Abstract: The present invention relates to a multirotor wind turbine comprising at least two rotor nacelle assemblies mounted to a support arrangement via respective yawing systems, and a toe angle control system for controlling the toe angles of the rotor nacelle assemblies with respect to the support arrangement; wherein the toe angle control system is configured to operate in a first mode in which the rotor nacelle assemblies are held at positive toe angles while the wind turbine is generating power in a main production mode; wherein the toe angle control system is further configured to monitor the operating mode of the wind turbine, and to switch to a second mode in which the yawing systems of the rotor nacelle assemblies are operated to reduce the toe angles of the rotor nacelle assemblies if an operating mode-based trigger condition has been met.

Abstract: The present invention relates to controlling a wind turbine with a scaled power coefficient where the scaled power coefficient is determined in an adjustment process. In particular is disclosed control of a wind turbine in a partial load operation mode based on a tip-speed ratio (TSR) tracking scheme which based on an estimated wind speed determines a power setpoint. The disclosed adjustment process comprises setting a scaled power coefficient as a predetermined power coefficient multiplied by a scaling factor; adding a time-varying perturbation signal to the power setpoint; determining a transfer function from the perturbation signal to a power error; evaluate the frequency response of the transfer function over a time period to determine the scaling factor which minimizes the gain of the transfer function; and setting the operating power coefficient as the scaled power coefficient.

Abstract: A method of damping oscillations in a multi-rotor wind turbine and a wind turbine are provided. The wind turbine comprises a wind turbine support structure and at least a first nacelle with a first rotor and a second nacelle with a second rotor, at least one of the nacelles being located at a position away from a central longitudinal axis of the wind turbine support structure. The method comprises the steps of receiving and processing motion data, selecting a damping algorithm and generating a pitch control signal. The processing comprises determining at least one prominent oscillation mode of the wind turbine support structure and selecting a corresponding damping algorithm.

Abstract: The present invention relates to controlling a wind turbine with a scaled power coefficient where the scaled power coefficient is determined in an adjustment process. In particular is disclosed control of a wind turbine in a partial load operation mode based on a tip-speed ratio (TSR) tracking scheme which based on an estimated wind speed determines a power setpoint. The disclosed adjustment process comprises setting a scaled power coefficient as a predetermined power coefficient multiplied by a scaling factor; adding a time-varying perturbation signal to the power setpoint; determining a transfer function from the perturbation signal to a power error; evaluate the frequency response of the transfer function over a time period to determine the scaling factor which minimizes the gain of the transfer function; and setting the operating power coefficient as the scaled power coefficient.

Abstract: A method and a device for dampening movement in a multiple rotor (MR) wind turbine located at sea and comprising a tower (2) extending in an upwards direction, a load carrying structure (3, 4) forming a first section (3) and a second section (4), the first and second sections extending in different directions away from the tower (2). To provide efficient dampening of the movement, the method comprises tethering a first body (20) to the first section (3), the first body being at least partly submerged into the sea.

Abstract: Embodiments herein describe in-plane vibration damping techniques for MR turbines. The MR turbines can include arms that extend from a common tower and support multiple rotors. Because the rotors are disposed laterally away from the tower, side-to-side motion of the tower causes the rotors to have an angled trajectory that includes both lateral and vertical displacement. In addition, a rotor disposed on one side of the tower in MR turbine can have a very different trajectory than a rotor disposed on the opposite side of the tower. To account for the vertical displacement and the different trajectories, in one embodiment, a controller can use different phase offsets for each rotor when calculating pitch offsets for performing in-plane vibration damping. In another embodiment, the controller can use both the lateral and vertical accelerations of the rotors to identify the pitch offsets for the rotors to perform in-plane vibration damping.

Abstract: The invention relates to a method for controlling a wind turbine during start up, from a non-producing operation mode to a power producing operation mode when limit cycles occur during start-up. Limit cycles are detected when a number of cut-in transitions or a number of cut-out transitions are detected. A cut-in transition is when the wind turbine fails starting up despite having the wind speed or rotor speed normally required to enter a power producing operation mode. A cut-out transition is occurring when the wind turbine is falling out of power producing operation mode after having entered the power producing operation mode.

Abstract: A first aspect of the invention provides a method of testing a yaw system (200) of a wind turbine, the wind turbine comprising a rotor; the yaw system (200) comprising a yaw gear (202) coupled to the rotor so that rotation of the yaw gear (202) causes yaw rotation of the rotor, and first and second sub-systems (204a, 204b), the first sub-system (204a) comprising a first pinion gear (206a) and a first drive motor (208a) coupled to the yaw gear (202) by the first pinion gear (206a), the second sub-system (204b) comprising a second pinion gear (206b) and a second drive motor (208b) coupled to the yaw gear (202) by the second pinion gear (206b).

Abstract: The present invention relates to a multirotor wind turbine comprising at least two rotor nacelle assemblies mounted to a support arrangement via respective yawing systems, and a toe angle control system for controlling the toe angles of the rotor nacelle assemblies with respect to the support arrangement; wherein the toe angle control system is configured to operate in a first mode in which the rotor nacelle assemblies are held at positive toe angles while the wind turbine is generating power in a main production mode; wherein the toe angle control system is further configured to monitor the operating mode of the wind turbine, and to switch to a second mode in which the yawing systems of the rotor nacelle assemblies are operated to reduce the toe angles of the rotor nacelle assemblies if an operating mode-based trigger condition has been met.

Abstract: A method for detecting and controlling whirling oscillations of the blades of a wind turbine is presented. The detection of the whirling oscillations is based on measurement signal indicative of blade oscillations, and a rotation transformation of the measurement signal from a measurement frame into at least one target frame based on the whirling oscillation frequency. The rotation-transformation comprises a backward or forward rotation transformation direction relative to a rotor rotation direction. The control is based on an oscillation component obtained from the rotation-transformed measurement signal where the oscillation component is indicative of the whirling oscillation in the backward and/or forward rotation direction.

Abstract: A method for controlling a multirotor wind turbine comprising two or more energy generating units is disclosed. At least one load carrying structure is connected to a foundation or to a tower via a yaw arrangement, and the load carrying structure carries the at least two energy generating units. A requirement to a change in operation of at least a first of the energy generating units is detected. Control commands for the first energy generating unit and for at least a second energy generating unit, mounted on the same load carrying structure, are generated. The control commands cause the required change in operation, and the control commands cause coordinated operation of at least the first energy generating unit and the second energy generating unit. The control commands are generated under the constraint that a yaw moment of the yaw arrangement is maintained below a predefined threshold level.

Abstract: Embodiments herein describe in-plane vibration damping techniques for MR turbines. The MR turbines can include arms that extend from a common tower and support multiple rotors. Because the rotors are disposed laterally away from the tower, side-to-side motion of the tower causes the rotors to have an angled trajectory that includes both lateral and vertical displacement. In addition, a rotor disposed on one side of the tower in MR turbine can have a very different trajectory than a rotor disposed on the opposite side of the tower. To account for the vertical displacement and the different trajectories, in one embodiment, a controller can use different phase offsets for each rotor when calculating pitch offsets for performing in-plane vibration damping. In another embodiment, the controller can use both the lateral and vertical accelerations of the rotors to identify the pitch offsets for the rotors to perform in-plane vibration damping.

Abstract: A multiple rotor (MR) wind turbine comprising a tower (21) extending in an upwards direction, a load carrying structure (22) extending in an outwards direction and being fixed to the tower, and an energy generating unit (54) fixed to the load carrying structure, wherein the outwards direction is transverse to the upwards direction, the wind turbine further comprising a hoisting line (53) for communication of objects (52) to and from the energy generating unit (54), the hoisting line being windable from an attachment point (55) of the load carrying structure or from the energy generating unit. To allow positioning of hosted objects near the tower, or at selectable distance from the tower, the hoisting line extends from the attachment point via a suspension point (56) to a lifting point (57) where the object (52) can be attached, and the suspension point (56) is movable outside the load carrying structure.

Abstract: A method and a device for dampening movement in a multiple rotor (MR) wind turbine located at sea and comprising a tower (2) extending in an upwards direction, a load carrying structure (3, 4) forming a first section (3) and a second section (4), the first and second sections extending in different directions away from the tower (2). To provide efficient dampening of the movement, the method comprises tethering a first body (20) to the first section (3), the first body being at least partly submerged into the sea.

Abstract: Control of a multi-rotor wind turbine system. A local controller is arranged for each wind turbine module and implementing a local model predictive control (MPC) routine. A central controller is arranged to determine a set of operational constraints of the wind turbine modules. Based on a current operational state of the wind turbine module and the set of operational constraints, one or more predicted operational trajectories are calculated and used for controlling the wind turbine module.

Abstract: A first aspect of the invention provides a method of monitoring the condition of a yaw system of a wind turbine, the wind turbine comprising a rotor, the yaw system arranged to control a yaw rotation of the rotor, the method comprising: providing design data 5 representing an expected relationship between yaw moment and yaw rotation speed; measuring a pair of parameters, the pair of parameters comprising a yaw moment parameter indicative of a yaw moment applied to the yaw system, and a yaw rotation speed parameter indicative of a yaw rotation speed caused by the yaw moment; using the design data to evaluate whether the pair of parameters deviates from the expected 10 relationship; and determining a condition of the yaw system on the basis of the evaluation.

Abstract: A method for operating a wind turbine with hinged wind turbine blades is disclosed. The wind turbine comprises an adjustable biasing mechanism arranged to apply an adjustable biasing force to each wind turbine blade which biases the wind turbine blade towards a position defining a minimum pivot angle or towards a position defining maximum pivot angle. A biasing force is selected for each wind turbine blade and the selected biasing force is applied to the respective wind turbine blades. The wind turbine is operated while monitoring rotor unbalance of the wind turbine. In the case that the rotor unbalance exceeds a first threshold value at least one of the wind turbine blades is selected, and the biasing force applied to the selected wind turbine blade(s) is adjusted.

Abstract: The invention relates to a method for controlling a wind turbine during start up, from a non-producing operation mode to a power producing operation mode when limit cycles occur during start-up. Limit cycles are detected when a number of cut-in transitions or a number of cut-out transitions are detected. A cut-in transition is when the wind turbine fails starting up despite having the wind speed or rotor speed normally required to enter a power producing operation mode. A cut-out transition is occurring when the wind turbine is falling out of power producing operation mode after having entered the power producing operation mode.

Abstract: A system (24) and method are described herein for manufacturing a wind turbine blade (22) proximate to the final installation site of a wind turbine (10). The system (24) includes a creel (72) of feeders (74) configured to apply strengthening elements (62) onto a plurality of shell core sections (26) coupled together and fed through the creel (72). The shell core sections (26) include an external surface (56) with a plurality of external grooves (58) recessed into the external surface (56) such that the strengthening elements (62) are laid into the external grooves (58). The system (24) also includes a deposition station (78) configured to apply an outer surface material layer (82) in fluid form to cover the external surface (56) and the plurality of strengthening elements (62).

Abstract: A method for controlling a multirotor wind turbine is disclosed. A first operational state of each of the energy generating units of the wind turbine is obtained. A difference in thrust acting on at least two of the energy generating units is detected. At least one constraint parameter of the set of operational constraints is adjusted in accordance with prevailing operating conditions and in accordance with the detected difference in thrust, and a new operational state for at least one of the energy generating units is derived, based on the at least one adjusted constraint parameter, the new operational state(s) counteracting the detected difference in thrust. Finally, the wind turbine is controlled in accordance with the new operational states for the energy generating units.