Fatigue Testing Device for Wind Turbine Blade Testing, a Method of Testing Wind Turbine Blades and a Control System for a Blade Testing Actuator

• US 20100175480A1
• Filed: 05/30/2008
• Published: 07/15/2010
• Est. Priority Date: 05/30/2007
• Status: Active Grant

• Current Assignee: Vestas Wind Systems A/S
• Original Assignee: Vestas Wind Systems A/S
• Inventors: Guy, Stuart
• Granted Patent: US 8,393,216 B2
• Time in Patent Office: Days
• US Class Current: 73/660
• CPC Class Codes: G01M 5/0016 of aircraft wings or blades
• CPC Class Codes: G01M 7/022 Vibration control arrangements, e.g. for generating random vibrations
• CPC Class Codes: G01N 2203/0023 Bending
• CPC Class Codes: G01N 2203/0073 Fatigue
• CPC Class Codes: G01N 3/20 by applying steady bending forces G01N3/26, G01N3/28 take precedence
• CPC Class Codes: G01N 3/32 by applying repeated or pulsating forces

Abstract

The invention provides a fatigue exciter for wind turbine blades. Wind turbine blades require excitation at or near their natural frequency to induce bending moments that simulate in service loadings and must be easily controllable and with the minimum of unnecessary added mass or force. The invention provides a device and a method by which force controlled feedback is used for finding an optimal excitation frequency. This force could be provided e.g. by a digital signal generator.

Claims

1. A fatigue testing device for wind turbine blade testing, the device comprising an actuator adapted to deflect the blade at an excitation frequency and a control system adapted to find a natural frequency for the blade and to set the excitation frequency to the natural frequency.

2. A device according to claim 1, wherein the control system is adapted to find the natural frequency by modulation of the excitation frequency.

3. A device according to claim 2, being further adapted, during modulation of the excitation frequency, to provide an input signal significant for an increase or decrease of an input force necessary to deflect the blade and to provide an output signal significant for an amplitude of the deflection.

4. A device according to claim 2, wherein the control system is adapted to bring a blade under test up to an initial load at an initial frequency within 10 percent under the blades recorded natural frequency.

5. A device according to claim 4, wherein the initial frequency is determined by a pre-test frequency sweep.

6. A device according to claim 3, further adapted to determine a ratio between the input force and the amplitude.

7. A device according to claim 3, further adapted to select an excitation frequency based on the ratio, the input signal, or the output signal.

8. A device according to claim 7, wherein the selection facilitates a minimal ratio between the input force and the amplitude.

9. A device according to claim 1, wherein the actuator is arranged not to influence the natural frequency of the blade.

10. A device according to claim 9, wherein the actuator is supported without weighing down the blade.

11. A fatigue testing device according to claim 1, further comprising at least one strain sensitive structure being attachable to the blade, the device being further adapted to modulate the excitation frequency based on a signal generated by the strain sensitive structure.

12. A fatigue testing device according to claim 1, further comprising an additional actuator adapted to deflect the blade at an additional excitation frequency.

13. A fatigue testing device according to claim 12, wherein the additional excitation frequency is adjustable.

14. A fatigue testing device according to claim 13 wherein the additional excitation frequency is adjustable independently upon the excitation frequency.

15. A fatigue testing device according to claim 1, comprising fixation means for fixation of a first portion of the blade to an external object.

16. A fatigue testing device according to claim 15, further comprising additional fixation means for fixation of a second portion of the blade to an external object.

17. A fatigue testing device according to claim 15, wherein at least one of the fixation means is adjustable to allow fixation at different locations along the blade.

18. A method of testing a wind turbine blade, the method comprising the steps of:

fixating a blade to a bench,

providing an input force for operating the actuator to apply, at an excitation frequency, a cyclic load to the blade at a location at a distance from the hub end,

modulating the excitation frequency and input force,

determining an amplitude of the movement of the blade, and

selecting an excitation frequency based on a ratio between the input force and the amplitude.

19. A method according to claim 18, wherein the step of modulating the excitation frequency and input force, determining an amplitude of the movement of the blade, and selecting an excitation frequency based on a ratio between the input force and the amplitude is repeated several times during a test of a blade.

20. A control system for controlling a testing device for wind turbine blades, the testing device comprising an actuator, the control system being adapted to modulate an excitation frequency at which the actuator applies a load to the blade, to modulate an input force provided for the actuator to apply the load to the blade, to determine an amplitude of movement of the blade and to select an excitation frequency based on a ratio between the input force and the amplitude.