Controlling flap loading on a wind turbine blade based on predicted flap loading
Techniques for controlling loading on a wind turbine blade in the flap-wise direction. A system model has a description of flap loading on the blade and is used to predict flap loading on the blade over a prediction horizon using the system model. A dynamic flap loading limit is determined based on predicted flap loading and a measured flap loading, and a constraint is defined to limit flap loading on the blade based on the dynamic flap loading limit. The predicted flap loading is used in a cost or performance function, and the cost function is optimized subject to the constraint to determine pitch for the blade to control flap loading on the blade. Advantageously, the dynamic limit varies based on discrepancies between predicted and measured flap loading to allow for adaptive back-off from extreme loads prior to such loads building up or being exceeded.
1. A method of controlling flap loading on a wind turbine blade, the method comprising:
measuring a first flap loading on the wind turbine blade;
estimating a wind speed;
determining a thrust force based on the estimated wind speed;
determining a second flap loading on the blade over a prediction horizon based on the thrust force;
determining a dynamic flap loading limit based on the second flap loading and the first flap loading;
defining a constraint to limit flap loading on the blade based on the dynamic flap loading limit;
optimizing a cost function comprising the second flap loading subject to the constraint to produce an optimized cost function;
determining at least one control output based on the optimized cost function; and
controlling a pitch of the blade based on the at least one control output such that flap loading on the blade remains below a flap loading threshold.
2. The method according to claim 1 , wherein the dynamic flap loading limit is an adjustment to a maximum design limit of the blade.
3. The method according to claim 2 , wherein the adjustment includes a term dependent on a difference between the first flap loading and the second flap loading.
4. The method according to claim 3 , wherein the difference between the first flap loading and the second flap loading is scaled in the adjustment by a decaying function of time.
5. The method according to claim 2 , wherein the adjustment includes a term dependent on a rate of change of a difference between the first flap loading and the second flap loading.
6. The method according to claim 2 , wherein determining the adjustment comprises application of a low-pass filter.
7. The method according to claim 1 , wherein the constraint is a slack constraint defining that flap loading on the blade is less than or equal to a sum of the dynamic flap loading limit and a non-negative slack variable, and wherein optimizing the cost function comprises determining a value of the slack variable.
8. The method according to claim 7 , wherein the slack variable is penalized in the cost function by a penalty parameter.
9. The method according to claim 1 , wherein the first flap loading is based on sensor output data received from one or more flap loading sensors of the blade.
10. The method according to claim 9 , wherein the sensor output data is received from a plurality of the flap loading sensors, and wherein the first flap loading is determined to be a maximum value of the received sensor output data.
11. A controller for controlling flap loading on a wind turbine blade, the controller comprising:
an input/output interface;
a memory containing instructions; and
a processor communicatively connected to the interface and memory and programmed by the instructions to perform an operation comprising:
measuring a first flap loading on the wind turbine blade;
estimating a wind speed;
determining a thrust force based on the estimated wind speed;
determining a second flap loading on the blade over a prediction horizon based on the thrust force;
determining a dynamic flap loading limit based on the second flap loading and the first flap loading;
defining a constraint to limit the flap loading on the blade based on the dynamic flap loading limit;
optimizing a cost function comprising the second flap loading subject to the constraint to produce an optimized cost function;
determining at least one control output based on the optimized cost function; and
controlling a pitch of the blade based on the at least one control output such that flap loading on the blade remains below a flap loading threshold.
12. A wind turbine, comprising:
a tower;
a nacelle disposed on the tower;
a rotor extending from the nacelle and having a plurality of blades disposed on a distal end; and
a controller configured to perform an operation comprising:
measuring a first flap loading on a blade of the plurality of blades;
estimating a wind speed;
determining a thrust force based on the estimated wind speed;
determining a second flap loading on the blade based on the thrust force;
determining a dynamic flap loading limit based on the second flap loading and the first flap loading;
defining a constraint to limit flap loading on the blade based on the dynamic flap loading limit;
optimizing a cost function comprising the second flap loading subject to the constraint to produce an optimized cost function;
determining at least one control output based on the optimized cost function; and
controlling a pitch of the blade based on the at least one control output such that flap loading on the blade remains below a flap loading threshold.
13. The wind turbine of claim 12 , wherein the constraint is a slack constraint defining that flap loading on the blade is less than or equal to a sum of the dynamic flap loading limit and a non-negative slack variable, and wherein optimizing the cost function comprises determining a value of the slack variable.