WO2022105975A1 - Wind turbine boost setting - Google Patents

Wind turbine boost setting Download PDF

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Publication number
WO2022105975A1
WO2022105975A1 PCT/DK2021/050337 DK2021050337W WO2022105975A1 WO 2022105975 A1 WO2022105975 A1 WO 2022105975A1 DK 2021050337 W DK2021050337 W DK 2021050337W WO 2022105975 A1 WO2022105975 A1 WO 2022105975A1
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WO
WIPO (PCT)
Prior art keywords
speed
period
during
power
wind turbine
Prior art date
Application number
PCT/DK2021/050337
Other languages
French (fr)
Inventor
Karthik Krishnan JAMUNA
Jesper Hede BAASTRUP
Mu WEI
Original Assignee
Vestas Wind Systems A/S
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Publication date
Application filed by Vestas Wind Systems A/S filed Critical Vestas Wind Systems A/S
Publication of WO2022105975A1 publication Critical patent/WO2022105975A1/en

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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
    • F03D7/0276—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
    • 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
    • F03D7/0296—Controlling wind motors  the wind motors having rotation axis substantially parallel to the air flow entering the rotor to prevent, counteract or reduce noise emissions
    • 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
    • F05B2270/335—Output power or torque
    • 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

Definitions

  • the present invention relates to a method of controlling a wind turbine, and a wind turbine control system.
  • wind speed measurements upstream of a wind turbine are received and a determination of an indication of a current wind speed at the wind turbine is made.
  • the indication may include below rated wind speed or above rated wind speed. It is determined if the wind speed is in an up transition region or a down transition region based on the received one or more wind speed measurements and the indication of said current wind speed. If determined that said wind speed is in an up transition region or a down transition region, then a boost action is performed.
  • a first aspect of the invention provides a method of controlling a wind turbine, the method comprising: controlling the wind turbine during a variable speed period in accordance with a variable speed region of a partial load speed curve so that a power of the wind turbine is below a rated power and a generator speed of the wind turbine is below a rated generator speed; controlling the wind turbine during a boost period in accordance with a boost region of the partial load speed curve so that the power is below the rated power and the generator speed is above the rated speed; and controlling the wind turbine during a full load period so that the power is at the rated power and the generator speed is at the rated speed.
  • the method further comprises monitoring the power during the full load period, and starting the boost period in response to the monitored power falling below the rated power.
  • the method further comprises monitoring a wind speed during the full load period, and starting the boost period in response to the monitored wind speed falling below a wind speed threshold.
  • the wind speed threshold may be set on the basis of an air density.
  • the method further comprises monitoring the power during the boost period, and reducing the generator speed during the boost period in response to the monitored power rising above a threshold.
  • the method further comprises monitoring a wind speed during the boost period, and reducing the generator speed during the boost period in response to the monitored wind speed rising above a wind speed threshold.
  • the wind speed threshold may be set on the basis of an air density.
  • the method further comprises controlling the wind turbine during a first part of the boost period in accordance with the boost region of the partial load speed curve so that the power is below the rated power and the generator speed is above the rated speed; and controlling the wind turbine during a second part of the boost period to reduce the generator speed back to the rated speed.
  • the generator speed is controlled during the boost period on the basis of a torque input.
  • the generator speed changes during the variable speed period and/or during the boost period.
  • the method further comprises controlling the wind turbine during the boost period to reduce the generator speed and transition from the boost period into the full load period or into the variable speed period.
  • the method further comprises controlling the wind turbine during the boost period so that a tower oscillation of the turbine does not exceed a predetermined threshold.
  • the generator speed is restricted to a maximal generator speed.
  • the generator speed is more than 1% greater than the rated speed.
  • a further aspect of the invention provides a wind turbine control system, wherein the control system has a variable speed setting which is configured to control a wind turbine in accordance with a variable speed region of a partial load speed curve so that a power of the wind turbine is below a rated power and a generator speed of the wind turbine is below a rated generator speed; the control system has a boost setting which is configured to control the wind turbine in accordance with a boost region of the partial load speed curve so that the power is below the rated power and the generator speed is above the rated speed; and the control system has a full load setting which is configured to control the wind turbine so that the power is at the rated power and the generator speed is at the rated speed.
  • Figure 1 schematically illustrates a wind turbine
  • Figure 2 schematically illustrates a control system for controlling the wind turbine
  • Figure 4 is a graph showing a boost operation mode
  • Figure 5 is a graph showing the performance of the wind turbine during an up-transition in the wind boost operation mode
  • Figure 6 is a graph showing the performance of the wind turbine during a downtransition in the wind boost operation mode
  • Figure 7 is a graph showing the performance of the wind turbine during an up-transition into an indefinite boost period
  • Figure 10 shows power curves associated with baseline and boost settings, and low air density
  • Figure 11 shows speed curves associated with baseline and boost settings, and low air density
  • Figure 12 shows speed curves associated with baseline and boost settings, and normal air density
  • Figure 13 shows power curves associated with baseline and boost settings, and normal low air density
  • Figure 15 shows an example of control logic of the control system when it is in its boost operation mode
  • Figure 16 shows an example of a look-up table used in the control logic of Figure 15.
  • FIG. 1 illustrates, in a schematic perspective view, a wind turbine 10.
  • the wind turbine 10 includes a tower 12, a nacelle 13 at the top of the tower, and a rotor 14 operatively coupled to a generator housed inside the nacelle 13.
  • the nacelle houses miscellaneous components required for converting wind energy into electrical energy and various components needed to operate, control, and optimize the performance of the wind turbine 10.
  • the rotor 14 of the wind turbine includes a central hub 15 and a plurality of blades 16 that project outwardly from the central hub 15. In the illustrated embodiment, the rotor 14 includes three blades 16, but the number may vary.
  • the wind turbine 10 may be included among a collection of other wind turbines belonging to a wind power plant, also referred to as a wind farm or wind park, that serve as a power generating plant connected by transmission lines with a power grid.
  • the power grid generally consists of a network of power stations, transmission circuits, and substations coupled by a network of transmission lines that transmit the power to loads in the form of end users and other customers of electrical utilities.
  • FIG. 2 schematically illustrates an embodiment of a wind turbine control system 20 configured to control the wind turbine 10.
  • the control system 20 may be placed inside the nacelle 13 and/or distributed at a number of locations inside the turbine.
  • some, or all, elements of the control system 20 may be placed in a remote power plant controller (not shown).
  • the blades 16 are mechanically connected to an electrical generator 22 via a gearbox 23. In direct drive systems, and other systems, the gearbox 23 may not be present.
  • the electrical power generated by the generator 22 is injected into a power grid 24 via an electrical converter 25.
  • the electrical generator 22 and the converter 25 may be based on a full scale converter (FSC) architecture or a doubly fed induction generator (DFIG) architecture, but other types may be used.
  • FSC full scale converter
  • DFIG doubly fed induction generator
  • the control system 20 comprises a number of elements, including at least one main controller 21.
  • the control system 20 ensures that in operation the wind turbine generates a requested power output level. This is obtained by adjusting the pitch angle of the blades 16 and/or the power extraction of the converter 25.
  • the control system comprises a pitch system including a pitch controller 27 using a pitch reference 28, and a power system including a power controller 29 using a power reference 26.
  • the rotor blades 16 can be pitched by a pitch mechanism.
  • the rotor comprises an individual pitch system which is capable of individual pitching of the rotor blades, and may comprise a common pitch system which adjusts all pitch angles on all rotor blades at the same time.
  • the control system 20 further comprises a wind load block 210, configured to determine a direction (and optionally magnitude) of a wind load acting on the wind turbine.
  • the main controller 21 comprises a data processing system, and a computer program product comprising software code adapted to control the wind turbine 10 when executed on the data processing system, the computer program product being adapted to control the wind turbine as described below.
  • the control system 20 has a baseline operation mode, and a boost operation mode.
  • Figure 3 is a graph showing how the control system 10 controls the power injected into the grid 24, the speed of the generator 22, and the pitch of the blades 16, when operating in its baseline operation mode.
  • the baseline operation mode has a partial load region between 3 and 13 m/s; and a full load region above 13 m/s.
  • the partial load region has three regions (labelled I, II and II) and the partial load region is labelled as region IV.
  • the graph of Figure 3 shows a speed curve 30; a power curve 32; and a pitch curve 35.
  • Region II is a variable speed region in which the turbine is controlled in accordance with a linear portion of the speed curve 30 so that the power coefficient C p is set to a maximum value C p *.
  • the power is below a rated power and the generator speed is below a rated generator speed.
  • Region III is a fixed-speed region in which the generator speed is fixed.
  • the power coefficient C p drops below the maximum value C p *.
  • the generator speed is set to the rated speed (for example 1680 rpm) and the power is below the rated power.
  • Region IV is a full load region in which the turbine is controlled so that the power is fixed at the rated power (for example 300 kW) and the generator speed is fixed at the rated speed.
  • Figure 4 is a graph showing how the control system 10 controls power, generator speed and blade pitch when operating in its boost operation mode.
  • control system When it is operating in the boost operation mode, the control system has three settings in which the wind turbine performs as shown in Figure 4.
  • control system 10 When the control system 10 is in its variable speed setting, it is configured to control the wind turbine in accordance with a first region 42a of a partial load power curve 42 so that the power is below a rated power; and in accordance with a variable speed region 40a of a partial load speed curve 40 so the generator speed is below a rated generator speed.
  • This variable speed setting corresponds with Region II in the baseline operation mode of Figure 3.
  • the pitch does not change when the control system 10 is in its variable speed setting, as indicated at 44a.
  • control system 10 When the control system 10 is in its full load setting, it is configured to control the wind turbine so that the power is at the rated power and the generator speed is at the rated speed.
  • This full load setting corresponds with Region IV in the baseline operation mode of Figure 3.
  • control system 10 In its full load setting the control system 10 sets constant power and speed reference (rated power and rated speed values) and keeps to those by changing the pitch. In this case the pitch increases with wind speed as indicated by pitch curve 45.
  • control system 10 When the control system 10 is in its boost setting, it is configured to control the wind turbine in accordance with a second region 42b of the power curve 42 so that the power is below the rated power; and in accordance with a boost region 40b, 40c of the partial load speed curve 40 so the generator speed is above the rated speed.
  • the pitch does not change initially (as indicated at 44b), to remain at optimum power coefficient (C p *) then increases slightly as indicated at 44c.
  • the increase of pitch at 44c is more an aerodynamic aspect than a control aspect.
  • Figure 5 shows how the control system operates the wind turbine during an up- transition of the wind, when the wind speed 50 is increasing and the control system is in boost operation mode.
  • variable speed time period (t1 to t2) the wind speed increases from v1 to v2.
  • the control system is in its variable speed setting so the wind turbine is controlled in accordance with the variable speed region 40a of the partial load speed curve so that the power is below the rated power and the generator speed is below the rated generator speed.
  • the turbine is controlled so that the power coefficient Cp is set to a maximum value C p *.
  • This optimal power coefficient is achieved by setting the blade pitch so that a tip speed ratio A of the wind turbine is set to an optimal value A* and thus achieve the maximum power coefficient C p *.
  • the wind speed v may be measured, and the power P may be set to be proportional to v3 (where v is the wind speed).
  • the turbine may be controlled on the basis of an optimum speed set point shown in Eq.
  • w op t is the optimum speed set point
  • GearRatio is the gear ratio of the gearbox 23
  • PartLoadLambdaOpt is the optimal value (A*) of the tip speed ratio (the ratio between the tangential speed of the tip of a blade and the speed of the wind)
  • RotorRadius is the radius of the rotor 14, and windspeed is the speed of the wind.
  • the wind speed threshold v2 may be set on the basis of an air density. The air density may be measured, or estimated for example based on the altitude of the wind turbine.
  • a first (low power) part (t2 to t3) of the boost period the turbine continues to be controlled on the basis of the optimum speed set point shown in Eq. 1.
  • the pitch remains constant so that the tip speed ratio value of the wind turbine is set to the same value A* as during the variable speed period.
  • the tip speed ratio is set to achieve maximum power coefficient C p * during both the variable speed period (t1 to t2) and the first part (t2 to t3) of the boost period.
  • the generator speed increases from t2 to t3 in accordance with the first part 40b of the boost region of the partial load speed curve.
  • the increased rotational speed decreases the efficiency (Cp) of the transfer of energy from the wind to the rotor.
  • the efficiency (Cp) of the transfer of energy from the wind to the rotor remains substantially unchanged.
  • the power is monitored during the boost period, and the control system reduces the generator speed during a second (high power) part (t3 to t4) of the boost period in response to the monitored power rising above a power threshold at time t3 - for instance a set percentage of the rated power.
  • the pitch increases (in accordance with the partial load pitch curve 44c) and the tip speed ratio changes.
  • the generator speed decreases from t3 to t4 in accordance with the second part 40c of the boost region of the partial load speed curve.
  • the power coefficient C p drops below the maximum value C p * and the tip speed ratio A is no longer optimal.
  • the generator speed remains above the rated speed and the power remains below the rated power.
  • the wind turbine is controlled during the second part (t3 to t4) of the boost period to reduce the generator speed and transition from the boost period into a full load period.
  • the generator speed may rise to a maximum at time t3 which is, for example, in a range of 1-10% greater than the rated speed.
  • the control system 20 At time t4 the wind speed has reached v4, the power has reached rated power, and the generator speed has dropped to the rated speed. This triggers the control system 20 to switch to its full load setting, so the power is kept at the rated power and the generator speed is kept at the rated speed.
  • the wind turbine is controlled during the full load period by changing the blade pitch angle of the wind turbine in accordance with the full load pitch curve 45, so that the power remains at the rated power and the generator speed remains at the rated speed despite the changes in wind speed.
  • Figure 5 shows how the control system operates the wind turbine during an up- transition of the wind, when the wind is increasing.
  • the periods follow the time order: variable speed period, boost period, full load period.
  • Figure 6 shows how the control system operates the wind turbine during a downtransition of the wind, when the wind 60 is decreasing.
  • full load period boost period
  • variable speed period The control of the wind turbine in the various periods shown in Figure 6 is identical to the equivalent periods in Figure 5, but reversed in time.
  • the power is monitored during the full load period (before time t5), and the control system increases the generator speed during a first (high power) part of the boost period (t5 to t6).
  • the boost period is triggered in response to the monitored power falling below the rated power at time t5.
  • other triggers may be used to trigger the boost period, such as a wind speed (measured by a wind speed sensor) falling below a wind speed threshold v4.
  • the wind speed threshold v4 may be set on the basis of an air density.
  • the air density may be measured, or estimated for example based on the altitude of the wind turbine.
  • the power is also monitored during the boost period, and the control system reduces the generator speed during a second (low power) part of the boost period (t5 to t6) in response to the monitored power falling below the power threshold at time t6, or the wind speed falling below v3.
  • the wind speed threshold v3 may be set on the basis of an air density.
  • the air density may be measured, or estimated for example based on the altitude of the wind turbine.
  • the pitch control changes in response to the monitored power crossing a power threshold at either time t3 or time t6. This ensures that the generator speed does not go too high above the rated speed when the control system is in its boost setting.
  • a maximal generator speed may be set, so that the generator speed during the boost period is restricted to a maximal generator speed.
  • the pitch control may change in response to the generator speed reaching the maximal generator speed, the change of pitch control keeping the generator speed below the maximal generator speed.
  • the power is greater during the full load period than during the boost period, and greater during the boost period than during the variable speed period.
  • the generator speed is greater during the boost period than during the full load period, and greater during the full load period than during the variable speed period.
  • the generator speed changes during the variable speed period and during the boost period, but does not change during the full load period (despite the change in the wind speed during the full load period).
  • the wind speed increases or decreases continuously.
  • the wind speed 70 increases to v3 but does not reach v4; and in the example of Figure 8 the wind speed 80 decreases to v3 but does not drop further to v2.
  • the wind turbine remains in a boost setting for an indefinite period of time. So in the example of Figure 7 the control system 10 switches from its variable speed setting into its boost setting at time t10 without later switching into its full load setting; and in the example of Figure 8 the control system 10 switches from its full load setting into its boost setting at time t12 without later switching into its variable speed setting.
  • a boost action is only performed for a limited time.
  • the present invention may enable a boost action to be performed for a long or indefinite length of time.
  • Figure 9 shows speed curves which relate the generator speed to the wind speed: a baseline speed curve 90 associated with a baseline setting of the control system, a speed curve 91 associated with a 5% boost setting of the control system; and a speed curve 92 associated with a 10% boost setting of the control system.
  • the speed curve 91 associated with a 5% boost setting has a boost region in which the generator speed increases to 5% above the rated speed; and the speed curve 92 associated with a 10% boost setting has a boost region in which the generator speed increases to 10% above the rated speed.
  • Figure 10 shows power curves which relate the power to the wind speed: a baseline power curve 100 associated with the baseline setting of the control system, a power curve 101 associated with a 5% boost setting of the control system; and a power curve 102 associated with a 10% boost setting of the control system.
  • the power curve 101 associated with a 5% boost setting has a boost region in which the power is higher than the baseline speed curve 100; and the power curve 101 associated with a 10% boost setting has a boost region in which the power is higher than both the baseline speed curve 100 and the power curve 101.
  • Figure 11 shows speed curves which relate the generator speed to the power: a baseline speed curve 110 associated with the baseline setting of the control system, a speed curve 111 associated with the 5% boost setting of the control system; and a speed curve 112 associated with the 10% boost setting of the control system.
  • the speed curve 111 associated with a 5% boost setting has a boost region in which the generator speed increases to 5% above the rated speed; and the speed curve 112 associated with a 10% boost setting has a boost region in which the generator speed increases to 10% above the rated speed.
  • FIGs 9-11 show the power and speed performance of the wind turbine where the air density is relatively low (air density 0.95 kg/m3). At this low air density the Annual Energy Production (AEP) benefits from the boost operation mode are 2.95% and 4.05% for a 5% and 10% allowed increase of the generator speed, respectively.
  • AEP Annual Energy Production
  • Figures 12-14 show equivalent curves associated with a more normal air density (1.225 kg/m3). At this normal air density, the AEP benefits from the boost operation mode are lower: 0.76% and 1.48% for a 5% and 10% allowed increase of the generator speed, respectively.
  • Figure 12 shows a baseline speed curve 120, a speed curve 121 associated with a 5% boost setting, and a speed curve 122 associated with a 10% boost setting. Note that the boost regions of the speed curves 121 , 122 occupy a more narrow range of wind speeds in Figure 12 than in Figure 9.
  • Figure 13 shows a baseline power curve 130, a power curve 131 associated with a 5% boost setting, and a power curve 132 associated with a 10% boost setting. Note that the boost regions of the power curves 131 , 132 are not much different to the baseline curve 130.
  • Figure 14 shows a baseline speed curve 140, a speed curve 141 associated with a 5% boost setting, and a speed curve 142 associated with a 10% boost setting. Note that the boost regions of the speed curves 141 , 142 occupy a more narrow range of wind speeds in Figure 14 than in Figure 11.
  • Figure 15 show an example of how the control system 20 may be configured to control the wind turbine in accordance with the boost region 40b, 40c of the partial load speed curve.
  • the control system 20 controls the generator speed on the basis of a power input.
  • a low pass filter 150 receives the power input, and outputs a filtered power signal. This is input into a look-up table 151 which outputs a gain value. The gain value is applied to a speed ref input, to generate a boost speed signal which is input to a switch 152. The speed ref input determines the rated speed, and the gain value determines how high the generator speed can increase during the boost period, relative to the rated speed.
  • Figure 16 shows an example of the look-up table for a 5% boost setting of the control system.
  • the horizontal axis in Figure 16 shows relative power, i.e. the proportion of rated power.
  • the gain value is set to 1.05 so the generator speed is allowed to increase to a maximal generator speed 5% above the rated generator speed.
  • the gain value decreases linearly with power.
  • the gain value has reduced to 1 .00.
  • the maximum allowed speed is decreased as the power approaches rated power.
  • Activation logic 153 operates the switch 152, which can switch between the boost speed signal and the speed ref input.
  • the output of the switch 152 is input to a dynamic rate limiter 154, which generates a speed output.
  • the control system 20 than controls the wind turbine so that the generator speed is set by the speed output.
  • the control system 20 controls the generator speed on the basis of a power input, wherein the power input is indicative of a power being generated by the wind turbine.
  • the control system 20 may control the generator speed on the basis of a load input.
  • a lookup table like Figure 16 may be used, but with load on the X-axis.
  • the load input may be indicative of a load on a blade, or a load on the tower for example.
  • the control system 20 may control the generator speed on the basis of a torque input, for instance indicative of a torque on the gearbox.
  • a look-up table like Figure 16 may be used, but with torque on the X-axis.
  • control system 20 may control the generator speed on the basis of a wind speed input, for instance indicative of a speed of the wind incident on the wind turbine as measured by a wind speed sensor.
  • a look-up table like Figure 16 may be used, but with wind speed on the X-axis.
  • a requirement may be set to limit the oscillation of the tower. For instance a tower acceleration x-direction RMS signal may be calculated, and used to limit the boosting, or switch to the baseline operation mode, if its value is too high.
  • a pitch angle requirement may also be used, to limit or prevent boosting if the pitch angle is too high.
  • This pitch angle requirement may operate as follows: during full load operation, high wind fluctuations may cause the control system 20 to quickly de-rate both power and generator speed, with the pitch remaining high (as indicated by full load pitch curve 45). In this situation, the control system will not switch into its boost operation mode because the pitch is too high. This prevents the boost operation mode being used at high wind speeds.
  • the boost operation mode may be operated during the full lifetime of the wind turbine, or it may only be introduced during a later part of the life of the wind turbine (for instance the last 5 or 8 years) when there is less risk from fatigue.
  • a fatigue evaluation may be performed, and the boost period is enabled dependent on the result of the fatigue evaluation.
  • the fatigue evaluation may be a fatigue valuation of the wind turbine, or a fatigue evaluation of other similar turbines.
  • a load evaluation may be performed, and the boost period enabled dependent on the result of the load evaluation.
  • the load evaluation may evaluate load data from blade load sensors, tower load sensors or other load sensors; and the load data may be evaluated to assess whether it is safe to initiate a boost period, or continue a boost period.
  • the embodiments of the invention provide various methods of controlling a wind turbine.
  • the wind turbine is controlled during a variable speed period in accordance with a variable speed region of a partial load speed curve so that a power of the wind turbine is below a rated power and a generator speed of the wind turbine is below a rated generator speed.
  • the performance of the wind turbine follows the variable speed region of the partial load speed curve.
  • the variable speed region of the partial load speed curve may relate generator speed to wind speed, or it may relate generator speed to an operating parameter of the wind turbine, such as the power.
  • the wind turbine is also controlled during a boost period in accordance with a boost region of the partial load speed curve so that the power is below the rated power and the generator speed is above the rated speed. In other words, the performance of the wind turbine follows the boost region of the partial load speed curve.
  • the boost region of the partial load speed curve may relate generator speed to wind speed, or it may relate generator speed to an operating parameter of the wind turbine, such as the power. Controlling the wind turbine in accordance with the boost region of the partial load speed curve enables the boost period to last for a long time (as long as the wind conditions remain the same) and enables the efficiency (Cp) of the transfer of energy from the wind to the rotor during the boost period to be kept relatively high.

Abstract

A method of controlling a wind turbine. The wind turbine is controlled during a variable speed period in accordance with a variable speed region of a partial load speed curve so that a power of the wind turbine is below a rated power and a generator speed of the wind turbine is below a rated generator speed. During a boost period the wind turbine is controlled in accordance with a boost region of the partial load speed curve so that the power is below the rated power and the generator speed is above the rated speed. During a full load period the power is at the rated power and the generator speed is at the rated speed.

Description

WIND TURBINE BOOST SETTING
FIELD OF THE INVENTION
The present invention relates to a method of controlling a wind turbine, and a wind turbine control system.
BACKGROUND OF THE INVENTION
It is desirable to operate a wind turbine to capture maximum power from the wind without violating the structural integrity of the wind turbine.
EP 2826992A1 describes a method comprising: increasing a rotational speed of the rotor from a typical rotational speed to an increased rotational speed. This decreases the efficiency (Cp) of the transfer of energy from the wind to the rotor.
In WO 2014/053136, wind speed measurements upstream of a wind turbine are received and a determination of an indication of a current wind speed at the wind turbine is made. The indication may include below rated wind speed or above rated wind speed. It is determined if the wind speed is in an up transition region or a down transition region based on the received one or more wind speed measurements and the indication of said current wind speed. If determined that said wind speed is in an up transition region or a down transition region, then a boost action is performed.
SUMMARY OF THE INVENTION
A first aspect of the invention provides a method of controlling a wind turbine, the method comprising: controlling the wind turbine during a variable speed period in accordance with a variable speed region of a partial load speed curve so that a power of the wind turbine is below a rated power and a generator speed of the wind turbine is below a rated generator speed; controlling the wind turbine during a boost period in accordance with a boost region of the partial load speed curve so that the power is below the rated power and the generator speed is above the rated speed; and controlling the wind turbine during a full load period so that the power is at the rated power and the generator speed is at the rated speed.
Optionally, the method further comprises controlling the wind turbine so that a tip speed ratio of the wind turbine is set to the same value during both the variable speed period and at least part of the boost period. Optionally, the method further comprises controlling the wind turbine so that a tip speed ratio of the wind turbine is set to achieve maximum power coefficient during both the variable speed period and during at least part of the boost period.
Optionally, the method further comprises monitoring the power during the full load period, and starting the boost period in response to the monitored power falling below the rated power.
Optionally, the method further comprises monitoring a wind speed during the full load period, and starting the boost period in response to the monitored wind speed falling below a wind speed threshold. The wind speed threshold may be set on the basis of an air density.
Optionally, the method further comprises monitoring the power during the boost period, and reducing the generator speed during the boost period in response to the monitored power rising above a threshold.
Optionally, the method further comprises monitoring a wind speed during the boost period, and reducing the generator speed during the boost period in response to the monitored wind speed rising above a wind speed threshold. The wind speed threshold may be set on the basis of an air density.
Optionally, the method further comprises controlling the wind turbine during a first part of the boost period in accordance with the boost region of the partial load speed curve so that the power is below the rated power and the generator speed is above the rated speed; and controlling the wind turbine during a second part of the boost period to reduce the generator speed back to the rated speed.
Optionally, the power is greater during the full load period than during the boost period, and greater during the boost period than during the variable speed period.
Optionally, the generator speed is controlled during the boost period on the basis of a power input. Optionally, the generator speed is controlled during the boost period on the basis of a load input.
Optionally, the generator speed is controlled during the boost period on the basis of a torque input.
Optionally, the generator speed is controlled during the boost period on the basis of a wind speed input.
Optionally, the wind turbine is controlled during the boost period and/or during the full load period by changing a blade pitch angle of the wind turbine.
Optionally, the generator speed changes during the variable speed period and/or during the boost period.
Optionally, the method further comprises controlling the wind turbine during the boost period to reduce the generator speed and stop the boost period.
Optionally, the method further comprises controlling the wind turbine during the boost period to reduce the generator speed and transition from the boost period into the full load period or into the variable speed period.
Optionally, the method further comprises controlling the wind turbine during the boost period so that a tower oscillation of the turbine does not exceed a predetermined threshold.
Optionally, during the boost period the generator speed is restricted to a maximal generator speed.
Optionally, during the boost period the generator speed is more than 1% greater than the rated speed.
Optionally, the method further comprises performing a fatigue or load evaluation and enabling the boost period dependent on the result of the evaluation. Optionally, a wind speed incident on the wind turbine varies during the variable speed period, and/or during the boost period, and/or during the full load period.
Optionally, the partial load speed curve relates the generator speed to the power.
Optionally, the partial load speed curve relates the generator speed to wind speed.
A further aspect of the invention provides a wind turbine control system, wherein the control system has a variable speed setting which is configured to control a wind turbine in accordance with a variable speed region of a partial load speed curve so that a power of the wind turbine is below a rated power and a generator speed of the wind turbine is below a rated generator speed; the control system has a boost setting which is configured to control the wind turbine in accordance with a boost region of the partial load speed curve so that the power is below the rated power and the generator speed is above the rated speed; and the control system has a full load setting which is configured to control the wind turbine so that the power is at the rated power and the generator speed is at the rated speed.
A further aspect of the invention provides a computer program product comprising software code adapted to control a wind turbine when executed on a data processing system, the computer program product being adapted to perform the method of the first aspect of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described with reference to the accompanying drawings, in which:
Figure 1 schematically illustrates a wind turbine;
Figure 2 schematically illustrates a control system for controlling the wind turbine;
Figure 3 is a graph showing a baseline operation mode;
Figure 4 is a graph showing a boost operation mode;
Figure 5 is a graph showing the performance of the wind turbine during an up-transition in the wind boost operation mode;
Figure 6 is a graph showing the performance of the wind turbine during a downtransition in the wind boost operation mode; Figure 7 is a graph showing the performance of the wind turbine during an up-transition into an indefinite boost period;
Figure 8 is a graph showing the performance of the wind turbine during a downtransition into an indefinite boost period;
Figure 9 shows speed curves associated with baseline and boost settings, and low air density;
Figure 10 shows power curves associated with baseline and boost settings, and low air density;
Figure 11 shows speed curves associated with baseline and boost settings, and low air density;
Figure 12 shows speed curves associated with baseline and boost settings, and normal air density;
Figure 13 shows power curves associated with baseline and boost settings, and normal low air density;
Figure 14 shows speed curves associated with baseline and boost settings, and normal air density;
Figure 15 shows an example of control logic of the control system when it is in its boost operation mode; and
Figure 16 shows an example of a look-up table used in the control logic of Figure 15.
DETAILED DESCRIPTION OF EMBODIMENT(S)
Figure 1 illustrates, in a schematic perspective view, a wind turbine 10. The wind turbine 10 includes a tower 12, a nacelle 13 at the top of the tower, and a rotor 14 operatively coupled to a generator housed inside the nacelle 13. In addition to the generator, the nacelle houses miscellaneous components required for converting wind energy into electrical energy and various components needed to operate, control, and optimize the performance of the wind turbine 10. The rotor 14 of the wind turbine includes a central hub 15 and a plurality of blades 16 that project outwardly from the central hub 15. In the illustrated embodiment, the rotor 14 includes three blades 16, but the number may vary.
The wind turbine 10 may be included among a collection of other wind turbines belonging to a wind power plant, also referred to as a wind farm or wind park, that serve as a power generating plant connected by transmission lines with a power grid. The power grid generally consists of a network of power stations, transmission circuits, and substations coupled by a network of transmission lines that transmit the power to loads in the form of end users and other customers of electrical utilities.
Figure 2 schematically illustrates an embodiment of a wind turbine control system 20 configured to control the wind turbine 10. The control system 20 may be placed inside the nacelle 13 and/or distributed at a number of locations inside the turbine. Optionally some, or all, elements of the control system 20 may be placed in a remote power plant controller (not shown).
The blades 16 are mechanically connected to an electrical generator 22 via a gearbox 23. In direct drive systems, and other systems, the gearbox 23 may not be present. The electrical power generated by the generator 22 is injected into a power grid 24 via an electrical converter 25. The electrical generator 22 and the converter 25 may be based on a full scale converter (FSC) architecture or a doubly fed induction generator (DFIG) architecture, but other types may be used.
The control system 20 comprises a number of elements, including at least one main controller 21. In general, the control system 20 ensures that in operation the wind turbine generates a requested power output level. This is obtained by adjusting the pitch angle of the blades 16 and/or the power extraction of the converter 25. To this end, the control system comprises a pitch system including a pitch controller 27 using a pitch reference 28, and a power system including a power controller 29 using a power reference 26. The rotor blades 16 can be pitched by a pitch mechanism. The rotor comprises an individual pitch system which is capable of individual pitching of the rotor blades, and may comprise a common pitch system which adjusts all pitch angles on all rotor blades at the same time. The control system 20 further comprises a wind load block 210, configured to determine a direction (and optionally magnitude) of a wind load acting on the wind turbine.
The main controller 21 comprises a data processing system, and a computer program product comprising software code adapted to control the wind turbine 10 when executed on the data processing system, the computer program product being adapted to control the wind turbine as described below.
The control system 20 has a baseline operation mode, and a boost operation mode. Figure 3 is a graph showing how the control system 10 controls the power injected into the grid 24, the speed of the generator 22, and the pitch of the blades 16, when operating in its baseline operation mode. The baseline operation mode has a partial load region between 3 and 13 m/s; and a full load region above 13 m/s. The partial load region has three regions (labelled I, II and II) and the partial load region is labelled as region IV.
The graph of Figure 3 shows a speed curve 30; a power curve 32; and a pitch curve 35.
Region II is a variable speed region in which the turbine is controlled in accordance with a linear portion of the speed curve 30 so that the power coefficient Cp is set to a maximum value Cp*. The power is below a rated power and the generator speed is below a rated generator speed.
Region III is a fixed-speed region in which the generator speed is fixed. The power coefficient Cp drops below the maximum value Cp*. In region III, the generator speed is set to the rated speed (for example 1680 rpm) and the power is below the rated power.
Region IV is a full load region in which the turbine is controlled so that the power is fixed at the rated power (for example 300 kW) and the generator speed is fixed at the rated speed.
Figure 4 is a graph showing how the control system 10 controls power, generator speed and blade pitch when operating in its boost operation mode.
When it is operating in the boost operation mode, the control system has three settings in which the wind turbine performs as shown in Figure 4.
When the control system 10 is in its variable speed setting, it is configured to control the wind turbine in accordance with a first region 42a of a partial load power curve 42 so that the power is below a rated power; and in accordance with a variable speed region 40a of a partial load speed curve 40 so the generator speed is below a rated generator speed. This variable speed setting corresponds with Region II in the baseline operation mode of Figure 3. The pitch does not change when the control system 10 is in its variable speed setting, as indicated at 44a.
When the control system 10 is in its full load setting, it is configured to control the wind turbine so that the power is at the rated power and the generator speed is at the rated speed. This full load setting corresponds with Region IV in the baseline operation mode of Figure 3.
In its full load setting the control system 10 sets constant power and speed reference (rated power and rated speed values) and keeps to those by changing the pitch. In this case the pitch increases with wind speed as indicated by pitch curve 45.
When the control system 10 is in its boost setting, it is configured to control the wind turbine in accordance with a second region 42b of the power curve 42 so that the power is below the rated power; and in accordance with a boost region 40b, 40c of the partial load speed curve 40 so the generator speed is above the rated speed. The pitch does not change initially (as indicated at 44b), to remain at optimum power coefficient (Cp*) then increases slightly as indicated at 44c. The increase of pitch at 44c is more an aerodynamic aspect than a control aspect.
Figure 5 shows how the control system operates the wind turbine during an up- transition of the wind, when the wind speed 50 is increasing and the control system is in boost operation mode.
During a variable speed time period (t1 to t2) the wind speed increases from v1 to v2. The control system is in its variable speed setting so the wind turbine is controlled in accordance with the variable speed region 40a of the partial load speed curve so that the power is below the rated power and the generator speed is below the rated generator speed.
During the variable speed time period (t1 to t2) the turbine is controlled so that the power coefficient Cp is set to a maximum value Cp*. This optimal power coefficient is achieved by setting the blade pitch so that a tip speed ratio A of the wind turbine is set to an optimal value A* and thus achieve the maximum power coefficient Cp*. For example the wind speed v may be measured, and the power P may be set to be proportional to v3 (where v is the wind speed). During the variable speed time period (t1 to t2) the turbine may be controlled on the basis of an optimum speed set point shown in Eq. 1 :
Figure imgf000011_0001
where wopt is the optimum speed set point; GearRatio is the gear ratio of the gearbox 23, PartLoadLambdaOpt is the optimal value (A*) of the tip speed ratio (the ratio between the tangential speed of the tip of a blade and the speed of the wind); RotorRadius is the radius of the rotor 14, and windspeed is the speed of the wind.
During a boost time period (t2 to t4) the wind speed increases from v2 to v4. At time t2 the generator speed reaches the rated speed, and this triggers the control system 20 to switch to its boost setting so the wind turbine is controlled in accordance with the boost region 40b, 40c of the partial load speed curve so that the power is below the rated power and the generator speed is above the rated speed. In this example, reaching the rated speed triggers the control system to switch to its boost setting. In other examples, other triggers may be used, such as the power reaching a threshold or a wind speed (measured by a wind speed sensor) reaching or rising above a wind speed threshold v2. Optionally the wind speed threshold v2 may be set on the basis of an air density. The air density may be measured, or estimated for example based on the altitude of the wind turbine.
In a first (low power) part (t2 to t3) of the boost period, the turbine continues to be controlled on the basis of the optimum speed set point shown in Eq. 1. The pitch remains constant so that the tip speed ratio value of the wind turbine is set to the same value A* as during the variable speed period. Thus the tip speed ratio is set to achieve maximum power coefficient Cp* during both the variable speed period (t1 to t2) and the first part (t2 to t3) of the boost period. The generator speed increases from t2 to t3 in accordance with the first part 40b of the boost region of the partial load speed curve.
In EP 2826992A1 , the increased rotational speed decreases the efficiency (Cp) of the transfer of energy from the wind to the rotor. In contrast, during the first (low power) part (t2 to t3) of the boost period the efficiency (Cp) of the transfer of energy from the wind to the rotor remains substantially unchanged. The power is monitored during the boost period, and the control system reduces the generator speed during a second (high power) part (t3 to t4) of the boost period in response to the monitored power rising above a power threshold at time t3 - for instance a set percentage of the rated power.
In the second (high power) part (t3 to t4) of the boost period the pitch increases (in accordance with the partial load pitch curve 44c) and the tip speed ratio changes. The generator speed decreases from t3 to t4 in accordance with the second part 40c of the boost region of the partial load speed curve. The power coefficient Cp drops below the maximum value Cp* and the tip speed ratio A is no longer optimal. The generator speed remains above the rated speed and the power remains below the rated power. The wind turbine is controlled during the second part (t3 to t4) of the boost period to reduce the generator speed and transition from the boost period into a full load period.
The generator speed may rise to a maximum at time t3 which is, for example, in a range of 1-10% greater than the rated speed.
At time t4 the wind speed has reached v4, the power has reached rated power, and the generator speed has dropped to the rated speed. This triggers the control system 20 to switch to its full load setting, so the power is kept at the rated power and the generator speed is kept at the rated speed. The wind turbine is controlled during the full load period by changing the blade pitch angle of the wind turbine in accordance with the full load pitch curve 45, so that the power remains at the rated power and the generator speed remains at the rated speed despite the changes in wind speed.
Figure 5 shows how the control system operates the wind turbine during an up- transition of the wind, when the wind is increasing. Thus the periods follow the time order: variable speed period, boost period, full load period.
Figure 6 shows how the control system operates the wind turbine during a downtransition of the wind, when the wind 60 is decreasing. Thus the periods follow the time order: full load period, boost period, variable speed period. The control of the wind turbine in the various periods shown in Figure 6 is identical to the equivalent periods in Figure 5, but reversed in time. The power is monitored during the full load period (before time t5), and the control system increases the generator speed during a first (high power) part of the boost period (t5 to t6). The boost period is triggered in response to the monitored power falling below the rated power at time t5. In other examples, other triggers may be used to trigger the boost period, such as a wind speed (measured by a wind speed sensor) falling below a wind speed threshold v4. Optionally the wind speed threshold v4 may be set on the basis of an air density. The air density may be measured, or estimated for example based on the altitude of the wind turbine.
The power is also monitored during the boost period, and the control system reduces the generator speed during a second (low power) part of the boost period (t5 to t6) in response to the monitored power falling below the power threshold at time t6, or the wind speed falling below v3. Optionally the wind speed threshold v3 may be set on the basis of an air density. The air density may be measured, or estimated for example based on the altitude of the wind turbine.
In the examples above, the pitch control changes in response to the monitored power crossing a power threshold at either time t3 or time t6. This ensures that the generator speed does not go too high above the rated speed when the control system is in its boost setting. In an alternative example, a maximal generator speed may be set, so that the generator speed during the boost period is restricted to a maximal generator speed. In this case, the pitch control may change in response to the generator speed reaching the maximal generator speed, the change of pitch control keeping the generator speed below the maximal generator speed.
Note that the power is greater during the full load period than during the boost period, and greater during the boost period than during the variable speed period. On the other hand, the generator speed is greater during the boost period than during the full load period, and greater during the full load period than during the variable speed period.
The generator speed changes during the variable speed period and during the boost period, but does not change during the full load period (despite the change in the wind speed during the full load period).
In the two schematic examples given above, the wind speed increases or decreases continuously. In the example of Figure 7, the wind speed 70 increases to v3 but does not reach v4; and in the example of Figure 8 the wind speed 80 decreases to v3 but does not drop further to v2. In both examples, the wind turbine remains in a boost setting for an indefinite period of time. So in the example of Figure 7 the control system 10 switches from its variable speed setting into its boost setting at time t10 without later switching into its full load setting; and in the example of Figure 8 the control system 10 switches from its full load setting into its boost setting at time t12 without later switching into its variable speed setting.
In WO 2014/053136 a boost action is only performed for a limited time. As illustrated by Figures 7 and 8, the present invention may enable a boost action to be performed for a long or indefinite length of time.
Figure 9 shows speed curves which relate the generator speed to the wind speed: a baseline speed curve 90 associated with a baseline setting of the control system, a speed curve 91 associated with a 5% boost setting of the control system; and a speed curve 92 associated with a 10% boost setting of the control system. The speed curve 91 associated with a 5% boost setting has a boost region in which the generator speed increases to 5% above the rated speed; and the speed curve 92 associated with a 10% boost setting has a boost region in which the generator speed increases to 10% above the rated speed.
Figure 10 shows power curves which relate the power to the wind speed: a baseline power curve 100 associated with the baseline setting of the control system, a power curve 101 associated with a 5% boost setting of the control system; and a power curve 102 associated with a 10% boost setting of the control system. The power curve 101 associated with a 5% boost setting has a boost region in which the power is higher than the baseline speed curve 100; and the power curve 101 associated with a 10% boost setting has a boost region in which the power is higher than both the baseline speed curve 100 and the power curve 101.
Figure 11 shows speed curves which relate the generator speed to the power: a baseline speed curve 110 associated with the baseline setting of the control system, a speed curve 111 associated with the 5% boost setting of the control system; and a speed curve 112 associated with the 10% boost setting of the control system. The speed curve 111 associated with a 5% boost setting has a boost region in which the generator speed increases to 5% above the rated speed; and the speed curve 112 associated with a 10% boost setting has a boost region in which the generator speed increases to 10% above the rated speed.
Figures 9-11 show the power and speed performance of the wind turbine where the air density is relatively low (air density 0.95 kg/m3). At this low air density the Annual Energy Production (AEP) benefits from the boost operation mode are 2.95% and 4.05% for a 5% and 10% allowed increase of the generator speed, respectively.
Figures 12-14 show equivalent curves associated with a more normal air density (1.225 kg/m3). At this normal air density, the AEP benefits from the boost operation mode are lower: 0.76% and 1.48% for a 5% and 10% allowed increase of the generator speed, respectively.
Figure 12 shows a baseline speed curve 120, a speed curve 121 associated with a 5% boost setting, and a speed curve 122 associated with a 10% boost setting. Note that the boost regions of the speed curves 121 , 122 occupy a more narrow range of wind speeds in Figure 12 than in Figure 9.
Figure 13 shows a baseline power curve 130, a power curve 131 associated with a 5% boost setting, and a power curve 132 associated with a 10% boost setting. Note that the boost regions of the power curves 131 , 132 are not much different to the baseline curve 130.
Figure 14 shows a baseline speed curve 140, a speed curve 141 associated with a 5% boost setting, and a speed curve 142 associated with a 10% boost setting. Note that the boost regions of the speed curves 141 , 142 occupy a more narrow range of wind speeds in Figure 14 than in Figure 11.
Figure 15 show an example of how the control system 20 may be configured to control the wind turbine in accordance with the boost region 40b, 40c of the partial load speed curve. In this example, the control system 20 controls the generator speed on the basis of a power input.
A low pass filter 150 receives the power input, and outputs a filtered power signal. This is input into a look-up table 151 which outputs a gain value. The gain value is applied to a speed ref input, to generate a boost speed signal which is input to a switch 152. The speed ref input determines the rated speed, and the gain value determines how high the generator speed can increase during the boost period, relative to the rated speed.
Figure 16 shows an example of the look-up table for a 5% boost setting of the control system. The horizontal axis in Figure 16 shows relative power, i.e. the proportion of rated power. When the power is between 65% and 95% of the rated power, then the gain value is set to 1.05 so the generator speed is allowed to increase to a maximal generator speed 5% above the rated generator speed. When the power is between 95% and 100% of the rated power, the gain value decreases linearly with power. When the power reaches 100% of the rated power, the gain value has reduced to 1 .00. Thus the maximum allowed speed is decreased as the power approaches rated power.
Activation logic 153 operates the switch 152, which can switch between the boost speed signal and the speed ref input.
The output of the switch 152 is input to a dynamic rate limiter 154, which generates a speed output. The control system 20 than controls the wind turbine so that the generator speed is set by the speed output.
In the example of Figures 15 and 16, the control system 20 controls the generator speed on the basis of a power input, wherein the power input is indicative of a power being generated by the wind turbine. In an alternative embodiment, the control system 20 may control the generator speed on the basis of a load input. In this case, a lookup table like Figure 16 may be used, but with load on the X-axis. The load input may be indicative of a load on a blade, or a load on the tower for example. In a further alternative embodiment, the control system 20 may control the generator speed on the basis of a torque input, for instance indicative of a torque on the gearbox. In this case, a look-up table like Figure 16 may be used, but with torque on the X-axis. In another alternative embodiment, the control system 20 may control the generator speed on the basis of a wind speed input, for instance indicative of a speed of the wind incident on the wind turbine as measured by a wind speed sensor. In this case, a look-up table like Figure 16 may be used, but with wind speed on the X-axis.
In order to protect the structural integrity of the wind turbine, a requirement may be set to limit the oscillation of the tower. For instance a tower acceleration x-direction RMS signal may be calculated, and used to limit the boosting, or switch to the baseline operation mode, if its value is too high.
In order to eliminate unwanted behaviour, e.g. at high wind, a pitch angle requirement may also be used, to limit or prevent boosting if the pitch angle is too high. This pitch angle requirement may operate as follows: during full load operation, high wind fluctuations may cause the control system 20 to quickly de-rate both power and generator speed, with the pitch remaining high (as indicated by full load pitch curve 45). In this situation, the control system will not switch into its boost operation mode because the pitch is too high. This prevents the boost operation mode being used at high wind speeds.
The boost operation mode may be operated during the full lifetime of the wind turbine, or it may only be introduced during a later part of the life of the wind turbine (for instance the last 5 or 8 years) when there is less risk from fatigue.
Optionally a fatigue evaluation may be performed, and the boost period is enabled dependent on the result of the fatigue evaluation. The fatigue evaluation may be a fatigue valuation of the wind turbine, or a fatigue evaluation of other similar turbines.
Optionally a load evaluation may be performed, and the boost period enabled dependent on the result of the load evaluation. The load evaluation may evaluate load data from blade load sensors, tower load sensors or other load sensors; and the load data may be evaluated to assess whether it is safe to initiate a boost period, or continue a boost period.
In summary, the embodiments of the invention provide various methods of controlling a wind turbine.
The wind turbine is controlled during a variable speed period in accordance with a variable speed region of a partial load speed curve so that a power of the wind turbine is below a rated power and a generator speed of the wind turbine is below a rated generator speed. In other words, the performance of the wind turbine follows the variable speed region of the partial load speed curve. The variable speed region of the partial load speed curve may relate generator speed to wind speed, or it may relate generator speed to an operating parameter of the wind turbine, such as the power. The wind turbine is also controlled during a boost period in accordance with a boost region of the partial load speed curve so that the power is below the rated power and the generator speed is above the rated speed. In other words, the performance of the wind turbine follows the boost region of the partial load speed curve. The boost region of the partial load speed curve may relate generator speed to wind speed, or it may relate generator speed to an operating parameter of the wind turbine, such as the power. Controlling the wind turbine in accordance with the boost region of the partial load speed curve enables the boost period to last for a long time (as long as the wind conditions remain the same) and enables the efficiency (Cp) of the transfer of energy from the wind to the rotor during the boost period to be kept relatively high.
Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

Claims

1. A method of controlling a wind turbine, the method comprising: controlling the wind turbine during a variable speed period in accordance with a variable speed region of a partial load speed curve so that a power of the wind turbine is below a rated power and a generator speed of the wind turbine is below a rated generator speed; controlling the wind turbine during a boost period in accordance with a boost region of the partial load speed curve so that the power is below the rated power and the generator speed is above the rated speed; and controlling the wind turbine during a full load period so that the power is at the rated power and the generator speed is at the rated speed.
2. The method of claim 1 , further comprising controlling the wind turbine so that a tip speed ratio of the wind turbine is set to the same value during both the variable speed period and at least part of the boost period.
3. The method of claim 1 or 2, further comprising controlling the wind turbine so that a tip speed ratio of the wind turbine is set to achieve maximum power coefficient during both the variable speed period and during at least part of the boost period.
4. The method of any preceding claim, further comprising monitoring the power during the full load period, and starting the boost period in response to the monitored power falling below the rated power; or monitoring a wind speed during the full load period, and starting the boost period in response to the monitored wind speed falling below a wind speed threshold.
5. The method of any preceding claim, further comprising monitoring the power during the boost period, and reducing the generator speed during the boost period in response to the monitored power rising above a threshold; or monitoring a wind speed during the boost period, and reducing the generator speed during the boost period in response to the monitored wind speed rising above a wind speed threshold.
6. The method of claim 4 or 5, further comprising setting the wind speed threshold on the basis of an air density.
7. The method of any preceding claim, comprising controlling the wind turbine during a first part of the boost period in accordance with the boost region of the partial load speed curve so that the power is below the rated power and the generator speed is above the rated speed; and controlling the wind turbine during a second part of the boost period to reduce the generator speed back to the rated speed.
8. The method of any preceding claim, wherein the power is greater during the full load period than during the boost period, and greater during the boost period than during the variable speed period.
9. The method of any preceding claim, wherein the generator speed is controlled during the boost period on the basis of a power input, a load input, a torque input or a wind speed input.
10. The method of any preceding claim, wherein the wind turbine is controlled during the boost period and/or during the full load period by changing a blade pitch angle of the wind turbine.
11. The method of any preceding claim, wherein the generator speed changes during the variable speed period and/or during the boost period.
12. The method of any preceding claim, further comprising controlling the wind turbine during the boost period to reduce the generator speed and stop the boost period.
13. The method of any preceding claim, further comprising controlling the wind turbine during the boost period to reduce the generator speed and transition from the boost period into the full load period or into the variable speed period.
14. The method of any preceding claim, further comprising controlling the wind turbine during the boost period so that a tower oscillation of the turbine does not exceed a predetermined threshold.
15. The method of any preceding claim, wherein during the boost period the generator speed is restricted to a maximal generator speed. 19
16. The method of any preceding claim, wherein during the boost period the generator speed is more than 1 % greater than the rated speed.
17. The method of any preceding claim, further comprising performing a fatigue or load evaluation and enabling the boost period dependent on the result of the evaluation.
18. The method of any preceding claim, wherein a wind speed incident on the wind turbine varies during the variable speed period, and/or during the boost period, and/or during the full load period.
19. The method of any preceding claim, wherein the partial load speed curve relates the generator speed to the power, or the partial load speed curve relates the generator speed to wind speed.
20. A wind turbine control system, wherein: the control system has a variable speed setting which is configured to control a wind turbine in accordance with a variable speed region of a partial load speed curve so that a power of the wind turbine is below a rated power and a generator speed of the wind turbine is below a rated generator speed; the control system has a boost setting which is configured to control the wind turbine in accordance with a boost region of the partial load speed curve so that the power is below the rated power and the generator speed is above the rated speed; and the control system has a full load setting which is configured to control the wind turbine so that the power is at the rated power and the generator speed is at the rated speed.
21. A computer program product comprising software code adapted to control a wind turbine when executed on a data processing system, the computer program product being adapted to perform the method of any of claims 1-19.
PCT/DK2021/050337 2020-11-17 2021-11-17 Wind turbine boost setting WO2022105975A1 (en)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20030185665A1 (en) * 2000-03-08 2003-10-02 Hansen Lars H. Method of operating a turbine
WO2014053136A1 (en) 2012-10-02 2014-04-10 Vestas Wind Systems A/S Wind turbine control
EP2826992A1 (en) 2013-07-16 2015-01-21 Siemens Aktiengesellschaft Method and arrangement for controlling a wind turbine
EP3032095A1 (en) * 2014-12-10 2016-06-15 ALSTOM Renewable Technologies Methods of operating a wind turbine and wind turbines
EP3351789A1 (en) * 2017-01-24 2018-07-25 Hitachi, Ltd. Wind power generation system or method of operating wind power generation system

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20030185665A1 (en) * 2000-03-08 2003-10-02 Hansen Lars H. Method of operating a turbine
WO2014053136A1 (en) 2012-10-02 2014-04-10 Vestas Wind Systems A/S Wind turbine control
EP2826992A1 (en) 2013-07-16 2015-01-21 Siemens Aktiengesellschaft Method and arrangement for controlling a wind turbine
EP3032095A1 (en) * 2014-12-10 2016-06-15 ALSTOM Renewable Technologies Methods of operating a wind turbine and wind turbines
EP3351789A1 (en) * 2017-01-24 2018-07-25 Hitachi, Ltd. Wind power generation system or method of operating wind power generation system

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