A METHOD AND A DEVICE FOR DETERMINING TORSIONAL DEFORMATION IN A DRIVETRAIN

Abstract

A method of determining torsional deformation in a drivetrain e.g. of a wind turbine. To provide a reliable and simple deformation assessment, the method comprises the step of generating a first signal representing first rotational speed of a low speed shaft, generating a second signal representing the second rotational speed of a high speed shaft, and determining torsional deformation based on changes in the ratio between the first and second signals.

Claims

1. A method of determining torsional deformation in a drivetrain in a wind turbine which includes a first shaft and a second shaft connected by a gearbox providing a difference between a first rotational speed of the first shaft and a second rotational speed of the second shaft, the method comprising: generating a first signal representing the first rotational speed, generating a second signal representing the second rotational speed, and determining torsional deformation based on the first and second signals.

2. A method according to claim 1, where the torsional deformation is based on a ratio between the first and second signals.

3. A method according to claim 1, comprising the generating a third signal which includes the first and second signals.

4. A method according to claim 3, comprising the detecting a change in a frequency which is represented by the third signal.

5. A method according to claim 3, comprising the detecting a phase shift in the third signal.

6. A method according to claim 3, comprising the comparing the third signal with a reference signal.

7. A method according to claim 6, where the reference signal is based on at least one of the first and the second signals.

8. A method according to claim 6, where the comparing of the third signal with a reference value is carried out continuously.

9. A method according to claim 1, where at least one of the first and second signals is determined as an average of a plurality of measurements.

10. A method according to claim 1, where at least one of the first, second, and third signal is filtered.

11. A method according to claim 1, comprising a first step of determining, at a first point in time, a first ratio of the first shaft rotational speed to the second shaft rotational speed, a second step of determining, at a second point in time, a second ratio of the first rotational speed to the second rotational speed, a third step of providing a value representing a difference between the first ratio and the second ratio, and a fourth step of comparing the value with a reference value.

12. A method according to claim 11, where the first to fourth step is repeated continuously.

13. A method according to claim 1, where at least one of the first shaft rotational speed and the second shaft rotational speed is determined by an instrument that generates pulses related to shaft rotations.

14. A method according to claim 1, where at least one of the first, second, and third signal is determined during power production by the wind turbine.

15. A wind turbine comprising a drivetrain with a high speed shaft (HS) and a low speed shaft (LS), the first shaft and second shaft being connected by a transmission providing a nominal ratio between a first shaft rotational speed of first shaft and a second shaft rotational speed of second shaft, the wind turbine further comprising a controller configured perform an operation of determining torsional deformation in the drivetrain, the operation comprising: generating a first signal representing the first rotational speed, generating a second signal representing the second rotational speed, and determining torsional deformation based on the first and second signals.

16. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1 illustrates a wind turbine with a controller embedded in the nacelle;

[0035] FIG. 2 illustrates a drivetrain in the wind turbine;

[0036] FIG. 3 illustrates the first and second signals obtained from pole bands;

[0037] FIG. 4 illustrates the third signal constituting a mix of the first and second signal;

[0038] FIG. 5 illustrates the third signal after smoothening; and

[0039] FIG. 6 illustrates the process of mixing the first and the second signals.

DETAILED DESCRIPTION

[0040] Further scope of applicability of the present invention will become apparent from the following detailed description and specific examples. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the scope of the invention will become apparent to those skilled in the art from this detailed description.

[0041] FIG. 1 illustrates a wind turbine 1 with a tower 2, a nacelle 3, and blades 4. The blades are attached to the hub 5 which forms part of the drivetrain 6 located inside the nacelle.

[0042] FIG. 2 illustrates the drivetrain 6 without the hub 5. The drivetrain comprises a flange 7 for attaching the hub, a shaft 8 connecting the gearbox 9 to the flange 7 and an output 10 for driving e.g. an electrical generator.

[0043] The gearbox 9 converts a low speed to high speed such that the generator is driven by the output 10 at a speed which is high relative to the rotational speed of the shaft 8 and hub.

[0044] The conversion from the low speed to the high speed is at a fixed ratio which means that in an ideal situation without any deformation in the drivetrain, the ratio between the rotational speed of the shaft 8 and the rotational speed of the shaft 10 would be constant. Herein, the shaft 8 is referred to as second shaft and the shaft 10 is referred to as HS.

[0045] Two pole bands 11, 12 are attached to the drivetrain on opposite sides of the gearbox. This allows determination of torsional deformation in the gearbox.

[0046] The pole bands communicate with the controller 13, e.g. by wireless. The controller could be housed locally in the nacelle, or it could be constituted by a central computer system communicating with a plurality of wind turbines.

[0047] The controller is configured to detect torque and to detect a change in torque applied by the hub to the drivetrain. For this purpose, the controller is configured to combine signals from the two pole bands 11, 12 and to compare the resulting, third signal, with the signal from one of the pole bands. The resulting signal is evaluated and a phase shift and/or a change in frequency is determined.

[0048] The controller may further be configured for additional control purpose. The controller may e.g. be configured for changing the power production, e.g. by de-rating the power production or for stopping the wind turbine based on the determined torque or based on variations in the torque. The controller may e.g. be configured for controlling blade pitching.

EXAMPLE

[0049] The following example illustrates a situation where the second shaft has 200 pulses per revolution and a phase shift of 0.1 degrees occurs on the second shaft compared the first shaft due to angular deformation.

[0050] The pulses from the second shaft will then be shifted 200*0.1=20 relative to the pulses from the first shaft which will also lead to a phase shift of the mixed, third, signal of 20. This can be detected either as a phase shift or as a temporary shift in frequency. Thus a small change in the shafts relations, results in a larger change in the third signal.

[0051] FIG. 3 illustrates two signals. The signal marked 14 is the pulses from the pole band 11 on the hub side of the gearbox, and the signal marked 15 is the pulses from the pole band 12 on the other side of the gearbox.

[0052] FIG. 4 illustrates the mixed, third, signal. In the disclosed embodiment, the signal is mixed by ex-or. This is a simple way to mix two digital signals, but many other ways may apply.

[0053] FIG. 5 illustrates the mixed, third, signal after being smoothed.

[0054] FIG. 6 illustrates the process of mixing the first and second signals. In the illustrated example, HS denotes a High speed shaft signal, e.g. the first signal, and LS denotes a low speed shaft signal, e.g. the second signal. In the process called phase and frequency compare, deviations in the phase or frequency is detected to evaluate a change in torque.

[0055] Both digital and analogue method can be used for the data and signal processing.

[0056] A change in the sine-shape indicates a change in torque, and a phase shift of a static sine-shape indicates a level of a constant torque.