電 機 工程 學 刊

INTERNATIONAL JOURNAL OF ELECTRICALENGINEERING (IJEE)

Form for Response to Review (Form-09b)

Paper Number: <<R1_ES-19-000091>>Author(s): <<Jingrong Yu, Ruoxue Yu, Xianfu Lin, Maoyun Liu>>Paper Title: <<Harmonic Stability Analysis for Multi-functional Grid-connected

Inverter>>

A. List of changes according to the reviewers’ comments (use extra sheets ifnecessary):

The authors would like to thank the Editor and the anonymous Reviewers for their time inevaluating our submission, and the very constructive comments and suggestions provided,which have helped us greatly to improve the quality and the presentation of our paper. Inlight of the comments and suggestions from the Editor and the anonymous Reviewers, wehave substantially revised the paper. In the revised manuscript, the main changes arehighlighted in yellow for clarity and easy reference. We hope that the revision now meetsthe expectation of reviewers, and is suitable for publication in IJEE.

RESPONSE TO Editors1：This paper is needed to make major revisions according to the reviewers' comments.Response: The reviewers’ comments are all revised in the revised manuscript, and the mainchanges are highlighted in yellow for clarity and easy reference. We hope that the revisionnow meets the expectation of reviewers, and is suitable for publication in IJEE.

RESPONSE TO REVIEWER #1

The paper analyzes the controller of phase locked loop that influence on the stability andthe performance of the multi-functional grid-connected inverter (MF-GCI) with voltageharmonics compensation (VHC). From the results of analysis, the bus voltage is improvedand the corresponding THD is decreased with bus voltage harmonic compensation, but theoutput current of GCI seem contains a large THD. When the PLL stability margin increases,the bus voltage is further distorted, nevertheless, the harmonic stability and bus voltageharmonic quality on MF-GCI are hardly influenced by the change of PLL bandwidth.General Response: We are deeply grateful and appreciate for your positive comments andgood suggestions on our paper. We feel that the suggested changes have helped us improveour paper significantly. Please find below details of how each point has been fullyaddressed.

1. The parameters of the PI controller of PLL should be detailed illustrated (Kppll=? adKipll=?) in Fig.6.Response 1：Many thanks for the good comments. Following the kind suggestion, theparameters of the PI controller of PLL in Fig. 6 are added in the revised paper, which aregiven as follows for quick reference.Revised manuscript:

According to the system parameters in Table Ι, the frequency characteristics of theequivalent negative frequency output impedance of the qq frmae and qd frame of MF-GCIwithout considering the PLL and considering the PLL with keeping 1ipllk constant andsetting 1ppllk and 10ppllk respectively are shown in Fig. 6.

(a) (b)

Fig.6. The negative frequency output impedance of MF-GCI without considering PLL andconsidering PLL with keeping kipll=1 constant and setting kppll=1 and kppll=10,respectively.(a)The output impedance of qq frame(b) The output impedance of qd fame

2.In page 11, “From Fig.16 and Fig.17, it can be found that with the increasing ….” Shouldbe “From Fig.9 and Fig.10, it can be found that with the increasing…..”.Response 2：I'm very sorry for the mistake, the relevant revises in the revised paper are asfollows for quick reference:Revised manuscript:

From Fig.9 and Fig.10, it can be found that with the increasing of PLL stability margin, thebus voltage harmonic compensation function will be deteriorated, and harmonic resonanceinstability may occur.

3.In page 14, “Fig.18 illustrates that the harmonic stability……”, is it Fig.11?Response 3：I'm very sorry for the mistake, the relevant revises in the revised paper are asfollows for quick reference:Revised manuscript:

Fig.11 illustrates that the harmonic stability and bus voltage harmonic quality on MF-GCIare hardly influenced by the change of PLL bandwidth. The results well agree with thetheoretical analysis in section ΙΙΙ.

4.In ”Fig.16. Adding the voltage harmonic compensation function with increasing the PLLbandwidth by Kipll=1,Kppll=1,10,20,50 “. The Kipll=1, Kppll=1,10,20,50 should beKppll=1,Kipll=1,10, 20, 50 as illustrated in page 17 line, 6.Response 4：I'm very sorry for the mistake, the relevant revises in the revised paper are asfollows for quick reference:Revised manuscript:

Fig.16. Adding the voltage harmonic compensation function with increasing the PLLbandwidth by 1ppllk , 50,20,10,1ipllk (a)Bus voltage(b)Output current of GCI

5.The system parameter of the filter capacitance Cf do not show in table I and in equations,it should be illustrated that the filter capacitance Cf in the paper whether it will influencedthe system stability.Response 5：It is a very good question.Response (1): The parameter of filter capacitance Cf is added in the Table I, and thecorrespond equations is present in eq. (13) of revised paper.Response (2): In this paper, the filter capacitance is equivalent into the input impedance of

gird, and the system stability is depended on phase difference of the interconnection pointbetween the output impedance of MF-GCI and the input impedance of grid. Therefore,different value of Cf will change the impedance interconnection point, and the system’sunstable frequency will be changed. However, in this paper, the major objection is toanalyze the influence of PLL on the output impedance of MF-GCI, and the input impedanceof gird will not be influence by PLL. Thus only Cf=12.5μf is considered in this paper.

Summarizing above analyses, some relevant explanations are added in the revised paper,and the revised contents are given as follows for quick reference:Revised manuscript:

From (9), the MF-GCI is controlled as current source and it can be represented by aNorton circuit. The total impedance of filter capacitance Zcfdq for MF-GCI, and cableimpedance Zgdq, are equivalent to the equivalent input impedance Zegdq(s), expressed in (13),of grid. What’s more, the non-linear load in dq-frame is represented as a harmonic currentsource hdqi , and the grid voltage is represented by gdqv . Therefore, the small-signal model of

Fig. 1 is shown in Fig. 3. It is known that the input impedance of gird Zegdq(s) will not beinfluenced by PLL. To more clearly analyze the influence of PLL on MF-GCI, the uniqueparameters of Zegdq(s) is considered in this paper and listed in Table I.

11

1

11

1

1

111 )()(

ggg

ggg

ff

ff

gdqcfdqegdq

RsLLwLwRsL

sCCwCwsC

ZZsZ

(13)

Fig. 3. Small signal equivalent circuit for three-phase grid-connected system

TABLE ΙSYSTEM PARAMETERS

Symbol Parameters Value Symbol Parameters Value

Vg Grid voltage 350 V ki Integrator gain 80

Id D channel current 70 A Rg Grid resistance 0.5 Ω

Iq Q channel current 0 A Lg Grid inductance 0.5 mH

Rf Filter resistance 0.1 Ω kppll PLL proportional gain 0.1

Lf Filter inductance 4 mH kipll PLL integrator gain 10

Vdc DC-link voltage 600 V wbc Resonance bandwidth 15

kp Proportional gain 0.05 kr Resonance gain 15

Cf Capacitance 12.5 μf

RESPONSE TO REVIEWER #2

The paper investigates the harmonic stability analysis for a multi-functional grid -connectedinverter. The details are clearly discussed. Several experimental results are shown to verifythe simulation analysis. In addition, the paper is well written. As a result, the paper can beaccepted after the following minor points have been revised.General Response: We are deeply grateful and appreciate for your positive comments andgood suggestions on our paper. We feel that the suggested changes have helped us improveour paper significantly. Please find below details of how each point has been fullyaddressed.

1. Page 16 14(a)(b), and Fig. 15(a)(b), and page 17, Fig. 16(a)(b) the upper parts, such as:Tek, stop, 261.6 ms, et al. should be removed to improve the quality of these figures.Response 1：Thanks for the good suggestions, the Fig. 14, Fig. 15 and Fig .16 are revisedand as follows for quick reference:Revised manuscript:

(a) (b)

Fig.14. Adding the voltage harmonic compensation function with increasing the PLLstability margin by 1ipllk , 501ppllk (a)Bus voltage(b)Output current of GCI

(a) (b)

Fig.15. Adding the voltage harmonic compensation function with increasing the PLLstability margin by 1ipllk , 201ppllk (a)Bus voltage(b)Output current of GCI

(a) (b)

Fig.16. Adding the voltage harmonic compensation function with increasing the PLLbandwidth by 1ppllk , 50,20,10,1ipllk (a)Bus voltage(b)Output current of GCI

2. Page 19, reference [7] March need to revise to Mar.reference [8] JUL. need to revise to Jul.Response 2：Thanks for the good comments, the relevant revises in the revised paper are asfollows:Revised manuscript:

(1)R. T. Hock, Y. R. de Novaes and A. L. Batschauer, "A Voltage Regulator for PowerQuality Improvement in Low-Voltage Distribution Grids," IEEE Trans. Power Electron,vol. 33, no. 3, pp. 2050-2060, Mar. 2018.(2)C. Nie, Y. Wang, W. Lei, M. Chen, Y. Zhang, “An Enhanced Control Strategy forMultiparalleled Grid-Connected Single-Phase Converters With Load Harmonic CurrentCompensation Capability” IEEE Trans. Ind. Electron, vol. 65, no. 7, pp. 5623-5633, Jul.2018.

3. Page 12, Fig. 7(a),(b),(c) and (d) are too small. Please revise it.Response 3：Thanks for the good comments, the quality of Fig. 7 has been revised in therevised paper and as follows for quick reference:Revised manuscript:

Fig.7. The bode of MF-GCI output impedance and grid-side input impedance

with 1ipllk (a) 1ppllk (b) 10ppllk (c) 20ppllk (d) 50ppllk

4. Page 13, Fig. 8 is too small. Please revise it.Response 4：Thanks for the good comments, the quality of Fig. 8 has been revised in therevised paper and as follows for quick reference:Revised manuscript:

Fig.8. The qq frame negative frequency output impedance of GCI

Once again, we would like to thank the reviewer for the helpful comments. We hope ourreplies and revisions can address the comments of the reviewer.

B. Points of the reviewers’ comments which have not been followed in the revisions(specify your reasons clearly):The reviewers’ comments are all revised in the revised paper, and there have no thereviewers’ comments which have not been followed in the revisions.

Signature of Author: Jingrong Yu, Ruoxue Yu, Xianfu Lin, Maoyun LiuDate:2020-03-20