Abstract: There is provided a method for controlling a hydraulic pitch force system (220) so as to reduce or eliminate a decrease in hydraulic oil pressure (241) if a hydraulic system parameter value is outside a hydraulic system parameter range, the method comprising: Obtaining (690) the hydraulic system parameter value, and operating the hydraulic pitch force system (220) according to a reduced mode (692) if the hydraulic system parameter value is outside the hydraulic system parameter range, wherein in the reduced mode one or more pitch based activities are reduced (694) or suspended. An advantage thereof may be that it enables keeping the wind turbine in production in certain instances rather than shutting down the wind turbine. In aspects, there is furthermore presented a computer program product, a pitch control system (250) and a wind turbine (100).

Abstract: A method of controlling a wind turbine comprising at least one rotor blade, and at least one accelerometer housed within a nacelle or a tower of the wind turbine. The method comprises: determining a whirling mode frequency for the wind turbine; measuring an acceleration signal that is indicative of the movement of the nacelle of the wind turbine; determining a frequency spectrum of the measured acceleration signal in the proximity of the determined whirling mode frequency; determining a characteristic value that is representative of the energy content of the measured acceleration signal having the determined frequency spectrum; and performing at least one control action if the characteristic value exceeds a predetermined threshold.

Abstract: Embodiments of the present invention relate to control of a wind turbine during a recovery period after a grid fault. It is disclosed to operate a wind turbine during the recovery period to determine the actual pitch angle of the rotor blades and the actual wind speed, and based on that determining a desired pitch angle of the rotor blades, as well as a pitch ramp rate so that the actual pitch angle can be brought to match the desired pitch angle before the end of the recovery period. In embodiments, the steps performed in the recovery mode are repeated at intervals during the recovery period.

Abstract: A method of calibrating load sensors of a wind turbine, and a wind turbine for such load sensor calibration, are disclosed. The wind turbine comprises a rotor, a plurality of rotor blades, and a plurality of load sensors associated with the rotor blades. While the rotor is rotating, at least one of the rotor blades is moved from a first calibration position to a second calibration position, and load values from the load sensors are measured. The number of rotor blades being moved is at least one fewer than the number of the plurality of rotor blades. The rotation of the rotor may be during idling of the wind turbine. The movement of the blade(s) may be to change the pitch angle of the blade(s). At least one of the rotor blades not being moved to a calibration position may also be moved, for example to control the rotational speed of the rotor.

Abstract: There is provided a pitch control system (210) for controlling a pitch force system (220) for pitching a blade (103) of a wind turbine (100), the pitch control system (210) being arranged for activating (682) an auxiliary pitch force subsystem (224) at an initiation point in time where a main pitch force is sufficient to pitch the blade (103) into a target pitch value. An advantage thereof may be that tracking of a target pitch value may be improved and the impact on the pitch force system (220) may be reduced. In aspects, there is furthermore presented a hydraulic pitch system (206), a wind turbine (100), a method and a computer program product.

Abstract: A sensor system for a wind turbine blade, the system comprising: a blade load sensor providing a load measurement; a processing unit interfaced with the blade load sensor and configured to provide a corrected load parameter as an output. The processing unit includes: an axial force estimation module that determines an estimated axial force on the wind turbine blade in a direction along the length of the blade; and a load calculation module that 10 determines the corrected load parameter based on the estimated axial force and the load measurement of the blade load sensor.

Abstract: A method, a controller and a wind turbine with a controller for controlling the wind turbine in a cluster of wind turbines. Each wind turbine is controlled individually and each windturbine is configured to deliver power to the same utility grid. According to the method a delivery from a first wind turbine is reduced from a present power level to a reduced power level in response to an initial frequency of the utility grid exceeding a first threshold value; and the wind turbine is allowed to continue delivering power at the reduced power level.

Abstract: A method of controlling a wind turbine comprising at least one rotor blade, and at least one accelerometer housed within a nacelle or a tower of the wind turbine. The method comprises: determining a whirling mode frequency for the wind turbine; measuring an acceleration signal that is indicative of the movement of the nacelle of the wind turbine; determining a frequency spectrum of the measured acceleration signal in the proximity of the determined whirling mode frequency; determining a characteristic value that is representative of the energy content of the measured acceleration signal having the determined frequency spectrum; and performing at least one control action if the characteristic value exceeds a predetermined threshold.

Abstract: There is provided a method for controlling a hydraulic pitch force system (220) so as to reduce or eliminate a decrease in hydraulic oil pressure (241) if a hydraulic system parameter value is outside a hydraulic system parameter range, the method comprising: Obtaining (690) the hydraulic system parameter value, and operating the hydraulic pitch force system (220) according to a reduced mode (692) if the hydraulic system parameter value is outside the hydraulic system parameter range, wherein in the reduced mode one or more pitch based activities are reduced (694) or suspended. An advantage thereof may be that it enables keeping the wind turbine in production in certain instances rather than shutting down the wind turbine. In aspects, there is furthermore presented a computer program product, a pitch control system (250) and a wind turbine (100).

Abstract: There is provided a pitch control system (210) for controlling a pitch force system (220) for pitching a blade (103) of a wind turbine (100), the pitch control system (210) being arranged for activating (682) an auxiliary pitch force subsystem (224) at an initiation point in time where a main pitch force is sufficient to pitch the blade (103) into a target pitch value. An advantage thereof may be that tracking of a target pitch value may be improved and the impact on the pitch force system (220) may be reduced. In aspects, there is furthermore presented a hydraulic pitch system (206), a wind turbine (100), a method and a computer program product.

Abstract: Embodiments of the present invention relate to control of a wind turbine during a recovery period after a grid fault. It is disclosed to operate a wind turbine during the recovery period to determine the actual pitch angle of the rotor blades and the actual wind speed, and based on that determining a desired pitch angle of the rotor blades, as well as a pitch ramp rate so that the actual pitch angle can be brought to match the desired pitch angle before the end of the recovery period. In embodiments, the steps performed in the recovery mode are repeated at intervals during the recovery period.

Abstract: A sensor system for a wind turbine blade, the system comprising: a blade load sensor providing a load measurement; a processing unit interfaced with the blade load sensor and configured to provide a corrected load parameter as an output. The processing unit includes: an axial force estimation module that determines an estimated axial force on the wind turbine blade in a direction along the length of the blade; and a load calculation module that 10 determines the corrected load parameter based on the estimated axial force and the load measurement of the blade load sensor.

Abstract: A method of calibrating load sensors of a wind turbine, and a wind turbine for such load sensor calibration, are disclosed. The wind turbine comprises a rotor, a plurality of rotor blades, and a plurality of load sensors associated with the rotor blades. While the rotor is rotating, at least one of the rotor blades is moved from a first calibration position to a second calibration position, and load values from the load sensors are measured. The number of rotor blades being moved is at least one fewer than the number of the plurality of rotor blades. The rotation of the rotor may be during idling of the wind turbine. The movement of the blade(s) may be to change the pitch angle of the blade(s). At least one of the rotor blades not being moved to a calibration position may also be moved, for example to control the rotational speed of the rotor.

Abstract: A wind turbine control system suitable for minimizing actuation of pitch actuators is disclosed. The control system uses an error gain schedule in full load control for reducing pitch actuation when the difference between the rotor speed and the reference rotor speed is not critical for the load of wind turbine components. The error gain schedule may be a nonlinear function which reduces the gain for low rotor speed errors. The use of the error gain schedule may reduce wear of the pitch actuators and may improve reduction of structural oscillations since focus removed from tracking the rotor speed reference when the speed error is low.

Abstract: For optimising annual energy production in a wind turbine, the invention provides a method by which operation of the turbine in accordance with different pre-specified modes depending on the wind direction towards the turbine is enabled. The modes may include pitch and/or power control strategies. The invention further provides a control system for a wind turbine adapted to operate in accordance with the method, and a wind turbine with such a control system.

Abstract: A wind turbine control system suitable for minimising actuation of pitch actuators is disclosed. The control system uses an error gain schedule in full load control for reducing pitch actuation when the difference between the rotor speed and the reference rotor speed is not critical for the load of wind turbine components. The error gain schedule may be a nonlinear function which reduces the gain for low rotor speed errors. The use of the error gain schedule may reduce wear of the pitch actuators and may improve reduction of structural oscillations since focus removed from tracking the rotor speed reference when the speed error is low.