U.S. patent application number 12/771715 was filed with the patent office on 2010-11-11 for wind turbine.
This patent application is currently assigned to VESTAS WIND SYSTEMS A/S. Invention is credited to Poul Brandt Christensen.
Application Number | 20100283246 12/771715 |
Document ID | / |
Family ID | 42224495 |
Filed Date | 2010-11-11 |
United States Patent
Application |
20100283246 |
Kind Code |
A1 |
Christensen; Poul Brandt |
November 11, 2010 |
WIND TURBINE
Abstract
A method of controlling a wind turbine having a rotor and a
generator for producing power, the wind turbine being designed for
a nominal load, the method comprising the steps of: determining a
current load acting on at least a part of the wind turbine;
calculating a load error, the load error representing the
difference between the nominal load and the current load;
controlling the wind turbine based on the load error; wherein the
step of controlling the wind turbine comprises altering a parameter
of the wind turbine so that the power or torque produced by the
generator is altered.
Inventors: |
Christensen; Poul Brandt;
(Ry, DK) |
Correspondence
Address: |
WOOD, HERRON & EVANS, LLP
2700 CAREW TOWER, 441 VINE STREET
CINCINNATI
OH
45202
US
|
Assignee: |
VESTAS WIND SYSTEMS A/S
Randers SV
DK
|
Family ID: |
42224495 |
Appl. No.: |
12/771715 |
Filed: |
April 30, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61176253 |
May 7, 2009 |
|
|
|
Current U.S.
Class: |
290/44 |
Current CPC
Class: |
Y02E 10/728 20130101;
F03D 1/06 20130101; Y02E 10/72 20130101; F03D 7/043 20130101; F05B
2270/331 20130101; F03D 13/20 20160501; F03D 7/0292 20130101; F03D
7/0272 20130101; F05B 2270/1032 20130101; F03D 9/25 20160501 |
Class at
Publication: |
290/44 |
International
Class: |
H02P 9/04 20060101
H02P009/04 |
Foreign Application Data
Date |
Code |
Application Number |
May 7, 2009 |
DK |
PA 2009 00592 |
Claims
1. A method of controlling a wind turbine having a rotor and a
generator for producing power, the wind turbine being designed for
a nominal load, the method comprising the steps of: determining a
current load acting on at least a part of the wind turbine;
calculating a load error, the load error representing a difference
between the nominal load and the current load; controlling the wind
turbine based on the load error; wherein the step of controlling
the wind turbine comprises altering a parameter of the wind turbine
so that the power or torque produced by the generator is
altered.
2. A method of controlling a wind turbine according to claim 1,
wherein if the current load is higher than the nominal load, the
power produced by the generator is decreased such that the current
load is equal to or lower than the nominal load.
3. A method of controlling a wind turbine according to claim 1,
wherein if the current load is lower than the nominal load, the
power produced by the generator is increased.
4. A method according to claim 3, wherein the power produced by the
generator is increased until the current load is equal to the
nominal load.
5. A method according to claim 1, wherein the parameter of the wind
turbine to be altered is at least one of: a pitch angle of one or
more rotor blades; the speed of revolution of the rotor; and a
power reference of the generator.
6. A method according to claim 5, wherein the parameter of the wind
turbine to be altered is selected based on the load error.
7. A method according to claim 1, wherein the wind turbine is
designed for a plurality of nominal loads, each of the plurality of
nominal loads being associated with a different component of the
wind turbine; the method further comprising the steps of:
determining a plurality of current loads, each of the plurality of
current loads acting on the different components of the wind
turbine which are associated with at least one of the nominal
loads; calculating a plurality load errors for each of the
plurality of current loads, each load error representing the
difference between the nominal load and the associated current
load; and controlling the wind turbine based on the plurality of
load errors; wherein the step of controlling the wind turbine
comprises altering a parameter of the wind turbine so that the
power produced by the generator is altered.
8. A method of controlling a wind turbine according to claim 1,
wherein the wind turbine is erected on a location, the method
further comprising the steps of: defining a plurality of sectors
each specifying a range of wind directions towards the wind
turbine; defining, for each sector, an expected wind load from the
specified directions and a sector control strategy which is based
on a predetermined comparison between the expected wind load and
the nominal load; determining a current wind direction; before
controlling the wind turbine based on the load error, controlling
the wind turbine in accordance with the sector control strategy
defined for the sector to which the current wind direction
corresponds; and then controlling the wind turbine based on the
load error.
9. A method of controlling a wind turbine according to claim 1,
wherein the wind turbine is erected on a location, the method
further comprising the steps of: defining a plurality of sectors
each specifying a range of wind directions towards the wind
turbine; defining, for each sector, an expected wind load from the
specified directions and a sector control strategy which is based
on a predetermined comparison between the expected wind load and
the nominal load; determining a current wind direction; and after
the step of controlling the wind turbine based on the load error,
controlling the wind turbine in accordance with the sector control
strategy defined for the sector to which the current wind direction
corresponds.
10. A method according to claim 9, wherein the step of defining for
each sector an expected wind load comprises the step of:
determining the current loads acting on at least a part of the wind
turbine over a period of time for each sector, and calculating the
expected wind load for each sector based on accumulated values of
the current loads over the period of time.
11. A method according to claim 9, wherein the step of controlling
the wind turbine in accordance with the sector control strategy
defined for the sector to which the current wind direction
corresponds comprises the step of: selecting one control strategy
from a plurality of control strategies defined for each sector,
wherein the selection is based on the expected wind load.
12. A method according to claim 9, wherein each sector control
strategy is defined based on an expected wind load from wind from
the corresponding sector of wind directions towards the turbine for
a specific geographical location.
13. A method according to claim 9, wherein a given power output of
the wind turbine as a function of wind speed is defined for a range
of wind speeds, the given power output as a function of wind speed
being the same for all sectors; and the sector control strategy for
each sector controls the wind turbine such that the power output of
the wind turbine is either: below the given power output for a
given wind speed; or equal to the given power output for a given
wind speed; or above the given power output for a given wind
speed.
14. A control system for a wind turbine having a rotor and a
generator for producing power, the wind turbine being designed for
a nominal load, the control system having a control structure
adapted to: determine a current load acting on at least a part of
the wind turbine; calculate a load error, the load error
representing a difference between the nominal load and the current
load; control the wind turbine based on the load error by altering
a parameter of the wind turbine so that the power or torque
produced by the generator is altered.
15. A control system according to claim 14, wherein the control
system is adapted to carry out the method according to claim 1.
16. A wind turbine for converting between wind energy and
electrical energy, the wind turbine comprising a control system
according to claim 14.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority under 35 U.S.C.
.sctn.119(a) to DK Application No. PA 2009 00592, filed May 7,
2009. This application also claims the benefit of U.S. Provisional
Application No. 61/176,253, filed May 7, 2009. Each of these
applications is incorporated by reference herein in its
entirety.
TECHNICAL FIELD
[0002] The present invention relates to a method of controlling a
wind turbine which is designed for a specific nominal load, i.e.,
design load. The invention further relates to a control system in
accordance with the method and to a wind turbine including such a
control system.
BACKGROUND
[0003] A wind turbine obtains power by converting the force of the
wind into torque acting on the drive train, i.e., on the rotor
blades and thus on the main shaft and thereby typically on an
electrical generator rotated by the main shaft directly or through
a gearbox. The power which the wind turbine receives and which
therefore potentially can be transferred to the drive train depends
on several conditions including the wind speed and the density of
the air, i.e., the site conditions.
[0004] Even though a desire to increase productivity requests
conversion of the highest possible amount of wind energy to
electrical energy, the structural limitations of the wind turbine,
i.e., the design loads, define safety limits for the allowed load
on the wind turbine. In practice, the wind load depends on various
weather conditions including the average wind speed, wind peaks,
the density of the air, the turbulence, wind shear, and shift of
wind, and the impact of the wind load on the wind turbine and
thereby the load on the wind turbine can be adjusted for a current
wind condition by changing various settings on the wind
turbine.
[0005] Even though the loading of a wind turbine is determined by a
number of weather conditions and settings on the wind turbine, the
wind turbines of today are typically controlled in accordance with
a relatively simple and reliable control strategy according to
which the turbine is shut down completely at wind speeds above a
certain safety value.
[0006] Though representing a potentially very safe way of operating
a wind turbine, the complete shut down represents drawbacks, e.g.,
due to the fact that any major change in power production may
influence the supplied power grid in a negative way.
SUMMARY
[0007] According to a first aspect of the present invention there
is provided a method of controlling a wind turbine having a rotor
and a generator for producing power, the wind turbine being
designed for a nominal load, the method comprising the steps
of:
[0008] determining a current load acting on at least a part of the
wind turbine;
[0009] calculating a load error, the load error representing the
difference between the nominal load and the current load;
[0010] controlling the wind turbine based on the load error;
[0011] wherein the step of controlling the wind turbine comprises
altering a parameter of the wind turbine so that the power or
torque produced by the generator is altered.
[0012] According to embodiments of the invention, the wind loads
acting on the turbine, or different components of the turbine are
monitored and the turbine is controlled in dependence on those
current wind loads. This allows the wind turbine to maximise its
power production and reduce the loads that it is subjected to, thus
increasing the life of the wind turbine. When the power or torque
produced by the generator is altered, this means that the
instantaneous power or torque produced by the generator is altered.
By nominal load or design load, it is meant the load that the wind
turbine, or the individual component parts are designed for. An
individual turbine may have a nominal load for a first site and a
second nominal load for a second site--for example, the turbine in
the first site may have a design life of 20 years and in the second
site a design life of 25 years. The turbine in the second location
is the same as the turbine in the first location, but as it is
expected to have a life of 5 more years, the nominal load of the
second turbine will be different to the nominal load of the first
turbine.
[0013] Determining a current load acting on at least a part of the
wind turbine may comprise calculating a rain flow count or a
standard deviation of a measured load or signal from a sensor over
a predetermined period of time, when controlling the wind turbine
to account for operational loads.
[0014] By "representing" is herein meant that the load error is the
difference or at least represents the difference in one or some
other way.
[0015] If the current load is higher than the nominal load, the
power or torque produced by the generator may be decreased such
that the current load is equal to or lower than the nominal load.
It is the instantaneous power or torque produced by the generator
that is reduced. The wind turbine is run less aggressively so that
the output power is less and the loads are consequently lower at
all wind speeds, thus extending the wind turbine's life by ensuring
that the loads acting on the wind turbine are always within the
design loads.
[0016] If the current load is lower than the nominal load, the
power produced by the generator may be increased. It is the
instantaneous power or torque produced by the generator that is
increased. This could be done by allowing the wind turbine to run
aggressively, i.e., to produce more power at all wind speeds when
the wind conditions are benign--as the loads acting on the wind
turbine during benign wind conditions are lower than the design
loads. The power produced by the generator may be increased until
the current load is equal to the nominal load.
[0017] The parameter of the wind turbine to be altered may be at
least one of: a pitch angle of at least one of the rotor blades;
the speed of revolution of the rotor; or a power reference of the
generator.
[0018] The parameter of the wind turbine to be altered may be
selected based on the load error. Each parameter to be altered will
have a different effect on the power production and the
increase/reduction in the loads which the wind turbine is subjected
to. By selecting the parameter to be altered based on the actual
load error, any production loss can be minimised when the loads are
above the nominal loads; or production gain is maximized when the
loads are below the nominal loads.
[0019] The wind turbine may be designed for a plurality of nominal
loads, each of the plurality of nominal loads being associated with
a different component of the wind turbine; and the method may
further comprise the steps of:
[0020] determining a plurality of current loads, each of the
plurality of current loads acting on the different components of
the wind turbine which are associated with at least one of the
nominal loads;
[0021] calculating a plurality of load errors for each of the
plurality of current loads, each load error representing the
difference between the nominal load and the associated current
load;
[0022] controlling the wind turbine based on the plurality of load
errors;
[0023] wherein the step of controlling the wind turbine comprises
altering a parameter of the wind turbine so that the power or
torque produced by the generator is altered.
[0024] Preferably, the wind turbine is erected on a location, and
the method may further comprise the steps of: defining a plurality
of sectors each specifying a range of wind directions towards the
wind turbine, defining, for each sector, an expected wind load from
the specified directions and a sector control strategy which is
based on a predetermined comparison between the expected wind load
and the nominal load; determining a current wind direction; before
controlling the wind turbine based on the load error, controlling
the wind turbine in accordance with the sector control strategy
defined for the sector to which the current wind direction
corresponds; and then controlling the wind turbine based on the
load error.
[0025] By first controlling the wind turbine in dependence on what
sector the wind turbine is facing, before the control based on the
load error, allows the power production to be maximised and the
loads to be minimised. This is because the wind turbine has
knowledge of the expected wind loads from each sector so it can
react quickly, if the control based on the load error is not quick
enough to react. The expected wind loads may be known from a site
survey such as a meteorological mast, or may have been accumulated
over a period of time by the wind turbine itself.
[0026] However, the method may further comprise the steps of
defining a plurality of sectors each specifying a range of wind
directions towards the wind turbine; defining, for each sector, an
expected wind load from the specified directions and a sector
control strategy which is based on a predetermined comparison
between the expected wind load and the nominal load; determining a
current wind direction; and after the step of controlling the wind
turbine based on the load error, controlling the wind turbine in
accordance with the sector control strategy defined for the sector
to which the current wind direction corresponds.
[0027] By first controlling the wind turbine based on the load
error and then controlling the wind turbine based on the sector
control strategy allows more control of the turbine. For instance,
the control based on the load error may alter the loads so that
they are within a certain amount of the design loads, and then the
control based on the sector control strategy can alter the loads so
that they are even closer to the design loads.
[0028] The step of defining for each sector an expected wind load
may comprise the step of: determining the current loads acting on
at least a part of the wind turbine over a period of time for each
sector, and calculating the expected wind load for each sector
based on accumulated values of the current loads over the period of
time. In this way, the expected wind loads are actually calculated
at the turbine over a period of time, rather than being pre-stored
in the turbine controller.
[0029] The step of controlling the wind turbine in accordance with
the sector control strategy defined for the sector to which the
current wind direction corresponds may comprise the step of:
selecting one control strategy from a plurality of control
strategies defined for each sector, wherein the selection is based
on the expected wind load. In effect, the selection of the sector
control strategy is done at the wind turbine during operation,
rather than being pre-stored in the turbine controller.
[0030] Each sector control strategy may be defined based on an
expected wind load from wind from the corresponding sector of wind
directions towards the turbine for a specific geographical
location.
[0031] A given power output of the wind turbine as a function of
wind speed may be defined for a range of wind speeds, the given
power output as a function of wind speed being the same for all
sectors; and the sector control strategy for each sector controls
the wind turbine such that the power output of the wind turbine is
either: below the given power output for a given wind speed; or
equal to the given power output for a given wind speed; or above
the given power output for a given wind speed. By "given power
output of the wind turbine as a function of wind speed" is meant
the power curve of the wind turbine.
[0032] According to a second aspect of the present invention, there
is provided a control system for a wind turbine having a rotor and
a generator for producing power, the wind turbine being designed
for a nominal load, the control system having a control structure
adapted to:
[0033] determine a current load acting on at least a part of the
wind turbine;
[0034] calculate a load error, the load error representing the
difference between the nominal load and the current load;
[0035] control the wind turbine based on the load error by altering
a parameter of the wind turbine so that the power or torque
produced by the generator is altered.
[0036] The control system may be adapted to carry out the
activities as described above in relation to the first aspect of
the invention.
[0037] According to a third aspect of the invention, there is
provided a wind turbine, in particular a horizontal type wind
turbine, which includes a control system according to the second
aspect of the invention or which is controlled in whatever way in
accordance with the method of the first aspect of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] The invention will now be described by way of example with
reference to following figures in which:
[0039] FIG. 1 illustrates schematically a wind turbine rotor and a
controller;
[0040] FIG. 2 illustrates a typical power curve of a prior art wind
turbine;
[0041] FIG. 3 illustrates a power curve of a wind turbine according
to the invention; and
[0042] FIG. 4 illustrates a schematic of the control of the wind
turbine.
DETAILED DESCRIPTION
[0043] Further scope of applicability of the present invention will
become apparent from the following detailed description and
specific examples. However, it should be understood that the
detailed description and specific examples, while indicating
preferred embodiments of the invention, are given by way of
illustration only, since various changes and modifications within
the scope of the invention will become apparent to those skilled in
the art from this detailed description.
[0044] FIG. 1 illustrates schematically a wind turbine rotor 10
connected to a controller 11. In a typical horizontal axis wind
turbine, a wind turbine rotor comprises three rotor blades and a
hub. The hub is connected to a nacelle which is situated at the top
of a tower. The nacelle houses the drive train (i.e. the rotating
shafts, gearbox and generator) and the control systems for
operating the wind turbine.
[0045] The controller 11 receives data from various sensors on the
wind turbine and these sensors are illustrated schematically as
12.
[0046] FIG. 2 illustrates a power curve of a conventional wind
turbine plotting wind speed on the x axis against power on the y
axis. Curve 20 is the nominal power curve for the wind turbine and
defines the power output by the wind turbine generator as a
function of wind speed. As is well known in the art, the wind
turbine starts to generate power at a cut in wind speed Vmin. The
turbine then operates under part load (also known as partial load)
conditions until the rated wind speed is reached at point Vr. At
the rated wind speed at point Vr the rated generator power is
reached. The cut in wind speed in a typical wind turbine is 3 m/s
and the rated wind speed is 12 m/s. At point Vmax is the cut out
wind speed, this is the highest wind speed at which the wind
turbine may be operated while delivering power. At wind speeds
equal to and above the cut out wind speed the wind turbine is shut
down for safety reasons, in particular to reduce the loads acting
on the wind turbine.
[0047] FIG. 3 illustrates a power curve of a wind turbine operated
according to the present invention. As mentioned above, the power
curve 20 is the nominal power curve. A wind turbine is
conventionally designed to withstand certain loads, such as the
rotor blade root flap bending moment, the tower base bending moment
and the main shaft design load. These are the "design or nominal
loads" which should not be exceeded, and so the turbine has a
nominal power curve, at which the turbine will be operated when
experiencing design wind conditions.
[0048] As shown in FIG. 3, the turbine is controlled such that it
can produce more or less power than the normal power curve in both
the part load and the full load regions. The term "over-rating" is
understood to mean producing more than the nominal power during
full load operation. The term "de-rating" is understood to mean
producing less than the nominal power during full load operation.
In the invention, the turbine can produce more or less power in
both the full load and the part load regions. Thus the term
"over-producing" is used to refer to an increase in power
production in both the part load and the full load region compared
to the normal power curve; and the term "under-producing" is used
to refer to a decrease in power production in both the part load
and the full load region compared to the normal power curve. When
the turbine is over-producing, the turbine is run more aggressive
than normal and the generator has a power output which is higher
than the nominal power for a given wind speed. The over-producing
is shown in FIG. 3 as area 21. When the turbine is under-producing,
the turbine is run less aggressive than normal and the turbine
generator has a power output which is lower than the nominal power
for a given wind speed. The under-producing is shown in FIG. 3 as
area 22. It should be noted that the areas 21 and 22 extend into
the part load region as well as the full load region. When the
turbine is over-producing the loads acting on the turbine are
increased and when the turbine is under-producing the loads acting
on the turbine are decreased.
[0049] The control method and how the power of the turbine is
altered are explained in detail with reference to FIG. 4. FIG. 4
shows a wind turbine 1 having a rotor 10. The controller 11
includes a load estimator 30, a load error calculation unit 31, a
load and power control unit 32 and a load supervisor 33.
[0050] When the turbine is in operation, the sensors 12 monitor the
loads that different components of the turbine are subjected to.
These monitored loads are loads that should not be exceeded when
the turbine is in operation and include the blade root flap bending
moment, the tower base bending moment and the main shaft load.
Sensors 12 such as strain gauges, accelerometers and speed
measurements record data on the rotor, the tower and the main shaft
as is well known in the art, in particular by measuring important
variables in the turbine (speed, rotor blade pitch, wind speed,
blade flap moment, tower accelerometer etc.). The data from the
sensors is input to the load estimator 30 which derives the current
load that each component is subjected to.
[0051] A memory 34, such as look up table, contains data relating
to the design load of each component. This is the nominal load that
each component is designed to withstand during normal operation of
the wind turbine and should normally not be exceeded.
[0052] The load error calculation unit 31 calculates a difference
between the design load and the current load of each component.
This calculation is based on the load output from the load
estimator 30 and the design loads stored in the memory 34.
[0053] The load errors are then input into the load and power
control unit 32 which contains algorithms for the optimisation of
power production while ensuring that none of the loads are above
the design loads. The load and power control unit 32 controls a
number of parameters which when altered have the effect of changing
the power or torque of the generator. This consequently affects
that the loads that the turbine is operating under. These
parameters can include:
[0054] pitch control of the rotor blades about a pitch set point,
in part load and full loads operation; or
[0055] speed control of the rotor about a speed set point, which is
controlling the rotor speed about a reference rotor speed. For
instance, in part load operation a tip speed ratio of the rotor
blades is calculated. The tip speed ratio is the ratio of the speed
of the tip of the blades relative to the approaching wind speed. In
the part load region the power generated by the turbine can be
regulated by the tip speed ratio, so if the rotor speeds up or
down, the output power changes; or
[0056] setting a power reference about a power set point in a
converter of the wind turbine which the wind turbine can follow,
and setting a pitch angle of the rotor blades; i.e., the power
output can be changed dynamically by changing the power reference
when there is a converter.
[0057] The adjusted parameters which are controlled by the load and
power control unit 32 are applied to the wind turbine 1 which has
the effect that the turbine will be subjected to new and different
loads. In use, the signals from the load and power control unit are
sent to a conventional wind turbine controller (not shown in FIG.
4) which contains the conventional control algorithms for
controlling the wind turbine. These new loads are then measured by
the sensors 12 and the load estimator 30 and the process repeats
itself.
[0058] The load and power controller 32 controls the turbine such
that if the current load is higher than the design load for a
particular component, the power produced by the generator is
decreased so that that the current load is equal to or lower than
the design load for that component. In addition, if the current
load is lower than the design load for a particular component, the
power produced by the generator is increased. This allows the
optimisation of the power production because when the turbine is
subjected to loads below the design loads, for instance in benign
wind conditions, the turbine can over-produce to increase power
production. Even though the turbine over-produces, the design loads
cannot be exceeded because the loads that the turbine is currently
subjected to are constantly monitored. Similarly, when the current
loads exceed the design loads, the turbine under-produces so that
the generator produces less power--although the turbine
under-produces, the loads that the turbine is subjected to are less
so that the turbine can continue to produce power without shutting
down completely. Accordingly, the turbine is controlled in
dependence on the loads acting on the turbine. The controller 11
controls the operation based on measured loads, rather than wind
speed.
[0059] A conventional wind turbine will typically have a Vmax cut
out wind speed of 25 m/s (referring to FIG. 2). However, with the
controller 11, the loads can be monitored and if it is determined
that at 25 m/s the loads acting on the turbine are not above the
design loads, it is not necessary to shut the turbine down.
Instead, the turbine can continue to produce power until the
current loads reach the design loads. The load supervisor 33
ensures that if a load error is too high for too long, the wind
turbine is shut down completely to alleviate loads acting on the
turbine.
[0060] The load estimator 30 also estimates fatigue and extreme
loads acting on the wind turbine components. These should be
matched up against the design loads 34 to calculate the load error
in the load error calculation unit 31.
[0061] In one implementation, the load estimator 30 calculates a
rain flow count or a standard deviation of a measured load or
signal from a sensor over a predetermined period of time, when
controlling the wind turbine to account for fatigue loads. The load
estimator 30 may also calculate a risk of an extreme load occurring
in the future. The fatigue loads and the "extreme loads risk" are
included in the current loads sent to the load error calculation
unit 31. An example of the extreme loads risks is the following: a
tilt load of 100 (dimensionless amount) is measured and the load
estimator 30 calculates (based on the behaviour/statistics of the
load signal or wind conditions) for safety that it is 99% certain
that the tilt load will not exceed 150. There is no value in
knowing what has happened in the past for an extreme load, for
example there is no value in knowing that 10 seconds ago a design
extreme load was exceeded. It is not possible to estimate extreme
loads as they can occur suddenly, for instance if a rotor blade
collides with the tower it is too late to alter the control of the
wind turbine; instead it is necessary to need to know the risk of a
rotor blade hitting the tower.
[0062] The fatigue loads and the extreme loads form part of the
current loads input to the load error calculation unit.
[0063] As mentioned above, the parameters that may be used to
control the wind turbine are the speed set point of the rotor, the
power set point of the generator and the pitch set point of the
rotor blades. The load and power control unit 32 needs to know
which parameter should be changed for a given current load
condition.
[0064] All the parameters that can be changed to control the
turbine have a signature associated with them which identifies
exactly how and when the parameter is changed, what the effect will
be on the power generated by the wind turbine, and the loads acting
on the wind turbine. For instance, the load and power control unit
32 will know that if the rotor blades are pitched by a certain
amount, what the consequential effect will be on the power
generated and the loads acting on the components of the wind
turbine. Accordingly, if the loads acting on the wind turbine are
high and it is desirable to de-rate the wind turbine to reduce the
loads acting on the wind turbine, the parameter selected by the
load and power control unit 32 to de-rate the turbine is chosen
based on that parameter which will reduce the loads with the lowest
cost; where cost refers to the loss in power production.
[0065] For example, if the wind turbine experiences high tilt load
from wind shear on the rotor, say at 15% above the design load, and
it is known that speed de-rating (by changing the speed of the
rotor) will change this tilt load by 10% for every 100 rpm
de-rating of the generator speed (there is a fixed gear ratio
between the rotor rpm and the generator rpm); the load and power
control unit would select this tunable and adjust the generator
speed reference down by 150 rpm.
[0066] A combination of parameters to be changed may also be used.
For instance, if power de-rating (by changing the power set point)
decreases the tilt load on the turbine by 10% and decreases the
power production by 5% and there is another parameter (such as
changing the rotor speed) that can be changed that also decreases
the tilt load by 10% but only decreases the power production by 4%,
the parameter to be selected to control the turbine will be the one
that decreases the power production by 4% because the relevant load
is decreased below design loads while keeping the lowest production
loss.
[0067] In addition, if the turbine experiences design loads being
exceeded on several main components the controller 11 may need to
do several things (i.e., speed de-rate and power de-rate), but the
basic concept is still to select the parameters(s) which solve the
load issue with the lowest total cost (lost production). Whenever
the turbine is experiencing loads below design loads on several
components, the controller 11 may do several things (e.g. power
over-rating and speed over-rating) to maximize production while
keeping loads within design loads.
[0068] These signatures are defined before the wind turbine is
erected and stored in the load and power control unit 32. They are
calculated using computer simulations of a wind turbine
over-producing and under-producing and observing what happens with
the loads that the wind turbine is subjected to.
[0069] However, it is also possible for a generic signature to be
assigned to each parameter and during the course of the turbine
operating, the signatures can adapt by artificial intelligence.
[0070] In a further implementation, the load and power controller
32 can determine how the turbine is controlled based on the
direction that the turbine is facing. The area around the turbine
is divided up into a number of sectors, for example twelve sectors
each of 30 degrees. The load and power controller 32 can store
knowledge on each sector relating to the previous current loads the
turbine has experienced in that sector. For instance, due to local
geographic conditions, when the wind comes from a first sector, A,
the loads on the turbine are generally low as the wind loads are
benign because the turbulence is low. However, when the winds come
from a second sector, B, the loads on the turbine are generally
high as the wind loads are high because the turbulence is high or
that sector is prone to gusts.
[0071] A specific example of the sector control is as follows: The
controller 11 operates for one month and during this time the
controller 11 identifies that sector A is a very benign sector and
therefore the power output of the generator is over-rated to 110%
of the nominal power output at a given wind speed. The controller
11 also identifies that in sector B the wind loads are high due to
regular gusts and the turbine generator is de-rated to 50% of the
nominal power output for a given wind speed to avoid increasing the
loads acting on the turbine. The control algorithms in the load and
power controller 32 may be very slow because they need a lot of
data over time from the sensors 12 to be able to control the
turbine, so moving from one sector to another it will take a long
time for the wind turbine to adapt to the new sector with the
result that the wind turbine may be exposed to critical loads if
moving to sector B or the power production will not be optimised if
moving to sector A. But, to avoid this time delay problem, if the
wind switches from sector A to sector B, the load and power control
unit 32 will resume the algorithms from where it left off the last
time the turbine was operating in sector B, i.e., at 50% de-rated;
and when the wind switches from sector B to sector A the algorithms
would `resume` from last setting when the wind turbine was
operating in sector A i.e. 110% over-rated. This sector dependency
may also include the possibility of `season` dependency as well,
i.e., the controller 11 knows what time of day or what time of year
it is, and what the expected wind loads from each sector will be as
a function of time. In a further implementation, a plurality of
neighbouring wind turbines in a wind farm are connected. The
controllers 11 of each wind turbine are connected to each other and
receive data on what the expected wind loads are in each sector.
With a plurality of wind turbines, the knowledge of the expected
wind load from each sector will be generated faster than a single
wind turbine operating alone; so for instance, rather than it
taking a month to identify that sector A is a benign sector, it
will only take 1 to 2 days to identify that it is a benign
sector.
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