Blade pitch controller for a wind turbine
A blade pitch controller for a wind turbine includes a nominal control system and a tower feedback loop. The tower feedback loop includes a filtering system. The filtering system is arranged to control wind turbine blade pitch so as to provide additional effective stiffness to the wind turbine in response to motion of the wind turbine which is above a filter frequency of the filtering system.
1. A blade pitch controller for a wind turbine, wherein the wind turbine comprises an elongate tower with a nacelle and a rotor attached to the upper end of the tower, the rotor comprising a plurality of blades, wherein the blade pitch controller comprises a nominal control system arranged to control the blade pitch of the wind turbine in order to optimise power production and a tower feedback loop, wherein the tower feedback loop comprises a filtering system and a feedback controller, wherein the filtering system is arranged to receive at least one of position and velocity measurements or estimates of the wind turbine as input and to output at least one of filtered position and velocity measurements or estimates of the wind turbine, and the feedback controller is arranged to receive at least one of the output filtered position and velocity measurements or estimates of the wind turbine from the filtering system and to output a blade pitch reference signal determined from at least one of the filtered position and velocity measurements or estimates of the wind turbine to the nominal control system, such that the tower feedback loop is arranged to control wind turbine blade pitch so as to provide additional effective stiffness to the wind turbine in response to motion of the wind turbine above a filter frequency of the filtering system.
2. A blade pitch controller as claimed in claim 1 , wherein the filtering system comprises one or more of a high-pass filter, a low-pass filter and a notch filter.
3. A blade pitch controller as claimed in claim 2 , wherein the filter frequency of the filtering system is the filter frequency of the high-pass filter.
4. A blade pitch controller as claimed in claim 1 , wherein the tower feedback loop is arranged to control wind turbine blade pitch so as to provide additional effective stiffness to the wind turbine in response to both wave- and wind-induced motion of the wind turbine; and/or in response to motion of the wind turbine within a bandwidth of a blade pitch actuator.
5. A blade pitch controller as claimed in claim 1 , wherein at least one of position and velocity measurements and estimates of the wind turbine are provided as input to the filtering system.
6. A blade pitch controller as claimed in claim 5 , wherein at least one of the position and velocity measurements and estimates are provided from one or more sensors located on a tower or foundation of the wind turbine.
7. A blade pitch controller as claimed in claim 6 , wherein the one or more sensors are located at or near a water line on the wind turbine.
8. A blade pitch controller as claimed in claim 1 , wherein the filtering system is arranged to output at least one of filtered position and velocity measurements and estimates of the wind turbine.
9. A blade pitch controller as claimed in claim 1 , wherein the filtering system is arranged to filter position and velocity measurements and estimates of the wind turbine differently.
10. A blade pitch controller as claimed in claim 1 , wherein the filtering system is arranged to filter out at least one of static and quasi-static motion; and motion at a blade passing frequency.
11. A blade pitch controller as claimed in claim 1 , wherein the tower feedback loop further comprises a feedback controller.
12. A blade pitch controller as claimed in claim 11 , wherein the feedback controller is arranged to determine a blade pitch reference signal from at least one of filtered position and velocity measurements and estimates of the wind turbine output from the filtering system.
13. A method of controlling blade pitch of a wind turbine, the method comprising using a blade pitch controller with a with a filtering system as defined in claim 1 to control the blade pitch by determining a blade pitch reference signal from at least one of filtered position and velocity measurements or estimates of the wind turbine, and adjusting the blade pitch based on the blade pitch reference signal, so as to provide additional effective stiffness to the wind turbine in response to motion of the wind turbine above a filter frequency of the filtering system.
14. A method as claimed in claim 13 , the method comprising controlling wind turbine blade pitch so as to provide additional effective stiffness to the wind turbine in response to both wave- and wind-induced motion of the wind turbine.
15. A method as claimed in claim 13 , the method comprising controlling wind turbine blade pitch so as to provide additional effective stiffness to the wind turbine in response to motion of the wind turbine within a bandwidth of a blade pitch actuator.
16. A method as claimed in claim 13 , the method comprising using the filtering system to filter at least one of position and velocity measurements and estimates of the wind turbine.
17. A method as claimed in claim 13 , the method comprising at least one of:
filtering position and velocity measurements or estimates of the wind turbine differently;
filtering out at least one of static and quasi-static motion; and
filtering out motion at a blade passing frequency.
18. A wind turbine comprising a blade pitch controller as claimed in claim 1 .
19. A tower feedback controller for a blade pitch controller for a wind turbine, wherein the wind turbine comprises an elongate tower with a nacelle and a rotor attached to the upper end of the tower, the rotor comprising a plurality of blades, wherein the tower feedback controller comprises a filtering system, wherein the filtering system is arranged to receive at least one of position and velocity measurements or estimates of the wind turbine as input and to output at least one of filtered position and velocity measurements or estimates of the wind turbine, and the feedback controller is arranged to receive at least one of the output filtered position and velocity measurements or estimates of the wind turbine from the filtering system and to output a blade pitch reference signal determined from at least one of the filtered position and velocity measurements or estimates of the wind turbine to a nominal control system arranged to control the blade pitch of the wind turbine in order to optimise power production, such that the filtering system is arranged to control wind turbine blade pitch so as to provide additional effective stiffness to the wind turbine in response to motion of the wind turbine above a filter frequency of the filtering system.