Synchronization and Control of a Single-Phase Grid-Tied Inverter under Harmonic Distortion
Round 1
Reviewer 1 Report
As you can see there are only a few minor corrections to add and I expect to receive your revision as soon as possible.
Minor Errors:
Line: 96 == In the propsoed ..:=> proposed
Line : 107 please check Equation ( 17) , there is no “=”
Lines: 121 and 131 shortcut BW is not explained
Line : 141 is shortcut RK4 , is ? Runge Kutta 4th
Line: 244 add subsection 9 , Reference:
Author Response
As you can see there are only a few minor corrections to add and I expect to receive your revision as soon as possible.
RESPONSE: Thank you for your review. Please see our actions to address the comments as follows
1. Line: 96 == In the propsoed ..:=> proposed
Response: Sorry about that. It has been fixed in the revised version along with other typos.
2. Line : 107 please check Equation ( 17) , there is no “=”
Response: Equation (17) is fixed in the revised version.
3. Lines: 121 and 131 shortcut BW is not explained
Response: The shortcut BW has been replaced with "bandwidth" in the revised manuscript.
4. Line : 141 is shortcut RK4 , is ? Runge Kutta 4th
Response: That's right. It has been fixed in in the revised manuscript.
5. Line: 244 add subsection 9 , Reference:
Response: Done!
Reviewer 2 Report
Experimental study cases (voltage distortion) are very limited.
No comparison with other recent PLL/FLL works in terms of harmonics mitigation performance.
Extenstion of the previous work of authors [22] with harmonic distortion.
However the experimental results do not show specific improvement.
Author Response
1. Experimental study cases (voltage distortion) are very limited.
Response: We agree that the experiments are limited in the sense that we have worked with low voltages. However, the experiments were desined to prove the concept given limitations in terms of lab safety and facilities. We have used 5% in the 2nd harmonic and 13% in the 3rd harmonic, or an overall grid voltage THD of 14%, to prove the concept using experiments. It was experimentally verified that adding two notch filters at the second and third harmonics in the synchronization loop can effectively attenuate the ripples as shown in Fig 9(b). These results confirm the analysis provided in Section III of the paper and simulation results in Fig 6.
2. No comparison with other recent PLL/FLL works in terms of harmonics mitigation performance.
Response: We have actually provided comparative experiments. The proposed FLL with harmonic damping filters was compared to the response of a SOGI-FLL as shown in Fig. 7. It was shown that if the grid contains harmonics, the SOGI-FLL frequency tracking accuracy is significantly reduced. The effect of harmonic disotortions on overall current control scheme was tested. A pure PR controller cannot compenstate the grid haromnics due to its limited bandwidth and thus additional HC filters are required. The adaptive nature of the proposed controller results in improved THD performance when compared to the non-adaptive case.
3. Extenstion of the previous work of authors [22] with harmonic distortion.
However the experimental results do not show specific improvement.
Response: The work is an extension of a previous work but we do not agree that any specific improvements have not been achieved. As presented in the paper, although the emulated grid voltage was distorted, the THD of the
output current was 3% which could not be achieved without using the adaptive method and harmonic compensations. The THD of the output current was increased to 8.7% which is above the THD requirement of IEEE 1547 for output current (below 5% THD).
Reviewer 3 Report
The paper proposes a novel frequency locked loop structure with adaptive notch filters than can provide accurate estimation for grid phase and frequency and can increase the efficiency of single-phase inverter controller working under harmonic distortion.
- The contribution of the article is not well explained so the authors in abstract needs to add a clear sentence like the one I wrote above about their contribution.
- The authors in conclusion mention that this paper as a study for synchronization and control of single phase inverters under harmonics distortion which is confusing (the paper proposes new FLL to adapt to distortion and compares the results with and without the new FLL). A clear writing of the paper contribution that is the design of novel FLL with notch filter that can provide accurate estimation for grid phase and frequency to work under distortion with high efficiency is needed.
- the authors work is mainly on proportional resonant current controllers a brief sentence about other controllers that may be used like PI, Fuzzy, Fuzzy-PI is needed.
- future work section maybe a nice edition.
-small mistake remove all Fig in text with Figure.
-it is better to take a picture that include all devices in the hardware setup figure like power analyser oscilloscope etc.
Author Response
The paper proposes a novel frequency locked loop structure with adaptive notch filters than can provide accurate estimation for grid phase and frequency and can increase the efficiency of single-phase inverter controller working under harmonic distortion.
The contribution of the article is not well explained so the authors in abstract needs to add a clear sentence like the one I wrote above about their contribution.
Response: Thank you for your suggestion. We have revised the abstract and included the contribution.
The authors in conclusion mention that this paper as a study for synchronization and control of single phase inverters under harmonics distortion which is confusing (the paper proposes new FLL to adapt to distortion and compares the results with and without the new FLL). A clear writing of the paper contribution that is the design of novel FLL with notch filter that can provide accurate estimation for grid phase and frequency to work under distortion with high efficiency is needed.
Response: Thank you for this suggestion. We have modified the conclusion section to address the above comment.
the authors work is mainly on proportional resonant current controllers a brief sentence about other controllers that may be used like PI, Fuzzy, Fuzzy-PI is needed.
future work section maybe a nice edition.
Response: We have added the following sentence to the conclusion to address the above comments: Suggested future research would include extension to the case of three phase FLLs and utilization of other such as fuzzy, neural, and neuro-fuzzy methods.
small mistake remove all Fig in text with Figure.
Response: Done!
it is better to take a picture that include all devices in the hardware setup figure like power analyser oscilloscope etc.
Response: We have replaced Figure 8 with a new figure to address the above comment.
Round 2
Reviewer 1 Report
Now, author responses and the revised manuscript.
Author Response
Thank you for the comments.
Reviewer 2 Report
Please include some possible answers (or related explanations) to following questions in your manuscript.
1. Why the harmonics of test voltage is 2nd and 3rd mainly? How much/many range of harmonics this algorithm can cover ?
2. What is the careful point when you design the notch filter in the proposed algorithm?
Author Response
Why the harmonics of test voltage is 2nd and 3rd mainly? How much/many range of harmonics this algorithm can cover ?
RESPONSE: The 2nd and 3rd harmonics were considered since they are the most prevalent harmonics as considered by other works. The algorithm can be extended to higher harmonics using a similar adaptation scheme used for designing the notch filters for 2nd and 3rd harmonics but we did not do that in this research. We have added the following sentences to the conclusion to address this comment: "Also this work considered the design of adaptive notch filters to handle the second and third harmonics which may be sufficient in many applications. If necessary, a further extension of this research would involve extension of the adaptive notch filters to include higher harmonics."
What is the careful point when you design the notch filter in the proposed algorithm?
RESPONSE: Proper choise of extremun seeking parameters.
Reviewer 3 Report
I want to thank authors for their response on my comments
Author Response
Thank you for the constructive comments.
Round 3
Reviewer 2 Report
Conclusion is fully revised and more informative now.
It is desirable to have author's comments on the cases where the higher order harmonics are also included in voltage.
I think there is practical limit of the order of harmonics this algorithm can handle.
Author Response
Conclusion is fully revised and more informative now.
RESPONSE: Thank you!
It is desirable to have author's comments on the cases where the higher order harmonics are also included in voltage.
RESPONSE: We have revised the conclusion section to address the reviewer's comment as follows: "Furthermore, this work considered the design of adaptive notch filters to handle the second and third harmonics only. In many applications, the amplitudes of harmonic voltages drop significantly beyond the third harmonics. As such, one may neglect their effects depending on the parameters of the grid and regulations related to total harmonic distortion. However, if required, the same adaptive scheme can be extended to build notch filters to further reduce higher harmonics. The above issues are worth investigation in future research.
I think there is practical limit of the order of harmonics this algorithm can handle.
RESPONSE: Agreed. As indicated in the conclusion these may be subject of further research.
