Abstract:
The present invention provides an improvement for use in a wind turbine ( 20 ) having a plurality of variable-pitch blades ( 24 ) mounted on a hub ( 23 ) for rotation relative to a nacelle ( 22 ). The improvement broadly includes: a electro-hydraulic actuator ( 25 ) for controlling the pitch of one of the blades, the actuator including: a motor ( 26 ) adapted to be supplied with a current; a pump ( 27 ) driven by the motor and arranged to provide a hydraulic output as a function of the current supplied to the motor; and a hydraulic actuator ( 28 ) operatively arranged to selectively vary the pitch of the associated blade as a function of the hydraulic output of the pump; and wherein the motor, pump and actuator are physically arranged within the hub of the wind turbine.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates generally to the field of wind turbines, and, more particularly, to an improved wind turbine having a plurality of electro-hydraulic actuators mounted on the rotatable hub of the turbine for independently controlling the pitch of a like plurality of blades. 
       BACKGROUND ART 
       [0002]    Wind turbines are, of course, known. In recent years, many of the problems of having a wind turbine supply power synchronously to an electrical grid have been addressed and overcome. 
         [0003]    Wind turbines today are relatively sophisticated. They are typically mounted on a tower, and have plurality of blades (normally three) mounted on a hub for rotation about a horizontal axis relative to a nacelle. The nacelle may be aimed into the direction of the oncoming wind. Each of the blades is typically of variable pitch, and the pitch of each blade may be controlled independently of the others. These blades are typically arranged at 120° intervals. When one blade is pointing aiming downwardly toward the 6 o&#39;clock position, the wind proximate the ground is typically less than the speed of the wind moving over the other two blades. Hence, the pitch of each blade is controlled independently of one another with the goal trying to normalize (i.e., keep reasonably constant) the rotational speed of the hub from ground effects, gusts, etc. 
         [0004]    Heretofore, wind turbines have been characterized as being of the electrical-type or of the hydraulic-type. In either case, the generator is typically mounted in the nacelle. Control signals and power are supplied up through the tower, and to a pitch-controlling mechanism. In both cases, this pitch-controlling mechanism has been heretofore mounted in the nacelle, and this necessitates a type of slip ring joint between the nacelle and the rotatable hub. In addition, this arrangement has been accompanied by the use of a large bull gear, and with various hoses within the hub. The life expectancy of such an arrangement has been as short as about four years due to excessive wear on the bull gear caused principally by variations in the speed of the wind. 
         [0005]    Accordingly, it would be generally desirable to provide an improved wind turbine in which the pitch-controlling electro-hydraulic actuator is mounted within the hub, rather then on the nacelle. 
       DISCLOSURE OF THE INVENTION 
       [0006]    With parenthetical reference to the corresponding parts, portions or surfaces of the disclosed embodiment, merely for purposes of illustration and not by way of limitation, the present invention provides an improvement for use in a wind turbine ( 20 ) having a plurality of variable-pitch blades ( 24 ) mounted on a hub ( 23 ) for rotation relative to a nacelle ( 22 ). 
         [0007]    The improvement broadly includes: a electro-hydraulic actuator ( 25 ) for controlling the pitch of one of the blades, the actuator including: a motor ( 26 ) adapted to be supplied with a current; a pump ( 27 ) driven by the motor and arranged to provide a hydraulic output as a function of the current supplied to the motor; and a hydraulic actuator ( 28 ) operatively arranged to selectively vary the pitch of the associated blade as a function of the hydraulic output of the pump; and wherein the motor, pump and actuator are physically arranged within the hub of the wind turbine. 
         [0008]    In one form, the wind turbine has three of the variable-pitch blades ( 24 ) mounted on the hub, and wherein one of the electro-hydraulic actuators ( 25 ) is provided for each of the blades. 
         [0009]    The motor may be a d.c. brushless motor. 
         [0010]    The pump may be a fixed displacement pump. 
         [0011]    In the preferred embodiment, the polarity of the hydraulic output from the pump is a function of the polarity of the current supplied to the motor. 
         [0012]    The actuator may have a piston ( 30 ) slidably mounted within a cylinder ( 31 ) and sealingly separating a first chamber ( 35 ) on one side of the piston from a second chamber ( 36 ) on the other side of the piston, and wherein a rod ( 32 ) is mounted on the piston and extends through chamber ( 35 ) and penetrates and end wall of the cylinder such that the piston has unequal-area surfaces facing into the chambers. The improved actuator may further include a hydraulic reservoir ( 41 ) and an anti-cavitation valve ( 57 ) operatively arranged between the tank and the actuator such that hydraulic fluid will flow from the reservoir to the chamber facing the larger-area piston face when such chamber is expanding, and will flow to the reservoir from the chamber facing the larger-area piston face when such chamber is contracting. 
         [0013]    The hydraulic reservoir may be pressurized. 
         [0014]    The anti-cavitation valve may operate automatically as a function of the polarity of the hydraulic output of the pump. 
         [0015]    The improvement may further include a pressure relief valve ( 48 ,  52 ) operatively arranged to limit the maximum pressure of the pump hydraulic output. 
         [0016]    The pump may have a high-pressure side and a low-pressure side, and a case drain. 
         [0017]    A bypass valve ( 54 ) may be positioned selectively operable to communicate the high- and low-pressure sides. 
         [0018]    The case drain ( 40 ) may communicate with the reservoir through a filter. 
         [0019]    The improvement may further include a restricted orifice ( 56 ) in series with the bypass valve. 
         [0020]    The improvement may further include: a source ( 62 ) of pressurized hydraulic fluid communicating via a conduit ( 63 ) with the chamber into which the small-area piston surface faces, and a normally-open solenoid valve ( 64 ) arranged in the conduit, and wherein the solenoid valve is arranged to be opened in the event of a power failure to permit hydraulic fluid to flow from the source through the conduit and into the chamber into which the small-area piston surface faces to cause such chamber to expand and to urge the piston to move toward a position relative to the cylinder at which the blade is feathered. 
         [0021]    The improvement may further include blocking valves ( 59 ,  60 ) operatively arranged to selectively isolate the pump from the small- and large-area actuator chambers. 
         [0022]    Power and/or control signals to the motor are preferably supplied form the nacelle to the hub through a contactless rotary transformer. Examples of these are shown and described in U.S. Pat. Nos. 5,608,771, 6,813,316 and 5,572,178, the aggregated disclosures of which are hereby incorporated by reference. 
         [0023]    Accordingly, the general object of the invention is to provide an improved electro-hydraulic actuator for use in a wind turbine to control the pitch of one of a plurality of variable-pitch blades thereon. 
         [0024]    Another object is to provide an improved electro-hydraulic actuator for use in a wind turbine, wherein the major components of the actuator are mountable on the rotating hub and not on the nacelle. 
         [0025]    Another object is to provide an improved actuator for use in a wind turbine, and wherein the actuator contains a fail-safe mechanism for urging the associated blade to move toward a feathered position in the event of a power failure or interruption. 
         [0026]    These and other objects and advantages will become apparent from the foregoing and ongoing written specification, the drawings and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  is an isometric view of the upper marginal end portion of a wind turbine, showing fragmentary portions of the variable-pitch blades as being mounted on the hub for rotation about a horizontal axis relative to a nacelle. 
           [0028]      FIG. 2  is a hydraulic schematic of the improved electro-hydraulic actuator. 
           [0029]      FIG. 3  is a left side elevation of an improved electro-hydraulic actuator for controlling the pitch of one of the blades. 
           [0030]      FIG. 4  is a top plan view of the actuator shown in  FIG. 3 . 
           [0031]      FIG. 5  is a left end elevation of the actuator shown in  FIG. 4 . 
           [0032]      FIG. 6  is a block diagram of the circuit for independently controlling the three blades. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0033]    At the outset, it should be clearly understood that like reference numerals are intended to identify the same structural elements, portions or surfaces consistently throughout the several drawing figures, as such elements, portions or surfaces may be further described or explained by the entire written specification, of which this detailed description is an integral part. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this invention. As used in the following description, the terms “horizontal”, “vertical”, “left”, “right”, “up” and “down”, as well as adjectival and adverbial derivatives thereof (e.g., “horizontally”, “rightwardly”, “upwardly”, etc.), simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms “inwardly” and “outwardly” generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate. 
         [0034]    Referring now to the drawings, and more particularly to  FIG. 1  thereof, an improved wind turbine, generally indicated at  20 , is shown as being mounted on the upper marginal end portion of a tower, a fragmentary portion of which is generally indicated at  21 . A nacelle  22  is rotatably mounted on the upper marginal end portion of the tower for rotation about a vertical axis y-y. A hub  23  is mounted on the nacelle for rotation about a horizontal axis x-x. A plurality of blades, severally indicated at  24 , are mounted on the hub for rotation therewith. The pitch of each blade is independently controllable by means of the improved electro-hydraulic actuators disclosed herein. A main shaft (not shown) transfers rotational movement of the hub into the nacelle, to drive a generator (not shown) in the usual manner. The nacelle also includes various usual and typical items such as gear box (not shown) for increasing the speed of the driven shaft, transformers (not shown), and the like. 
         [0035]    Heretofore, the mechanism for controlling the pitch of the blades was mounted on the nacelle, and control was transferred to the hub by means of a bull gear. In the present invention, however, the electro-hydraulic actuators are mounted within the hub, and the bull gear can be eliminated altogether. 
         [0036]    Referring now to  FIG. 2 , the improved electro-hydraulic actuator  25  is schematically indicated as including a motor  26 , a pump  27  driven by the motor, and a double-acting hydraulic actuator, generally indicated at  28 . 
         [0037]    In the preferred embodiment, the motor is a brushless D.C. motor that is supplied with a current from the nacelle via a contactless rotary transformer (not shown). When the supplied current is of one polarity, the motor will rotate in one direction. When the supplied current supplied is of the opposite polarity, the motor will rotate in the opposite direction. 
         [0038]    Pump  27  is preferably a fixed displacement pump, and is connected to the motor by means of a shaft  29 . 
         [0039]    The actuator  28  is shown as having a piston  30  slidably mounted within a cylinder  31 . A rod  32  as its left end mounted on the piston, and penetrates the cylinder right end wall. An eye  33  is mounted on the right end of rod  32 . Another eye  34  is shown as being mounted on the cylinder left end wall. The piston is slidably mounted within the cylinder, and sealingly separates a leftward chamber  35  from a rightward chamber  36 . The entire circular vertical end surface of piston  30  faces into left chamber  35 . However, an annular vertical surface of the piston faces rightwardly into right chamber  36 . The entire electro-hydraulic actuator is mounted within the rotatable hub of the wind turbine. Eye  34  is mounted to the rotatable hub, and eye  33  is mounted to a lever arm (not shown) connected to control the pitch of the associated blade. 
         [0040]    One side of pump  27  communicates with actuator left chamber  35  via a conduit  38 , and the opposite side of pump  27  communicates with actuator right chamber  36  via a conduit  39 . A drain conduit  40  communicates a portion of the pump flow with a reservoir  41  via a filter  42  and a check valve  43 . More particularly, conduit  40  extends between the case drain and the filter, conduit  44  communicates the filter  42  with check valve  43 , and conduit  45  communicates check valve  43  with another conduit  46  communicating with the reservoir or tank  41 . This tank is shown as having a diaphragm, and is gas pressurized to a pressure of about 90-250 psi. 
         [0041]    Conduit  38  communicates with tank  41  via a conduit  47  which includes a high-pressure relief valve  48 , connected conduits  49 ,  50  and  46 . Conduit  39  communicates with tank  41  via conduit  51  which contains another high-pressure relief valve  52 , and connected conduits  49 ,  50  and  46 . The function of pressure relief valves  48 ,  52  is to provide a relief for an over pressure condition depending on the polarity of the pump operation. Conduit  38  also communicates with conduit  39  via a conduit  53 , a bypass solenoid  54 , and a conduit  55  containing a restricted orifice  56 . 
         [0042]    Conduits  38  and  39  also communicate with one another via a conduit  54 , an anti-cavitation valve  55 , and a conduit  56 . Solenoid-operated bypass valves  57 ,  60  are positioned in conduit  38 ,  39 , respectively. The anti-cavitation valve  57  is a type of inverse shuttle valve that samples the pressure of the fluid in conduits  38 ,  39 , and moves automatically in response to the pressure differential therebetween. The function of anti-cavitation valve  57  is to accommodate the volumetric changes between opposed actuator chambers  35 ,  36 . In other words, when piston moves leftwardly within the cylinder, the volume of fluid removed from collapsing left chamber  35  will be greater than the volume of fluid supplied to expanding right chamber  36 . The anti-cavitation valve functions to permit the excess or differential fluid to flow through conduits  46 ,  49 ,  50  to the reservoir. Conversely, when the actuator piston moves rightwardly relative to the cylinder, a differential amount of fluid may flow from reservoir  41  through conduit  46  and the anti-cavitation valve into the expanding left actuator chamber. 
         [0043]    A charge fitting  61  communicates with conduit  39  to allow fluid to be added to the system. A fail-safe accumulator  62  communicates with conduit  39  via a conduit  63  containing a normally-opened solenoid valve  64 . 
         [0044]    When the wind turbine is first started, bypass valves  59 ,  60  are closed, and fluid is first pumped into accumulator  62  to charge and pressurize this accumulator to about 3,000 psi. Thereafter, valves  59 ,  60  are opened to permit fluid to flow to the actuator. 
         [0045]    The function of the fail-safe accumulator  62  is to provide a source of pressurized hydraulic fluid to the system in the event of a loss of power to the motor. In the event of a power failure, fail-safe accumulator  62  will provide a source of pressurized hydraulic fluid to displace the actuator rod leftwardly toward a feathered positioned of the blade. 
         [0046]    A commercial form of the apparatus is depicted in  FIGS. 3-5 , in which the same number is used to refer to the parts previously described. 
         [0047]    Referring now to  FIG. 6 , a larger control system for independently controlling the pitch of each of three blades is depicted. A signal from a three phase slip ring  65  is supplied to each of three motor controllers  66 A,  66 B,  66 C. Each motor controller supplies a signal to a power stage  67 A,  67 B,  67 C, respectively, which in turn supplies the current of the appropriate magnitude and polarity to electro-hydraulic actuators A, B and C, respectively. The position of each rod  32  is monitored via an LVDT  68 A,  68 B,  68 C, respectively, and the position signals are then fed back to their associated motor controllers,  66 A,  66 B,  66 C, respectively. A rotating optical ring for data transmission  69  also provides an input signal to each motor controller. Thus, in this manner, the system may control the pitch of each blade independently. Of course, the arrangement shown in  FIG. 6  is specific to a three-bladed wind turbine. If a greater or lesser number of blades were to be employed, the number of actuators would be correspondingly adjusted. 
       Modifications 
       [0048]    The present invention expressly contemplates that many changes and modifications may be made. In the improved wind turbine, an electro-hydraulic actuator is provided for each blade so that the pitch of the various blades can be controlled independently of one another. While it is presently preferred to use a D.C. brushless motor, other types of motors may be used as well. Similarly, while the fixed-displacement pump is presently preferred, other types of pumps might possibly be substituted therefore. 
         [0049]    The actuator might, of course, have a rod penetrating both cylinder end walls. However, this would like interfere with the nose of the hub. Nevertheless, if arrangement could be accommodated, there would be no need for the anti-cavitation valve since the volume of the expanding chamber would equal the volume of the collapsing chamber. 
         [0050]    If desired, the motor controller and the power stage can be incorporated directly into the improved hub-mounted electro-hydraulic actuator. 
         [0051]    Therefore, while the presently-preferred form of the improvement has been shown and described, and several modifications thereof discussed, persons skilled in this art will readily appreciate that various additional changes and modifications may be made without departing from the spirit of the invention, as defined and differentiated by the following claims.