Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
  • F03D—WIND MOTORS
  • F03D7/00—Controlling wind motors 
  • F03D7/02—Controlling wind motors  the wind motors having rotation axis substantially parallel to the air flow entering the rotor
  • F03D7/0204—Controlling wind motors  the wind motors having rotation axis substantially parallel to the air flow entering the rotor for orientation in relation to wind direction
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
  • F03D—WIND MOTORS
  • F03D7/00—Controlling wind motors 
  • F03D7/02—Controlling wind motors  the wind motors having rotation axis substantially parallel to the air flow entering the rotor
  • F03D7/022—Adjusting aerodynamic properties of the blades
  • F03D7/0224—Adjusting blade pitch
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
  • F03D—WIND MOTORS
  • F03D7/00—Controlling wind motors 
  • F03D7/02—Controlling wind motors  the wind motors having rotation axis substantially parallel to the air flow entering the rotor
  • F03D7/022—Adjusting aerodynamic properties of the blades
  • F03D7/024—Adjusting aerodynamic properties of the blades of individual blades
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
  • F03D—WIND MOTORS
  • F03D7/00—Controlling wind motors 
  • F03D7/02—Controlling wind motors  the wind motors having rotation axis substantially parallel to the air flow entering the rotor
  • F03D7/0276—Controlling wind motors  the wind motors having rotation axis substantially parallel to the air flow entering the rotor controlling rotor speed, e.g. variable speed
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
  • F03D—WIND MOTORS
  • F03D7/00—Controlling wind motors 
  • F03D7/02—Controlling wind motors  the wind motors having rotation axis substantially parallel to the air flow entering the rotor
  • F03D7/028—Controlling wind motors  the wind motors having rotation axis substantially parallel to the air flow entering the rotor controlling wind motor output power
  • F03D7/0292—Controlling wind motors  the wind motors having rotation axis substantially parallel to the air flow entering the rotor controlling wind motor output power to reduce fatigue
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
  • F03D—WIND MOTORS
  • F03D7/00—Controlling wind motors 
  • F03D7/02—Controlling wind motors  the wind motors having rotation axis substantially parallel to the air flow entering the rotor
  • F03D7/04—Automatic control; Regulation
  • F03D7/042—Automatic control; Regulation by means of an electrical or electronic controller
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
  • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
  • F05B2240/00—Components
  • F05B2240/90—Mounting on supporting structures or systems
  • F05B2240/93—Mounting on supporting structures or systems on a structure floating on a liquid surface
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
  • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
  • F05B2240/00—Components
  • F05B2240/90—Mounting on supporting structures or systems
  • F05B2240/95—Mounting on supporting structures or systems offshore
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
  • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
  • F05B2260/00—Function
  • F05B2260/82—Forecasts
  • F05B2260/821—Parameter estimation or prediction
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
  • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
  • F05B2270/00—Control
  • F05B2270/10—Purpose of the control system
  • F05B2270/1016—Purpose of the control system in variable speed operation
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
  • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
  • F05B2270/00—Control
  • F05B2270/10—Purpose of the control system
  • F05B2270/109—Purpose of the control system to prolong engine life
  • F05B2270/1095—Purpose of the control system to prolong engine life by limiting mechanical stresses
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
  • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
  • F05B2270/00—Control
  • F05B2270/30—Control parameters, e.g. input parameters
  • F05B2270/321—Wind directions
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
  • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
  • F05B2270/00—Control
  • F05B2270/30—Control parameters, e.g. input parameters
  • F05B2270/327—Rotor or generator speeds
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
  • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
  • F05B2270/00—Control
  • F05B2270/30—Control parameters, e.g. input parameters
  • F05B2270/331—Mechanical loads
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
  • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
  • F05B2270/00—Control
  • F05B2270/40—Type of control system
  • F05B2270/404—Type of control system active, predictive, or anticipative
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
  • F05B—INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G
  • F05B2270/00—Control
  • F05B2270/80—Devices generating input signals, e.g. transducers, sensors, cameras or strain gauges
  • F05B2270/808—Strain gauges; Load cells
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E10/00—Energy generation through renewable energy sources
  • Y02E10/70—Wind energy
  • Y02E10/72—Wind turbines with rotation axis in wind direction
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E10/00—Energy generation through renewable energy sources
  • Y02E10/70—Wind energy
  • Y02E10/727—Offshore wind turbines

Definitions

• This invention relates to a method for adjusting the angle of the rotor blades about their own longitudinal axis in a wind power plant in such manner that the thrust of the rotor on the tower is controlled and kept within desired values without the average output of the wind power plant being affected to any noticeable degree.
• This has the advantage that the load variations on the rotor blade and tower are reduced, thereby substantially reducing fatigue of these heavily loaded components.
• Momentary wind velocity is defined as the momentary wind velocity that is measured at a particular point in time.
• Average or levelled wind velocity is defined as the average or approximately the average of the momentary wind velocity for a certain period. This period will typically be longer than three seconds and normally in the range of 10 minutes to one hour, but it can also be longer. When the wind velocity is used to control the wind turbine, scaling or fractions of such measured values will also be covered by this definition.
• Pitch angle in this patent application is defined as the rigid body torsion of a rotor blade about its own longitudinal axis relative to a fixed starting position for this angle. By pitching the blades, the forces on the rotor for a given momentary wind velocity can be varied.
• Rotor axial force is defined as the thrust that is transferred from the rotor towards the mill housing and which is directed essentially along the rotational axis of the rotor axis. This force consists of the total thrust in the wind direction from the rotor blades and may be both positive and negative at different times during the operation of the wind power plant.
• Nominal wind velocity is defined as the wind velocity at which the wind power plant first achieves full output. This may typically be in the range of 12-14 m/s.
• Converter unit is the unit which generates or converts energy from the wind/rotation of the rotor blades into electric power or other mechanical power.
• This unit may typically be a generator, a mechanical pump, a gear unit or the like.
• generator is used for the most part, but it is clear that generator can be replaced by any type of suitable converter unit as mentioned here.
• a floating structure of this kind will primarily be affected by two types of forces that will control the motion pattern and stresses on the floating structure. These are waves forces against the floating part of the structure and thrust on the rotor from the wind, referred to herein as the rotor axial force.
• the dominant forces acting on the structure will usually be, in addition to gravitational forces, the thrust on the rotor from the wind.
• the rotor provides a constant output power, equal to the nominal output of the plant, for wind velocities that are higher than necessary in order to achieve full output (nominal output).
• One of the methods is stall regulation of the rotor blades. This method turns the blades into the wind so that the angle of attack of the relative wind against the wing profile is increased and the rotor blades reach stall.
• the other regulating method is pitch regulation of the blades whereby the blades are turned in the opposite direction to that in stall regulation so that the wind is released by reducing the angle of attack of the relative wind against the wing profile.
• pitch regulation is a last regulating method which is called pitch regulation in this application.
• the rotor rpm for wind velocities above the nominal wind velocity will be regulated so that the rotor output which is equal to the rotor torque multiplied by the angular speed (rotational speed in radians) is kept as constantly equal to the nominal output of the wind power plant as possible.
• a control unit controls the pitch angle of the rotor blades continuously.
• Output and rotor axial force are non-linear values as a function of variation of the wind velocity.
• the rotor axial force may thus have large variations. These force variations cause major fatigue loads on the blades and tower structure, which in many cases can be dimensioning for these structural elements.
• the above-described effect that increased wind velocity reduces the rotor axial force because of the pitch regulation may also have negative effects on the motion pattern of the wind power plant.
• the relative wind velocity against the rotor will increase, which will result in a reduced rotor thrust because the pitch regulation tries to maintain constant output, which in turn will increase the movement of the tower against the wind.
• Patent No. US-4201514 describes a method for regulating the pitch angle of the individual rotor blades in relation to variations of the wind velocity. .
• the regulation describes how the torque of the individual blades about the rotor axis is automatically held constant in changing wind velocities.
• This has the same effect as for other prior art as described above. That is to say that the forces acting in the direction of the rotational direction of the blades, i.e., perpendicular to the wind direction, and which cause the blade to rotate, are held constant.
• a side effect of this is that the thrust of the blade in the wind direction will vary in the same way as described above for other prior art.
• this prior art will have the same effect on fatigue of the blades and tower because of varying thrust on the rotor blades when an attempt is made to hold the rotor torque constant.
• the object of the invention is to overcome the disadvantages of the prior art.
• a method for controlling the output of a wind power plant comprising a converter unit, wherein when the output power of the converter unit is within a given range, the pitch angle of the rotor blades is changed with a view to minimising variations of the thrust of the rotor blades in the wind direction individually or collectively, and when the output power of the converter unit is outside this range, the pitch angle of the rotor blades is changed with a view to bringing the output power within the range.
• variations of the thrust of the rotor blades in the wind direction are minimised by regulating towards a calculated target value for the thrust of the rotor blades in the wind direction, the target value for the thrust in the wind direction being different for different average wind velocities.
• the target value for the thrust of the rotor blades in the wind direction is adjusted in relation to average converter unit output or rotor speed over a given period of time. In still another embodiment of the invention, the target value for the thrust of the rotor blades in the wind direction is pre-defined and related to given average wind velocities.
• the thrust of the rotor blades in the wind direction is in addition adjusted by changing the rotor rpm by adjusting the generator rotation resistance moment and/or rotor brakes.
• the momentary thrust of the rotor blades in the wind direction is determined directly or indirectly by means of strain gauges, wind velocity measurements, by measuring geometric deflection of the blades, measuring the generator torque and/or measuring the generator output together with simultaneous measurement of the pitch angles of the blade or blades, and/or by measuring or using the pitch moment of the blades about the rotational axis of the pitch bearing either by mounting the blades leaning backwards in the pitch bearing, or by shaping the blades so that the impact point of the wind on the blade is behind the rotational axis of the pitch bearing in relation to the rotational direction of the rotor.
• the pitch angle of the rotor blades is in addition changed with a view to minimising direction errors for the wind power plant.
• the direction error is corrected if it is outside a given range.
• the pitch angle of the rotor blades is adjusted differently for different rotational positions. In one embodiment, the pitch angles of the rotor blades are adjusted individually and/or independent of one another.
• the wind field in a plane substantially perpendicular to the wind direction is predicted by using directly or indirectly measured values of the wind forces acting on the rotor blade or blades that is/are at the front in relation to the rotational direction of the rotor.
• the thrust of the rotor blades in the wind direction is used actively to counteract motions of the wind power plant tower by regulating the pitch angles of the rotor blades.
• one or more anemometers/wind gauges are placed in a suitable location or locations on the wind power plant so that the spatial distribution of the wind velocity can be recorded and interpolations between the different anemometers can be made to form a picture of the distribution of the wind across the sweeping area of the rotor. This can be done by placing anemometers at substantially different heights and in substantially different horizontal positions. This spatial distribution of the momentary wind velocity can then be used to individually regulate the pitch of the rotor blades, optionally all the blades may be pitch-regulated collectively.
• the wind field in a plane that is essentially perpendicular to the wind direction can be predicted by using directly or indirectly measured values of the wind forces which act on the rotor blade or blades which is/are at the front in relation to the rotational direction of rotor.
• the rotor may advantageously be positioned downwind of the tower so that the anemometers record the wind velocity before it impinges on the rotor.
• directly or indirectly measured values of the thrust on the blade that is at the front in relation to the rotational direction of the rotor, of a given blade can be used to predict the wind field into which the given blade will move.
• the optimal pitch angle of the blades can be calculated in advance so that there is little or no delay between the aerodynamic forces and the pitch response of the rotor blades.
• sudden changes in the momentary wind velocity can be predicted.
• the time delay from when the measurements are made until the actual wind velocity occurs in the rotor can be calculated.
• the controller unit that controls the pitch regulations is given access to all these measurements and can at any given time use this information to optimise the pitch angles of the blades.
• the blades will initially be turned so that the axial force on the rotor is reduced. This is countered by increasing the rotational speed of the rotor by means of reduced or no pitch response whilst the generator torque optionally at the same time is reduced in accordance with input from the control unit which also will help to increase the rotational speed of the rotor. Both the rotor axial force and the output of the generator can then be held almost constant at optimal pitch angle within a small wind velocity increase. At a wind increase of about 10%>, the rotational speed according to this method must be increased by about 10% to obtain both unchanged rotor axial force and unchanged output to the generator. The pitch angle must be changed at the same time. A similar method is used when there is a decrease in momentary wind velocity, but in that case the rotational speed of the rotor is reduced whilst the generator torque is, optionally simultaneously, increased in accordance with input from the control unit.
• the average generator output will be almost unchanged, i.e., equal to the nominal output (rated power), whilst the axial force for a given average wind velocity can be held constant or almost constant, typically within a +/-20% variation of the momentary wind velocity.
• the rotor axial force target value
• Acceptable maximum and minimum values for the generator output variations around a mean value can be pre-programmed, and the pitch controller unit will then calculate optimal momentary pitch angles so that the rotor axial force is held as constant as possible around the said calculated target value whilst the generator output is maintained within the pre-programmed bandwidth.
• the calculated target value for the rotor axial force will therefore vary with different average wind velocities. Within each average wind velocity, an attempt will then be made to keep the axial force almost constant using pitch regulation.
• the average wind velocity may, for example, be the mean of the last 10 minutes.
• pre-calculated values may be used for the target values of the axial force for given average wind velocity intervals, e.g., divided into intervals of 0.1 m/s differences.
• pitch regulation can be carried out giving priority to not varying the generator output by more than the typical approximately +/- 10% as described above.
• the rotor axial force will start to vary, but also in these cases this variation will be substantially less than for pitch regulation according to the prior art.
• the same method as described above can also be used to actively regulate the rotor axial force in relation to a given mean value. If the rotor axial force in this way is actively controlled with varying value, this can be used, e.g., to apply forces to the tower in counter phase with its motions so that the motions of the tower are dampened.
• the motions of the tower can, e.g., be recorded using an accelerometer.
• the axial force can be used actively in a similar manner to counter any forces that try to turn the rotor out of the wind. This can be done by controlling the individual force of the rotor blades in the wind direction so that any torques that try to turn the rotor and/or the nacelle and/or the tower out of the wind are countered, reduced or eliminated by cyclically changing the individual pitch angle of the blades according to the physical position of each individual blade at any given time, so that the axial force on the rotor is greater on one side or the other of the vertical axis of the rotor, as required.
• the pitch angle is increased, e.g., by 0.5 degrees, and when the same blade passes the opposite side, the pitch angle is decreased correspondingly. Therefore, this does not need to have any effect on the total rotor output or the total rotor axial force.
• the extra cyclic pitch variation is superposed only on the calculated pitch angle according to the above-described method in order to control the total rotor axial force.
• This described cyclic pitch regulation can also be used to actively control the rotor so that parts of, or optionally the whole of the wind power plant in the case of a floating plant, can be held in the desired position relative to the wind direction.
• the thrust variations in the wind direction on each individual blade can be reduced by changing the pitch angle according to the above-described method in order to control the momentary thrust of the blade in the wind direction.
• the blade can then be controlled individually in relation to its position in its orbit and to measured values of the wind velocities in different positions in or around the sweeping area of the rotor.
• the measured axial force will be recorded and included in the pitch controller unit for calculation of optimal pitch angle at any given time according to the described method.
• the pitch controller unit instead of just using measured wind velocity and pitch angle to calculate the rotor axial force, several other direct or indirect methods can be used.
• the longitudinal axis of the blade deviates slightly from the pitch bearing shaft axis so that the longitudinal axis of the blades does not intersect the rotor rotational axis, and the pitch moment which then occurs can be measured via hydraulic pressure via the blade pitch control system and the axial force can then be calculated; or
• strain gauges on the blades and/or on the main shaft of the rotor and/or on other parts of the wind power plant;
• Fig. 1 shows a floating wind power plant 1 with rotor 2 which may have a horizontally or substantially horizontally mounted rotor axis 1 1 mounted downwind of tower 4.
• the figure also shows mill housing 3, anemometers 5, anchor connection 6 and anchor 7.
• Fig. 2 shows a wind power plant 1 located on land or in shallow water with rotor 2 which has a horizontally or substantially horizontally mounted rotor axis 1 1 mounted upwind of tower 4.
• the figure also shows mill housing 3 and anemometers 5.
• Fig. 3 shows a wind power plant 1 that is located either on land or in shallow water or floating in water with rotor blades 13 which are rotatably mounted about their longitudinal axis or substantially about their longitudinal axis 14 with pitch bearings 10.
• Fig. 4 is a flow diagram illustrating the method according to the invention.
• Fig. 5 is a flow diagram for an optional part of the method according to the invention.
• a wind power plant 1 with a horizontal or substantially horizontal rotor axis 1 1 consists of one or more rotor blades 1 ) which together form a rotor 2, where the rotor blades in a coordinated manner or individually can be turned (pitched) around their own longitudinal axis or essentially around their own longitudinal axis 14 primarily in order to control the rotor 2 output to the generator (not shown), and where the rotor shaft is secured in a mill housing 3 and the rotor shaft is connected to the generator optionally via a transmission system (gear).
• the pitch regulation of the rotor blades is carried out by a pitch control unit which on the basis of different recorded operational information, wind measurements etc. transmits a signal to the pitch motors indicating the amount of the required change in pitch angle at any given time.
• the mill housing may be mounted on a tower 4 which is fixedly mounted on land 9 or on the seabed 8 or which is a part of a floating device or which itself constitutes a floating device with optionally one or more anchor connections 6 to an anchor 7 on the seabed 8.
• the design of the anchor system 6, 7 is of no importance for the described method.
• One of the objects of the method described below is to reduce the variations of the rotor axial force compared with the prior art, whilst the resultant output to the generator is not significantly affected or is maintained within acceptable limits in relation to limitations of the drive gear, generator and power grid. It is also an object of the method to use the rotor axial force to actively counter the motions of a floating wind power plant. Furthermore, it is an object of the described method to control and counter rotational forces about the vertical axis 12 of the tower and to reduce the aerodynamic force variation on each individual blade through a whole rotation cycle resulting from different wind velocities at different levels (vertical wind shear) and in the horizontal direction parallel to the rotor plane (horizontal wind shear).
• One or more anemometers 5 are placed in a suitable location or locations on the wind power plant 1 so that the spatial distribution of the wind velocity can advantageously be recorded and interpolations between the different anemometers can be made to form a picture of the distribution of the wind across the sweeping area of the rotor. This can be done by placing anemometers at substantially different levels and in substantially different horizontal positions. This spatial distribution of the momentary wind velocity can then be used to individually regulate the pitch of the rotor blades, optionally all the blades can be pitch- regulated collectively.
• the rotor 2 may advantageously be positioned downwind of the tower 4 so that the anemometers record the wind velocity before it impinges on the rotor.
• the optimal pitch angle of the blades can be calculated in advance so that there is little or no delay between aerodynamic forces and the pitch response of the rotor blades.
• sudden changes of the momentary wind velocity can be predicted.
• the controller unit (not shown) that controls the pitch regulation is given access to all these measurements and can at any given time use this information to optimise the pitch angles of the blades 13.
• the controller unit (not shown) that controls the pitch regulation is given access to all these measurements and can at any given time use this information to optimise the pitch angles of the blades 13.
• the rotational speed of the rotor 2 will be increased by means of reduced pitch response compared to the prior art, whilst the generator torque is, optionally simultaneously, reduced in accordance with input from the control unit, which will also help to increase the rotational speed of the rotor 2. Since the rotor axial force in general is increased on increased rpm for a given rotor output, the reduced rotor axial force resulting from the pitch turning of the blades in response to the increased momentary wind velocity can be compensated.
• both the rotor axial force and the output of the generator can be held almost constant by increasing the rotational speed of the rotor and with optimal pitch angle.
• the rotational speed must according to this method be increased by about 10% to obtain both unchanged rotor axial force and unchanged output to the generator.
• the pitch angle must be changed at the same time.
• the average generator output will be almost unchanged, i.e., equal to the nominal output (rated power), whilst the axial force for a given average wind velocity can be held constant or almost constant, typically within a +/-20% variation of the momentary wind velocity.
• the rotor axial force (target value), which corresponds to the nominal output of the generator, can be calculated.
• Acceptable maximum and minimum values for generator output variations around a mean value can be pre-programmed, and the pitch controller unit will then calculate optimal momentary pitch angles (in response to the momentary wind velocity) so that the rotor axial force is held as constant as possible around said calculated target value whilst the generator output is maintained within the pre-programmed bandwidth.
• the calculated target value for rotor axial force will vary with different average wind velocities. Within each average wind velocity, an attempt will then be made to keep the axial force almost constant around this target value using pitch regulation.
• the average wind velocity may, for example, be the mean of the last 10 minutes.
• pre-calculated values may be used for the target values of the axial force for given average wind velocity intervals, e.g., divided into intervals of 0.1 m/s differences.
• pitch regulation can be carried out giving priority to not varying the generator output by more than the typical bandwidth of about +/- 10% as described.
• the rotor axial force will start to vary, but also in these cases this variation will be substantially less than for pitch regulation according to the prior art.
• the same method as described above can also be used to actively regulate the rotor axial force around a given mean value. If the rotor axial force is in this way actively controlled with varying value, this can be used, e.g., to apply forces to the tower 1 in counter phase with its motions so that the motions of the tower are dampened. This is particularly advantageous for floating wind power plants.
• the control unit will in this case also have access to the motions of the tower.
• the motions of the tower can, e.g., be recorded using an accelerometer or other suitable measuring method.
• the axial force can be used actively in a similar manner to counter any forces that try to turn the rotor out of the wind. This can be done by controlling the individual force of the rotor blades in the wind direction so that any torques that try to turn the rotor and/or the mill housing and/or the tower out of the wind are countered, reduced or eliminated by cyclically changing the individual pitch angle of the blades according to the physical position of each individual blade at any given time, so that the axial force on the rotor is greater on one side or the other of the vertical axis of the rotor as required.
• the pitch angle is increased, e.g., by 0.5 degrees, and when the same blade passes the opposite side, the pitch angles is decreased correspondingly. Therefore, this does not need to have any effect on the total rotor output or the total rotor axial force.
• the extra cyclic pitch variation is superposed on the calculated pitch angle according to the above-described method in order to control the total rotor axial force.
• This described cyclic pitch regulation can also be used to actively control the rotor 2 so that parts of, or optionally the whole of the wind power plant in the case of a floating plant, can be held in the desired position relative to the wind direction.
• the thrust variations in the flap direction (normally approximately the same as the wind direction) on each individual blade (which together constitute the rotor axial force) is reduced by changing the pitch angle according to the above- described method in order to control the momentary thrust of the blade in the wind direction.
• the blade can then be controlled individually in relation to its position in its orbit and to directly or indirectly measured values of the wind velocities in different positions in or around the sweeping area of the rotor.
• the measured or calculated axial force will be recorded and included in the pitch controller unit for calculation of optimal pitch angle at any given time according to the described method.
• the longitudinal axis 14 of the blade deviates slightly from the pitch bearing shaft axis so that the longitudinal axis 14 of the blades does not intersect the rotor rotational axis 1 1 and the pitch moment which then occurs can be measured via hydraulic pressure via the blade pitch control system, and the rotor blade thrust in the wind direction for each individual blade can then be calculated; or
• strain gauges on the blades 13 and/or on the main shaft of the rotor and/or on other parts of the wind power plant; or Indirectly by measuring the pitch angles of the blade(s) 13 and the rotor 2 torque directly or by recording other parameters such as the generator torque, output etc. and then the corresponding rotor axial force of the rotor can be calculated.
• FIG. 4 By measuring deflection of the blades using a mechanical or electronic measuring system.
• An embodiment of the method according to the invention is illustrated in Fig. 4 by means of a flow chart. The method is based on the determination in 40 of whether an instantaneous/momentary rotor speed, or optionally output power of the generator is within a range of the nominal value for the wind power plant, in the example, by determining whether the rotor speed or optionally the output power of the generator is within +/- 10% of the nominal value.
• the instantaneous/momentary rotor speed optionally the output power of the generator
• an attempt will be made to minimise the rotor axial force variations, optionally the thrust of each blade in the wind direction individually, by regulating towards a target value for the axial force.
• average rotor speed or average generator output power for a given time t e.g., the last 10 minutes, is above or below the nominal output of the wind power plant. According to this, the target value for the rotor axial force is adjusted in 45, 46.
• a new target value for the axial force can be calculated on the basis of the mean value of the axial force over a given period of time t, for example, of 10 minutes with a given incremental increase or reduction of the target value for axial force depending upon whether it is desired to increase or decrease the average output of the generator.
• the target value for the rotor axial force may also optionally be a pre-calculated value related to the average wind velocity. The instantaneous value of the rotor axial force is then compared in 47 with the target value for the axial force as achieved in 45/46 and the rotor blade pitch angle is then changed in 48 and 49 in accordance with this comparison.
• the instantaneous/momentary rotor speed, or optionally the output power of the generator, as calculated in 40 is outside the given range, an attempt is made to come within this range by adjusting the pitch angle in the same way as in the prior art in order to bring the rotor speed, or optionally the average output power of the generator within the desired range, e.g., within +/-10% of the nominal.
• the pitch angle is adjusted in 42/43 according to the calculation in 41 of whether instantaneous/momentary rotor speed, or optionally output power of the generator, is above or below the desired range.
• the pitch angle is adjusted primarily with a view to maintaining a constant rotor axial force regulated towards a slow-varying target value, and unlike the prior art, the pitch angle will only be adjusted to the extent necessary to bring generator output power or rotor speed within the desired range.
• the pitch angle of the rotor blades can be adjusted either for all the rotor blades collectively, or for each individual rotor blade.
• directional information for the wind power plant can be taken into account, in addition to the aforementioned moments, with a view to holding the wind power plant in a stable position.
• This information 50 is taken into account in step 47 in the figure.
• Figure 5 illustrates in more detail the steps for providing this directional information.
• step 51 sinus( ⁇ ) is calculated or recorded, where ⁇ is the rotational position of the blade, i.e., it describes where in the rotation each individual rotor blade is.
• step 52 it is decided whether the direction error of the wind power plant direction relative to the wind direction is outside a given range, in this case +/-5°. If the direction error is within the range, no action is taken, but if the direction error is outside the range, a rotational mechanism for the tower is optionally triggered and a signal is calculated in 55, 56 according to which side of the range the direction error is on. The information provided in 55 or 56 is superposed on the control signals provided to adjust the pitch angle with respect to the rotor axial force variations, optionally the thrust of each individual blade in the wind direction.
• the direction error information comprises information about rotational position, i.e., the pitch angle is adjusted individually for each blade according to its momentary rotational position. This means that the thrust of each individual blade in the wind direction is adjusted differently for the different rotational positions so that a force effect is obtained that counters the direction error for the wind power plant.

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