US20130195653A1

US20130195653A1 - Wind turbine and vibration damping method thereof

Info

Publication number: US20130195653A1
Application number: US13/361,502
Authority: US
Inventors: Kentaro Hayashi; Naoyuki Nagai; Tsuyoshi Wakasa
Original assignee: Mitsubishi Heavy Industries Ltd
Current assignee: Mitsubishi Heavy Industries Ltd
Priority date: 2012-01-30
Filing date: 2012-01-30
Publication date: 2013-08-01

Abstract

There are provided a TMD adjusted to damp vibration in a natural frequency of a wind turbine, an AVC adjusted to damp vibration in a variable frequency of turbulent wind flowing into the wind turbine and/or a frequency of a rotation speed of a wind-turbine blade, and a pitch-angle control portion provided with a correction portion which adjusts a damping frequency of the AVC. The AVC is configured to obtain the damping force by changing the pitch angle of the wind-turbine blade.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a wind turbine and a vibration damping method thereof.
2. Description of Related Art
A wind turbine which converts wind energy to electric power and generates the electric power has drawn attention as clean energy. Since a wind turbine has a structure in which heavy articles such as a wind-turbine blade, a gear box, a power generator and the like are mounted on an upper part of a tower having the height of several tens meters in general, vibration induced by fluctuation in the wind speed flowing into the wind turbine cannot be ignored. Such vibration increases a fatigue load of a structural material of the wind turbine and reduces the life of the wind turbine.
On the other hand, high-rise structures such as a building employs AMD (Active Mass Damper) in order to damp vibration caused by wind. However, the AMD requires an actuator which drives an added mass in addition to the added mass, whereby cost and weight are increased. Particularly if it is applied to a wind turbine, the weight of the upper part of the tower is further increased, which is not preferable.
U.S. Pat. No. 5,442,883 discloses the invention in which an added mass is reduced only by combining a passive damper with the AMD. However, since an actuator which drives the added mass is still needed, the increase in weight is not fundamentally solved.
PCT International Publication No. WO 2005/083266 discloses the invention of active vibration damping of a wind turbine provided with a pitch-angle control mechanism which can control a pitch angle of a wind-turbine blade without providing a special actuator for damping vibration. Specifically, a pitch-angle instruction is outputted to the pitch-angle control mechanism so as to obtain a thrust power for damping vibration.
The dominant vibration of a wind turbine is vibration caused by turbulent wind, vibration caused by a rotor rotation speed (1N, 3N; N is a rotation speed (3N refers to the case of three blades)), and vibration caused by a natural vibration frequency (1st, 2nd) of the wind turbine itself as illustrated in FIG. 13. In this case, the rotor rotation speed component can be reduced by balancing the wind turbine blades or the like, and the turbulent wind component and the tower natural vibration frequency component can be reduced by active vibration damping or a passive damper.
However, as illustrated in the figures, since a frequency band which needs to be damped is wide in a wind turbine, the following problems occur. That is, as illustrated in FIG. 13, since a peak level with high damping effect is in inverse proportion to the frequency band in which a damping effect is exerted in general, if a large damping effect is to be obtained, the frequency band should be small (see a curve L1), while if a wide frequency band is to be obtained, the peak level becomes low (see a curve L2). Therefore, it is difficult to obtain a large damping effect in all the frequency bands of vibration specific to a wind turbine.

BRIEF SUMMARY OF THE INVENTION

The present invention was made in view of such circumstances and has an object to provide a wind turbine which can exert a large damping effect in a wide frequency band specific to a wind turbine and a vibration damping method thereof.
In order to achieve the above object, the wind turbine and the vibration damping method of the present invention employ the following means.
That is, a wind turbine according to a first aspect of the present invention is provided with a passive damper adjusted so as to damp vibration in a natural vibration frequency of the wind turbine, an active damper adjusted so as to damp variation in a variable frequency of turbulent wind flowing into the wind turbine and/or variation in an n-th (n is a natural number) frequency of a rotation speed of a wind-turbine blade, and an active-damper control portion which controls a damping frequency of the active damper.
Since the natural vibration frequency of a wind turbine is uniquely determined by the shape or constitution of the wind turbine, the vibration in the natural vibration frequency is damped by a passive damper which can adjust damping by fixing the frequency to a specific one.
On the other hand, the variable frequency of the turbulent wind flowing into the wind turbine varies by wind conditions such as weather, season, time and the like. Also, the n-th frequency of the rotation speed of the wind-turbine blade also varies depending on the rotation speed of the wind-turbine blade. Therefore, for the vibration in these frequencies, an active damper (AVC, for example; Active Vibration Control) which can dynamically change the damping frequency by the active-damper control portion is used.
As described above, the active damper and the passive damper are made to bear the respective corresponding frequencies, and the damping effects of the respective dampers can be effectively exerted.
Moreover, in the wind turbine of the present invention, the active damper obtains a damping force by changing a pitch angle of a wind-turbine blade.
In the wind turbine according to the first aspect of the present invention, an active damper which exerts a damping action by using wind energy through change of a pitch angle of a wind-turbine blade is preferably employed. In this case, limited wind energy is used as a damping force. In the present invention, since the active damper is concentrated to a predetermined frequency for damping, the damping force can be exerted by effectively using the wind energy.
Moreover, in the wind turbine according to the first aspect of the present invention, it is preferable that an anemometer which detects a flow speed of the wind flowing into the wind turbine and the active-damper control portion controls the active damper on the basis of the flow speed detected by the anemometer.
The active damper is controlled in accordance with fluctuation of a wind speed detected by the anemometer. Since the control is made in accordance with fluctuation in speed of the inflow wind as above, vibration damping can be performed with better responsiveness than the case of vibration damping after vibration actually generated in the wind turbine is obtained by an acceleration sensor or the like.
Moreover, in the wind turbine according to the first aspect of the present invention, the passive damper is a tuned mass damper, and the tuned mass damper preferably uses a wind-turbine constituent element capable of relative movement with respect to the wind turbine main body as an added mass.
As the passive damper, a tuned mass damper (TMD) is preferable. That is because, by selecting an existing wind-turbine constituent element provided in order to exert a function of the wind turbine, not for the purpose of damping, the passive damper can be constituted without adding a special added component. As a result, the weight of the wind turbine does not have to be increased for damping vibration.
As a wind-turbine constituent element selected as an added mass, a nacelle cover, a transformer, a ladder (elevating ladder), a platform of a tower (foothold), a cable suspended downward from the nacelle, a turning module which turns the nacelle in a yaw direction and the like capable of relative movement with respect to the wind turbine main body can be cited, for example.
Moreover, in the wind turbine according to the first aspect of the present invention, the passive damper is a tuned liquid damper, and the tuned liquid damper preferably uses operating oil or lubricant oil stored in a wind-turbine main body as an added mass.
As the passive damper, a tuned liquid damper (TLD) is preferably used. That is because, by selecting operating oil or lubricant oil stored in the wind turbine, the passive damper can be constituted without adding a special added component. As a result, the weight of the wind turbine does not have to be increased for damping vibration.
As the operating oil or machine oil selected as the added mass, operating oil in a reservoir tank of a hydraulic device, lubricant oil in a gear box and the like can be cited, for example.
Also, a vibration damping method of a wind turbine according to a second aspect of the present invention is a vibration damping method of a wind turbine provided with a passive damper adjusted so as to damp vibration in a natural frequency of a wind turbine and an active damper and controls a damping frequency of the active damper so as to damp vibration in a variable frequency of turbulent wind flowing into the wind turbine and/or variation in a n-th (n is a natural number) frequency of the rotation speed of a wind-turbine blade.
Since the natural vibration frequency of a wind turbine is uniquely determined by the shape or constitution of the wind turbine, the vibration in the natural vibration frequency is damped by a passive damper which can adjust damping by fixing the frequency to a specific one.
On the other hand, the variable frequency of the turbulent wind flowing into the wind turbine varies by wind conditions such as weather, season, time and the like. Also, the n-th frequency of the rotation speed of the wind-turbine blade also varies depending on the rotation speed of the wind-turbine blade. Therefore, for the vibration in these frequencies, an active damper (AVC, for example; Active Vibration Control) which can dynamically change the damping frequency is used.
As described above, the active damper and the passive damper are made to bear the respective corresponding frequencies, and the damping effects of the respective dampers can be effectively exerted.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 illustrates a basic idea of a vibration damping method of a wind turbine of the present invention.

FIG. 2 illustrates a method of changing a damping frequency in accordance with a turbulent wind component of wind.

FIG. 3 illustrates a method of changing a damping frequency in accordance with a change in a rotor rotation speed.

FIG. 4 is a block diagram illustrating a constitution of an AVC.

FIG. 5 is a diagram illustrating a vibration model of a TMD.

FIG. 6 is a perspective view illustrating an embodiment in which an added mass of the TMD is a nacelle cover.

FIG. 7 illustrates a mounting structure of the nacelle cover shown in FIG. 6, in which (a) is a side view and (b) is a rear view.

FIG. 8 illustrates a fixed portion between the nacelle cover and a frame, in which (a) illustrates a structure of the present invention of fixation using an elastic member, and (b) illustrates a general structure of fixation using a rigid member.

FIG. 9 is a side view illustrating an embodiment in which the added mass of the TMD is a ladder.

FIG. 10 is a side view illustrating an embodiment in which the added mass of the TMD is a platform.

FIG. 11 is a side view illustrating an embodiment in which the added mass of the TMD is a cable.

FIG. 12 is a side view illustrating an embodiment in which the added mass of the TMD is a lower module of a nacelle.

FIG. 13 illustrates vibration generated in the wind turbine with respect to a frequency.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment according to the present invention will be described below by referring to the attached drawings.
FIG. 1 illustrates a basic idea of vibration damping of the present invention. The lateral axis of FIG. 1( a) indicates a frequency [Hz], and the vertical axis indicates a vibration level [dB] in a nacelle installed on an upper part of a tower of a wind turbine. As illustrated in FIG. 1( a), vibration caused by a frequency component of turbulent wind, vibration in a rotor rotation speed (1N), vibration in a primary component (1st) of a natural vibration frequency of the wind turbine itself, vibration in a rotation speed (3N) three times of the rotor rotation speed, and vibration in a secondary component (2nd) of the natural vibration frequency of the wind turbine itself appear in the order from the low-frequency side. The relationship between the frequency in the rotor rotation speed (1N) and the primary natural vibration frequency (1st) might be opposite depending on the natural vibration frequency of the wind turbine itself. Also, the vibration appearing in the rotation number (3N) three times of the rotor rotation speed is caused by the fact that the number of wind-turbine blades is three.
The lateral axis in FIG. 1( b) indicates a frequency [Hz], and the vertical axis indicates a damped amount [dB] by a vibration damping device. As illustrating in this figure, in the present invention, a passive damper (specifically, a TMD) is made to function by making adjustment to the primary natural frequency (1st), and an active vibration damping (AVC; active damper) is made to function by making adjustment to the turbulent wind frequency component (and/or the 1N component of the rotor rotation speed).
Particularly, with regard to the active damping, as illustrated in FIG. 2, a frequency band is preferably adjusted in accordance with fluctuation in the turbulent wind component. Also, with regard to the active vibration damping, the frequency band is preferably adjusted in accordance with fluctuation in the rotor rotation speed (1N) as illustrated in FIG. 3.
FIG. 4 illustrates a specific configuration for performing the above-described active vibration damping. The active vibration damping in this figure uses the same method as Patent Document 2.
In this figure, a rotation output of a rotor 4 rotated by wind-turbine blades 3 is led to a gear box 7. The rotation output whose rotation speed is increased by the gear box 7 is led to a power generation system 9 and converted to an electric output. The power output from the power generation system 9 is supplied to a system, not shown. A pitch-angle control mechanism 11 is provided on each of the wind-turbine blades 3. By means of this pitch-angle control mechanism, the pitch angle of the wind-turbine blade 3 is changed as appropriate from the fine side in which a rotation output is obtained by receiving wind flowing into the wind-turbine blades 3 to the feather side in which the wind flows through.
A pitch-angle instruction value θ inputted into the pitch-angle control mechanism 11 is created in a pitch-angle control portion 13. The pitch-angle control portion 13 is provided with a pitch-angle setting portion 15 which sets a pitch angle on the basis of a power output value P outputted from the power generation system 9. The pitch angle of the wind-turbine blade 3 is by this pitch-angle setting portion 15 so as to have a desired output power value. The pitch angle set by the pitch-angle setting portion 15 is sent to a correction portion 17.
In the correction portion 17, the pitch angle is corrected on the basis of a turbulent wind frequency obtained from turbulent wind information obtaining means 19 and outputs it as the pitch-angle instruction value θ. As the turbulent wind information obtaining means 19, an optical-fiber strain meter which obtains load fluctuation of the wind-turbine blade 3 can be cited, for example. Alternatively, a laser Doppler anemometer or an ultrasonic Doppler anemometer may be installed in the wind turbine so as to measure the wind speed on the upstream side of the wind turbine for feed-forward control of a pitch angle. A pitch angle is changed so as to damp vibration in the frequency band of the turbulent wind component in a concentrated manner by obtaining a turbulent wind component as above. Specifically, a pitch angle is controlled so that thrust force to cancel vibration of a tower caused by the turbulent wind component. In the correction portion 17, even if the frequency band of the turbulent wind component is changed, the pitch angle is dynamically changed in accordance with this change.
Also, into the correction portion 17, an output value from rotor rotation speed obtaining means 21 which obtains the rotation speed of the rotor rotated by the wind-turbine blades 3 is inputted. By obtaining the rotor rotation speed as above, the pitch angle is changed so as to damp the vibration in the rotor rotation speed (1N) in a concentrated manner. Specifically, the pitch angle is controlled so as to generate a thrust force to cancel vibration of a tower caused by rotation of the rotor. In the correction portion 17, even if the rotor rotation speed is changed, the pitch angle is dynamically changed in accordance with this change so as to perform vibration damping.
The active vibration damping of the present invention damps vibration only in accordance with the turbulent wind component or the rotor rotation speed (1N). However, if these frequency components are close to each to other or if a peak level of the damping vibration effect is lowered so as to allow a wider damping frequency band, vibration damping may be performed in accordance with the both.
FIG. 5 illustrates a vibration model of a TMD (Tuned Mass Damper) adjusted so as to damp the vibration in the primary natural vibration frequency (1st) of the wind turbine itself.
In this figure, reference character m1 denotes a mass of the wind turbine, and reference character m2 denotes an added mass used for the TMD. Also, reference character y denotes a displacement direction in vibration.
The vibration model in FIG. 5 is expressed by an expression as follows:
My″+Cy′+ky=F
Here, M, C, k, y, and F are expressed by the following matrix:
$M = (\begin{matrix} m 1 & 0 \\ 0 & m 2 \end{matrix})$ $C = (\begin{matrix} c 1 + c 2 & - c 2 \\ - c 2 & c 2 \end{matrix})$ $k = (\begin{matrix} k 1 + k 2 & - k 2 \\ - k2 & k 2 \end{matrix})$ $y = (\begin{matrix} y 1 \\ y 2 \end{matrix})$ $F = (\begin{matrix} F 1 \\ 0 \end{matrix})$
In the present invention, as the added mass m2 expressed by the above expression, an existing wind-turbine constituent element provided in order to exert the function of the wind turbine, not for the purpose of damping, is used. A specific example will be described below.
FIGS. 6 to 8 illustrate a case in which the mass of a nacelle cover is used as the added mass m2. As illustrated in FIG. 6, the nacelle cover 30 is mounted capable of displacement on a frame 32 fixed to the upper end of a tower 2.
FIG. 7 illustrates a mounting structure of the nacelle cover 30 to the frame 32. FIG. 7( a) is a side view and FIG. 7( b) is a rear view of FIG. 7( a). As illustrated in the figures, the frame 32 and the nacelle cover 30 are connected to each other by a linear guide 34, whereby the nacelle cover 30 can reciprocally move with respect to the frame 32. Also, a plurality of elastic members (rubber or the like) 36 which becomes a spring element and damping element of the TMD are provided between the frame 32 and the nacelle cover 30. The elastic members 36 are, as illustrated in FIG. 8, preferably rubber inserted between the frame 32 and the nacelle cover 30. FIG. 8( b) illustrates a structure as a comparative example, and a rigid member 38 such as metal or the like in general is provided.
FIG. 9 illustrates a case in which the mass of a ladder (elevation ladder) 40 installed in the tower 2 of the wind turbine is used as the added mass m2. The upper end of the ladder 40 is rotatably supported by a pin at a predetermined fixed position 42 on the upper end of the tower 2. In pin supporting, a spring element and a damping element of the TMD are given by interposing a predetermined elastic member (rubber or the like). The lower end of the ladder 40 is not fixed but left as a free end so that the ladder 40 swings using the upper end as a swing center. A stopper is preferably provided so that the ladder 40 does not collide against a wall part of the tower 2 if the ladder 40 swings.
FIG. 10 illustrates an example in which the mass of a platform 44 in the tower 2 is used as the added mass m2. The platform 44 is used as a foothold for workers. As illustrated in the figure, the platform 44 has a suspended structure using support members 45. The platform 44 is configured to swing around fixed positions 46 on the upper end of the support members 45. When the support members 45 are to be fixed, the spring element and the damping element of the TMD are given by interposing a predetermined elastic member (rubber or the like).
FIG. 11 illustrates a case in which a part of the mass of a cable 50 extending from the nacelle 5 to the ground is used as the added mass m2. Specifically, the mass of the cable 50 above a pulley 52 is used as the added mass m2. In this case, elasticity of the cable 50 itself is used as the spring element and the damping element of the TMD.
FIG. 12 illustrates a case in which the nacelle 5 is divided vertically into two parts, which are an upper module 5 a and a lower module 5 b, and the mass of the lower module 5 b is used as the added mass m2.
In the upper module 5 a, a gear box, a power generator and the like are arranged. In the lower module 5 b, a yaw turning motor which turns the nacelle 5 and a yaw brake are arranged. The lower module 5 b is capable of relative movement with respect to the upper module 5 a. Also, an elastic member is arranged so that the spring element and the damping element of the TMD are given, though not shown, when the upper module 5 a and the lower module 5 b are relatively moved.
Also, though not shown, a transformer in the nacelle is made relatively movable with respect to the nacelle main body, and the mass of this transformer may be used as the added mass m2. Moreover, other than the above, any wind-turbine constituent element can be used as an added mass of the TMD by installing it relatively movable with respect to the nacelle or the tower as long as it has an appropriate weight as the added mass.
Also, though not shown, a TLD (Tuned Liquid Damper) may be used instead of the TMD. In this case, operating oil or lubricant oil stored in the nacelle is preferably used as the added mass. Specifically, the operating oil in a reservoir tank of a hydraulic device, the lubricant oil in the gear box and the like can be cited.
As described above, according to this embodiment, the following working effects can be exerted.
Since the natural vibration frequency of a wind turbine is uniquely determined by the shape or constitution of the wind turbine, the vibration in the natural vibration frequency is damped by a TMD (or a TLD) which can adjust damping by fixing the frequency to a specific one.
On the other hand, the variable frequency of the turbulent wind flowing into the wind turbine varies by wind conditions such as weather, season, time and the like. Also, the n-th frequency of the rotation speed of the wind-turbine blade also varies depending on the rotation speed of the wind-turbine blade. Therefore, for the vibration in these frequencies, an AVC, which can dynamically change the damping frequency, is used.
As described above, TMD and AVC are made to bear the respective corresponding frequencies, and the damping effects of the respective dampers can be effectively exerted.
The AVC which uses wind energy by changing the pitch angle of the wind-turbine blade 3 so as to exert the damping action is employed. In this case, though limited wind energy is used as a damping force, the AVC is concentrated to a predetermined frequency to perform damping in this embodiment, and thus, the wind energy can be effectively used and the damping force can be exerted.
The AVC is controlled in accordance with fluctuation in the wind speed detected by an anemometer such as an optical-fiber strain meter, a laser Doppler anemometer and the like. Since control is made in accordance with fluctuation in the inflow wind speed as above, vibration damping can be performed with better responsiveness than the case of vibration damping after vibration actually generated in the wind turbine is obtained by an acceleration sensor or the like.
Also, by selecting the existing wind-turbine constituent element provided in order to exert the function of the wind turbine, not for the purpose of vibration damping, as the added mass, the TMD can be configured without adding a special component. As a result, the weight of the wind turbine does not have to be increased for damping vibration.
Since the existing liquid in the nacelle is used and a special component is not added in configuring the TLD, the weight of the wind turbine does not have to be increased for damping vibration.

Claims

What is claimed is:

1. A wind turbine comprising:

a passive damper adjusted to damp vibration in a natural vibration frequency of the wind turbine;

an active damper adjusted to damp variation in a variable frequency of turbulent wind flowing into the wind turbine and/or variation in a n-th (n is a natural number) frequency of a rotation speed of a wind-turbine blade; and

an active-damper control portion which adjusts a damping frequency of the active damper.

2. The wind turbine according to claim 1, wherein

the active damper obtains the damping force by changing a pitch angle of the wind-turbine blade.

3. The wind turbine according to claim 1, further comprising:

an anemometer which detects a flow speed of wind flowing into the wind turbine, wherein

the active-damper control portion controls the active damper on the basis of the wind speed detected by the anemometer.

4. The wind turbine according to claim 2, further comprising:

5. The wind turbine according to claim 1, wherein

the passive damper is a tuned mass damper; and

the tuned mass damper uses a wind-turbine constituent element made relatively movable with respect to a wind-turbine main body as an added mass.

6. The wind turbine according to claim 2, wherein

the passive damper is a tuned mass damper; and

7. The wind turbine according to claim 3, wherein

the passive damper is a tuned mass damper; and

8. The wind turbine according to claim 4, wherein

the passive damper is a tuned mass damper; and

9. The wind turbine according to claim 1, wherein

the passive damper is a tuned liquid damper; and

the tuned liquid damper uses operating oil or lubricant oil stored in the wind-turbine main body as an added mass.

10. The wind turbine according to claim 2, wherein

the passive damper is a tuned liquid damper; and

11. The wind turbine according to claim 3, wherein

the passive damper is a tuned liquid damper; and

12. The wind turbine according to claim 4, wherein

the passive damper is a tuned liquid damper; and

13. A vibration damping method of a wind turbine provided with a passive damper adjusted to damp vibration in a natural frequency of the wind turbine and an active damper, comprising

controlling a damping frequency of the active damper so as to damp vibration in a variable frequency of turbulent wind flowing into the wind turbine and/or variation in a n-th (n is a natural number) frequency of a rotation speed of a wind-turbine blade.