Abstract:
A wind turbine with a passive pitch control system is disclosed. The wind turbine comprises a tower with a nacelle mounted to the tower. A hub is rotatably mounted to the nacelle. The hub has a plurality of blades extending therefrom with each blade rotatable around a longitudinal axis of each blade. A pitch control system is operatively associated with each blade. The pitch control system controls the pitch of each blade around the blade&#39;s longitudinal axis. In a preferred embodiment, the pitch control system comprises a flyweight governor and a preloaded spring biased against each other.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates generally to wind turbines and, more particularly, to an improved design for a passive pitch control system which includes a flyweight governor. 
       BACKGROUND 
       [0002]    In recent years, wind turbines have been integrated into electric power generation systems to create electricity to support the needs of both industrial and residential applications. These wind turbines capture the kinetic energy of the wind and convert it into electricity. A typical wind turbine includes a set of two or three large blades mounted to a hub. Together, the blades and hub are referred to as the rotor. The rotor is connected to a main shaft, which in turn, is connected to a generator. When the wind causes the rotor to rotate, the kinetic energy of the wind is captured and converted into rotational energy. The rotational energy of the rotor is translated along the main shaft to the generator, which then converts the rotational energy into electricity. 
         [0003]    Nearly all wind turbines utilize pitch control systems to control how the turbine blades interact with the wind. The pitch control system rotates each blade around the longitudinal axis of the blade in order to effectively capture wind or not capture wind to avoid damage of the turbine at high speed winds. The pitch, or angle, of the blade around the longitudinal axis can greatly affect the generated power output. 
         [0004]    When there is a continual flow of wind, the wind turbine can generate significantly more power if the blades are pitched to capture the wind. In order to increase the amount of wind captured by the rotor, the turbine blades can be pitched toward a power position. A power position is a lower pitch angle that aligns the blade to capture wind, or pitches the blade into greater influence of the wind. In particular, the blades are perpendicular to the flow of the wind, which causes the rotor to rotate faster. This in turn increases the torque on the main shaft that is delivered to the electric generator, resulting in increased output power. 
         [0005]    At times when there are high speed winds that could cause damage to the wind turbine by overspeeding, it would be ideal for the blades to be pitched to capture less wind energy. In order to decrease the amount of wind captured by the rotor, the blades can be pitched toward a feather position. A feather position is a higher pitch angle where the blade is not aligned to capture wind, or angled away from influence of the wind. In particular, the blades are parallel to the flow of the wind. This in turn decreases the torque on the main shaft that is delivered to the electric generator, resulting in decreased power output. 
         [0006]    Pitch control systems can be active or passive. Active pitch control systems utilize hydraulic, pneumatic, or electro-mechanical actuators in concert with a closed loop control system to drive the blades to a specific angle of attack. These systems are both accurate and fast. However, active pitch control systems are rather expensive and can consume a large percentage of the wind turbine&#39;s own generated output power. Wind turbine designers have explored several passive pitch control architectures including aerodynamic pitch control, aerodynamic stall blades, passive yaw systems, and flexible blades. However, a need still exists for a simplified, accurate passive pitch control system. This invention is directed to solving this need and provides a way to reduce the cost and complexity of the wind turbine blade pitch control system by utilizing a flyweight governor. 
       SUMMARY OF THE INVENTION 
       [0007]    According to one embodiment of the present disclosure, a wind turbine is disclosed. The wind turbine may comprise a tower, a nacelle mounted at a top of the tower with the nacelle containing at least one generator, a hub rotatably mounted to the nacelle, a main shaft operatively connected between the hub and the generator, a plurality of blades radially extending from the hub with each blade mounted for rotation around a longitudinal axis of each blade, and a pitch control system adapted to control a pitch of each blade around each longitudinal axis. The pitch control system may comprise a flyweight mechanism and a preloaded spring, the flyweight mechanism and preloaded spring being biased against each other. 
         [0008]    According to another embodiment, a windpower generator system is disclosed. The windpower generator system may comprise a rotatable hub, a plurality of blades radially extending from the hub with each blade mounted for rotation around a longitudinal axis of each blade, and a pitch control system operatively associated with each blade to control a pitch of each blade around the longitudinal axis of each blade. The pitch control system may comprise a flyweight mechanism and a preloaded spring, the flyweight mechanism and preloaded spring being biased against each other. The hub, blades, and pitch control system may all be provided as an assembly which is stationary relative to ground. 
         [0009]    According to yet another embodiment, a method for generating electricity from wind is disclosed. The method may comprise providing a tower with a nacelle mounted to the tower, a hub being rotatably mounted to the nacelle and including a plurality of blades radially extending therefrom, each blade being rotatable about its longitudinal axis. The method may further comprise using the blades to capture the kinetic energy of wind, converting the kinetic energy of wind into rotational energy with at least one shaft which rotates as the wind forces the plurality of blades and hub to rotate, and using a pitch control system to control the pitch of the blades around the longitudinal axis of each blade. The pitch control system may comprise a flyweight mechanism and a preloaded spring, the flyweight mechanism and preloaded spring being biased against each other. 
         [0010]    Other advantages and features will be apparent from the following detailed description when read in conjunction with the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a perspective view of a wind turbine made according to one embodiment of the present disclosure; 
           [0012]      FIG. 2  is a cross-sectional view of the wind turbine of  FIG. 1  taken along line  2 - 2 , with the pitch control system and blades in power position; 
           [0013]      FIG. 3  is a cross-sectional view of the wind turbine of the present disclosure, with the pitch control system and blades in feather position; 
           [0014]      FIG. 4  is a cross-sectional view of a wind turbine made according to another embodiment of the present disclosure, with the pitch control system, mechanical trigger mechanism, and blades set in the initial feather position; 
           [0015]      FIG. 5  is a cross-sectional view of the wind turbine of the present disclosure, with the pitch control system, mechanical trigger mechanism, and blades in power position; and 
           [0016]      FIG. 6  is a cross-sectional view of the wind turbine of the present disclosure, with the pitch control system, mechanical trigger mechanism, and blades in feather position. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Referring to  FIGS. 1 and 2 , a wind turbine  10  according to an embodiment of the present disclosure is shown. While all components of the wind turbine are not shown or described, the wind turbine  10  may include a vertically oriented tower  12 , which has a stationary base  14  and body element  16 . The stationary base  14  of the tower  12  is permanently situated on the ground G and therefore, the wind turbine  10  is structurally stable and cannot be moved. The body element  16  is attached to the stationary base  14  and extends upwards to a height at which the wind turbine  10  can optimally capture the kinetic energy of the wind. A nacelle  18  is rotatably mounted on top of the body element  16  of the tower  12 . A hub  20  is mounted for rotation to the nacelle  18 . The hub  20  is mounted to a main shaft  26 , which is operatively connected to the generator  28 . 
         [0018]    Radially extending from the hub  20  are a plurality of blades  22 . Each of the blades  22  is mounted for rotation around a longitudinal axis A of each blade  22 . A pitch control system  24  is secured to each blade  22  to control the pitch of each blade  22  around the longitudinal axis A of the blade  22 . 
         [0019]    According to one embodiment of the present disclosure, the turbine blades  22  can be mounted to the hub  20  through a base section  30  and supported for rotation by thrust bearings  32 . The blades  22  are mounted for rotation around the longitudinal axis A. Each blade  22  is secured to the pitch control system  24  through a pin  34 . The pitch control system  24  includes a flyweight mechanism  42  and a preloaded spring  44  coiled around the main shaft  26 . The flyweight mechanism  42  includes a pin housing member  50 , sliding member  60 , and a flyweight governor  62 . The pin housing member  50  of the flyweight mechanism  42  receives the pin  34  of the blade  22  and is mounted on the sliding member  60 . Through the mating engagement of the pin  34  and the pin housing member  50 , the pitch control system  24  is secured to the blade  22 . 
         [0020]    The sliding member  60  of the flyweight mechanism  42  is generally cylindrical in shape and situated around the main shaft  26 . Although shown and described as having a cylindrical shape, the sliding member  60  of the flyweight mechanism could have any shape, including but not limited to cubical, spherical, conical, and tubular, without departing from the scope of this disclosure. The sliding member  60  includes a first rigid protrusion  64  at one end and a second rigid protrusion  66  at the other end. The first protrusion  64  of the cylindrical sliding member  60  engages and acts against the preloaded spring  44 . The second protrusion  66  of the cylindrical sliding member  60  is in contact with and engages the flyweight governor  62 . 
         [0021]    As shown in  FIG. 2 , when there is no wind present, the blades  22  of the wind turbine  10  are set in the power position. The blades  22  optimally capture the wind when pitched in power position. In the power position, the blade  22  is pitched into greater influence of the wind (i.e. perpendicular to the flow of the wind). As the wind flows, the plurality of blades  22  and hub  20  rotate about the main shaft axis B. The hub  20 , which is mounted to the main shaft  26 , causes the main shaft  26  to also rotate about main shaft axis B. The main shaft  26 , which is operatively connected to the generator  28 , delivers this rotational energy to the generator  28 . The generator  28  subsequently converts the rotational energy into electricity. 
         [0022]    As the hub  20  and blades  22  are rotating, the flyweight mechanism  42 , being biased against the preloaded spring  44 , governs the speed of the wind turbine  10 . The flyweight governor  62  has a flyweight  70 , lever  72 , and roller  74 . The flyweight  70  is pivotally mounted to a support structure  80  on the back wall  82  of the hub  20 . The roller  74  of the flyweight governor contacts the second rigid protrusion  66  and engages the sliding member  60 . The lever  72  extends from the flyweight  70  and is mounted to the roller  74 . The lever connects the flyweight  70  to the roller  74 . In the figures, only one flyweight  70 , lever  72 , roller  74 , etc. are shown. However, two or more flyweights evenly spaced around the main shaft axis B would not be outside the scope of the invention. In fact, such an arrangement may allow for proper balance. 
         [0023]    As the windflow increases, the hub  20  rotates faster, and the centrifugal force within the hub causes the flyweight  70  to move away from the main shaft axis B and radially outward toward the sidewall  84  of the hub  20 , as shown in  FIG. 3 . Consequently, the roller  74 , which is attached to the flyweight  70  by the lever  72  and engaged to the sliding member  60  at second protrusion  66 , pushes the sliding member  60  against the preloaded spring  44  and compresses it. In addition, since the pin housing member  50  and engaged pin  34  are mounted on the moving sliding member  60 , the blade  22  (which is attached to the pin  34 ) also moves and changes its pitch angle around the longitudinal axis A. As a result of the varying rotation and centrifugal force within the hub, the flyweight mechanism  42  and preloaded spring  44  act against each other to passively control the blade pitch and establish rotational equilibrium based on the windflow and the load applied to the wind turbine  10 . 
         [0024]    In the case of high wind events, when the rotation of the hub  20  has reached its maximum limit, the blades  22  are pitched in the feather position, as shown in  FIG. 3 . In the feather position, the turbine blades are pitched to capture less wind. Feather position is the position in which the blades are angled away from the influence of the wind (i.e. parallel to the flow of the wind). More specifically, the flyweight  70  is forced against the sidewall  84  of the hub  20 . The roller  74  simultaneously pushes the sliding member  60  toward the preloaded spring  44 , and the attached pin housing member  50  and pin  34  move the blade  22  around longitudinal axis A so that it is parallel to the windflow. In this way, no damage is caused to the wind turbine because it is not subject to overspeeding. Unlike wind turbines that utilize brakes, the pitch control system  24  of the present disclosure sheds the load caused by high-speed winds when the blades are pitched in feather position, thereby eliminating drag, overheating, and damage to the blades, generator, bearings, gears, and other components of the wind turbine system. 
         [0025]    When the wind slows down and reciprocally the rotation of the hub  20  decreases, the centrifugal force within the hub decreases. As a result of the decreased centrifugal force pushing the flyweight  70  against the sidewall  84  of the hub  20 , the preloaded spring  44  is able to decompress and, in turn, push the sliding member  60  toward the back wall  82  of the hub  20 . As the sliding member  60  is pushed back, the roller  74  is also pushed toward the back wall  82  and the flyweight  70  moves radially inward toward the main shaft axis B and away from the sidewall  84  of the hub  20 . Therefore, when there is little to no wind, the blade  22  will be in power position and ready to capture wind again, as shown in  FIG. 2 . 
         [0026]    In addition, a maximum speed of the wind turbine can be predetermined by setting the load of the preloaded spring  44 . More specifically, a speed control fastener  90  can secure the nose cone  92  of the hub  20  to the end of the main shaft  26 , preferably by threaded engagement. The nose cone  92  and speed control fastener  90  can be rotatably adjusted on the hub about the main shaft axis B. The preloaded spring  44  is compressed between the nose cone  92  and the first protrusion  64  of the sliding member  60 . Thus, the load on the spring  44  is determined by the amount of compression caused by the adjustable nose cone  92  and speed control fastener  90  against the spring  44 . The amount of compression on the preloaded spring  44  governs the overall speed of the wind turbine  10  by determining the resistance biased against the flyweight mechanism  42 . The higher the preloaded spring  44  is initially compressed, the more flyweight mechanism  42  force will be required to overcome the preloaded spring  44 . The higher flyweight mechanism  42  force will be generated by higher rotational speeds. Therefore, as the preloaded spring  44  is set to a higher state of pre-load, the wind turbine will settle at a higher operating speed. Similarly, less initial pre-load on the preloaded spring  44  will result in a lower speed of the wind turbine. Although a nose cone  92  and speed control fastener  90  are shown and described herein, it will be understood that other methods of creating the initial spring pre-load including, for example, but not limited to, shims, threaded screws, different spring rate springs, pneumatic springs, trapping air in a bladder to push against the flyweight mechanism, and magnetic springs, may all be used for altering the turbine operating speed without departing from the scope of this disclosure. 
         [0027]    According to another embodiment of the present disclosure shown in  FIGS. 4-6 , the pitch control system  124  may also include a mechanical trigger mechanism  140  in addition to the flyweight mechanism  142 , and the preloaded spring  144  coiled around the main shaft  126 . When there is no wind present for which the wind turbine  110  to capture, the blades  122  are initially set in the feather position, as shown in  FIG. 4 . The mechanical trigger mechanism  140  includes a pin housing member  150  and a second spring  152 . The pin housing member  150  of the trigger mechanism  140  receives the pin  134  of the blade  122 . Through the mating engagement of the pin  134  and the pin housing member  150 , the pitch control system  124  is secured to the blade  122 . The second spring  152  of the trigger mechanism  140  is coiled around the main shaft  126  and sliding member  160 . Specifically, the second spring  152  is compressed between the pin housing member  150  and the second rigid protrusion  166  of the sliding member  160 . In this way, the second spring  152  is biased against the pin housing member  150 . Thus, when there is no wind to move the blades  122 , the second spring  152  acts against the pin housing member  150  and pin  134  to keep the blade  122  in feather position. 
         [0028]    When enough wind flows by the wind turbine  110  to induce a high starting torque, the blades  122  are moved to power position, as shown in  FIG. 5 . More specifically, the force of the wind causes each blade  122  to centrifugally twist around the longitudinal axis A. This torque, or centrifugal twisting motion, of the blade is transferred through to the base section  130 , connected pin  134 , and associated pin housing member  150 . The pin housing member  150  is moved against and compresses the second spring  152 . Thus, the blade  122  is pitched into greater influence of the wind (i.e. perpendicular to the flow of the wind), or power position. 
         [0029]    As the windflow increases, the hub  120  rotates faster, and the centrifugal force within the hub causes the flyweight 1   170  to move away from the main shaft axis B and radially outward toward the sidewall  184  of the hub  120 , as shown in  FIG. 6 . Consequently, the roller  174 , which is attached to the flyweight  170  by the lever  172  and engaged to the sliding member  160  at second protrusion  166 , pushes the sliding member  160  against the preloaded spring  144  and compresses it. In addition, since the pin housing member  150  and engaged pin  134  are mounted on the moving sliding member  160 , the blade  122  (which is attached to the pin  134 ) also moves and changes its pitch angle around longitudinal axis A. As a result of the varying rotation and centrifugal force within the hub  120 , the flyweight mechanism  142  and preloaded spring  144  act against each other to passively control the blade pitch and establish rotational equilibrium based on the windflow. 
         [0030]    In the case of high wind events, when the rotation of the hub  120  has reached its maximum limit, the blades  122  are pitched in the feather position, as shown in  FIG. 6 . When the wind slows down and reciprocally the rotation of the hub  120  decreases, the centrifugal force within the hub decreases. As a result of the decreased centrifugal force pushing the flyweight  170  against the sidewall  184  of the hub  120 , the preloaded spring  144  is able to decompress and, in turn, push the sliding member  160  toward the back wall  182  of the hub  120 . As the sliding member  160  is pushed back, the roller  174  is also pushed toward the back wall  182  and the flyweight  170  moves radially inward toward the main shaft axis B and away from the sidewall  184  of the hub  120 . At the same time, the second spring  152  of the trigger mechanism  140  decompresses as the second protrusion  166  of the sliding member  160  moves towards the back wall  182  of the hub  120 . Therefore, when there is no wind, the blade  122  will be set in the initial feather position and ready to capture wind again, as shown in  FIG. 4 . 
         [0031]    From the foregoing detailed description, it is apparent that the disclosure described is an inexpensive, simple, efficient, and reliable form of passive pitch control utilized to control the rotational speed of the wind turbine. While the foregoing detailed description has been given and provided with respect to certain specific embodiments, it is to be understood that the scope of the disclosure should not be limited to such embodiments, but that the same are provided simply for enablement and best mode purposes. The breadth and spirit of the present disclosure is broader than the embodiments specifically disclosed and encompassed within the claims appended hereto.