MPPT Circuit Using Time Exponential Rate Perturbation and Observation for Enhanced Tracking Efficiency for a Wide Resistance Range of Thermoelectric Generator

Round 1

Reviewer 1 Report

This manuscript reported a maximum power point tracking (MPPT) circuit to extract the maximum electrical energy from thermoelectric generators. By using the time exponential rate P&O, the MPPT circuit observes the power change by comparing PMOS on-time and perturbs the power by adjusting NMOS on-time exponentially, showing an enhanced tracking efficiency from 98.9% to 99.5% for a wide range of TEG. The results are promising, and I will recommend the publication of this manuscript after the authors can address the following concerns.

1. Although the simulation results using a voltage source are attractive, but with real TEGs, are there any difficulties the authors foresee? Any unideal factors may degrade the actual performance of the circuit?
2. There are two figures in Figure 10, please denote them more properly.
3. How to obtain the tracking efficiency should be explained a bit more.
4. How is the adaptability of the proposed circuit when the characteristics of TEG are out of the modeling range (50-400 mV, 1-12 Ω)?
5. Please double check the main text carefully, since there are some typos and many “Error! Reference source not found.” from time to time.

Author Response

Dear Reviewers:

Thank you for your letter and for the reviewers’ comments concerning our manuscript entitled “MPPT Circuit Using Time Exponential Rate Perturbation and Observation for Enhanced Tracking Efficiency for a Wide Resistance Range of Thermoelectric Generator” ( Manuscript ID: applsci-1207241 ). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made corrections which we hope meet with approval. The revised portions are highlighted by using the "Track Changes" function in Microsoft Word. We had revised our manuscript carefully following the reviewers' comments using point-by-point responses.

Once again, thank you very much for your comments and suggestions.

Thank you and best regards.

Yours sincerely,

Jie Miao

Responds to the reviewer’s comments:

Review 1:

This manuscript reported a maximum power point tracking (MPPT) circuit to extract the maximum electrical energy from thermoelectric generators. By using the time exponential rate P&O, the MPPT circuit observes the power change by comparing PMOS on-time and perturbs the power by adjusting NMOS on-time exponentially, showing an enhanced tracking efficiency from 98.9% to 99.5% for a wide range of TEG. The results are promising, and I will recommend the publication of this manuscript after the authors can address the following concerns.

1. Although the simulation results using a voltage source are attractive, but with real TEGs, are there any difficulties the authors foresee? Any unideal factors may degrade the actual performance of the circuit?

Owing to the limitation of objective condition and the reason of economy, the chip has not taped out to the foundry. To simplify the simulation, a voltage source and a resistor are connected in series to mimic the TEG. According to Reference [7], the internal resistance of the TEG hardly changes at room temperature. To establish a well-controlled experimental environment, some researchers [20,21] also used a power source and a resistor to emulate the TEG in the experiment.

2. There are two figures in Figure 10, please denote them more properly.

Thanks for your suggestion, and we have added an explanation, which is “There is an enlarged view of the simulation results at the bottom of the figure.” in Line 199.

3. How to obtain the tracking efficiency should be explained a bit more.

Thanks for your comment. The explanation of how to obtain the tracking efficiency during simulation has been added in Section 4 in Line 205, which is “The input power of the DC-DC converter is obtained by the calculator module embedded in Spectre. The input power is divided by the ideal maximum power output of the TEG to obtain the tracking efficiency of the proposed MPPT circuit.”

And we also explained the tracking efficiency in Section 2 in Line 96, which is “tracking efficiency, which is the ratio of input power to ideal maximum input power”.

4. How is the adaptability of the proposed circuit when the characteristics of TEG are out of the modeling range (50-400 mV, 1-12 Ω)?

The proposed circuit is specifically designed for the modeling range (50-400 mV, 1-12 Ω), which is the application condition of most wearable devices. When the output voltage of the TEG is less than 50mV, the voltage is too low to startup the circuit.

5. Please double-check the main text carefully, since there are some typos and many “Error! Reference source not found.” from time to time.

We apologized for those typos and revised the errors. These “Error! Reference source not found.” cannot quote the correct figure number when the manuscript is uploaded.

Review 2:

The paper presents a method - time exponential rate perturbation and observation P&O to extract maximum power from TEG. The model was only validated by simulation and compared with other methods from specialized literature. This method also has to be validated experimentally. The authors must consider some TEGs for this (perhaps different materials).

 Thank you for the reviewer's suggestions to our manuscript. We acknowledge the positive comments, which are valuable for improving the quality of our manuscript. Owing to the limitation of objective condition and the reason of economy, the chip has not taped out to the foundry. Taking into account the different materials of TEGs, the proposed circuit is designed for a wide TEG internal resistance range (1-12 Ω).

Some comments:

1. Please avoid “etc”

Thanks for your suggestion. We have added more explanation, which is “rich thermal energy, no pollution, and no noise”, to replace the word “etc” in the abstract in Line 14.

2. Please explain PMOS, NMOS, CMOS

Thank you to point out this error. We have added the full names of those abbreviations when PMOS, NNOS, and CMOS first appear in the abstract and main text.

3. Please don't use lumpy references, such as [1-6] and others.

We only used lumpy references ([1-6] and [7-12]) in the introduction. Those references are cited to explain that energy harvesting technology and thermoelectric generator are getting more and more attention in recent years.

4. L36 Please corrects the error. (there are also others)

We apologized for those typos and revised the errors. These “Error! Reference source not found.” cannot quote the correct figure number when the manuscript is uploaded.

5. The introduction is incomplete and vague. Please rewrite it so that the reader can better understand the state of the art and the novelty of your work.

Thanks for this good comment. We have added Figure 2 and some sentences in Line 55 to explain the FOCV technique more clearly. And we also have rewritten the last paragraph in the introduction to explain the organization of the paper more clearly.

6. L90 Please explain better Eq.8

Eq.8 is derived from Eq.7. We have explained the constant ε more clearly, which is “where ε is any constant in the range of 0 to 1” in Line 98. To achieve a coherent text, the sentence “By analyzing Eq. (7) and Eq. (8), we find that…” has been added in Line 99 in the revised manuscript. Thanks for your comment.

Reviewer 2 Report

The paper presents a method - time exponential rate perturbation and observation P&O to extract maximum power from TEG. The model was only validated by simulation and compared with other methods from specialized literature. This method also has to be validated experimentally. The authors must consider some TEGs for this (perhaps different materials).

Some comments:

Please avoid “etc”

Please explain PMOS, NMOS, CMOS

Please don't use lumpy references, such as [1-6] and others.

L36 Please corrects the error. (there are also others)

The introduction is incomplete and vague. Please rewrite it so that the reader can better understand the state of the art and the novelty of your work.

L90 Please explain better Eq.8

Author Response

Dear Reviewers:

Thank you for your letter and for the reviewers’ comments concerning our manuscript entitled “MPPT Circuit Using Time Exponential Rate Perturbation and Observation for Enhanced Tracking Efficiency for a Wide Resistance Range of Thermoelectric Generator” ( Manuscript ID: applsci-1207241 ). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made corrections which we hope meet with approval. The revised portions are highlighted by using the "Track Changes" function in Microsoft Word. We had revised our manuscript carefully following the reviewers' comments using point-by-point responses.

Once again, thank you very much for your comments and suggestions.

Thank you and best regards.

Yours sincerely,

Jie Miao

Responds to the reviewer’s comments:

Review 1:

This manuscript reported a maximum power point tracking (MPPT) circuit to extract the maximum electrical energy from thermoelectric generators. By using the time exponential rate P&O, the MPPT circuit observes the power change by comparing PMOS on-time and perturbs the power by adjusting NMOS on-time exponentially, showing an enhanced tracking efficiency from 98.9% to 99.5% for a wide range of TEG. The results are promising, and I will recommend the publication of this manuscript after the authors can address the following concerns.

1. Although the simulation results using a voltage source are attractive, but with real TEGs, are there any difficulties the authors foresee? Any unideal factors may degrade the actual performance of the circuit?

Owing to the limitation of objective condition and the reason of economy, the chip has not taped out to the foundry. To simplify the simulation, a voltage source and a resistor are connected in series to mimic the TEG. According to Reference [7], the internal resistance of the TEG hardly changes at room temperature. To establish a well-controlled experimental environment, some researchers [20,21] also used a power source and a resistor to emulate the TEG in the experiment.

2. There are two figures in Figure 10, please denote them more properly.

Thanks for your suggestion, and we have added an explanation, which is “There is an enlarged view of the simulation results at the bottom of the figure.” in Line 199.

3. How to obtain the tracking efficiency should be explained a bit more.

Thanks for your comment. The explanation of how to obtain the tracking efficiency during simulation has been added in Section 4 in Line 205, which is “The input power of the DC-DC converter is obtained by the calculator module embedded in Spectre. The input power is divided by the ideal maximum power output of the TEG to obtain the tracking efficiency of the proposed MPPT circuit.”

And we also explained the tracking efficiency in Section 2 in Line 96, which is “tracking efficiency, which is the ratio of input power to ideal maximum input power”.

4. How is the adaptability of the proposed circuit when the characteristics of TEG are out of the modeling range (50-400 mV, 1-12 Ω)?

The proposed circuit is specifically designed for the modeling range (50-400 mV, 1-12 Ω), which is the application condition of most wearable devices. When the output voltage of the TEG is less than 50mV, the voltage is too low to startup the circuit.

5. Please double-check the main text carefully, since there are some typos and many “Error! Reference source not found.” from time to time.

We apologized for those typos and revised the errors. These “Error! Reference source not found.” cannot quote the correct figure number when the manuscript is uploaded.

Review 2:

The paper presents a method - time exponential rate perturbation and observation P&O to extract maximum power from TEG. The model was only validated by simulation and compared with other methods from specialized literature. This method also has to be validated experimentally. The authors must consider some TEGs for this (perhaps different materials).

 Thank you for the reviewer's suggestions to our manuscript. We acknowledge the positive comments, which are valuable for improving the quality of our manuscript. Owing to the limitation of objective condition and the reason of economy, the chip has not taped out to the foundry. Taking into account the different materials of TEGs, the proposed circuit is designed for a wide TEG internal resistance range (1-12 Ω).

Some comments:

1. Please avoid “etc”

Thanks for your suggestion. We have added more explanation, which is “rich thermal energy, no pollution, and no noise”, to replace the word “etc” in the abstract in Line 14.

2. Please explain PMOS, NMOS, CMOS

Thank you to point out this error. We have added the full names of those abbreviations when PMOS, NNOS, and CMOS first appear in the abstract and main text.

3. Please don't use lumpy references, such as [1-6] and others.

We only used lumpy references ([1-6] and [7-12]) in the introduction. Those references are cited to explain that energy harvesting technology and thermoelectric generator are getting more and more attention in recent years.

4. L36 Please corrects the error. (there are also others)

We apologized for those typos and revised the errors. These “Error! Reference source not found.” cannot quote the correct figure number when the manuscript is uploaded.

5. The introduction is incomplete and vague. Please rewrite it so that the reader can better understand the state of the art and the novelty of your work.

Thanks for this good comment. We have added Figure 2 and some sentences in Line 55 to explain the FOCV technique more clearly. And we also have rewritten the last paragraph in the introduction to explain the organization of the paper more clearly.

6. L90 Please explain better Eq.8

Eq.8 is derived from Eq.7. We have explained the constant ε more clearly, which is “where ε is any constant in the range of 0 to 1” in Line 98. To achieve a coherent text, the sentence “By analyzing Eq. (7) and Eq. (8), we find that…” has been added in Line 99 in the revised manuscript. Thanks for your comment.

Round 2

Reviewer 2 Report

The authors corrected the majority of the requests and improved the paper.