carefully checked and modified.

Reply:

The mathematical notation was corrected throughout the manuscript using the suffixes with the same format.

2. In formula (10), Lsr is incorrectly written as Lsrm. The equations in formula (18) and formula (33) should be left aligned uniformly.

Reply:

The notation indicated in formula (10) was corrected. In addition, the format of formulas (18) and (33) was corrected.

3. It should be pay attention to the punctuation standards. For example the semicolons at the end of line 222 and the end of line 235 missing a period. Missing colon at the end of line 257. The page numbers in reference 10 from 0 to 0, some of the charts in the manuscript are not formatted properly.

Reply:

The indicated punctuation errors were corrected. The notation of the number of pages in reference 10 was corrected. All charts’ format was standardized, using the same font, etc.

4. Figures 7 and Figures 9 are repeated. There is an error in the legend in Figure 12 and the actual value and reference value was reversed.

Reply:

Figure 7, which was duplicated, was removed. The legend of Figure 12

 was corrected. The signal legend in Figure 12 was corrected.

Author Response File: Author Response.pdf

Reviewer 2 Report

In the manuscript "Fault-tolerant controller applied to wind system using a doubly-fed induction generator", a certain way of control a wind energy device was considered. The manuscript refers to optimizing the wind energy capture and improving the power factor of the system under study.

General remarks:

   In the reviewer's opinion, the issues discussed were presented accurately and legibly, and at a good editorial level. The article is well organized. The individual stages of the analysis are formulated clearly, even didactically. The presented results show that the presented system works properly, meeting the design expectations - at least at the computer simulation level.

   However, the declaration: “The wind system controller is designed seeking the goal of maximizing the wind energy and consuming reactive energy from the utility grid.”, see lines 390-391 of the manuscript, does not seem to be sufficiently confirmed/exposed. Appropriate comparisons, perhaps in the form of tables, comparing the achievements achieved against the initial system would be useful.

Some specific remarks:

   With regard to Figure 7: Rotor speed and torque tracking under phase-to-ground fault condition. This figure is not mentioned in the text of the manuscript. Additionally, it is identical to Figure 9.

  With regard to References:

      - the presentation of the current state of achievements in the area analyzed by the    authors, included in the list of literature, seems to be too limited.

       - is the first author in positions [8], [9] and [10] the same person?

Author Response

Revisor 2.

Dear Reviewer,

We appreciate your valuable time reviewing our article. We have taken all your comments into account and adjusted the article. Below we show both your comments and our reply. Besides, it has been attached the new version of the manuscript.

The report is attached.

Author Response File: Author Response.pdf

Reviewer 3 Report

Dear authors, 

the paper proposes a fault-tolerant controller applied to a DFIG wind system. The fault tolerant controller would be a parallel one, for both positive and negative sequence voltages aiming to maintain the wind turbine continuously working, with no fault protection detection. Some questions arise after reading the paper: 

1) How different is the proposed controller from similar schemes for voltage sag ride through? 

2) The system is mathematical modeled but no figure is presented with block diagrams showing the model and the proposed controller. It is very hard to follow the explanation without figures. Include figures of the control scheme with the models in block diagrams. 

3) In the simulation results, after the fault is cleared, the rotor speed does not return to its pre-fault speed, although the electromagnetic torque recovers itself. So, when does the rotor speed return to its pre-fault condition? 

4) Include a picture showing the system implemented in Matlab/simulink. 

5) Figures with the current rms would help to follow the avoidance of overload when positive and negative control is used. Include them. 

line 168 - "Rs and Rr are the stator are rotor" - should be Rs and Rr are the stator and rotor resistances 

Author Response

Revisor 3.

Dear Reviewer,

We appreciate your valuable time reviewing our article. We have taken all your comments into account and adjusted the article. Below we show both your comments and our reply. Besides, it has been attached the new version of the manuscript.

The report is attatched.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The submission has been greatly improved and is worthy of publication

Reviewer 3 Report

The authors have answered all the questions and the reviewer's demands were all implemented.