WO2020125879A1 - Levelling of fatigue levels of power generating units of a power plant comprising one or more wind turbine generators - Google Patents

Levelling of fatigue levels of power generating units of a power plant comprising one or more wind turbine generators Download PDF

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Publication number
WO2020125879A1
WO2020125879A1 PCT/DK2019/050368 DK2019050368W WO2020125879A1 WO 2020125879 A1 WO2020125879 A1 WO 2020125879A1 DK 2019050368 W DK2019050368 W DK 2019050368W WO 2020125879 A1 WO2020125879 A1 WO 2020125879A1
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WO
WIPO (PCT)
Prior art keywords
power
power generating
fatigue
generating units
generating unit
Prior art date
Application number
PCT/DK2019/050368
Other languages
French (fr)
Inventor
Mu WEI
Karthik KRISHNAN JAMUNA
Jacob Quan KIDMOSE
Søren Sønderbo ANDERSEN
Søren KAPPELGAARD
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Vestas Wind Systems A/S
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Application filed by Vestas Wind Systems A/S filed Critical Vestas Wind Systems A/S
Publication of WO2020125879A1 publication Critical patent/WO2020125879A1/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
    • F03D7/04—Automatic control; Regulation
    • F03D7/042—Automatic control; Regulation by means of an electrical or electronic controller
    • F03D7/048—Automatic control; Regulation by means of an electrical or electronic controller controlling wind farms
    • 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
    • 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
    • F05B2270/103—Purpose of the control system to affect the output of the engine
    • F05B2270/1033—Power (if explicitly mentioned)
    • 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
    • F05B2270/332—Maximum loads or fatigue criteria
    • 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 invention relates to control of power plants, particularly power plants which has one or more wind turbines and to determination and dispatching of power set points to the power generating units of the power plant.
  • a power plant comprising a plurality of power generating units may require repeated and unpredictable service operations which may not be acceptable in view of the maintenance costs of the power plant.
  • EP 2 896 102 B1 discloses a method for an intelligent dispatching of the power production to wind turbines and optional compensation equipment of a wind power plant, as the power producing units of a wind power plant.
  • the invention relates to a case where the requested produced power is less than the total capacity of the power plant, and the invention relates to utilizing this situation to dispatch set points to the wind turbines and the compensation equipment based on correction factors relating to the operating conditions of the wind park.
  • This method may increase the wind turbines' lifetime, help in scheduling maintenance and expand the electrical operating range of the wind power plant.
  • EP 2 896 102 B1 addresses operation of power plants and increase of the lifetime
  • the inventors of the present invention has appreciated that an improved solution is of benefit, and has in consequence devised the present invention.
  • a method for controlling power generation from a power plant which comprises a plurality of power generating units including at least one wind turbine generator is presented, where the power generation system is connected to an electrical power grid for supplying power from the power generating units to the electrical power grid, and where at the power generating units are controllable to produce power dependent on individual power set points, the method comprises:
  • the fatigue level is indicative of a combined accumulated loading of one or more mechanical components of the power generating unit
  • the fatigue level is an accumulated fatigue load, i.e. a fatigue load accumulated over time.
  • the accumulated fatigue loading of the one or more components is combined into the combined accumulated fatigue level.
  • the adjusting is carried out by adjusting power set points down for power generating units having fatigue levels above the threshold and adjusting power set points up for power generating units having fatigue levels below the threshold.
  • the determination of the adjustments of the power set points can be performed according to different methods.
  • the fatigue level threshold is determined as an average of the fatigue levels of the power generating units.
  • the adjustment of the power set points will result in a levelling of the fatigue levels towards the average fatigue level.
  • the fatigue level threshold is a user determined threshold.
  • the user is able to reduce or increase the mechanical loading of the power generating units.
  • the adjustment of the power set points is performed subject to a constraint of reducing differences between the fatigue levels and the fatigue level threshold.
  • Various mathematical optimization or adjustment algorithms can be defined to achieve adjustments of the power set points to achieve the desired levelling of the fatigue loads.
  • the adjustment of the power set point of each power generating unit is performed subject to a constraint of maintaining a power reference for a desired power production of the power plant. Since the power plant controller may be set to generate a desired power from the power plant, the adjustment of the power set points may be constrained in the sense that the power plant reference should be maintained. According to an embodiment, the adjustment of the power set point of each power generating unit is determined dependent on a difference between the fatigue level of the respective power generating unit and the fatigue level threshold. For example, the adjustment of the power set point may be performed as a linear function of the difference between the fatigue level of the respective power generating unit and the fatigue level threshold.
  • the adjustment of the power set point of each power generating unit may include
  • the available power is the maximum power that can be produced by one of the power generating units and the actual power production is the power supplied to the electrical power grid
  • each power generating unit is determined dependent on the available power level or actual power production of the respective power generating unit multiplied with a scaling factor which corresponds to the difference between the fatigue level of the respective power generating unit and the fatigue level threshold.
  • the adjustment of the power set point can be performed based on the available power level or the actual power production of a power generating unit for increases or decreases of the power reference, respectively.
  • the adjustment of the power set point of each power generating unit is determined as the available power level or the actual power production of the respective power generating unit multiplied with the scaling factor and divided by a total available power of the power plant or a total actual power production of the power plant.
  • the available power levels or actual power productions are available active power levels or actual active power productions and the power set points are active power set points.
  • the fatigue level for each of the power generating units is obtained based on measured data from sensors of each of the power generating units.
  • the fatigue level for each of the power generating units is obtained based on a weighted sum of component fatigue levels of one or more components of each power generating unit.
  • the fatigue level is determined as a fatigue margin based on differences between component fatigue levels of one or more
  • the fatigue level may be determined as a level which increases as the fatigue load accumulates, or the fatigue level may be determined as a level which decreases as the accumulated fatigue load approaches the design limit.
  • the fatigue level for each power generating unit turbine is weighted dependent on a rate of change of fatigue levels determined for one or more components.
  • the weighting of the fatigue level can be modified to allow a higher mechanical loading of that power generating unit, i.e. the fatigue level is increased or decreased dependent on whether the fatigue level is determined as a margin relative to a design limit or is determined as a level which increases with the accumulation of fatigue loading.
  • a second aspect of the invention relates to a central controller for controlling power production of a power plant which comprises a plurality of power generating units including at least one wind turbine generator, where the power plant is connected to an electrical power grid for supplying power from the power generating units to the electrical power grid, and where at the central controller is arranged to dispatch individual power set-points to the power generating units, and where the central controller is arranged to perform the method according to the first aspect.
  • a third aspect of the invention relates to a power plant which comprises a plurality of power generating units including at least one wind turbine generator and the central controller according to the second aspect.
  • a fourth aspect of the invention relates to a computer program product
  • Fig. 1 shows a power plant which comprises a plurality of power generating units such as wind turbines,
  • Fig. 2 shows a configuration of the power plant and dispatcher
  • Fig. 3 illustrates levelling of fatigue loads of the of power generating units
  • Fig. 4 illustrates an implementation of the control method for controlling power set points of the power generating units.
  • Fig. 1 shows a power plant 100 which comprises a plurality of power generating units 101 such as wind turbines.
  • the power plant 100 may be a renewable power plant comprising only renewable power generating units.
  • the power generating units 101 may consist of different types of power generating units, e.g. different types of renewable power generating units such as solar power units 103 (e.g. photovoltaic solar panels) and wind turbines.
  • the different types of power generating units 101 may also include fossil based power production units, e.g. diesel engines.
  • at least one of the power producing units 101 of the power plant 100 is a wind turbine.
  • the power plant 100 may comprise at least three power generating units 101 of the same or different types, i.e.
  • the power plant 100 may consist only of wind turbines 102 and in this case at least three wind turbines 102.
  • the power plant 100 comprises at least two wind turbines 102 and at least one or two other power generating units 101.
  • the power plant is connectable with an electrical power grid (not shown) for supplying power from the power generating units 101 to the electrical power grid.
  • the power plant 100 is controlled by a central controller 110.
  • the central controller 110 is arranged to control power generation from the power generating units 101 according to a power plant reference Pplant_ref which defines the desired power to be supplied to the grid from the power plant 100.
  • the central controller is arranged to dispatch power set-points Pset to the power generating units, i.e. individual power set-points to each power generating unit 101 which sets the desired power productions.
  • the power set-points Pset may be determined by the central controller 110 dependent on the power plant reference Pplant_ref so that the sum of power set-points Pset corresponds to the power plant reference Pplant_ref.
  • an objective of the central controller 110 or a dispatcher comprised by the central controller is to ensure that the demanded power (e.g. from the
  • TSO Transmission System Operator
  • the wind turbine 101 may comprise a tower and a rotor with at least one rotor blade, such as three blades.
  • the rotor is connected to a nacelle which is mounted on top of the tower and being adapted to drive a generator situated inside the nacelle.
  • the rotor is rotatable by action of the wind.
  • the wind induced rotational energy of the rotor blades is transferred via a shaft to the generator.
  • the wind turbine is capable of converting kinetic energy of the wind into mechanical energy by means of the rotor blades and, subsequently, into electric power by means of the generator.
  • the generator may include a power converter for converting the generator AC power into a DC power and a power inverter for converting the DC power into an AC power to be injected into the electrical power grid.
  • the generator of the wind turbine 102, or other power generating unit 101 is controllable to produce power corresponding to the power set-point Pset provided by the central controller 110.
  • the output power may be adjusted according to the power set-point by adjusting the pitch of the rotor blades or by controlling the power converter to adjust the power production. Similar adjustment possibilities exists for other power generating units 101.
  • any reference to power such as power plant reference Pplant_ref, power set points Pset, available power Pav and produced power Pprod can define active, reactive or apparent power levels.
  • the power levels such as Plant_ref, Pset, Pav, Pprod and other related power levels are active power levels.
  • Fig. 2 exemplifies the arrangement of the calculation modules inside a dispatcher.
  • the power generating units 101 are wind turbine generators 102, but the power generating units could also comprise a mix of wind turbine generators and other types of power generating units. Therefore, in order to keep the description general, reference is made to power generating units 101 unless the specific contest relates to a wind turbine example.
  • the dispatcher 201 is disclosed as being part of a central controller 110.
  • the dispatcher receives the power plant reference Pplant_ref and determines the power set points Pset, e.g. power set points Psetl, Pset2, Psetn for the respective wind turbine generators WTG1, WTG2, ...,WTGn, based on a plurality of status feedback signals.
  • the feedback signals comprise the available power of the individual power generating units Pavl...Pavn and the produced power of individual power generating units Pprodl...Prodn.
  • Pavl is the power available from a wind turbine 102 at the given time, calculated based on the current wind speed and other parameters limiting the power production.
  • the available power of the power system is therefore the aggregation of the individual available powers.
  • Pprod l is the power produced by a specific wind turbine 102 at the given time.
  • the determination of the individual power set points Pset is determined based on available power of the individual power generating units Pavl...Pavn. In case the power plant reference Pplant_ref is decreased, the determination of the individual power set Pset is determined based on and the produced power of individual power generating units Pprodl... Prod n.
  • the actual power production Pprodl..Prodn of the power generating units 101 is fed to a feeder line, which is connected to a Point of common coupling (PCC) via a transformer.
  • PCC Point of common coupling
  • the aggregated power production is measured by means of a power meter.
  • the measured power (P measurement) is communicated to the PPC.
  • the mechanical and electrical components of the power generating units e.g. wind turbine generators, are exposed to fatigue loading which require repairing and replacement of the components.
  • a control mechanism is not present between a monitoring system for monitoring the fatigue loading and the dispatcher of the power plant controller, it is not possible to adapt the determination of the power set points Pset dependent on the fatigue loading or the monitoring of the fatigue loading.
  • Examples of the mechanical components of the wind turbines generators which may be exposed to fatigue loading comprise the gearbox, the generator, the rotor, the yaw system, blades and other components.
  • Fig. 3 illustrates a method according to an embodiment for controlling power generation from the power plant 100 by determining power set points for at least some of the power generating units based on a comparison of fatigue levels Flev of the power generating units with a fatigue level threshold, Fthreshold.
  • the power plant 110 comprises a plurality of power generating units 101.
  • the method may involve determination of power set points for all units 101 in the power plant 110 or for a fraction of the units 101 based on power and fatigue data from the same units.
  • the method is based on fatigue levels Flev which have been obtained for each of the power generating units 101, i.e. at least for a fraction of the power generating units of the power plant 100.
  • the fatigue level for a given power generating unit 101 can be a fatigue level for one or more individual components of the power generating unit or for the entire power generating unit 101, or other fatigue level associated with the power generating unit 101.
  • the fatigue level may be determined as a combined accumulated fatigue level of one or more mechanical components of the power generating unit.
  • the fatigue level for one component e.g. the gearbox
  • the combined accumulated fatigue level Flev may be determined as the fatigue level accumulated over any period of time, such as minutes, hours, days, years or or the entire period of operation of the power generating unit.
  • the combined accumulated fatigue level Flev is compared with a fatigue level threshold Fthreshold.
  • the fatigue level threshold can be determined as an average of the fatigue levels of the power generating units.
  • the average of the fatigue levels can be determined as the sum of the fatigue levels of the plurality of power generating unit 101 divided by the number of the power generating units.
  • the fatigue level threshold can be determined as an accumulated averaging over a pre-defined time window, e.g. over a period such as as minutes, hours, days, years or the entire period of operation of the power generating units.
  • the fatigue level threshold can be determined as an instantaneous level.
  • the fatigue level threshold can also be determined as a time average based on a probability distribution function. To facilitate comparison between the combined accumulated fatigue level Flev, in short fatigue level Flev, and the fatigue level threshold Fthreshold, Flev and Fthreshold may determined for the same averaging period of time.
  • the fatigue level threshold Fthreshold may be determined as a user determined threshold.
  • the owner of the power plant may set a low Fthreshold to reduce fatigue loading, or opposite set a high Fthreshold to enable a a maximum utilization of the power production capabilities.
  • Fig. 3 shows the fatigue levels Flev obtained for power generating units Unitl- Unitn.
  • Fig. 3 shows an example of the fatigue level threshold Fthreshold_av where it is determined as an average of the individual fatigue levels and an example of the fatigue level threshold Fthreshold_user where it is determined as a user defined threshold.
  • Power generating units Unitl, Unit3, Unit4, Unit 6 and Unitn have fatigue levels Flev which are higher than the average fatigue level threshold Fthreshold_av, while the units Unit2 and Unit5 have fatigue levels Flev below the average fatigue level threshold Fthreshold_av. Examples of the percentage differences between the fatigue levels Flev and the fatigue level threshold are given in Fig. 3 for each power generating unit.
  • the dispatcher 201 determines adjustments of the power set points Pset for each power generating unit dependent on the fatigue levels and the fatigue level threshold. This implies that the power set points for power generating units 101 with power levels Flev above the fatigue level threshold Fthreshold are reduced compared to their respective present set points, and the power levels Flev below the fatige level threshold Fthreshold are increased compared to their respective power set points.
  • the differences AF should be understood generally as a quantification of the variance of the fatigue levels or other quantification of the variation of the fatigue levels.
  • the adjustments of the power set-points may be performed subject to a
  • a function which quantifies the differences e.g. a sum of absolute values of the individual differences abs(Fthreshold-FlevJ) over the power generating units UnitJ or a sum of scaled differences abs(Fthreshold-Flev)xA, where A may be a monotonically increasing function of the difference, i.e.
  • A(Fthreshold-Flev) can be used as an optimization function which could be used the determine the individual adjustments of the power set points Pset, e.g. by determining adjustments which minimizes the optimization function.
  • the adjustment of the power set points of the generating units are performed subject to a constraint of maintaining the power plant reference
  • Pplant_ref for the desired power production of the power plant. Accordingly, a mathematical function may be set up which determines the power set points subject to maintaining a constant or substantially constant power reference Pplant_ref.
  • the adjustment of the power set point of each power generating unit is determined dependent on a difference between the fatigue level Flev of the respective power generating unit and the fatigue level threshold Fthreshold.
  • the adjustment may be determined dependent on a scaling factor, Si, which corresponds to the difference between the fatigue level of the respective power generating unit and the fatigue level threshold Fthreshold.
  • the scaling factor Si may be determined dependent on the difference Flev - Fthreshold, e.g. as (Flev - Fthresholdj/Fthreshold.
  • the scaling factor Si may be equal to the percentages of the over and under fatigue levels in Fig. 3.
  • the available power level Pav and/or the actual power level Pprod may be determined for the plurality power generating units of the power plant 110, or at least a fraction thereof. It may not be necessary to obtain both the available power level Pav and the actual power level Pprod since the available power level Pav may only be required in case of an increase in the power plant reference Plant_ref and since the actual power level Pprod may only be required in case of a decrease in the power plant reference Plant_ref. Thus, in general at least one power level, Pav and/or Pprod, may be obtained for each of the power generating units.
  • the available power level Pav and the actual power level Pprod are both referred to as the power level Plev of a power generating unit 101.
  • the adjustment of the power set-point Pset of each power generating unit is determined dependent on the available power level Pav or the actual power production Pprod of the respective power generating unit multiplied with a scaling factor Si which corresponds to the difference between the fatigue level Flev of the respective power generating unit and the fatigue level threshold Fthreshold.
  • the scaling factor Si may be equal to the percentages shown in Fig. 3.
  • Si*Pprodl/Pprodtot for Unitl where APset is the adjustment of the present Power set point Pset.
  • the total available power Pavtot is the total available power for the power plant 100 and the total actual power production Pprodtot is the total power production of the power plant 100.
  • the power set points Pset for at least a fraction of the power generating units 101 is adjusted or checked based on the comparison of the fatigue levels Flev with the fatigue level threshold, Fthreshold. For example, the adjustment may be performed
  • the above examples and embodiments applies in the same way in case the user defined fatigue level threshold Fthreshold_user is used in stead of the average fatigue level threshold Fthreshold_av.
  • the adjustments of the power set point Pset are adjusted dependent on the differences between the individual fatigue levels Flev of the power generating units 101 and the user defined fatigue level threshold Fthreshold_user.
  • all power generating units have fatigue levels Flev above the user defined fatigue level threshold.
  • the adjustment implies a decrease of all power set points, but with the largest percentage decrease for the power generating units with the largest fatigue levels Flev.
  • the fatigue level for each of the power generating units may be obtained based on measured data from sensors of each of the power generating units.
  • sensors include blade root torque sensors and tower acceleration sensors.
  • the blade root torques can be used to estimate hub moments based on co-ordinate transformations with respect to the pitch angle and hub radius. From the hub moments, the tilt & yaw moments on the main bearing can be estimated based on the azimuth position. From the power and generator speed signal, torque on the gearbox can be calculated, with estimate on the gear train and electrical efficiency.
  • the tower acceleration sensor can be used to find the acceleration levels at tower top, this multiplied with the tower top mass gives the tower top moments. From the tower top moments, the tower bottom moments can be calculated.
  • the entire wind turbine loads can be estimated, e.g. the loads of the blades, blade bearing, hub, pitch system, main bearing, gearbox, tower, foundation, etc.
  • the fatigue level Flev for an individual power generating unit can be determined from a combination of the accumulated fatigue levels of one or more of components.
  • the fatigue level for each of the power generating units may be obtained based on a weighted sum of component fatigue levels of one or more mechanical
  • each power generating unit For example, rotational parts in the blade bearing, gearbox, replaceable parts like bolts are required to be serviced or replaced during annual servicing. Accordingly, particularly up to a planned service, the fatigue level of such components may be weighted higher (unless the accumulated fatigue level is critical) in order to exploit the capacity of such components. For example, the weighting factor of the gearbox may be increased from a factor one up to a factor two since replacement of gearbox components is planed in near future.
  • the fatigue level may be determined as a fatigue margin based on differences between component fatigue levels of one or more components and predetermined design fatigue limits of the one or more components. Accordingly, the fatigue level may be in the form of a margin which indicates a distance between the actual fatigue level and a design limit of a given component.
  • the fatigue level Flev for a given power generating unit may be determined by weighting the accumulated fatigue level as a function of the rate-of-change of the fatigue level for that component. Accordingly, a trend of fatigue level
  • a rapid increase of the trend of fatigue level for specific component could cause the power generating unit 101 to have lower life time and, in this time, accumulated fatigue level could be given lower weightage such that the power plant controller 110 or dispatcher could react to ensure that such power generating unit 101 is given a low prioritization.
  • the power generating unit 101 could be given a higher priority.
  • Fig. 4 illustrates a possible implementation of the control method described in various embodiments.
  • the implementation may include a monitoring system 401 including sensors Sl-Sn such as torque and accelerations sensors.
  • the sensors provide load data to a fatigue level calculation module 402 which determines accumulated fatigue levels Flev for different components Cl-Cn based on different sensor input.
  • the module 402 may be comprised by individual power generating units 101, by the power plant controller 110 or may be implemented in other ways.
  • a module 402 may be provided for each power generating unit 101 to determine fatigue loads for that power generating unit 101, or the module 402 may be common for all power generating units and arranged to determine fatigue loads for all units 101 based on data from sensors Sl-Sn from all power
  • the accumulated fatigue levels are made available for the adjusting module 403 which determines the power set point adjustments.
  • the adjusting module 403 may be implemented in the central power plant controller 110.
  • the adjusted power set points are made available for the dispatcher 201 which is arranged to dispatch the power set points Psetl- Psetn to the power generating units 101.

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  • Sustainable Development (AREA)
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Abstract

The invention relates to controlling power generation from a power plant which includes power generating units including at least one wind turbine generator. Based on obtained fatigue levels of the power generating units and a comparison of the obtained fatigue levels of the power generating units with a fatigue level threshold the power set points of the power generating units are adjusted dependent on the fatigue levels and the fatigue level threshold to achieve a levelling of the individual fatigue levels of the power generating units.

Description

LEVELLING OF FATIGUE LEVELS OF POWER GENERATING UNITS OF A POWER PLANT COMPRISING ONE OR MORE WIND TURBINE GENERATORS
FIELD OF THE INVENTION
The invention relates to control of power plants, particularly power plants which has one or more wind turbines and to determination and dispatching of power set points to the power generating units of the power plant.
BACKGROUND OF THE INVENTION
Mechanical and electrical components of the power generating units such as wind turbine generators are exposed to fatigue loading. Fatigue loading may reduce lifetime, increase power production costs, increase the need for service operations for repairing and replacing components. The fatigue load of components of the power generating units may be monitored in order to be able to take actions such as unplanned service operations to avoid serious failures of the power generating unit. Thus, a power plant comprising a plurality of power generating units may require repeated and unpredictable service operations which may not be acceptable in view of the maintenance costs of the power plant.
In view of the present solutions which are available for operating a power plant with a plurality of power generating units, there is a need for solutions which improve operation of power plants to provide improved handling of fatigue loads, e.g. in order to reduce production costs, increase reliability, improve production stability and to increase length of service intervals and lifetime of the power generating units.
EP 2 896 102 B1 discloses a method for an intelligent dispatching of the power production to wind turbines and optional compensation equipment of a wind power plant, as the power producing units of a wind power plant. The invention relates to a case where the requested produced power is less than the total capacity of the power plant, and the invention relates to utilizing this situation to dispatch set points to the wind turbines and the compensation equipment based on correction factors relating to the operating conditions of the wind park. This method may increase the wind turbines' lifetime, help in scheduling maintenance and expand the electrical operating range of the wind power plant.
Whereas EP 2 896 102 B1 addresses operation of power plants and increase of the lifetime, the inventors of the present invention has appreciated that an improved solution is of benefit, and has in consequence devised the present invention.
SUMMARY OF THE INVENTION
It is an object of the invention to improve control of power plants to alleviate one or more of the above mentioned problems, and therefore to provide a method which provides an improved way of handling fatigue loads.
In a first aspect of the invention, a method for controlling power generation from a power plant which comprises a plurality of power generating units including at least one wind turbine generator is presented, where the power generation system is connected to an electrical power grid for supplying power from the power generating units to the electrical power grid, and where at the power generating units are controllable to produce power dependent on individual power set points, the method comprises:
- obtaining a fatigue level for each power generating unit, where the fatigue level is indicative of a combined accumulated loading of one or more mechanical components of the power generating unit,
- comparing the obtained fatigue levels of the power generating units with a fatigue level threshold,
- based on the comparison, adjust the power set point for each power generating unit dependent on the fatigue levels and the fatigue level threshold so as to reduce differences between fatigue levels of the power generating units during future operation.
The fatigue level is an accumulated fatigue load, i.e. a fatigue load accumulated over time. The accumulated fatigue loading of the one or more components is combined into the combined accumulated fatigue level.
In general, the adjusting is carried out by adjusting power set points down for power generating units having fatigue levels above the threshold and adjusting power set points up for power generating units having fatigue levels below the threshold. The determination of the adjustments of the power set points can be performed according to different methods.
Advantageously, by performing the adjustment of power set points in this way, differences between fatigue levels of the power generating units are levelled implying that service requirements of power generating units may become more predictable, e.g. so that instead of performing service of a specific component of only one power generating unit, the same service can be planned for a higher number of power generating units. Furthermore, frequent failures of highly loaded units can be reduced due to the levelling of the fatigue loads.
According to an embodiment, the fatigue level threshold is determined as an average of the fatigue levels of the power generating units. Advantageously, by determining the threshold as an average of the fatigue levels, the adjustment of the power set points will result in a levelling of the fatigue levels towards the average fatigue level.
According to an embodiment, the fatigue level threshold is a user determined threshold. Advantageously, by setting a user defined threshold, the user is able to reduce or increase the mechanical loading of the power generating units.
According to an embodiment, the adjustment of the power set points is performed subject to a constraint of reducing differences between the fatigue levels and the fatigue level threshold. Various mathematical optimization or adjustment algorithms can be defined to achieve adjustments of the power set points to achieve the desired levelling of the fatigue loads.
According to an embodiment, the adjustment of the power set point of each power generating unit is performed subject to a constraint of maintaining a power reference for a desired power production of the power plant. Since the power plant controller may be set to generate a desired power from the power plant, the adjustment of the power set points may be constrained in the sense that the power plant reference should be maintained. According to an embodiment, the adjustment of the power set point of each power generating unit is determined dependent on a difference between the fatigue level of the respective power generating unit and the fatigue level threshold. For example, the adjustment of the power set point may be performed as a linear function of the difference between the fatigue level of the respective power generating unit and the fatigue level threshold.
For example, the adjustment of the power set point of each power generating unit may include
- obtaining an available power level or an actual power production for each of the power generating units, where the available power is the maximum power that can be produced by one of the power generating units and the actual power production is the power supplied to the electrical power grid, and
- wherein the adjustment of the power set-point of each power generating unit is determined dependent on the available power level or actual power production of the respective power generating unit multiplied with a scaling factor which corresponds to the difference between the fatigue level of the respective power generating unit and the fatigue level threshold.
Advantageously, when the adjustment is performed in response to an increase or decrease of the power plant reference, the adjustment of the power set point can be performed based on the available power level or the actual power production of a power generating unit for increases or decreases of the power reference, respectively.
According to an embodiment, the adjustment of the power set point of each power generating unit is determined as the available power level or the actual power production of the respective power generating unit multiplied with the scaling factor and divided by a total available power of the power plant or a total actual power production of the power plant.
According to an embodiment, the available power levels or actual power productions are available active power levels or actual active power productions and the power set points are active power set points. According to an embodiment, the fatigue level for each of the power generating units is obtained based on measured data from sensors of each of the power generating units.
According to an embodiment, the fatigue level for each of the power generating units is obtained based on a weighted sum of component fatigue levels of one or more components of each power generating unit.
Advantageously, using differentiated weighting of the fatigue level, it is possible to accelerate further fatigue loading of a particular component, e.g. by setting a low weighting factor. This could be relevant if a replacement is planned in near future. Further accumulated fatigue loading of a component could be slowed, e.g. by setting a high weighting factor. This could be relevant if the fatigue level of a component is becoming critical, e.g. to avoid critical faults.
According to an embodiment, the fatigue level is determined as a fatigue margin based on differences between component fatigue levels of one or more
components and predetermined design fatigue limits of the one or more
components. Thus, the fatigue level may be determined as a level which increases as the fatigue load accumulates, or the fatigue level may be determined as a level which decreases as the accumulated fatigue load approaches the design limit.
According to an embodiment, the fatigue level for each power generating unit turbine is weighted dependent on a rate of change of fatigue levels determined for one or more components.
Accordingly, if a power generating unit has a slow increase of the accumulate fatigue load, the weighting of the fatigue level can be modified to allow a higher mechanical loading of that power generating unit, i.e. the fatigue level is increased or decreased dependent on whether the fatigue level is determined as a margin relative to a design limit or is determined as a level which increases with the accumulation of fatigue loading.
A second aspect of the invention relates to a central controller for controlling power production of a power plant which comprises a plurality of power generating units including at least one wind turbine generator, where the power plant is connected to an electrical power grid for supplying power from the power generating units to the electrical power grid, and where at the central controller is arranged to dispatch individual power set-points to the power generating units, and where the central controller is arranged to perform the method according to the first aspect.
A third aspect of the invention relates to a power plant which comprises a plurality of power generating units including at least one wind turbine generator and the central controller according to the second aspect.
A fourth aspect of the invention relates to a computer program product
comprising software code adapted to control a power plant when executed on a data processing system, the computer program product being adapted to perform the first aspect.
In general, the various aspects and embodiments of the invention may be combined and coupled in any way possible within the scope of the invention.
These and other aspects, features and/or advantages of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will be described, by way of example only, with reference to the drawings, in which
Fig. 1 shows a power plant which comprises a plurality of power generating units such as wind turbines,
Fig. 2 shows a configuration of the power plant and dispatcher,
Fig. 3 illustrates levelling of fatigue loads of the of power generating units, and Fig. 4 illustrates an implementation of the control method for controlling power set points of the power generating units. DESCRIPTION OF EMBODIMENTS
Fig. 1 shows a power plant 100 which comprises a plurality of power generating units 101 such as wind turbines. The power plant 100 may be a renewable power plant comprising only renewable power generating units. In general, the power generating units 101 may consist of different types of power generating units, e.g. different types of renewable power generating units such as solar power units 103 (e.g. photovoltaic solar panels) and wind turbines. The different types of power generating units 101 may also include fossil based power production units, e.g. diesel engines. According to an embodiment, at least one of the power producing units 101 of the power plant 100 is a wind turbine. The power plant 100 may comprise at least three power generating units 101 of the same or different types, i.e. a mix, of different types of power generating units. For example, the power plant 100 may consist only of wind turbines 102 and in this case at least three wind turbines 102. In another example, the power plant 100 comprises at least two wind turbines 102 and at least one or two other power generating units 101.
The power plant is connectable with an electrical power grid (not shown) for supplying power from the power generating units 101 to the electrical power grid. The power plant 100 is controlled by a central controller 110. The central controller 110 is arranged to control power generation from the power generating units 101 according to a power plant reference Pplant_ref which defines the desired power to be supplied to the grid from the power plant 100. Furthermore, the central controller is arranged to dispatch power set-points Pset to the power generating units, i.e. individual power set-points to each power generating unit 101 which sets the desired power productions. The power set-points Pset may be determined by the central controller 110 dependent on the power plant reference Pplant_ref so that the sum of power set-points Pset corresponds to the power plant reference Pplant_ref.
Throughout this description, power reference is used for the demanded power for the wind power plant, whereas power set-point is used for the demanded power for the individual power generating units. Thus, an objective of the central controller 110 or a dispatcher comprised by the central controller is to ensure that the demanded power (e.g. from the
Transmission System Operator (TSO)) is delivered as fast as possible, this applies both to increase and decrease in the power reference, Pplant_ref.
The wind turbine 101 may comprise a tower and a rotor with at least one rotor blade, such as three blades. The rotor is connected to a nacelle which is mounted on top of the tower and being adapted to drive a generator situated inside the nacelle. The rotor is rotatable by action of the wind. The wind induced rotational energy of the rotor blades is transferred via a shaft to the generator. Thus, the wind turbine is capable of converting kinetic energy of the wind into mechanical energy by means of the rotor blades and, subsequently, into electric power by means of the generator. The generator may include a power converter for converting the generator AC power into a DC power and a power inverter for converting the DC power into an AC power to be injected into the electrical power grid.
The generator of the wind turbine 102, or other power generating unit 101, is controllable to produce power corresponding to the power set-point Pset provided by the central controller 110. For wind turbines, the output power may be adjusted according to the power set-point by adjusting the pitch of the rotor blades or by controlling the power converter to adjust the power production. Similar adjustment possibilities exists for other power generating units 101.
Herein any reference to power such as power plant reference Pplant_ref, power set points Pset, available power Pav and produced power Pprod can define active, reactive or apparent power levels. According to an embodiment, the power levels, such as Plant_ref, Pset, Pav, Pprod and other related power levels are active power levels.
Fig. 2 exemplifies the arrangement of the calculation modules inside a dispatcher. In this example, the power generating units 101 are wind turbine generators 102, but the power generating units could also comprise a mix of wind turbine generators and other types of power generating units. Therefore, in order to keep the description general, reference is made to power generating units 101 unless the specific contest relates to a wind turbine example.
It can be seen that the dispatcher 201 is disclosed as being part of a central controller 110. The dispatcher receives the power plant reference Pplant_ref and determines the power set points Pset, e.g. power set points Psetl, Pset2, Psetn for the respective wind turbine generators WTG1, WTG2, ...,WTGn, based on a plurality of status feedback signals. The feedback signals comprise the available power of the individual power generating units Pavl...Pavn and the produced power of individual power generating units Pprodl...Prodn.
Pavl is the power available from a wind turbine 102 at the given time, calculated based on the current wind speed and other parameters limiting the power production. Thus, the available power of the power system is therefore the aggregation of the individual available powers. Pprod l is the power produced by a specific wind turbine 102 at the given time.
In case the power plant reference Pplant_ref is increased, the determination of the individual power set points Pset is determined based on available power of the individual power generating units Pavl...Pavn. In case the power plant reference Pplant_ref is decreased, the determination of the individual power set Pset is determined based on and the produced power of individual power generating units Pprodl... Prod n.
The actual power production Pprodl..Prodn of the power generating units 101 is fed to a feeder line, which is connected to a Point of common coupling (PCC) via a transformer. At the PCC the aggregated power production is measured by means of a power meter. The measured power (P measurement) is communicated to the PPC.
The mechanical and electrical components of the power generating units, e.g. wind turbine generators, are exposed to fatigue loading which require repairing and replacement of the components. When a control mechanism is not present between a monitoring system for monitoring the fatigue loading and the dispatcher of the power plant controller, it is not possible to adapt the determination of the power set points Pset dependent on the fatigue loading or the monitoring of the fatigue loading.
On the other hand, by introducing such a control mechanism it is possible to determine the power set points Pset dependent on the fatigue level obtained for each of the of power generating units.
Examples of the mechanical components of the wind turbines generators which may be exposed to fatigue loading comprise the gearbox, the generator, the rotor, the yaw system, blades and other components.
Fig. 3 illustrates a method according to an embodiment for controlling power generation from the power plant 100 by determining power set points for at least some of the power generating units based on a comparison of fatigue levels Flev of the power generating units with a fatigue level threshold, Fthreshold.
The power plant 110 comprises a plurality of power generating units 101. The method may involve determination of power set points for all units 101 in the power plant 110 or for a fraction of the units 101 based on power and fatigue data from the same units.
The method is based on fatigue levels Flev which have been obtained for each of the power generating units 101, i.e. at least for a fraction of the power generating units of the power plant 100. The fatigue level for a given power generating unit 101 can be a fatigue level for one or more individual components of the power generating unit or for the entire power generating unit 101, or other fatigue level associated with the power generating unit 101. Thus, the fatigue level may be determined as a combined accumulated fatigue level of one or more mechanical components of the power generating unit. For example, the fatigue level for one component, e.g. the gearbox, is accumulated over some period of time, and the accumulated fatigue levels for different components, e.g. the gearbox and the blades, may be combined into an aggregated fatigue level. Examples of determining fatigue levels are provided later in the description. The combined accumulated fatigue level Flev may be determined as the fatigue level accumulated over any period of time, such as minutes, hours, days, years or or the entire period of operation of the power generating unit.
The combined accumulated fatigue level Flev is compared with a fatigue level threshold Fthreshold. The fatigue level threshold can be determined as an average of the fatigue levels of the power generating units. The average of the fatigue levels can be determined as the sum of the fatigue levels of the plurality of power generating unit 101 divided by the number of the power generating units. The fatigue level threshold can be determined as an accumulated averaging over a pre-defined time window, e.g. over a period such as as minutes, hours, days, years or the entire period of operation of the power generating units. The fatigue level threshold can be determined as an instantaneous level. The fatigue level threshold can also be determined as a time average based on a probability distribution function. To facilitate comparison between the combined accumulated fatigue level Flev, in short fatigue level Flev, and the fatigue level threshold Fthreshold, Flev and Fthreshold may determined for the same averaging period of time.
Alternatively, the fatigue level threshold Fthreshold may be determined as a user determined threshold. For example, the owner of the power plant may set a low Fthreshold to reduce fatigue loading, or opposite set a high Fthreshold to enable a a maximum utilization of the power production capabilities.
Fig. 3 shows the fatigue levels Flev obtained for power generating units Unitl- Unitn. Fig. 3 shows an example of the fatigue level threshold Fthreshold_av where it is determined as an average of the individual fatigue levels and an example of the fatigue level threshold Fthreshold_user where it is determined as a user defined threshold.
Power generating units Unitl, Unit3, Unit4, Unit 6 and Unitn have fatigue levels Flev which are higher than the average fatigue level threshold Fthreshold_av, while the units Unit2 and Unit5 have fatigue levels Flev below the average fatigue level threshold Fthreshold_av. Examples of the percentage differences between the fatigue levels Flev and the fatigue level threshold are given in Fig. 3 for each power generating unit.
In order to reduce differences AF between fatigue levels Flev between the power generating units such as between pairs of power generating units, or e.g. the differences between the maximal and minimum fatigue levels or the difference between the average or sum of differences between individual fatigue levels Flev and the average Fthreshold_av, the dispatcher 201 determines adjustments of the power set points Pset for each power generating unit dependent on the fatigue levels and the fatigue level threshold. This implies that the power set points for power generating units 101 with power levels Flev above the fatigue level threshold Fthreshold are reduced compared to their respective present set points, and the power levels Flev below the fatige level threshold Fthreshold are increased compared to their respective power set points. The differences AF should be understood generally as a quantification of the variance of the fatigue levels or other quantification of the variation of the fatigue levels.
By reducing the fatigue level differences AF by controlling the power set points dependent on differences between the fatigue levels and the fatigue level threshold, a levelling of the individual fatigue levels is obtained over time.
The adjustments of the power set-points may be performed subject to a
constraint of reducing differences between the fatigue levels and the fatigue level threshold. Thus, a function which quantifies the differences, e.g. a sum of absolute values of the individual differences abs(Fthreshold-FlevJ) over the power generating units UnitJ or a sum of scaled differences abs(Fthreshold-Flev)xA, where A may be a monotonically increasing function of the difference, i.e.
A(Fthreshold-Flev), can be used as an optimization function which could be used the determine the individual adjustments of the power set points Pset, e.g. by determining adjustments which minimizes the optimization function.
In an example, the adjustment of the power set points of the generating units are performed subject to a constraint of maintaining the power plant reference
Pplant_ref for the desired power production of the power plant. Accordingly, a mathematical function may be set up which determines the power set points subject to maintaining a constant or substantially constant power reference Pplant_ref.
In another example, the adjustment of the power set point of each power generating unit is determined dependent on a difference between the fatigue level Flev of the respective power generating unit and the fatigue level threshold Fthreshold. For example, the adjustment may be determined dependent on a scaling factor, Si, which corresponds to the difference between the fatigue level of the respective power generating unit and the fatigue level threshold Fthreshold. The scaling factor Si may be determined dependent on the difference Flev - Fthreshold, e.g. as (Flev - Fthresholdj/Fthreshold. Thus, the scaling factor Si may be equal to the percentages of the over and under fatigue levels in Fig. 3. The adjustment may be determined as a percentage of the scaling factor Si, e.g. Pset = Pset_p + K*Si*Pset_p, where K is a value between 0 and 1, and Pset_p is the present value of Pset.
The available power level Pav and/or the actual power level Pprod may be determined for the plurality power generating units of the power plant 110, or at least a fraction thereof. It may not be necessary to obtain both the available power level Pav and the actual power level Pprod since the available power level Pav may only be required in case of an increase in the power plant reference Plant_ref and since the actual power level Pprod may only be required in case of a decrease in the power plant reference Plant_ref. Thus, in general at least one power level, Pav and/or Pprod, may be obtained for each of the power generating units.
The available power level Pav and the actual power level Pprod are both referred to as the power level Plev of a power generating unit 101.
In an example the adjustment of the power set-point Pset of each power generating unit is determined dependent on the available power level Pav or the actual power production Pprod of the respective power generating unit multiplied with a scaling factor Si which corresponds to the difference between the fatigue level Flev of the respective power generating unit and the fatigue level threshold Fthreshold. The scaling factor Si may be equal to the percentages shown in Fig. 3. Further, the adjustment of the power set points may be determined as the available power level Pav or the actual power production Prod of the respective power generating unit multiplied with the scaling factor and divided by a total available power Pavtot the power plant 100 or a total actual power production Pprodtot of the power plant, e.g. as APset = Si*Pavl/Pavtot or APset =
Si*Pprodl/Pprodtot for Unitl, where APset is the adjustment of the present Power set point Pset. The total available power Pavtot is the total available power for the power plant 100 and the total actual power production Pprodtot is the total power production of the power plant 100.
Thus, in response to a change in the power plant reference Pplant_ref, or in response to a an event such as a periodic calculation event, the power set points Pset for at least a fraction of the power generating units 101 is adjusted or checked based on the comparison of the fatigue levels Flev with the fatigue level threshold, Fthreshold. For example, the adjustment may be performed
periodically, e.g. once a day or once per hour, in order to continuously levelling the fatigue levels.
In case of an increase in the power plant reference Plant_ref, the adjustment of the power set points may be determined dependent on the available power Pav of the power generating units, e.g. as APset = Si*Pavl/Pavtot.
In case of a decrease in the power plant reference Plant_ref, the adjustment of the power set points may be determined dependent on the actual power production Pprod of the power generating units, e.g. as or APset =
S i * Pp rod 1/ Pp rod tot .
The above examples and embodiments applies in the same way in case the user defined fatigue level threshold Fthreshold_user is used in stead of the average fatigue level threshold Fthreshold_av. Thus, the adjustments of the power set point Pset are adjusted dependent on the differences between the individual fatigue levels Flev of the power generating units 101 and the user defined fatigue level threshold Fthreshold_user. In the example in Fig. 3, all power generating units have fatigue levels Flev above the user defined fatigue level threshold.
Accordingly, the adjustment implies a decrease of all power set points, but with the largest percentage decrease for the power generating units with the largest fatigue levels Flev.
The fatigue level for each of the power generating units may be obtained based on measured data from sensors of each of the power generating units. In case of wind turbine generators 102, examples of such sensors include blade root torque sensors and tower acceleration sensors. The blade root torques can be used to estimate hub moments based on co-ordinate transformations with respect to the pitch angle and hub radius. From the hub moments, the tilt & yaw moments on the main bearing can be estimated based on the azimuth position. From the power and generator speed signal, torque on the gearbox can be calculated, with estimate on the gear train and electrical efficiency. The tower acceleration sensor can be used to find the acceleration levels at tower top, this multiplied with the tower top mass gives the tower top moments. From the tower top moments, the tower bottom moments can be calculated. In general, with such sensors or with external sensors or with a surrogate model, the entire wind turbine loads can be estimated, e.g. the loads of the blades, blade bearing, hub, pitch system, main bearing, gearbox, tower, foundation, etc.
Based on the determined component loads and structural information such as material-types and structural dimensions, the fatigue level of individual
components can be determined and thereby the accumulation of fatigue loads over time. The fatigue level Flev for an individual power generating unit can be determined from a combination of the accumulated fatigue levels of one or more of components.
The fatigue level for each of the power generating units may be obtained based on a weighted sum of component fatigue levels of one or more mechanical
components of each power generating unit. For example, rotational parts in the blade bearing, gearbox, replaceable parts like bolts are required to be serviced or replaced during annual servicing. Accordingly, particularly up to a planned service, the fatigue level of such components may be weighted higher (unless the accumulated fatigue level is critical) in order to exploit the capacity of such components. For example, the weighting factor of the gearbox may be increased from a factor one up to a factor two since replacement of gearbox components is planed in near future.
The fatigue level may be determined as a fatigue margin based on differences between component fatigue levels of one or more components and predetermined design fatigue limits of the one or more components. Accordingly, the fatigue level may be in the form of a margin which indicates a distance between the actual fatigue level and a design limit of a given component.
The fatigue level Flev for a given power generating unit may be determined by weighting the accumulated fatigue level as a function of the rate-of-change of the fatigue level for that component. Accordingly, a trend of fatigue level
accumulation can be used as weighting factor. A rapid increase of the trend of fatigue level for specific component could cause the power generating unit 101 to have lower life time and, in this time, accumulated fatigue level could be given lower weightage such that the power plant controller 110 or dispatcher could react to ensure that such power generating unit 101 is given a low prioritization. In opposite scenario, if the fatigue level accumulation trend is slow, the power generating unit 101 could be given a higher priority.
Fig. 4 illustrates a possible implementation of the control method described in various embodiments. The implementation may include a monitoring system 401 including sensors Sl-Sn such as torque and accelerations sensors. The sensors provide load data to a fatigue level calculation module 402 which determines accumulated fatigue levels Flev for different components Cl-Cn based on different sensor input. The module 402 may be comprised by individual power generating units 101, by the power plant controller 110 or may be implemented in other ways. Thus, a module 402 may be provided for each power generating unit 101 to determine fatigue loads for that power generating unit 101, or the module 402 may be common for all power generating units and arranged to determine fatigue loads for all units 101 based on data from sensors Sl-Sn from all power
generating units. The accumulated fatigue levels are made available for the adjusting module 403 which determines the power set point adjustments. The adjusting module 403 may be implemented in the central power plant controller 110. The adjusted power set points are made available for the dispatcher 201 which is arranged to dispatch the power set points Psetl- Psetn to the power generating units 101.
Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is to be interpreted in the light of the accompanying claim set. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. Also, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.

Claims

1. A method for controlling power generation from a power plant (100) which comprises a plurality of power generating units (101) including at least one wind turbine generator, where the power generation system is connected to an electrical power grid for supplying power from the power generating units to the electrical power grid, and where at the power generating units (101) are controllable to produce power dependent on individual power set points (Pset), the method comprises:
- obtaining a fatigue level (Flev) for each power generating unit, where the fatigue level is indicative of a combined accumulated fatigue loading of one or more mechanical components of the power generating unit,
- comparing the obtained fatigue levels of the power generating units with a fatigue level threshold (Fthreshold),
- based on the comparison, adjust the power set point for each power generating unit dependent on the fatigue levels and the fatigue level threshold so as to reduce differences (AF) between fatigue levels of the power generating units during future operation.
2. A method according to claim 1, wherein the fatigue level threshold (Fthreshold) is determined as an average of the fatigue levels of the power generating units.
3. A method according to any of the preceding claims, wherein the fatigue level threshold is a user determined threshold (Fthreshold_user). 4. A method according to any of the preceding claims, wherein the adjustment of the power set-points is performed subject to a constraint of reducing the differences (AF) between the fatigue levels and the fatigue level threshold.
5. A method according to any of the preceding claims, wherein the adjustment of the power set-point of each power generating unit is performed subject to a constraint of maintaining a power reference (Pplant_ref) for a desired power production of the power plant.
6. A method according to any of the preceding claims, wherein the adjustment of the power set point of each power generating unit is determined dependent on a difference between the fatigue level of the respective power generating unit and the fatigue level threshold.
7. A method according to claim 6, comprising
- obtaining an available power level (Pav) or an actual power production (Pprod) for each of the power generating units, where the available power is the maximum power that can be produced by one of the power generating units and the actual power production is the power supplied to the electrical power grid, and
- wherein the adjustment of the power set-point of each power generating unit is determined dependent on the available power level or actual power production of the respective power generating unit multiplied with a scaling factor (Si) which corresponds to the difference between the fatigue level of the respective power generating unit and the fatigue level threshold.
8. A method according to claim 7, wherein the adjustment of the power set point of each power generating unit is determined as the available power level (Pav) or the actual power production (Prod) of the respective power generating unit multiplied with the scaling factor (Si) and divided by a total available power (Pavtot) of the power plant or a total actual power production (Pprodtot) of the power plant.
9. A method according to any of the preceding claims, wherein the
available power level is an available active power levels or the actual power production is an actual active power production and the power set points are active power set points.
10. A method according to any of the preceding claims, wherein the fatigue level (Flev) for each of the power generating units is obtained based on measured data from sensors of each of the power generating units.
11. A method according to any of the preceding claims, wherein the fatigue level for each of the power generating units is obtained based on a weighted sum of component fatigue levels of one or more components of each power generating unit.
12. A method according to any of the preceding claims wherein the fatigue level for each power generating unit turbine is weighted dependent on a rate of change of fatigue levels determined for one or more components. 13. A central controller (110) for controlling power production of a power plant
(100) which comprises a plurality of power generating units (101) including at least one wind turbine generator (102), where the power plant is connected to an electrical power grid for supplying power from the power generating units to the electrical power grid, and where at the central controller is arranged to dispatch individual power set-points to the power generating units, and where the central controller is arranged to perform the method according to claims 1-12.
14. A power plant (100) which comprises a plurality of power generating units
(101) including at least one wind turbine generator and the central controller (110) according to claim 13.
15. A computer program product comprising software code adapted to control a power plant (100) when executed on a data processing system, the computer program product being adapted to perform the method of any of the claims 1-12.
PCT/DK2019/050368 2018-12-18 2019-11-28 Levelling of fatigue levels of power generating units of a power plant comprising one or more wind turbine generators WO2020125879A1 (en)

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