Electronically Controlled Actuators for a Micro Wind Turbine Furling Mechanism^†

Round 1

Reviewer 1 Report

English language should be improved. Paper is Well written AND topic is interesting. Contributions Are clearly presented and are relevant. I have no major objections on tiha paper.

Author Response

Thank you for your appreciations. The text of the paper was written to our best English language knowledge.

Reviewer 2 Report

In this paper, the authors proposed a limited angle torque actuator solution for overspeed protection of small wind turbines. The paper is well structured with experimental validation. It is not difficult to follow.

-The major concern is the contribution of the paper. The authors list several current solutions for wind turbine overspeed protection in section 1, including LAT. However, there lacks an in-depth discussion on their pros and cons, and why the study in this paper is necessary and what problem this study addressed. Also, the authors provided very detailed design of the angular bipolar control and angular motor control circuits. However, the design of such circuits seems not new topics, especially considering that motor control is a very mature area. Therefore, it is not clear what is the contribution or new in this paper.

-The authors showed the FEM analysis in Figure 3 but without any further explanation. Is there anything new or contribution can be claimed on the design side?

-How the bipolar control will respond if the wind speed is oscillating and the resulting input voltage oscillates around the set threshold voltage? will the LAT actuator also oscillate? There should be a control logic to prevent this from happening.

-In figure 6, there is only one coil shown, but in Figure 1, the design shows that there are two coils on each side.

-Figure 9e, "T3-T5 command voltage" => "T3-T4 command voltage". Also, are figures on the left column have the same x-axis as those on the right column? e.g. seems that the "pulse" in Figure 9a and Figure 9b are not with the same width

Author Response

Thank you for your detailed comments and questions!

Hereafter the responses preceded by you comments:

Reviewer: In this paper, the authors proposed a limited angle torque actuator solution for overspeed protection of small wind turbines. The paper is well structured with experimental validation. It is not difficult to follow.

Authors: Thank you!

Reviewer: The major concern is the contribution of the paper. The authors list several current solutions for wind turbine overspeed protection in section 1, including LAT. However, there lacks an in-depth discussion on their pros and cons, and why the study in this paper is necessary and what problem this study addressed. Also, the authors provided very detailed design of the angular bipolar control and angular motor control circuits. However, the design of such circuits seems not new topics, especially considering that motor control is a very mature area. Therefore, it is not clear what is the contribution or new in this paper.

Authors: The advantages and disadvantages of some known solutions, for overspeed protection of small wind turbines, where already presented in the original submitted paper (lines from 39 to 47). Also, in lines 48 to 49, 66 to 69, the text has been updated to include the specific advantages or disadvantages of the other existing solutions presented in this paper, that where not included in the original submitted version.

Regarding the contribution of this paper beyond state of the art, the LAT actuator represents a new design, especially in terms of materials used: the stator poles are made from ordinary rectangular steel profiles and a segment of the turbine tail is used to close the magnetic circuit. This lowers the cost of materials used to manufacture this device. Also, this paper is introducing two control methods that are based on regular motor control approaches. The application specifics are imposing the detection of the threshold input voltage and a proper limiting action. Considering the application specifics, the design and implementation of the detection stages with at least two levels, the command procedures/limitations and the practical implementations of the angular bipolar and motor control circuits are also considered contributions of this paper.

Reviewer: The authors showed the FEM analysis in Figure 3 but without any further explanation. Is there anything new or contribution can be claimed on the design side?

Authors: As stated above, the LAT actuator represents a new design, especially in terms of materials used: the stator poles are made from ordinary rectangular steel profiles and a segment of the turbine tail is used to close the magnetic circuit. This lowers the cost of materials used to manufacture this device.

Reviewer: How the bipolar control will respond if the wind speed is oscillating and the resulting input voltage oscillates around the set threshold voltage? will the LAT actuator also oscillate? There should be a control logic to prevent this from happening.

Authors: Thank you very much for the useful comment. For this reason, we have used 2 comparators to detect 2 voltage levels. The interval between these two values can be set to prevent these oscillations to appear. In this interval the actuator is not performing any action, and this interval can be changed to cope with the application specifics. In view of this, we have updated the paper at page 7, rows 173-175.

Reviewer: In figure 6, there is only one coil shown, but in Figure 1, the design shows that there are two coils on each side.

Authors: Thank you for this remark. Only one of the two coils is shown to allow the visualization of magnetic flux density under the coils. The text was updated  at rows 149 and 150.

Reviewer: Figure 9e, "T3-T5 command voltage" => "T3-T4 command voltage". Also, are figures on the left column have the same x-axis as those on the right column? e.g. seems that the "pulse" in Figure 9a and Figure 9b are not with the same width

Authors: We have corrected the “T5” mistake in Fig. 9e. We would like to thank the reviewer for the very good observation regarding the x-axis representations. Every experiment result presented in Fig. 9 is individually made for different time actions of the input voltage, thus the widths of the command pulse and the actuator voltage does not necessarily match between the oscilloscope pictures. We have inserted in the paper these explications (page 7, rows 191-194).

Reviewer 3 Report

In this article, the authors presented electronically controlled actuators for micro wind turbines' furling mechanism. The whole contents are written with appropriate data and results with numerical simulations and a circuit model in part. It is recommended to be published in energies in the present form.

Author Response

Thank you for the recognition of our work and for the paper publication proposal.

Round 2

Reviewer 2 Report

The authors addressed my concerns. I recommend publication of this paper.