ORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)
1. Title of the Invention:
“SYSTEM AND METHOD OF DECOUPLING DRIVETRAIN
RELATED POWER OSCILLATIONS OF AN INVERTER-BASED
RESOURCE FROM ACTIVE POWER INJECTED INTO THE
ELECTRICAL GRID”
2. APPLICANT (S) –
(a) Name : General Electric Company
(b) Nationality : American
(c)Address : 1 River Road Schenectady, New York 12345,
United States of America.
The following specification particularly describes the invention and the manner
in which it is to be performed.
2
FIELD
[0001] The present disclosure relates in general to inverter-based resources, and more
particularly to systems and methods for decoupling drivetrain related power oscillations of
an inverter-based resource from active power injected into the electrical grid.
5
BACKGROUND
[0002] Power generating assets may take a variety of forms and rely on renewable
and/or nonrenewable sources of energy. Those power generating assets relying on
renewable sources of energy may generally be considered one of the cleanest, most
10 environmentally friendly energy sources presently available. For example, wind turbines
have gained increased attention in this regard. A modern wind turbine typically includes a
tower, a generator, a gearbox, a nacelle, and one or more rotor blades. The nacelle includes
a rotor coupled to the gearbox and to the generator. The rotor and the gearbox are mounted
on a bedplate support frame located within the nacelle. The rotor blades capture kinetic
15 energy of wind using known airfoil principles. The rotor blades transmit the kinetic energy
in the form of rotational energy so as to turn a shaft coupling the rotor blades to the gearbox,
or if the gearbox is not used, directly to the generator. The generator then converts the
mechanical energy to electrical energy and the electrical energy may be transmitted to a
converter and/or a transformer housed within the tower and subsequently deployed to a
20 utility grid. Modern wind power generation systems typically take the form of a wind farm
having multiple wind turbine generators that are operable to supply power to a transmission
system providing power to an electrical grid.
[0003] Wind turbines can be distinguished in two types: fixed speed and variable speed
turbines. Conventionally, variable speed wind turbines are controlled as current sources
25 connected to an electrical grid. In other words, the variable speed wind turbines rely on a
grid frequency detected by a phase locked loop (PLL) as a reference and inject a specified
amount of current into the grid. The conventional current source control of the wind
turbines is based on the assumptions that the grid voltage waveforms are fundamental
voltage waveforms with fixed frequency and magnitude and that the penetration of wind
30 power into the grid is low enough so as to not cause disturbances to the grid voltage
magnitude and frequency. Thus, the wind turbines simply inject the specified current into
the grid based on the fundamental voltage waveforms.
3
[0004] Modern day wind turbine generators utilize grid-connected power converters to
achieve certain special dynamic control functions (in addition to the primary control
functions of regulating speed and power), such as damping drivetrain torsional oscillations
and damping tower oscillations. These control functions change the active power injected
5 into the grid at a particular frequency. The power oscillation components are usually at a
known frequency dictated by the dimensions and physics of the wind turbine. These control
functions are practical since grid-forming resources (mostly synchronous machines) are
generally abundantly available in most applications such that these other resources can
accommodate the change in active power injected by the wind turbine generators.
10 [0005] However, as conventional synchronous machines connected to grids may be
retired or replaced in the years to come, a consequence of this structural change to the grid
is that the ability of the wind turbine generator to freely change power into the grid may be
more constrained. For this reason, alternative resources that can supply the power needs
for these control functions would be beneficial.
15 [0006] In view of the foregoing, the art is continuously seeking new and improved
systems and methods for decoupling drivetrain related power oscillations of an inverterbased resource from active power injected into the electrical grid.
BRIEF DESCRIPTION
20 [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 an aspect, the present disclosure is directed to a method for decoupling a
mechanical drivetrain resonance mode of an inverter-based resource from the external
25 electrical system. The inverter-based resource has a power converter, a generator, and an
energy buffer. The method includes receiving, via a controller, one or more voltage
feedback signals at a node between the inverter-based resource and the external electrical
system. The method also includes filtering, via the controller, the one or more voltage
feedback signals to extract changes in a voltage at a frequency associated with the drivetrain
30 resonance mode. Moreover, the method includes determining, via the controller, at least
one current command or power command based on the filtered one or more voltage
feedback signals. Further, the method includes controlling the power converter according
4
to the at least one current command and controlling the energy buffer according to the
power command so as to reduce or eliminate the changes in the voltage at the frequency
associated with the drivetrain resonance mode.
[0009] In another aspect, the present disclosure is directed to an inverter-based resource
5 connected to an electrical grid. The inverter-based resource includes a generator, a power
converter coupled to the generator, and a controller having at least one processor configured
to perform a plurality of operations. The plurality of operations includes receiving one or
more voltage feedback signals at a node between the inverter-based resource and the
external electrical system, filtering the one or more voltage feedback signals to extract
10 changes in voltage at a frequency associated with the drivetrain resonance mode,
determining at least one current command or power command based on the filtered one or
more voltage feedback signals, and controlling the power converter according to the at least
one current command and controlling the energy buffer according to the power command
so as to reduce or eliminate the changes in the voltage at the frequency associated with the
15 drivetrain resonance mode.
[0010] 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,
20 serve to explain the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] 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
25 makes reference to the appended figures, in which:
[0012] FIG. 1 illustrates a perspective view of an embodiment of an inverter-based
resource configured as a wind turbine power system according to the present disclosure;
[0013] FIG. 2 illustrates a schematic diagram of an embodiment of an electrical system
for use with an inverter-based resource configured as a wind turbine power system
30 according to the present disclosure;
[0014] FIG. 3 illustrates a block diagram of an embodiment of a controller for use with
an inverter-based resource according to the present disclosure;
5
[0015] FIG. 4 illustrates a flow diagram of one embodiment of a method for decoupling
power oscillations from an inverter-based resource connected to an electrical grid from a
total power output of the inverter-based resource according to the present disclosure;
[0016] FIG. 5 illustrates a schematic diagram of an embodiment of an algorithm
5 implemented by a controller for decoupling power oscillations from an inverter-based
resource connected to an electrical grid from a total power output of the inverter-based
resource according to the present disclosure;
[0017] FIG. 6 illustrates a schematic diagram of an embodiment of an electrical system
for use with a inverter-based resource configured as a wind turbine power system according
10 to the present disclosure, particularly illustrating a change for a power command of an
energy buffer of the inverter-based resource and a change in the reactive current command
for a power converter being sent to an energy buffer control and a line converter control,
respectively;
[0018] Repeat use of reference characters in the present specification and drawings is
15 intended to represent the same or analogous features or elements of the present invention.
DETAILED DESCRIPTION
[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
20 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
25 invention covers such modifications and variations as come within the scope of the
appended claims and their equivalents.
[0020] As used herein, the terms “first”, “second”, and “third” may be used
interchangeably to distinguish one component from another and are not intended to signify
location or importance of the individual components.
30 [0021] The terms “coupled,” “fixed,” “attached to,” and the like refer to both direct
coupling, fixing, or attaching, as well as indirect coupling, fixing, or attaching through one
or more intermediate components or features, unless otherwise specified herein.
6
[0022] Approximating language, as used herein throughout the specification and
claims, is applied to modify any quantitative representation that could permissibly vary
without resulting in a change in the basic function to which it is related. Accordingly, a
value modified by a term or terms, such as “about”, “approximately”, and “substantially”,
5 are not to be limited to the precise value specified. In at least some instances, the
approximating language may correspond to the precision of an instrument for measuring
the value, or the precision of the methods or machines for constructing or manufacturing
the components and/or systems. For example, the approximating language may refer to
being within a 10 percent margin.
10 [0023] Here and throughout the specification and claims, range limitations are
combined and interchanged, such ranges are identified and include all the sub-ranges
contained therein unless context or language indicates otherwise. For example, all ranges
disclosed herein are inclusive of the endpoints, and the endpoints are independently
combinable with each other.
15 [0024] Generally, the present disclosure is directed to a system and method for
decoupling drivetrain-related power oscillations of an inverter-based resource (that are
driven by a mechanical drivetrain resonance or forced oscillation mode within an inverterbased resource) from the active power injected into the external electrical system. As such,
the inverter-based resource can manage loading on the drivetrain independent of the
20 external electrical system conditions or topology. In an embodiment, the inverter-based
resource may be a wind turbine power system, a solar power system, a hydro-generator, or
combinations thereof. In addition, the system and method of the present disclosure is also
configured to decouple background electrical system oscillations caused by other assets
connected to the external electrical system from the inverter-based resource, thereby
25 decoupling the inverter-based resource and the external electrical system for certain types
of oscillation modes. For the present disclosure, the external electrical system may be the
bulk power system (e.g., the grid), a microgrid, or an electrical island in which one or more
of the inverter-based resources are one of the primary generators within the network and
electrical power flow is dominated by local loads.
30 [0025] In particular, in an embodiment, the inverter-based resource includes an energy
buffer that is used to decouple power oscillations from the inverter-based resource from the
total power output of the inverter-based resource. For example, in an embodiment, the
7
power oscillations into the grid can be significantly reduced or eliminated by being
absorbed by the energy buffer. Further, in an embodiment, the power rating of the energy
buffer may be relatively small with respect to the inverter-based resource rating (e.g., from
about 5% to about 10% of the rating). The energy buffer may include a battery energy
5 storage device, one or more capacitors, or a resistive element (such as a dynamic brake), or
combinations thereof. In an embodiment, if a resistive element is used for the energy buffer,
an ‘offset’ power may be required to achieve a bidirectional change in power to decouple
the oscillations. Accordingly, in an embodiment, to achieve the intended behavior, the
energy buffer is controlled in such a way to create a “stiff” terminal voltage at
10 predetermined frequencies associated with a mechanical resonance mode of the IBR. By
creating this stiff voltage, the change in power caused by the inverter-based resource can
be absorbed by the energy buffer.
[0026] Similarly, any oscillations in grid voltage magnitude, frequency, or angle at the
predetermined frequency would be decoupled from the inverter-based resource, thereby
15 buffering the inverter-based resource from any background oscillations in the grid itself or
from other grid-forming or grid-following devices connected nearby. This is particularly
important for grid-forming inverter-based resources, where active power generated is
sensitive to these grid oscillations.
[0027] In an embodiment, the systems and methods of the present disclosure employ
20 an algorithm for creating a stiff voltage at the inverter-based resource terminals at certain
predetermined frequencies. For example, in an embodiment, the algorithm is configured to
receive and filter one or more voltage feedback signals relating to a voltage at a frequency
associated with the drivetrain resonance mode to extract changes in the voltage at the
frequency associated with the drivetrain resonance mode. Thus, the algorithm is configured
25 to determine at least one shunt current command or shunt power command based on the
filtered one or more voltage feedback signals. Accordingly, the algorithm is further
configured to control the power converter according to the current command and the energy
buffer according to the power command so as to reduce or eliminate the changes in the
voltage at the frequency associated with the drivetrain resonance mode.
30 [0028] More specifically, in particular embodiments, for example, the algorithm
includes receiving x and y voltage feedbacks calculated based on abc feedback signals and
synchronous reference frame transformation. The voltage feedbacks can then be filtered,
8
e.g., via a high pass filter, to remove direct current (DC) components associated with
fundamental frequency. Moreover, in an embodiment, the algorithm includes calculating
an angle rotating at a desired pre-determined frequency associated with the inverter-based
resource. In addition, the algorithm is configured to rotate the filtered voltage feedback to
5 a reference frame rotating at the desired pre-determined frequency. In this reference frame,
components of the terminal voltage oscillating at the desired pre-determined frequency
appear as DC signals. Furthermore, the rotated voltage feedbacks may again be filtered,
e.g., via a low pass filter to remove higher-frequency components not associated with
frequency components of interest. The calculated voltage feedbacks can then be used in an
10 integral controller, where the intended reference voltage at this frequency is set to zero (0).
In such embodiments, the output of the integral controller may be a shunt current injection
need to drive the changes in voltage at the pre-determined frequency to zero. As such, in
an embodiment, the algorithm includes rotating the desired current back to the synchronous
reference frame. This rotation may also include a predetermined phase shift setting that can
15 be tuned for the application. Thus, the algorithm is configured to calculate a change to a
power command for the energy buffer and/or a change for a reactive current command to
the power converter (e.g., particularly the line side converter in wind turbine applications).
[0029] Referring now to the drawings, FIG. 1 illustrates a perspective view of one
embodiment of a inverter-based resource 100 according to the present disclosure. As
20 shown, the inverter-based resource 100 may be configured as a wind turbine 102. In an
additional embodiment, the inverter-based resource 100 may, for example, be configured
as a hydroelectric plant, a fossil fuel generator, and/or a hybrid power generating asset.
[0030] When configured as a wind turbine 102, the inverter-based resource 100 may
generally include a tower 104 extending from a support surface 103, a nacelle 106 mounted
25 on the tower 104, and a rotor 108 coupled to the nacelle 106. The rotor 108 includes a
rotatable hub 110 and at least one rotor blade 112 coupled to and extending outwardly from
the hub 110. For example, in the illustrated embodiment, the rotor 108 includes three rotor
blades 112. However, in an alternative embodiment, the rotor 108 may include more or
less than three rotor blades 112. Each rotor blade 112 may be spaced about the hub 110 to
30 facilitate rotating the rotor 108 to enable kinetic energy to be transferred from the wind into
usable mechanical energy, and subsequently, electrical energy. For instance, the hub 110
may be rotatably coupled to an electric generator 118 (FIG. 2) of an electrical system 200
9
(FIG. 2) positioned within the nacelle 106 to permit electrical energy to be produced.
[0031] The wind turbine 102 may also include a controller 120 centralized within the
nacelle 106. However, in other embodiments, the controller 120 may be located within any
other component of the wind turbine 102 or at a location outside the wind turbine 102.
5 Further, the controller 120 may be communicatively coupled to any number of the
components of the wind turbine 102 in order to control the components. As such, the
controller 120 may include a computer or other suitable processing unit. Thus, in several
embodiments, the controller 120 may include suitable computer-readable instructions that,
when implemented, configure the controller 120 to perform various different functions,
10 such as receiving, transmitting and/or executing wind turbine control signals.
[0032] Furthermore, as depicted in FIG. 1, in an embodiment, the inverter-based
resource 100 may include at least one operational sensor 122. The operational sensor(s)
122 may be configured to detect a performance of the inverter-based resource 100, e.g., in
response to the environmental condition. In an embodiment, the operational sensor(s) 122
15 may be configured to monitor a plurality of electrical conditions, such as slip, stator voltage
and current, rotor voltage and current, line-side voltage and current, DC-link charge and/or
any other electrical condition of the inverter-based resource 100.
[0033] It should also be appreciated that, as used herein, the term “monitor” and
variations thereof indicates that the various sensors of the inverter-based resource 100 may
20 be configured to provide a direct measurement of the parameters being monitored or an
indirect measurement of such parameters. Thus, the sensor(s) 122 described herein may,
for example, be used to generate signals relating to the parameter being monitored, which
can then be utilized by the controller 120 to determine a condition or response of the
inverter-based resource 100.
25 [0034] Referring now to FIG. 2, wherein an exemplary electrical system 200 of the
inverter-based resource 100 is illustrated. As shown, the generator 118 may be coupled to
the rotor 108 (e.g., either directly or through a gearbox 124) for producing electrical power
from the rotational energy generated by the rotor 108. Accordingly, in an embodiment, the
electrical system 200 may include various components for converting the kinetic energy of
30 the rotor 108 into an electrical output in an acceptable form to an electrical grid 202 via grid
bus 204. For example, in an embodiment, the generator 118 may be a double-fed induction
generator (DFIG) having a stator 206 and a generator rotor 208. The generator 118 may be
10
coupled to a stator bus 210 and a power converter 220 via a rotor bus 212. In such a
configuration, the stator bus 210 may provide an output multiphase power (e.g., three-phase
power) from a stator of the generator 118, and the rotor bus 212 may provide an output
multiphase power (e.g., three-phase power) of the generator rotor 208 of the generator 118.
5 Additionally, the generator 118 may be coupled via the rotor bus 212 to a rotor side
converter 222. The rotor side converter 222 may be coupled to a line-side converter 224
which, in turn, may be coupled to a line-side bus 214.
[0035] In an embodiment, the rotor side converter 222 and the line-side converter 224
may be configured for normal operating mode in a three-phase, pulse width modulation
10 (PWM) arrangement using insulated gate bipolar transistors (IGBTs) Other suitable
switching devices may be used, such as insulated gate commuted thyristors, MOSFETs,
bipolar transistors, silicone-controlled rectifiers, and/or other suitable switching devices.
Furthermore, as shown, the rotor side converter 222 and the line-side converter 224 may be
coupled via a DC link 226 across a DC link capacitor 228. In addition, as shown, the power
15 converter 220 may include an energy buffer 238, such as a battery energy storage device,
one or more capacitors, or a resistive element (such as a dynamic brake), or combinations
thereof.
[0036] In an embodiment, the power converter 220 may be coupled to the controller
120 configured as a converter controller 230 to control the operation of the power converter
20 220. For example, the converter controller 230 may send control commands to the rotor
side converter 222 and the line-side converter 224 to control the modulation of switching
elements used in the power converter 220 to establish a desired generator torque setpoint
and/or power output.
[0037] As further depicted in FIG. 2, the electrical system 200 may, in an embodiment,
25 include a transformer 216 coupling the inverter-based resource 100 to the electrical grid
202 (or another type of electrical system, such as a microgrid or electrical island with loads).
The transformer 216 may, in an embodiment, be a three-winding transformer which
includes a high voltage (e.g., greater than 12 KVAC) primary winding 217. The high
voltage primary winding 217 may be coupled to the electrical grid 179. The transformer
30 216 may also include a medium voltage (e.g., 6 KVAC) secondary winding 218 coupled to
the stator bus 210 and a low voltage (e.g., 575 VAC, 690 VAC, etc.) auxiliary winding 219
coupled to the line bus 214. It should be appreciated that the transformer 216 can be a
11
three-winding transformer as depicted, or alternatively, may be a two-winding transformer
having only the primary winding 217 and the secondary winding 218; may be a
four-winding transformer having the primary winding 217, the secondary winding 218, the
auxiliary winding 219, and an additional auxiliary winding; or may have any other suitable
5 number of windings.
[0038] In an embodiment, the electrical system 200 may include various protective
features (e.g., circuit breakers, fuses, contactors, and other devices) to control and/or protect
the various components of the electrical system 200. For example, the electrical system
200 may, in an embodiment, include a grid circuit breaker 232, a stator bus circuit breaker
10 234, and/or a line bus circuit breaker 236. The circuit breaker(s) 232, 234, 236 of the
electrical system 200 may connect or disconnect corresponding components of the electrical
system 200 when a condition of the electrical system 200 approaches a threshold (e.g., a
current threshold and/or an operational threshold) of the electrical system 200.
[0039] Referring now to FIG. 3, a block diagram of an embodiment of suitable
15 components that may be included within a controller 300 of the inverter-based resource
100, such as the wind turbine 102, is illustrated. For example, as shown, the controller 300
may be the turbine controller 120 or the converter controller 230. Further, as shown, the
controller 120 includes one or more processor(s) 302 and associated memory device(s) 304
configured to perform a variety of computer-implemented functions (e.g., performing the
20 methods, steps, calculations and the like and storing relevant data as disclosed herein).
Additionally, the controller 300, may also include a communications module 306 to
facilitate communications between the controller 300, and the various components of the
inverter-based resource 100. Further, the communications module 306 may include a
sensor interface 308 (e.g., one or more analog-to-digital converters) to permit signals
25 transmitted from the sensor(s) 122 to be converted into signals that can be understood and
processed by the processors 302. It should be appreciated that the sensor(s) 122 may be
communicatively coupled to the communications module 306 using any suitable means.
For example, the sensor(s) 122 may be coupled to the sensor interface 308 via a wired
connection. However, in other embodiments, the sensor(s) 122 may be coupled to the
30 sensor interface 308 via a wireless connection, such as by using any suitable wireless
communications protocol known in the art.
[0040] As used herein, the term “processor” refers not only to integrated circuits
12
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. Additionally, the memory
device(s) 304 may generally include memory element(s) including, but not limited to,
5 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) 304 may generally be configured
to store suitable computer-readable instructions that, when implemented by the processor(s)
10 302, configure the controller 300 to perform various functions as described herein, as well
as various other suitable computer-implemented functions.
[0041] Referring now to FIG. 4, a flow diagram of an embodiment of a method 400 for
decoupling power oscillations from an inverter-based resource, such as inverter-based
resource 100, connected to an electrical grid from a total power output of the inverter-based
15 resource is illustrated according to the present disclosure. The method 400 may be
implemented using, for instance, the controller 300 of the present disclosure discussed
above with references to FIGS. 1-3. FIG. 4 depicts steps performed in a particular order
for purposes of illustration and discussion. Those of ordinary skill in the art, using the
disclosures provided herein, will understand that various steps of the method 400, or any of
20 the methods disclosed herein, may be adapted, modified, rearranged, performed
simultaneously, or modified in various ways without deviating from the scope of the present
disclosure.
[0042] As shown at (402), the method 400 includes receiving, via a controller, one or
more voltage feedback signals at a node between the inverter-based resource and the
25 external electrical system. As shown at (404), the method 400 includes filtering, via the
controller, the one or more voltage feedback signals to extract changes in the voltage at the
frequency associated with the drivetrain resonance mode. As shown at (406), the method
400 includes determining, via the controller, at least one current command or power
command based on the filtered one or more voltage feedback signals. As shown at (408),
30 the method 400 includes controlling the power converter according to the at least one
current command and controlling the energy buffer according to the power command so as
to reduce or eliminate the changes in the voltage at the frequency associated with the
13
drivetrain resonance mode.
[0043] The method 400 of FIG. 4 can be better understood with reference to FIG. 5. In
particular, FIG. 5 illustrates a schematic diagram of an embodiment of an algorithm 500
that can be implemented by the controller 300 for decoupling power oscillations from an
5 inverter-based resource, such as inverter-based resource 100, connected to an electrical grid
from a total power output of the inverter-based resource is illustrated according to the
present disclosure. As shown, the algorithm 500 receives one or more inputs. In particular
embodiments, as shown, the input(s) may include, for example, one or more voltage
feedback signals 502 relating to a voltage at a frequency associated with the drivetrain
10 resonance mode. In particular, as shown, the voltage feedback signal(s) 502 may include x
and y voltage feedback signals (e.g., VMxyFbk). These x and y voltage feedbacks
correspond to voltages at a node between the electrical system and the IBR, such as voltages
at the primary winding of the IBR terminals or the secondary of the IBR terminals (or other
node through which the entirety of output current of the IBR flows). In addition, as shown,
15 the algorithm 500 is configured to calculate an angle 510 (e.g., DtdAng) rotating at a desired
predetermined frequency (e.g., Fdtd) associated with the inverter-based resource 100.
[0044] Further, in an embodiment, as shown, the algorithm 500 may include filtering
the voltage feedback signal(s) to extract changes in the voltage at the frequency associated
with the drivetrain resonance mode. In particular embodiments, as shown, the algorithm
20 500 may include filtering, via a first filter 504, the voltage feedback signal(s) 502 to remove
one or more direct current (DC) components associated with a fundamental frequency. An
output of the first filter 504 is represented as 506 in FIG. 5. For example, as shown, the
first filter 504 may be a high-pass filter. In addition, as shown, the algorithm 500 is
configured to filter, via a second filter 514, the voltage feedback signals 502 to remove high
25 frequency components not associated with the desired predetermined frequency. An output
of the second filter 514 is represented as 516 in FIG. 5. In certain embodiments, for
example, the second filter 514 may be a low-pass filter.
[0045] In further embodiments, as shown at 508, the algorithm 500 may also include
rotating the filtered voltage feedback signals 506 (e.g., VMxyFbkHp) (i.e., after the first
30 filter 504) from a synchronous reference frame to a reference frame rotating at the desired
predetermined frequency based on the angle 510. The rotated signal is represented as 512
in FIG. 5. In such embodiments, in the reference frame, components of a terminal voltage
14
of the inverter-based resource 100 oscillating at the desired predetermined frequency appear
as direct current (DC) signals. Thus, as shown, the second filtering step can be employed
after rotating the filtered voltage feedback signals 506 (e.g., VMxyFbkHp) from the
synchronous reference frame to the reference frame rotating at the desired predetermined
5 frequency based on the angle 510.
[0046] Moreover, as shown, the algorithm 500 is further configured to determine at
least one current command 532 (ΔILyDtd) or a power command 530 (e.g., ΔDcPCmd)
based on the filtered voltage feedback signal(s) (represented by 516). The at least one
current command or power command are intended to be reflected as shunt (or parallel)
10 current/power injection at the node (or close to) for which the changes in voltage are being
measured (for example, in a double-fed type generator, this can naturally be injected
through the line-side converter since it injects a shunt current/power at a node between the
external electrical system and the IBR generator). More specifically, as shown, the
algorithm 500 is configured to generate, via an integral controller 518, an output 520 using
15 the rotated voltage feedback signal(s) 516. In such embodiments, as shown, an intended
reference voltage at the desired predetermined frequency (e.g., Fdtd) of the integral
controller 518 is set to zero (0) and the output 520 of the integral controller 518 is the
desired current associated with the desired predetermined frequency.
[0047] Thus, in an embodiment, as shown at 522, the algorithm 500 is configured to
20 determine the current command 532 (ΔILyDtd) or a power command 530 (e.g., ΔDcPCmd)
based on the filtered one or more voltage feedback signals 516 by rotating the output 520
associated with the desired predetermined frequency back to the synchronous reference
frame to generate a desired current 528 (e.g., ΔILxyDtd). Accordingly, in such
embodiments, the algorithm 500 is configured to determine the current command 532
25 (ΔILyDtd) or a power command 530 (e.g., ΔDcPCmd) based on the desired current 528.
[0048] Still referring to FIG. 5, as shown, the algorithm 500 may also apply a
predetermined phase shift setting 524 during the rotation at 522. In such embodiments, the
predetermined phase shift setting 524 may be determined as a function of the angle 510 and
a drivetrain angle 526 (e.g., θdtd). In an embodiment, the drivetrain angle 526 may be tuned
30 at the design stage to give a reasonable decoupling of grid/drivetrain oscillations for a wide
range of possible external electrical system types. Alternatively, this setting may be tuned
on a site-by-site basis to optimize performance for the application.
15
[0049] Thus, as shown in FIG. 6, the current command 532 (ΔILyDtd) or a power
command 530 (e.g., ΔDcPCmd) can be sent to an energy buffer control 534 and a line
converter control 536, respectively, e.g., of the converter controller 230. In an embodiment,
if the energy buffer 238 is a dynamic brake, the algorithm 500 may be selectively enabled
5 upon detection of an island condition. Otherwise, in an embodiment, the algorithm 500
may operate continuously.
[0050] Accordingly, the current command 532 (ΔILyDtd) or a power command 530
(e.g., ΔDcPCmd) is configured to achieve the intended behavior to decouple power
oscillations from the inverter-based resource 100 from a total power output of the inverter10 based resource 100. In particular embodiments, for example, the energy buffer 238 is
controlled in such a way to create a “stiff” terminal voltage (e.g., VM in FIG. 6) at
predetermined frequencies. By creating this stiff voltage, the change in power caused by
the wind turbine 102 can be absorbed by the energy buffer 238.
[0051] Similarly, any oscillations in grid voltage magnitude, frequency, or angle at the
15 predetermined frequency are decoupled from the wind turbine 102, thereby buffering the
wind turbine 102 from any background oscillations in the grid itself or from other gridforming or grid-following devices connected nearby. This is particularly important for gridforming wind turbines, where active power generated is sensitive to these grid oscillations.
[0052] Furthermore, the skilled artisan will recognize the interchangeability of various
20 features from different embodiments. Similarly, the various method steps and features
described, as well as other known equivalents for each such methods and feature, can be
mixed and matched by one of ordinary skill in this art to construct additional systems and
techniques in accordance with principles of this disclosure. Of course, it is to be understood
that not necessarily all such objects or advantages described above may be achieved in
25 accordance with any particular embodiment. Thus, for example, those skilled in the art will
recognize that the systems and techniques described herein may be embodied or carried out
in a manner that achieves or optimizes one advantage or group of advantages as taught
herein without necessarily achieving other objects or advantages as may be taught or
suggested herein.
30 [0053] Further aspects of the invention are provided by the subject matter of the
following clauses:
[0054] A method for decoupling a mechanical drivetrain resonance mode of an inverter-
16
based resource from the external electrical system, the inverter-based resource having a
power converter, a generator, and an energy buffer, the method comprising: receiving, via
a controller, one or more voltage feedback signals at a node between the inverter-based
resource and the external electrical system; filtering, via the controller, the one or more
5 voltage feedback signals to extract changes in a voltage at a frequency associated with the
drivetrain resonance mode; determining, via the controller, at least one current command
or power command based on the filtered one or more voltage feedback signals; and
controlling the power converter according to the at least one current command and
controlling the energy buffer according to the power command so as to reduce or eliminate
10 the changes in the voltage at the frequency associated with the drivetrain resonance mode.
[0055] The method of any preceding clause, wherein the one or more voltage feedback
signals comprise x and y voltage feedback signals.
[0056] The method of any preceding clause, further comprising calculating, via the
controller, an angle rotating at a desired predetermined frequency associated with the
15 inverter-based resource.
[0057] The method of any preceding clause, wherein filtering the one or more voltage
feedback signals to extract the changes in the voltage at the frequency associated with the
drivetrain resonance mode further comprises: filtering, via a first filter, the one or more
voltage feedback signals to remove one or more direct current (DC) components associated
20 with a fundamental frequency; and subsequently filtering, via a second filter, the one or
more voltage feedback signals to remove high frequency components not associated with
the desired predetermined frequency.
[0058] The method of any preceding clause, wherein the first filter is a high-pass filter
and the second filter is a low-pass filter.
25 [0059] The method of any preceding clause, further comprising: rotating, via the
controller, the one or more voltage feedback signals from a synchronous reference frame to
a reference frame rotating at the desired predetermined frequency after filtering via the first
filter and before filtering via the second filter, wherein in the reference frame, components
of a terminal voltage of the inverter-based resource oscillating at the desired predetermined
30 frequency appear as direct current (DC) components.
[0060] The method of any preceding clause, wherein determining the at least one
current command or the power command based on the filtered one or more voltage feedback
17
signals further comprises: generating, via an integral controller of the controller, an output
using the rotated one or more voltage feedback signals, wherein an intended reference
voltage at the desired predetermined frequency of the integral controller is set to zero (0)
and the output of the integral controller is a shunt current injection needed to drive the
5 changes in the voltage at the predetermined frequency to zero.
[0061] The method of any preceding clause, wherein determining the at least one
current command or the power command based on the filtered one or more voltage feedback
signals further comprises: rotating the output associated with the desired predetermined
frequency back to the synchronous reference frame to generate a desired current; and
10 determining the at least one current command or the power command based on the desired
current.
[0062] The method of any preceding clause, wherein rotating the output associated with
the desired predetermined frequency back to the synchronous reference frame further
comprises applying a predetermined phase shift setting.
15 [0063] The method of any preceding clause, wherein the energy buffer comprises one
of a dynamic brake, a capacitor, or a battery.
[0064] The method of any preceding clause, wherein the inverter-based resource
comprises one of a wind turbine power system, a solar power system, a hydro-generator, or
combinations thereof.
20 [0065] An inverter-based resource connected to an external electrical system, the
inverter-based resource comprising: a generator; an energy buffer; a power converter
coupled to the generator; and a controller comprising at least one processor configured to
perform a plurality of operations, the plurality of operations comprising: receiving one or
more voltage feedback signals at a node between the inverter-based resource and the
25 external electrical system; filtering the one or more voltage feedback signals to extract
changes in voltage at a frequency associated with a drivetrain resonance mode; determining
at least one current command or power command based on the filtered one or more voltage
feedback signals; and controlling the power converter according to the at least one current
command and controlling the energy buffer according to the power command so as to
30 reduce or eliminate the changes in the voltage at the frequency associated with the drivetrain
resonance mode.
[0066] The inverter-based resource of any preceding clause, wherein the one or more
18
voltage feedback signals comprise x and y voltage feedback signals.
[0067] The inverter-based resource of any preceding clause, wherein the plurality of
operations further comprises: calculating an angle rotating at a desired predetermined
frequency associated with the inverter-based resource.
5 [0068] The inverter-based resource of any preceding clause, wherein filtering the one
or more voltage feedback signals to extract the changes in the voltage at the frequency
associated with the drivetrain resonance mode further comprises: filtering, via a first filter,
the one or more voltage feedback signals to remove one or more direct current (DC)
components associated with a fundamental frequency; and subsequently filtering, via a
10 second filter, the one or more voltage feedback signals to remove high frequency
components not associated with the desired predetermined frequency.
[0069] The inverter-based resource of any preceding clause, wherein the plurality of
operations further comprises: rotating the one or more voltage feedback signals from a
synchronous reference frame to a reference frame rotating at the desired predetermined
15 frequency after filtering via the first filter and before filtering via the second filter, wherein
in the reference frame, components of a terminal voltage of the inverter-based resource
oscillating at the desired predetermined frequency appear as direct current (DC)
components.
[0070] The inverter-based resource of any preceding clause, wherein determining the
20 at least one current command or the power command based on the filtered one or more
voltage feedback signals further comprises: generating, via an integral controller of the
controller, an output using the rotated one or more voltage feedback signals, wherein an
intended reference voltage at the desired predetermined frequency of the integral controller
is set to zero (0) and the output of the integral controller is a shunt current injection needed
25 to drive the changes in the voltage at the predetermined frequency to zero.
[0071] The inverter-based resource of any preceding clause, wherein determining the
at least one current command or the power command based on the filtered one or more
voltage feedback signals further comprises: rotating the output associated with the desired
predetermined frequency back to the synchronous reference frame to generate a desired
30 current; and determining the at least one current command or the power command based on
the desired current.
[0072] The inverter-based resource of any preceding clause, wherein rotating the output
19
associated with the desired predetermined frequency back to the synchronous reference
frame further comprises applying a predetermined phase shift setting.
[0073] The inverter-based resource of any preceding clause, wherein the energy buffer
comprises one of a dynamic brake, a capacitor, or a battery, and wherein the inverter-based
5 resource comprises one of a wind turbine power system, a solar power system, a hydrogenerator, or combinations thereof.
[0074] 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
10 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

We Claim:
1. A method for decoupling a mechanical drivetrain resonance mode of an
inverter-based resource from an external electrical system, the inverter-based resource
5 having a power converter, a generator, and an energy buffer, the method comprising:
receiving, via a controller, one or more voltage feedback signals at a node between
the inverter-based resource and the external electrical system;
filtering, via the controller, the one or more voltage feedback signals to extract
changes in a voltage at a frequency associated with the drivetrain resonance mode;
10 determining, via the controller, at least one current command or power command
based on the filtered one or more voltage feedback signals; and
controlling the power converter according to the at least one current command and
controlling the energy buffer according to the power command so as to reduce or eliminate
the changes in the voltage at the frequency associated with the drivetrain resonance mode.
15
2. The method of claim 1, wherein the one or more voltage feedback signals
comprise x and y voltage feedback signals.
3. The method of claim 1, further comprising calculating, via the controller, an
20 angle rotating at a desired predetermined frequency associated with the inverter-based
resource.
4. The method of claim 3, wherein filtering the one or more voltage feedback
signals to extract the changes in the voltage at the frequency associated with the drivetrain
25 resonance mode further comprises:
filtering, via a first filter, the one or more voltage feedback signals to remove one
or more direct current (DC) components associated with a fundamental frequency; and
subsequently filtering, via a second filter, the one or more voltage feedback signals
to remove high frequency components not associated with the desired predetermined
30 frequency.
5. The method of claim 4, wherein the first filter is a high-pass filter and the
21
second filter is a low-pass filter.
6. The method of claim 4, further comprising:
rotating, via the controller, the one or more voltage feedback signals from a
5 synchronous reference frame to a reference frame rotating at the desired predetermined
frequency after filtering via the first filter and before filtering via the second filter,
wherein in the reference frame, components of a terminal voltage of the inverterbased resource oscillating at the desired predetermined frequency appear as direct current
(DC) components.
10
7. The method of claim 6, wherein determining the at least one current
command or the power command based on the filtered one or more voltage feedback signals
further comprises:
generating, via an integral controller of the controller, an output using the rotated
15 one or more voltage feedback signals,
wherein an intended reference voltage at the desired predetermined frequency of the
integral controller is set to zero (0) and the output of the integral controller is a shunt current
injection needed to drive the changes in the voltage at the predetermined frequency to zero.
20 8. The method of claim 7, wherein determining the at least one current
command or the power command based on the filtered one or more voltage feedback signals
further comprises:
rotating the output associated with the desired predetermined frequency back to the
synchronous reference frame to generate a desired current; and
25 determining the at least one current command or the power command based on the
desired current.
9. The method of claim 8, wherein rotating the output associated with the
desired predetermined frequency back to the synchronous reference frame further
30 comprises applying a predetermined phase shift setting.
10. The method of claim 1, wherein the energy buffer comprises one of a
22
dynamic brake, a capacitor, or a battery.
11. The method of claim 1, wherein the inverter-based resource comprises one
of a wind turbine power system, a solar power system, a hydro-generator, or combinations
5 thereof.
12. An inverter-based resource connected to an external electrical system, the
inverter-based resource comprising:
a generator;
10 an energy buffer;
a power converter coupled to the generator; and
a controller comprising at least one processor configured to perform a plurality of
operations, the plurality of operations comprising:
receiving one or more voltage feedback signals at a node between the inverter-based
15 resource and the external electrical system;
filtering the one or more voltage feedback signals to extract changes in voltage at a
frequency associated with a drivetrain resonance mode;
determining at least one current command or power command based on the filtered
one or more voltage feedback signals; and
20 controlling the power converter according to the at least one current command and
controlling the energy buffer according to the power command so as to reduce or eliminate
the changes in the voltage at the frequency associated with the drivetrain resonance mode.
13. The inverter-based resource of claim 12, wherein the one or more voltage
25 feedback signals comprise x and y voltage feedback signals.
14. The inverter-based resource of claim 12, wherein the plurality of operations
further comprises:
calculating an angle rotating at a desired predetermined frequency associated with
30 the inverter-based resource.
15. The inverter-based resource of claim 14, wherein filtering the one or more
23
voltage feedback signals to extract the changes in the voltage at the frequency associated
with the drivetrain resonance mode further comprises:
filtering, via a first filter, the one or more voltage feedback signals to remove one
or more direct current (DC) components associated with a fundamental frequency; and
5 subsequently filtering, via a second filter, the one or more voltage feedback signals
to remove high frequency components not associated with the desired predetermined
frequency.
16. The inverter-based resource of claim 15, wherein the plurality of operations
10 further comprises:
rotating the one or more voltage feedback signals from a synchronous reference
frame to a reference frame rotating at the desired predetermined frequency after filtering
via the first filter and before filtering via the second filter,
wherein in the reference frame, components of a terminal voltage of the inverter15 based resource oscillating at the desired predetermined frequency appear as direct current
(DC) components.
17. The inverter-based resource of claim 16, wherein determining the at least
one current command or the power command based on the filtered one or more voltage
20 feedback signals further comprises:
generating, via an integral controller of the controller, an output using the rotated
one or more voltage feedback signals,
wherein an intended reference voltage at the desired predetermined frequency of the
integral controller is set to zero (0) and the output of the integral controller is a shunt current
25 injection needed to drive the changes in the voltage at the predetermined frequency to zero.
18. The inverter-based resource of claim 17, wherein determining the at least
one current command or the power command based on the filtered one or more voltage
feedback signals further comprises:
30 rotating the output associated with the desired predetermined frequency back to the
synchronous reference frame to generate a desired current; and
determining the at least one current command or the power command based on the
24
desired current.
19. The inverter-based resource of claim 18, wherein rotating the output
associated with the desired predetermined frequency back to the synchronous reference
5 frame further comprises applying a predetermined phase shift setting.
20. The inverter-based resource of claim 12, wherein the energy buffer
comprises one of a dynamic brake, a capacitor, or a battery, and wherein the inverter-based
resource comprises one of a wind turbine power system, a solar power system, a hydro10 generator, or combinations thereof.