System and method for operating inverter-based resources using interleaved pulse modes

Abstract

A method for operating a plurality of inverter-based resources (IBRs) connected to a power grid at a point of common coupling (PCC) includes providing a pulse pattern for at least two of the IBRs to respective local controllers of the at least two IBRs. The method also includes receiving, via the respective local controller, one or more measured electrical signals from the power grid. Further, the method includes establishing, via the respective local controller, a timing reference for interleaving pulse patterns for the at least two IBRs based on the one or more measured electrical signals from the power grid. Further, the method includes operating the at least two IBRs in parallel on the power grid via the respective local controllers using the pulse patterns and the timing reference such that the pulse patterns interleave each other to reduce voltage distortion at the PCC.

Description

Technical Field

[0001] The present disclosure relates generally to inverter-based resources, and more particularly to interleaving pulse patterns for inverter-based resources, such as wind turbines. Background Art

[0002] Modern wind turbines are commonly used to supply electricity to the power grid. This type of wind turbine generally includes a tower and a rotor arranged on the tower. The rotor, which generally includes a hub and a plurality of rotor blades, begins to rotate under the influence of the wind acting on the rotor blades. Such rotation generates torque, which is generally transmitted to the generator directly or through a gearbox through the rotor shaft. The generator generates electricity, which can be supplied to the power grid. The hub can be rotatably coupled to the front of the nacelle. In addition, the hub can be connected to the rotor shaft, and then the rotor shaft can be rotatably mounted in the nacelle using one or more rotor shaft bearings (rotor shaft bearings) arranged in a frame inside the nacelle. The nacelle is a housing arranged at the top of the tower, which contains and protects, for example, a gearbox (if present) and a generator and, depending on the wind turbine, contains and protects other components, such as a power converter and / or auxiliary systems.

[0003] Wind turbines are often grouped together in a "wind farm", which generally refers to a common geographical location with multiple wind turbines. These wind turbines may be connected to a local (internal) power grid of the wind farm. The internal grid of the wind farm may include multiple strings, and multiple wind turbines may be connected to each of these strings. The power grid of the wind farm may be connected to the main power grid at a point of common coupling (PCC).

[0004] The trend in the field of wind turbines is to place wind turbines in offshore wind farms. Offshore wind farms can be connected to the mainland power grid via high voltage transmission lines, such as high voltage alternating current (HVAC) transmission or high voltage 30 direct current (HVDC) transmission.

[0005] Wind turbines can supply power to the internal wind farm grid at a voltage of, for example, 33 kilovolts (kV) or 66 kV. At the substation, the voltage can be stepped up to several hundred kV using (one or more) high-voltage transformers. The high-voltage electrical power can then be supplied to high-voltage transmission lines connected to the mainland power grid. The substation may also include, for example, circuit breakers, surge arresters, capacitor banks, etc.

[0006] Like most renewable energy sources, wind turbines typically include power electronic conversion to regulate the power injected into the power grid. These power conversion systems include inverters that produce some energy outside the nominal grid frequency, usually described as harmonics. This is a basic characteristic of all inverter-based resources (IBRs). As more and more IBRs are connected to the electric power grid, the combined effect of their individual harmonics can become significant. The effects are greatly amplified by the inevitable resonances within the electric power network.

[0007] A well-known and very effective means to mitigate the effects of IBR harmonics is to include damping filters on the power grid. However, such filters may be expensive or impractical in some instances, for example for offshore wind farms.

[0008] Therefore, the traditional approach to mitigating harmonics is by improving the control algorithms of the IBR converters in a way that minimizes the impact on grid voltage distortion. However, due to the large amplification associated with grid resonances, minimizing harmonics from individual IBRs may not be sufficient to provide effective mitigation.

[0009] To overcome this inherent limitation, methods of interleaving the converter controls of a group of IBRs within a facility have been proposed, for example, as taught in EP2209200B1, entitled "Electrical System and Control Method", filed on August 12, 2009. However, such prior art methods rely on communication between the controllers of the various IBRs to achieve the desired interleaving. This communication requirement can be problematic because it necessitates the establishment of a precise timing reference against which all IBRs in the group are referenced to ensure effective interleaving.

[0010] Thus, the present disclosure is generally directed to systems and methods for operating an IBR pair using an interleaved pulse pattern without requiring communication between their respective individual controllers. Summary of the invention

[0011] 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.

[0012] In aspect, the present disclosure relates to a method for operating a plurality of inverter-based resources connected to a power grid at a common coupling point. The method includes providing a pulse pattern for at least two of the plurality of inverter-based resources to a corresponding local controller of at least two of the plurality of inverter-based resources. The method also includes receiving one or more measured electrical signals from the power grid via the corresponding local controller. In addition, the method includes establishing a timing reference for interleaving the pulse pattern for at least two of the plurality of inverter-based resources via the corresponding local controller based on the one or more measured electrical signals from the power grid. In addition, the method includes operating at least two of the plurality of inverter-based resources in parallel on the power grid via the corresponding local controller using the pulse pattern and the timing reference, so that the pulse patterns are interleaved with each other to reduce voltage distortion at the common coupling point.

[0013] In another aspect, the present disclosure relates to a wind farm connected to a power grid. The wind farm includes a plurality of wind turbines and a plurality of local controllers connected in parallel to the power grid at a common coupling point. Each of the plurality of wind turbines is controlled by a local controller among the plurality of local controllers. Each of the plurality of local controllers includes a pulse mode programmed therein. The plurality of local controllers are configured to perform one or more operations. The (one or more) operations include, but are not limited to, receiving one or more measured electrical signals from the power grid, establishing a timing reference for interleaving the pulse mode for at least two of the wind turbines based on the one or more measured electrical signals from the power grid, and operating at least two of the wind turbines in parallel on the power grid using the pulse mode and the timing reference so that the pulse modes are interleaved with each other to reduce voltage distortion at the common coupling point.

[0014] In yet another aspect, the present disclosure relates to a method for operating a plurality of inverter-based resources connected to a power grid at a common coupling point. The method includes determining a pulse pattern for each of the plurality of inverter-based resources. In addition, the method includes receiving one or more measured voltage signals from the power grid via respective local controllers of the plurality of inverter-based resources. In addition, the method includes establishing, via respective local controllers, a timing reference for interleaving the pulse patterns for the plurality of inverter-based resources based on the one or more measured voltage signals. In addition, the method includes operating, via respective local controllers, the plurality of inverter-based resources in parallel on the power grid using the pulse patterns and the timing reference, such that the pulse pattern pairs of the plurality of inverter-based resources are interleaved to reduce voltage distortion at the common coupling point.

[0015] 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

[0016] 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:

[0017] Figure 1 A perspective view showing an embodiment of a wind turbine according to the present disclosure;

[0018] Figure 2 Shown suitable for Figure 1 A schematic diagram of an embodiment of a full power conversion system for use with a wind turbine as shown in;

[0019] Figure 3 Shown suitable for Figure 2 A schematic diagram of an embodiment of an individual inverter used in a full power conversion system shown in;

[0020] Figure 4 Shown in Figure 3 the nature of the voltage at the AC side of an inverter of a full power conversion system, which is a result of the gating control used with that inverter;

[0021] Figure 5 A schematic diagram showing an example embodiment of an offshore wind farm according to the present disclosure;

[0022] Figure 6 A flow chart illustrating an embodiment of a method for operating a plurality of inverter-based resources connected to a power grid at a point of common coupling according to the present disclosure;

[0023] Figure 7 A schematic diagram showing an embodiment of a string of inverter-based resources according to the present disclosure; and

[0024] Figure 8 A flow chart illustrating another embodiment of a method for operating a plurality of inverter-based resources connected to a power grid at a point of common coupling according to the present disclosure.

[0025] Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention. DETAILED DESCRIPTION

[0026] Reference will now be made in detail to embodiments of the present invention, one or more examples of which are shown 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 shown 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 fall within the scope of the appended claims and their equivalents.

[0027] The terms “coupled,” “fixed,” “attached to,” and the like refer to both directly coupled, fixed, or attached, as well as indirectly coupled, fixed, or attached through one or more intermediate components or features, unless otherwise specified herein.

[0028] In addition, those skilled in the art will recognize the interchangeability of various features from different embodiments. Similarly, the various method steps and features described, as well as other known equivalents for each such method and feature, can be mixed and matched by those of ordinary skill in the art to construct additional systems and techniques according to the principles of the present disclosure. Of course, it is to be understood that not all such purposes or advantages described above may be achieved according to any particular embodiment. Thus, for example, those skilled in the art will recognize that the systems and techniques described herein may be embodied or performed in a manner that achieves or optimizes one advantage or a group of advantages as taught herein, without having to achieve other purposes or advantages as may be taught or suggested herein.

[0029] In general, the present disclosure relates to systems and methods for operating at least two inverter-based resources in parallel on a power grid. More specifically, on each inverter-based resource, the present disclosure utilizes timing information derived from a locally sensed grid voltage so that the harmonic currents from the group are approximately canceled. Therefore, in an embodiment, the converter pulse pattern can be designed so that the selected harmonics have a combination of amplitude and phase relative to the fundamental frequency voltage, and when the group is operating on the power grid, the net effect of those selected harmonics is canceled. In an embodiment, for example, a group of at least two inverter-based resources can have two different pulse modes selected at commissioning. The characteristics of the pulse mode can have, for example, the same amplitude of the selected harmonics, however, the phase angles can be offset by 180 degrees relative to each other. Since the grid voltage provides a means for maintaining the two inverter-based resources to perform the desired interleaving function, the corresponding local controllers of the two inverter-based resources can operate independently of each other to establish a timing reference for the interleaved pulse mode, and only utilize one or more measured electrical signals without communicating with each other.

[0030] Now referring to the accompanying drawings, Figure 1A perspective view of a portion of an inverter-based resource, such as a wind turbine 100, is shown. The wind turbine 100 includes a housing for a generator ( Figure 1 The nacelle 102 is mounted on a tower 104 (part of which is located at Figure 1 104). The tower 104 may have any suitable height that facilitates operation of the wind turbine 100 as described herein. The wind turbine 100 also includes a rotor 106 that includes a plurality of rotor blades 108, such as three rotor blades 108, attached to a rotating hub 110. Alternatively, the wind turbine 100 may include any number of rotor blades 108 that facilitate operation of the wind turbine 100 as described herein. In an embodiment, the wind turbine 100 may also include a generator operatively coupled to the rotor 106 and the generator ( Figure 1 The gear box (not shown) Figure 1 not shown).

[0031] Reference now Figure 2 , a schematic diagram of an embodiment of a full power conversion system 200 that may be used with wind turbine 100 according to the present disclosure is shown. Thus, in an embodiment, as shown, power conversion system 200 is configured to supply power to power grid 212.

[0032] In addition, as shown, the power conversion system 200 may include a three-phase power converter system. More specifically, as shown, the power conversion system 200 includes a generator 118 coupled to a power conversion assembly 210. The power conversion assembly 210 includes a generator side power converter 220 for AC-DC conversion, and the generator side power converter 220 is electrically coupled to a line side power converter 222 for DC-AC conversion. In addition, as shown, the generator side power converter 220 is coupled to the line side power converter 222 via a single direct current (DC) link 226. In addition, as shown, the power conversion system 200 further includes a main transformer 234 electrically coupled between the power conversion assembly 210 and the power grid 212.

[0033] Thus, DC power is transmitted from DC link 226 to line-side power converter 222, and line-side power converter 222 acts as an inverter configured to convert the DC electric power from DC link 226 into three-phase sinusoidal AC electric power having a predetermined voltage, current, and frequency. This conversion is monitored and controlled via converter controller 262. Power conversion assembly 210 compensates or adjusts the frequency of the three-phase power from generator 118 for changes in wind speed at, for example, hub 110 and rotor blades 108.

[0034] Additionally, in an embodiment, as shown, power conversion system 200 may include a switchgear assembly 228 having one or more sensors coupled between main transformer 234 and grid 212. Thus, in such an embodiment, switchgear assembly 228 connects power conversion system 200 to a string of other wind turbine generators (e.g., WTGs). Additionally, in such an embodiment, the sensor(s) of switchgear assembly 228 are configured to detect voltage and / or current that may be used by converter controller 262 as described herein.

[0035] Still refer to Figure 2 , the power conversion system 200 may also be coupled to the turbine controller 202 and / or the converter controller 262 in electronic data communication to control the operation thereof. For example, in an embodiment, the converter controller 262 is configured to receive a control signal from the turbine controller 202. The control signal is based on a sensed condition or operating characteristic of the wind turbine 100 and the power conversion system 200. The control signal is received by the turbine controller 202 and used to control the operation of the power conversion assembly 210. Feedback from one or more sensors may be used by the power conversion system 200 to control the power conversion assembly 210 via the converter controller 262.

[0036] The turbine controller 202 and / or converter controller 262 include at least one processor and memory, at least one processor input channel, at least one processor output channel, and may include at least one computer. As used herein, the term computer is not limited to integrated circuits known in the art as computers, but refers broadly to processors, microcontrollers, microcomputers, programmable logic controllers (PLCs), application specific integrated circuits, and other programmable circuits, and these terms may be used interchangeably herein. In an exemplary embodiment, the memory may include, but is not limited to, computer readable media, such as random access memory (RAM). Alternatively, one or more storage devices, such as floppy disks, compact disk read only memory (CD-ROM), magneto-optical disks (MODs), and / or digital versatile disks (DVDs) may also be used. In addition, in an exemplary embodiment, additional input channels ( Figure 2 The output channels (not shown) may be, but are not limited to, computer peripherals associated with an operator interface, such as a mouse and a keyboard. In addition, in an exemplary embodiment, additional output channels may include, but are not limited to, an operator interface monitor ( Figure 2 not shown).

[0037] The processor for turbine controller 202 and / or converter controller 262 processes information transmitted from a plurality of electrical and electronic devices, which may include, but are not limited to, voltage and current transducers. RAM and / or storage devices store and transfer information and instructions to be executed by the processor. RAM and / or storage devices may also be used to store temporary variables, static (i.e., unchanging) information and instructions, or other intermediate information and provide them to the processor during execution of instructions by the processor. The instructions executed include, but are not limited to, resident conversion and / or comparator algorithms. Execution of instruction sequences is not limited to any specific combination of hardware circuitry and software instructions.

[0038] Converter controller 262 is substantially similar to turbine controller 202 and is coupled in electronic data communication with turbine controller 202, as is typically done in Figure 2 . Moreover, in the exemplary embodiment, converter controller 262 is physically integrated within power conversion assembly 210. Alternatively, converter controller 262 has any configuration that facilitates operation of power conversion system 200 as described herein.

[0039] Reference now Figure 3 , showing that it is suitable for Figure 2 Schematic diagram of an embodiment of an individual inverter (e.g., line-side converter 222) used in a full power conversion system as shown in FIG. Figure 3 As shown in FIG, a wind turbine generator (eg, WTG) is connected to a three-phase AC load (eg, Figure 2 212 of the power grid). In addition, as shown, the generator 118 is represented as a DC source. Therefore, in an embodiment, it should be understood that there are several forms of AC-DC converters (e.g., multi-stage), and several converters within the IBR may also be included, all of which operate according to commands from the converter controller 262. In particular, as shown, the line side converter 222 is a three-phase assembly having a plurality of semiconductor power switches 224 (e.g., insulated gate bipolar transistors (IGBTs)). In other embodiments, the semiconductor power switch 224 may be any other type of switching device now known in the art or later developed.

[0040] Thus, in an embodiment, generator side power converter 220 and line side power converter 222 may be configured in a three-phase synchronous gated configuration including IGBT switching devices operated as known in the art. In another embodiment, generator side power converter 220 and line side power converter 222 may be configured in a three-phase pulse width modulation (PWM) gated configuration including IGBT switching devices operated as known in the art. Alternatively, generator side power converter 220 and line side power converter 222 have any configuration using any switching device that facilitates operation of power conversion system 200 as described herein.

[0041] Reference now Figure 4 ,like Figure 2 and Figure 3 The generator side power converter 220 and / or the line side converter 222 shown in FIG. 5 have a voltage waveform 500 (also referred to herein as a pulse mode). In such an embodiment, when the pulse mode includes a fundamental frequency component shown by a sine waveform 502, the voltage waveform 500 is the actual voltage at the AC terminal of the converter. The pulse mode includes distortion components as are well known in the art. The frequency, amplitude, and phase of the distortion components are functions of the switching time.

[0042] Furthermore, in embodiments, there are several means to create the switching times of the voltage waveform 500, all designed to match the voltage of the generator side power converter 220 and / or the line side converter 222 to the commands created by higher level control functions (e.g., current regulators, etc.). In certain embodiments, the switching times are defined by gating logic (e.g., pulse width modulation (PWM) or synchronous gating).

[0043] For example, in one embodiment, PWM is used, whereby the gate time is established at a fixed rate based on the instantaneous voltage amplitude expected in the next switching interval. In this example, the switching rate is significantly faster than the grid frequency, for example, a switching rate of several kHz is used, while the grid frequency is 60Hz or 50Hz.

[0044] Another approach is synchronous gating, where the switching times are based on an angle reference provided by a phase locked loop that is synchronized with the fundamental frequency component of the positive sequence voltage measured at the bus. With synchronous gating, the pulse pattern is predetermined by calculation and programmed into the gating control. The pulse pattern is determined in a manner that minimizes the selected harmonics. An advantage of synchronous gating over PWM is the ability to achieve slower device switching rates than would be required with the PWM approach.

[0045] Reference now Figure 5, a schematic diagram of an embodiment of an offshore wind farm 300 is shown according to the present disclosure. As shown, the wind farm 300 includes a substation 302 located at a common connection point 308. In addition, as shown, in an embodiment, the wind farm 300 includes one or more wind farm strings 304 connected in parallel to the common connection point and including a plurality of wind turbines 306. The wind farm strings 304 may also be referred to as "lines" or "feeders". One or more of the wind farm strings 304 may include wind turbines, such as the wind turbines 100 described herein. In the illustrated embodiment, all strings 304 have the same length and the same number of wind turbines 306. However, in other embodiments, it should be understood that the strings 304 may also have different lengths (and thus different capacitances), as well as different numbers of wind turbines 306.

[0046] In further embodiments, it should also be appreciated that although strings 304 are depicted as being substantially parallel to one another, strings 304 may be arranged in a variety of ways depending on the layout of wind farm 300. For example, in an embodiment, strings 304 may extend radially away from common connection point 308.

[0047] Still refer to Figure 5 As described, wind farm 300 may be an offshore wind farm. In addition, substation 302 may include a high voltage transformer and may be connected to a high voltage transmission line 310, such as an HVAC or HVDC transmission line. Such a high voltage transmission line may be several kilometers long, such as 20 km, 70 km, or more. High voltage transmission line 310 may be connected to a point of common coupling (PPC) 312 with a mainland power grid 314. Reference numeral 316 represents a coastline.

[0048] Thus, in an embodiment, an object of the present disclosure is to have different switching times on adjacent generators 254 of a string 304 so that selected harmonics of the voltage will be 180 degrees out of phase. This will result in currents at those harmonics entering the string 304 at one connection and being extracted at the connection point of the adjacent generator 254, thereby not entering the substation with the resulting distortion of the voltage at the substation. This is generally referred to as "interleaving." As used herein, interleaving is a well-known way of canceling out net harmonics from multiple converters. For example, when multiple converters are included, interleaving is widely used in converter-based systems, such as explained in U.S. Patent No. 7,944,068, filed on June 30, 2008, entitled "Optimizing converter protection for wind turbine generators," which is incorporated herein by reference in its entirety.

[0049] However, in the present disclosure, the difference in gating timing must be implemented in some way. Prior art systems utilize communication between controllers to achieve this function. However, the present disclosure implements such interleaving without turbine-to-turbine communication. In particular, the systems and methods of the present disclosure utilize a voltage measured at an inverter-based resource to set the timing of the gating logic. This voltage will typically be very similar between adjacent inverter-based resources on a string (e.g., string 304). Therefore, this voltage can be used to determine a reference time for gating logic to obtain effective interleaving.

[0050] In the examples, and now with reference to Figure 6 , a flowchart of an illustrative method 400 for operating multiple inverter-based resources connected to a power grid at a point of common coupling according to some embodiments of the present disclosure is shown. The flowcharts and methods described herein do not imply a fixed order of steps, and embodiments of the present invention may be implemented in any practicable order. Note that any of the methods described herein may be performed by hardware, software, or any combination of these. For example, a non-transitory computer-readable storage medium may store instructions thereon that, when executed by a machine, result in the execution of any of the embodiments described herein.

[0051] As shown at (402), the method 400 includes providing a pulse pattern for at least two of the plurality of inverter-based resources to respective local controllers of at least two of the plurality of inverter-based resources. In an embodiment, for example, the pulse pattern may be determined offline (e.g., at commissioning of the inverter-based resources) and provided to the local turbine controller 202 at installation and at any time during operation of the wind farm 300. In a particular embodiment, for example, the pulse pattern for the inverter-based resources may be determined based on one or more selected harmonics. The selected harmonic(s) may include, for example, a combination of an amplitude and a phase angle relative to a fundamental frequency voltage.

[0052] Thus, in certain embodiments, the method 400 may further include storing the pulse pattern for at least two of the plurality of inverter-based resources in respective local controllers (eg, the turbine controller 202 ) of the at least two of the plurality of inverter-based resources.

[0053] As shown at (404), the method 400 includes receiving one or more measured electrical signals from the power grid via the respective local controllers. The electrical signals may include, for example, voltage, current, or a combination or function thereof. Thus, as shown at (406), the method 400 includes establishing, via the respective local controllers, a timing reference for interleaving a pulse pattern for at least two inverter-based resources of the plurality of inverter-based resources based on the one or more measured electrical signals from the power grid.

[0054] In addition, as shown at (408), the method 400 includes operating at least two of the plurality of inverter-based resources in parallel on the power grid via respective local controllers using a pulse pattern and a timing reference such that the pulse patterns are interleaved with each other to reduce voltage distortion at a point of common coupling. In such an embodiment, the inverter-based resources may be operated using synchronous gating or pulse width modulation. Thus, in such an embodiment, when the two inverter-based resources are operating on the power grid in an interleaved pulse pattern, the net effect of the selected harmonic(s) cancels each other out.

[0055] Thus, for the disclosed method, the grid voltage provides a means of maintaining individual inverter-based resources that perform the desired interleaving function, such that communication between the respective controllers is not needed or required. In particular, in an embodiment, the respective local controllers operate independently of each other to establish a timing reference for the interleaved pulse pattern, and utilize only one or more measured electrical signals without communicating with each other.

[0056] Reference now Figure 7 , a schematic diagram of an embodiment of a string 250 of inverter-based resources 252 according to the present disclosure is shown. As shown, each inverter-based resource 252 includes a generator 254 and a back-to-back power conversion system 256 coupled to a high voltage bus 260 of the string 250 via a transformer 258. However, providing Figure 8 2 to illustrate a method of obtaining a desired timing reference even when some impedance (e.g., Z12) exists between the connection points. In such an embodiment, establishing the desired timing reference requires measuring the current flow (e.g., I12) on the portion of the string 250 between adjacent generators 254. This current flow can be sensed within the switchgear assembly of each individual inverter-based resource, so no communication is required between the controllers.

[0057] Reference now Figure 8, a flow chart of another illustrative method 700 for operating a plurality of inverter-based resources connected to a power grid at a point of common coupling according to some embodiments of the present disclosure is shown. As shown at (702), the method 700 includes determining a pulse pattern for each of the plurality of inverter-based resources. As shown at (704), the method 700 includes receiving one or more measured voltage signals from the power grid via respective local controllers of the plurality of inverter-based resources. As shown at (706), the method 700 includes establishing, via the respective local controllers, a timing reference for interleaving the pulse patterns for the plurality of inverter-based resources based on the one or more measured voltage signals. Thus, as shown at (708), the method 700 includes operating the plurality of inverter-based resources in parallel on the power grid via the respective local controllers using the pulse patterns and the timing reference such that the pulse pattern pairs of the plurality of inverter-based resources are interleaved to reduce voltage distortion at the point of common coupling.

[0058] Although in this disclosure wind turbines and wind farms are generally illustrated and explained as offshore wind turbines and wind farms, it should be clear that the same or similar arrangements may also be used onshore.

[0059] Further aspects of the invention are provided by the subject matter of the following clauses: Clause 1. A method for operating a plurality of inverter-based resources connected to a power grid at a point of common coupling, the method comprising: providing a pulse pattern for at least two of the plurality of inverter-based resources to respective local controllers of at least two of the plurality of inverter-based resources; receiving one or more measured electrical signals from a power grid via the respective local controller; establishing, via the respective local controllers, a timing reference for interleaving pulse patterns for at least two inverter-based resources of the plurality of inverter-based resources based on one or more measured electrical signals from the power grid; and At least two inverter-based resources of the plurality of inverter-based resources are operated in parallel on the power network via the respective local controllers using the pulse patterns and the timing reference such that the pulse patterns are interleaved with each other to reduce voltage distortion at the point of common coupling. Clause 2. The method of clause 1, wherein providing a pulse pattern for the at least two inverter-based resources of the plurality of inverter-based resources further comprises: The pulse pattern for the at least two inverter-based resources among the plurality of inverter-based resources is determined based on one or more selected harmonics comprising a combination of amplitude and phase angle relative to a fundamental frequency voltage, such that when the at least two inverter-based resources among the plurality of inverter-based resources are operating on the power grid, net effects of the one or more selected harmonics cancel each other out. Clause 3. The method of clause 2, wherein the pulse pattern comprises a first pulse pattern having a first amplitude of the selected harmonic and a second pulse pattern having a second amplitude of the selected harmonic, wherein the first amplitude and the second amplitude of the selected harmonic are equal. Clause 4. The method of clause 3, wherein the first pulse pattern has a first phase angle and the second pulse pattern has a second phase angle, the first phase angle being offset 180 degrees from the second phase angle. Clause 5. The method of any of the preceding clauses, wherein operating at least two inverter-based resources of the plurality of inverter-based resources in parallel on the power network further comprises utilizing synchronous gating. Clause 6. The method of any of the preceding clauses, wherein operating at least two inverter-based resources of the plurality of inverter-based resources in parallel on the power network further comprises utilizing pulse width modulation. Clause 7. The method according to any of the preceding clauses, further comprising: predetermining offline a pulse pattern of at least two inverter-based resources of the plurality of inverter-based resources; and The pulse patterns of at least two inverter-based resources of the plurality of inverter-based resources are stored in respective local controllers of at least two inverter-based resources of the plurality of inverter-based resources. Clause 8. The method of any of the preceding clauses, wherein the respective local controllers operate independently of one another to establish a timing reference for interleaving the pulse pattern and utilize only one or more measured electrical signals without communicating with one another. Clause 9. The method of any preceding clause, wherein one or more of the plurality of inverter-based resources are wind turbines. Clause 10. A wind farm connected to an electricity grid, comprising: a plurality of wind turbines connected in parallel to the power grid at a point of common coupling; a plurality of local controllers, each wind turbine of the plurality of wind turbines being controlled by one of the plurality of local controllers, each local controller of the plurality of local controllers including a pulse mode programmed therein, the plurality of local controllers being configured to perform one or more operations, the one or more operations comprising: receiving one or more measured electrical signals from the power grid; establishing a timing reference for interleaving a pulse pattern for at least two of the wind turbines based on one or more measured electrical signals from the power grid; and At least two of the wind turbines are operated in parallel on the power grid using the pulse patterns and the timing reference such that the pulse patterns are interleaved with each other to reduce voltage distortion at the point of common coupling. Clause 11. A wind farm according to clause 10, wherein the pulse mode of each wind turbine of the plurality of wind turbines is predetermined based on one or more selected harmonics comprising a combination of amplitude and phase angle relative to a fundamental frequency voltage, such that when at least two wind turbines of the plurality of wind turbines are operating on the power grid, the net effects of the one or more selected harmonics cancel each other out. Clause 12. A method for operating a plurality of inverter-based resources connected to a power grid at a point of common coupling, the method comprising: determining a pulse pattern for each inverter-based resource of the plurality of inverter-based resources; receiving one or more measured voltage signals from the power grid via respective local controllers of the plurality of inverter-based resources; establishing, via the respective local controllers, a timing reference for interleaving pulse patterns for the plurality of inverter-based resources based on the one or more measured voltage signals; and The plurality of inverter-based resources are operated in parallel on the power network via the respective local controllers using the pulse patterns and the timing reference such that pulse pattern pairs of the plurality of inverter-based resources are interleaved to reduce voltage distortion at the point of common coupling. Clause 13. The method of clause 12, wherein determining a pulse pattern for each inverter-based resource of the plurality of inverter-based resources further comprises: A pulse pattern is determined for each inverter-based resource of the plurality of inverter-based resources based on one or more selected harmonics comprising a combination of magnitude and phase angle relative to a fundamental frequency voltage, such that when at least two of the plurality of inverter-based resources are operating on the power network, a net effect of the one or more selected harmonics cancels each other out. Clause 14. The method of clause 13, wherein the amplitudes of the pulse pattern pairs are equal. Clause 15. The method of clause 14, wherein phase angles of the pulse pattern pairs are offset from one another according to a number of the plurality of inverter-based resources. Clause 16. The method of any of clauses 12-15, wherein determining a pulse mode for each inverter-based resource in the plurality of inverter-based resources further comprises: A pulse pattern for each inverter-based resource of the plurality of inverter-based resources is predetermined offline. Clause 17. The method of any of clauses 12-16, wherein operating at least two inverter-based resources of the plurality of inverter-based resources in parallel on the power network further comprises utilizing synchronous gating. Clause 18. The method of any of clauses 12-17, wherein operating at least two inverter-based resources of the plurality of inverter-based resources in parallel on the power network further comprises utilizing pulse width modulation. Clause 19. A method according to any of clauses 12-18, wherein the respective local controllers operate independently of each other to establish a timing reference for interleaving the pulse pattern and utilize only the one or more measured electrical signals without communicating with each other. Clause 20. The method of any of clauses 12-19, wherein one or more of the plurality of inverter-based resources are wind turbines.

[0060] This written description uses examples, including the best mode, to disclose the invention, and also enables any person skilled in the art to practice the invention, including making and using any device or system and performing any combined method. The patent scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. If such other examples include structural elements that are not different from the literal language of the claims, or if such other examples include equivalent structural elements that are not substantially different from the literal language of the claims, such other examples are intended to be within the scope of the claims.

Claims

1. A method for operating a plurality of inverter-based resources connected to a power grid at a point of common coupling, the method comprising: providing a pulse pattern for at least two of the plurality of inverter-based resources to respective local controllers of the at least two of the plurality of inverter-based resources; receiving one or more measured electrical signals from the power grid via the respective local controller; establishing, via the respective local controller, a timing reference for interleaving the pulse patterns for the at least two inverter-based resources of the plurality of inverter-based resources based on the one or more measured electrical signals from the power grid; as well as The at least two inverter-based resources of the plurality of inverter-based resources are operated in parallel on the power network via the respective local controllers using the pulse patterns and the timing reference such that the pulse patterns are interleaved with each other to reduce voltage distortion at the point of common coupling.

2. The method according to claim 1, wherein: Providing the pulse pattern for the at least two inverter-based resources of the plurality of inverter-based resources further comprises: The pulse pattern for the at least two inverter-based resources among the plurality of inverter-based resources is determined based on one or more selected harmonics including a combination of amplitude and phase angle relative to a fundamental frequency voltage, such that when the at least two inverter-based resources among the plurality of inverter-based resources are operating on the power grid, the net effects of the one or more selected harmonics cancel each other out.

3. The method according to claim 2, wherein: The pulse pattern includes a first pulse pattern having a first amplitude of a selected harmonic and a second pulse pattern having a second amplitude of the selected harmonic, wherein the first amplitude and the second amplitude of the selected harmonic are equal.

4. The method according to claim 3, wherein: The first pulse pattern has a first phase angle and the second pulse pattern has a second phase angle, the first phase angle being offset 180 degrees from the second phase angle.

5. The method according to claim 1, wherein: Operating the at least two inverter-based resources of the plurality of inverter-based resources in parallel on the power network further includes utilizing synchronous gating.

6. The method according to claim 1, wherein: Operating the at least two inverter-based resources of the plurality of inverter-based resources in parallel on the power network further includes utilizing pulse width modulation.

7. The method according to claim 1, further comprising: predetermining offline the pulse pattern for the at least two inverter-based resources of the plurality of inverter-based resources; as well as The pulse patterns for the at least two of the plurality of inverter-based resources are stored in the respective local controllers of the at least two of the plurality of inverter-based resources.

8. The method according to claim 1, wherein: The respective local controllers operate independently of each other to establish the timing reference for interleaving the pulse pattern and utilize only one or more measured electrical signals without communicating with each other.

9. The method according to claim 1, wherein: One or more inverter-based resources of the plurality of inverter-based resources are wind turbines.

10. A wind farm connected to a power grid, comprising: a plurality of wind turbines connected in parallel to the power grid at a point of common coupling; a plurality of local controllers, each wind turbine of the plurality of wind turbines being controlled by one of the plurality of local controllers, each local controller of the plurality of local controllers including a pulse mode programmed therein, the plurality of local controllers being configured to perform one or more operations, the one or more operations comprising: receiving one or more measured electrical signals from the power grid; establishing a timing reference for interleaving the pulse patterns for the at least two of the wind turbines based on the one or more measured electrical signals from the power grid; and The at least two of the wind turbines are operated in parallel on the power grid using the pulse patterns and the timing reference such that the pulse patterns are interleaved with each other to reduce voltage distortion at the point of common coupling.

11. The wind farm according to claim 10, wherein: The pulse pattern for each wind turbine of the plurality of wind turbines is predetermined based on one or more selected harmonics comprising a combination of magnitude and phase angle relative to a fundamental frequency voltage, such that when the at least two wind turbines of the plurality of wind turbines are operating on the power grid, a net effect of the one or more selected harmonics cancels each other out.

12. A method for operating a plurality of inverter-based resources connected to a power grid at a point of common coupling, the method comprising: determining a pulse pattern for each inverter-based resource of the plurality of inverter-based resources; receiving one or more measured voltage signals from the power grid via respective local controllers of the plurality of inverter-based resources; establishing, via the respective local controllers, a timing reference for interleaving the pulse patterns for the plurality of inverter-based resources based on the one or more measured voltage signals; as well as The plurality of inverter-based resources are operated in parallel on the power network via the respective local controllers using the pulse patterns and the timing reference such that pulse pattern pairs of the plurality of inverter-based resources are interleaved to reduce voltage distortion at the point of common coupling.

13. The method according to claim 12, wherein: Determining the pulse pattern for each inverter-based resource of the plurality of inverter-based resources further comprises: The pulse pattern for each inverter-based resource of the plurality of inverter-based resources is determined based on one or more selected harmonics comprising a combination of amplitude and phase angle relative to a fundamental frequency voltage, such that when at least two of the plurality of inverter-based resources are operating on the power grid, net effects of the one or more selected harmonics cancel each other out.

14. The method according to claim 13, wherein: The amplitudes of the pulse pattern pair are equal.

15. The method according to claim 14, wherein: Phase angles of the pulse pattern pairs are offset from each other according to a number of the plurality of inverter-based resources.

16. The method according to claim 12, wherein: Determining the pulse pattern for each inverter-based resource of the plurality of inverter-based resources further comprises: The pulse pattern for each inverter-based resource of the plurality of inverter-based resources is predetermined offline.

17. The method according to claim 12, wherein: Operating the at least two inverter-based resources of the plurality of inverter-based resources in parallel on the power network further includes utilizing synchronous gating.

18. The method according to claim 12, wherein: Operating the at least two inverter-based resources of the plurality of inverter-based resources in parallel on the power network further includes utilizing pulse width modulation.

19. The method according to claim 12, wherein: The respective local controllers operate independently of each other to establish a timing reference for interleaving the pulse pattern and utilize only the one or more measured electrical signals without communicating with each other.

20. The method according to claim 12, wherein: One or more inverter-based resources of the plurality of inverter-based resources are wind turbines.

Images