Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this manuscript, the authors focus on the modernization of the power system for heritage trams and proposes a hybrid power supply architecture that integrates lithium-ion batteries (LIBs), inductive wireless charging (IPT), and battery swapping (BS). The study estimates energy consumption demands through kinematic simulations, optimizes the IPT system design using finite element analysis (FEA), and validates the feasibility of the proposed solution through multi-scenario comparisons. However, shortcomings remain in areas such as the analysis of battery performance compatibility, validation of dynamic characteristics of the charging system, and feasibility of practical implementation, which require further refinement. For improving the manuscript, the authors could consider the following comments.

1. Absence of battery thermal management and safety design: The LIB trailer employs a dual-battery stacked configuration (Fig. 9), yet no cooling solution is mentioned.
2. The IPT system is designed with a charging power of 3 kW, corresponding to a charging rate of approximately 0.075C for a 40kWh battery, which falls into the category of ultra-low C-rate charging. Please provide a detailed explanation of the battery's charging efficiency, polarization characteristics, and impact on cycle life under this specific charging rate.
3. Inconsistent expression of some technical terms was observed:

A: BC-BS hybridization is occasionally written as CB and CS hybridized,

B: while dynamic IPT and "DIPT are used interchangeably without standardization, impairing reading coherence.

4. Deficiencies in reference citations were identified:

A: In Section 3.5, the formula describing the power relationship lacks citation of its theoretical source.

B: No reference is provided for the magnetic permeability testing method of magnetic concrete, and several key data points lack supporting literature.

5. Please add the error range of the coupling coefficient in Figures 13-14.
6. The missing column headers in Table 2 affect the accurate interpretation of the data.
7. Please provide the test data on retired battery characteristics and improve the safety and thermal management design of the battery system.

Author Response

1. Absence of battery thermal management and safety design: The LIB trailer employs a dual-battery stacked configuration (Fig. 9), yet no cooling solution is mentioned.

Thank you for pointing out this oblivion.

The thermal management and safety design of the dual battery stacked configuration (Fig. 9) has been added to the text: “As a safety measure, between the two battery packs, there is a gap of 50 mm, which allows the insertion of computer fans for the cooling off the LIBs.  The brakes of the trailer car have electric deployments that can lock the wheels in case of a battery fire.”

2. The IPT system is designed with a charging power of 3 kW, corresponding to a charging rate of approximately 0.075C for a 40kWh battery, which falls into the category of ultra-low C-rate charging. Please provide a detailed explanation of the battery's charging efficiency, polarization characteristics, and impact on cycle life under this specific charging rate.

Thank you for your comment. The following is our explanation:

Charging efficiency: At ~0.075C, Li-ion cells typically exhibit >99% coulombic efficiency.

Polarization characteristics: Ohmic, charge-transfer and concentration polarizations scale with current, at ~0.075C the total overpotential is limited to only tens of millivolts, minimizing heat generation. For a 40 kWh pack (~360 V, ~111 Ah), the charge current is ~8.3 A; even with a conservative pack DC resistance of 50–100 mΩ, loss is only ~3 to 7 W, and entropic heat is negligible.

Cycle life impact: Such mild charge rates reduce stress mechanisms, such as Li plating risk, SEI thickening due to high overpotentials), which generally improves cycle life relative to higher-C charging. The trade-off is longer charging time.

3. Inconsistent expression of some technical terms was observed:

A: BC-BS hybridization is occasionally written as CB and CS hybridized,

B: while dynamic IPT and "DIPT are used interchangeably without standardization, impairing reading coherence.

Thank you. The revised text consistently uses BC-BS hybridization to describe the combined approach and DWPT (dynamic wireless power transfer) and DIPT (dynamic inductive power transfer) to describe the charging system.

4. Deficiencies in reference citations were identified:

A: In Section 3.5, the formula describing the power relationship lacks citation of its theoretical source.

B: No reference is provided for the magnetic permeability testing method of magnetic concrete, and several key data points lack supporting literature.

The magnetic permeability testing method for magnetic concrete is provided in Reference [37], which details the experimental procedure and measurement approach used.

5. Please add the error range of the coupling coefficient in Figures 13-14.

6. The missing column headers in Table 2 affect the accurate interpretation of the data.

The missing column headers in Table 2 have now been added.

7. Please provide the test data on retired battery characteristics and improve the safety and thermal management design of the battery system.

Thank you for the suggestion. We have not have any retired batteries at this stage.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Referee’s comments

To the paper entitled “Power Supply Analysis for a Historical Trolley Battery Trailer with Wireless Charging and Battery Swap Technologie” by Karl Lin et al.

Nowadays an actual problem is to provide electrification of municipal transport by means of continuous wireless charging involving lithium-ion battery (LIB). However only a few attempts to develop the system of inductive power transfer (IPT), but these technologies have a great potential for rail electrification. A main problem is power demand for the operation of train traffic. The authors developed a hybrid power-supply architecture, which involves the technologies of LIBs (Nissan Leaf rechargeable batteries for cars), inductive wireless battery charging (BC), and battery swapping (BS) technologies. This is for providing a long-time trip (20 km) of historical trolley in textile country in Gaston County, North Carolina. To analyze the power demand, finite element analysis (FEA) has been applied to design an IPT system. Two transmitter materials were used: W–I ferrite cores and magnetic-concrete slabs. The advantages and disadvantages of these materials were analyzed. The paper could be recommended for the specialists in the fields of energetics, physics of solid state and electrochemistry (who occupies LIBs).

As for my opinion, minor revision is required. The comments are given below.

Abstract.

Descript IPT in the beginning of abstract (line 3). Moreover, it is recommended to make the abstract slightly shorter (200 words maximum according to the instruction for authors). I cannot understand: is the abstract includes 2 parts? If yes, it is too long.

Fig. 2. The map is incomprehensible. Please show stops: according to the plot of velocity vs distance, a distances between stops are approximately similar. Is the orange curve a run of trolley? What are green curves? What are color spots (from red to blue according to the scale)? Please explain this in the figure capture.

Eq. 3. Is this an original equation? If no, give a reference. It is also interesting how it was obtained.

Eq. 4 is missed.

Figs. 6-8 can be merged and marked as a,b,c. It is the same for tables 1,2, figs. 11-12, 13-14.

Section 4.2. You give a list of 7 points. It means you have 7 scenarios?

Section 4.4. Please number the expressions for Es and Ed. It is the same for the expression in page 17?

Some data of Table 3 are incomprehensible. $$ means, for instance, 10-90 dollars, SSS – 100-999. Is it right?

A list of symbols and abbreviations is very welcome.

Author Response

Abstract.

Descript IPT in the beginning of abstract (line 3). Moreover, it is recommended to make the abstract slightly shorter (200 words maximum according to the instruction for authors). I cannot understand: is the abstract includes 2 parts? If yes, it is too long.

The abstract has been revised according to the journal’s word limit requirement (200 words maximum). The abstract has been consolidated into a single, concise part to avoid the impression of being separated into two sections.

Fig. 2. The map is incomprehensible. Please show stops: according to the plot of velocity vs distance, a distances between stops are approximately similar. Is the orange curve a run of trolley? What are green curves? What are color spots (from red to blue according to the scale)? Please explain this in the figure capture.

Thank you. Figure 2 has been revised to include the locations of the stops and a clearer explanation of the plotted elements.

Eq. 3. Is this an original equation? If no, give a reference. It is also interesting how it was obtained.

Eq. 4 is missed.

Thank you, the problem is solved.

Figs. 6-8 can be merged and marked as a,b,c. It is the same for tables 1,2, figs. 11-12, 13-14.

Thank you for your suggestion.  We keep them separate in order to provide clearer visualization and easier interpretation of the distinct results.

Section 4.2. You give a list of 7 points. It means you have 7 scenarios?

Yes.

Section 4.4. Please number the expressions for Es and Ed. It is the same for the expression in page 17?

Thank you, the expressions have been added.

Some data of Table 3 are incomprehensible. $$ means, for instance, 10-90 dollars, SSS – 100-999. Is it right?

The symbols in Table 3 do not represent exact dollar ranges, instead, they are relative cost indicators for each scenario.

A list of symbols and abbreviations is very welcome.

The list has been provided.

Author Response File: Author Response.pdf