Wind turbine control system having a thrust sensor

1. A wind turbine control system comprising:

an axial thrust sensor integrated in a bearing assembly of a rotor shaft;

a braking system coupled to the rotor shaft; and

a turbine controller that regulates a rate of deceleration of the rotor shaft so not to exceed a maximum allowed deceleration rate,

wherein the braking system is activated when an axial thrust load is detected that exceeds an over-thrust threshold.

2. The wind turbine control system of claim 1 , wherein the thrust sensor comprises a rotor axial load sensor.

3. The wind turbine control system of claim 1 , wherein the axial thrust sensor is a torque/axial thrust sensor.

4. The wind turbine control system of claim 1 , wherein the braking system comprises a blade pitch control system.

5. The wind turbine control system of claim 1 , wherein the braking system comprises electrical braking.

6. The wind turbine control system of claim 5 , wherein the braking system comprises mechanical braking actuating a disk or drum brake coupled to the rotor shaft.

7. The wind turbine control system of claim 6 , wherein a wind turbine has two-blades and a teetering hub.

8. The wind turbine control system of claim 7 , wherein the braking system is coupled to a yaw control system, and a yaw angle between wind speed direction and rotor axis is increased when the axial thrust load is detected.

9. A method of controlling speed of a rotor shaft of a wind turbine, comprising:

sensing an axial thrust load integrated in a bearing assembly of the rotor shaft;

measuring the axial thrust load;

comparing the measured axial thrust load to an over-thrust threshold;

calculating a deceleration rate of the rotor shaft;

comparing the calculated deceleration rate to a maximum deceleration allowed;

activating a braking system when the over-thrust threshold is exceeded; and

modulating the braking system to cause an actual deceleration rate to be no greater than the maximum deceleration rate allowed.