Method for controlling a wind turbine with increased safety

1. A pitch control system for a wind turbine, the pitch control system comprising:

a controller configured to detect a failure of a resolver that controls a first pitch motor of a first pitch drive of the wind turbine as a first error situation, to detect a failure of a blade encoder that measures a position of a first rotor blade that is driven by the first pitch drive as a second error situation, and to detect a failure of an emergency power back-up system for the first pitch drive as a third error situation, and

wherein the controller is further configured to:

initiate a first error procedure based on the detection of the first error situation in absence of the second and the third error situations;

initiate a second error procedure based on the detection of the second error situation in absence of the first and the third error situations;

initiate a third error procedure based on the detection of the first and the second error situations occurring at the same time in absence of the third error situation, wherein the third error procedure is different to the first error procedure and to the second error procedure;

initiate a fourth error procedure based on the detection of the third error situation in absence of the first and the second error situations;

initiate the third error procedure based on the detection of the first, the second and the third error situations occurring at the same time;

initiate the first and the fourth error procedures based on the detection of the first and the third error situations occurring at the same time in absence of the second error situation; and

initiate the second and fourth error procedures based on the detection of the second and the third error situations occurring at the same time in absence of the first error situation.

2. The pitch control system of claim 1 , wherein:

the third error procedure comprises at least one of interrupting a power supply to the first pitch motor, blocking a control signal for the first pitch motor, engaging a brake to block movement of the first rotor blade, or requesting at least a second pitch drive of the wind turbine to attain a neutral position.

3. The pitch control system of claim 1 , wherein once the first or the second error situation has been detected, the respective terror situation is upheld despite the respective error having disappeared.

4. The pitch control system of claim 1 , wherein the first error procedure comprises the first pitch motor being switched to a self-sensing mode in which it controls its speed by sensing its own current supply.

5. The pitch control system of claim 1 , wherein the first error procedure comprises applying a limitation to the first pitch drive.

6. The pitch control system of claim 5 , wherein the limitation comprises a speed limit or an acceleration limit.

7. The pitch control system of claim 1 , wherein the second error procedure comprises calculating the position of the first rotor blade from data from the resolver.

8. The pitch control system of claim 1 , wherein the fourth error procedure comprises turning the first rotor blade into a neutral position.

9. The pitch control system of claim 1 , wherein the fourth error procedure comprises applying a limitation to the first pitch drive.

10. The pitch control system of claim 9 , wherein the limitation comprises a speed limit or an acceleration limit.

11. The pitch control system of claim 1 , wherein:

the first error procedure comprises the pitch drive motor being switched to a self-sensing mode in which it controls its speed by sensing its own current supply;

the second error procedure comprises the position of the rotor blade being calculated from data from the resolver for the pitch drive;

the third error procedure comprises at least one of interrupting a power supply to the first pitch motor, blocking a control signal for the first pitch motor, engaging a brake to block movement of the first rotor blade, requesting at least a second pitch drive of the wind turbine to attain a neutral position; and

the fourth error procedure comprises applying a limitation to the pitch drive of the wind turbine.

12. A method of operating a pitch control system of a wind turbine, the method comprising:

detecting for presence of:

a failure of a resolver that controls a first pitch motor of a first pitch drive of the wind turbine as a first error situation;

a failure of a blade encoder that measures a position of a first rotor blade that is driven by the first pitch drive as a second error situation; and

a failure of an emergency power back-up system for the first pitch drive as a third error situation, and

initiating a first error procedure in a case of the detection of the first error situation in absence of the second and the third error situations;

initiating a second error procedure in a case of the detection of the second error situation in absence of the first and the third error situations;

initiating a third error procedure in a case of the detection of the first and the second error situations occurring at the same time in absence of the third error situation, wherein the third error procedure is different to the first error procedure and to the second error procedure;

initiating a fourth error procedure in a case of the detection of the third error situation in absence of the first and the second error situations;

initiating the third error procedure in a case of the detection of the first, the second and the third error situations occurring at the same time;

initiating the first and the fourth error procedures in a case of the detection of the first and the third error situations occurring at the same time in absence of the second error situation; and

initiating the second and fourth error procedures in a case of the detection of the second and the third error situations occurring at the same time in absence of the first error situation.