Power Loss Analysis and a Control Strategy of an Active Cell Balancing System Based on a Bidirectional Flyback Converter

Round 1

Reviewer 1 Report

In this study, the authors discussed the power loss of an active cell balancing system based on the use a bidirectional flyback converter. A control strategy was proposed. The article is well written, clearly presented, and logically structured. I have enjoyed reading the work of the authors and recommend this article for publication minor revision.

My specific comments for the authors to improve the quality of their paper are as follows:

1) Abstract: The abstract should also contain quantitative information to highlight the significance of this research. 

2) Citations: Lumps of references should be avoided. 

3) Line 164: The figure entitled "The power loss of MOSFET under switching" is not labeled. 

4) Please consider combine or delete some figures/tables to reduce their total numbers. If not possible, some figures can be included as supplementary materials.

Author Response

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Reviewer 2 Report

The authors present a study on the efficiency of an active cell balancing circuit based in a bidirectional flyback converter. The subject is interesting and fit the Applied Science Journal topics. However, the document does not present some important information and should be improved before publication.

The following are some questions and recommendations that the authors should address to improve the paper:

1. The authors should introduce in the abstract the target application of the BMS. Consumer electronics? Electric mobility? Renewable energy storage applications?
2. The authors should improve the literature review and highlight the innovation of the proposed work. In the introduction the authors write “So far, many researchers have proposed various kinds of balance circuit architectures [4-12]. Amin employed a passive balancing BMS that combines the power resistor and MOSFET internal resistance as a balancing resistor to save the space [4]. Antonio Manenti proposed a BMS architecture based on cell redundancy [5]. Kyung-Min Lee introduced an LC series resonate circuit as an energy carrier, which transfers the balancing energy directly from the highest charged cell to the lowest charge cell [6]. Ming Liu utilized megahertz multiple-receiver wireless power transfer to achieve battery cell equalization [7]. Federico Baronti described the design and safety verification of a novel charge equalizer with a fully distributed architecture, which not only perfectly fits the typical partitioning of a battery into modules, but also achieves the system with a simple circuit structure [8]. Federico Baronti also designed a high-efficiency digitally controlled charge equalizer for series connected cells based on switching converter and super-capacitor [9]. Wangxin Huang presented an energy sharing state-of-charge(SOC) balancing control scheme based on a distributed BMS architecture where the dc bus voltage regulation system and the cell balancing system are combined into a single system [10]. Mohammad Abdul Hannan achieved cell-balancing by a bidirectional flyback dc-dc converter [11]. Sang-Won LEE raised a modularized design of active cell-to-cell/module-to-module charge equalizer [12].” However, this is just a list of existing works. The authors should perform a critical analysis of each one of these woks highlighting the advantages and disadvantages of the proposed BMS systems, and comparing them to the solution adopted in this work.
3. In section 2 “Hardware description of the proposed cell balancing system”, before the description of the implemented system the author should present the system requirements. What are the main specifications wanted for the BMS. What is the desirable balancing current? how many cells needs to be balanced? What is the maximum/minimum cell voltages? What is the target efficiency? Is the developed system a full scale or reduced scale prototype? Without the system specification it is not possible to evaluate the results obtained.

4. Before the introduction of the equations used to calculate the losses the authors should present the main voltage and current waveforms for one or two switching periods in order to facilitate the understanding of the calculations.
5. The authors present all the loss calculation methodologies prior to refer that the converter is working in the continuous current mode (CCM).
6. The authors should introduce all the variables used in the equations. For example, in equation 12, the authors use the Ve, that seems to be effective volume of the core, without presenting it. Thera are many variables without description.
7. In table 2, beyond the main characteristics the authors should present the models of the main circuit components, MOSFETs, Gate Drivers, differential voltage sensors, photoMOS Relays, etc.
8. The authors should describe how the experimental results are obtained and the used equipment.
9. The authors should clarify if the power used to feed the electronic circuits is considered in the efficiency determination.
10. The authors should compare the achieved efficiency with other works in the literature.
11. The authors should present the flyback main voltage and current waveforms in the cell-to-pack and pack-to-cell operating modes, highlighting the synchronous rectification functionality.
12. Why the measured battery voltages present so big oscillations?
13. The authors should clarify if the balancing times are in accordance with the expectations and if the system can be used with used with true microgrid storage batteries with 100 Ah or 200 Ah or needs to be oversized.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

The paper presents “The Power Loss Analysis and a Control Strategy of an Active Cell Balancing System Based on a Bidirectional Flyback Converter”. The addressed topic is interesting, however, not well framed with the scope of the journal, since it is more aligned with, for instance, the MDPI electronics.

1. A structure based on the flyback converter is used for balancing the voltage across a set of batteries. Several papers can be found in the literature showing the application of this converter for this purposed, therefore, the contribution of this paper is questionable.
2. The developed prototype is prepared to balance six batteries?
3. A photo of the batteries and the laboratory setup is welcome as complement of figure 8.
4. How the efficiency was measured?
5. In figure 10 why the 6 voltages are not converging to the same value? A maximum error of 100 mV was achieved. What is the practical meaning of this value? It is considerable? It will affect the performance of the battery pack? Please, clarify.
6. In figures 10, 11 and 12 why such variation of voltages in the measurements?
7. A space must be added between the value and the unit, for instance, 1 A and not 1A.
8. The reference list is acceptable.

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

It is an intersting work, well written.

The idea of using a single switching converter and a switch array for battery balancing management is not completely new. Nevertheless the authors implemented it using an intreresting approach and provide clear explanation of both design and experimental results.

I recommend publication.

Author Response

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Round 2

Reviewer 2 Report

The authors improved the paper significantly, however, important information is missing.

The following are recommendations that the authors should address to improve the paper:

1. In table I, the authors should clarify if the values of balancing current presented refer to the low voltage side or high voltage side.
2. In table 2, beyond the main characteristics the authors should present the models (references, part numbers, etc.) of the main circuit components, MOSFETs, Gate Drivers, differential voltage sensors, photoMOS Relays, etc. The authors present the value of the Rds(on), however these values change with the temperature, and with Vgs. The datasheet of the MOSFET is the best document for readers to confirm the selected values and even evaluate the circuit under different operating conditions.
3. In the experimental results section, the authors should introduce a figure similar to figure 6, with experimental measurements with the developed prototype.

Author Response

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Reviewer 3 Report

Dear Authros. All of my previous comments were clarified. Thank you.

Round 3

Reviewer 2 Report

The authors complied with all my recommendations. I have no further observations. Congratulations to authors for their work.