WIND TURBINE SHUTDOWN SYSTEM

Abstract: The wind turbine (10) incorporates a wind vane (105) which mechanically controls a valve (100) that directs the output of a turbine driven hydraulic pump (75) to yaw the turbine out of the wind upon a loss of system power or load. The turbine yaws out of the wind at an angular rate that is roughly proportional to rotor speed so that excessive teeter amplitudes are not encountered. The mechanically driven pump advantageously provides power to yaw the rotor out of the wind even if all electrical power is lost.

Description: This invention relates to wind turbines and more particularly to a wind turbine which yaws out of the wind in an emergency. Some wind turbines utilize a rotor which includes one or more fixed pitch, airfoil blades. The blades are connected via a teetering hub, a shaft and a gearbox to an electric generator or alternator. The power output of the wind turbine is regulated by controlling the angle (known as yaw angle) between a plane formed by the rotating blades and the direction of the wind. Full power may be achieved when the plane of the blades is perpendicular to the direction of the wind (i.e. "into" the wind). No power is achieved (and the aerodynamic torque upon the rotor is minimized) when the plane of the blades is parallel to the direction of the wind (i.e. "out" of the wind). The power output of the system may be varied by yawing the rotor angularly by degree into and out of the wind. Some systems have automatic controls which set the yaw angle to optimize the power output of the system. In an emergency, as when the system load is lost or the automatic control has lost power, the wind turbine must be yawed out of the wind to prevent the blades from overspeeding. Overspeeding may cause severe damage to wind turbine components. In US-A-4 372 732, which discloses a wind turbine according to the precharacterizing portion of independent claim 1, a windmill holding tall is rotated away from the windmill rotor shaft axis to move the blades out of the wind. The windmill shaft actuates through a crank mechanism a piston-cylinder unit to pressurize a hydraulic fluid for driving a hydraulic motor connected to an electric generator. In case of overpressurization a first hydraulic cylinder is operated to rotate the tail of the windmill from its operating plane. In case of loss of hydraulic fluid a second cylinder moves the tail to its furtherest angular position away from the rotor axis. A minimum hydraulic fluid pressure in the second cylinder maintains the windmill tail in its operating position. The object of the invention is to provide a wind turbine having fixed blades and being capable of yawing the wind turbine blade into and out of the wind to optimize power output and capable of yawing the wind turbine blade out of the wind in the event of an emergency without encountering excessive teeter amplitudes. According to the invention, to achieve this, there is provided a wind turbine comprising a fixed pitch airfoil blade mounted on a rotatable hub, a hydraulic pump driven by said blade and having a pump outlet, and hydraulic motor means for yawing the blade into and out of a wind stream during normal operation of the wind turbine and for yawing the blade out of the wind stream in an emergency condition, characterized by said hydraulic means having first control circuit means including a directional valve receiving hydraulic fluid from the pump outlet, and means directed by a controller for positioning the directional valve to control hydraulic fluid flow to the hydraulic motor means to drive said motor means for yawing the blade into and out of the wind stream to optimize power output during said normal operation of the wind turbine, and a second control circuit means effective in an emergency condition for mechanically controlling in response to a wind vane hydraulic fluid flow from said pump outlet to said directional valve to further position said directional valve and thereby further control said hydraulic fluid flow to said hydraulic motor means such that the blade is yawed out of the wind In said emergency condition. The pump driven by the blade yaws the blade at a rate that is roughly proportional to blade speed so that excessive teeter amplitudes are not encountered. The blade driven pump provides power to yaw the blade out of the wind even If all electrical power is lost. Advantageous features of the wind turbine are recited in the dependent claims 2 to 6. These and other features and advantages of the present invention will become more apparent in the light of the following detailed description of a best mode embodiment thereof, as illustrated in the accompanying drawing, wherein: Fig. 1 relates to a wind turbine which incorporates the emergency shutdown system of the invention; and Fig. 2 shows a schematic diagram of the emergency shutdown system of Fig. 1. Referring to Figure 1, a wind turbine 10 is shown. The wind turbine comprises a pair of airfoil blades 15 and 20 that are mounted to a teetering rotatable hub 25. The blades and the hub form a rotor. The hub is pivotally connected to shaft 30 by a teeter pin 35. The shaft 30 connects to a gearbox 40 which steps up the rotational speed of the hub and blades to a value equal to the desired speed of rotation of electric generator or alternator 45. The generator or alternator is connected to the gearbox by shaft 50. A nacelle 55 encloses the generator, the gearbox, the connecting shafts, a yaw bearing 60, which rotatably supports the nacelle in a tall, flexible, tower 65, and the emergency shutdown and control system 70. The emergency shutdown and control system 70 includes: a first circuit including a pressure regulated, variable displacement pump 75, a command valve 80, a directional valve 85, and a yaw motor 90; and, a second circuit including a check valve 95, a control valve 100, a mechanical wind vane 105, and a camming mechanism 110 for connecting the wind vane and the control valve. The first and second circuits are controlled by a conventional electrical controller (not shown). The controller may have a circuit (not shown), as is known in the art, for comparing the yaw angle of the rotor with a yaw angle of the rotor that was commanded by the controller. The pump 75 is driven mechanically by the rotor or by any known means such as a shaft 110. The pump draws hydraulic fluid 115 from a reservoir 120 via line 125. The pump impels the fluid to the directional and command valves 85, 80 via line 130 and to the second circuit via line 135. A relatively small amount of the fluid in line 130 is directed to the command valve 80 via line 140 and a relatively large amount of the fluid in line 130 is directed to the directional valve 85 via line 145. The command valve is positioned electrically by the controller, as is known in the art, to direct fluid to the left side 150 of the directional valve via line 155 or to the right side 160 of the directional valve via line 165. The directional valve 85 selectively directs the relatively large amount of fluid to drive the yaw motor 90 in a first rotational direction via line 170 or to drive the yaw motor in a second rotational direction via line 175. The yaw motor drives yaw gear 180 which, in turn, cooperates with the yaw bearing 60 to angularly rotate the rotor into and out of the wind as desired. A pair of pressure relief valves 185 and accumulators 190 protect the yaw motor from pressure overloads as is known in the art. As noted supra, the pump 75 directs fluid to the second circuit via line 135. The check valve 95, which is normally closed by a solenoid 195, regulates flow from line 135 to the control valve 100 via line 200. The wind vane is attached to the control valve by the camming mechanism 110. The camming mechanism 110 is comprised of a cam wheel 205, which is attached to the wind vane by a shaft 210, and a cam rider 215, which is attached via a plunger 220 to the control valve. The cam wheel has a center C, a pair of relatively flat, nulling portions 225, a top portion 230 having a radius R1 which progressively decreases for about 90° from each nulling portion, and a bottom portion 235 having a radius R2 which progressively increases for about 90° from each nulling portion. The cam wheel 205 is freely rotatable within the emergency shutdown and control system such that the position of the cam wheel is determined by the position of the vane 105. The cam rider follows the contour of the cam wheel as the rotor yaws into and out of the wind. The position of the control valve is mechanically determined by the yaw angle of the rotor and the position of the wind vane. As shown, clockwise rotation of the cam wheel pushes the control valve via the cam rider and the plunger to the left. Conversely, counterclockwise rotation of the cam allows the valve to move towards the right. Also, as shown, counterclockwise rotation of the nacelle 55 (and the emergency shutdown and control system) causes the cam rider 215 to follow the contour of the cam wheel to push the control valve to the left. Conversely, clockwise rotation of the nacelle allows the control valve to move towards the right as the cam rider follows the contour of the cam wheel. The control valve is connected to the left side 150 of the directional valve via line 240 and line 155 and to the right side 160 of the directional valve via line 245 and line 165. During normal operation, the controller positions the command valve 80 which, as is known in the art, sends a portion of the hydraulic fluid to either the left side 150 or right side 160 of the directional valve 85. The directional valve having been positioned by the hydraulic fluid, in turn, directs the output of the pump in line 145 to the yaw motor 90 which drives yaw gear 180 which cooperates with the yaw bearing to yaw the turbine into or out of the wind as required. The solenoid 195 is receiving an electrical signal from the controller so that hydraulic fluid does not flow through the second circuit. In an emergency situation (such as a loss of system load or power, or the rotor is not being positioned to the desired yaw angle), an electrical signal is not sent by the controller to the solenoid 195. As a result, the solenoid is deactivated and the check valve 95 allows hydraulic fluid to flow to the control valve 100. The vane 105 continuously positions the cam wheel 205. As the rotor yaws, the cam rider 215 follows the contour of the cam wheel thereby positioning the control valve 100. The control valve then directs a relatively large flow of hydraulic fluid via lines 240 and 155 to the left side 150 of the directional valve, or via lines 245 and 165 to the right side 160 of the directional valve 85 to move the blades out of the wind. Such relatively large flow overpowers any flow from the command valve 80 to position the directional valve to drive the yaw motor 90. The cam rider 215 follows the contour of the cam wheel 205 until the cam rider is disposed upon a null portion 225 of the cam wheel at which point the control valve 100 is nulled and does not allow flow therethrough. The rotor is now out of the wind, effectively minimizing aerodynamic rotor torque so that overspeed of the blades is avoided. As the rotor moves out of the wind, the blades slow. Since the output of the pump is roughly proportional to the speed of rotor rotation, the rate of yaw diminishes as the rotor moves out of the wind. Excessive teeter is thereby avoided as teeter amplitude versus yaw rate is inversely proportional to the rotor speed. While a particular embodiment of the present invention has been shown and described, it will be appreciated by those skilled in the art that various equivalent constructions may be employed without departing from the present invention and the true spirit and scope. For instance, one of ordinary skill in the art, may substitute an optical or other signal for the electrical signal provided by the controller to position the command valve 80 and the check valve 95.

Claims: 1. Wind turbine comprising a fixed pitch airfoil blade (15, 20) mounted on a rotatable hub (25), a hydraulic pump (75) driven by said blade (15, 20) and having a pump outlet, and hydraulic motor means (90) for yawing the blade (15, 20) into and out of a wind stream during normal operation of the wind turbine and for yawing the blade (15, 20) out of the wind stream in an emergency condition, characterized by said hydraulic means having first control circuit means including a directional valve (85) receiving hydraulic fluid from the pump outlet, and means directed by a controller for positioning the directional valve (85) to control hydraulic fluid flow to the hydraulic motor means (90) to drive said motor means (90) for yawing the blade (15, 20) into and out of the wind stream to optimize power output during said normal operation of the wind turbine, and a second control circuit means effective in an emergency condition for mechanically controlling in response to a wind vane (105) hydraulic fluid flow from said pump outlet to said directional valve (85) to further position said directional valve (85) and thereby further control said hydraulic fluid flow to said hydraulic motor means (90) such that the blade (15, 20) is yawed out of the wind in said emergency condition. 2. Wind turbine according to claim 1, characterized in that said second control circuit means comprises a first valve (95) controlled by a signal provided by said controller, said first valve (95) allowing said second flow of said hydraulic output therethrough upon a cessation of said signal thereto, and a second valve (100) for controlling said second flow to said directional valve (85) for said further positioning of said directional valve (85), and means for positioning said second valve (100) such that said blade (15, 20) is yawed out of the wind. 3. Wind turbine according to claim 2, characterized in that said means for positioning said second valve (100) comprises a camming means (110) attached to said wind vane (105) and to said control valve (100) for positioning said control valve (100) as a function of an angle between a plane formed by said rotating blade (15, 20) and the direction of the wind stream, said camming means (110) nulling said control valve (100) if said vane is oriented approximately 0° to said direction of said wind stream. 4. Wind turbine according to claim 3, characterized in that said camming means (110) comprises a camming wheel (205) attached to and rotating with the wind vane (105), and a cam rider (215) attaching to said control valve (100), said cam rider (215) following the contour of said camming wheel (205) as said camming wheel (205) and said cam rider (215) rotate relative to each other to position said control valve (100). 5. Wind turbine according to claim 4, characterized in that said camming wheel (205) has a center (C), a pair of relatively flat nulling portions (225), a portion (230) having a radius (R1) which progressively decreases for about 90° from each nulling portion (225) and a portion (235) having a radius (R2) which progressively increases for about 90° from each nulling portion (225). 6. Wind turbine according to claim 1, characterized in that the means directed by said controller comprises a command valve (80) for directing hydraulic fluid flow from the pump outlet to the directional valve (85) to position said directional valve (85).

Inventors: PARKER, JOEL E., STOLTZE, CHRISTOPHER L.
Applicants: UNITED TECHNOLOGIES CORPORATION
Application year: 1989
Main classification: F03D7
IPC codes: F03D7, F03D1, F03D11