A Comprehensive Review of Small-Signal Stability and Power Oscillation Damping through Photovoltaic Inverters

Round 1

Reviewer 1 Report

This paper summarizes the research efforts of small signal stability and oscillation damping control related to photovoltaic generation. The references used in this paper almost cover the current research in this area. Reviewer has questions and suggestions in the following areas for discussion.

1. The photovoltaic control method given in this paper is PQ control. However, photovoltaic generation generally adopts DC voltage control, not PQ control.
2. There is a sentence " This is confirmed in [30], where a review of 45 different inverter topologies is presented" at line 117. What does "45 different inverter topologies" mean? Please check it.
3. The section 3 summarizes the research in the area of small signal stability related to photovoltaic generation, but the readability of this part is very poor. Suggest authors summarize this part in a table.
4. The voltage-source inverters are mentioned in many places in the paper. But the photovoltaic inverters are current-source inverters.
5. The section 4 introduces some current power oscillation damping control methods, but the introduction of this control methods is rough. Suggest authors give more details such as control system diagrams.

Author Response

Dear Reviewer,

On behalf of all authors, I would like to thank you for the time you dedicated to reviewing our paper, the useful comments, and the positive assessment!

We have the following response to your comments.

1. You are right about the DC voltage control. The active power output depends on the DC voltage and vice versa. We clarified this in the text.
2. Regarding what “45 different inverter topologies” means. The topology of the PV inverters can be quite diverse: single-stage, two-stage, multi-stage, with or without a transformer, voltage-source or current-source, etc. The efficiency of all types of topologies is studied in [Dogga, R.; Pathak, M. K. Recent Trends in Solar PV Inverter Topologies. Sol. Energy 2019, 183 (February), 57–73. https://doi.org/10.1016/j.solener.2019.02.065].
3. We realized that the readability of section 3 generally may seem confusing at some points since some of the presented research results contradict each other. This is why we summarized the main findings in the bullets on lines 310-352. We believe that adding a table on top of that would be redundant, hence unnecessary.
4. Most modern PV inverters have parallel capacitors in the DC link, hence they are operated as a voltage-source. This is clearly indicated in [Dogga, R.; Pathak, M. K. Recent Trends in Solar PV Inverter Topologies. Sol. Energy 2019, 183 (February), 57–73. https://doi.org/10.1016/j.solener.2019.02.065].
5. Figures 5 to 9 all present the point where the POD stabilizing signal is injected. The POD box is not presented with more details because in the majority of cases this is the well-known PID regulator (or just its P, I, or D components) or a series of lead-lag transfer functions. In the rest of the cases, the POD is a synthesized controller or an artificial neural network, which cannot be depicted with a more detailed and specific diagram. In the end, we tried to keep those figures more general, because it is possible to inject one type of POD in a different junction of the control diagram. This way we avoid a possible misconception that, let’s say a PID stabilizer, can be connected only to one specific location in the inverter control.

Reviewer 2 Report

This paper is a review on the impact of PV generation on small-signal stability. Also, power oscillation damping control systems through PV inverters has been studied. Their realization has been assessed and summarized in this paper as well.

The subject is interesting; however, the authors should pay attention to the following comments to improve the quality of the paper.

1-In the abstract, the authors have mentioned that:

 “This paper focuses on the methods that ensure the rotor angle stability of electric power systems that is most frequently analyzed with small-signal models.”

This sentence must be corrected. The rotor angle stability is used for transient stability analysis of synchronous generators and not for small-signal stability.

2-The authors must review the newly published review papers and discuss the differences with their paper. For example:

[A] Warrier, P.; Shah, P. Fractional Order Control of Power Electronic Converters in Industrial Drives and Renewable Energy Systems: A Review. IEEE Access 2021, 9, 58982–59009.

[B] Mahdi Saadatmand, G. B. Gharehpetian, Innocent Kamwa, Pierluigi Siano, Josep M. Guerrero, Hassan Haes Alhelou, “A Survey on FOPID Controllers for LFO Damping in Power Systems Using Synchronous Generators, FACTS Devices and Inverter-based Power Plants”, Energies, Vol. 14, Issue 18, 5983, DOI: 10.3390/en14185983

The following paper is also a key paper:

WECC. Renewable Energy Modeling Task Force: WECC PV Power Plant Dynamic Modeling Guide; Western Electricity Coordinating Council: Salt Lake City, UT, USA, 2014.

3-In the introduction, the authors should present the review papers published on PV systems interactions with power systems from different point of views including other issues, such as voltage stability, frequency stability and rotor angle stability, and then focus on the main subject.

4-In the introduction, it must clearly be said and it must be clear to the reader, the importance of having a review on small-signal stability and power oscillation damping through photovoltaic inverters.

5-In the title of the paper, it has been said:

“A comprehensive review of small-signal stability and power 2 oscillation damping through photovoltaic inverters”.

This means that the study should consider power system and microgrids. In case of power systems, the authors must study the PV farms. Therefore, the paper must consider and review both cases, that is:

a- small-signal stability and power oscillation damping in microgrids, and

b- small-signal stability and power oscillation damping in power systems.

6-The paper conclusion must present the future direction of researches on the subject of the paper and research gaps.

Author Response

Dear Reviewer,

On behalf of all authors, I would like to thank you for the time you dedicated to reviewing our paper, the useful comments, and the overall positive assessment!

We have the following response to your comments.

1. According to the commonly accepted IEEE and CIGRE definitions [A], the rotor angle stability is divided into two subcategories depending on the magnitude of the disturbance: (i) small-signal stability and (ii) transient stability. While (ii) is more accurate as it solves the nonlinear set of DAE, it does not readily provide much detailed information. On the other hand, (i) provides information about the different oscillatory modes - their frequency, damping, and contributing factors. This motivates our claim that the rotor angle stability is most frequently analyzed with small-signal, i.e. linearized models. Moreover, the design and tuning of POD and PSS controllers are most commonly based on small-signal models.
2. The WECC guidelines [B] are an excellent document. Thank you for that recommendation. We have added it as a reference. That guideline is mostly based on the work of Clark and Miller [C], which we already had in the reference list.
   
   [D] and [E] are excellent surveys on the application of fractional order control for many different applications, including POD. Thank you for proposing those references. They were actually published slightly after we completed our database searches, which is probably why we have missed them. We have corrected this mistake and included them in the reference list and the introduction. While [D] and [E] focus solely on fractional-order controllers, our review attempts to present a wide range of POD topologies.
3. We included a few comments and references regarding the impact of PV generation on the power system’s voltage and frequency stability in the introduction.
4. Тhe importance of this review is strongly emphasized in the introduction on lines from 104 to 113.
5. The small-signal stability and power oscillation damping in bulk power systems are studied in sections 3 and 4. The same aspects for microgrids are presented in section 5.
6. We extended the future research aspects in the conclusions.
   
   

In the end, I would like to note that the English language and style of the paper are edited by a professional native editor and the text is completely free of any spelling or grammar errors.

Response references

[A] P. Kundur et al., “Definition and classification of power system stability,” IEEE Trans. Power Syst., vol. 19, no. 3, pp. 1387–1401, 2004, doi: 10.1109/TPWRS.2004.825981.

[B] WECC Solar Plant Dynamic Modeling Guidelines; 2014.

[C] Clark, K.; Miller, N. W. Modeling of GE Solar Photovoltaic Plants for Grid Studies. 2009.

[D] Warrier, P.; Shah, P. Fractional Order Control of Power Electronic Converters in Industrial Drives and Renewable Energy Systems: A Review. IEEE Access 2021, 9, 58982–59009. https://doi.org/10.1109/ACCESS.2021.3073033.

[E] Saadatmand, M.; Gharehpetian, G. B.; Kamwa, I.; Siano, P.; Guerrero, J. M.; Alhelou, H. H. A Survey on FOPID Controllers for LFO Damping in Power Systems Using Synchronous Generators, FACTS Devices and Inverter-Based Power Plants. Energies 2021, Vol. 14, Page 5983 2021, 14 (18), 5983. https://doi.org/10.3390/EN14185983.

Reviewer 3 Report

The paper seems to sound, but there many points should be addressed before publishing the paper which are:

The synchronous generator model used to study the problem is missed, which is big mistake. 

study such important topic the stability index should be provided, here is missed.

Details results for the contribution of POD control contribution to rotor angle stability, frequency stability and voltage stability should be compared in figures.

The following references can be useful in the synchronous generator model used for stability study:

*“Modeling the Synchronous Generator Excitation Systems Using Artificial Neural Network" International Review of Automatic Control, Vol. 3, No. 5, Sept., 2010, pp. 72-80.

*“Simulated Annealing Approach Based HVDC FACTS Controller for Power Systems Stabilization" International Review of Automatic Control, Vol. 3, No. 5, Sept., 2010, pp. 125-132.

*“Voltage Magnitude and Phase Angle Control of Static Phase Shifter for Damping Subsynchronous Resonance Oscillations", International Review of Automatic Control, 3, No. 4, July, 2010, pp. 411-417.

*“Wavelet Neurofuzzy Controller For Enhancement of Multimachine Power System Stability",The Journal of Engineering Science, Faculty of Engineering, Assuit University, Assiut, Egypt, Vol. 33, No. 2, pp. 583-597, March 2005.

*"Transient Stability Enhancement Using Self Adjusting-Flexible Variable Series Capacitor Compensation", Electric Power Systems Research Journal, Vol. 50, pp.219-225, 1999.

The conclusions and abstract should be rewritten in a focused form.

The drawback of POD nowadays should be given

Author Response

Dear Reviewer,

On behalf of all authors, I would like to thank you for the time you dedicated to reviewing our paper, the useful comments, and the positive assessment!

We have the following response to your comments.

You correctly noted that the model of the synchronous machine is of crucial importance for studying the power system stability. However, the goal of the paper is:

• To review, summarize and discuss the existing studies regarding the impact or PV generation on the power system’s small-signal stability.
• To review, summarize and discuss the current state-of-the-art in developing power oscillation damping control for PV inverter systems that improve the small-signal stability of the synchronous generators in the electric power system.

Hence, the goal of our submission is not to conduct and present a specific test case, but to extract the most useful insights from the currently available research publications. This is the reason why the synchronous machine model is not included in the paper. But we agree that this is an important aspect, therefore, in the introduction of the current text revision, we guide the reader to relevant references. Unfortunately, we could not find the paper you suggested online since the electronic catalog of the journal goes back no further than 2013, so we used other papers.

In this paper, we reviewed more than 30 different POD controller designs and tuning techniques, which makes it impossible to implement and compare all of them with simulations. Also, like noted above, the goal of the paper has never been to set up a test case. For that reason, we don’t present a graphical comparison.

In reality, many of the POD structures are capable of achieving somewhat similar performance. Hence, the essence of our work in terms of POD is in the careful analysis of their structure, appropriateness and practical applicability of the feedback signals, injection points, and tuning techniques. The advantages and disadvantages of the different POD developments are discussed and sections 4, 5, and 6. Moreover, in section 7 we argue that the current state-of-the-art has not reached the required technology readiness level and we propose two possible solutions and guidelines for future research that would make the POD for PV inverters practical for large-scale implementation in electric power systems.

Based on the recommendations of all reviewers, we improved the quality of the introduction and the conclusions. The English language and style of the paper are edited by a professional native editor and the text is completely free of any spelling or grammar errors.

Round 2

Reviewer 2 Report

No Comment.