Battery Active Grouping and Balancing Based on the Optimal Energy Transfer Direction
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors(1) Figure 1(b) in Section 2.1 illustrates the topology of eight batteries, but the specific battery parameters are not detailed. It is recommended to provide supplementary information.
(2) Is the setting of parameter necessary when solving for the equilibrium direction in Section 3.5?
(3) Please explain the meanings of λ1 and λ2 in the text?
(4) And what are the principles for their selection?
(5) The style of Figure 6 is inconsistent with the other figures in the manuscript. Please make the necessary revisions.
（6）The introduction section should incorporate the latest research findings. The references cited should be expanded further and the citation format should be standardized.
Author Response
Reviewer 1：
(1) Figure 1(b) in Section 2.1 illustrates the topology of eight batteries, but the specific battery parameters are not detailed. It is recommended to provide supplementary information.
Reply: Thanks for your comments. The specific battery parameters have been added to Section 2.7 of the revised manuscript, as following:
“The battery capacity is 20Ah. The maximum equalization current and energy transfer efficiency of the equalizer in the equalization circuit are set to 20A and 0.9 respectively, and the sampling period is Ts=1s, and each PWM cycle is simulated in 25 steps.”
(2) Is the setting of parameter c necessary when solving for the equilibrium direction in Section 3.5?
Reply: Parameter c must be set. If parameter c is not set, it is impossible to determine the priority of battery charging and discharging, which will lead to inaccurate solution of the balancing path and may increase the balancing loss and balancing time.
(3) Please explain the meanings of λ1 and λ2 in the text?
Reply: In the objective function, λ1 represents the speed at which the SOC in the battery pack tends to be consistent, and λ2 represents the energy consumed in the internal resistance during the balancing process.
(4) And what are the principles for their selection?
Reply: The selection of the weighting coefficients λ1 and λ2 is not an optimization process, but rather a result of continuous trials to obtain a relatively better value. In practical situations, users can choose different weights according to their actual needs to achieve different goals. For example, to shorten the balancing time, λ2 can be made smaller. It can be seen from Figure 5 that λ2=1×10−4 achieves a good balance between balancing time and balancing loss. Therefore, this paper selects this weight for simulation comparison and analysis.
(5) The style of Figure 6 is inconsistent with the other figures in the manuscript. Please make the necessary revisions.
Reply: The style of Figure 6 has been modified as follows:
Figure 6 Initial SOC distribution of battery pack, (a) Case one, (b) Case two.
(6) The introduction section should incorporate the latest research findings. The references cited should be expanded further and the citation format should be standardized.
Reply: The introduction section has been revised and updated with the latest research findings. And the format of the references has been adjusted to comply with the standards.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Comments and Suggestions for AuthorsDear authors,
the paper "Battery active grouping equalization based on the optimal energy transfer direction and equalization current" proposes a dynamic equalization topology, reducing equalization times and energy loss, helping to increase equalization speed.
Address some issues, detailed below:
1) Introduction - Lithium-ion batteries ware widely used- Lithium-ion batteries were widely used
2) introduction - inter-group (outer layer) and intra-group (inner layer). a reconfigura- - inter-group (outer layer) and intra-group (inner layer). A reconfigura- (capital letter)
3) Introduction - proposed an MPC equalization control strategy - proposed a MPC equalization control strategy
4) At the end of introduction, a summary of the next section should be incorporated.
5) 2.1 Topology oriented towards dynamic grouping equalization - Is this topology a proposition by the authors or it has been proposed by others? If the authors propose it, explain it in more detail. If not, include the reference.
Author Response
Reviewer 2：
(1) Introduction - Lithium-ion batteries ware widely used- Lithium-ion batteries were widely used
Reply: Thanks for your comments. The incorrect spelling has been corrected in the revised manuscript.
(2) introduction - inter-group (outer layer) and intra-group (inner layer). a reconfigura- - inter-group (outer layer) and intra-group (inner layer). A reconfigura- (capital letter)
Reply: The lowercase letters at the beginning of the sentences have been replaced with uppercase letters in the revised manuscript.
(3) Introduction - proposed an MPC equalization control strategy - proposed a MPC equalization control strategy
Reply: The word “an” has been replaced with “a” in the revised manuscript.
(4) At the end of introduction, a summary of the next section should be incorporated.
Reply: A summary of the next section has be incorporated at the end of introduction, as following:
“This study proposes a dynamic grouping equalization topology that combines reconfigurable circuits with Buck-Boost circuits. This topology allows for dynamic grouping of series-connected cells, enabling multi-to-multi cell equalization through a switching array. A model predictive control (MPC) based control strategy is introduced to optimize the energy transfer direction and equalization current. This design not only flexibly schedules the flow of energy but also avoids energy loss during transmission, thereby enhancing the battery's endurance while extending the overall service life of the battery pack.”
(5) 2.1 Topology oriented towards dynamic grouping equalization - Is this topology a proposition by the authors or it has been proposed by others? If the authors propose it, explain it in more detail. If not, include the reference.
Reply: The balancing topology was proposed by the author, and the details regarding the balancing topology have been added to the revised manuscript, as following:
“For batteries in a static state, regardless of the initial SOC distribution, adaptive grouping of non-adjacent batteries can be performed according to the balancing strategy. There are three working modes: balancing between any single cell to any other single cell, balancing between a group of multiple cells to a single cell, and balancing between multiple cells to multiple cells. In the charging and discharging mode of the battery, the balancing topology still has these three working modes. However, when performing balancing between multiple cells and multiple cells, the grouping method is based on adjacent cells.”
Author Response File: Author Response.docx
Reviewer 3 Report
Comments and Suggestions for AuthorsThis study proposed a battery active grouping equalization control strategy based on model predictive control, promoting cell consistency, equalization speed, and energy loss during the battery equalization process. The dynamic group equalization topology based on reconfigurable circuits can achieve dynamic grouping. Using a battery state observation estimator and the MPC controller, multiple non-adjacent cells can realize simultaneous equalization in a single equalization process. An algorithm is designed to determine the optimal energy transfer direction and the optimal equalization current. The objective function of this algorithm incorporates weight coefficients that represent the relative importance of equalization time and energy loss. Simulation tests are conducted to evaluate the battery pack state-of-charge root mean square, average temperature, and equalization time under various weight coefficients. The paper has some interesting points, but the following defects must be considered:
- The paper does not follow the journal guidelines
- The title must be refined. The twice usage of equalization must be avoided.
- In the introduction section, add the research gap, contribution, and paper structure.
- Description of the considered problem in section 3 needs more attention.
- The simulation results are poor in presentation and analysis
- The conclusion needs to be extended to cover the main findings
Revise
Author Response
Reviewer 3：
(1) The paper does not follow the journal guidelines
Reply: Thanks for your comments. The manuscript has been revised in accordance with the journal's guidelines to meet the publication requirements of the journal.
(2) The title must be refined. The twice usage of equalization must be avoided.
Reply: The title has been refined, which is “Battery active grouping and balancing based on the optimal energy transfer direction”.
(3) In the introduction section, add the research gap, contribution, and paper structure.
Reply: The research gap, contribution, and paper structure have been added in revised manuscript. For example:
“Currently, research on active equalization methods mainly focuses on cell-to-cell equalization, pack-to-cell equalization, and equalization among adjacent battery cells. There is relatively less research on equalization among non-adjacent battery cells. The existing equalization topologies have issues such as long equalization time and poor flexibility of equalization paths. In practical use, the distribution of battery charge in a battery pack is relatively complex, and more flexible equalization paths are needed to shorten the equalization time. Most equalization control strategies currently consider only a single objective. Multi-objective control strategies that take into account equalization time, equalization losses, and equalization paths will be a key focus for future research.”
(4) Description of the considered problem in section 3 needs more attention.
Reply: The description of the considered problem has been modified.
(5) The simulation results are poor in presentation and analysis
Reply: To better present the simulation results, an additional set of data has been added and a detailed analysis has been conducted. For example:
Figure 9 Equalization simulation results MPC-based, (a) for case one, (b) for case two.
“The balancing simulation results of the two groups show a consistent situation. It is worth noting that in the fixed grouping simulation, since the SOC distribution of the second group does not allow adjacent batteries to be grouped for balancing at the beginning of the balancing process, the increase in balancing time is relatively large compared to the first group. However, both dynamic grouping and MPC-based balancing can achieve grouping of non-adjacent batteries for balancing, so the simulation time difference corresponding to the two groups of SOC is not significant.”
(6) The conclusion needs to be extended to cover the main findings
Reply: The main finding has been added into the conclusion section, as following:
“Compared with the fixed grouping balancing strategy, the dynamic grouping balancing strategy reduces the balancing time by 38.6%, decreases the variance of the battery pack SOC by 20.44% after balancing is completed, and slightly decreases the energy transfer efficiency by 0.36%. Com-pared with the dynamic grouping balancing strategy, the MPC-based battery pack balancing strategy, which selects the optimal energy transfer direction and can dynamically calculate the balancing current, reduces the balancing time by 8.7%, decreases the variance of the battery pack SOC by 37.38% after balancing is completed, and slightly decreases the energy transfer efficiency by 0.22%.”
Author Response File: Author Response.docx
Reviewer 4 Report
Comments and Suggestions for AuthorsThis work proposes a battery equalization control strategy based on model predictive control (MPC) that enhances cell consistency, equalization speed, and reduces energy loss. The paper introduces a dynamic grouping equalization topology that combines reconfigurable circuits with Buck-Boost circuits. This approach addresses key issues in battery management, such as equalization time, energy loss, and cell consistency. The use of MPC ensures the optimal energy transfer direction and equalization current for better battery performance. The strategy, utilizing dynamic grouping and a state observation estimator, outperforms traditional methods by reducing equalization time by 43.93%, decreasing SOC variance by 50.18%, and improving energy transfer efficiency by 0.59%. The paper provides valuable insights; however, some revisions are necessary for further consideration of this manuscript. Below are some comments:
- The paper requires reorganization. The methodologies should be consolidated into a separate section, and the results and discussions should also be grouped together for better clarity and coherence.
- Appropriate references for the equations should be cited.
- More detailed descriptions of the Simulink blocks are necessary to enhance the clarity and comprehensibility of the model. Specifically, explanations of the simulation parameters should be provided.
- Some figures lack the units of the plotted parameters. Please, revise.
- The proposed method is not fully validated in large-scale battery packs. Experimental calibration is recommended to enrich this study. At least, the authors are required to compare their results with existing related practical investigations.
- As this study is simulation-based, more scenarios (at least one extra scenario) with different initial SOC distributions are required to be applied.
- More details about the discussion of the figures are needed, especially for figures 6, 7, 8, and 9.
- It is required to provide a comparison of the equalization speed at different operating frequencies.
- The limitations of the proposed model and future work should be highlighted before the conclusions.
- The conclusions section needs to be revised to clearly summarize the key findings and results of the study. A well-structured conclusion should highlight the main outcomes, their significance, and any potential implications or future directions. The authors are advised to rewrite this section and provide the most important quantitative results as well.
The text should be proofread to minimize typographical and grammatical errors.
Author Response
Reviewer 4：
(1) The paper requires reorganization. The methodologies should be consolidated into a separate section, and the results and discussions should also be grouped together for better clarity and coherence.
Reply: Thanks for your comments. The content of the manuscript has been reorganized and consists of the following four parts: Introduction, Methodologies, The results and discussions, and Conclusions.
(2) Appropriate references for the equations should be cited.
Reply: Appropriate references for the equations have been cited in the revised manuscript.
(3) More detailed descriptions of the Simulink blocks are necessary to enhance the clarity and comprehensibility of the model. Specifically, explanations of the simulation parameters should be provided.
Reply: The simulation parameters have been added to Section 2.7 of the revised manuscript, as following:
“The battery capacity is 20Ah. The maximum equalization current and energy transfer efficiency of the equalizer in the equalization circuit are set to 20A and 0.9 respectively, and the sampling period is Ts=1s, and each PWM cycle is simulated in 25 steps.”
(4) Some figures lack the units of the plotted parameters. Please, revise.
Reply: The figures lack the units of the plotted parameters have been revised, for example:
Figure 5 (a) Root mean square variation of battery pack SOC, (b) Average temperature change of battery pack.
(5) The proposed method is not fully validated in large-scale battery packs. Experimental calibration is recommended to enrich this study. At least, the authors are required to compare their results with existing related practical investigations.
Reply: The effectiveness of the proposed method is verified by comparing the MPC-based balancing with fixed grouping and dynamic grouping.
(6) As this study is simulation-based, more scenarios (at least one extra scenario) with different initial SOC distributions are required to be applied.
Reply: The second scenario different initial SOC distributions was to be applied, and the corresponding simulation results were analyzed, as follows:
Figure 6 Initial SOC distribution of battery pack, (a) Case one, (b) Case two.
(7) More details about the discussion of the figures are needed, especially for figures 6, 7, 8, and 9.
Reply: More details about the discussion of the figures6, 7, 8, and 9 were added into the revised manuscript, for example:
“The balancing simulation results of the two groups show a consistent situation. It is worth noting that in the fixed grouping simulation, since the SOC distribution of the second group does not allow adjacent batteries to be grouped for balancing at the beginning of the balancing process, the increase in balancing time is relatively large compared to the first group. However, both dynamic grouping and MPC-based balancing can achieve grouping of non-adjacent batteries for balancing, so the simulation time difference corresponding to the two groups of SOC is not significant.”
(8) It is required to provide a comparison of the equalization speed at different operating frequencies.
Reply: In our previous work (Energies. 2022, 15, 3263), the impact of switching frequency on the balancing effect was investigated. Therefore, this manuscript selects a medium-sized switching frequency to balance the relationship between balancing speed and losses.
(9) The limitations of the proposed model and future work should be highlighted before the conclusions.
Reply:
(10) The conclusions section needs to be revised to clearly summarize the key findings and results of the study. A well-structured conclusion should highlight the main outcomes, their significance, and any potential implications or future directions. The authors are advised to rewrite this section and provide the most important quantitative results as well.
Reply: The conclusions section has been rewritten, and the most important quantitative results have been provided, as following:
“This work addresses the issues of equalization speed and energy loss in lithium battery management by developing a dynamic group equalization topology and an optimization model focused on optimal energy transfer direction and loss reduction. A dynamic equalization topology, combining reconfigurable and Buck-Boost circuits, reduces equalization times, energy loss, and boosts speed. A MPC-based optimization method controls battery pack SOC and current, achieving optimal energy transfer and current control. Selecting appropriate weight coefficients balances equalization time and energy loss, ensuring faster, more efficient SOC consistency. Compared with the fixed grouping balancing strategy, the dynamic grouping balancing strategy reduces the balancing time by 38.6%, decreases the variance of the battery pack SOC by 20.44% after balancing is completed, and slightly decreases the energy transfer efficiency by 0.36%. Compared with the dynamic grouping balancing strategy, the MPC-based battery pack balancing strategy, which selects the optimal energy transfer direction and can dynamically calculate the balancing current, reduces the balancing time by 8.7%, decreases the variance of the battery pack SOC by 37.38% after balancing is completed, and slightly decreases the energy transfer efficiency by 0.22%. The results show the MPC-based strategy outperforms dynamic grouping in SOC consistency and speed, with slightly lower energy loss. For large battery packs, its speed advantage is more evident.”
(11) The text should be proofread to minimize typographical and grammatical errors.
Reply: The total manuscript has been checked again, and many typographical and grammatical errors have been corrected. Parts of the paper have been rewritten.
Author Response File: Author Response.docx
Round 2
Reviewer 3 Report
Comments and Suggestions for AuthorsNo other comments
Reviewer 4 Report
Comments and Suggestions for AuthorsThe authors have addressed the issues raised from the previous review. Thus, I recommend possible acceptance of this work.
