Control of a wind turbine with a fault condition

1. A method of controlling a wind turbine, the method comprising:

calculating, based on a current operational state of the wind turbine, a control trajectory comprising a time series of at least one variable;

calculating, using a model predictive control (MPC) routine applied to some or all of the current operational state, two or more complete safe-mode trajectories corresponding to two or more possible fault conditions of the wind turbine, wherein each of the two or more complete safe-mode trajectories comprises a time series of at least one variable;

generating, in the absence of a fault signal indicating a fault condition, one or more control signals according to the control trajectory; and

responsive to receiving the fault signal:

determining a type of the fault condition indicated by the fault signal;

selecting, based on the type of the fault condition, one of the two or more complete safe-mode trajectories; and

generating one or more control signals according to the selected safe-mode trajectory.

2. The method according to claim 1 , wherein during safe-mode operation of the wind turbine, the selected safe-mode trajectory is repeatedly calculated as a receding horizon trajectory, and

wherein generating one or more control signals according to the selected safe-mode trajectory comprises generating the one or more control signals using a last-calculated safe-mode trajectory.

3. The method according to claim 1 , wherein the selected safe-mode trajectory is a shutdown trajectory.

4. The method according to claim 3 , wherein the time series of the shutdown trajectory spans an entirety of a shutdown process of the wind turbine,

wherein a complete shutdown trajectory is calculated prior to initiation of the shutdown process, and

wherein generating one or more control signals according to the safe-mode trajectory comprises generating the one or more control signals using the complete shutdown trajectory.

5. The method according to claim 3 , wherein the shutdown trajectory is a first complete shutdown trajectory,

wherein at least one other of the two or more complete safe-mode trajectories comprises a second complete shutdown trajectory, and

wherein selecting one of the two or more complete safe-mode trajectories comprises selecting one of the first complete shutdown trajectory and the second complete shutdown trajectory based on the fault signal.

6. The method according to claim 3 , wherein the time series of the shutdown trajectory spans an entirety of a two-step shutdown process of the wind turbine,

wherein in a first step of the shutdown process, the safe-mode trajectory is calculated to bring the wind turbine to a safe region from where a safe shutdown trajectory is known, and

wherein in a second step of the shutdown process, a pre-defined safe shutdown trajectory is used for bringing the wind turbine to a full stop.

7. The method according to claim 1 , wherein the two or more complete safe-mode trajectories are continuously calculated during operation of the wind turbine.

8. The method according to claim 1 , wherein for each of the two or more complete safe-mode trajectories, the corresponding possible fault condition is included in the MPC routine as one or more constraints.

9. The method according to claim 1 , further comprising:

calculating a predicted operational state trajectory,

wherein the two or more complete safe-mode trajectories are calculated using the predicted operational state trajectory.

10. The method according to claim 9 , further comprising:

performing at least one validation routine to determine whether the predicted operational state trajectory is valid for a future time slot, and

generating the fault signal responsive to determining that the predicted operational state trajectory is not valid.

11. The method according to claim 1 , further comprising:

acquiring sensor data relating to a physical state of the wind turbine; and

determining, using the sensor data, the current operational state of the wind turbine.

12. The method according to claim 1 , wherein the MPC routine is applied to a reduced model based on a subset of the current operational state of the wind turbine.

13. The method according to claim 1 , further comprising:

performing at least one validation routine to determine whether the control trajectory is valid for a future time slot, and

generating the fault signal responsive to determining that the control trajectory is not valid.

14. The method according to claim 1 , further comprising:

performing at least one validation routine to determine whether at least one of the complete safe-mode trajectories is valid for a future time slot, and

generating one or more control signals using a predetermined shutdown trajectory responsive to determining that the at least one safe-mode trajectory is not valid.

15. The method according to claim 1 , further comprising:

determining whether a future time slot of the control trajectory comprises an operational state from which a solution to calculating the safe-mode trajectory cannot be found.

16. The method according to claim 1 , wherein the MPC routine is implemented in a normal control domain of a controller of the wind turbine, and wherein the two or more complete safe-mode trajectories are calculated in the normal control domain.

17. The method according to claim 16 , wherein the controller further comprises a safety domain, the method further comprising:

performing a validation routine implemented in the safety domain to validate the two or more complete safe-mode trajectories.

18. The method according to claim 1 , wherein the MPC routine is implemented in a safety domain of a controller of the wind turbine, and wherein the two or more complete safe-mode trajectories are calculated in the safety domain.

19. The method according to claim 1 , wherein the control trajectory is calculated using the MPC routine.

20. A control system for controlling at least one wind turbine, the control system comprising:

at least one controller comprising a processor, the at least one controller configured to:

determine a current operational state of the wind turbine;

calculate, based on the current operational state, a control trajectory comprising a time series of at least one variable;

calculate, using a model predictive control (MPC) routine applied to some or all of the current operational state, two or more complete safe-mode trajectories corresponding to two or more possible fault conditions of the wind turbine, wherein each of the two or more complete safe-mode trajectories comprises a time series of at least one variable;

generate, in the absence of a fault signal indicating a fault condition, one or more control signals according to the control trajectory; and

responsive to receiving the fault signal:

determine a type of the fault condition indicated by the fault signal;

select, based on the type of the fault condition, one of the two or more complete safe-mode trajectories; and

generate one or more control signals according to the selected safe-mode trajectory.