A Buck-Boost Converter with Extended Duty-Cycle Range in the Buck Voltage Region for Renewable Energy Sources

Round 1

Reviewer 1 Report

1. The overall design of the topology is simple which is good in terms of the practical applications. Too many components increase the complexity of the system.

2. Add some practical applications of such a converter with proper references.

3. Add the power loss analysis.

4. The introduction section can be updated using latest DC/DC converter topologies like  A High Voltage Gain Multi-Stage DC-DC Boost Converter with Reduced Voltage Stress, A new family of high gain boost DC-DC converters with reduced switch voltage stress for renewable energy sources, etc. Design of components and power loss analysis can also be added as given in these papers.

5. Improve the comparative study.  Use latest topologies like A high gain noninverting DC–DC converter with low voltage stress for industrial applications for comparison.

6. Add some results with a change in load or source.

7. Add the experimental setup diagram.

Author Response

First of all, we would like to take this opportunity to sincerely thank to the reviewers and the editorial board for their valuable remarks and comments on the manuscript. Remarks and comments suggested by reviewers have been applied in the manuscript and responses to reviewers are detailed here.

Author’s Response to Comments of the Reviewer#1

1) The overall design of the topology is simple which is good in terms of the practical applications. Too many components increase the complexity of the system.

Response to Reviewer Comment 1:

Thank you very much for your analysis, comments and the observations.

 

2) Add some practical applications of such a converter with proper references.

Response to Reviewer Comment 2:

Thank you very much for your very pertinent question. The main application for this converter is to be used in PV generators. One problem that exists in PV generators is that the output voltage of the PV panel is that the voltage presents variations since it is function of the irradiance. So, for example when the PV panel is shadowed its power and voltage will both drop, therefore the panel DC-DC converter must change the voltage gain if the output voltage needs to be maintained. This will happen in grid isolated panels where, to output a constant voltage, the panel is power derated, e.g. not operated at the maximum power point. Thus, the paper proposed converter was designed to normally operate in the Buck region. When shadowing occurs, the PV panel voltage drop enforces the converter to operate in the Boost region, as shown in the paper simulation and experimental results.

In order to clarify this aspect, we introduce new sentences in the introduction and in section 2, as well as, references about the use of this kind of converter in PV applications subject to shadowing.

 

3) Add the power loss analysis.

Response to Reviewer Comment 3:

This question is very pertinent. Indeed, this is a very important issue that was not introduced in the manuscript. Thus, we implemented extra experimental tests in order to determine the efficiency and the power-loss breakdown of the converter. The results can be seen in a new table 2 and in Fig. 26. Figure 27 shows the converter power-loss breakdown.

 

4) The introduction section can be updated using latest DC/DC converter topologies like A High Voltage Gain Multi-Stage DC-DC Boost Converter with Reduced Voltage Stress, A new family of high gain boost DC-DC converters with reduced switch voltage stress for renewable energy sources, etc. Design of components and power loss analysis can also be added as given in these papers.

Response to Reviewer Comment 4:

We clearly understand the concern of the reviewer. Indeed, you are right. Thus, we improved the introduction section taking into consideration the latest DC/DC converter topologies. Besides that we have also added the power loss analysis.

 

5) Improve the comparative study. Use latest topologies like A high gain noninverting DC–DC converter with low voltage stress for industrial applications for comparison.

Response to Reviewer Comment 5:

Thank you very much for your suggestion. We will introduce in the paper a new section 3.3 with a comparative study. Besides, table 1 also compares efficiencies of DC-DC buck-boost converters with similar topologies.

 

6) Add some results with a change in load or source.

Response to Reviewer Comment 6:

Indeed, this part needed to be improved. Thus, we introduce a new transient test related to PV generators. One important particular aspect is cloud shadowing of PV panels that originates a temporary reduction of the solar irradiance, and as a consequence a reduction of the panel voltage and power. Thus, tests with a suddenly drop voltage in the input source (PV) and recover after some time were made (new figs. 13, 14, 24 and 25). In order to maintain the same output voltage the duty cycle was changed to mitigate the converter input voltage variations. During the shadowing input voltage disturbances the converter operation changed from the buck to the boost mode and returned to the buck mode after the shadowing vanishes.

 

7) Add the experimental setup diagram.

Response to Reviewer Comment 7:

Thank you very much for mentioning this important aspect. Thus, we introduced in the manuscript the laboratory experimental setup used to obtain the experimental results.

Reviewer 2 Report

The paper topic is interesting. But there is no compare between conventional or exist techniques and the proposed one. You should provide Comparative study to address the powerful and flexibility of the suggested technique. Figure 1 must be cited.

Author Response

First of all, we would like to take this opportunity to sincerely thank to the reviewers and the editorial board for their valuable remarks and comments on the manuscript. Remarks and comments suggested by reviewers have been applied in the manuscript and responses to reviewers are detailed here.

 

Author’s Response to Comments of the Reviewer#2

The paper topic is interesting. But there is no compare between conventional or exist techniques and the proposed one. You should provide Comparative study to address the powerful and flexibility of the suggested technique. Figure 1 must be cited.

Response to Reviewer Comment 1:

Thank you very much for your analysis, comments and the observations. Regarding the comparative study you pointed very well an important aspect. Indeed, there is lack of this important study. Thus, we introduce a new section 3.3 in which we present a comparative study, together with table 1 for efficiency comparisons. We also cited in the text Fig. 1, as well as, we introduce a reference regarding this topology.

 

Reviewer 3 Report

The manuscript presents research related to improving the characteristics of power electronic devices based on synthesis of new circuit configurations. The advantages of the proposed new control strategy are proven through modeling and experimental results.

In general, the work is on a current topic, has good potential for development, and my overall assessment is positive. My main observations and comments are as follows:

- it would be useful to make a comparison with the classic DC/DC converter in terms of load on the semiconductor devices and especially in terms of efficiency and possibilities for linearization of the transmission characteristic;

- it would be useful in addition to the advantages in the conclusion section for the authors to comment on the disadvantages of the proposed new circuit configuration. In this way, a complete picture of its qualities, capabilities and application limitations will be obtained;

- as notations and abbreviations are used in the text, I recommend authors to add a list of used notations at the beginning or end of the manuscript.

Author Response

First of all, we would like to take this opportunity to sincerely thank to the reviewers and the editorial board for their valuable remarks and comments on the manuscript. Remarks and comments suggested by reviewers have been applied in the manuscript and responses to reviewers are detailed here.

 

Author’s Response to Comments of The Reviewer #3

The manuscript presents research related to improving the characteristics of power electronic devices based on synthesis of new circuit configurations. The advantages of the proposed new control strategy are proven through modeling and experimental results.

In general, the work is on a current topic, has good potential for development, and my overall assessment is positive. My main observations and comments are as follows:

Response to Reviewer Comment:

Thank you very much for your analysis, comments and the observations.

 

1) It would be useful to make a comparison with the classic DC/DC converter in terms of load on the semiconductor devices and especially in terms of efficiency and possibilities for linearization of the transmission characteristic.

Response to Reviewer Comment 1:

You focused in very important aspects, that indeed we do not introduced in the manuscript. In the revised paper we introduced several improvements regarding several of these aspects. We introduce a comparative study between this topology and existing ones with similar characteristics. Besides that, in another comparative study we present the efficiencies of the proposed topology compared to converters such as the Cuk, SEPIK, and classic buck-boost. Finally, we introduced a study about the power-loss breakdown of the converter. We thank the reviewer for suggesting the study of the linearization of the transmission characteristic, which is part of the stability studies to be made in further work, as stated in previous answers to reviewers.

 

2) It would be useful in addition to the advantages in the conclusion section for the authors to comment on the disadvantages of the proposed new circuit configuration. In this way, a complete picture of its qualities, capabilities and application limitations will be obtained.

Response to Reviewer Comment 2:

We fully agree with your important comment. In reality, as in any converter, this one also presents disadvantages. One of the disadvantages is that the efficiency is in general slightly lower than the efficiency of classical converters with buck-boost characteristics. Another aspect is that, although under the theoretical point of view the voltage gain can be infinite (for a duty-cycle of one), in practice due to the non-idealities of the converter reactive components and semiconductors the boost gain is limited, like in many boost converters. Thus, compared to other topologies our proposal trades maximum boost gain for higher buck operating range. In the manuscript these aspects were clarified.

 

3) As notations and abbreviations are used in the text, I recommend authors to add a list of used notations at the beginning or end of the manuscript.

Response to Reviewer Comment 3:

Thank you very much for your suggestion. A nomenclature will be introduced in the paper.

 

Reviewer 4 Report

Here are my comments regarding the proposed buck-boost converter. Some are minor cosmetic while some are more fundamental requiring more clarification:

- There are several grammar errors in the paper. Please Proofread.

- Capital letters are used in many unnecessary cases (e.g. Buck-Boost). Please proofread.

- Line 47: "To increase the output voltage a step-up converter with duty-cycle close to 1 can be used". For an ideal classic boost converter, D=1, theoretically leads to infinite voltage. This statement needs to be modified.

- Most of the literature review is spent on discussing different boost technologies. The main contribution of this paper is extending the buck region of a buck-boost converter (from 0-0.5 to 0-0.6). The need for such extension is only discussed in the last paragraph of the introduction without any relevant references. 

- Line 76: "Actually, in many of these applications regular converters are inadequate, since the specified range of input voltage and/or output voltages requires a wide range of conversion ratios." Examples of such cases should be presented with proper literature review and analysis.

- For the operation mode 1, please provide a solid proof that D1 will be reverse biased based on different duty cycles and different inductor and capacitor values and initial conditions .

- The DCM analysis is missing. Is this buck-boost converter to be used only in CCM mode?

- Equation 8 uses voltage ripple to calculate the capacitance value. This is only true for ideal capacitors. In real capacitors, the majority of voltage ripple is due to ESR (the internal resistance). The capacitive voltage drop due to charge or discharge is usually much smaller than resistive voltage drop.

- Line 167: "The voltage rating of the diode D1 is equal to the voltage across the power switch Sw in the OFF state. While the voltage ratings of both diodes (D2 and D3) are half the voltage of the power switch, Sw." These sentences are not trivial. Please provide more discussion.

- What is I0 in equation 10 and how was this equation derived?

- Units need to be separated from numbers by a space, e.g. 100 V

- One of the concerns for buck-boost converters is their stability in open- and closed-loop applications. No frequency-response analysis is provided in this paper. Please derive the transfer function of this system to find the stability region of your proposed converter based on different duty-cycle values.

- A picture of the experimental setup as well as the equipment's detailed data should be provided.

- Experimental results agree with the simulation results. Were the non-ideal characteristics of the switch, diodes, inductors, and capacitors (such as internal resistance, reverse recovery, forward voltage drop, and switching rise/fall times) included in the simulation? The analysis provided was limited to the ideal case. 

- Application of this work is not clear? What is the main benefit or need for increasing the buck range of a buck-boost converter? 

- The inductor and capacitor values and their corresponding physical size and price should be compared with other buck-boost converters such as the classic buck-boost and other models such as SEPIC, Cuk, and flyback.

- THD and losses of this converter should be calculated and compared with other topologies.

- Transient behavior of the circuit is shown in one case. Please provide the general formulation for damping factor and natural frequency of the response to have more insight about the settling time and overshoot values for different duty cycles and inductor/capacitor/load values. 

 

Author Response

First of all, we would like to take this opportunity to sincerely thank to the reviewers and the editorial board for their valuable remarks and comments on the manuscript. Remarks and comments suggested by reviewers have been applied in the manuscript and responses to reviewers are detailed here.

Author’s Response to Comments of The Reviewer #4

Here are my comments regarding the proposed buck-boost converter. Some are minor cosmetic while some are more fundamental requiring more clarification:

1) There are several grammar errors in the paper. Please Proofread.

Response to Reviewer Comment 1:

Thank you very much for your analysis, comments, and the observations. We appreciate the suggestion of the reviewer for punctuations marks. We reviewed the manuscript in order to correct grammar errors.

 

2) Capital letters are used in many unnecessary cases (e.g. Buck-Boost). Please proofread.

Response to Reviewer Comment 2:

Thank you very much for your analysis, we agree with the reviewer. We appreciate and follow the suggestion of the reviewer for capital letters.

 

3) Line 47: "To increase the output voltage a step-up converter with duty-cycle close to 1 can be used". For an ideal classic boost converter, D=1, theoretically leads to infinite voltage. This statement needs to be modified.

Response to Reviewer Comment 3:

Thank you very much for noticing this lapse. Indeed, you are completely right. The part of the text “with duty-cycle close to 1” does not make sense. Thus, we delete that part. The sentence is changed to “To increase the output voltage a step-up converter can be used, such as the classic DC-DC boost converter [15,16].”

 

4) Most of the literature review is spent on discussing different boost technologies. The main contribution of this paper is extending the buck region of a buck-boost converter (from 0-0.5 to 0-0.6). The need for such extension is only discussed in the last paragraph of the introduction without any relevant references.

Response to Reviewer Comment 4:

You are completely right. Indeed, this discussion was practically not made. In this way, we introduce in the introduction a much more complete discussion and new references regarding this aspect.

 

5) Line 76: "Actually, in many of these applications regular converters are inadequate, since the specified range of input voltage and/or output voltages requires a wide range of conversion ratios." Examples of such cases should be presented with proper literature review and analysis.

Response to Reviewer Comment 5:

Thanks for the suggestion. Examples are now included and discussed in the introduction, where it is written:

“Many new topologies with buck-boost characteristics have been proposed also. Usually, the topologies are developed to change the range of the buck and boost regions [38, 40]. The generality of the proposals were engineered to increase the boost region and to obtain high boost gains. However, in those topologies the buck region is limited to a very small range of duty-cycles. In fact, practically there are no works regarding the increase of the buck region. Nevertheless, the increase of the buck region can be very interesting to overcome shadowing limitations in the series connection of PV panels (PV strings), where each panel has its own micro DC-DC converter for maximum power point tracking of each PV, or when the DC output voltage needs to be constant in grid isolated PV panels. In PV generators the output voltage of the PV panel is a function of the solar irradiance. This irradiance will deeply drop when hard shadows cover some PV panels of the series connected string, leading to significant output power drops in each shadowed PV. Being series connected, as the series current of the string must be the same, the only way to harvest the highly reduced power produced by a shadowed panel is to enforce the micro DC-DC converter to operate in the buck region. Thus, the here proposed micro DC-DC converter may be planned to normally operate in the limit of the buck region, near the boost region. When shadowing of some PV panels occurs, the shadowed panes go into the lower end of the buck region while the non-shadowed PV panels of the series string may operate in the boost region. However, only few works have addressed this issue [41-43]. The solution presented in these works, is characterized by complex circuits.”

 

6) For the operation mode 1, please provide a solid proof that D1 will be reverse biased based on different duty cycles and different inductor and capacitor values and initial conditions.

Response to Reviewer Comment 6:

- Thank you very much for this question. In initial conditions in which the circuit is considered with capacitor voltages and inductors at zero, the cathode of the diode D1 is connected at the positive terminal of the input source. So, at the limit the diode supports an anode cathode voltage that is the input voltage source with the minus signal. When the circuit is in operation, the diode D1 is reverse biased when the switch S_w is ON. In this condition, the anode to cathode voltage applied to the diode is the sum of the input source voltage with the capacitor voltage C1 (-Vi-Vc1). The voltage in capacitor C1 never inverts its voltage polarity since it is charged by the inductor L1 and in this case the negative voltage of this capacitor terminal is connected to the anode of diode D1. Even in the situation that eventually the current in inductor L1 becomes zero, if the inductor L2 carries a current, then the capacitor still maintains is discharging mode. If the capacitor reverses its polarity, the diode D3 will become forward biased, and because of that the capacitor will be disconnected from inductor L2. Simulations and experimental results confirm that D1 is reverse biased when the switch S_w is ON. A clarification of this aspect has been introduced in the manuscript in part 2, Operation mode 1, S_w is driven ON.

 

7) The DCM analysis is missing. Is this buck-boost converter to be used only in CCM mode?

Response to Reviewer Comment 7:

- You are completely right, the converter is needed to operate only in CCM. The proposed converter main application is in PV panels, which must be operated in the maximum power point, at very small deviation (ripple) around the maximum power point. To minimize the switching ripple, for a given set of inductors and capacitors most DC-DC converters must operate in CCM. Furthermore the extended duty-cycle range of the proposed convert may also extend the CCM operation, being of very little interest the operating the converter in DCM.  

 

8) Equation 8 uses voltage ripple to calculate the capacitance value. This is only true for ideal capacitors. In real capacitors, the majority of voltage ripple is due to ESR (the internal resistance). The capacitive voltage drop due to charge or discharge is usually much smaller than resistive voltage drop.

Response to Reviewer Comment 8:

- You are completely right. Our idea to use the voltage ripple comes from the consideration of ideal devices (zero ESR). In the paper we have included a sentence emphasizing the “small enough ESR”. Small enough ESR capacitors should be used to avoid much bigger capacitances, and therefore avoid high short-circuit energy, while still having output voltage ripple due to the increased ESR of big capacitors. If needed the ESR can be considered in the capacitor design the result leading to bigger capacitances.

 

9) Line 167: "The voltage rating of the diode D1 is equal to the voltage across the power switch Sw in the OFF state. While the voltage ratings of both diodes (D2 and D3) are half the voltage of the power switch, Sw." These sentences are not trivial. Please provide more discussion.

Response to Reviewer Comment 9:

Thank you very much for noticing this aspect that was not well explained. Regarding diode D1, the voltage rating is equal to the voltage across the power switch Sw in the OFF mode since the voltage across the switch and diode D1 is given by the same mesh given by input voltage source V1, switch Sw, capacitor C1 and diode D1). This analysis can be better explained through Fig. 3 a) and 3 b). Regarding the voltage ratings of the diodes D2 and D3, they were wrongly written in the paper. Thank you very much for noticing this lapse. In reality, the voltage rating of the diode D2 is given by the input source voltage Vi. From figure 3 b), it is seen that when D1 and D3 are ON, the input source voltage is directly applied to D2. Regarding the voltage rating of the diode D3, it is function of the capacitor C1 voltage since when it is in OFF mode (Fig. 3 a)) due to the ON mode of the transistor, capacitor C1 is directly applied to this diode. The clarification of this subject is now introduced in the manuscript in section 3.2.

 

10) What is I0 in equation 10 and how was this equation derived?

Response to Reviewer Comment 10:

Indeed, this was not clear. Io represents the load current. The determination of Io can be obtained from the nominal power of the converter and operation voltage value of the output DC/DC converter, supposing a conservative converter. In the manuscript we introduce a clarification about this aspect after eq. (11).

 

11) Units need to be separated from numbers by a space, e.g. 100 V

Response to Reviewer Comment 11:

Thank you very much for your analysis. In the paper we will separate the units from numbers by a space.

 

12) One of the concerns for buck-boost converters is their stability in open- and closed-loop applications. No frequency-response analysis is provided in this paper. Please derive the transfer function of this system to find the stability region of your proposed converter based on different duty-cycle values.

Response to Reviewer Comment 12:

We thank the reviewer for the suggestion. All the presented simulation and experimental results in steady-state, in transient state, and in perturbed operation show that the converter is open-loop and closed-loop stable. To illustrate the potential of the new proposed topology we think the presented results are demonstrative and, as a first paper in the topology, the stability study would not significantly add to the already presented study of the operating modes, inductor and capacitor sizing, semiconductor ratings, the comparison to similar topologies and efficiency measurements. Therefore, we appreciate the reviewer suggestion as a good future work, that we intend to carry on to continue the characterization of this new proposed topology.

 

13) A picture of the experimental setup as well as the equipment's detailed data should be provided.

Response to Reviewer Comment 13:

We fully agree with this aspect to improve the quality of the manuscript. We introduced a photograph of the laboratory prototype and workbench.

 

14) Experimental results agree with the simulation results. Were the non-ideal characteristics of the switch, diodes, inductors, and capacitors (such as internal resistance, reverse recovery, forward voltage drop, and switching rise/fall times) included in the simulation? The analysis provided was limited to the ideal case.

Response to Reviewer Comment 14:

- Thank you to point out this question. Although the theoretical analysis has assumed ideal components, the simulation study has considered some non-ideal characteristics of the components, such as resistive losses, forward voltage drops and switching losses. The simulation was implemented in the program Matlab/Simulink and the Power Systems Toolbox in which each component can be modeled taking into account some non-ideal characteristics, which was the case. Although the simulation results are not completely equal to the experimental results, we think they can be considered very similar.

 

15) Application of this work is not clear? What is the main benefit or need for increasing the buck range of a buck-boost converter? 

Response to Reviewer Comment 15:

Thank you very much for your very pertinent question. The main application for this converter is to be used in PV generators. As said in previous responses, in PV generators the output voltage and output power show important disturbances when the PV panel is shaded (by clouds for example). Therefore, the shadowed PV panel voltage drop needs a converter able to change the voltage gain from the buck region to the boost region. The proposed converter was designed to have an extended buck voltage range of duty-cycles, so that the converter can operate normally in the extended buck region and quickly go the boost region when the PV panel is shadowed, in the case a constant output voltage is needed. Another application is as the maximum power point tracking DC-DC converter for each PV panel of a series connected string so that when shadowed the converter can be operated has a boost or as a buck to ensure that the string series current is the same in all converters.

In order to clarify this aspect, we introduce a clarification in the introduction and in section 2, as well as, references about the use of this kind of converter in PV applications subject to shadows.

 

16) The inductor and capacitor values and their corresponding physical size and price should be compared with other buck-boost converters such as the classic buck-boost and other models such as SEPIC, Cuk, and flyback.

Response to Reviewer Comment 16:

Thank you very much for this question. Under the point of view of the design of the components, this converter has components sized identically to the corresponding ones in the Cuk converter. To clarify this issue we introduce a comment in the manuscript.

 

17) THD and losses of this converter should be calculated and compared with other topologies.

Response to Reviewer Comment 17:

You are completely right. Aspects not included in the manuscript were the losses and efficiency of the converter. In the revised paper we introduce the efficiency, efficiency comparisons and the converter power-loss breakdown. Regarding the efficiency comparisons, given the difficulty to rapidly implement more complex topologies, we did a study considering low component count, well known topologies such as the Cuk, SEPIK, classic buck-boost and the here proposed converter. Regarding the THD, we do not understand which is the THD that is referred. Usually, we determine the THD in the case of inverters, but for DC/DC converter in DC quantities the ripple is the factor used in the paper to size the reactive elements. We have analyzed several papers about DC-DC converters, and we did not saw tests about THD.

 

18) Transient behavior of the circuit is shown in one case. Please provide the general formulation for damping factor and natural frequency of the response to have more insight about the settling time and overshoot values for different duty cycles and inductor/capacitor/load values.

Response to Reviewer Comment 18:

- Indeed, the transient behavior was only given for one case. In the revised version, we introduce several new tests, typical of shadowing in PV panels. Thus, we introduce one test in which there is a suddenly drop of the input voltage and we have shown the converter is able to recover from that voltage drop, going into the boost mode. The duty cycles of the converter are adjusted to maintain a constant output voltage, as usually required in grid isolated PV generators. We appreciate the reviewer suggestion as a good topic for future work, and as said we are going to carry on to determine open-loop and closed-loop damping factors and resonant frequency to completely characterize the new topology.

 

Round 2

Reviewer 2 Report

Thank you for addressing the suggested comments.

Author Response

We would like to sincerely thank the reviewer once again, for their valuable observations and comments on the manuscript.

Reviewer 3 Report

The authors revised the manuscript according to my comments and recommendations. I have no further comments.

Author Response

We would like to sincerely thank the reviewer once again, for their valuable observations and comments on the manuscript.

Reviewer 4 Report

The authors have answered most of my questions clearly. Thank you.

 

I have some more comments:

1. Please provide the values of the equipment in your experimental setup. In Figure 15, can you please provide labels for the parts and equipment?

2. Figure 27 could be smaller. Please add label for each sector of the pi chart.

3.  For the loss calculation section, please list the losses that was considered (switching, conduction).

4. The conclusion section could be more concise.

5. There are many grammar errors in the paper. Proofreading by a professional editor is recommended.

Some grammar errors.

e,g, "To analyze in detail the efficiency of the converter efficiency"

Mosfet -> MOSFET

"From these results it is seen that the losses associate to the power semiconductors are dominant."

"it is possible to verify that the D1 reverse voltage, in absolute value, double the corresponding value in diodes D2 and D3."

 

Author Response

Firstly, we would like to sincerely thank the reviewer, once again, for their valuable observations and comments on the manuscript in this second round. The observations and comments suggested by the reviewer have been applied to the manuscript, and the responses to the reviewer have also been presented in detail.

 

1. Please provide the values of the equipment in your experimental setup. In Figure 15, can you please provide labels for the parts and equipment?

Response to Reviewer Comment 1:

Thank you very much for your very pertinent question/suggestion. Thus, we introduced in figure 15 of the laboratory experimental setup, the labels to identify the parts of the equipment used.

 

2. Figure 27 could be smaller. Please add label for each sector of the pi chart.

Response to Reviewer Comment 2:

Thank you very much for your suggestion. You are right, the graph of the figure can be smaller. Thus, we have reduced the size of the graph in figure 27 and put the label in each sector of the chart.

 

3. For the loss calculation section, please list the losses that was considered (switching, conduction).

Response to Reviewer Comment 3:

Thank you very much for your suggestion. We will mention in the paper the losses that were considered in the calculation.

 

4. The conclusion section could be more concise.

Response to Reviewer Comment 4:

We thank the reviewer for the suggestion. We review some aspects of the conclusion section in order to make it more succinct.

 

5. There are many grammar errors in the paper. Proofreading by a professional editor is recommended.

Response to Reviewer Comment 5:

Thank you very much for your analysis, comments, and observations. We appreciate the suggestion of the reviewer for punctuation marks. We reviewed the manuscript in order to correct grammar errors.