Coordinated Control System between Grid–VSC and a DC Microgrid with Hybrid Energy Storage System
, Édinson Franco-Mejía 2, Edwin Rivas Trujillo 3, José Luis Rodriguez-Amenedo 1 and Santiago Arnaltes 1Round 1
Reviewer 1 Report
This paper investigates the coordinated control system between grid-VSC and a DC Microgrid with Hybrid Energy Storage System. The paper is generally well-written, and there are several suggestions.
- Please give the diagram of the control strategy in Section 3.
- Analysis and discussion on the operation modes of the whole DC Microgrid should be given. How to control these inverters and converters in each mode? Please make justifications.
- Literature review is not sufficient, especially for the latest control method for DC Microgrid. For example, Resilient Control and Analysis for DC Microgrid System under DoS and Impulsive FDI Attacks, 2021, doi: 10.1109/TSG.2021.3072218.
- There is no need to state that "All simulations were carried out in MATLAB 2020". It is better to make some statements on how much cases studies are carried out and what to obtain in the simulations.
- Please check the editing of the paper, such as "where" and "Where" after the equations. Please also check all the equations and the associated explanation of each variable.
- The caption of each figure should be rewritten to make the figure well illustrated. For example, "Figure 4 Connection and power flow in Mode 2", what is the meaning of "connection"?
Author Response
This paper investigates the coordinated control system between grid-VSC and a DC Microgrid with Hybrid Energy Storage System. The paper is generally well-written, and there are several suggestions.
We thank Reviewer 1 for his interesting comments and suggestions; and for giving us the opportunity to improve the paper.
1. Please give the diagram of the control strategy in Section 3.
In section 3 the HESS and GVS control diagrams have been included. These schemes explain how the coordinated regulation of the proposed control is fulfilled.
2. Analysis and discussion on the operation modes of the whole DC Microgrid should be given. How to control these inverters and converters in each mode? Please make justifications.
To improve clarity of the modes of operation, a state diagram explaining the operation of the system was included and control diagrams were added for the converters. In addition, a brief explanation was added to the document, detailing the modes of operation and control.
3. Literature review is not sufficient, especially for the latest control method for DC Microgrid. For example, Resilient Control and Analysis for DC Microgrid System under DoS and Impulsive FDI Attacks, 2021, doi: 10.1109/TSG.2021.3072218.
More references have been added in the article and also the reference mentioned by you
12.Shahid, M.; Khan, M.; Hashmi, K.; Habib, S.; Jiang, H.; Tang, H. A Control Methodology for Load Sharing System Restoration in Islanded DC Micro Grid with Faulty Communication Links. Electronics 2018, 7(6), 90.
15.X. -K. Liu, C. Wen, Q. Xu and Y. -W. Wang, "Resilient Control and Analysis for DC Microgrid System Under DoS and Im-pulsive FDI Attacks," in IEEE Transactions on Smart Grid, vol. 12, no. 5, pp. 3742-3754, Sept. 2021
18.Xiong, X.; Yang, Y. A Photovoltaic-Based DC Microgrid System: Analysis, Design and Experimental Results. Electronics 2020, 9(6), 941.
4. There is no need to state that "All simulations were carried out in MATLAB 2020". It is better to make some statements on how much cases studies are carried out and what to obtain in the simulations.
Thank you for your recommendations. But it has been mentioned that the simulations have been carried out by MATLAB 2020, to highlight that these have been carried out through computer simulations and not experimentally. The number of simulations carried out and their results are developed in section 4.
5. Please check the editing of the paper, such as "where" and "Where" after the equations. Please also check all the equations and the associated explanation of each variable.
The word: “Where” has been replaced with the word “where”. Also it has checked all the equations and the associated explanation of each variable.
6. The caption of each figure should be rewritten to make the figure well illustrated. For example, "Figure 4 Connection and power flow in Mode 2", what is the meaning of "connection"?
The captions of Figures 7, 8, and 9 have been changed. The word “connection” has been replaced with the word “Voltage”
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Dear Authors,
This paper presented a coordinated control system for a microgrid with hybrid energy storage system. Following are my comments
- Please check the paper thoroughly for grammatical mistakes and consistency. For example, at few places state-of-the-charge is denoted as SOC and at few places it is denoted as SoC. Please be consistent with the abbreavations.
- Why is the source supplying 1130 W which is greater than the load demand of 1100 W? Is it due to MPPT?
- The novelty of the paper is the addition of super capacitor for energy storage. However, its application is not shown in the simulation results. Please include additional simulation results that depicts the application of super capacitor.
- Kindly show the simulation parameters for the circuit and include the picture of the simulation schematic from Matlab/Simscape.
- Please explain what triggers the various modes of operation. Is it the DC bus voltage?
- Please add additional results by showing the transitions from one mode to another.
- The strength of the paper can be increased by adding experimental results if possible.
- Please add additional references from MDPI electronics.
Author Response
This paper presented a coordinated control system for a microgrid with hybrid energy storage system. Following are my comments
We thank Reviewer 2 for his interesting comments and suggestions; and for giving us the opportunity to improve the paper.
1.Please check the paper thoroughly for grammatical mistakes and consistency. For example, at few places state-of-the-charge is denoted as SOC and at few places it is denoted as SoC. Please be consistent with the abbreavations.
The abbreviations have been corrected throughout the document.
2. Why is the source supplying 1130 W which is greater than the load demand of 1100 W? Is it due to MPPT?
The photovoltaic array has certain nominal values. We wanted to show a simulation as close to reality as possible. The 1130W value is due to the MPPT control and the nominal values of the photovoltaic array.
3. The novelty of the paper is the addition of super capacitor for energy storage. However, its application is not shown in the simulation results. Please include additional simulation results that depicts the application of super capacitor.
Figures 6 and 7 show the action of the supercapacitor. Its behavior has been highlighted depending on the control system of Figure 3
4. Kindly show the simulation parameters for the circuit and include the picture of the simulation schematic from Matlab/Simscape.
Thank you for your comments. Figure number 1 has been modified to indicate the topology of the studied system. Below is the schematic figure in Matlab / Simscape.
This figure is quite information-dense and could confuse readers.
Therefore, it has been decided not to include it in the paper. Instead, Figure 1 has been improved.
5. Please explain what triggers the various modes of operation. Is it the DC bus voltage?
The state diagram in Figure 8 shows how the system can evolve depending on the regulation of the DC bus (VDC), the regulation of the AC bus (VK) and the power flows (P and Q).
The regulated voltage is the voltage on the DC bus within the microgrid. Fig. 1 has been enhanced to indicate the DC bus.
6. Please add additional results by showing the transitions from one mode to another.
Thankful to the reviewer for the suggestion but Figure 6 through Figure 9 show the transitions from one operating point to another. Therefore, we consider that the transitions are displayed.
7. The strength of the paper can be increased by adding experimental results if possible.
Unfortunately, due to the short time we have to do this review, it would be very tedious and labor-intensive to run an experimental test. For a future article we will try to carry out an experimental test.
8. Please add additional references from MDPI electronics.
The following references have been added.
12. Shahid, M.; Khan, M.; Hashmi, K.; Habib, S.; Jiang, H.; Tang, H. A Control Methodology for Load Sharing System Restora-tion in Islanded DC Micro Grid with Faulty Communication Links. Electronics 2018, 7(6), 90.
18. Xiong, X.; Yang, Y. A Photovoltaic-Based DC Microgrid System: Analysis, Design and Experimental Results. Electronics 2020, 9(6), 941.
Author Response File: Author Response.pdf
Reviewer 3 Report
This paper studies the coordinated control system for grid-VSC and a DC Microgrid with Hybrid Energy Storage System. The content lacks technical contributions. Thus I do not recommend the publication of this paper. The comments are as follows:
1. The literature review is not well written. It is hard to identify the critical problems in the coordinated control of MGs. The contributions of this paper are not clearly presented, and there is no comparison with existing works.
2. The models of Section 2 are from existing works. It is too simple for the proposed strategy in (6). It only considers the power balancing problems.
3. Some simulation results are presented. However, the proposed method itself lacks technical contribution. The proposed coordinated control method does not offer innovation for the research community.
Author Response
This paper studies the coordinated control system for grid-VSC and a DC Microgrid with Hybrid Energy Storage System. The content lacks technical contributions. Thus I do not recommend the publication of this paper. The comments are as follows:
We thank Reviewer 3 for his interesting comments and suggestions
1. The literature review is not well written. It is hard to identify the critical problems in the coordinated control of MGs. The contributions of this paper are not clearly presented, and there is no comparison with existing works.
The coordinated control strategy proposed in the paper follows our research and the research of other authors with regards to the control of DC microgrid and VSC connecting to the grid. However, we have no knowledge of existing similar work on the simultaneous operation between DC microgrid and VSC connecting to the grid. Therefore, and unfortunately, we cannot compare our results with others from previous work; though when considering the two parts of the problem separately (DCMG and GVSC), our results are consistent with those from previous research.
The critical problem is formulated as: the regulation of the DC voltage and the power flow to find a stable operating point between the different active elements that supply the load in the DC microgrid. Both the introduction and the abstract express the main problem that we are developing in this paper.
2. The models of Section 2 are from existing works. It is too simple for the proposed strategy in (6). It only considers the power balancing problems.
The models used in this and other articles are based on previous works duly cited in the references. In the paper [6], the authors limit themselves to the control of the microgrid in DC, taking the SoC of the batteries as a novelty.
In our work we extend the application considering not only the batteries but also a supercapacitor to improve the dynamic performance and the useful life of the batteries as shown in [22]. In addition, the control for VK regulation in the PCC (AC side) is expanded, showing the interaction between the two systems as a function of power flows and regulation needs.
3. Some simulation results are presented. However, the proposed method itself lacks technical contribution. The proposed coordinated control method does not offer innovation for the research community.
In section 3 the control diagrams and the states of the proposed operating modes have been added showing the performance of the battery with the supercapacitor. Although the controls are standard, their coordination is not so simple and they require a suitable formulation for their correct operation.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Dear Authors,
Thank you for answering all my queries. The paper has been significantly improved compared to the previous version.
Reviewer 3 Report
I do not have further comments.
