Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to a windpower system or wind
turbine and more particularly to apparatus for
controlling the pitch of variable pitch turbine blades in
such a system in response to wind speed changes. The
present windpower system is especially useful for
generating electrical energy. An overview of windpower
systems used for such a purpose is contained in an
article by E. Henson, entitled "Electrical Energy from
the Wind." found in the Energy Technology Handbook
1~ at 6-1~2 et ~ (1977).
Background of the Invention
There are~ in present day use, numerous different
types of windpower systems or wind turbines used to
1~ generate electrical power. These systems usually include
a shaft-mounted turbine whose torque output is used to
drive an electrical generator. When wind conditions are
favorable, the electrical output from the generator is
- coupled into the electrical utilities' transmission
2~ lines. On the other hand when the wind speed is too low,
the generator is isolated from those lines. In order to
operate the generator at its optimum speed or maximum
power output, the wind turbine must produce a selected
relatively constant torque despite changes in wind speed.
This is accomplished in most systems by sensing the
rotational speed of the turbine. To maintain constant
output power then, the pitch of the turbine blades is
varied so that the blades intercept more or less of the
moving air stream momentum thereby to regulate the torque
output of the turbine and, as a result, its speed.
Prior windpower systems have employed pitch angle
control mechanisms which are either more complex or less
effective than that of this invention. Therefore, they
are unduly costly to manufacture and repair, or are less
3~ effective in controlling the speed of the turbine. For
r~
example, some conventional turbines employ hydraulic
pistons to change the blade pitch, with the fluid flow
in the pistons being controlled by a speed-controlling
governorO Examples of s~ch arrangements are disclosed in
U.S. Patent 2,832,895 and on page 3~1 of Van Nostrand's
Scient _ ic Encyclopedla, Third Edition 1958. In another
system, described in U.S. Patent 2,583,369, the turbLne
hub is slidably mounted on its shaft. The turbine blades
are terminated inside the hub by cams which slide in
lU slots on that shaft. Also, springs bias the hub to a
reference position on the shaft. As the wind exerts
pressure on the blades, the hub slides in one direction
or the other on its shaft so that the blades are cammed
to the proper pitch.
1~ Still another rather complex pitch control mechanism
is disclosed in U.S. Patent 2,360,792. That mechanism
includes a hydraulic actuator and hydraulic compensated
governor. The actuator's piston is connected to the
turbine blades and the movement of the piston changes the
2~ blade pitch. In response to wind speed changes, the
hydraulic governor delivers fluid under pressure to the
actuator to cause the blades to assume their proper
pitch.
Other prior windpower systems utilize various
electrical components to control blade pitch, examples of
same being described in U.S. Patents 3,974,395; 4,095,120
and 4,160,170. However those arrangements require slip
~ rings and other sliding electrical contact elements which
are prone to failure due to surface corrosion, wear and
contamination by dirt and moisture. In short, then, the
prior systems are not as simple and trouble-free as they
might be. ~lso some of them do not maintain adequate
control over the turbine during unusual circumstances
such as the occurrence of sudden strong winds which
subject -the components o-E the system to unusually high mechanical
stressA
Also, in wind turbines such as this, it is essential
that the pitch control mechanism be designed such that anticipated
modes oE failure drive the blades to their Eeather position at
which they produce little or no torque so the turbine stops. For
that purpose, prior apparatus rely on spring forces, complex
battery-powered motor systems, or the self-feathering aerodynamic
properties of the turbine itself. In some circumstances, such as
where the blades or the pitch control mechanism is sei~ed or ice-
locked, these forces may be insufficient to feather the blades so
that considerable damage to the turbine may result.
Summary of the Invention
Accordingly the present invention aims to provide an
improved windpower system or wind turbine.
The invention provides a windpower system comprising A.
a support, B. a turbine shaft rotatively mounted to the support,
C. a turbine having variable pitch blades rotatively mounted to a
hub connected to one end of said turbine shaft, D. torque take-oEf
means connected to said turbine shaft, E. a control shaft rotative-
ly mounted to the support, F. means for increasing blade pitch
when the rotation of the turbine shaft in an intended wind-driven
direction is faster than that of the control shaft and decreasing
blade pitch when the turbine-shaft rotation in the intended direc-
tion is slower than the control-shaft rotation in the intended
direction, and G. an electrical brake acting between the support
and the control shaft so that by engaging the brake, the blades
can be moved to their fully feathered position solely by the torque
developed by the rotati.ng turbine, said electrlcal brake engaging
when deenergized so that in the event of a power failure, the
turbine blades are feathered.
The invention also provides a windpower system for
generating a rated output power comprising: A. a support; B. a
turbine shaft rotatably mounted on the support; C. a turbine to be
propelled by wind, the turbine includi.ng a hub and having variable-
pitch blades rotatably mounted on the hub for rotation among posi-
tions including a full-power position, a feathered position, and
a so-called scram position between the latter two positions; D. a
generator coupled to the turbi.ne shaft for driving by the turbine
to generate power; E. means for monitoring the pitch of the blades
to indicate when the blades are in the feathered position, the
scram position, and the full-power position; and F. means for
controlling the blade pitch to tend to achieve the rated output
power but for moving the blades to their feathered positions if
wind speed is so high that the rated output power is sustained
even when the blades are in their scram positions.
The system disclosed herein achieves unusually close
control over the pitch of the system's turbine blades in response
to wind speed changes, and in conjunction with an electrical gener-
ator produces maximum electrical power output under a wide variety
of different wind conditions. The windpower system shuts down
rapidly in response to excessive wind speed and other emergency
situations and develops unusually large forces to feather the
blades in an emergency in the event they have become seized or ice-
bound.
The windpower system can operate for a prolonged period
~ 5~ .
withou-t maintenance and utili~es, to a large extent, conventional
off-the-shelf components so that the cost O r the system is kept to
a minimum. The individual parts can be repaired or replaced
relatively easlly in a minimum amount of time.
The invention accordingly comprises the features of con-
struction, combination of elements and arrangement of parts which
wil:l be exemplified in the following detailed description, and the
scope of the invention will be indicated in the claims.
Briefly, the present windpower system is designed to be
pivotally mounted atop a high tower so that it can swivel or yaw
with the result that the turbine blades always intercept the wind
stream. Usually the windpower system or turbine is one of many
situated on a "farm" with the electrical outputs of all of the
systems being coupled into the power grid of a nearby electrical
utility. Each system provides an electrical output to the utility
as long as the prevailing wind speed exceeds a minimum value. When
the wind speed drops below that value, no useful power output can
be developed by the turbine and, therefore, the system is decoupled
from the power grid.
Each system comprises a tubular turbine shaft which is
rotatably mounted on a frame support. A turbine is connected to
the end of that shaft. When the turbine is rotated by air currents,
the torque on that shaft is
5a
coupled, via a speed increasing transmission, to the
shaft of an electrical generator mounted to the support,
causing the generator to develop electric power for
delivery to the utility.
The system employs variable pitch turbine blades
whose pitch angle can be varied to facilitate turbine
start-up and shut-down, and to limit turbine torque
output when wind speed exceeds that necessary to produce
rated power from the yenerator. For this, the rotary
motion of the turbine shaft is also coupled by a clutch
to a coaxially-mounted, tubular, control shaft. The
control shaft is internally threaded to accept a threaded
pitch actuating r~d, which extends from the control shaft
into the turbine hub. There, it is connected to the
blades by bell cranks so that linear movements of the
actuating rod result in changes in the pitch angle of the
turbine blades. The same linkages in the hub also
rotatively connect the actuating rod to the turbine sha~t
so that those two elements rotate in unison.
The system further includes a reversible servomotor
for rotating the control shaft thereby to adjust the
relative speed of the control and turbine shafts. When
the turbine blades are oriented at the correct pitch for
2~ the prevailing wind speed, the system controller engages
the clutch, thereby rotatively coupling the control shaft
to the turbine shaft so that those shafts, as well as the
actuating rod, rotate in unison. Consequently, there is
no linear movement of the actuating rod as would change
the pitch of the turbine blades.
~ owever, if the wind speed changes, the system's
controller disengages the clutch and drives the
servomotor so as to rotate the control shaft either
faster or slower than the turbine shaft, thereby to cause
the actuating rod to advance or retract by the necessary
amount to adjust the pitch angle of the blades for that
different wind speed. Thus, in a particular embodiment,
if the wind speed decreases, the motor rotates the
control shaft faster than the turbine shaft so as to
retract the actuating rod and move the blade pitch angle
toward the full-power position (i.e. a pitch angle of
approximately 0), with the result that the turbine
develops more torque and speeds up. Conversely, if the
wind speed increases, the motor rotates the control shaft
slower than the turbine shaft. This causes the actuating
1~ rod to advance and thereby move the pitch angle of the
blades toward the feather position (i.e. a pitch angle
of 90), with the result that the turbine produces less
torque and slows down. Thus, the linear or axial position
of the actuating rod provides a direct indication of the
lS blade pitch and thus wind speed.
It is important to note that through the use of the
aforesaid coaxial differential shaft arrangement, the
system is able to transfer control forces to the rotating
~ turbine blades from a fixed rotary servomotor without the
2~ need for rotary electrical or hydraulic couplings, swivel
joints, swash plates, or other such wear-prone parts as
are found on conventional wind turbines.
A blade pitch sensor responds to the linear position
of the actuating rod and applies signals to the
controller which indicate when the blades are feathered
and, when they are at the full-power position. The sensor
also signals the controller when the blades are at the
so-called start position (i.e. a pitch angle of
approximately 45) which is the optimum position of the
blades for initiating turbine rotation~ and when the
blades are at a so-called scram angle. This angle
depends upon the mechanical limits of the turbine. More
particularly, each turbine has a maximum safe wind speed
at which it can operate at full power. Operation of the
turbine above that point jeopardizes the fatigue life of
J~
the blades, tower and other mechanical components of the
turbine. Thus if the turbine is operating at its maximum
rated speed and the blades have had to be feathered back
as far as the scram angle (e.g. 20), ~his indicates a
wind speed unsafe for continued operation of the turbine.
In this situation, the controller responds to a signa]
from the pitcb sensor and activates the servomotor so
that the control shaft is rotated much slower than, or
even in the opposite direction from, the turbine shaft.
1~ Resultantly, the blades are moved to their feathered
position quite rapidly and the turbine halts.
The present system also includes provision for
stopping the turbine in the event of a power failure to
the system or under other emergency conditions such as a
1~ failure of pitch servo motor. For this purpose, the
system emplo~s an electrical brake acting between the
control shaft and the support. During normal operation
of the turbine, electrical power to the brake, derived
from the network which also tools the generator,
2~ disengages the brake, so that the control shaft is free
to rotate relative to the support. However, if when the
turbine is operating, the connection to the power network
should be interrupted so that blade pitch is no longer
under control, not only is the clutch disengaged, but the
de-energized brake engages and couples the control shaft
directly to the support. Since the turbine continues to
turn, the actuating rod is advanced so that the blades
are brought to their fully feathered position thereby
halting the turbine. Failsafe feathering, when power is
interrupted, is vital because under such a condition, the
generator will be unloaded and the sudden loss of
torsional load on the turbine will cause it to rapidly
accelerate to a destructive overspeed condition if no
feathering action is taken.
3~
The same emergency braking action occurs if the
blades do not assume a certain pitch angle after they are
directed to do so by the controller. For example, if
under unsafe wind conditions, the blades reach the scram
angle, yet fail to feather within a short time interval
because of a malfunction of the servomotor, the
controller de-energizes the brake thereby simulating a
power failure. The brake thereupon couples the control
shaft to the support so that the blades are again driven
1~ to the feathered position. Thus the brake serves as a
back-up for the servomotor in a scram situation. It is
important to appreciate that in this failsafe mode of
operation, the blades are feathered solely due to the
motion of the wind-driven turbine relative to the braked
1~ control shaft. Since the moving turbine possesses a
considerable amount of torque, it can apply considerable
force to drive the blades to the safe feathered position
in the event they are ice-bound or the pitch control
mechanism has seized.
2~ Furthermore, in the present system as soon as the
blades are feathered, the actuating rod mechanically
disengages the brake so that the control shaft is
decoupled from the support, while at the sa~e time the
rod is coupled to the control shaft. Now, the control
shaft, actuating rod, and turbine shaft all rotate in
unison so that there can be no linear movement of the
actuating rod and, thus, no movement of the blades from
the feathered position.
In a system such as this, it is, of course,
3~ desirable to operate the generator so that it produces
maximum output power. On the o~her hand, it is essential
that the system including blades, transmission,
generator, and tower not be stressed beyond their
mechanical or thermal limits. To satisfy these
constraints, the system monitors the output power from
the generator and varies the pitch of the blades to limit
generator output to its maximum power rating. Instead of
measuriny the generator output directly, however, the
system employs a generator o~ the induction type which
operates normally at a speed somewhat greater than its
nominal synchronous speed. ~he deviation from
synchronous speed is referred to as "slip" given in
absolute RPM or as a fraction or percentage of
synchronous speed. It is characteristic of such a
lU generator that its output power varies directly with the
amount of slip. Therefore, the shaft speed of the
generator which changes with slip, provides a direct
indication of the generator output. A tachometer
monitors that speed and applies a signal to the
1~ controller. The controller, in turn, controls the clutch
and the servomotor so as to vary the pitch of the turbine
blades from their aforesaid maximum power position as
needed to limit output power from the generator to its
maximum rating despite changing wind conditions.
When the present system is started, we will assume
the blades are feathered and the turbine is stationary.
A signal from a central control station causes the
controller to decouple the clutch and drive the
servomotor so that the motor rotates the control shaft.
This retracts the actuating rod thereby moving the blade
pitch angle toward the start position. When the pitch
sensor detects that the blades have reached start-up
pitch, the controller engages the clutch and stops the
servomotor so that the blades remain at this pitch angle.
If wind speed is above the minimum necessary to
sustain useful power output ~rom the turbine, the turbine
will be accelerated to a start-up speed. If this speed
is sustained for a brief period, the controller will
again disengage the clutch and activate the servomstor to
33 move the turbine blades to their full-power position.
When the generator tachometer indicates a speed-producing
positi~e slip so ~hat the ~enerator is producing useful
power, the controller effects connection of the generator
to the power grid.
As the wind speed increases~ the generator speed
increases until the generator reaches the allowed maximum
power. At this point, the generator speed sensor issues
a signal to the controller causing it to decouple the
clutch and activate the servomotor to rotate the control
lU shaft relative to the turbine shaft to move the blade
pitch toward feather. As a result, the turbine slows
down to maintain the generator at its maximum power
output condition. ~onversely, a subsequent decrease in
wind speed causes the controller to move the blade pitch
toward the full-power position to maintain the generator
at maximum power.
If the wind speed should increase to the point where
the pitch of the blades has to be moved to the scram
angle in order to maintain the generator at its rated
2~ output, indicating excessive strong winds, the controller
disengages the clutch and activates the servomotor so as
to move the blades to feather thereby stopping the
turbine.
Since the present system is composed primarily of
rugged mechanical parts, many of which are off-the-shelf
items, the cost of manufacturing and assembling the
system can be kept to a minimum. Furthermore, repairs,
when needed, can be made relatively quickly so that the
downtime of the system is also a minimum. Finally,
3~ because of its mode of achieving blade pitch control, the
system responds quickly and reliably to rapid wind speed
changes and is fully protected in the event of excessive
wind speeds or emergencies that might cause thermal or
mechanical damage to the system.
Brief_Description o the Draw nq_
For a fuller understanding of the nature and objects
¦ of the invention, reference should be had to the
following detailed description, taken in connection with
the accompanying drawings, in which:
FIG. 1 is a fragmentary perspective view with parts
broken away of a tower-mounted windpower system
incorporating the invention;
FIG. 2 is a sectional view on a larger scale showing
lU the FIG. 1 system in greater detail;
FIG. 3 is a schematic diagram showing the control
section of the FIG. 1 system;
FIG. 4 is a schematic diagram showing the system's
blade pitch control linkage in greater detail;
1~ FIG. 5 is a schematic diagram illustrating the
profile of each blade of the system; and
FIG. 6 is a graphical diagram illustrating the
operation of the FIG. 1 system.
2~ Description of the Preferred Embodiment
While the windpower system specifically described
herein is used to drive a generator to deliver electrical
power to a utility network ("grid"), it should be
understood that the same basic system can also be used as
the motive means for "stand alone" electric generators,
irrigation pumps, compressors, conveyors, etc.
Referring now to FIG. 1, the windpower system or
wind turbine shown generally at 10 comprises a frame
support 12 secured to the top of a tower 14 by way of a
rotary mounting 16 which permits the support to swivel or
yaw. The tower 14 is typically 50 to 150 feet high
depending upon the prevailing winds at the particular
site. The system includes a rotary turbine shaft 18
which is terminated by a turbine indicated generally
at 24. The position and ~he turbine 24 relative to the
rotary mounting 16 is such that the support 12 swivels as
needed to maintain the turbine downwind. If desired, a
yaw control (not shown) can be included which will
positively rotate the support through its mounting 16 so
S that as the wind direction changes the turbine 24 is kept
downwind.
The illustrated turbine 24 is designed so that the
intercepted air stream turns it in a selected direction,
i.e. counterclockwise as viewed in FIG. 1. Torque is
1~ taken from the shaft 18 by way of a transmission
indicated generally at 26. Since the illustrated
windpower system is used to gene~ate electricity, the
transmission output shaft 26a is coupled via a universal
coupling 19 to the shaft 28a of a generator 28 to run the
1~ generator at high speed.
Thus, when the turbine 24 turns, the generator 28
produces an electrical output which is conducted from the
system by way of a cable 36 extending through tower 14 to
the electrical load. In most applications, the
electrical power is fed into the local utility grid.
In the illustrated system, the turbine blades 24a
are rotatively mounted in the turbine hub 24b and
provision is made for adjusting the pitch of these
blades. More particularly, a pitch control section
2~ indicated generally at 44 is mounted to transmission 26.
In response to generator speed changes, the control
section 44 moves an actua~ing rod 46 extending axially
through shaft 18 from that section to the ~urbine 24.
Inside the hub 24b, the rod is connected by way of
three bell cranks 48 to the inner ends of the blades 24a.
The bell crank 48 connection between rod 46 and one such
blade 24a is shown in detail in FIG. 4. As seen there,
the inner end of blade 24a carries an eccentric
member 45. Also, a three-armed spider 46a is mounted to
3~ the end of rod 46. A link 47 is pivotally connected at
14
its opposite ends to member 45 and an arm of the spider
so that linear movement of rod 46 in one direction or the
other rotates the blades 24a in one direction or the
other to change their pitch. Similar links 47 connect
the other two arms of spider 46a to the remaining two
turbine blades 24a. In order to rotatively couple rod 46
to the turbine shaft 18 while permitting axial movement
of the rod relative to the shaft, a reduced diameter
shaft end segment 18a is formed with a lengthwise
lU slot 51. Also, a pin or roller bearing 53 attached to
rod 46 projects into that slot, functioning more or less
as a cam follower.
As shown in FIG. 5, the blades 24a themselves are
shaped as air foils. Furthermore, they have an
1~ appreciable twist from root to tip. Typically as shown
in that figure, the blade tip is oriented about 45
relative to the root of the blade.
A streamlined ventilated housing or cowl shown in
dotted lines at 49 in FIG. 1 encloses the support 12 and
2~ other components of the system except, of course, the
turbine 24.
Refer now to FIG. 2 which shows the components of
the pitch control section 44 in greater detail. The
shaft 18 projects into a housing 50, where it is formed
with a counterbore 52 in order to receive a flanged
tubular extension 54. The extension is rotatively
coupled to the shaft by pins 55 extending through the
extension flange into the end of the shaft. Positioned
coaxially within shaft 18 and its extension 54 is a
tubular control shaft 66. Shaft 66 has a reduced
diameter segment 66a within extension 54 which forms a
seat for a bearing unit 68 located inside extension 54 at
one end thereof. A second bearing unit 68 spaced from
the first by a tubular spacer 72 is located at ~he
opposite end of extension 54. The axial position of the
shaft 66 relative to the bearing units and extension 54
is maintained by a locking ring 74 which engages in a
circumferential groove 76 formed in shaft segment 66a
beyond the bearing units 68.
The opposite end of shaft 66 is journaled by way of
a bearing unit 78 located in the end wall 50a of
housing 50 remote from the turbine. In the illustrated
system, a reduced diameter segment 66b of control
shaft 66 extends through an internal neck 50b formed in
1~ housing 12 intermediate the ends thereof. A bushing 82
is engage~ on shaft segment 66b. The bushing has an
internal key 82a which slidably engages in a longitudinal
keyway 84 in the shaft segment so that the bushing is
rotatively locked to the shaft. The bushing 82 rotates
1~ relative to housing neck 50b by way of a bearing unit 85
which seats against the bases of the bushing and neck.
Locking rings 86 and 88 engage in circular grooves
inscribed around the outside of bushing 82 and the inside
of neck 50b so that the bushing is locked to the housing
2~ axially, but can rotate relative thereto. A third
locking ring 90 seats in a groove formed in control shaft
section 66b just to the left of bushing 82 to fix the
axial position of the clutch 94 on the control shaft and
to absorb thrust.
Referring to FIGS. 1 and 2, the pitch actuating
rod 46 leading from the turbine 24 extends into control
section 44 and more specifically into the end of the
tubular control shaft 66. Furthermobre, that end of
rod 46 is externally threaded at 4~a to mesh wi~h a
3~ nut 92 ormed at the end of control shaft 66~ Also, as
described above in connection with FIG. 4, rod 46 is
constrained to rotate with the turbine shaft 18, yet is
movable axially relative to that shaft by virtue of the
pin-in-slot connection between the rod and shaft. As
3~ noted previously, the lengthwise or axial movement of the
16
pitch actuating rod 46 changes the pitch o-f the turbine blades 24a in one direc-
tion or the other depending upon whether the control shaft is rotated at a
faster or slower rate than the turbine sha:Et 18.
For example, assuming sha-ft 18 is rotatillg in a counterclockwise
direction as shown in FIG. 1 and the rod thread 46_ is a right hand thread, if
shaft 66 i.s rotated at the same speed as shaft 18, then no relative movement
occurs between the control shaft nut 92 and the threaded end 46b oE the actuat-
ing rod7 since that rod turns with shaft 18. Accordingly, there is no change
in the pitch angle of the blades. On the other hand, if shaft 66 is rotated
counterclockwise, as viewed in FIG. 1, at a faster rate than shaft 18, the
threaded engagement of the nut 92 with the rod end 46b causes the rod to re-
tract lengthwise into the shaft 66, i.e., toward the left in FIG. 2. This
lengthwise movement of the rod 46, in turn, rotates the blades 24a so as to
move them toward their full-power position. Conversely, if the shaft 66 is
held stationary or is rotated clockwise~ as viewed in FIG. 1, then the relative
rotary motion of the cont-rol rod threads 46b, with respect to the nut 92 will
move the control rod 46 out of the shaft 66 so ~hat the turbine blades are
moved toward their feathered position.
In order to control the relative rotation of the control shaft and
turbine shaft, the illustrated control section 44 includes a clutch shown gener-
ally at 94 which operates between the shaft 18 and the control shaEt 66. The
clutch 94 includes a discoid clutch plate 96 secured by threaded fasteners 98
to the inner end wall 54a of shaft extension 54. The plate 96 and its connec-
tion to extension 54 are such that the plate can ~lex axially to some extent.
Disposed directly opposite plate 96 is a second clutch plate 102 having a
tubular extension 102a engaged on the control shaft segment 66b. The plate
extension 102a has an internal key 104 which slidably
engages in keyway 84 in that segment so that the
plate 102 rotates with the control shaft. Encircling the
clutch plate extension on a sleeve bearing 105 is an
electromagnetic toroidal wire coil and polepiece
unit 106. A discoid plate 108 is attached to coil
polepiece unit 106 and is restrained from rotation by
pins 110 fitted to internal flange 50c in housing 50.
Plate 102 is normally disengaged from plate 96 so that
lU shaft 18 (and rod 46) rotates independently of control
shaft 66. However, when the clutch coil and polepiece
unit 106 is energized, the clutch plate 96 is flexed
axially into frictional engagement with plate 102 so that
shafts 66 and 18 rotate in unison. As noted previously,
1~ as long as there is no relative movement between those
two shafts, there is no axial movement of pitch actuating
rod 46 and, therefore, no change in the pitch of the
blades 24a.
Such relative movement is effected by disengaging
2~ the clutch 94 and rotating the shaft 66 at a faster or
slower rate than shaft 18. In the illustrated system,
this is accomplished by means of a reversible
servomotor 116 mounted to a radial enlargement 50d of
housing 50. The shaft 116a of the motor carries a
2~ pulley 118 which is connected by a belt 122 to a larger
pulley 124 coupled to control shaft 66. More
particularly, the pulley 124 is engaged on a tapered
locking bushing 126 which encircles shaft 66 just inboard
of its bearing 78. The bushing has an internal key 126a
3~ which slidably engages in a keyway 128 formed in
shaft 66. Pulley 124 is secured to the bushing by
appropriate threaded fasteners 132 extending through
openings in the bushing flange and turned down into
threaded passages 134 in the pulley so as to engage the
3~ pulley with the tapered bushing. As will be described in
detail later, the motor 116 is connec~ed in a servo loop
which varies the speed of the motor as the wind speed
changes. Therefore, the motor rotates control shaft 66
relative to turbine shaft 18 (and rod 46) to move the
actuating rod 46 so as to feather the turbine blades when
the wind speed exceeds that required to develop generator
rated power and to move them ~oward their full-power
position when the wind speed falls below that which will
sustain rated generator output.
In the illustrated preferred embodiment of the
system, provision is also made for fully feathering the
turbine blades so as to stop the rotation of the
turbine 24 and its shaft 18 in the event of a power
failure or any other failure which disables the
servomotor 116. More particularly and referring to
FIG. 2, a brake shown generally at 142 is provided in
section 44 which acts between the control shaft 66 and
the housing 50 to bring the shaft 66 to a complete stop.
With the shaft 66 stopped, the continued rotation of the
shaft 18 and the pitch actuating rod 46 to which it is
linked causes the rod 46 to move out of the control shaft
nut 92 so as to rotate the blades 24a to their feathered
position. As they approach that position, the blades
gather less wind and, accordingly, the turbine 24
gradually slows to a stop.
The brake 142 comprises a flanged brake housing 144
secured to the housing flange 50c by bolts 146 extending
through the brake housing flange and turned down into
threaded openings 148 in housing flange 50c. Inside the
brake housing 44 is a discoid brake shoe 152 mounted to a
hub 154 which extends out through an opening 144a in the
hrake housing. Hub 154 has a key 154a which is slidably
engaged in the control shaft key way 128 so ~hat the hub
and brake shoe rotate with that shaft.
19
Also, positioned inside the brake housing 144 is a
discoid plug 158 which is spaced opposite the brake
shoe 152. Beyond the plug is a bushing 162, slidably
mounted to shaft segment 66b. Also a ring or collar 164
is rotatively mounted to that bushing by way of a bearing
unit 166. Bolts 172 are slidably received in
openings 174 in collar 164. These bolts extend through
registering openings 176 in plug 158 which openings are
counterbored at 176a to accept compression springs 180.
lU Located between the brake shoe 152 and plug 158 is
an annular plate or disk 182. A circular array of
threaded openings 184 are formed in plate 182 which
openings are threaded to receive the bolts 172. Thus the
plate is held by the bolts 172 in register with brake
1~ shoe 152. Furthermore, the plate is biased against the
brake shoe by the springs 180. However, there is
sufficient clearance between the engaging plate and the
plug 158 to permit the plate to be retracted against the
plug, with the bolts 172 sliding in the plug openings 176
and the collar openings 174 toward the right in FIG. 2.
Belleville spring washers 185 are included under the
heads of bolts 172. These are substantially stiffer than
springs 180 and are not materially compressed by the
force required translate collar 164 to close the gap
between brake disk 182 and plug 158. ~owever, when this
gap is closed, the Belleville spring washers 185 allow
collar 164 to be translated by a small additional amount
without applying destructive tensile loads on bolts 172.
A wire coil 185 is contained in the plug 158 which, when
energized, moves the plate 182 to its retracted position.
Thus as long as the brake coil 186 is energized, the
control shaft 66 is free to rotate within the housing 50.
However, whenever the brake coil is de energized due to a
power failure, the springs 180 press the plate against
the brake shoe 152 which is secured by way of brake
housing 144 to the housing 50. ~herefore, the control
shaft 66 to which the plate 182 is connected is rapidly
brought to a stop. Note that in the event of such a
power failure, the clutch 94 will be disengaged thereby
decoupling the control shaft nut 92 and control rod
screw 46a so that shaft 66 is free to move independently
of the turbine shaft 18.
Assuming that the turbine shaft 18 and actuating
rod 46 are rotating counterclockwise as indicated, their
rotary motion relative to the stopped shaft 66 causes the
actuating rod 46 to move out of the control shaft,
i.e. toward the riyht in FIG. 2. This results in the
blades 24a being brought to their feathered position so
that the chord surfaces of the blades 24a no longer
intercept the moving air stream. Accordinglyr the
turbine 24 slows down and eventually will come to a stop.
It should be appreciated, then, that, since the brake
engages when de-energized, the control section 44
operates in a fail-safe mode in that, in the event of a
power failure, the brake 142 always operates to s~op the
turbine 24.
When the blades 24a are brought to their fully
feathered position, the turbine 24 may still be rotating
2~ due to its inertia. Means to disengage the brake must
therefore be provided to prevent further advance of the
blade beyond the feathered position which could destroy
components of the pitch control mechanism. More
particularly and still r~efebrring to FIG. 2, actuating
rod 46 has an extension 4~ which projects through the
~-~ housing end wall 50a. Mounted to that extension is a
collar 194. Also, the end 66d of the shaft 66 projects
through the same wall opposite the collar. The relative
positions of the collar and the shaft are such that when
3~ the actuating rod 46 advances to a position corresponding
to the feathered position of the blades 24a, the
21
brake 142 is released mechanically. More particularly, a
circular array of three push rod~ or keys 204 are
slidably positioned in longitudinal passages 206 in the
wall of control shaft section 66b. The inner ends 204a
of the rods engage ~he bushing 162. Their outer
ends 204b project out beyond the shaft end 66d. The
positions of the rod ends 204b are such that at blade
feather, the collar 194 engages the rods which thereupon
shift the bushing 162 toward the right in FIG. 2 to
1~ disengage the plate 182 from the brake shoe 152.
As mentioned previously, Belleville spring
washers 185, present under the heads of bolts 172, are
substantially stiffer than springs 180 and are therefore
not materially compressed by the actuating force applied
to separate the braking surfaces of plate 182 and
shoe 152.
Now while the brake can no longer retard the
rotation of the control shaft, the inertial and
frictional torque of the de-energized servomotor
2~ multiplied by the step-up ratio of the pulleys 118
and 124 can still retard rotation of that shaft. This
would attempt to drive the mechanism further in the
feather direction if turbine rotation has not ceased at
this point. Such further drive in the feather direction
could damage pitch control mechanism components. This
possibility is precluded in the present arrangement,
however, by further displacement of protruding rods 204b
permitted by the Belleville washers and the engagement of
collar face 194a and control shaft end 66d which clutch-
like action, rotatively couples the actuating rod andcontrol shaft so that no further relative motion of those
parts is possible, whereupon the blades are effectively
locked in the feathered position.
The objective of the present system is to operate
the wind turbine 24 as closely as possible to maximum
efficiency to obtain maximum output power from the
generator 28, while protecting both the turbine and
generator from mechanical or ~hermal damage. For this
purpose, then, the control section 44 includes an
electronic controller shown generally at 206 in FIGS. 1
and 3. The controller monitors the generator output and
responds to changes in wind speed so as to control the
pitch of the turbine blades. When wind speed is less or
equal to that which will sustain rated generator power
1~ output, near-optimal power output is provided by holding
the blades at their full-power pitch position and no
servo action is required. However, when wind speed
exceeds that required for rated output, the blades are
moved toward the feathered position so as to limit
lj generator output power to the rated level.
Preferably, the generator 28 is an asynchronous
induction motor operated as a generator. Accordingly,
its output power is directly related to the amount of
"slip" and therefore to shaft speed. A tachometer 208
mounted to the transmission 26 as shown in FIG. 1
measures the speed of the generator shaft 28a and applies
a corresponding electrical signal to controller 206 or
more particularly to a microprocessor 210 in that
contIol~er. Also coupled to the processor 210 is a
signal from a pitch sensor 212 which reflects the pitch
of the turbine blades 24a. In response to those signals,
the processor operates the clutch 94 and brake 142 by way
of their drivers 214 and 216 respectively and motor 116
via its driver 218 to maintain the blade pitch at the
correct angle for maximum generator output or which
limits output to rated output.
To start the system assuming the turbine blades are
in the fully feathered position, a signal from a remote
site control station 224 (FIG. 3) is applied by way of a
35 control cable 226 extending through tower 14 to the
controller's processor 210. This causes the processor to
issue signals to clutch driver 216 and motor driver 218
thereby releasing the clutch and causing motor 116 to
rotate control shaft 66 faster than turbine shaft 18
(which is stationary). This, in turn, moves the pitch of
blades 24a to a so-called start position between the
feathered and full-power positions, e.g. to a pitch angle
of 45~ This start position of the blades enables the
turbine to start rotating most easily from a dead stop.
lU The pitch ~ensor 212 detects when the blades have reached
that angle and issues a signal to processor 210 causing
it to inhibit the drive current to motor 116 and actuate
clutch 94 so that the blades remain in that start
position. The system is now operating in Region I as
1~ shown in FIG. 6.
The turbine remains in this start-up mode with the
blades 24a at their start position until the wind speed
exceeds a selected minimum value, e.g. 12 mph. When the
wind does exceed that speed, iE the system's
controller 206, which monitors the speed of generator 28,
senses that the generator speed has exceeded a selected
magnitude, e.g. 250 rpm for a certain time e.g. 30
seconds, the controller causes the blades to be moved to
their full power position. That is, ~he controller
disengages the clutch 94 and activates servomotor 116
until the blades have moved to the full power angle, e.~.
about 0, after which the motor is disabled and the
clutch re-engaged to lock the blades at that angle.
~ ith the blades at the full-power position, as the
wind speed increases, the generator speed increases.
Resultantly, the generator output power increases as
shown by the waveform P in the Region II in FIG. 6. When
the generat~r reaches or exceeds synchronous speed, the
controller 110 closes switch 227 to connect the
3~ generator 28 to the power grid.
24
On the other hand, if that start-up speed is reached
only momentarily due to a stray wind gust, the blades
remain at their start angle and ~he turbine simply idles
in operating Region I with the generator isolated from
the utility grid.
In a typical installation, the maximum power level
is reached at a "rated" wind speed of
approximately 22 mph. When the generator speed reaches
the speed for maximum power, this condition is sensed by
lU tachometer 208 and the processor 210 with which it
communicates. In response to this condition, the
processor momentarily decouples the clutch 94 and
energizes servomotor 116 to move the blades 24 toward
their feathered position. Resultantly, the turbine slows
1~ down by the amount that will limit the generator power at
that maximum. In other words, the blades are moved
toward the feathered position to limit the torque output
of the turbine when the wind speed exceeds the system's
rated wind speed. Then, as a result of subsequent
2~ increases or decreases in wind speed, the controller
decouples the clutch and operates the servomotor to move
the blades away from or toward their full-power position
to compensate for the wind speed change in order to
maximize generator output power in Region II winds or
2~ limit power to its rated output in Region III winds. The
system is now operating in Region III of FIG. 6.
If the wind should die (i.e. fall into Region I) so
that the generator is not delivering useful power to the
utility grid for a prescribed time, this condition is
30 sensed by the tachometer 208 and processor 210. The
processor thereupon opens the electrical switch 227 to
the grid and returns the turbine blades 24a to their
start-up position. On the other had, if wind speed
increases dangerously, e.g. to 41 mph in Region IV of
3~ FIG. 6 to the point where the blades have had to be moved
to the scram angle (e.g. 20~) in order to maintain the
rated generator output, the controller disengages the
clutch 94 and drives the servomotor 116 in the opposite
direction from the turbine. This relative motion fully
feathers the blades to avoid damage to the system.
Further, if the processor 210 does not receive a
signal from the pitch sensor 208 within a veey short time
interval, e.g. 10 seconds indicating that the blades are
not feathered due, for example, to a damaged motor 116 or
lU a broken pulley belt 122, the processor de-energizes
motor 116, the clutch 94 and the brake 142. This results
in the blades being feathered by the force provided by
the rotating turbine as discussed above, albeit at a
slower rate than if feathered by the servomotor.
1~ Likewise, if there is a power failure to the system, the
clutch and brake are de-energized with the same results.
Indeed, the processor 210 initiates this fail-safe
braking mode when any command to feather from the
processor fails to accomplish that result within a
2~ selected time-out period or the generator power output is
not reduced below the selected rated value.
The pitch sensor 212 may be any one of a variety of
different types. For example, simple mechanical, optical
or magnetic switches responding to the lengthwise
position of actuating rod extension ~* may be used, one
switch closing when the blades are feathered at 90, a
second switch closing when they are at the 45 start-up
angle, a third when they are at the 20 scram angle, and
a fourth switch closing when they are at the full-power
pitch angle of 0. The switches are connected to apply
appropriate voltage levels to the controller
processor 210 to cause the processor to produce the
necessary outputs for properly controlling the clutch,
brake and servomotor in control section 4~ as discussed
33 above. Alternatively, a digital encoder (incremental or
26
absolute~ or a potentiometer (plus an analog to digital converter) driven by
the actuating rod extension 46c may be used to communicate the pitch position
to the processor 210. These alternatives allow positions to be adjusted by pro-
cessor soEtware changes or by commands received from the site control station
22~. These devices also allow the site control station to monitor blade pitch
more closely, Eor example, to obtain diagnostic i.nformation.
In FIG. 3 we have illustrated a particularly accurate sensor 212 for
monitoring blade pitch continuously. Here, the end of rod extension 46c pro-
jects into the end of a slide 232 having a square cross-section wherein it
engages a square slider 234 which is movable along the slide. A rotary connec-
tion is provided between the rod extension 46c and the slider to accommodate
the rotary motion of the extension. Attached to the nut is one end of a flat
flexible s-trap 236 whose opposite end is wound up on a roller 238. The roller
is spring biased to wind up the strap and its shaft 238a is coupled to the
shaft of a digital shaft encoder 242. Thus the digital output of the encoder
reflects the linear position of the rod extension 46c upon which depends the
pitch of blades 24a.
It will thus be seen that the objects set forth above, among those
made apparent from the preceding description, are efficiently attained. Also
certain changes may be made in the above construction without departing from
the scope of the invention. For example, the clutch ~4 and motor 116 may be
substituted for by a single synchronous servomotor to rotate control shaft 66
at the correct speed relative to turbine shaft 18 in response to control
signals from processor 210 to control blade pitch. Alternatively, countershaft
means may be provided to derive clockwise and counterclockwise torque from the
wind torque, selectively coupled through electrical clutches to the pitch con-
trol shaft 66 to effect changes in pitch. In this case, the capacity of motor
27
116 may be substantially reduced since it would only be required to slowly move
the pitch angle from the feather position to the start-up angle to permit start-
up rotation of the turbine. Therefore, it is intended that all matter con-
tained in the abo-ve description or shown in the accompanying drawings be inter-
preted as illustrative and not in a limiting sense.
It is also to be understood that the following claims are intended to
cover all of the generic and speci:Eic features of the invention herein des-
cribed.
