Improved Repetitive Control for an LCL-Type Grid-Tied Inverter with Frequency Adaptive Capability in Microgrids

Round 1

Reviewer 1 Report

The article has merit to publish

Author Response

Please see the attachment. Revisions are highlighted in yellow in the second half of the updated manuscript (supplementary material for review).

Author Response File: Author Response.pdf

Reviewer 2 Report

1) At the end of the 1. Introduction section add a new paragraph such as: "The rest of the paper is organized as it follows: Section 2. Grid-tied Inverter System Modeling presents..., Section 3.... details, Section 4. ...is focused on... and the final Conclusions section synthesizes ....etc"

2) If cited, the figures  below the picture must also have at the end their citation from the References section. Thus it becomes more clear what was taken from the existing literature and what is the innovation/novelty that this paper brings.

3) Make sure that each figure (as blocks) and each equation/relation have the symbols specified/detailed also in the text (what do they represent and, if necessary, some details). This confers more clarity for any reader, more or less specialist in the domain (by example, PWM, ZOH, Q(z) etc.)

4) For all cited equations indicate the reference in brackets, and for all proposed equations by the authors explain/demonstrate/specify the idea etc where do they come from.

5) Don't spit a phrase with a figure/table, place them elsewhere in the text, close to the place where they where cited in the text.

6) Conclusions may enumerate the innovations/novelty that the paper brings to the existing literature (qualitative but also synthetic quantitative results) and finally should provide some possible further development directions.

Author Response

Please see the attachment. Revisions are highlighted in yellow in the second half of the updated manuscript (supplementary material for review).

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments to Authors:
This paper proposes the improved repetitive control. I have some comments that are expected to be addressed in the manuscript as follows

1. In the introduction section, the overview of the recently works should be expressed more detail. Some sentences should be checked and clarified the contribution of the paper.

2. The comparison between proposed method and existed methods should be considered.

3. The control system can be analyzed and explained in detail.

Author Response

Please see the attachment. Revisions are highlighted in yellow in the second half of the updated manuscript (supplementary material for review).

Author Response File: Author Response.pdf

Reviewer 4 Report

In this paper, an adaptive controller is proposed to retune the inverter parameters when the frequency of the grid changes. Simulation results verify the performance of the proposed controller. I am still not convinced about contribution of this paper because: 

1- The main concern is about stability of this approach for the proposed application. Although stability of the control loop is studied individually, the impact of the grid on the stability of a grid-tied inverter is missed. In fact, stability of a grid-connected inverter depends on the ratio of the grid impedance to the inverter impedance, see e.g. Mauricio Cespedes and Jian Sun, IEEE TRANSACTIONS ON SUSTAINABLE ENERGY, 2014. Authors have to carefully study this impact.

2- In deriving Q_1(z) in Eq. (5), there is a multiplication of Q(z)*Q(z). That is a source of increasing sensitivity to variation of parameters. I ask authors to compare the performance of RC and IRC when any variation happens in parameters of Q(z).

3- Figure 8 is well-known in the community and can be removed.

4- "N" is defined as the order of RC in this paper. Considering this, what does exactly (Z^-201.6) mean in line 155? Do you mean we need oversampling? We normally have access to (Z^-201) and (Z^-202), and no sample in between.

5- Results of Figs. 15-20 can be represented in a table, no need for figures indeed.

6- With wider bandwidth, the controller will be more sensitive to noise in measurements. Authors have to elaborate in this issue.

Author Response

Please see the attachment. Revisions are highlighted in yellow in the second half of the updated manuscript (supplementary material for review).

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Thanks for your response.

Author Response

We would like to thank the reviewer for your thoughtful review of our manuscript. We have carefully checked our manuscript to ensure it is ready for publication.

Reviewer 4 Report

I would like to thank authors for addressing my previous comments. All my comments have been addressed and I do not have any new one. Just please go through the text to improve its level of English. Please pay special attention to articles 'a/an' and 'the'.

Author Response

Please see the attachment. Revisions are highlighted in yellow in the second half of the updated manuscript (supplementary material for review).

Author Response File: Author Response.pdf