Robust H∞ Design for Resonant Control in a CVCF Inverter Application over Load Uncertainties
Round 1
Reviewer 1 Report
It is an interesting study on resonant control for standalone inverters, aiming at high power quality achievement. My comments are the following ones:
1) PLEASE correct kilo (k) in your manuscript.
2) RL value is too high, so power losses should be notable. Why don't you use a smaller RL value? Does RL-value affect the proposed control scheme?
3) How comes sample time to be equal to the switching period? What do you mean with the term "sample time"? PLEASE, dive details on the controol loop implementation for the experimental procedure.
Author Response
Comments to the Author
It is an interesting study on resonant control for standalone inverters, aiming at high power quality achievement. My comments are the following ones:
1) PLEASE correct kilo (k) in your manuscript.
This issue has been corrected in the paper new version.
2) RL value is too high, so power losses should be notable. Why don't you use a smaller RL value? Does RL-value affect the proposed control scheme?
Due to the laboratory resources, we have connected three inductors to achieve a 900 uH inductance for the LC filter. The resistance of each inductor has been experimentally measured and determined as 0.5 ohms. For that reason, the resulting value of the resistance RL is 1.5 ohms. However, the proposed design is a general technique and if other value for RL is used, the adjustment of the weighting functions will accomplish the design objectives. No additional issues or problems are expected to arise due to different values in the LC filter.
3) How comes sample time to be equal to the switching period? What do you mean with the term "sample time"? PLEASE, dive details on the controol loop implementation for the experimental procedure.
The reviewer is right, the correct term is sampling time. This term has been corrected in the reviewed version.
The description of the implementation platform has been added. A picture showing the experimental setup has been included in the paper new version.
Effectively, the sampling and switching frequency are the same. The experimental platform is XPC-Target, which is the Rapid Control Prototyping System developed by Matlab. This platform allows the real time execution of the controller at the specified sampling frequency. As a reference, the XPC-Target platform is very similar in performance to the well-known DSpace 1104 system.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The paper is well written and well organized. The model, control design and performances are well presented and discussed, which could be interesting for readers studying VSI. I have no further comments. Publish as it is.
Author Response
Comments to the Author
The paper is well written and well organized. The model, control design and performances are well presented and discussed, which could be interesting for readers studying VSI. I have no further comments. Publish as it is.
We would like to thank the reviewer for his positive comment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Dear Authors; Editor;
Thank you for sharing this proposal. However, this proposal is interesting but to publish in this journal it needs more improve.
1] Introduction part need to have paper organization.
2] Introduction need to have a block diagram regarding your method and need to explain the sub-block step-by-step.
3] Please add your research novelty in the introduction "very clear".
4] As the reviewer experiences, the H-infinity is a model-reference technique, so, how this technique can solve the challenge of uncertainties.
5] How you can proof that, proposed method is robust (based on mathematical technique)?
Regards,
Author Response
Comments to the Author
Thank you for sharing this proposal. However, this proposal is interesting but to publish in this journal it needs more improve.
1] Introduction part need to have paper organization.
The paper organization has been added to the introduction section in the new version of the paper.
2] Introduction need to have a block diagram regarding your method and need to explain the sub-block step-by- step.
A block diagram describing the proposed design has been added at the end of Section 3.
3] Please add your research novelty in the introduction "very clear".
The novelty of the paper has been clarified in the introduction section. The contributions are:
- The proposed methodology achieves a robust design with multiple resonant elements. The methodology includes the design of the necessary weighting functions to accomplish stability and performance.
- The design includes robustness to deal with the uncertainty introduced by the unknown loads in a direct way.
- The procedure is based on classical H-infinity design. In this way, the proposed approach is simple and does not need additional mathematical conditions to achieve stability, performance and robustness.
4] As the reviewer experiences, the H-infinity is a model- reference technique, so, how this technique can solve the challenge of uncertainties.
In the context of Robust Control Theory, the H∞ design is a technique aimed to obtain controllers that assure the robust stability of a system. In order to provide a controller that achieves the necessary closed loop robustness, the H∞ design takes the nominal model of the plant and adds an uncertainty model. In our work, the uncertainty model is directly associated to the unknown loads connected to the system. As a result, the controller will provide robustness against loads in concordance to the chosen uncertainty model.
This fact has been clarified in the paper
5] How you can proof that, proposed method is robust (based on mathematical technique)?
The H∞ design, as proposed here, guaranties the robust stability of the closed loop system. This is because the H∞ design is based on the small gain theorem.
This fact has been clarified in the paper
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Authors have partially responded to the reviewer comments. It is still unclear to me the fact that sampling and switching frequency are the same. In addition, I can't understand how such a high RL value (1.5 Ohms) does not have any significant effect on the voltage quality at the load side, taking for granted the high current values and the reported non-linear loads.
Author Response
see attached .pdf
Author Response File: Author Response.pdf
Reviewer 3 Report
Dear Authors, Editor;
Thank you for your revision. My comment is clear, and I accepted your manuscript for publication in this journal.
Regards,
Author Response
Thank you.
Round 3
Reviewer 1 Report
Authors have improved their paper according to the reviewers' suggestions.
