Highly Robust Active Damping Approach for Grid-Connected Current Feedback Using Phase-Lead Compensation

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript is very well written. For the most part it is written very clearly.

I have found some minor typos and they are as follows:
1. GPI(s) as is written in line 97 is not presented in Figure 2 as is claimed.

2. I am not sure if minus sign in (3) is correct because in Figure 2 there is already minus sign at the sum block. Similar remark is to equation (6). 

3. GLCL(4) in equation (4) can be shown in Figure 2 just for clarity.

4. In Table 1 there are some strange sounding names there.

a) "Machine-side inductance" - there is no machine in the described system.

b) "Resonant coefficient" - which is given to integral gain

c) "Number of links" - which is probably given to number of submodules (SM) or H-bridges.

d) Triangle Carrier Amplitude - this parameter is perhaps not necessary. Because the cascade H-bridge converter uses phase-shifted PWM, the carrier signals have standardized maximum values (amplitude term is reserved only for sinusoidal signals not for triangular), therefore I see this parameter as unnecessary. 

I have some significant remark

5. In the whole manuscript I have not found any description what is fR not fr but fR. You can use Figure 4 for explaining what is fR or you can write equation how this frequency is defined. 

Other remarks:

6. Equation (11) is not a loop gain, but loop gain frequency. 

7. Authors can add some information about the resultant frequency of the converter which in CHB converter is product of fSw * NSM. And if it is interesting about the ratio between L1/L2. 

Thank you 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The paper proposes an improved grid-current-feedback active damping (GCFAD) strategy for LCL-type cascaded H-bridge static var generator (SVG) systems, addressing digital control delays that narrow the damping region and reduce robustness. By incorporating a phase-lead compensator, the damping range is expanded, enhancing stability and adaptability under varying grid conditions. In addition, simulation results show reduced resonance, lower THD, and improved performance in weak grids environments, demonstrating the possible effectiveness of the proposed method in enhancing system robustness and stability. Moreover, this paper is generally well written and organized with detailed explanations of the methodology and discussions of the obtained results. Meanwhile, I have a few questions and suggestions for the authors:

 

1.       In the Introduction, can the authors add some background information about static var generators (SVG) and their main features?  Also, what are the weak grid environments? Why is the resonant issue of LCL-type cascaded H-bridge SVGs particularly prominent under these conditions?

2.       In Figure 1, what does ‘SM’ stand for? Is it the H-bridge shown in the first block?

3.       In Figure 2, why does the digital control delay (modelled as Gd) cause potential instability issue for the system? Why not use a faster controller with wider bandwidth and shorter delay to solve the instability problem? Are there any technical barriers or cost-related considerations which impact the delay of digital control?

4.       Are the current control loops in Figure 2 and Figure 3 equivalent? If so, how does the virtual impedance Zeq(s) come into play in Figure 3?

5.       Can the authors provide further explanations on the bode plots shown in Figure 6? What are the implications of system stability as the grid impedance Lg decreases?

6.       In Figure 10, to attain a wide positive damping range (0,0.45fs),  m=0.95 is highlighted as the optimal value. In fact, the root locus is at the boundary of the unit circle. In real world applications, the choice of such value can potentially cause instabilities in the system in light of non-idealities and parasitic elements. How can m be properly selected in such conditions?

7.       How can the proposed phase-lead compensator with transfer function Gc be implemented in real-world applications?

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

In the cover letter, the authors have satisfactorily addressed most of my questions and suggestions regarding the initial paper. To further enhance the revised manuscript, I recommend incorporating key discussions and explanations from the cover letter, where applicable. Overall, the authors' responses are informative and satisfactory.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf