U.S. patent application number 13/613410 was filed with the patent office on 2014-03-13 for voltage control in a doubly-fed induction generator wind turbine system.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. The applicant listed for this patent is Anthony Michael Klodowski, Robert Gregory Wagoner. Invention is credited to Anthony Michael Klodowski, Robert Gregory Wagoner.
Application Number | 20140070536 13/613410 |
Document ID | / |
Family ID | 49150795 |
Filed Date | 2014-03-13 |
United States Patent
Application |
20140070536 |
Kind Code |
A1 |
Wagoner; Robert Gregory ; et
al. |
March 13, 2014 |
VOLTAGE CONTROL IN A DOUBLY-FED INDUCTION GENERATOR WIND TURBINE
SYSTEM
Abstract
Systems and methods for regulating voltage in a doubly fed
induction generator (DFIG) system are provided. More particularly,
the voltage of the auxiliary power feed in a DFIG wind turbine
system can be regulated by outputting reactive power from a power
converter to a reactive element coupled between the auxiliary power
feed and a stator bus. The reactive element can include a winding
of the transformer used to couple the wind turbine system to the
electrical grid and/or an inductive element coupled between the
output of the power converter and the stator bus. The voltage of
the auxiliary power feed can be maintained within a reduced
operating range while an increased operating range can be provided
for wind turbine system
Inventors: |
Wagoner; Robert Gregory;
(Roanoke, VA) ; Klodowski; Anthony Michael;
(Hardy, VA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Wagoner; Robert Gregory
Klodowski; Anthony Michael |
Roanoke
Hardy |
VA
VA |
US
US |
|
|
Assignee: |
GENERAL ELECTRIC COMPANY
Schenectady
NY
|
Family ID: |
49150795 |
Appl. No.: |
13/613410 |
Filed: |
September 13, 2012 |
Current U.S.
Class: |
290/44 |
Current CPC
Class: |
H02P 9/007 20130101;
H02P 2101/15 20150115 |
Class at
Publication: |
290/44 |
International
Class: |
H02P 9/04 20060101
H02P009/04 |
Claims
1. A wind turbine system, comprising: a wind driven doubly fed
induction generator having a rotor and a stator, the stator
providing AC power to a stator bus; a power converter coupled to
the rotor of said doubly fed induction generator, said power
converter providing an output to a line bus; a transformer coupled
to the stator bus; an auxiliary power feed coupled to the at least
one power converter; at least one reactive element coupled between
the auxiliary power feed and the stator bus; and a control system
configured to control said power converter, said control system
configured to regulate the voltage of said auxiliary power feed by
outputting reactive power from the power converter to the at least
one reactive element.
2. The wind turbine system of claim 1, wherein the transformer
comprises a primary winding coupled to an electrical grid and a
secondary winding coupled to the stator bus.
3. The wind turbine system of claim 2, wherein the at least one
reactive element comprises an inductive element coupled between the
output of the power converter and the stator bus.
4. The wind turbine system of claim 1, wherein the transformer
comprises a primary winding coupled to an electrical grid, a
secondary winding coupled to the stator bus, and an auxiliary
winding coupled to the line bus.
5. The wind turbine system of claim 4, wherein the at least one
reactive element comprises the auxiliary winding.
6. The wind turbine system of claim 5, wherein the at least one
reactive element further comprises an inductive element coupled
between the output of said power converter and the auxiliary
winding.
7. The wind turbine system of claim 1, wherein the system further
comprises one or more fuses, circuit breakers, or contactors
coupled between the output of the power converter and the
transformer.
8. The wind turbine system of claim 1, wherein said control system
is configured to adjust an output reactive power of said power
converter based on a voltage associated with the transformer to
regulate the voltage of said auxiliary power feed.
9. The wind turbine system of claim 8, wherein the voltage
associated with said transformer is a voltage associated with a
primary winding of the transformer, the primary winding coupled to
an electrical grid.
10. The wind turbine system of claim 8, wherein the voltage
associated with said transformer comprises is a voltage associated
with a secondary winding of the transformer, the secondary winding
coupled to the stator bus.
11. The wind turbine system of claim 8, wherein said control system
is configured to adjust the output reactive power of said power
converter to maintain the voltage of the auxiliary power feed to be
within about .+-.10% of the nominal voltage of the auxiliary power
feed.
12. A method for regulating an auxiliary power feed of a wind
turbine system, the wind turbine system comprising a wind driven
doubly fed induction generator having a rotor and a stator, the
stator providing AC power to a stator bus, the wind turbine system
further comprising a power converter coupled to the rotor of the
doubly fed induction generator, the power converter providing an
output to a line bus, the auxiliary power feed coupled to the
output of the power converter, the method comprising: monitoring a
voltage associated with a transformer coupling the wind turbine
system to an electrical grid; identifying a reactive power output
for the power converter based on the voltage associated with the
transformer, the reactive power output identified to regulate the
voltage of the auxiliary power feed; and controlling the power
converter to provide the identified reactive power output to the
line bus.
13. The method of claim 12, wherein the identified reactive power
output is provided to at least one reactive element coupled between
the auxiliary power source and the stator bus.
14. The method of claim 12, wherein the reactive power output is
identified to maintain the voltage of the auxiliary power feed to
be within about .+-.10% of the nominal voltage of the auxiliary
power feed.
15. The method of claim 12, wherein the voltage associated with
said transformer is a voltage associated with a primary winding of
the transformer, the primary winding coupled to an electrical
grid.
16. The method of claim 12, wherein the voltage associated with
said transformer comprises a voltage associated with a secondary
winding of the transformer, the secondary winding coupled to the
stator bus.
17. A control system for controlling a power converter of a wind
turbine system, the wind turbine system comprising a wind driven
doubly fed induction generator having a rotor and a stator, the
stator providing AC power to a stator bus, the power converter
coupled to the rotor of the doubly fed induction generator, the
power converter providing an output to a line bus, the wind turbine
system further comprising an auxiliary power feed coupled to output
of the power converter, the control system comprising: a sensor
configured to provide a signal indicative of a voltage associated
with a transformer coupling the wind turbine system to an
electrical grid; and a controller configured to control the power
converter based on the signal indicative of the voltage associated
with the transformer to regulate the voltage of the auxiliary power
feed; wherein said controller is configured to regulate the voltage
of the auxiliary power feed by controlling the power converter to
provide reactive power to a reactive element coupled between the
output of the power converter and the stator bus.
18. The control system of claim 17, wherein the voltage associated
with the transformer is a voltage associated with a primary winding
of the transformer, the primary winding coupled to an electrical
grid.
19. The control system of claim 17, wherein the voltage associated
with the transformer comprises is a voltage associated with a
secondary winding of the transformer, the secondary winding coupled
to the stator bus.
20. The control system of claim 17, wherein the controller is
configured to control the power converter to adjust the reactive
power provided to the reactive element to maintain the voltage of
the auxiliary power feed to be within about .+-.10% of the nominal
voltage of the auxiliary power feed.
Description
FIELD OF THE INVENTION
[0001] The present disclosure relates generally to renewable energy
sources, and more particularly to a systems and methods of
regulating voltage in a doubly fed induction generator wind turbine
system.
BACKGROUND OF THE INVENTION
[0002] Wind turbines have received increased attention as a
renewable energy source. Wind turbines use the wind to generate
electricity. The wind turns multiple blades connected to a rotor.
The spin of the blades caused by the wind spins a shaft of the
rotor, which connects to a generator that generates electricity.
Certain wind turbine systems include a doubly fed induction
generator (DFIG) to convert wind energy into electrical power
suitable for output to an electrical grid. DFIGs are typically
connected to a converter that regulates the flow of electrical
power between the DFIG and the grid. More particularly, the
converter allows the wind turbine to output electrical power at the
grid frequency regardless of the rotational speed of the wind
turbine blades.
[0003] A typical DFIG system includes a wind driven DFIG having a
rotor and a stator. The stator of the DFIG is coupled to the
electrical grid through a stator bus. A power converter is used to
couple the rotor of the DFIG to the electrical grid. The power
converter can be a two-stage power converter including both a rotor
side converter and a line side converter. The rotor side converter
can receive alternating current (AC) power from the rotor via a
rotor bus and can convert the AC power to a DC power. The line side
converter can then convert the DC power to AC power having a
suitable output frequency, such as the grid frequency. The AC power
is provided to the electrical grid via a line bus. An auxiliary
power feed can be coupled to the line bus to provide power for
components used in the wind turbine system, such as fans, pumps,
motors, and other components of the wind turbine system.
[0004] A typical DFIG system includes a two-winding transformer
having a high voltage primary (e.g. greater than 12 KVAC) and a low
voltage secondary (e.g. 575VAC, 690VAC, etc.) to couple the DFIG
system to the electrical grid. The high voltage primary can be
coupled to the high voltage electrical grid. The stator bus
providing AC power from the stator of the DFIG and the line bus
providing AC power from the power converter can be coupled to the
low voltage secondary. In this system, the output power of the
stator and the output power of the power converter are operated at
the same voltage and combined into the single transformer secondary
winding at the low voltage.
[0005] More recently, DFIG systems have included a three winding
transformer to couple the DFIG system to the electrical grid. The
three winding transformer can have a high voltage (e.g. greater
than 12 KVAC) primary winding coupled to the electrical grid, a
medium voltage (e.g. 6 KVAC) secondary winding coupled to the
stator bus, and a low voltage (e.g. 575VAC, 690VAC, etc.) auxiliary
winding coupled to the line bus. The three winding transformer
arrangement can be preferred in increased output power systems
(e.g. 3 MW systems) as it reduces the current in the stator bus and
other components on the stator side of the DFIG, such as a stator
synch switch.
[0006] Typically, the output voltage of the DFIG system on the
primary winding of the transformer (e.g. a two winding transformer
or a three winding transformer) can have a maximum continuous
operating range of nominal voltage .+-.10%. Standard components of
a wind turbine system which are powered by the auxiliary feed
coupled to the line bus are typically designed to accommodate this
range of nominal voltage .+-.10%. However, the operating range of
new DFIG wind turbine systems has increased to accommodate a wider
operating range on the primary of the transformer, such as nominal
voltage .+-.15%.
[0007] A wider operating range on the primary winding of the
transformer causes the voltage on the auxiliary power feed used to
power components of the wind turbine system to have the possibility
of being higher or lower than the ratings of the standard
components powered by the auxiliary power feed. As a result,
special components (e.g. components with higher ratings) may be
required to accommodate the wider operating range. These special
components can cost significantly more than standard components,
and may require special qualification testing. In certain cases,
special components that can accommodate a wider operating range may
not be available at all, in which case major redesign of sections
of the wind turbine system may be necessary. Consequently,
providing a wider operating range on the primary of the transformer
of the DFIG system (e.g. nominal voltage .+-.15%) can lead to
significant drawbacks, including higher auxiliary system cost,
longer development schedules, and other drawbacks.
[0008] Thus, a need exists for a system and method for improved
voltage control in a DFIG wind turbine system. A system and method
that can accommodate a wider operating range (e.g. nominal voltage
.+-.15%) on the primary winding of the transformer while
maintaining a standard operating range (e.g. nominal voltage
.+-.10%) for the auxiliary power feed would be particularly
useful.
BRIEF DESCRIPTION OF THE INVENTION
[0009] 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.
[0010] One exemplary aspect of the present disclosure is directed
to a wind turbine system. The wind turbine system includes a wind
driven doubly fed induction generator having a rotor and a stator.
The stator provides AC power to a stator bus. The wind turbine
system further includes a power converter coupled to the rotor of
the doubly fed induction generator. The power converter provides an
output to a line bus. The wind turbine system further includes a
transformer coupled to the stator bus, an auxiliary power feed
coupled to the at least one power converter, and at least one
reactive element coupled between the auxiliary power feed and the
stator bus. The at least one reactive element can be a winding of
the transformer or a separate reactive element, such as an
inductive element coupled between the auxiliary power feed and the
stator bus. The system further includes a control system configured
to control the power converter. The control system is configured to
regulate the auxiliary power feed by outputting reactive power from
the power converter to the at least one reactive element.
[0011] Another exemplary aspect of the present disclosure is
directed to a method for regulating an auxiliary power feed of a
wind turbine system. The method includes monitoring a voltage
associated with a transformer coupling the wind turbine system to
an electrical grid and identifying a reactive power output for a
power converter based on the voltage associated with the
transformer. The reactive power output is identified to regulate
the voltage of the auxiliary power feed. The method further
includes controlling the power converter to provide the identified
reactive power output to a line bus coupled to the power
converter.
[0012] Yet another exemplary aspect of the present disclosure is
directed to a control system for controlling a power converter of a
wind turbine system. The control system includes a sensor
configured to provide a signal indicative of a voltage associated
with a transformer coupling the wind turbine system to an
electrical grid. The control system further includes a controller
configured to control the power converter based on the signal
indicative of the voltage associated with the transformer to
regulate the voltage of the auxiliary power feed. The controller is
configured to regulate the voltage of the auxiliary power feed by
controlling the power converter to provide reactive power to a
reactive element coupled between the output of the power converter
and a stator bus.
[0013] 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
[0014] 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:
[0015] FIG. 1 depicts an exemplary DFIG wind turbine system
according to an exemplary embodiment of the present disclosure;
[0016] FIG. 2 depicts an exemplary DFIG wind turbine system
according to an exemplary embodiment of the present disclosure;
[0017] FIG. 3 depicts an exemplary DFIG wind turbine system
according to an exemplary embodiment of the present disclosure;
and
[0018] FIG. 4 depicts an exemplary method for regulating an
auxiliary power feed of a DFIG wind turbine system according to an
exemplary embodiment of the present disclosure.
DETAILED DESCRIPTION OF THE INVENTION
[0019] 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.
[0020] Generally, the present disclosure is directed to systems and
methods for regulating voltage in a doubly fed induction generator
(DFIG) system. The DFIG system can include a wind driven doubly fed
induction generator having a rotor and a stator. The stator can
provide AC power to a stator bus. The rotor can provide AC power to
a power converter. The power can provide an output to a line bus.
The stator bus and the line bus can be coupled to an electrical
grid through a transformer, such as a two-winding transformer or a
three-winding transformer. An auxiliary power feed can be coupled
to the output of the power converter. The auxiliary power feed can
provide power for various components of the wind turbine system,
such as fans, pumps, motors, and other components of the wind
turbine system.
[0021] According to aspects of the present disclosure, the voltage
of the auxiliary power feed can be regulated by outputting reactive
power from the power converter to a reactive element coupled
between the auxiliary power feed and the stator bus. The reactive
element can include a winding of the transformer used to couple the
wind turbine system to the electrical grid and/or an inductive
element coupled between the output of the power converter and the
stator bus. Outputting reactive power to at least one reactive
element can cause a voltage reduction between the transformer and
the auxiliary power feed.
[0022] As a result, the voltage of the auxiliary power feed can be
maintained within a reduced operating range while an increased
operating range can be provided for the voltage of a primary
winding of the transformer coupled to an electrical grid. For
instance, the operating range of the auxiliary power feed can be
maintained to be nominal voltage .+-.10% while the operating range
of the primary winding of the transformer can be nominal voltage
.+-.15%. In this manner, the operating range of the wind turbine
system can be increased without having to redesign or accommodate
special components in the auxiliary power system of the wind
turbine system.
[0023] FIG. 1 depicts an exemplary doubly-fed induction generator
(DFIG) wind turbine system 100 according to an exemplary embodiment
of the present disclosure. In the exemplary system 100, a rotor 106
includes a plurality of rotor blades 108 coupled to a rotating hub
110, and together define a propeller. The propeller is coupled to
an optional gear box 112, which is, in turn, coupled to a generator
120. In accordance with aspects of the present disclosure, the
generator 120 is a doubly fed induction generator (DFIG) 120.
[0024] DFIG 120 is typically coupled to a stator bus 122 and a
power converter 130 via a rotor bus 124. The stator bus 122
provides an output multiphase power (e.g. three-phase power) from a
stator of DFIG 120 and the rotor bus 124 provides an output
multiphase power (e.g. three-phase power) of the rotor of DFIG 120.
Referring to the power converter 130, DFIG 120 is coupled via the
rotor bus 124 to a rotor side converter 132. The rotor side
converter 132 is coupled to a line side converter 134 which in turn
is coupled to a line side bus 138.
[0025] In exemplary configurations, the rotor side converter 132
and the line side converter 134 are configured for normal operating
mode in a three-phase, pulse width modulation (PWM) arrangement
using insulated gate bipolar transistors (IGBTs) as switching
devices. Other suitable switching devices can be used, such as
insulated gate commuted thyristors, MOSFETs, bipolar transistors,
silicon controlled rectifiers, or other suitable switching devices.
The rotor side converter 132 and the line side converter 134 can be
coupled via a DC link 135 across which is the DC link capacitor
136.
[0026] The power converter 130 can be coupled to a controller 140
to control the operation of the rotor side converter 132 and the
line side converter 134. For instance, the controller 140 can send
control commands to the rotor side converter 132 and line side
converter 134 to control the modulation of switching elements (such
as IGBTs) used in the power converter 130 to provide a desired real
and reactive power output. The controller 140 can be any suitable
control circuit. For instance, in one aspect the controller can
include summers, compensating regulators, and other devices used to
process signals received at the controller 140. In another
embodiment, the controller 140 can include a processing device
(e.g. microprocessor, microcontroller, etc.) executing
computer-readable instructions stored in a computer-readable
medium. The instructions when executed by the processing device can
cause the processing device to perform control operations, such as
regulating voltage of the DFIG wind turbine system 100 according to
any exemplary aspects of the present disclosure.
[0027] As illustrated, the system 100 includes a transformer 160
coupling the wind turbine system 100 to an electrical grid 180. The
transformer 160 of FIG. 1 is a three-winding transformer that
includes a high voltage (e.g. greater than 12 KVAC) primary winding
162 coupled to the electrical grid, a medium voltage (e.g. 6 KVAC)
secondary winding 164 coupled to the stator bus 122, and a low
voltage (e.g. 575 VAC, 690 VAC, etc.) auxiliary winding 166 coupled
to the line bus 138.
[0028] An auxiliary power feed 170 is coupled to the output of the
power converter 130. The auxiliary power feed 170 acts as a power
source for various components of the wind turbine system 100. For
instance, the auxiliary power feed 170 can power fans, pumps,
motors, and other suitable components of the wind turbine system
100.
[0029] In operation, power generated at DFIG 120 by rotating the
rotor 106 is provided via a dual path to electrical grid 180. The
dual paths are defined by the stator bus 122 and the rotor bus 124.
On the rotor bus side 124, sinusoidal multi-phase (e.g.
three-phase) alternating current (AC) power is provided to the
power converter 130. The rotor side power converter 132 converts
the AC power provided from the rotor bus 124 into direct current
(DC) power and provides the DC power to the DC link 135. Switching
devices (e.g. IGBTs) used in parallel bridge circuits of the rotor
side power converter 132 can be modulated to convert the AC power
provided from the rotor bus 124 into DC power suitable for the DC
link 135.
[0030] The line side converter 134 converts the DC power on the DC
link 135 into AC power at a frequency suitable for the electrical
grid 180. In particular, switching devices (e.g. IGBTs) used in
bridge circuits of the line side power converter 134 can be
modulated to convert the DC power on the DC link 135 into AC power
on the line side bus 138. The power from the power converter 130
can be provided via the auxiliary winding 166 of the transformer
160 to the electrical grid 180.
[0031] Various circuit breakers, fuses, switches, contactors, and
other devices, such as grid breaker 158, stator bus breaker 156,
stator sync switch 154, and line bus breaker 152, can be included
in the system 100 to connect or disconnect corresponding buses, for
example, when current flow is excessive and can damage components
of the wind turbine system 100 or for other operational
considerations. Additional protection components can also be
included in the wind turbine system 100.
[0032] The power converter 130 can receive control signals from,
for instance, the control system 142 via the controller 140. The
control signals can be based, among other things, on sensed
conditions or operating characteristics of the wind turbine system
100. For instance, the control signals can be based on sensed
voltage associated with the transformer 160 as determined by a
voltage sensor 144. As another example, the control signals can be
based on sensed voltage associated with the auxiliary power feed
170 as determined by a voltage sensor 146.
[0033] Typically, the control signals provide for control of the
operation of the power converter 130. For example, feedback in the
form of sensed speed of the DFIG 120 can be used to control the
conversion of the output power from the rotor bus 156 to maintain a
proper and balanced multi-phase (e.g. three-phase) power supply.
Other feedback from other sensors can also be used by the control
system 174 to control the power converter 162, including, for
example, stator and rotor bus voltages and current feedbacks. Using
the various forms of feedback information, switching control
signals (e.g. gate timing commands for IGBTs), stator synchronizing
control signals, and circuit breaker signals can be generated.
[0034] According to aspects of the present disclosure, the voltage
of the auxiliary power feed 170 can be regulated by the controller
140. In particular, the controller 140 can control the power
converter 130 to output excess reactive power to a reactive element
coupled between the power converter 130 and the stator bus 122 to
regulate the voltage of the auxiliary power feed 170. Outputting
the reactive power to the reactive element will influence the
voltage of the line bus 138 and correspondingly the voltage at the
auxiliary power feed 170. As a result, the auxiliary power feed 170
can be regulated to operate within a narrower operating range when
compared to the operating range of the wind turbine system 100.
[0035] In the embodiment shown in FIG. 1, the controller 140 can
monitor a voltage associated with the transformer 160 using voltage
sensor 144. The voltage associated with the transformer 160 can be
the voltage of the primary winding 162 or the voltage of a
secondary winding, such as the voltage of secondary winding 164 or
auxiliary winding 166. Based on the voltage associated with the
transformer 160, the controller 140 can identify a reactive power
output for the power converter 130 to maintain the voltage of the
auxiliary power feed 130 to be within a predefined tolerance of
nominal voltage for the auxiliary power feed 170, such as within
10% of the nominal voltage of the auxiliary power feed 170. The
controller 140 can then send control commands to the power
converter 130, such as gate timing commands for IGBTs used in the
line side converter 134 and/or the rotor side converter 132, to
control the power converter 130 to output the identified reactive
power from the power converter 130 to a reactive element coupled
between the auxiliary power feed 170 and the stator bus 122.
[0036] In the embodiment shown in FIG. 1, the reactive element is
the auxiliary winding 166 of the transformer 160. More
particularly, the impedance of the auxiliary winding 166 of the
transformer 160 can be sufficient to allow regulation of the
auxiliary power feed 130 by outputting reactive power to the
auxiliary winding 166 of the transformer. The excess reactive power
supplied to the auxiliary winding 166 will influence the voltage of
the auxiliary power feed 170 such that the operating range of the
auxiliary power feed 170 can be maintained within a predetermined
tolerance of nominal voltage. For instance, the auxiliary power
feed 170 can be maintained within an operating range of nominal
voltage .+-.10%, while the voltage on the primary winding 162 of
the transformer 160 can be maintained within an operating range of
nominal voltage .+-.15%.
[0037] In a particular implementation, the controller 140 can be
configured to monitor the voltage of the auxiliary power feed 170
to determine whether the auxiliary winding remains within the
predetermined tolerance of nominal voltage. For instance, the
controller 140 can monitor the voltage associated with the
auxiliary power feed 170 using voltage sensor 146. If the voltage
exceeds or falls below a certain threshold, such as within 10% of
nominal voltage for the auxiliary power feed, the controller 140
can control the power converter 130 to adjust the reactive power
output of the power converter 130 until the voltage of the
auxiliary power feed 170 is maintained within the predetermined
tolerance.
[0038] In this manner, the controller 140 can regulate the voltage
of the auxiliary power feed 170 to be within a predefined operating
range while allowing the wind turbine system 100 to have an
increased operating range output. As a result, standard components
can be used in the auxiliary power system of the wind turbine
system 100, leading to lower cost, shorter design/development/test
schedule, and reduced engineering effort.
[0039] FIG. 2 depicts a DFIG wind turbine system 200 according to
another exemplary embodiment of the present disclosure. The DFIG
wind turbine system 200 is substantially similar to the wind
turbine system 100 of FIG. 1, except that the DFIG wind turbine
system 200 of FIG. 2 includes an additional reactive element,
namely an inductive element 172, coupled between the output of the
power converter 130 and the auxiliary winding 166. Certain circuit
breakers, switches, contacts, and other devices are not illustrated
in FIG. 2 for purposes of clarity of illustration.
[0040] Similar to the system 100 depicted in FIG. 1, the controller
140 can regulate the voltage of the auxiliary power feed 170 by
controlling the power converter 130 to output reactive power to a
reactive element coupled between the auxiliary power feed 170 and
the stator bus 122. In the embodiment of FIG. 2, the reactive
element includes the auxiliary winding 166 of the transformer 160
as well as the additional inductive element 172 coupled between the
auxiliary power feed 170 and the auxiliary winding 166. The
inductive element 172 can be external to or a part of the power
converter 130.
[0041] The inductive element 172 can provide any additional
impedance necessary for regulating the auxiliary power feed 170 by
outputting reactive power from the power converter 130. For
instance, if the impedance of the auxiliary winding 166 of the
transformer 160 is not sufficient to allow for regulation of the
auxiliary power feed 170 by outputting reactive power from the
power converter 130, the additional inductive element 172 can be
included between the auxiliary power feed 170 and the auxiliary
winding 166 of the transformer to provide the required additional
impedance.
[0042] FIG. 3 depicts a DFIG wind turbine system 300 according to
yet another exemplary embodiment of the present disclosure. The
DFIG wind turbine system 300 of FIG. 3 is similar to the DFIG wind
turbine system 100 of FIG. 1, except that the DFIG wind turbine
system 300 includes a two-winding transformer 190 coupling the wind
turbine system 300 to an electrical grid 180. The two-winding
transformer 190 includes a primary winding 192 coupled to the
electrical grid 180 and a secondary winding 194 coupled to the
stator bus 122 and to the line bus 138.
[0043] Similar to the system 100 depicted in FIG. 1, the controller
140 can regulate the voltage of the auxiliary power feed 170 by
controlling the power converter 130 to output reactive power to a
reactive element coupled between the auxiliary power feed 170 and
the stator bus 122. In the system 300 of FIG. 3, the reactive
element includes an inductive element 172 coupled between the
auxiliary power feed 170 and stator bus 122. The inductive element
172 can be external to or a part of the power converter 130. The
inductive element 172 can provide the required impedance necessary
for regulating the auxiliary power feed 170 by outputting reactive
power from the power converter 130.
[0044] FIG. 4 depicts a flow diagram of an exemplary method (400)
for regulating the auxiliary power feed of a DFIG wind turbine
system. The method (400) will be discussed with reference to the
exemplary DFIG wind turbine system 100 of FIG. 1. However, the
method (400) can be implemented using any suitable system. In
addition, although FIG. 4 depicts steps performed in a particular
order for purposes of illustration and discussion, the methods
discussed herein are not limited to any particular order or
arrangement. One skilled in the art, using the disclosures provided
herein, will appreciate that various steps of the methods can be
omitted, rearranged, combined and/or adapted in various ways.
[0045] At (402), the method includes monitoring a voltage
associated with a transformer coupling the DFIG system to the
utility grid. For instance, the method can include monitoring, with
voltage sensor 144, the voltage of transformer 160. The voltage
associated with the transformer 160 can be a voltage associated
with the primary winding 162, secondary winding 164, and/or
auxiliary winding 166 of the transformer 160. The sensor 144 can
provide a signal indicative of the voltage associated with the
transformer to the controller 140.
[0046] At (404), the method includes identifying a reactive power
output for the power converter based on the voltage associated with
the transformer. For instance, the controller 140 can process the
signal indicative of the voltage associated with the transformer
received from the sensor 144 to identify a necessary reactive power
output for the power converter 130 to maintain the voltage of the
auxiliary power feed 170 within a predefined threshold of nominal
voltage, such as within .+-.10% of nominal voltage of the auxiliary
power feed 170. The reactive power output can be identified using
any suitable process or technique, such as by accessing a model
defining the relationships between one or more components of the
DFIG system.
[0047] Once the reactive power output has been identified, a power
converter can be controlled to output the identified reactive power
to at least one reactive element to regulate the voltage of the
auxiliary power feed (406). For instance, the controller 140 can
send control commands to the power converter 130 to control the
power converter 130 to output the identified reactive power to the
reactive element. In one aspect, the control commands can control
the modulation of switching devices (IGBTs) used in the power
converter 130 such that the power converter 130 provides the
identified reactive power to the reactive element.
[0048] To ensure that the auxiliary power feed of the DFIG system
remains within a predetermined tolerance (e.g. within 10% of
nominal voltage), the method can further include monitoring the
voltage of the auxiliary power feed to determine if the auxiliary
power is maintained within the predetermine tolerance (408). For
instance, the voltage sensor 146 can monitor the voltage of the
auxiliary power feed 170 and provide a signal indicative of the
voltage to the controller 140. The controller 140 can determine
whether the voltage is within the predetermined tolerance based on
the signal received from the voltage sensor 146.
[0049] If the voltage of the auxiliary power feed is within the
predetermined tolerance, the method can include maintaining the
reactive power output of the power converter (410). For instance,
the controller 140 can send control commands to the power converter
130 to maintain the reactive power output of the power converter
130. Otherwise, the method can adjust the reactive power output of
the power converter until the voltage of the auxiliary power feed
is within the predetermined tolerance (412). For instance the
controller 140 can send control commands to the power converter to
adjust the reactive power output of the power converter 130 until
the voltage of the auxiliary power feed 170 is within the
predetermined tolerance. The method can then return to (402) where
the voltage of the auxiliary power feed continues to be regulated
by monitoring the voltage associated with the transformer and
outputting a reactive power from the power converter identified
based on the voltage associated with the transformer.
[0050] 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.
* * * * *