Overspeed protection system and method

Abstract

An overspeed protection system for a wind turbine having a hub and at least one rotor blade mounted to the hub includes a rotation sensor adapted for measuring a rotor speed of said wind turbine; a comparator connected to the rotation sensor and adapted for comparing the measured rotor speed with a predetermined threshold value of the rotor speed wherein the comparator outputs a signal indicative of the comparison; and an auxiliary pitch drive controller connected to the comparator and adapted to receive the signal indicative of the comparison, the auxiliary pitch drive controller being further adapted for controlling a pitch drive unit of the wind turbine independently of a main turbine controller and, if the threshold value is exceeded, to adjust a pitch angle of the rotor blade of the wind turbine so that aerodynamic braking of the wind turbine is effected.

1 . An overspeed protection system for a wind turbine having a hub and at least one rotor blade mounted to said hub, comprising:
 a rotation sensor adapted for measuring a rotor speed of said wind turbine;   a comparator connected to said rotation sensor and adapted for comparing the measured rotor speed with a predetermined threshold value of said rotor speed wherein the comparator outputs a signal indicative of said comparison; and,   an auxiliary pitch drive controller connected to said comparator and adapted to receive said signal indicative of the comparison, the auxiliary pitch drive controller being further adapted for controlling a pitch drive unit of the wind turbine independently of a main turbine controller and, if said threshold value is exceeded, to adjust a pitch angle of the rotor blade of the wind turbine so that aerodynamic braking of the wind turbine is effected.   
     
     
         2 . The overspeed protection system according to  claim 1 , wherein the system is adapted to be installed in the hub of said wind turbine and to operate self-sustained therein. 
     
     
         3 . The overspeed protection system according to  claim 1 , wherein the rotation sensor is selected from the group consisting of a pendulum device, a gravitational force detection element, an acceleration sensor, a dynamo-electric generator, an optical detector, and any combination thereof. 
     
     
         4 . The overspeed protection system according to  claim 3 , wherein the rotation sensor is a pendulum device adapted to oscillate in accordance with the rotor speed. 
     
     
         5 . The overspeed protection system according to  claim 4 , wherein the pendulum device comprises a pendulum coupled to an electric switch such that the switch is operated in accordance with the rotor speed. 
     
     
         6 . The overspeed protection system according to  claim 5 , further comprising a low-pass filter adapted for low-pass filtering an output signal of the electric switch. 
     
     
         7 . The overspeed protection system according to  claim 6 , further wherein the low-pass filter has a cut-off frequency which is in the range from about 50% to about 150% of the rotor speed threshold value. 
     
     
         8 . The overspeed protection system according to  claim 1 , wherein the system is connectable to an auxiliary power supply located at the hub. 
     
     
         9 . The overspeed protection system according to  claim 8 , wherein the auxiliary power supply is selected from the group consisting of a battery, a capacitor, an electric generator, a solar panel, and any combination thereof. 
     
     
         10 . The overspeed protection system according to  claim 1 , further comprising a switching device adapted to connect the pitch drive unit of the wind turbine to the auxiliary pitch drive controller, the switching device being activated if said rotor speed threshold value is exceeded. 
     
     
         11 . The overspeed protection system according to  claim 1 , wherein the pitch drive unit comprises at least one electric pitch motor and said auxiliary pitch drive controller is adapted to control said electric pitch motor. 
     
     
         12 . A wind turbine, comprising:
 a rotatable hub and at least one rotor blade mounted to said hub, wherein a pitch angle of said rotor blade can be adjusted by a pitch drive system;   a speed sensor adapted for measuring a rotational speed of said wind turbine;   a detection unit connected to said speed sensor and adapted for detecting if the measured rotational speed exceeds a predetermined threshold value; and,   an auxiliary pitch drive controller adapted to adjust a pitch angle of said rotor blade to effect aerodynamic braking of the wind turbine if said threshold value is exceeded, the auxiliary pitch drive controller being located within said hub and operable independent of wind turbine components not located in or at the hub.   
     
     
         13 . The wind turbine according to  claim 12 , wherein the rotation sensor is a pendulum device adapted to oscillate in accordance with the rotor speed, the pendulum being coupled to an electric switch such that the switch is operated in accordance with the rotor speed. 
     
     
         14 . The wind turbine according to  claim 13 , further comprising a low-pass filter adapted for low-pass filtering an output signal of the electric switch, the low-pass filter having a cut-off frequency which is in the range from about 50% to about 150% of the rotational speed threshold value. 
     
     
         15 . The wind turbine according to  claim 12 , wherein the auxiliary pitch drive controller is connected to an auxiliary power supply located at the hub via a switching device, the switching device being operated upon exceeding of the rotational speed threshold value. 
     
     
         16 . The wind turbine according to  claim 12 , wherein the wind turbine comprises a plurality of rotor blades and the auxiliary pitch drive controller is adapted to adjust the pitch angle of each rotor blade. 
     
     
         17 . The wind turbine according to  claim 12 , wherein the wind turbine comprises a plurality of rotor blades and a plurality of auxiliary pitch drive controllers, each rotor blade being connected to an auxiliary pitch drive controller, each auxiliary pitch drive controller being adapted to adjust the pitch angle of the rotor blade to which it is connected. 
     
     
         18 . A method for preventing an overspeed condition of a wind turbine, the method comprising:
 measuring a rotational speed of a hub of said wind turbine;   comparing the measured rotational speed with a predetermined threshold value;   if the measured rotational speed exceeds the threshold value, operating an auxiliary pitch drive controller independent of a main turbine controller so that a pitch angle of at least one rotor blade of the wind turbine is adjusted to effect aerodynamic braking of the wind turbine.   
     
     
         19 . The method according to  claim 18 , wherein the gradient of an acceleration signal is evaluated for determining the rotational speed. 
     
     
         20 . The method according to  claim 18 , wherein an overspeed relais is operated on the basis of the measured rotational speed, the overspeed relais connecting the auxiliary pitch drive controller to a pitch drive unit of said rotor blade.