Blade pitch control
A method of controlling blade pitch angle, including comparing demanded and measured blade pitch angle and calculating any difference therebetween, in a primary electrical control system, where there is a difference, applying torque to a blade pitch regulator to reduce the magnitude of the difference to zero, and in a secondary electrical control system, where the difference is greater than a pre-determined threshold, applying torque to a blade pitch regulator to reduce the magnitude of the difference to the threshold. Also an electrical system of blade pitch angle control for a set of blades including primary and secondary electrical control systems, means for comparing demanded and measured blade pitch angle and calculating any difference therebetween, a look-up function having the difference as its input and outputting a required torque, and a torque regulator to apply the required torque to the set of blades.
1. A method of controlling blade pitch angle using a primary and a secondary electrical control system, the method comprising the steps of:
a. Comparing a demanded and a measured blade pitch angle and calculating any difference therebetween,
b. in the primary electrical control system, where there is a difference, applying a torque to a blade pitch regulator to reduce the magnitude of the difference to zero, and
c. in the secondary electrical control system, where the difference is greater than a pre-determined threshold, applying a further torque to a blade pitch regulator to reduce the magnitude of the difference to the pre-determined threshold.
2. A method as claimed in claim 1 wherein step 1a is performed independently for each of the primary and secondary electrical control systems.
3. A method as claimed in claim 1 wherein the difference is positive when the measured blade pitch angle is more coarse than the demanded blade pitch angle.
4. A method as claimed in claim 3 wherein the torque and the further torque are applied to change the blade pitch angle to be finer than its measured blade pitch angle.
5. A method as claimed in claim 1 wherein the torque and the further torque applied are proportional to the difference.
6. A method as claimed in claim 1 wherein above the threshold both the primary and secondary electrical control systems apply torque to the blade pitch regulator.
7. A method as claimed in claim 1 wherein, in the event of a failure of at least one of the primary and secondary electrical control systems, the method further comprises the step of applying a failsafe torque control to the blade pitch angle to achieve a failsafe condition.
8. An electrical system of blade pitch angle control for a set of blades, the system comprising:
a. a primary electrical control system comprising a primary look-up function,
b. a secondary electrical control system comprising a secondary look-up function,
c. means for comparing a demanded and a measured blade pitch angle and calculating any difference therebetween, the means coupled to the primary and secondary electrical control systems,
d. the primary look-up function having the difference as its input and outputting a required torque,
e. the secondary look-up function having the difference as its input and outputting a further required torque, the output being zero below an input threshold, and
f. a torque regulator coupled to the primary and secondary electrical control systems to apply the required torque and the further required torque to the set of blades.
9. A system as claimed in claim 8 wherein each of the primary and secondary electrical control systems comprises means for calculating the any difference and a torque regulator.
10. A system as claimed in claim 8 wherein the required torque and the further required torque is proportional to the difference.
11. A system as claimed in claim 8 wherein the system further comprises trip logic that triggers when at least one of the primary and secondary electrical control systems fails.
12. A system as claimed in claim 11 wherein, when one of the primary and secondary electrical control systems fails, the trip logic triggers that electrical control system to trip.
13. A system as claimed in claim 11 wherein, when one of the primary and secondary electrical control systems fails, the trip logic triggers both electrical control systems to trip.
14. A system as claimed in claim 11 wherein the trip logic triggers a mechanical response.