System and method for reducing power oscillations generated by inverter-based resources and injected into electrical grid

Abstract

A method for reducing power oscillations generated by an inverter-based resource system and injected into a power grid includes communicatively coupling a system-level energy buffer circuit with a system-level controller. The system-level controller is communicatively coupled to a local controller of the inverter-based resources. The method also includes generating, via a system-level energy buffer circuit, an energy buffer for the inverter-based resource system. Further, the method includes applying an energy buffer to the power oscillations generated by the inverter-based resource system to decouple the power oscillations generated by the inverter-based resource system from the total output power of the inverter-based resource system.

Description

Technical Field

[0001] The present disclosure relates generally to inverter-based resources (IBRs), and more particularly, to systems and methods for decoupling drive train-related power oscillations from real power injected into a grid, thereby allowing the IBRs to manage loading on the drive train independent of grid conditions. Background Art

[0002] Wind power is considered to be one of the cleanest and most environmentally friendly energy sources currently available, and wind turbines have gained increasing attention in this regard. Modern wind turbines typically include a tower, a generator, a gearbox, a nacelle, and one or more rotor blades. The rotor blades are the main elements for converting wind energy into electrical energy. The blades typically have an airfoil-shaped cross-sectional profile so that during operation, air flows over the blades, thereby creating a pressure difference between their two sides. Therefore, a lift force directed from the pressure side to the suction side acts on the blades. The lift force generates a torque on the main rotor shaft, which is connected to a generator for generating electricity that is transmitted to a power grid. The power grid transmits electrical energy from the power generation facility to the end user.

[0003] Wind power generation is typically provided by a wind farm that includes a plurality of wind turbine generators (e.g., typically 100 or more). A typical wind farm has a field-level controller that regulates voltage, reactive power, and / or power factor at the wind farm interconnection point (i.e., the point at which the local wind turbine generators are connected to the grid; may also be referred to as a point of common coupling). In such a wind farm, the field-level controller achieves its control objectives by sending reactive power or reactive current commands to individual wind turbine generators within the wind farm. However, certain constraints of the local wind turbine generators within the wind farm may constrain the ability to supply reactive power. Such constraints may include, for example, voltage limits, reactive power limits, and / or current limits.

[0004] Modern wind turbine generators (WTGs) utilize grid-connected power converters to implement certain special dynamic control functions (in addition to the primary control functions of regulating speed and power), such as damping drive train torsional oscillations and damping tower oscillations. These control functions vary the active power injected into the grid at a specific frequency. The power oscillation component is typically at a known frequency determined by the size and physical characteristics of the WTG. These control functions are practical because the resources forming the grid (mainly synchronous machines) are available in large quantities in most applications, allowing these other resources to adapt to changes in the active power injected by the WTG.

[0005] WTG is a type of inverter-based resource (IBR), which means an inverter that converts direct current (DC) to alternating current (AC), and it can be used to interface any energy source to an ac power system. Therefore, energy sources may include, but are not limited to: renewable sources such as solar photovoltaic arrays, wind turbines, battery energy storage devices, supercapacitors; or fossil fuel-based sources such as diesel or natural gas generator sets; STATCOM, HVDC VSC; or any combination of these energy sources attached to a DC network. In addition, IBR can operate in grid tracking mode or grid forming mode.

[0006] As used herein, a grid tracking device utilizes a fast current regulation loop to control the active and reactive power exchanged with the grid. More specifically, an active power reference for the converter is generated by an energy source regulator (e.g., a turbine control portion of a wind turbine). This is communicated as a torque reference, which represents the lesser of the maximum available power from the energy source at that moment, or a reduction command from a higher-level grid controller. The converter controller then determines a current reference for the active component of the current to achieve the desired torque. Therefore, the WTG includes functionality to manage voltage and reactive power in a manner that generates commands for the reactive component of the current. A wide bandwidth current regulator then generates a command for the voltage to be applied to the system by the converter so that the actual current closely tracks the command.

[0007] Alternatively, a grid-forming converter provides a voltage source characteristic in which the angle and amplitude of the voltage are controlled to achieve the regulation function required by the grid. With this structure, current will flow according to the needs of the grid, while the converter facilitates the establishment of the voltage and frequency for the grid. This characteristic is comparable to that of a conventional generator based on a turbine-driven synchronous machine. Therefore, a grid-forming source must include the following basic functions: (1) support grid voltage and frequency (both real and reactive) for any current flow within the rating of the device; (2) prevent operation beyond the voltage or current capability of the device by allowing the grid voltage or frequency to change without disconnecting the device (disconnection is only allowed when the voltage or frequency is outside the limits established by the grid entity); (3) remain stable for any grid configuration or load characteristics, including serving isolated loads or connecting to other grid-forming sources, and switching between such configurations; (4) share the total load of the grid among other grid-forming sources connected to the grid; (5) ride through both major and minor grid disturbances, and (6) meet requirements (1)-(5) without requiring rapid communication with other control systems present in the grid, or externally generated logic signals related to changes in grid configuration.

[0008] In the coming years, many of the synchronous machines connected to the grid are likely to be retired. A consequence of this structural change in the grid is that the ability of an IBR (such as a group of WTGs) to freely vary the power entering the grid may become more restricted. For this reason, alternative resources that can supply the power requirements for these control functions would be beneficial.

[0009] Accordingly, the present disclosure is directed to systems and methods for decoupling drive train related power oscillations from active power injected into a grid, thereby allowing the WTG(s) to manage loading on the drive train independent of grid conditions. Summary of the invention

[0010] 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.

[0011] In aspect, the present disclosure is directed to a method for reducing power oscillations generated by a system of inverter-based resources and injected into a power grid. The method includes communicatively coupling a system-level energy buffer circuit to a system-level controller. The system-level controller is communicatively coupled to a local controller of the inverter-based resources. The method also includes generating an energy buffer for the system of inverter-based resources via the system-level energy buffer circuit. In addition, the method includes applying the energy buffer to the power oscillations generated by the system of inverter-based resources so as to decouple the power oscillations generated by the system of inverter-based resources from the total output power of the system of inverter-based resources.

[0012] In another aspect, the present disclosure is directed to a wind farm connected to an electric power grid. The wind farm includes a plurality of wind turbine generators, a farm-level controller, and a farm-level energy buffer circuit for reducing power oscillations generated by the plurality of wind turbine generators and injected into the electric power grid. The farm-level energy buffer circuit is communicatively coupled to the farm-level controller. The farm-level energy buffer circuit is configured to perform a plurality of operations, including but not limited to generating an energy buffer for the wind farm, and applying the energy buffer to the power oscillations generated by the plurality of wind turbine generators so as to decouple the power oscillations generated by the plurality of wind turbine generators from the total output power of the wind farm.

[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 present invention and, together with the description, serve to explain the principles of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] A complete and enabling disclosure of the present invention, including the best mode thereof, to one of ordinary skill in the art is set forth in the specification with reference to the accompanying drawings, in which:

[0015] Figure 1 illustrates a block diagram of a wind farm having a plurality of wind turbine generators coupled to a transmission grid in accordance with the present disclosure;

[0016] Figure 2 illustrates a block diagram of suitable components that may be included in an embodiment of a controller according to the present disclosure;

[0017] Figure 3 A flow chart illustrating an embodiment of a method for reducing power oscillations generated by a system of inverter-based resources and injected into a power grid according to the present disclosure;

[0018] Figure 4 illustrates a schematic diagram of an embodiment of a field level energy buffer circuit for generating an energy buffer according to the present disclosure;

[0019] Figure 5 A schematic diagram illustrating an embodiment of an algorithm for generating a stiff voltage at a collector bus at certain predetermined frequencies according to the present disclosure; and

[0020] Figure 6 A schematic diagram of an embodiment of a control structure for a grid tracking voltage source converter according to the present disclosure is illustrated, wherein new signals have been added to the power reference and the voltage reference to achieve a rigid voltage at the collector bus at certain predetermined frequencies. DETAILED DESCRIPTION

[0021] Reference will now be made in detail to embodiments of the present invention, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation of the present invention rather than by way of limitation of the present invention. In fact, it will be apparent to those skilled in the art that various modifications and variations may be made in the present invention without departing from the scope or spirit of the present invention. For example, a feature illustrated or described as a part of one embodiment may be used together with another embodiment to produce yet another embodiment. Therefore, it is intended that the present invention covers such modifications and variations as those within the scope of the appended claims and their equivalents.

[0022] In general, the present disclosure is directed to systems and methods for decoupling power oscillations associated with a transmission system from active power injected into a power grid, thereby allowing a system of one or more inverter-based resources (IBRs) to manage the load on the transmission system independently of grid conditions. Therefore, the systems and methods of the present disclosure include a system-level energy buffer circuit that decouples power oscillations from the IBRs from the total power output of the system (e.g., a wind farm). Using the system-level energy buffer circuit, power oscillations entering the grid can be significantly reduced or eliminated by being absorbed by an energy buffer generated by the system-level energy buffer circuit. In a specific embodiment, the system-level energy buffer circuit includes a voltage source converter, wherein the energy storage hardware is connected to the DC link. In addition, the system-level energy buffer circuit can have its own transformer that raises the voltage to the nominal collector bus voltage. In order to achieve the expected behavior, the system-level energy buffer circuit is controlled in such a way that a rigid collector bus voltage is generated at a predetermined frequency. By generating such a rigid voltage, power variations caused by a collection group or system of IBRs are absorbed by the energy buffer without requiring any feedback / communication between the energy buffer and the IBR itself.

[0023] As used herein, a "rigid" voltage may be achieved by either a grid tracking or a grid forming IBR, wherein the generation of a rigid voltage involves a control element that counteracts voltage variations at a certain electrical node. Thus, in an embodiment, generating a rigid voltage at a particular frequency involves a control system that largely prevents or minimizes variations in voltage amplitude and angle at that frequency. Thus, in an embodiment, an IBR that generates a rigid voltage supplies the necessary current / power flow to prevent or minimize variations in voltage amplitude and angle.

[0024] Now referring to the accompanying drawings, Figure 1 A block diagram of a wind farm 100 having a plurality of wind turbine generators 110 coupled to a transmission grid 190 is illustrated. Figure 1 Three wind turbines 110 are illustrated; however, any number of wind turbines may be included in the wind farm 100. In addition, as shown, each of the wind turbine generators 110 includes a local control 112 that responds to the condition of the wind turbine generator 110 being controlled. The local control 112 may include, for example, a turbine controller and / or a converter controller. In one embodiment, the local control 112 of each wind turbine generator 110 senses only the terminal voltage and current (via a potential and current transformer). The sensed voltage and current are used by the local control 112 to provide an appropriate response so that the (one or more) wind turbine generators 110 provide the desired reactive power.

[0025] Each wind turbine generator 110 is coupled to the collector bus 120 via a generator connection transformer 115 to provide real power and reactive power (respectively denoted as P and R) to the collector bus 120. wg and Q wg ). Generator connection transformers and collector busbars are known in the art.

[0026] The wind farm 100 provides real power output and reactive power output (respectively marked as P and wf and Q wf A farm level controller 150 communicatively coupled to the local control 112 senses the wind farm output and the voltage at the point of common coupling (PCC) 140 to provide a Q command signal 105 (Q CMD ), the Q command signal 105 indicates the desired reactive power at the generator terminals to ensure a reasonable distribution of reactive power among the wind turbines. In an alternative embodiment, for example, when (one or more) wind turbine generators are in manual mode or otherwise not in communication with the wind farm level controller 150, the Q command signal (Q CMD )105 can be used as local or operator level (by Figure 1 The "LOCAL" line in the .

[0027] Reference now Figure 2 , illustrates a block diagram of one embodiment of suitable components that may be included within a local control 112 and / or a farm level controller 150 according to aspects of the present disclosure. As shown, the local control 112 and / or the farm level controller 150 may include one or more processors 152 and associated memory devices 154 configured to perform various computer-implemented functions (e.g., perform methods, steps, calculations, etc., and store relevant data as disclosed herein). In addition, the local control 112 and the farm level controller 150 may also include a communication module 156 that is used to facilitate communication between the local control 112 and / or the farm level controller 150 and various components of the wind farm 100. In addition, the communication module 156 may include a sensor interface 158 (e.g., one or more analog-to-digital converters) that is used to allow signals transmitted from one or more sensors 160, 162, 164 to be converted into signals that can be understood and processed by the processor 152. It should be appreciated that the sensors 160, 162, 164 may be communicatively coupled to the communication module 156 using any suitable means. For example, as shown, sensors 160, 162, 164 are coupled to sensor interface 158 via a wired connection. However, in other embodiments, sensors 160, 162, 164 may be coupled to sensor interface 158 via a wireless connection, such as by using any suitable wireless communication protocol known in the art.

[0028] As used herein, the term "processor" refers not only to what is known in the art as an integrated circuit included in a computer, but also to controllers, microcontrollers, microcomputers, programmable logic controllers (PLCs), application specific integrated circuits, and other programmable circuits. In addition, the memory device(s) 154 may generally include memory elements, including but not limited to computer-readable media (e.g., random access memory (RAM)), computer-readable non-volatile media (e.g., flash memory), floppy disks, compact disk read-only memory (CD-ROM), magneto-optical disks (MOD), digital versatile disks (DVD), and / or other suitable memory elements. Such memory device(s) 154 may generally be configured to store suitable computer-readable instructions that, when implemented by the processor(s) 152, configure the local control 112 and / or field level controller 150 to perform various functions as described herein.

[0029] Sensors 160, 162, 164 may include any suitable sensors configured to provide feedback measurements to field level controller 150. In various embodiments, for example, sensors 160, 162, 164 may be any one or combination of voltage sensors, current sensors, and / or any other suitable sensors.

[0030] Return to reference Figure 1 The wind farm 100 also includes a field-level energy buffer circuit 130 according to the present disclosure. The details of the field-level energy buffer circuit 130 are referred to herein. Figure 3-Figure 6 Therefore, in an embodiment, the purpose of the field-level energy buffer circuit 130 is to decouple the power oscillations from the wind turbine generator 110 from the total power output of the wind farm 100. Therefore, using the field-level energy buffer circuit 130, the power oscillations entering the power grid can be significantly reduced and / or eliminated by being absorbed by the power variation 132 represented by ΔPeb. In addition, in an embodiment, the power rating of the power variation 132 is relatively small relative to the wind farm power rating, such as from about 5% to about 10% of the wind farm power rating.

[0031] Special References Figure 3-Figure 6 , illustrates embodiments of various systems and methods for reducing power oscillations generated by an inverter-based resource system (such as a wind farm 100) and injected into a power grid according to the present disclosure. In particular, Figure 3 1 is a flow chart illustrating one embodiment of a method 200 for reducing power oscillations generated by a system of inverter-based resources and injected into a power grid according to the present disclosure. For purposes of illustration and discussion, Figure 3The steps are depicted to be performed in a specific order. Using the disclosure provided herein, one of ordinary skill in the art will understand that the various steps of any of the methods disclosed herein may be deployed, omitted, rearranged or expanded in various ways without departing from the scope of the present disclosure.

[0032] As shown at (202), the method 200 includes communicatively coupling a system-level energy buffer circuit, such as a field-level energy buffer circuit 130, to a system-level controller, such as a field-level controller 150. Furthermore, in an embodiment, the system-level controller may be communicatively coupled to a local controller of an inverter-based resource, such as a wind turbine generator 110 having a local control 112.

[0033] As shown at (204), the method 200 includes generating an energy buffer for the system of inverter-based resources via a system-level energy buffer circuit (e.g., implemented by the power change ΔPeb 132). Therefore, as shown at (206), the method 200 includes applying the energy buffer to the power oscillations (e.g., ΔP1, ΔP2, ΔP3, etc.) generated by the system of inverter-based resources so as to decouple the power oscillations generated by the system of inverter-based resources from the total output power (e.g., ΔPtot) of the system of inverter-based resources.

[0034] refer to Figure 4-6 Better understanding Figure 3 Method 200. Figure 4 A schematic diagram of an embodiment of a field level energy buffer circuit 130 for generating a power variation 132 according to the present disclosure is illustrated. Referring now to Figure 5 , a schematic diagram illustrating an embodiment of an algorithm 300 for generating a stiffness voltage at a collector bus at certain predetermined frequencies, according to the present disclosure. Figure 6 A schematic diagram of an embodiment of a control structure 400 for a grid tracking voltage source converter according to the present disclosure is illustrated, wherein new signals have been added to the power reference and the voltage reference to achieve a rigid voltage at the collector bus at certain predetermined frequencies. It should also be understood that although Figure 6 A grid tracking voltage source converter is illustrated, but similar variations can equally be applied to a grid forming control structure to achieve similar performance.

[0035] In particular Figure 4As shown in , in an embodiment, the field level energy buffer circuit 130 includes a voltage source converter 134, wherein energy storage hardware 136 is connected to a DC link 138. In certain embodiments, for example, the energy storage hardware 136 may include a battery, a capacitor, and / or any other suitable type of energy storage system. In addition, as shown, the field level energy buffer circuit 130 may also have a transformer 142 that steps up the voltage to a nominal collector bus voltage, as described in more detail herein below. The output of the field level energy buffer circuit 130 is a power variation 132, which decouples the power oscillations generated by the system of inverter-based resources from the total output power of the system (e.g., ΔPtot), thereby reducing and / or eliminating power oscillations injected into the power grid.

[0036] More specifically, to achieve the desired behavior, the field level energy buffer circuit 130 is controlled in such a way that a "rigid" collector bus voltage is generated at a predetermined frequency. By generating this rigid voltage, power variations caused by the collective group of inverter-based resources are absorbed by the power variations 132 without the need for any feedback and / or communication between the power variations 132 and the inverter-based resources. Similarly, any oscillations in grid frequency or angle at the predetermined frequency can be decoupled from the inverter-based resources, thereby buffering the inverter-based resources from any background oscillations in the power grid. This can be particularly important for grid-forming wind turbines, where the generated active power is sensitive to these grid oscillations.

[0037] Special References Figure 5 , as mentioned, a schematic diagram of an embodiment of an algorithm 300 for generating a stiff voltage at a collector bus 120 at certain predetermined frequencies according to the present disclosure. In particular, as shown, the algorithm 300 receives one or more voltage or current feedbacks. For example, as shown, the algorithm 300 receives xy voltage and current feedback (e.g., VtxyFbk 302 and ItxyFbk 304), which can be calculated based on the abc feedback signal and the synchronous reference frame transformation. In addition, as shown, the algorithm 300 is configured to estimate the collector voltage feedback (e.g., VcxyFbk 308) using the impedance 306 of the transformer 142 of the field level energy buffer circuit 130 and the voltage and current feedback.

[0038] Furthermore, in an embodiment, the algorithm 300 includes applying one or more filters to the collector voltage feedback. In a specific embodiment, as an example, the algorithm 300 may include applying one or more first filters to the collector voltage feedback to remove one or more direct current (DC) components thereof associated with a fundamental frequency. Furthermore, in an embodiment, the algorithm 300 may include applying one or more second filters to the collector voltage feedback to remove high frequency components not associated with a drive train component of one or more of the inverter-based resources.

[0039] For example, as shown, the one or more first filters may include a high pass filter 310 (eg, DtdHpFW) applied to the collector voltage feedback to remove a DC component associated with the fundamental frequency. The output 312 of the high pass filter 310 is represented as a signal VcFbkHp.

[0040] Still reference Figure 5 , the algorithm 300 also includes calculating an angle 314 (e.g., DtdAng) that rotates at a predetermined frequency (e.g., Fdtd) associated with the drive train of the inverter-based resource(s). Thus, as shown at 316, the algorithm 300 includes rotating the output 312 to a reference frame that rotates at the predetermined frequency using the angle 314. In this reference frame, the component of the collector voltage that oscillates at the predetermined frequency will appear as a direct current (DC) signal.

[0041] In addition, as shown, one or more second filters may include a low pass filter 318 applied to the rotating collector voltage feedback to remove high frequency components not associated with the drive train components of interest. In addition, the algorithm 300 includes using the calculated voltage feedback in an integral controller 322, wherein, as shown at 320, the expected reference voltage at this frequency is set to zero. The output 324 of the integral controller 322 is a desired current associated with a predetermined frequency (e.g., ItxyDtd). Therefore, in an embodiment, as shown at 326, the algorithm 300 includes rotating the desired current 324 back to a synchronous reference frame to obtain a signal 328 (e.g., ΔItxyDtd). This rotation may also include a predetermined phase shift setting 330 (e.g., θdtd) that may be adjusted for the application. Therefore, as shown, the algorithm 300 calculates changes (e.g., ΔPwfRef and ΔVRef) in power and voltage references 332, 334 based on the desired current.

[0042] Reference now Figure 6, as mentioned, illustrates a schematic diagram of an embodiment of a control structure 400 for a grid tracking voltage source converter according to the present disclosure. In particular, as shown, new signals are illustrated as being implemented in the control structure 400, including changes in the power and voltage references 332, 334 (e.g., ΔPwfRef and ΔVRef) to achieve a rigid voltage at the collector bus at certain predetermined frequencies.

[0043] Specifically, as shown at 404, the control structure 400 receives a power reference (e.g., PwrRef 402) and a change in the power reference signal 332. The output 406 is constrained by the device limits (e.g., PwrRefLimH 408 and PwrRefLimL 410) to determine a power command (e.g., PwrCmd 412). Therefore, as shown, the power controller 414 receives the power command 412 and the power feedback signal 416 (e.g., PwrFbk) and generates a current command (e.g., Ixcmd 418).

[0044] In addition, as shown, the voltage controller 420 receives a voltage reference (e.g., VRef 422), which may come from a slower VAR regulation function or a plant-level volt / VAR regulator, and one or more voltage feedback signals (e.g., VxyFbk 424). As shown at 326, the voltage feedback signal may first be processed to generate a voltage feedback signal (e.g., VFbk 436) received by the voltage controller 420. The voltage controller 420 may then also generate a current command (e.g., IyCmd 422). The current commands 418, 422 may then be used by the current regulator 428 to generate corresponding voltage commands 430, 432 (e.g., VxCmd, VyCmd).

[0045] Still reference Figure 6 , the control structure 400 may also include a phase locked loop 434 that uses the voltage feedback signal(s) (e.g., VxyFbk 424) to generate a phase locked loop angle (e.g., θpll 434) and a phase locked loop angular frequency (e.g., ωpll 436). Thus, as shown, the phase locked loop angle 434 may be used to rotate the voltage commands 430, 432 to abc coordinates, as shown at 438, in order to generate a three-phase voltage command (e.g., VabcCmd 440). As shown at 442, the voltage command(s) 440 may be modulated using, for example, pulse width modulation (PWM) to generate a voltage command that may be sent to a converter controller (e.g., at Figure 1 4 and 5. The gate command 444 of the local control 112 shown in FIG. 4 is used to provide appropriate voltage control of the power converter.

[0046] Although the systems and methods described herein are generally applicable to wind farms having multiple wind turbines, it should be appreciated that the disclosed systems and methods of the present disclosure may be implemented using any other power system configured to supply power to a load for an application, such as a power grid, including, for example, a solar power system, a hydroelectric system, an energy storage power system, or a combination thereof.

[0047] Further aspects of the invention are provided by the subject matter of the following clauses: Clause 1. A method for reducing power oscillations generated by a system of inverter-based resources and injected into a power grid, the method comprising: communicatively coupling a system-level energy buffer circuit to a system-level controller communicatively coupled to a local controller of the inverter-based resource; generating an energy buffer for the system of inverter-based resources via the system-level energy buffer circuit; and The energy buffer is applied to the power oscillations generated by the system of inverter-based resources to decouple the power oscillations generated by the system of inverter-based resources from a total output power of the system of inverter-based resources. Clause 2. The method of clause 1, wherein the system-level energy buffer circuit is coupled to a collector bus of the system, the collector bus being coupled to the local controller of the inverter-based resource. Clause 3. The method of clause 2, wherein the system level energy buffer circuit comprises a voltage source converter, wherein energy storage hardware is connected to a DC link of the voltage source converter. Clause 4. The method of clause 3, wherein the energy storage hardware comprises at least one of one or more batteries or one or more capacitors. Clause 5. The method of clause 3, wherein the system-level energy buffer circuit comprises a transformer. Item 6. The method according to Item 5 further includes controlling the system-level energy buffer circuit to generate a rigid collector bus voltage at one or more predetermined frequencies, wherein, by generating the rigid collector bus voltage, the power oscillations generated by the inverter-based resource system are absorbed by the energy buffer without any feedback or communication between the system-level energy buffer circuit and the inverter-based resource system. Clause 7. A method according to clause 6, wherein oscillations of the grid frequency or grid angle at the one or more predetermined frequencies are also decoupled from the system of inverter-based resources, thereby buffering the system of inverter-based resources from background power oscillations in the power grid. Clause 8. The method of clause 6, wherein controlling the system level energy buffer circuit to generate the rigid collector bus voltage at the one or more predetermined frequencies further comprises: receiving one or more voltage or current feedbacks; calculating a collector voltage feedback based on an impedance of the transformer of the energy buffer and the one or more voltage or current feedbacks; applying one or more filters to the collector voltage feedback; calculating an angle of rotation at a predetermined frequency associated with a drive train component of one or more of the inverter-based resources; rotating the collector voltage feedback to a reference frame rotating at the predetermined frequency; determining, via an integral controller of the system level energy buffer circuit, a desired current associated with the predetermined frequency using the collector voltage feedback; and A change in power and a voltage reference for the voltage source converter is calculated based on the desired current. Clause 9. The method of clause 8, wherein the one or more voltage or current feedbacks include one or more xy voltage and current feedbacks calculated based on an abc feedback signal and a synchronous reference frame transformation. Clause 10. The method of clause 8, wherein controlling the system level energy buffer circuit to generate the rigid collector bus voltage at the one or more predetermined frequencies further comprises: The desired current is rotated back to a synchronous reference frame including an adjustable predetermined phase shift setting. Clause 11. The method of clause 8, wherein applying the one or more filters to the collector voltage feedback further comprises: applying one or more first filters to the collector voltage feedback to remove one or more direct current (DC) components thereof associated with the predetermined frequency; and One or more second filters are applied to the collector voltage feedback to remove high frequency components not associated with the powertrain components of one or more of the inverter-based resources. Clause 12. The method of any preceding clause, wherein the system of inverter-based resources is a grid-tracking inverter-based resource. Clause 13. The method of any preceding clause, wherein the system of inverter-based resources is a grid-forming inverter-based resource. Clause 14. The method of any preceding clause, wherein the energy buffer has a power rating from about 5% to about 10% of a power rating of the system of inverter-based resources. Clause 15. The method of any preceding clause, wherein the system of inverter-based resources is a wind farm comprising a plurality of wind turbines. Clause 16. A wind farm connected to an electricity grid, comprising: a plurality of wind turbine generators; Field level controller; and a field-level energy buffer circuit for reducing power oscillations generated by the plurality of wind turbine generators and injected into the power grid, the field-level energy buffer circuit being communicatively coupled to the field-level controller, Wherein the field level energy buffer circuit is configured to perform a plurality of operations, the plurality of operations comprising: generating an energy buffer for the wind farm; and The energy buffer is applied to the power oscillations generated by the plurality of wind turbine generators to decouple the power oscillations generated by the plurality of wind turbine generators from a total output power of the wind farm. Clause 17. The wind farm of Clause 16, wherein the farm level energy buffer circuit comprises a voltage source converter and a transformer, wherein energy storage hardware is connected to a DC link of the voltage source converter. Clause 18. The wind farm according to clauses 16-17, wherein the plurality of operations further comprises: The field level energy buffer circuit is controlled to generate a rigid collector bus voltage at one or more predetermined frequencies, wherein, by generating the rigid collector bus voltage, the power oscillations generated by the plurality of wind turbine generators are absorbed by the energy buffer without any feedback or communication between the field level energy buffer circuit and the plurality of wind turbine generators. Clause 19. The wind farm of clauses 16-18, wherein controlling the farm-level energy buffer circuit to generate the rigid collector bus voltage at the one or more predetermined frequencies further comprises: receiving one or more xy voltage and current feedbacks calculated based on the abc feedback signal and the synchronous reference frame transformation; calculating a collector voltage feedback based on an impedance of the transformer of the energy buffer and the one or more voltage or current feedbacks; applying one or more filters to the collector voltage feedback; calculating an angle of rotation at a predetermined frequency associated with a drive train component of one or more wind turbine generators of the plurality of wind turbine generators; rotating the collector voltage feedback to a reference frame rotating at the predetermined frequency; determining, via an integral controller of the field level energy buffer circuit, a desired current associated with the predetermined frequency using the collector voltage feedback; and A change in power and a voltage reference for the voltage source converter is calculated based on the desired current. Clause 20. The wind farm of clause 19, wherein controlling the farm-level energy buffer circuit to generate the rigid collector bus voltage at the one or more predetermined frequencies further comprises: The desired current is rotated back to a synchronous reference frame including an adjustable predetermined phase shift setting.

[0048] This written description uses examples, including the best mode, to disclose the invention, 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 combined 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 language of the claims.

Claims

1. A method for reducing power oscillations generated by a system of inverter-based resources and injected into a power grid, the method comprising: communicatively coupling a system-level energy buffer circuit to a system-level controller communicatively coupled to a local controller of the inverter-based resource; generating an energy buffer for the system of inverter-based resources via the system-level energy buffer circuit; as well as The energy buffer is applied to the power oscillations generated by the system of inverter-based resources to decouple the power oscillations generated by the system of inverter-based resources from a total output power of the system of inverter-based resources.

2. The method according to claim 1, wherein: The system-level energy buffer circuit is coupled to a collector bus of the system, the collector bus is coupled to the local controller of the inverter-based resource.

3. The method according to claim 2, wherein: The system level energy buffer circuit includes a voltage source converter with energy storage hardware connected to a DC link of the voltage source converter.

4. The method according to claim 3, wherein: The energy storage hardware includes at least one of one or more batteries or one or more capacitors.

5. The method according to claim 3, wherein: The system-level energy buffer circuit includes a transformer.

6. The method of claim 5, further comprising controlling the system level energy buffer circuit to produce a rigid collector bus voltage at one or more predetermined frequencies, wherein: By generating the rigid collector bus voltage, the power oscillations generated by the system of inverter-based resources are absorbed by the energy buffer without any feedback or communication between the system level energy buffer circuit and the system of inverter-based resources.

7. The method according to claim 6, wherein: Oscillations of grid frequency or grid angle at the one or more predetermined frequencies are also decoupled from the system of inverter-based resources, thereby buffering the system of inverter-based resources from background power oscillations in the power grid.

8. The method according to claim 6, wherein: Controlling the system level energy buffer circuit to generate the rigid collector bus voltage at the one or more predetermined frequencies further comprises: receiving one or more voltage or current feedbacks; calculating a collector voltage feedback based on an impedance of the transformer of the energy buffer and the one or more voltage or current feedbacks; applying one or more filters to the collector voltage feedback; calculating an angle of rotation at a predetermined frequency associated with a drive train component of one or more of the inverter-based resources; rotating the collector voltage feedback to a reference frame rotating at the predetermined frequency; determining, via an integral controller of the system level energy buffer circuit, a desired current associated with the predetermined frequency using the collector voltage feedback; and A change in power and a voltage reference for the voltage source converter is calculated based on the desired current.

9. The method according to claim 8, wherein: The one or more voltage or current feedbacks include one or more xy voltage and current feedbacks calculated based on an abc feedback signal and a synchronous reference frame transformation.

10. The method according to claim 8, wherein: Controlling the system level energy buffer circuit to generate the rigid collector bus voltage at the one or more predetermined frequencies further comprises: The desired current is rotated back to a synchronous reference frame including an adjustable predetermined phase shift setting.

11. The method according to claim 8, wherein: Applying the one or more filters to the collector voltage feedback further comprises: applying one or more first filters to the collector voltage feedback to remove one or more direct current (DC) components thereof associated with the predetermined frequency; and One or more second filters are applied to the collector voltage feedback to remove high frequency components not associated with the powertrain components of one or more of the inverter-based resources.

12. The method according to claim 1, wherein: The inverter-based resource system is a grid-tracking inverter-based resource.

13. The method according to claim 1, wherein: The inverter-based resource system is an inverter-based resource formed by a power grid.

14. The method according to claim 1, wherein: The power rating of the energy buffer is from about 5% to about 10% of the power rating of the system of inverter-based resources.

15. The method according to claim 1, wherein: The system of inverter-based resources is a wind farm comprising a plurality of wind turbines.

16. A wind farm connected to a power grid, comprising: a plurality of wind turbine generators; Field level controller; as well as a field-level energy buffer circuit for reducing power oscillations generated by the plurality of wind turbine generators and injected into the power grid, the field-level energy buffer circuit being communicatively coupled to the field-level controller, Wherein the field level energy buffer circuit is configured to perform a plurality of operations, the plurality of operations comprising: generating an energy buffer for the wind farm; as well as The energy buffer is applied to the power oscillations generated by the plurality of wind turbine generators to decouple the power oscillations generated by the plurality of wind turbine generators from a total output power of the wind farm.

17. The wind farm according to claim 16, wherein: The field level energy buffer circuit includes a voltage source converter and a transformer, wherein energy storage hardware is connected to a DC link of the voltage source converter.

18. The wind farm according to claim 17, wherein: The plurality of operations also include: The field level energy buffer circuit is controlled to generate a rigid collector bus voltage at one or more predetermined frequencies, wherein, by generating the rigid collector bus voltage, the power oscillations generated by the plurality of wind turbine generators are absorbed by the energy buffer without any feedback or communication between the field level energy buffer circuit and the plurality of wind turbine generators.

19. The wind farm according to claim 18, wherein: Controlling the field level energy buffer circuit to generate the rigid collector bus voltage at the one or more predetermined frequencies further comprises: receiving one or more xy voltage and current feedbacks calculated based on the abc feedback signal and the synchronous reference frame transformation; calculating a collector voltage feedback based on an impedance of the transformer of the energy buffer and the one or more voltage or current feedbacks; applying one or more filters to the collector voltage feedback; calculating an angle of rotation at a predetermined frequency associated with a drive train component of one or more wind turbine generators of the plurality of wind turbine generators; rotating the collector voltage feedback to a reference frame rotating at the predetermined frequency; determining, via an integral controller of the field level energy buffer circuit, a desired current associated with the predetermined frequency using the collector voltage feedback; and A change in power and a voltage reference for the voltage source converter is calculated based on the desired current.

20. The wind farm according to claim 19, wherein: Controlling the field level energy buffer circuit to generate the rigid collector bus voltage at the one or more predetermined frequencies further comprises: The desired current is rotated back to a synchronous reference frame including an adjustable predetermined phase shift setting.

Images