U.S. patent application number 16/419364 was filed with the patent office on 2020-11-26 for system and method for mitigating flicker in a power grid from a wind turbine power system.
The applicant listed for this patent is General Electric Company. Invention is credited to Werner Gerhard Barton, David Smith.
Application Number | 20200370536 16/419364 |
Document ID | / |
Family ID | 1000004139874 |
Filed Date | 2020-11-26 |
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United States Patent
Application |
20200370536 |
Kind Code |
A1 |
Smith; David ; et
al. |
November 26, 2020 |
SYSTEM AND METHOD FOR MITIGATING FLICKER IN A POWER GRID FROM A
WIND TURBINE POWER SYSTEM
Abstract
A method for compensating for flicker induced by a wind turbine
power system connected to a power grid includes operating a power
converter of the wind turbine power system based on a nominal
reactive current command and a nominal torque command. In response
to receiving a periodic torque command modifier, the method
includes determining a reactive current command modifier for the
power converter based on one or more operational parameters of the
wind turbine power system and/or the power grid and the torque
command modifier. The method also includes simultaneously modifying
the nominal reactive current command as a function of the reactive
current command modifier and the nominal torque command as a
function of the torque command modifier. Accordingly, modifying the
nominal torque command causes low-frequency voltage variations in
the power grid and simultaneously modifying the reactive current
command attenuates the low-frequency voltage variations.
Inventors: |
Smith; David; (Daleville,
VA) ; Barton; Werner Gerhard; (Gescher, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
General Electric Company |
Schenectady |
NY |
US |
|
|
Family ID: |
1000004139874 |
Appl. No.: |
16/419364 |
Filed: |
May 22, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F03D 7/028 20130101;
F03D 17/00 20160501; F03D 7/042 20130101; F03D 7/0272 20130101;
F03D 9/25 20160501 |
International
Class: |
F03D 7/04 20060101
F03D007/04; F03D 9/25 20060101 F03D009/25; F03D 17/00 20060101
F03D017/00; F03D 7/02 20060101 F03D007/02 |
Claims
1. A method for compensating for flicker induced by a wind turbine
power system connected to a power grid, the method comprising:
operating, via a controller, a power converter of the wind turbine
power system based on a nominal reactive current command and a
nominal torque command; in response to receiving a periodic torque
command modifier, determining, via the controller, a reactive
current command modifier for the power converter based on one or
more operational parameters of the wind turbine power system and/or
the power grid and a nominal torque command modifier;
simultaneously modifying, via the controller, the nominal reactive
current command as a function of the reactive current command
modifier and the nominal torque command as a function of the
nominal torque command modifier, wherein modifying the nominal
torque command causes low-frequency voltage variations in the power
grid and simultaneously modifying the nominal reactive current
command attenuates the low-frequency voltage variations,
correlating, via the controller, the periodic torque command
modifier with the one or more operational parameters as one or more
rotor blades passes a tower of the wind turbine power system and
simultaneously modifying the nominal reactive current command as a
function of the reactive current command modifier based on the
correlation.
2. The method of claim 1, wherein the one or more operational
parameters comprises at least one of a grid strength of the power
grid, a grid voltage, a voltage signal from a primary winding of a
main transformer of the wind turbine power system, a voltage signal
from a secondary winding of the main transformer, a speed signal
from a generator of the wind turbine power system, or an upstream
impedance from the wind turbine power system.
3. The method of claim 2, wherein the controller is a converter
controller of the power converter.
4. The method of claim 1, further comprising determining the
nominal reactive current command via a reactive power (VAR)
regulator module in the converter controller.
5. (canceled)
6. The method of claim 4, wherein determining the reactive current
command modifier for the power converter based on one or more
operational parameters of the wind turbine power system and/or the
power grid and the nominal torque command modifier further
comprises: determining a power command modifier as a function of
the periodic torque command modifier and the speed signal from the
generator.
7. The method of claim 6, wherein determining the reactive current
command modifier for the power converter based on one or more
operational parameters of the wind turbine power system and/or the
power grid and the nominal torque command modifier further
comprises: receiving the voltage signal from a primary winding of
the main transformer; filtering the voltage signal via a filter;
multiplying the filtered voltage signal by the power command
modifier to obtain a multiplied signal; integrating the multiplied
signal to obtain an integrated signal; multiplying the integrated
signal by the power command modifier to obtain a reactive power
command modifier; dividing the reactive power command modifier by
the voltage signal from the secondary winding of the main
transformer to obtain the reactive current command modifier.
8. The method of claim 7, wherein the filter is a high-pass
filter.
9. The method of claim 8, wherein simultaneously modifying the
nominal reactive current command as a function of the reactive
current command modifier and the nominal torque command as a
function of the torque command modifier further comprises: adding
the nominal reactive current command from the reactive power
regulator and the reactive current command modifier; and adding the
nominal torque command and the torque command modifier.
10. A wind turbine power system connected to a power grid,
comprising: a power converter; at least one sensor for monitoring
one or more operational parameters of at least one of the wind
turbine power system or the power grid; and, a converter controller
configured to control the power converter, the converter controller
configured to perform a plurality of operations, the plurality of
operations comprising: operating the power converter based on a
nominal reactive current command and a nominal torque command; in
response to receiving a periodic torque command modifier,
determining a reactive current command modifier for the power
converter based on the one or more operational parameters and/or
the power grid and a torque command modifier; and, simultaneously
modifying the nominal reactive current command as a function of the
reactive current command modifier and the nominal torque command as
a function of the torque command modifier, wherein modifying the
nominal torque command causes low-frequency voltage variations in
the power grid and simultaneously modifying the nominal reactive
current command attenuates the low-frequency voltage variations,
correlating the periodic torque command modifier with the one or
more operational parameters as one or more rotor blades passes a
tower of the wind turbine power system and simultaneously modifying
the nominal reactive current command as a function of the reactive
current command modifier based on the correlation.
11. The wind turbine power system of claim 10, wherein the one or
more operational parameters comprises at least one of a grid
strength of the power grid, a grid voltage, a voltage signal from a
primary winding of a main transformer of the wind turbine power
system, a voltage signal from a secondary winding of the main
transformer, a speed signal from a generator of the wind turbine
power system, or an upstream impedance from the wind turbine power
system.
12. The wind turbine power system of claim 11, wherein the
generator comprises a doubly-fed induction generator (DFIG).
13. (canceled)
14. The wind turbine power system of claim 11, further comprising a
turbine controller communicatively coupled to the converter
controller, the turbine controller configured to perform a
plurality of operations, comprising: determining a power command
modifier as a function of the periodic torque command modifier and
the speed signal from the generator.
15. The wind turbine power system of claim 14, wherein determining
the reactive current command modifier for the power converter based
on the one or more operational parameters and/or the power grid and
the torque command modifier further comprises: receiving the
voltage signal from a primary winding of the main transformer;
filtering the voltage signal via a filter; multiplying the filtered
voltage signal by the power command modifier to obtain a multiplied
signal; integrating the multiplied signal to obtain an integrated
signal; multiplying the integrated signal by the power command
modifier to obtain a reactive power command modifier; dividing the
reactive power command modifier by the voltage signal from the
secondary winding of the main transformer to obtain the reactive
current command modifier.
16. The wind turbine power system of claim 15, wherein the filter
is a high-pass filter.
17. The wind turbine power system of claim 15, further comprising
determining the nominal reactive current command via a reactive
power (VAR) regulator module.
18. The wind turbine power system of claim 17, wherein
simultaneously modifying the nominal reactive current command as a
function of the reactive current command modifier and the nominal
torque command as a function of the torque command modifier further
comprises: adding the nominal reactive current command from the
reactive power regulator and the reactive current command modifier;
and adding the nominal torque command and the torque command
modifier.
19. A method for mitigating low-frequency voltage variations in a
power grid caused by a wind turbine power system connected thereto,
the method comprising: receiving, via a controller, one or more
operational parameters of at least one of the wind turbine power
system or the power grid and a nominal torque command modifier;
and, modifying, via the controller, a reactive current command of
the wind turbine power system as a function of the one or more
operational parameters and the nominal torque command modifier
while simultaneously modifying a torque command of the power
converter based on the nominal torque command modifier,
correlating, via the controller, the periodic torque command
modifier with the one or more operational parameters as one or more
rotor blades passes a tower of the wind turbine power system and
simultaneously modifying the nominal reactive current command as a
function of the reactive current command modifier based on the
correlation.
20. The method of claim 19, wherein the one or more operational
parameters comprises at least one of a grid strength of the power
grid, a grid voltage, a voltage signal from a primary winding of a
main transformer of the wind turbine power system, a voltage signal
from a secondary winding of the main transformer, a speed signal
from a generator of the wind turbine power system, or an upstream
impedance from the wind turbine power system.
Description
FIELD
[0001] The present disclosure relates generally to wind turbines
and, more particularly, to a system and method for mitigating
flicker in a power grid caused by, for example, a changing torque
command of the wind turbine as each rotor blade passes the tower
thereof.
BACKGROUND
[0002] Wind power is considered one of the cleanest, most
environmentally friendly energy sources presently available, and
wind turbines have gained increased attention in this regard. A
modern wind turbine typically includes a tower, generator, gearbox,
nacelle, and one or more rotor blades. The rotor blades capture
kinetic energy of wind using known airfoil principles. For example,
rotor blades typically have the cross-sectional profile of an
airfoil such that, during operation, air flows over the blade
producing a pressure difference between the sides. Consequently, a
lift force, which is directed from a pressure side towards a
suction side, acts on the blade. The lift force generates torque on
the main rotor shaft, which is geared to a generator for producing
electricity.
[0003] In many wind turbines, the generator may be electrically
coupled to a bi-directional power converter that includes a
rotor-side converter joined to a line-side converter via a
regulated DC link. Such wind turbine power systems are generally
referred to as a doubly-fed induction generator (DFIG). DFIG
operation is typically characterized in that the rotor circuit is
supplied with current from a current-regulated power converter. As
such, the wind turbine produces variable mechanical torque due to
variable wind speeds and the power converter ensures this torque is
converted into an electrical output at the same frequency of the
grid.
[0004] During operation, wind impacts the rotor blades and the
blades transform wind energy into a mechanical rotational torque
that drives a low-speed shaft. The low-speed shaft is configured to
drive the gearbox that subsequently steps up the low rotational
speed of the low-speed shaft to drive a high-speed shaft at an
increased rotational speed. The high-speed shaft is generally
coupled to the generator so as to rotatably drive a generator
rotor. As such, a rotating magnetic field may be induced by the
generator rotor and a voltage may be induced within a generator
stator. Rotational energy is converted into electrical energy
through electromagnetic fields coupling the rotor and the stator,
which is supplied to a power grid via a grid breaker. Thus, the
main transformer steps up the voltage amplitude of the electrical
power such that the transformed electrical power may be further
transmitted to the power grid.
[0005] For some wind turbines, it is desirable to modify the torque
command of the power converter during operation of the wind turbine
as each rotor blade aligns with and passes the tower. This
modification, however, can tend to cause undesirable low-frequency
voltage variations on the power grid. Such variations are often
referred to as flicker. Thus, the term "flicker" as used herein
generally refers to variations in current or voltage on the power
grid that are perceptible at certain frequencies (e.g. from about 1
Hertz (Hz) to about 30 Hz). Oftentimes, grid requirements prohibit
connection to the power grid if flicker is present in a certain
amount.
[0006] Thus, the present disclosure is directed to a system and
method for compensating for such flicker to address the
aforementioned issues.
BRIEF DESCRIPTION
[0007] Aspects and advantages of the invention will be set forth in
part in the following description, or may be obvious from the
description, or may be learned through practice of the
invention.
[0008] In one aspect, the present disclosure is directed to a
method for compensating for flicker induced by a wind turbine power
system connected to a power grid. The method includes operating,
via a controller, a power converter of the wind turbine power
system based on a nominal reactive current command and a nominal
torque command. In response to receiving a periodic torque command
modifier, the method includes determining, via the controller, a
reactive current command modifier for the power converter based on
one or more operational parameters of the wind turbine power system
and/or the power grid and the torque command modifier. The method
also includes simultaneously modifying, via the controller, the
nominal reactive current command as a function of the reactive
current command modifier and the nominal torque command as a
function of the torque command modifier. Accordingly, modifying the
nominal torque command causes low-frequency voltage variations in
the power grid and simultaneously modifying the reactive current
command attenuates the low-frequency voltage variations.
[0009] In an embodiment, the operational parameter(s) may include
grid strength of the power grid, a grid voltage, a voltage signal
from a primary winding of a main transformer of the wind turbine
power system, a voltage signal from a secondary winding of the main
transformer, a speed signal from a generator of the wind turbine
power system, and/or an upstream impedance from the wind turbine
power system.
[0010] In another embodiment, the controller may be a converter
controller of the power converter. In an embodiment, the method may
also include determining the reactive current command via a
reactive power/VAR regulator module.
[0011] In further embodiments, the method may also include
correlating, via the converter controller, the periodic torque
command modifier with voltage variations as one or more rotor
blades passes the tower and simultaneously modifying the nominal
reactive current command as a function of the reactive current
command modifier based on the correlation.
[0012] In one embodiment, the method may include determining a
power command modifier as a function of the periodic torque command
modifier and the speed signal from the generator.
[0013] In several embodiments, determining the reactive current
command modifier for the power converter based on one or more
operational parameters of the wind turbine power system and/or the
power grid and the torque command modifier may include, for
example, receiving the voltage signal from a primary winding of the
main transformer, filtering the voltage signal via a filter (e.g. a
high-pass filter), multiplying the filtered voltage signal by the
power command modifier to obtain a multiplied signal, integrating
the multiplied signal to obtain an integrated signal, multiplying
the integrated signal by the power command modifier to obtain a
reactive power command modifier, and dividing the reactive power
command modifier by the voltage signal from the secondary winding
of the main transformer to obtain the reactive current command
modifier.
[0014] In another embodiment, simultaneously modifying, via the
controller, the nominal reactive current command as a function of
the reactive current command modifier and the nominal torque
command as a function of the torque command modifier may include
adding the nominal reactive current command from the reactive power
regulator and the reactive current command modifier and adding the
nominal torque command and the torque command modifier.
[0015] In another aspect, the present disclosure is directed to a
wind turbine power system connected to a power grid. The wind
turbine power system includes a power converter, at least one
sensor for monitoring one or more operational parameters of at
least one of the wind turbine power system or the power grid, and a
converter controller configured to control the power converter. The
converter controller is configured to perform a plurality of
operations, including but not limited to operating the power
converter based on a nominal reactive current command and a nominal
torque command, in response to receiving a periodic torque command
modifier, determining a reactive current command modifier for the
power converter based on the one or more operational parameters
and/or the power grid and the torque command modifier, and
simultaneously modifying the nominal reactive current command as a
function of the reactive current command modifier and the nominal
torque command as a function of the torque command modifier,
wherein modifying the nominal torque command causes low-frequency
voltage variations in the power grid and simultaneously modifying
the reactive current command attenuates the low-frequency voltage
variations. It should be understood that the wind turbine power
system may further include any of the additional features as
described herein.
[0016] In yet another aspect, the present disclosure is directed to
a method for mitigating low-frequency voltage variations in a power
grid caused by a wind turbine power system connected thereto. The
method includes receiving, via a controller, one or more
operational parameters of at least one of the wind turbine power
system or the power grid and a nominal torque command modifier. The
method also includes modifying, via the controller, a reactive
current command of the wind turbine power system as a function of
the one or more operational parameters and the nominal torque
command modifier while simultaneously modifying a torque command of
the power converter based on the nominal torque command modifier so
as to mitigate the low-frequency voltage variations. It should be
understood that the method may further include any of the
additional steps and/or features as described herein.
[0017] These and other features, aspects and advantages of the
present invention will become better understood with reference to
the following description and appended claims. The accompanying
drawings, which are incorporated in and constitute a part of this
specification, illustrate embodiments of the invention and,
together with the description, serve to explain the principles of
the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] A full and enabling disclosure of the present invention,
including the best mode thereof, directed to one of ordinary skill
in the art, is set forth in the specification, which makes
reference to the appended figures, in which:
[0019] FIG. 1 illustrates a perspective view of a portion of one
embodiment of a wind turbine according to the present
disclosure;
[0020] FIG. 2 illustrates a schematic view of one embodiment of an
electrical power system suitable for use with the wind turbine
shown in FIG. 1;
[0021] FIG. 3 illustrates a block diagram of one embodiment of a
controller suitable for use with the wind turbine shown in FIG.
1;
[0022] FIG. 4 illustrates a schematic diagram of one embodiment of
a power converter of a wind turbine according to the present
disclosure;
[0023] FIG. 5 illustrates a simplified, schematic diagram of one
embodiment of a system for compensating for flicker induced by a
wind turbine power system connected to a power grid according to
the present disclosure; and
[0024] FIG. 6 illustrates a detailed, schematic diagram of one
embodiment of a system for compensating for flicker induced by a
wind turbine power system connected to a power grid according to
the present disclosure.
DETAILED DESCRIPTION
[0025] Reference now will be made in detail to embodiments of the
invention, one or more examples of which are illustrated in the
drawings. Each example is provided by way of explanation of the
invention, not limitation of the invention. In fact, it will be
apparent to those skilled in the art that various modifications and
variations can be made in the present invention without departing
from the scope or spirit of the invention. For instance, features
illustrated or described as part of one embodiment can be used with
another embodiment to yield a still further embodiment. Thus, it is
intended that the present invention covers such modifications and
variations as come within the scope of the appended claims and
their equivalents.
[0026] Referring now to the drawings, FIG. 1 illustrates a
perspective view of a portion of one embodiment of a wind turbine
100 according to the present disclosure that is configured to
implement the method as described herein. The wind turbine 100
includes a nacelle 102 that typically houses a generator 118 (FIG.
2). The nacelle 102 is mounted on a tower 104 having any suitable
height that facilitates operation of wind turbine 100 as described
herein. The wind turbine 100 also includes a rotor 106 that
includes three blades 108 attached to a rotating hub 110.
Alternatively, the wind turbine 100 may include any number of
blades 108 that facilitates operation of the wind turbine 100 as
described herein.
[0027] Referring now to FIG. 2, a schematic view of one embodiment
of an electrical power system 200 that may be used with the wind
turbine 100 is illustrated. During operation, wind impacts the
blades 108 and the blades 108 transform wind energy into a
mechanical rotational torque that rotatably drives a low-speed
shaft 112 via the hub 110. The low-speed shaft 112 is configured to
drive a gearbox 114 that subsequently steps up the low rotational
speed of the low-speed shaft 112 to drive a high-speed shaft 116 at
an increased rotational speed. The high-speed shaft 116 is
generally rotatably coupled to a generator 118 so as to rotatably
drive a generator rotor 122 having field winding (not shown).
[0028] More specifically, in one embodiment, the generator 118 may
be a wound rotor, three-phase, doubly-fed induction (asynchronous)
generator (DFIG) that includes a generator stator 120 magnetically
coupled to a generator rotor 122. As such, a rotating magnetic
field may be induced by the generator rotor 122 and a voltage may
be induced within a generator stator 120 that is magnetically
coupled to the generator rotor 122. In such embodiments, the
generator 118 is configured to convert the rotational mechanical
energy to a sinusoidal, three-phase alternating current (AC)
electrical energy signal in the generator stator 120. The
associated electrical power can be transmitted to a main
transformer 234 via a stator bus 208, a stator synchronizing switch
206, a system bus 216, a main transformer circuit breaker 214, and
a generator-side bus 236. The main transformer 234 steps up the
voltage amplitude of the electrical power such that the transformed
electrical power may be further transmitted to a grid via a grid
circuit breaker 238, a breaker-side bus 240, and a grid bus
242.
[0029] In addition, the electrical power system 200 may include a
wind turbine controller 202 configured to control any of the
components of the wind turbine 100 and/or implement the method
steps as described herein. For example, as shown particularly in
FIG. 3, the controller 202 may include one or more processor(s) 204
and associated memory device(s) 207 configured to perform a variety
of computer-implemented functions (e.g., performing the methods,
steps, calculations and the like and storing relevant data as
disclosed herein). Additionally, the controller 202 may also
include a communications module 209 to facilitate communications
between the controller 202 and the various components of the wind
turbine 100, e.g. any of the components of FIG. 2.
[0030] Further, as shown in FIG. 3, the communications module 209
may include a sensor interface 211 (e.g., one or more
analog-to-digital converters) to permit signals transmitted from
one or more sensors to be converted into signals that can be
understood and processed by the processors 204. It should be
appreciated that the sensors (e.g. sensors 252, 254, 256, 258) may
be communicatively coupled to the communications module 209 using
any suitable means. For example, as shown in FIG. 3, the sensors
252, 254, 256, 258 may be coupled to the sensor interface 211 via a
wired connection. However, in other embodiments, the sensors 252,
254, 256, 258 may be coupled to the sensor interface 211 via a
wireless connection, such as by using any suitable wireless
communications protocol known in the art. As such, the processor
204 may be configured to receive one or more signals from the
sensors.
[0031] As used herein, the term "processor" refers not only to
integrated circuits referred to in the art as being included in a
computer, but also refers to a controller, a microcontroller, a
microcomputer, a programmable logic controller (PLC), an
application specific integrated circuit, and other programmable
circuits. The processor 204 is also configured to compute advanced
control algorithms and communicate to a variety of Ethernet or
serial-based protocols (Modbus, OPC, CAN, etc.). Additionally, the
memory device(s) 207 may generally comprise memory element(s)
including, but not limited to, computer readable medium (e.g.,
random access memory (RAM)), computer readable non-volatile medium
(e.g., a flash memory), a floppy disk, a compact disc-read only
memory (CD-ROM), a magneto-optical disk (MOD), a digital versatile
disc (DVD) and/or other suitable memory elements. Such memory
device(s) 207 may generally be configured to store suitable
computer-readable instructions that, when implemented by the
processor(s) 204, configure the controller 202 to perform the
various functions as described herein.
[0032] Referring back to FIG. 2, the generator stator 120 may be
electrically coupled to a stator synchronizing switch 206 via a
stator bus 208. In one embodiment, the generator rotor 122 may be
electrically coupled to a bi-directional power conversion assembly
210 or power converter via a rotor bus 212. Alternatively, the
generator rotor 122 may be electrically coupled to the rotor bus
212 via any other device that facilitates operation of electrical
power system 200 as described herein. In a further embodiment, the
stator synchronizing switch 206 may be electrically coupled to a
main transformer circuit breaker 214 via a system bus 216.
[0033] The power conversion assembly 210 may include a rotor filter
218 that is electrically coupled to the generator rotor 122 via the
rotor bus 212. In addition, the rotor filter 218 may include a
rotor-side reactor. A rotor filter bus 219 electrically couples the
rotor filter 218 to a rotor-side power converter 220. Further, the
rotor-side power converter 220 may be electrically coupled to a
line-side power converter 222 via a single direct current (DC) link
244. Alternatively, the rotor-side power converter 220 and the
line-side power converter 222 may be electrically coupled via
individual and separate DC links. In addition, as shown, the DC
link 244 may include a positive rail 246, a negative rail 248, and
at least one capacitor 250 coupled therebetween.
[0034] In addition, a line-side power converter bus 223 may
electrically couple the line-side power converter 222 to a line
filter 224. Also, a line bus 225 may electrically couple the line
filter 224 to a line contactor 226. In addition, the line filter
224 may include a line-side reactor. Moreover, the line contactor
226 may be electrically coupled to a conversion circuit breaker 228
via a conversion circuit breaker bus 230. In addition, the
conversion circuit breaker 228 may be electrically coupled to the
main transformer circuit breaker 214 via system bus 216 and a
connection bus 232. The main transformer circuit breaker 214 may be
electrically coupled to an electric power main transformer 234 via
a generator-side bus 236. The main transformer 234 may be
electrically coupled to a grid circuit breaker 238 via a
breaker-side bus 240. The grid circuit breaker 238 may be connected
to the electric power transmission and distribution grid via a grid
bus 242.
[0035] Referring particularly to FIGS. 2 and 4, alternating current
(AC) power generated at the generator stator 120 by rotation of the
rotor 106 is provided via a dual path to the grid bus 242. The dual
paths are defined by the stator bus 208 and the rotor bus 212. On
the rotor bus side 212, sinusoidal multi-phase (e.g. three-phase)
AC power is provided to the power conversion assembly 210. The
rotor-side power converter 220 converts the AC power provided from
the rotor bus 212 into DC power and provides the DC power to the DC
link 244. Switching elements 245 (e.g. diodes) used in bridge
circuits of the rotor side power converter 220 can be modulated to
convert the AC power provided from the rotor bus 212 into DC power
suitable for the DC link 244.
[0036] The line side converter 222 converts the DC power on the DC
link 244 into AC output power suitable for the electrical grid bus
242. In particular, switching elements 247 (e.g. IGBTs) used in
bridge circuits of the line side power converter 222 can be
modulated to convert the DC power on the DC link 244 into AC power
on the line side bus 225. The AC power from the power conversion
assembly 210 can be combined with the power from the stator 120 to
provide multi-phase power (e.g. three-phase power) having a
frequency maintained substantially at the frequency of the
electrical grid bus 242 (e.g. 50 Hz/60 Hz).
[0037] It should be understood that the rotor-side power converter
220 and the line-side power converter 222 may have any
configuration using any switching devices that facilitate operation
of electrical power system 200 as described herein. For example,
FIG. 4 illustrates a simplified schematic diagram of one embodiment
of a variable frequency drive (VFD) that maintains a constant
electrical frequency output on the grid side of the generator 118.
As shown, the VFD configuration includes a six-switch
voltage-sourced rectifier on the rotor side converter 220, the DC
link capacitor 250 to minimize DC voltage variation, and a
six-switch voltage-sourced inverter utilizing pulse width
modulation on the grid side. More specifically, as shown, the
rotor-side switching elements may be diodes 245 or
silicon-controlled rectifiers (SCR), while the grid side-switching
elements may be insulated gate bipolar transistors (IGBTs) 247. As
such, the magnitude and electrical frequency of the current
supplied to the generator rotor 122 through the VFD may be varied
to account for changes in the rotor shaft speed and to maintain a
constant output on the generator stator winding.
[0038] Further, the power conversion assembly 210 may be coupled in
electronic data communication with the turbine controller 202
and/or a separate or integral converter controller 262 (FIG. 2) to
control the operation of the rotor-side power converter 220 and the
line-side power converter 222. For example, during operation, the
controller 202 may be configured to receive one or more voltage
and/or electric current measurement signals from the first set of
voltage and electric current sensors 252. Thus, the controller 202
may be configured to monitor and control at least some of the
operational parameters associated with the wind turbine 100 via the
sensors 252. In the illustrated embodiment, each of the sensors 252
may be electrically coupled to each one of the three phases of the
power grid bus 242. Alternatively, the sensors 252 may be
electrically coupled to any portion of electrical power system 200
that facilitates operation of electrical power system 200 as
described herein. In addition to the sensors described above, the
sensors may also include a second set of voltage and electric
current sensors 254, a third set of voltage and electric current
sensors 256, a fourth set of voltage and electric current sensors
258 (all shown in FIG. 2), and/or any other suitable sensors.
[0039] It should also be understood that any number or type of
voltage and/or electric current sensors 252, 254, 256, 258 may be
employed within the wind turbine 100 and at any location. For
example, the sensors may be current transformers, shunt sensors,
rogowski coils, Hall Effect current sensors, Micro Inertial
Measurement Units (MIMUs), or similar, and/or any other suitable
voltage or electric current sensors now known or later developed in
the art.
[0040] Thus, the converter controller 262 is also configured to
receive one or more voltage and/or electric current feedback
signals from the sensors 252, 254, 256, 258. More specifically, in
certain embodiments, the current or voltage feedback signals may
include at least one of line feedback signals, line-side converter
feedback signals, rotor-side converter feedback signals, or stator
feedback signals.
[0041] For example, as shown in the illustrated embodiment, the
converter controller 262 receives voltage and electric current
measurement signals from the second set of voltage and electric
current sensors 254 coupled in electronic data communication with
stator bus 208. The converter controller 262 may also receive the
third and fourth set of voltage and electric current measurement
signals from the third and fourth set of voltage and electric
current sensors 256, 258. In addition, the converter controller 262
may be configured with any of the features described herein in
regards to the main controller 202. As such, the converter
controller 262 is configured to implement the various method steps
as described herein and may be configured similar to the turbine
controller 202.
[0042] Referring now to FIGS. 5 and 6, schematic diagrams of one
embodiment of a system 300 for compensating for flicker induced by
a wind turbine power system connected to a power grid, e.g. the
wind turbine 100 of FIGS. 1 and 2, are illustrated. As shown, the
system 300 may be implemented using the turbine controller 202
and/or the converter controller 262. More specifically, as shown,
the converter controller 262 may include a flicker compensation
module 264 and a reactive power (VAR) regulator module 266. Thus,
during normal operation of the wind turbine 100, the turbine
controller 202 operates the wind turbine 100 according to a nominal
torque command 302. In addition, the VAR regulator module 266 may
be configured to operate the power converter 210 of the wind
turbine power system 100 based on a nominal reactive current
command 350 (i.e. no flicker is present in the power grid). The VAR
regulator module 266 may be configured according to any suitable
configuration now known or later developed in the art.
[0043] In certain instances, however, it is desirable to modify the
torque command 302 to the converter as each rotor blade 108 aligns
with and passes the tower 104, e.g. via periodic torque command
modifier 304. In particular embodiments, for example, the flicker
compensation module 264 may be configured to correlate the periodic
torque command modifier 304 with voltage variations (e.g. the
output of 318) as one or more rotor blades 108 passes the tower
104. More specifically, as shown specifically in FIG. 6, the
turbine controller 202 is configured to calculate the nominal
torque command 302 and determine a net torque command 308 based on
the nominal torque command 302 and the periodic torque command
modifier 304 (e.g. by summing the nominal torque command 302 and
the periodic torque command modifier 304 via summer 306). Modifying
the torque command 302 in this manner and the resulting power
variations, however, can cause undesirable low frequency voltage
variations on the power grid (also referred to herein as
flicker).
[0044] Thus, in such instances, the flicker compensation module 264
of the converter controller 262 may receive the periodic torque
command modifier 304 from the turbine controller 202 as a separate
signal. This separate signal will indicate to the flicker
compensation module 264 that flicker is likely present in the power
grid. As such, the flicker compensation module 264 may also receive
one or more operational parameters 352 of the wind turbine power
system 100 and/or the power grid. For example, in an embodiment,
the operational parameter(s) 352 may include grid strength of the
power grid, a grid voltage, a voltage signal from a primary winding
of a main transformer of the wind turbine power system, a voltage
signal from a secondary winding of the main transformer, a speed
signal from a generator of the wind turbine power system, and/or an
upstream impedance from the wind turbine power system 100.
[0045] Accordingly, the flicker compensation module 264 is
configured to determine a reactive current command modifier 354 for
the power converter 210 based on the one or more operational
parameters 352 and the periodic torque command modifier 304. In
such embodiments, the converter controller 262 can then
simultaneously modify the nominal reactive current command 350 as a
function of the reactive current command modifier 354 with the
torque command 302, e.g. based on the correlation of the periodic
torque command modifier 304 with the voltage variations as one or
more rotor blades 108 passes the tower 104. Accordingly,
simultaneously modifying the nominal reactive current command 350
and the torque command 302 attenuates the low-frequency voltage
variations/flicker.
[0046] Referring specifically to FIG. 6, as shown, in one
embodiment, the flicker compensation module 264 may receive the
periodic torque command modifier 304 and determine a power command
modifier 314 as a function of the periodic torque command modifier
304 and, e.g. the speed signal 310 from the generator 118. For
example, as shown at 312, the periodic torque command modifier 304
may be multiplied by the speed signal 310 to obtain the power
command modifier 314.
[0047] In addition, as shown in the illustrated embodiment, the
flicker compensation module 264 may also receive the voltage signal
316 from a primary winding of the main transformer 234 and filter
the voltage signal 316 via a filter 318 (e.g. a high-pass filter).
The filtered voltage signal may then be multiplied by the power
command modifier 314 as shown at 320. The multiplied signal may
then be integrated via integrator 322 and multiplied by the power
command modifier 314 to obtain a reactive power command modifier
324. As such, the multiplier 320 and he integrator 322 are
configured to correlate the periodic torque command modifier 304
with the voltage variations as one or more rotor blades 108 passes
the tower 104. As shown at 328, the reactive power command modifier
324 can then be divided by the voltage signal 326 from the
secondary winding of the main transformer 234 to obtain the
reactive current command modifier 354.
[0048] Accordingly, as shown in FIG. 6, in one embodiment, the
system 300 can operate to simultaneously modify the nominal
reactive current command 350 and the nominal torque command 302 by
adding the nominal reactive current command 350 from VAR regulator
266 and the reactive current command modifier 354 from the flicker
compensation module 264 as shown at 358 (e.g. to obtain the net
reactive current command 356) and simultaneously adding the nominal
torque command 302 and the torque command modifier 304 as shown at
306 (e.g. to obtain the net torque 308).
[0049] This written description uses examples to disclose the
invention, including the best mode, and also to enable any person
skilled in the art to practice the invention, including making and
using any devices or systems and performing any incorporated
methods. The patentable scope of the invention is defined by the
claims, and may include other examples that occur to those skilled
in the art. Such other examples are intended to be within the scope
of the claims if they include structural elements that do not
differ from the literal language of the claims, or if they include
equivalent structural elements with insubstantial differences from
the literal languages of the claims.
* * * * *