WO2004088131A1

WO2004088131A1 - Self-regulating wind turbine

Info

Publication number: WO2004088131A1
Application number: PCT/CA2003/000467
Authority: WO
Inventors: François GAGNON; Jean Gagnon
Original assignee: ENERGIE PGE Inc
Current assignee: ENERGIE PGE Inc
Priority date: 2003-04-01
Filing date: 2003-04-01
Publication date: 2004-10-14
Anticipated expiration: 2005-10-01
Also published as: AU2003213937A1; CA2561793A1

Abstract

The self-regulating wind turbine has a supporting base, a generator mounted onto the base, and a rotor extending on a downwind side of the generator. The rotor has a hub rotatably coupled to the generator, a plurality of variable-pitch blades evenly distributed around the hub and radially projecting therefrom at a downwind angle from a rotation plane of the rotor, and means for adjusting a pitch of the blades as a function of a centrifugal force produced by rotation of the rotor.

Description

SELF-KEGUIATING WIND TURBINE

FIELD OF THE INVENTION

The present invention relates to wind turbines, and more particularly to a self-regulating wind turbine having variable-pitch blades.

BACKGROUND

One important problem in the use of wind turbines comes from a lack of constancy in the wind force and consequently in the rotation speed of the turbine's blades. A variation of the rotation speed directly causes an undesired variation of the power produced by the wind turbine. As no efficient means for storing large amount of energy yet exist, wind turbines directly provide the generated power to the appliances and electric loads connected thereto. Electronic devices must be relied upon whenever the rotation speed is not constant for regulating the power signal. It is thus highly desirable to obtain a rotation speed as constant as possible in spite of the wind force variations.

In the case of high power wind turbines connected to a network, the rotation speed is regulated in some way by the network itself. If the wind force increases, the wind turbine is slowed down by the network. The pitch of the blades can thus be fixed.

However, the rotation speed of off-network fixed pitch wind turbines is highly variable and under strong winds, the wind turbine may turn into a racing state and even reach rotation speeds causing damaging stresses. Manufacturers are thus trying to develop variable pitch wind turbines.

Known in the art are US patent Nos . 30,038 (Babcock) , 2,037,528 (Miller), 2,096,860 (Renquist et al.), 2,264,568 (Hamilton), 2,457,576 (Littrell) , 2,601,495 (Bell), 2,998,080 (Moore, Jr.), 4,140,435 (Huber) , 4,324,528 (Svenning) , 4,565,494 (Dinger) , 4,573,874 (Andersen et al.), 4,748,339 (Jamieson) , 4,877,374 (Burkett) , 5,108,260 (Monrose, III et al.), 5,180,284 (Monrose, III et al.) and 5,286,166 (Steward) , which provide examples of blade pitch adjusting devices and variable pitch wind turbines.

In large wind turbines, it is sometimes possible to change the pitch of the blades by means of electric motors . Such an arrangement is complex, expensive and requires an external power source for operating the motors.

In the case of wind turbines having a power rating below 100 k , attempts have been made to overcome this problem. In most cases, the solution consists in braking the rotation of the turbine when the speed becomes too high. The regulating arrangements still allow a significant variation of the rotation speed which impairs the constancy of the power output .

SUMMARY

An object of the present invention is to provide a self- regulating wind turbine which has a rotation speed which is nearly constant.

Another object of the present invention is to provide such a self-regulating wind turbine which is reliable, easy to build and which has a low construction cost.

Another object of the present invention is to provide such a self-regulating wind turbine which requires almost no maintenance and lubrication. Another object of the present invention is to provide such a self-regulating wind turbine which has a rotation speed unaffected by changes between load and no-load conditions . According to the present invention, there is provided a self-regulating wind turbine comprising a supporting base, a generator mounted onto the base, and a rotor extending on a downwind side of the generator. The rotor has a hub rotatably coupled to the generator, a plurality of variable-pitch blades evenly distributed around the hub and radially projecting therefrom at a downwind angle from a rotation plane of the rotor, and means for adjusting a pitch of the blades as a function of a centrifugal force produced by rotation of the rotor.

Preferably, the means for adjusting comprises respective telescopic arrangements between the blades and the hub, spring elements inside the telescopic arrangements exerting a pressure against the centrifugal force moving the blades away from the hub, and guiding elements arranged on the telescopic arrangements and guiding the blades along pitch changing courses as the blades radially move with respect to the hub.

Preferably, the pitch changing courses deflect along radial directions of the hub and define limits wherein the blades move nearest and farthest from the hub and have leading edges going from positive to negative limit angles with respect to a direction of rotation of the blades.

BRIEF DESCRIPTION OF THE DRAWINGS

A detailed description of preferred embodiments will be given herein below with reference to the following drawings, in which like numbers refer to like elements:

Figure 1 is a schematic side view of a self-regulating wind turbine according to the present invention, without the blades.

Figure 2 is a schematic front view of a rotor according to the present invention. Figures 3a-c are schematic side views showing different operating angles of a blade according to the present invention .

Figure 4 is a schematic partial side view of a blade according to the present invention.

Figure 5 is a schematic partial perspective view of a rotor according to the present invention.

Figures 6 and 7 are partial cross-section views of a blade pitch adjusting arrangement according to the present invention, in different operating positions respectively.

Figures 8 and 9 are schematic side views of a rotor according ,to the present invention, in different operating angles with respect to the wind.

Figures lOa-d are schematic side and perspective views of an oscillation-responsive safety brake according to the present invention, in braking and non-braking positions respectively.

Figure 11 is a schematic front view of a rotation speed- responsive safety brake according to the present invention, in braking position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to Figures 1 and 2, there are respectively shown a generator unit 2 and a rotor 8 forming a self- regulating wind turbine according to the present invention.

Referring to Figure 1, the generator unit 2 has a generator 4 mounted on a supporting base 6. The rotor 8 (partially shown in the Figure) extends on a downwind side 12 of the generator 4. Referring to Figure 2, the rotor 8 has a hub 16 rotatably coupled to the generator 4, e.g. through the generator's shaft 15. Referring to Figure 8, a number of variable-pitch blades 14 are evenly distributed around the hub 16 and radially project therefrom at a downwind angle 42 from a rotation plane 43 of the rotor 8.

Referring to Figures 2, 4 and 5, the rotor 8 is arranged so that the pitch of the blades 14 is adjusted as a function of a centrifugal force produced by rotation of the rotor 8. For this purpose, the rotor 8 has telescopic arrangements formed of sleeves 22 radially projecting from the hub 16 and slideably receiving bushings 20 mounted onto tubular shafts 18 projecting from the blades 14. Springs 30 inside the telescopic arrangements are arranged to exert a pressure against the centrifugal force moving the blades 14 away from the hub 16. Transverse pins 28 extending across the sleeves 22 and through slots 26 in the bushings 20 guide the blades 14 along pitch changing courses as the blades 14 radially move with respect to the hub 16. The pitch changing courses deflect along radial directions of the hub 16 and define limits wherein the blades 14 move nearest and farthest from the hub 16 and have leading edges 24 going from positive to negative limit angles with respect to a direction of rotation of the blades 14.

The pitch of the blades 14 is thus controlled by the centrifugal force. If the rotation speed increases, the blades 14 are urged away from the rotation center under the effect of the centrifugal force. Knowing the rigidity constant of the springs 30 and the mass of the blades 14, the stretching of the springs 30 can be easily calculated as a function of the rotation speed of the rotor 8. The specific shape of the slots 26 is determined to control the pitch of the blades 14. Depending on the rotation speed, the blades 14 will move away from or will move closer to the hub 16. Due to the specific shape of the slots 26, the blades 14 will rotate on their axis 44, thereby changing the pitch of the blades 14 with respect to the wind. More specifically, the centrifugal force F on the blades 14 is given by F = MV²/R where M is the mass of one of the blades 14, V is its rotation speed and R is the radius of the mass center from the rotation center. Since the return force .of a spring is given by F = K ΔX (where K is the rigidity constant of the spring and ΔX is the compressed length of the spring) , it is possible to chose the parameters of the springs 30 to be used to control the axial position of the blades 14 as a function of the rotation speed of the rotor 8.

Referring to Figures 3a-c, the wind turbine has been designed to operate at a constant speed of 75 RPM which has been found to provide the optimal power. If the wind drops, the turbine will begin to slow down. The pitch of the blades 14 will increase (as shown in Figure 3a) by the pulling effect of the springs 30 on the blades 14, thereby increasing the efficiency of the wind force and stabilizing the rotation speed. Conversely, if the wind increases, the turbine will speed up. The blades 14 will move away from the hub 16 and the slots 26 will force the blades 14 to reduce their pitch until it becomes nil (as shown in Figure 3b) . With a larger increase of the wind, the pitch of the blades 14 becomes negative (as shown in Figure 3c) and the wind force slows the blades 14 down until they return to a nil pitch. With tests and simulations, it is possible to determine the ideal pitch of the blades 14 as a function of the rotation speed to efficiently slow the wind turbine down and to bring it back to a proper rotation speed. With the information collected from the tests, it is possible to design the exact shape of the slots 26. The design is relatively simple and provides an unequalled accuracy of approx . ± 5 RPM. In the illustrated case, the slots 26 have been designed so that the attack angle of the blades 14 passes from 8 degrees to -12 degrees depending on the speed of the wind and the rotation speed of the blades 14. The shape of the slots 26 may be changed to suit particular operating conditions. For example, if the power provided by the wind turbine is too high for a specific application, the slots 26 may be modified so as to reduce the rotation speed of the blades 14 and the resulting optimal power. Other pitch limit angles may be chosen if desired. For example, the starting-up pitch (no speed) can be 10 degrees from 0 to 75 RPM, and then negative down to -12 degrees to reduce the speed if necessary. Optimization of the shape of the slots 26 can be made using information based on the speed of the wind, the rotation speed of the rotor 8, the pitch of the blades 14 and the produced power.

Referring to Figures 6 and 7, the springs 30 are initially compressed to maintain an attack angle of 10 degrees up to the nominal speed of 75 RPM. The spring 30 is compressed-mounted between stop rings 49 inwardly projecting in the tubular shafts 18 and rings 48 of piston-like members having a rod 32 passing through a central hole bored in the stop rings 49 and fastened to the transverse pin 28 through a mounting block 46.

Referring back to Figure 2, the shafts 18 are preferably integral parts of the blades 14 but can also be separate parts attached to the blades 14 if desired. The positions of the slots 26 and the pins 28 may be interchanged if desired.

In the illustrated case, three blades 14 are used. This number has been chosen to optimize the performance/cost ratio. The blades 14 should be aerodynamically designed to optimize the efficiency provided as a function of the desired operating parameters. Different blade shapes can be used, e.g. already available blades if desired. The bushings 20 are preferably made of nylon with built- in oil lubrication.

The rotor-blade assembly is also provided with a synchronization arrangement made of a rotary disk 34 mounted onto the hub 16, and arms 36 pivotally connected between the blades 14 and the rotary disk 34 and mutually transmitting radial displacements of the blades 14 to one another by rotation of the rotary disk 34. This mechanism is used to synchronize and balance the position of the blades 14 to make sure that they are all at the same distance from the rotation center and that they have all the same pitch with respect to wind. The synchronization arrangement reduces vibrations and oscillations of the wind turbine. Indeed, since it is practically impossible to have exactly the same force in the springs 30, the same frictional forces or the same strains on the three blades 14, the blades 14 would possibly move at slightly different distances from the rotation center with respect to one another even though they all rotate at the same speed. Since they may be at distances which are not exactly the same from the center, their attack angle can also be slightly different. The force of the wind would then be different on each blade 14 which would cause the wind turbine to oscillate about its axis. By synchronizing the position of the three blades 14, this problem is avoided. When the blades 14 move away from the hub 16, the arms 36 rotate the disk 34 on the hub 16 and force the other blades 14 to hold exactly the same distance from the hub 16 and consequently the same attack angle (by means of the slots 26) .

Preferably, the blades 14 have a rotation axis 44 extending at 1/5 from their leading edges 24 so that the forces applied on the lower and upper surfaces of the blades 14 are best arranged in order that the pitch of the blades 14 may be changed without strokes. The ideal position of the rotation axis 44 has been determined by a trial and error process, because it appeared highly difficult to apply theoretical notions due to the combination of two simultaneous movements (motion of the blade 14 away from the hub 16 and rotation of the blade 14 on itself) as well as the wind thrust on the blade 14 and the centrifugal force urging the blade 14 to react accordingly.

Referring to Figure 1, the supporting base 6 can be arranged to be mounted onto a tower (not shown in the Figures) . A nacelle 38 preferably encloses the generator 4 which is directly coupled to the rotor 8 supporting the blades 14, to facilitate as much as possible the wind motion. The supporting base 6 can be designed so as to be free to rotate about the axis of the tower so that the wind turbine turns in the appropriate direction under the simple effect of the wind (like a weathervane) . The nacelle 38 may have an aerodynamic ovoid shape truncated between the generator 4 and the rotor 8. The rotor 8 may then be provided with a mobile cover 40 having a complementary shape to the nacelle 38 and rotating about the rotation axis 44 of the rotor 8. The three sleeves 22 receiving the blades 14 project through the hull of the cover 40.

The supporting base 6 may be formed of a rotatable upper end 50 and a lower tower attachment frame 52. The upper end 50 has a mounting plate 54 on which the generator 4 is secured, e.g. with bolts, and superimposed cylinders 58a-c rotatable with respect to one another about their central axis through ball bearings 60a-b. A cylindrical column 62 extends upwardly through the ball bearings 60a-b. The lower frame 52 has a disk 56 for mounting the base 6 onto a tower, e.g. with bolts.

The transfer of electric power down to the ground level can be made using electric cables connected to the generator 4 preferably through an electric brush contact system installed at the junction level between the stationary and mobile parts of the supporting base 6.

Referring to Figures 8 and 9, to prevent oscillations of the wind turbine, the blades 14 are slanted on the downwind side at an angle 42 of approx. 13 degrees from the rotation plane 43. In this way, the blade 14 on the side of the wind (as depicted by arrow 108) shows a larger projected surface than the blade (s) on the opposite side, which leads the wind turbine to realign more quickly with respect to the wind direction and helps reducing the oscillations. The downwind angle 42 of 13 degrees has been found to be the optimal angle to reduce the oscillations based on confidential experimental tests. This angle 42 could be different depending on the size and design of the turbine's components, e.g. the blades, etc. Under no wind condition, the blades 14 have a pitch of 10 degrees with respect to the wind direction. Based on confidential experimental tests, this pitch has proven to be ideal for the starting-up of the wind turbine even under very weak winds.

Preferably, the wind turbine is equipped with safety brakes, one of which is responsive to vibrations or oscillations of the turbine, another one of which is responsive to the rotation speed of the rotor 8, both of which being arranged to actuate the braking system of the generator 4 when the oscillations or the rotation speed exceed a predetermined threshold.

Referring to Figures lOa-d, there is shown a braking device protecting the wind turbine from oscillations which may be too strong. The braking device has a support plate 88 which is mounted onto the generator 4 (see also Figure 1) . A lever 80 is pivotally connected to an end of the support plate 88. The lever 80 is used to actuate the braking system of the generator 4 which is connected to the projecting tab 82. The lever 80 is pressed downward by a spring-loaded arrangement made of an arm 84 and a stretched spring 86. A ball-bearing mounted wheel 90 attached to a cam 78 prevents the lever 80 from going down and actuating the braking system. The wheel 90 is applied against the bottom face of the lever 80 and the projecting plate 92. The cam 78 is free to pivot about the pivot pin 94. The oscillation of the wind turbine produces oscillation of a hanging weight 76 linked to the cam 78. If the oscillation becomes too large, the pivoting of the cam 78 thereby produced is enough to cause disengagement of the wheel 90 under the lever 80. The tension of the spring 86 then pushes the lever 80 downward thereby actuating the braking system connected to the tab 82. For a gradual braking effect, a damper 96 is installed between the support plate 88 and a hooking tab 98 at the end of the arm 84.

Referring to Figure 11, there is shown a braking device protecting the wind turbine from racing conditions, e.g. during a violent storm. The device is very simple and operated by centrifugal force. A disk 102 is mounted onto the shaft 15 (also shown in Figure 1) of the generator 4. A pivoting lever 104 is peripherally mounted on the disk 102 and is held back by a return spring 106 mounted between the lever 104 and the disk 102. When the rotation speed increases, the centrifugal force on the lever 104 becomes sufficiently large to exceed the tension in the spring 106. The lever 104 then begins to turn about the pivot axis 100. When the rotation speed becomes too high, the pivoting of the lever 104 becomes sufficiently important to make it hit the hanging weight 76 of the braking device shown in Figures lOa-d. The braking system of the generator 4 is then actuated and the wind turbine stops . One specific feature of the above safety brakes is that they are both mechanical in nature and do not require any external power supply.

The design of the wind turbine is very simple, easy to build, inexpensive and does not require maintenance or lubrication. The self-regulating mechanism allows to obtain a rotation speed sufficiently constant to avoid the need of electronics to control the rotation speed of the wind turbine. It is also possible to remove the load from the wind turbine (to disconnect the electric appliances) without any risk of racing. As a result of the steadiness of speed and because the rotation speed remains low, the wind turbine generates much less noise than existing models.

The speed of the wind turbine has been limited to 80 RPM for "esthetical" reasons. Greater the rotation of the rotor 8 is, greater the generated power is. However, when the speed becomes too high, the wind turbine is noisy and visually less attractive for people living close to it and who see it turning. Furthermore, since the blades 14 have been especially designed for the turbine, it provides at 80 RPM much more power than existing wind turbines operating at the same speed. Even under really strong winds, it can be expected that the speed of the wind turbine according to the • present invention will seldom exceeds 10 % of its nominal speed as a result of its self-regulating system.

While embodiments of this invention have been illustrated in the accompanying drawings and described above, it will be evident to those skilled in the art that changes and modifications may be made therein without departing from the essence of this invention.

Claims

CLAIMS :

1. A self-regulating wind turbine comprising: a supporting base; a generator mounted onto the base; and a rotor extending on a downwind side of the generator, the rotor having: a hub rotatably coupled to the generator; a plurality of variable-pitch blades evenly distributed around the hub and radially projecting therefrom at a downwind angle from a rotation plane of the rotor; and means for adjusting a pitch of the blades as a function of a centrifugal force produced by rotation of the rotor.

2. The self-regulating wind turbine according to claim

1, wherein the means for adjusting comprises respective telescopic arrangements between the blades and the hub, spring elements inside the telescopic arrangements exerting a pressure against the centrifugal force moving the blades away from the hub, and guiding elements arranged on the telescopic arrangements and guiding the blades along pitch changing courses as the blades radially move with respect to the hub.

3. The self-regulating wind turbine according to claim

2, wherein the pitch changing courses deflect along radial directions of the hub and define limits wherein the blades move nearest and farthest from the hub and have leading edges going from positive to negative limit angles with respect to a direction of rotation of the blades.

4. The self-regulating wind turbine according to claim 3, wherein: the telescopic arrangements comprise tubular shafts projecting from the blades, bushings mounted onto the shafts, and sleeves radially projecting from the hub and slideably receiving the bushings; and the guiding elements comprise slots extending in the bushings and defining the pitch changing courses, and transverse pins extending across the sleeves and through the slots in the bushings, the spring elements being compressed- mounted between stop rings inwardly projecting in the tubular shafts and piston-like members passing through the stop rings and fastened to the transverse pins.

5. The self-regulating wind turbine according to claim

3, wherein the positive and negative limit angles are substantially 10 degrees and -12 degrees respectively.

6. The self-regulating wind turbine according to claim 4, wherein each one of the shafts and each corresponding one of the blades form a unitary piece.

7. The self-regulating wind turbine according to claim

4, wherein the bushings comprise self-lubricating bushings.

8. The self-regulating wind turbine according to claim 7, wherein the self-lubricating bushings are made of nylon with built-in oil lubrication.

9. The self-regulating wind turbine according to claim 2, wherein the means for adjusting further comprises a synchronization arrangement balancing the pitch of the blades with one another.

10. The self-regulating wind turbine according to claim 9, wherein the synchronization arrangement comprises a rotary disk mounted onto the hub, and arms pivotally connected between the blades and the rotary disk and mutually transmitting radial displacements of the blades to one another by rotation of the rotary disk.

11. The self-regulating wind turbine according to claim 1, further comprising a nacelle covering the generator.

12. The self-regulating wind turbine according to claim 11, wherein the nacelle has an ovoid shape truncated between the generator and the rotor, the rotor being provided with a mobile cover having a complementary shape to the nacelle.

13. The self-regulating wind turbine according to claim 1, wherein the supporting base comprises a rotatable upper end to which the generator is secured, and a lower tower attachment frame.

14. The self-regulating wind turbine according to claim 1, wherein the downwind angle of the blades is substantially 13 degrees.

15. The self-regulating wind turbine according to claim 1, further comprising a safety brake responsive to oscillations of the self-regulating wind turbine and actuating a braking system of the generator when the oscillations exceed a predetermined threshold.

16. The self-regulating wind turbine according to claim 15, wherein the safety brake comprises a hanging weight linked to a cam arranged to disengage from and release a spring-loaded arm operatively connected to the braking system of the generator when oscillations of the weight exceed the predetermined threshold.

17. The self-regulating wind turbine according to claim 1, further comprising a safety brake responsive to rotation speed of the rotor and actuating a braking system of the generator when the rotation speed exceeds a predetermined threshold.

18. The self-regulating wind turbine according to claim 16, further comprising a safety brake responsive to rotation speed of the rotor and actuating a braking system of the generator when the rotation speed exceeds a predetermined threshold, wherein the safety brake responsive to rotation speed comprises a disk mounted onto a shaft of the generator, a pivoting lever peripherally mounted on the disk, and a return spring mounted between the lever and the disk and exerting a holding back pressure on the lever, the lever operatively pivoting out and hitting the weight of the safety brake responsive to oscillations under a centrifugal effect of the disk exceeding a predetermined threshold.

19. The self-regulating wind turbine according to claim 1, wherein the blades have a rotation axis extending at substantially 1/5 from leading edges thereof.