Control of a wind turbine with a fault condition

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

receiving a current operational state of the wind turbine;

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

generating, in the absence of a fault signal indicating a fault condition of the wind turbine, 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;

determining, based on the type of the fault condition, a cost function of a model predictive control (MPC) routine;

calculating, using the MPC routine, a safe-mode trajectory comprising a time series of at least one variable; and

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

wherein the time series of the safe-mode 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.

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

wherein generating one or more control signals according to the 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 safe-mode trajectory is continuously calculated during operation of the wind turbine.

4. The method according to claim 1 , wherein the fault condition is included in the MPC routine as one or more constraints.

5. The method according to claim 1 , further comprising calculating a predicted operational state trajectory, and wherein the safe-mode trajectory is calculated using the predicted operational state trajectory.

6. The method according to claim 1 , wherein receiving the current operational state of the wind turbine comprises:

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

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

8. 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.

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

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

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

10. The method according to claim 5 , 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:

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.

12. 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 safe-mode trajectory is calculated in the normal control domain.

13. The method according to claim 12 , wherein the controller further comprises a safety domain, the method further comprising:

performing a validation routine implemented in the safety domain to validate the safe-mode trajectory.

14. 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 safe-mode trajectory is calculated in the safety domain.

15. The method according to claim 1 , wherein the control trajectory is calculated using a model predictive control (MPC) routine.

16. A control system for a wind turbine, comprising:

a 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;

generate, in the absence of a fault signal indicating a fault condition of the wind turbine, 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;

determining, based on the type of the fault condition, a cost function of a model predictive control (MPC) routine;

calculating, using the MPC routine, a safe-mode trajectory comprising a time series of at least one variable; and

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

wherein the time series of the safe-mode 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.

17. A wind turbine park controller arranged for controlling one or more wind turbines of a wind turbine park, the wind turbine park controller comprising:

a controller configured to:

determine a current operational state of a selected wind turbine of the one or more wind turbines;

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

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

responsive to receiving the fault signal:

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

determining, based on the type of the fault condition, a cost function of a model predictive control (MPC) routine;

calculating, using the MPC routine, a safe-mode trajectory comprising a time series of at least one variable; and

generating one or more control signals for the selected wind turbine according to the safe-mode trajectory;

wherein the time series of the safe-mode 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.

18. A wind turbine comprising a control system adapted to perform the method according to claim 1 .