FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
5 AND
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
10 (See section 10; rule 13)
1. TITLE OF THE INVENTION :
WIND TURBINE AND METHOD FOR CONTROLLING A WIND TURBINE
15
2. APPLICANT :
(a) Name : Suzlon Energy Ltd.
(b) Nationality : Indian
20 (c) Address : Shrimali Society, Near Shri Krishna
Complex, Navrangpura, Ahmedabad 380
009, Gujarat, India
3. PREAMBLE TO THE DESCRIPTION:
25
The following specification particularly describes the invention and the manner in
which it is to be performed.
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Wind Turbine and Method for Controlling a Wind Turbine
5 The invention relates to a wind turbine according to the preamble cf claim 1 and to a method
for controlling a wind turbine according to the preamble of claim 13.
Such a wind turbine comprises a rotor being rotatable by wind, and a generator operatively
coupled to the rotor for generating electrical power trom the motive power cf the rotor. The
10 generator has at least ane electrical output for providing at least part of the generated
electrical power by providing electrical current. The wind turbine further comprises a
converter unit. The converter has an electrical input and an electrical output. The input cf the
converter unit is coupled to the output cf the generator, e.g. via a rotor circuit. The converter
unit is adapted for converting the electrical current provided by the generator, e.g. by
15 modifying the frequency, strength and/or voltage of the current, and providing the converted
electrical current directly or indirectly to an extern al electrical grid. The wind turbine further
comprises an additional energy source.
EP 2 306 001 A2 describes a wind turbine having an additional energy source in the form of
20 an energy storage. The energy storage is coupled either to a oe link of a converter, or to the
electrical grid.
In an electrical grid, power generation and load have to be balanced for maintaining stability
of the grid. One aspect in the grid stability is frequency stability. Frequency stability
25 represents the balancing response of power generation to the demanding characteristics of
the load. A balance between generation and load can result in a substantially constant value
of frequency, reflecting the normal operating conditions of the grid.
Referring to Fig. 4, und er normal conditions, the frequency (shown per unit, p.u. for
30 simplicity) is within a standard frequency range (SFR) around a nominal value, e.g. 50 Hz. A
balance between power generation and power consumption in the electrical grid results in a
value of frequency within the standard frequency range. This situation may change in case of
a grid fault or disturbance, e.g . in the case when one or more power generation units (e.g.
power plants) stop providing power, in particular when said generation units have an installed
35 capacity in the hundred-MW range. Such a fault may cause the frequency of the electrical
grid to experience high excursions with an increased rate of change in an under-frequency
region. The rate of change of frequency along with the entire frequency deviation is
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moderated down to a nadir by the cumulative inertia cf all generating units in the power
system. Damping may be provided by the inertia cf rotating masses cf synchronous
generators in conventional power plants.
5 Ouring a transient condition cf a grid disturbance, which causes the frequency cf the
electrical grid to deviate from its standard frequency range, the energy stored in the rotating
masses is synchronously released by all generators in a time range cf several seconds
within an inertial response (IR).
10 This is followed up by a recovery period, which normally includes an action cf conventional
power plants to restore the balance between power generation and load, and bring back the
frequency, e.g. by adjusting a speed of one or more generators, within its standard frequency
range.
15 The frequency restoration or recovery may be divided into a primary frequency control (PFC)
region or phase which is active, e.g., within the first seconds after the frequency drop. In the
case the reserves activated by PFC are not enough to restore the frequency, so called
secondary frequency control (SFC) mechanisms are deployed, e.g. by increasing power
generation by means of power plants that do not participate in the primary control.
20 Secondary frequency control may be active within the first minutes or half hour after the
disturbance.
With the increasing impact of renewable energy sources, in particular wind turbines, grid
code requirements become more and more demanding. The grid code serves to maintain
25 grid stability, e.g. by specifying a required behavior of a connected wind turbine when facing
disturbances in the grid.
30
It is an object of the present invention to provide an improved wind turbine and an improved
method for controlling a wind turbine which may fulfil demanding grid code requirements.
This object is solved by a wind turbine according to claim 1.
Accordingly, the additional energy source is electrically coupled to the input of the converter
unit for transmitting electrical power between the additional energy source and the input of
35 the converter unit.
By connecting the additional energy source to the rotor circuit, the inertial response behavior
of the wind turbine when facing a grid disturbance is improved. This is achievable by
releasing energy stored in the additional energy source into the electrical grid, e.g. in
5
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response to a detection cf the grid disturbance. Transmitting the energy via the rotor circuit
allow5 an efficient use cf the converter unit cf the wind turbine, in particular without
substantial modifications cf the converter unit. Therefore, the wind turbine may fulfil
demanding grid code requirements in a particularly effective mann er.
The generator may be a double fed induction generator (DFIG). Double fed induction
generators conventionally comprise astator circuit and a rotor circuit. The stator circuit may
be connected to the electrical grid, B.g. without an intermediate converter. The rotor circuit
may be connected (e.g. via slip-rings) to the converter unit cf the wind turbine. A double ted
10 induction generator allows to control the rotor voltage and/or current by controlling the
converter unit. Therefore, the double fed induetion generator may be kept synehronized with
the eleetrical grid while the wind turbine speed varies, thus increasing the wind turbine
effieieney. Using a double fed induetion generator may allow to use partial sealed eonverters.
Alternatively, the generator is another type of induction generator. The converter unit may
15 alternatively also be eonneeted with astator eireuit of (any type of) the generator.
The eonverter unit may eomprise a rotor-side converter and/or a grid-side eonverter. The
rotor-side converter and the grid-side converter may be connected with eaeh other via a OC
link. The rotor-side eonverter and/or grid-side eonverter may eomprise an AC input or AC
20 output. For an inereased efficiency, the converter unit, in particular the rotor-side converter
and/or the grid-side eonverter may be eontrollable, e.g. for adjusting a voltage, eurrent and/or
frequency at the output of the converter unit
The rotor-side eonverter may be an AC-to-OC eonverter. An AC input of the rotor-side
25 eonverter may serve as the input of the eonverter unit. The grid-side eonverter may be a OCto-
AC converter. An AC output of the grid-side converter may be connected to the electrical
grid, e.g. via a transformer. A OC output of the rotor-side eonverter may be eleetrieally
eoupled to a OC input of the grid-side eonverter, forming the OC link.
30 The additional energy souree may comprise a eonverter (an additional eonverter). An AC
output and/or input of the eonverter of the additional energy source may be electrieally
eonneeted to the AC input of the eonverter unit and/or to an AC output of the generator. The
converter of the additional energy source may be a bidirectional converter. The converter of
the additional energy souree may serve as an extra rotor-side eonverter. In this way, the
35 additional energy souree may effieiently provide and/or receive electrical power from the
generator.
- 4 - SLE1091N
The converter of the additional energy souree may be a Oe-ta-AC converter. By this a oe
Gurrent provided by the additional energy souree may be converted to an AC Gurrent and
provided to the converter unit (and, optionally, vice versal.
5 The additional energy souree may comprise a power storage unit for storing power for an
autonomous operation.
The power storage unit can comprise cr consist cf a battery, a supercapacitor and/or a
f1ywheel. Supercapacitors (also referred to as ultra-caps) have the advantage cf a
10 comparably quick response. Flywheels may operate at wide temperature ranges, have a long
life span and need little maintenance.
15
The output of the generator is electrically coupled to the input of the converter unit via a
circuit, e.g. the rotor circuit. The circuit may be a three-phase circuit.
The input of the converter unit is an AC input for recei ving AC current from the generator, in
particular from a rotor of the generator.
The wind turbine may further comprise a wind turbine generator controller (WTG controller).
20 The wind turbine generator controller may control the operation of the wind turbine, in
particular of a converter controller and the additional energy source. The wind turbine
generator controller may be adapted for monitoring a condition parameter of the electrical
grid. Based on the monitored condition parameter, the wind turbine generator controller may
control the additional energy source to provide electrical current to the input of the converter
25 unit and/or to receive electrical current from the generator.
Said condition parameter may particularly be a grid frequency or a grid voltage. A deviation
from a predefined nominal frequency and/or voltage may be detected by the wind turbine
generator controller. In response to this detection, the wind turbine generator controller may
30 command the additional energy source to provide energy to the converter unit and/or to
adjust a frequency, voltage and/or current provided by the converter of the additional energy
source.
The object is also solved by a method for controlling a wind turbine, in particular a wind
35 turbine according to any aspect or embodiment described herein, the method comprising the
steps of:
Generating electrical power by means of a generator mechanically coupled to a rotor of the
wind turbine; and providing the electrical power from the generator to an input of a converter
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unit. The converter unit converts the electrical power (e.g. by modifying a vortage, frequency
and/or current) from the generator and provides the converted electrical power at an output
to an electrical grid. Therein , the further step cf transmitting electrical power between an
additional energy souree and the input cf the converter unit is provided, the additional energy
5 souree belng electrically coupled to the input cf the converter unit.
The method may have the same advantages as the wind turbine described above, so
reference is made thereto.
10 The method may further comprise the step cf monitoring a condition parameter of the
electrical grid, and commanding the additional energy souree to provide electrical power to
the input of the converter unit based on the condition parameter.
15
20
25
30
The condition parameter may be a grid frequency or a grid voltage.
The steps of the method may be performed in the order as described, or they may be
performed in another order.
Embodiments of the invention are shown in the figures, where
Fig. 1
Fig. 2
Fig. 3
Fig. 4
shows a schematic view of a wind turbine with a tower, a nacelle and a
rotor;
shows a block diagram of various components of the wind turbine
according to Fig. 1;
shows a method for controlling a wind turbine; and
shows a frequency disturbance in an electrical grid and measures for
recovering the nominal frequency against time.
Fig. 1 shows a wind turbine 1 for generating electrical energy by rotation of a rotor 12 by
means of wind. The rotor 12 is mounted at a naeelle 11 arranged at an upper end 100 of a
tower 10 of the wind turbine 1. The tower 10 extends between its upper end 100 and a
35 foundation 101 at the ground. The tower 10 is elongate and has a longitudinal axis. The rotor
12 comprises several , in the present case three blades 121 mounted on a hub 120. The rotor
12 is rotatable around a rotor axis X with respeet to the naeelle 11 . The rotor blades 121 ean
be revolved within a rotor plane. In use, the rotor axis X is oriented substantially horizontally.
- 6 - SLE1091N
For an efficient extraction cf wind energy, the rotor 12 is oriented towards the wind. In
particular, the rotor plane is oriented perpendicular to the direction cf the incoming wind. For
this purpose, the naeelle 11 together with the rotor 12 is rotatable around a yaw axis Z with
respect to the tower 10. The yaw axis Z corresponds to the longitudinal axis cf the tower 10.
5 The yaw axis Z is substantially perpendicular to the rotor axis X.
10
15
The wind turbine 1 produces electrical power and provides the etectrical power to an
electrical grid. A plurality cf wind turbines 1 can be grouped into wind power parks and used
for bulk power production.
Since more and more wind turbines are deployed in the electrical grid and contribute to an
increasing share in the total generated energy, there is a need for wind turbine generators to
provide a contribution to the inertial response in accordance with specifications provided by
the grid code.
For this purpose, the wind turbine 1 according to Fig. 1 comprises an additional energy
source, as will be described in detail with reference to Fig. 2 below.
According to Fig. 2, the wind turbine 1 comprises a wind turbine generator 14 that transforms
20 mechanical power of the wind into electrical power and provides it to the electrical grid 2. For
this purpose, the generator 14 is mechanically coupled to the rotor 12 of the wind turbine 1
(via an option al gearbox 13). When the rotor 12 is rotated by the wind, a wind turbine torque
Twt is applied to the generator 14.
25 The wind turbine 1 may generally comprise a full size converter (FSC), which rectifies the
entire power produced by the generator 14 and inverts and/or injects it into the electrical grid
2, or a partial scale converter (PSC) , in particular for a use with a double fed induction
generator.
30 In the present example, the generator 14 of the wind turbine 1 is a double fed induction
generator. The generator 14 has a rotor output 140 providing electrical power from a rotor of
the generator 14. The generator 14 further has a stator output 141 providing electrical power
from a stator of the generator 14. 80th outputs 140,141 provide three-phase currents.
35 The stator output 141 of the generator 14 is connected to the electrical grid 2 by means of a
stator circuit 171 . The stator circuit 171 may be interrupted by an optional switch. Other wind
turbine generators may be connected to the stator circuit 171 via corresponding connectors
L 1, L2, L3. The stator circuit 171 is connected to the electrical grid 2 via a transformer 19 for
- 7 - SLE1091N
adjusting a voltage of the supplied electrical energy. Alternatively, no transformer 19 is
provided and the stator circuit 171 is directly coupled to the electrical grid 2.
The rotor output 140 of the generator 14 is connected to the electrical grid 2 by means of a
5 rotor circuit 170 and via a converter unit 15. The rotor circuit 170 electricatly connects the
rotor output 140 with an input 154 of the converter unit 15. The rotor circuit 170 is a threephase
circuit. The converter unit 15 may be utilized for maximum power production, impartial
to utility grid transient conditions. In the present example, the converter unit 15 is a partial
seale converter what may reduce the cost of the converter unit 15 when compared to a full
10 size converter.
The converter unit 15 converts electrical power provided at its input 154 by the generator 14
and provides it at an output 155. The output 155 of the converter unit 15 is electrically
connected with the stator circuit 171 via an optional filter 153, e.g. for reducing high-
15 frequency components in the current provided by the generator unit 15, and an optional
switch.
The converter unit 15 comprises a rotor-side converter 150 and a grid-side converter 151.
The rotor-side converter 150 is an AC-to-OC converter. The rotor-side converter 150 has an
20 alternating-current (AC) input that is adapted to receive alternating current from the rotor
output 140 of the generator 14. The AC input of the rotor-side converter 150 forms the (AC)
input 154 of the converter unit 15. The rotor-side converter 150 is adapted to convert the
alternating current provided at the input 154 to direct current (OC) and provide the direct
current at a OC output.
25
The DC output 01 the rotor-side converter 150 is electrically connected to a DC input 01 the
grid-side converter 151. The electrical connection of the rotor-side converter 150 with the
grid-side converter 151 forms a OC link. Optional capacitors 152 in the OC link, in particular
between two poles of the OC link, may filter possible AC components in the direct current
30 provided by the rotor-side converter 150.
The grid-side converter 151 is a OC-to-AC converter. It is adapted to convert direct current
provided at its OC input (via the OC link) into alternating current and provide the alternating
current at an AC output. The AC output of the grid-side converter 151 forms the (AC) output
35 155 of the converter unit 15.
A converter controller 161 controls the converter unit 15. For example, the converter
controller 161 may receive instructions by an external control of the electrical grid 2 or by a
wind turbine generator controller 160 of the wind turbine 1. Oepending on a condition
- 8 - SLE1091N
parameter, 8.g. a frequency, cf the electrical grid 2, the converter controller 161 adjusts the
converter unit 15. The adjusting may comprise an adjustment cf an amplitude cf the Gurrent
provided at the output 155.
5 For the case cf a grid frequency disturbance, the converter controller 161 may be adapted to
adjust the amplitude cf the Gurrent provided at the output 155 tor bringing the frequency back
to it5 nominal value. As power production cf the wind turbine 1 is coupled to the wind speed,
power provided by the generator cannat easily be increased tor contributing to the balance
between power generation and load in the electrical grid 2.
10
Therefore, the wind turbine 1 comprises an additional energy souree 18. The additional
energy source 18 may provide additional power when needed for balaneing the eleetrieal
grid 2.
15 Aeeording to Fig. 2, the additional energy source 18 is eleetrically eonneeted to the rotor
cireuit 170. Therefore, the additional energy souree 18 may provide eleetrieal power to the
input 154 of the eonverter unit 15 via the rator eireuit 170.
In ease of a grid disturbanee, the additional energy souree 18 may provide additional
20 eleetrieal power to the eonverter unit 15 as if the wind speed would have been inereased for
praviding additional power to the grid. Therefore, by using the eonverter 180 of the additional
energy souree 18 as a supplementary rotor-side eonverter, the inertial response of the
generator 14 may be improved.
25 On the other hand, the additional energy souree 18 mayaiso reeeive eleetrieal power fram
the rotor output 140 ot the generator 14, e.g. when there is too much wind energy tor the
eleetrieal grid 2 to aeeept. In this way, exeess energy may be buffe red by means of the
additional energy source 18 and pravided at a later stage when the load in the eleetrieal grid
2 exeeeds the power generation. For this purpose, the eonverter 180 of the additional energy
30 souree 18 may be a bidireetional eonverter.
This arrangement of the additional energy souree has several advantages. The eontral of the
eonverter unit 15 may be kept simple. No major modifieations of the setup of the wind turbine
1, in particular of the eonverter unit 15 (e.g. its eontrals and its arehiteeture), have to be done
35 with respeet to a wind turbine without an additional energy souree. Existing wind turbines
may be equipped with the additional energy souree 18.
The additional energy souree 18 eomprises a power storage unit 181 . The power storage unit
181 is adapted to store power. For example, the power storage unit 181 eomprises a battery,
- 9 - SLE1091N
a flywheel , a supercapacitor, cr a combination thereof. The power storage unit 181 is
electrically connected to a converter 180 cf the additional energy souree 18 via a oe link.
The converter 180 cf the additional energy souree 18 is provided in addition to and may be
arranged separated fram the converter unit 15. The converter 180 cf the additional energy
5 souree 18 has a three-phase AC output that is connected with the rotor circuit 170.
The wind turbine generator controller 160 controls the additional energy souree 18, 9.g.
whether it provides cr receives power, and how much. The wind turbine generator controller
160 also controls the converter controller 161 . In particular, the wind turbine generator
10 controller 160 may measure and/or monitor a condition parameter, in particular a grid
frequency and/or a grid voltage, of the electrical grid 2. Alternatively or additionally, the wind
turbine generator controller 160 may receive a control message from a controller of the
electrical grid 2, in particular a required rate of change of frequency (ROCOF) and/or a
steady-state deviation , and control the additional energy source in dependence of the control
15 message (in particular a voltage, a current and/or an amount of transferred power).
Oepending on the condition parameter, the wind turbine generator controller 160 may control
the wind turbine 1 to provide an additional power reference. In particular, the wind turbine
generator controller 160 may control the additional energy source 18 to provide electrical
20 power to the AC input 154 of the converter unit 15 or to receive and store energy from the
generator 14. The wind turbine generator controller 160 may alternatively or in addition
command the converter controller 161 to control the converter unit 15 to adjust the electrical
power provided at the AC output 155 of the converter unit 15, e.g. a voltage, frequency
and/or current.
25
The eonverler unit 15 and/or the additional energy souree 18 may be loeated within the
nacelle 11 or tower 10 of the wind turbine 1, or outside thereof, e.g. in aseparate building.
Fig. 3 shows a method for controlling a wind turbine, in particular the wind turbine 1
30 according to Fig. 1 and 2. The method comprises the following steps:
35
At step 8100, electrical power is generated by means of a generator 14 (directly or indirectly,
e.g. via a gearbox) mechanically coupled to a rotor 12 of the wind turbine 1, the rotor having
rotor blades 121 .
At step 8101 , the electrical power from the generator 14 is provided to an AC input 154 of a
converter unit 15. The con verter unit 15 converts the electrical power from the generator 14
and provides the converted electrical power at an AC output 155 of the converter unit 15 to
an electrical grid 2 (directly or indirectly, e.g. via a transformer).
5
- 10 - SLE1091N
At step 8103, additional electrical power is transmitted between an additional energy souree
18 and said AC input 154 of the converter unit 15. The additional energy souree 18 is
electrically coupled to the input 154 cf the converter unit 15.
In this way, energy from the additional energy souree 18 may be used for stabilizing the
electrical grid 2 in a particularly easy way and to fulfil demanding grid code requirements in a
simple manner.
10 At an optional step 8102, a condition parameter of the electrical grid 2 is monitored. The
additional energy souree 18 may be instructed to provide electrical power to the input 154 of
the converter unit 15 based on the condition parameter. Alternatively, the additional energy
source 18 may be instructed to receive electrical power from the generator 14 based on the
condition parameter. The condition parameter is, for example, a grid frequency or a grid
15 voltage. For example, the additional energy source 18 may be instructed to provide electrical
power to the input 154 of the converter unit 15 when the grid frequency is below a predefined
standard frequency range of the electrical grid. When the grid frequency is above the
standard frequency range of the electrical grid , the additional energy source 18 may be
instructed to receive electrical power from the generator 14 and store it in the power storage
20 unit. When the condition parameter is within a predefined range, e.g. when the grid
frequency is within the standard frequency range, it may be provided that in step 8102 the
additional energy source is not instructed to receive or provide electrical power, or it may be
instructed to not receive and provide any electrical power.
25 8tep 8102 may be performed before performing step 8103.
8tep 8102 may be repeated until the condition parameter is outside of a predefined range,
e.g. when the grid frequency is above or below the standard frequency range.
30 üptionally, the wind turbine generator controller 160 and the additional energy source 18 are
adapted to damp power oscillations of the wind turbine generator 14 and/or of other
generators in the electrical grid 2.
As another option, the wind turbine generator controller 160 and the additional energy source
35 18 may be adapted to provide power during a black start sequence.
The power oscillations and/or a black start may be detected by the wind turbine generator
controller 160 and/or may be communicated to the wind turbine generator controller 160 by a
controller of the electrical grid 2.
- 11 - SLE1091N
List of Reference Numbers
1 wind turbine
10 tower
5 100 upper end
101 foundation
11 nacelle
12 rotor
120 hub
10 121 blade
13 gearbox
14 generator
140 rotor output
141 stator output
15 15 converter unit
150 rotor-side converter
151 grid-side converter
152 capacitor
153 filter
20 154 input
155 output
160 wind turbine generator controller
161 converter controller
170 rotor circuit
25 171 stator circuit
18 additional energy source
180 converter
181 power storage unit
19 transformer
30 2 electrical grid
X rotor axis
Z yawaxis
5
10
15
- 12 - SLE1091N
Patent Claims
1. A wind turbine (1), comprising
a rotor (12),
a generator (14) mechanically coupled to the rotor (12) for generating electrical
power, the generator (14) having at least ane output (140) for providing the electrical
power,
a converter unit (15) having an input (154) and an output (155), the input (154) being
electrically coupled to the output (140) of the generator (14), the converter unit (15)
being adapted for converting the electrical power from the generator (14) and
providing the converted electrical power at the output (155) to an electrical grid (2),
and
an additional energy souree (18),
characterized in that
the additional energy souree (18) is electrically coupled to the input (154) of the
converter unit (15) for transmitting electrical power between the additional energy source
20 (18) and the input (154) ofthe converter unit (15).
2. The wind turbine (1) according to claim 1, wherein the generator (14) is a double fed
induction generator.
25 3. The wind turbine (1) according to claim 1 or 2 , wherein the converter unit (15) comprises
a rotor-side converter (150) and a grid-side converter (151).
4. The wind turbine (1) according to claim 3, wherein the rotor-side converter (150) is an
AC-to-Oe converter and provides the input (154) of the converter unit (15), and the grid-
30 side converter (151) is a OC-to-AC converter, a OC output of the rotor-side converter
(150) being electrically coupled to a oe input of the grid-side converter (151).
35
5. The wind turbine (1) according to any of the preceding claims, wherein the additional
energy source (18) comprises a converter (180), in particular a bidirectional converter.
6. The wind turbine (1) according to claim 5, wherein the converter (180) is a OC-to-AC
converter.
7. The wind turbine (1) according to any of the preceding claims, wherein the additional
40 energy source (18) comprises a power storage unit (181) for storing power.
- 13 - SLE1091N
8. The wind turbine (1) according to claim 7, wherein the power storage unit (181)
comprises a battery, a supercapacitor and/or a flywheel.
9. The wind turbine (1) according to any ofthe preceding claims, wherein the output (140)
5 cf the generator (14) is electrically coupled to the input (154) cf the converter unit (15)
via a fotor circuit (170).
10
10. The wind turbine (1) according to any cf the preceding claims, wherein the input (154) cf
the converter unit (15) is an AC input.
11 . The wind turbine (1) according to any cf the preceding claims, further comprising a wind
turbine generator controller (160) adapted for monitoring a condition parameter cf the
electrical grid (2), and for commanding the additional energy source (18) to provide
electrical power to the input (154) of the converter unit (15) based on the condition
15 parameter.
12. The wind turbine (1) according to claim 11, wherein the condition parameter is a grid
frequency or a grid voltage.
20 13. Method for controlling a wind turbine, in particular a wind turbine (1) according to any of
25
the preceding claims, comprising the steps of:
generating (S100) electrical power by means of a generator (14) mechanically
eoupled to arotor (12) of the wind turbine (1); and
providing (S101) the electrical power from the generator (14) to an input (154) of a
converter unit (15) , the converter unit (15) being adapted for converting the electrical
power from the generator (14) and providing the converted electrical power at an
output (155) to an eleetrieal grid (2);
30 characterized by
35
40
transmitting (S103) electrical power between an additional energy source (18) and
the input (154) of the converter unit (15), the additional energy souree (18) being
electrically coupled to the input (154) of the converter unit (15).
14. Method according to claim 13, further comprising the step of monitoring (S102) a
condition parameter of the electrical grid (2) , and commanding the additional energy
source (18) to provide electrical power to the input (154) of the converter unit (15) based
on the condition parameter.
15. Method according to claim 14, wherein the condition parameter is a grid frequency or a
grid voltage.