Note: Descriptions are shown in the official language in which they were submitted.
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SELF-REGULATING WIND TURBINE
FIEZD 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 tee
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 ~los. 30,038 (Babcock),
2,037,528 (Miller), 2,096,860 (Renquist et al.), 2,264,568
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(Hamilton), 2,457,576 (Zittrell), 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 kW, 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.
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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
30 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
30 blades.
Figure 2 is a schematic front view of a rotor according
to the present invention.
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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 10a-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.
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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
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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 = MV~/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 ~X
(where K is the rigidity constant of the spring and ~X 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 stabilising 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
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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.
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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
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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
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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 blades) 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 10a-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
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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
10a-d. The braking system of the generator 4 is then actuated
and the wind turbine stops.
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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.
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