Research on Energy Management Strategy for Series Hybrid Tractor under Typical Operating Conditions Based on Dynamic Programming

Round 1

Reviewer 1 Report

Dear Authors,

In order to improve the quality of the article, I propose to take into account detailed remarks:

1)      Abstract: It should emphasize the novelty of the manuscript. What are the advantages of the presented work over others devoted to the analyzed issue? What novelties does the article contain in relation to the authors' previously published works devoted to these models of energy management in the serial hybrid drive of a tractor?

2)      In the simulation analysis, information about the assumed resistance power (power demand) for the analyzed variants of tractor operation should be completed. If the values of power demand are related to the value of battery power (as, for example, in Figure 8 a), the operating time of the tractor during plowing when powered only by the battery with the parameters in Table 1 (without generator support) seems too long. Similarly, the SOC drop seems too low. The energy contained in the batteries is about 23.1 kWh (for a theoretical state of charge equal to 100%). In the analysis, for example, the authors assume an initial SOC of 80% for plowing, and after about 2,000 seconds the SOC is about 50% (for an energy management strategy based on dynamic programming). This corresponds to the consumption of about 7 kWh of battery energy until the internal combustion engine starts. Isn't this too low a value of energy consumption for tractor operation under plowing conditions for more than half an hour?

3)      The comparative analysis of fuel consumption is not fully meaningful. The final SOC value for the two analyzed strategies (PF and DP) differs (for example, for Plowing Condition the final SOC value for the PF strategy is about 51%, while for DF it is about 47%. Therefore, this difference should be addressed - it affects the demonstrated reduction in fuel consumption, which should be taken into account for the same final SOC values (the value of additional fuel consumption associated with the generator charging the battery to the same final SOC charge level can be determined).

4)      Conclusions: Considering the above comment, the values specified in the conclusions should be corrected.

Hope these comments can help you further improve the paper.

Best regards,

The manuscript needs proofreading - contains editorial and language errors:

- Chapters or subsections should not begin with a figure - this applies to Figure 7 (subsection 5.1), Figure 11 (subsection 5.2) and Figure 15 (subsection 5.3.).

 - The quality of Figures 7 and 11 needs to be improved - the enlarged, upper part of the figures is illegible; Similarly, the quality of Figure 15 needs to be improved for legibility of the descriptions, in the part of the graph referenced by an arrow.

- I suggest replacing the term "power battery power" with "power of battery".

Author Response

Responses to suggestions 1:

Hello, during the early stages of research for this paper, I read a large number of relevant literature and found that few studies on energy management strategies for hybrid tractors have simultaneously conducted modeling and experimental analysis on three typical operating conditions of tractors: plowing, rotary tilling, and transportation. This is not comprehensive enough for the research on energy management strategies for hybrid tractors. Therefore, compared to other similar studies and previously published research on energy management strategies for series hybrid tractors, the advantage and novelty of this paper lies in the establishment of energy management strategy models for three typical operating conditions of tractors: plowing, rotary tilling, and transportation, based on the dynamic programming algorithm. Under the same tractor simulation model, a comparative analysis is conducted to evaluate the energy optimization effects of the dynamic programming algorithm under various operating conditions of the tractor. This provides a more comprehensive reference for modeling and energy management strategies of series hybrid tractors.

Meanwhile, I have revised some parts of the abstract to emphasize the aforementioned content and the novelty of the manuscript. The revised parts are highlighted in different colors for your reference. Thank you for your suggestions.

Responses to suggestions 2:

Hello, regarding your suggestion that information on tractor power demand should be included in the simulation analysis, for a series hybrid tractor, the power of the entire machine comes from the drive motor, and the power demand of the drive motor can reflect the power demand of the entire machine. I have created images showing the power changes of the drive motor during the model simulation process, as shown in Figure 8(a), Figure 12(a), and Figure 16(a). These images can better reflect the load changes of the model during the simulation process. Thank you very much for your suggestion. At the same time, I have described these results in more detail and highlighted them in different colors in the text for your reference.

Regarding the issue you raised about the excessively low SOC decline trend during the simulation process, as can be seen from the parameters in Table 1, the series hybrid tractor model designed and built in this paper belongs to a medium-horsepower tractor, and the test conditions used for simulation are also under relatively low loads. Taking the plowing condition as an example, with a plowing depth of 25cm, it belongs to shallow plowing rather than deep plowing. As can be seen from the newly created Figure 8(a), the maximum power of the drive motor does not exceed 50kW, which is less than 80% of the rated power of the drive motor, indicating a relatively low load. Therefore, the decline trend of SOC and energy consumption are consistent with the simulation test. Once again, thank you for your suggestion regarding tractor power demand information.

Responses to suggestions 3:

Hello, the DP strategy optimizes the operating state of the engine based on the entire working condition, and it is very difficult to achieve the same final SOC value between the DP strategy and the PF strategy under the same working condition. Regarding your question, I also had the same doubt during the simulation test process. To address this, I consulted a large number of literature and sought advice from relevant researchers. The conclusion I drew is that, under the condition of ensuring that the SOC value of the tractor remains healthy throughout the entire operating condition, the energy management strategy can operate more actively in a pure electric mode, potentially achieving better fuel economy. Taking the plowing condition of this model as an example, the DP strategy consumes about 8.37% more battery SOC compared to the PF strategy, but it reduces fuel consumption by 25.28%. At the same time, I also mentioned in the paper that compared to the DP strategy, the PF strategy can result in frequent startup and shutdown of the engine throughout the working condition, which can further increase fuel consumption for the PF strategy. There have been some related studies on the DP strategy to maintain the final SOC value at an adjustable level, and I will continue to follow up on relevant research progress. Thank you very much for your suggestion.

Meanwhile, I have introduced a new chapter "6. Discussion" in the manuscript, describing the simulation test results and conclusions of this study, as well as explaining possible future research directions. I have highlighted these contents in different colors in the text for your reference. Thank you again for your suggestions.

Responses to suggestions 4:

As mentioned in Suggestion 3, I have reflected in the abstract and conclusion the additional battery SOC consumed and corresponding reduction in fuel consumption by the DP strategy compared to the PF strategy in various working conditions. I have highlighted these contents in different colors in the text for your reference. Thank you very much for your suggestion.

Responses to suggestions 5:

Hello, I have created new Figures 7, 11, and 15, and revised the beginnings of the chapters. Additionally, I have corrected the term "power battery power." I should carefully check the clarity of the figures and the grammatical issues in the manuscript. Thank you very much for your suggestions.

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper entitled "Research on Energy Management Strategy for Series Hybrid Tractor Under Typical Operating Conditions Based on Dynamic Programming” provides a short overview of research on different strategies that allow to reduce fuel consumption and demonstrates that the selected optimal hybrid energy management strategy, which is based on dynamic programming (DP), allowed 13-25% savings in 3 typical agricultural work tasks compared with a power following (PF) based energy management strategy. The article presents calculations on realistic components and provides reliable results without specifying specific details about the tractor or anything more specific in terms of Matlab/Simulink implementation, modeling and simulation.

The following suggestions for improvement may be useful to researchers who would benefit from the experience of this article:

Which parameter is presented on the engine contour plot in Fig.2?

How is related battery capacity, energy and power in this work?

Figures 10, 14 and 18 could specify also the specific agricultural task and how energy demanding it is compared to others?

Author Response

Responses to suggestions 1:

Hello, Figure 2 includes the MAP of engine fuel consumption rate, the optimal operating line of engine and the engine's external characteristic curve. I have added some explanations after Figure 2 and highlighted them in different colors in the text for your reference. Thank you for your suggestion.

Responses to suggestions 2:

Hello, as shown in formulas (22) and (23) in "3.8. Power Battery Model," the battery SOC is calculated based on battery capacity and power according to formula (22), and the current battery power is determined by formula (23).

Responses to suggestions 3:

Hello, regarding your suggestion on obtaining information about the power demand of tractors under various operating conditions, for the series hybrid tractor, the entire power of the machine comes from the drive motor. The power demand of the drive motor can reflect the power demand of the entire machine. I have created images showing the changes in power of the drive motor during the model simulation process, as illustrated in Figure 8(a), Figure 12(a), and Figure 15(a). These images better reflect the load changes under various operating conditions during the simulation process. Thank you very much for your suggestion. Additionally, I have described these results in greater detail and highlighted them in different colors in the text for your reference.

Author Response File: Author Response.pdf

Reviewer 3 Report

1) At the end of the introduction, briefly specify what each of the following sections of the work deals with.
2) Briefly describe the parameters mentioned in the first table.
3) The text in lines 107-113 "This section may be divided by subheadings. It should provide a concise and precise description of the experimental results, their interpretation, as well as the experimental conclusions that can be drawn. Based on the principle of forward modeling, this article uses the difference between the target vehicle speed and the current vehicle speed as input, and the acceleration pedal opening and the brake pedal opening as output to build a driver model based on PI control. The principle of the driver model is shown in the following equation:" requires citation.
4) Even if for specialists the notions in lines 122-129 "In the structure of a series hybrid system, the engine drives the generator to generate electricity through mechanical connection, and the engine and generator are not connected to the transmission system, relatively independent of the power system of the entire vehicle. Therefore, the engine and generator are usually considered as a whole, namely the generator set. The research on hybrid energy management strategies focuses on analyzing the fuel economy of tractors, so numerical modeling methods are adopted, considering only the input and output relationships of the generator set, as shown in the following equation:" are well known, the work must include here at least one citation from the specialized literature regarding these statements.
5) About the equation (3): if we are talking about a serious work, of great precision, do not round 9549.296586 to 9550; if you don't want to work with the comma, that is, with 9549.3, simply use the conversion value 9549 in the denominator of the relationship (3).
6) A few words about the diagram in Figure 2 are necessary here, immediately after Fig. 2.
7) The statements in lines 145-151 "The drive motor model employs a numerical modeling approach. The corresponding relationship between motor speed and motor torque is determined through drive motor bench test data using a look-up table method. The torque control mode is adopted, and the motor output is controlled through the accelerator pedal opening signal. The mathematical modeling principle of the drive motor is shown in Equation 7. Based on the drive motor bench test data, the drive motor's external characteristic curve is obtained, and then the motor efficiency MAP is obtained through interpolation fitting, as shown in Figure 3:" require citation.
8) Define vact (The current vehicle speed of the tractor) from equation (10), immediately after equation (10), and before equation (14).
9) Figure 4 requires a more detailed presentation.
10) I think that "4.1. Energy Management Strategy Based on Power Following" should have been put here 4.2.
11) Discuss in more detail the results obtained and presented in the diagrams in Figures 7-18.
12) The "5. Simulation and Result Analysis" section should be named "5. Simulation, Result Analysis, and Discussion", or add a supplementary section "Discussion".
13) Before the conclusions, introduce an additional section, about the possible future research opened by the new results introduced by the present work.

 Minor editing of the English language is required.

Author Response

Responses to suggestions 1:

Hello, I have revised the ending section of the introduction and briefly described the contents of each section of the manuscript. I have highlighted these changes in different colors for your reference. Thank you for your suggestions.

Responses to suggestions 2:

Hello, I have briefly described the content of Table 1 and highlighted it in different colors in the text for your reference. Thank you for your suggestions.

Responses to suggestions 3:

Hello, I should have carefully checked the content of the manuscript more thoroughly. I have now deleted the redundant parts and added the citation [31]. Thank you for your suggestion.

Responses to suggestions 4:

Hello, I have added the citation [32] to this section. Thank you for your suggestion.

Responses to suggestions 5:

Hello, I have noticed this issue and realized that I should have been more rigorous in considering the numerical values in the formula. I have followed your suggestion and corrected the value in the formula from 9550 to 9549. Thank you for your suggestion.

Responses to suggestions 6:

Hello, I have added some explanations after Figure 2 and highlighted them in different colors in the text for your reference. Thank you for your suggestion.

Responses to suggestions 7:

Hello, I have added the citation [33] to this section. Thank you for your suggestion.

Responses to suggestions 8:

Hello, I have already defined "vact" (the current speed of the tractor) in formula (2) of Section 3.1, Driver Model. I have highlighted this content in different colors in the text for your reference. Thank you for your suggestion.

Responses to suggestions 9:

Hello, I have added more descriptions to Figure 4. I have highlighted these changes in different colors in the text for your reference. Thank you for your suggestion.

Responses to suggestions 10:

Hello, I have noticed this issue and realized that I should have carefully checked the format of the manuscript. I have made the necessary corrections. Thank you very much for your suggestion.

Responses to suggestions 11:

Hello, I have created images that depict the power changes of the drive motor during the model simulation, as shown in Figure 8(a), Figure 12(a), and Figure 15(a). These images provide a better reflection of the load changes in the model during the simulation process. Additionally, I have provided a more detailed description of Figures 7-18. Thank you for your suggestions.

Responses to suggestions 12:

Hello, I have added a new section titled "6. Discussion" to the manuscript. Thank you very much for your suggestion.

Responses to suggestions 13:

Hello, I have introduced a new section, "6. Discussion," in the manuscript, which describes the simulation test results, as well as outlines potential future research directions. I have highlighted these contents in different colors in the text for your reference. Thank you for your suggestions.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The Authors have made significant improvements to the content of the manuscript and responded to all my comments.

In my opinion, the article in the current version can be accepted for publication in the World Electric Vehicle Journal.

Kind regards,