Sizing Methodology of a Fast Charger for Public Service Electric Vehicles Based on Supercapacitors

Round 1

Reviewer 1 Report

In this manuscript, the authors presented a model for sizing the components of a fast-charging station by using the mathematical expressions of all the electrical variables involved in vehicle charging to dimension each component. Topic addressed in the paper is of current interest. However, following points need to be addressed.

1. The manuscript requires careful proofreading. There are several grammatical and typographical mistakes in the paper. Therefore, moderate editing of English is required.

2. The literature review section does not exist in the manuscript. The authors should include some recent research articles from the existing literature on the topic addressed.

3. The authors should clearly state the contributions and novelty of their proposed work considering the existing literature.

4. The authors need to compare the results of their proposed strategy with that of already presented studies in the literature.

5. The authors should include graphs of charging and discharging of SCs located at the charging station.

6. Please mention the charging time of SCs of the charging station.

7. Please explain, how many electric vehicles can be charged from SCs of charging station after one complete charging and without any further charging till full discharge.

8. Please state, how SCs of charging station will handle the charging of multiple vehicles at the charging station, if discharging of SCs is fast and the charging is slow.

Author Response

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Reviewer 2 Report

This paper presented a new methodology for the dimensioning of a fast-charging station. The mathematical expressions of instantaneous current, peak current, charging time, dissipated energy and other data were obtained to analyze the elements of the system, such as the capacitance of the charger with different variable steps, the initial voltage of the charger and so on. I think this study can provide useful suggestions for the construction of fast charging stations for supercapacitors. Therefore, I suggest publish the paper on the applied sciences. 

Author Response

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Reviewer 3 Report

In this manuscript, a new methodology for sizing the type of EV fast-charging station is presented. The article has sufficient workload and clear logic. The discussion is according to the practical case and meets the theoretical analysis. The problems in the article are listed on the following aspects:

1. There is an error in Figure 2, which is inconsistent with the description in the article.

2. There are unexplained physical quantities in the article.

3. The expression is not standard and there are obvious non-English words.

4. The chart format is not uniform.

5. The diagrams of fast-charging system for the SCs should be shown in the paper in part 3.

6. The superiority of the advantages such as allowing energy to be quickly evacuated to the EV of the fast charger are not shown enough.

Author Response

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Reviewer 4 Report

The authors demonstrate undoubted expertise in dimensioning charging systems and the paper is extensive and interesting. However, I consider questionable a fundamental assumption made by the authors: the system of SCs can be represented by a simple RC circuit. The authors argue in line 93: "For this purpose, the RC series model of the SC  will be used. This model is the most widely used for sizing [18] and provides simple analytical expressions when studying constant power, ...". The reference cited to justify the use of a simple RC circuit [18] is another paper by the authors themselves which however does not fully justify this statement. As far as I know  using the SC rated data with a simple RC circuit, the estimation of the charging time or of the final voltage can easily fail, with percentage discrepancies with two figures. Since the authors do not use an experimental verification, I have some doubts and I fear that this paper could be misleading. 

Author Response

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Round 2

Reviewer 1 Report

The authors have satisfactorily addressed all the comments.

Author Response

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Reviewer 3 Report

This version has been improved in detail according to the opinions, but there are still some problems in the format that need to be modified, including the format of the table and the bold setting of the formula.

Author Response

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Reviewer 4 Report

The authors were convincing in justifying the adoption of the linear model of the capacitor for sizing purposes. I therefore believe that the paper, in its current form, can be published.

Please allow me some comments, with reference to the bibliography cited by the authors in their reply. According to [2] if SCs are inserted in an electrical system which somehow imposes the voltage, the linear approximation could be accepted. However, in some papers, as in [1], the SC is included in a PI control loop. So, behavior non-linear discrepancies due to design are compensated by the control. In [3] the RC model is utilized based on ref [58] where a RC model is utilized, but with a statistical non-linear estimator. In [6], the authors clearly say that “when a traditional supercapacitor voltage controller (SCVC) is employed in the filter-based HESS, precise sizing of the supercapacitor as well as finding filter parameters for the power allocation are challenging due to nonlinearities. These problems can be circumvented by using a supercapacitor energy controller (SCEC) …”. The paper [14] is based on very small and obsolete SCs. All other papers are based on model evaluations, without any experimental validation.

Author Response

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