Direct drive wind turbine and method for controlling an air gap

1. A direct drive wind turbine, comprising a rotor configured to rotate around a rotational axis and a generator, the rotor comprising a hub and a plurality of blades and being rotatably mounted on a frame, and the generator comprising a generator rotor and a generator stator, the rotational axis of the rotor defining an axial direction, wherein

the rotor hub includes a plurality of protrusions coupled to the generator rotor through a plurality of couplings, wherein the couplings are configured to transmit torque from the rotor hub to the generator rotor and to yield under loads in the axial direction, and

the wind turbine further comprising:

one or more dampers, disposed separately from the plurality of couplings, arranged between the rotor and the generator rotor and extending at least partially in the axial direction.

2. A direct drive wind turbine according to claim 1 , wherein at least one damper is passive.

3. A direct drive wind turbine according to claim 1 , wherein at least one damper is semi-active.

4. A direct drive wind turbine according to claim 3 , wherein said at least one semi-active damper is a magnetorheological or an electrorheological damper.

5. A direct drive wind turbine according to claim 3 , further comprising one or more sensors, wherein data collected by the sensors is used in the control of the semi-active dampers.

6. A direct drive wind turbine according to claim 1 , wherein at least one damper is an active damper.

7. A direct drive wind turbine according to claim 6 , further comprising one or more sensors, wherein data collected by the sensors is used in the control of the active dampers.

8. A direct drive wind turbine according to claim 1 , wherein the dampers also extend in a substantially radial direction.

9. A direct drive wind turbine, comprising:

a rotor and a generator, the rotor comprising a hub and a plurality of blades and being rotatably mounted on a frame, and the generator comprising a generator rotor and a generator stator,

the rotor hub including a plurality of protrusions coupled to the generator rotor through a plurality of couplings,

wherein the couplings are configured to transmit torque from the rotor hub to the generator rotor and to yield under loads in the axial direction, and

the wind turbine further comprising:

one or more semi-active or active dampers, disposed separately from the couplings, arranged between the rotor and the generator rotor and extending at least partially in an axial direction,

one or more sensors to measure or predict an acceleration of the rotor, and

a control system adapted to actuate the one or more semi-active or active dampers to reduce the transfer of a bending movement from the rotor to the generator rotor based on data collected by the one or more sensors.

10. A direct drive wind turbine, comprising:

a rotor and a generator, the rotor comprising a hub and a plurality of blades and being rotatably mounted on a frame, and the generator comprising a generator rotor and a generator stator, further comprising

a damper arranged between the rotor and the generator rotor and extending at least partially in an axial direction, wherein

the damper is attached to the rotor and/or generator rotor with a ball-socket joint.

11. A direct drive wind turbine, comprising:

a rotor and a generator, the rotor comprising a hub and a plurality of blades and being rotatably mounted on a frame, and the generator comprising a generator rotor and a generator stator, further comprising

a damper arranged between the rotor and the generator rotor and extending at least partially in an axial direction, wherein

the damper is attached to the rotor and/or generator rotor with a friction joint.