Method for operating wind farm

Abstract

The present disclosure relates to a method for operating a wind farm, in particular to a method for operating in a wind farm grid of a wind farm that is electrically disconnected from a utility grid, for example in which communication with a wind farm controller has been lost. The disclosure also relates to a wind farm, a wind farm grid and a wind turbine. A method includes, when a wind farm is disconnected from a utility grid, operating one or more first wind turbines to generate electrical power having a predetermined electrical characteristic, and delivering the electrical power having the predetermined electrical characteristic to a wind farm grid; and one or more second wind turbines detect the electrical power delivered to the wind farm grid and determine that the wind farm is disconnected from the utility grid by identifying a predetermined electrical characteristic.

Description

Technical Field

[0001] The present disclosure relates to a method for forming and operating a local power grid in a wind farm power grid of a wind farm that is electrically disconnected from a utility power grid. More specifically, the present disclosure relates to such a wind farm power grid, wherein communication between wind turbines and / or communication between wind turbines and a wind farm controller has been lost. The present disclosure also relates to a wind farm and a wind turbine. Background Art

[0002] Modern wind turbines are commonly used to supply electricity to the power grid. This type of wind turbine generally comprises a tower and a rotor arranged on the tower. The rotor, which typically comprises a hub and a plurality of blades, begins to rotate under the influence of the wind on the blades. The rotation generates a torque, which is usually transmitted to a generator via a rotor shaft directly ("direct drive" or "gearless") or by using a gearbox. In this way, the generator generates electricity that can be supplied to the power grid.

[0003] The wind turbine hub may be rotatably coupled to the front of the nacelle. The wind turbine hub may be connected to the rotor shaft, and the rotor shaft may then be rotatably mounted in the nacelle using one or more rotor shaft bearings arranged in a frame inside the nacelle. The nacelle is a housing arranged on top of the wind turbine tower that may contain and protect the gearbox (if present) and the generator (if not placed outside the nacelle), and depending on the wind turbine, further components (such as a power converter) and auxiliary systems.

[0004] When a wind turbine is disconnected from the grid, some associated auxiliary systems (e.g., communication systems and ventilation and temperature control systems) may remain operational until the electrical power provided by an auxiliary power source (such as a battery-based system, a supercapacitor (such as an uninterruptible power supply (UPS)), or a diesel generator) also runs out of power. Solar panels may also be used to provide auxiliary power. Another way to obtain auxiliary power may include operating a wind turbine to generate a small amount of electrical power and supplying the generated electrical power to one or more auxiliary systems.

[0005] The present disclosure relates in particular to a wind farm or a section of a wind farm in an island mode, i.e. a situation in which the wind farm grid is disconnected from the utility grid, and in which one or more wind turbines are operated to supply power to auxiliary systems. These auxiliary systems may be systems belonging to the wind turbine generating the power, or may be systems belonging to other wind turbines connected to the same grid.

[0006] In order to enter the island mode, one or more wind turbines in the wind farm may be configured as grid forming wind turbines. That is, when a disconnection from the power grid is detected, these grid forming turbines may act as leaders and are the first turbines to start operating in island mode. The remaining wind turbines of the island will follow the leading wind turbine, that is, they will be followers or non-grid forming wind turbines. When an "island" is formed, the wind turbines belonging to the island will be electrically connected between them, for example, the island may have multiple powered and interconnected strings, and multiple wind turbines are connected to each of the powered strings. In other words, a local grid is formed that electrically connects the leading wind turbine and the following wind turbines.

[0007] Non-grid built wind turbines need to know whether the grid present at their terminals is the utility grid or the local grid. If the voltage they register at their terminals is provided by the utility grid and the wind conditions allow, the wind turbines will attempt to start and inject power. However, if the wind farm is in island mode and one wind turbine provides a voltage detected by another wind turbine at its terminals, these wind turbines should not be started because the electrical power they may generate cannot be supplied to the utility grid and may result in over generation, causing unstable operation of the island.

[0008] During or after the formation of an island, the wind farm controller typically communicates with each wind turbine, in particular with their wind turbine controllers, to indicate this. Thanks to this communication, the grid following or non-grid building wind turbines know whether the grid present at their terminals is a utility grid or a local grid.

[0009] However, if communication between the wind park controller and one or more non-grid-bound wind turbines is lost, these wind turbines will not be able to identify what grid is present at their terminals, and / or in which mode they should operate.

[0010] The present disclosure is intended to enable non-grid-built wind turbines to distinguish whether they are electrically connected to the locally formed grid or to the utility grid during and after the formation of the locally formed grid, i.e., to determine whether the locally formed grid or the utility grid is present at their terminals. Throughout the present disclosure, the terms "local grid" and "locally formed grid" are interchangeable and are used to refer to a grid formed by, for example, one or more wind turbines when the wind farm is disconnected from the utility grid. That is, to generate electrical power that can be received and / or detected by other wind turbines independently of the utility grid. Summary of the invention

[0011] In one aspect of the present disclosure, a method for operating a wind farm is provided, the wind farm comprising a wind farm grid and a plurality of wind turbines connected to the wind farm grid. The method comprises: when the wind farm is disconnected from the utility grid, operating one or more first wind turbines of the plurality of wind turbines to generate electric power having predetermined electrical characteristics, and transmitting the electric power having the predetermined electrical characteristics to the wind farm grid. The method also comprises one or more second wind turbines of the plurality of wind turbines detecting the electric power transmitted to the wind farm grid, and determining that the wind farm is disconnected from the utility grid by identifying the predetermined electrical characteristics.

[0012] According to this aspect, the one or more second wind turbines may be able to determine whether they are electrically connected to the utility grid, or whether a local grid exists at their terminals, by receiving electrical power having predetermined electrical characteristics from the first wind turbine.

[0013] In this way, the second wind turbines can quickly and reliably identify which grid they have at their terminals and act accordingly. For example, they may avoid injecting electrical power into the wind farm grid if they detect that they are electrically connected to the local grid. This method may be particularly useful when communication with the wind farm controller has been lost and, for example, the second wind turbines do not know which grid is present at their terminals (because they cannot receive this information from the wind farm controller).

[0014] Throughout this disclosure, a utility grid may be understood as an electric power grid comprising, for example, a set of interconnected power lines and associated equipment for moving electric power between the interconnection point of a wind farm and the point at which the electric power is delivered, for example, to loads such as homes, factories and other consumers. In addition to one or more wind farms, different power plants (e.g., solar power plants, hydroelectric power plants, nuclear power plants, etc.) may be connected to the utility grid. The utility grid may be an electric power grid external to the wind farm.

[0015] Throughout this disclosure, a wind farm grid may be understood as an electrical grid within a wind farm, including, for example, a plurality of wind turbines of a wind farm. Electrical power may circulate within the wind farm grid. In some examples, one or more suitable auxiliary power sources, such as diesel generators, may help power or energize the wind farm grid. Thus, a wind farm grid may be an electrical grid internal to a wind farm. In some examples, a substation may form part of a wind farm grid.

[0016] When a wind turbine is (electrically) disconnected from the utility grid, it is understood that the wind turbine does not supply electrical power to the utility grid or does not obtain electrical power from the utility grid because the circuit breaker is opened or for other reasons. When one or more wind turbines are disconnected from the utility grid, they may form a local grid. For example, a portion of a wind farm grid may be energized by one or more wind turbines of the wind farm, and a local grid may be formed.

[0017] In a further aspect of the present disclosure, a method for determining whether a wind turbine has a locally formed power grid present at its terminals is provided. The method includes detecting, by the wind turbine, an electrical signal emitted by another wind turbine. The method also includes identifying that the locally formed power grid is present at the terminals of the wind turbine based on the detected electrical signal.

[0018] Thus, the wind turbine can determine that the energy is being provided by another wind turbine rather than being obtained from the utility grid.

[0019] In yet another aspect of the present disclosure, a first wind turbine is provided. The first wind turbine is configured to generate electric power having predetermined electrical characteristics, such as a power signal or a voltage signal, when the wind farm is disconnected from a utility grid, and transmit the electric power having the predetermined electrical characteristics to the wind farm grid, so that the predetermined electrical characteristics can be identified by a second wind turbine as being different from the electric power transmitted from the utility grid to the wind farm grid.

[0020] In yet another aspect of the present disclosure, a second wind turbine is provided. The second wind turbine is configured to detect electrical power having a predetermined electrical characteristic, such as a power signal or a voltage signal, delivered by the first wind turbine to the wind farm grid, and to determine that the wind farm is disconnected from the utility grid by identifying the predetermined electrical characteristic. The predetermined electrical characteristic is different from the electrical power delivered by the utility grid to the wind farm grid.

[0021] In another aspect of the present disclosure, a wind farm is provided. The wind farm includes a wind farm grid. The wind farm also includes one or more first wind turbines, which are configured to generate electric power with predetermined electrical characteristics when the wind farm is disconnected from the utility grid, and transmit the electric power with predetermined electrical characteristics to the wind farm grid. The wind farm also includes one or more second wind turbines, which are configured to detect the electric power transmitted to the wind farm grid and determine that the wind farm is disconnected from the utility grid by identifying the predetermined electrical characteristics.

[0022] Technical Solution 1. A method (100) for operating a wind farm (105), the wind farm (105) comprising a wind farm grid (108) and a plurality of wind turbines (10) connected to the wind farm grid (108), the method comprising:

[0023] When the wind farm (105) is disconnected from the utility grid (102), operating (110) one or more first wind turbines (111) of the plurality of wind turbines to generate electric power having predetermined electrical characteristics, and delivering the electric power having the predetermined electrical characteristics to the wind farm grid (108); and

[0024] One or more second wind turbines (112) of the plurality of wind turbines detect (120) the electrical power delivered to the wind farm grid (108) and determine that the wind farm (105) is disconnected from the utility grid (102) by identifying the predetermined electrical characteristic.

[0025] Technical Solution 2. A method according to Technical Solution 1, wherein the first wind turbine (111) is a grid-connected wind turbine configured to energize the wind farm grid (108), and wherein the second wind turbine (112) is a non-grid-connected wind turbine.

[0026] Technical Solution 3. The method according to Technical Solution 1 or Technical Solution 2, wherein the one or more second wind turbines (112) perform the detection and the determination (120) after losing communication with the wind farm controller (109).

[0027] Technical Solution 4. A method according to any one of Technical Solutions 1-3, wherein the predetermined electrical characteristic includes ripple.

[0028] Technical Solution 5. A method according to any one of Technical Solutions 1-4, wherein the predetermined electrical characteristic includes a frequency different from a frequency of the utility grid (102).

[0029] Technical Solution 6. A method according to any one of Technical Solutions 1-5, wherein the predetermined electrical characteristics include non-fundamental harmonics that are not present in the utility grid (102).

[0030] Technical Solution 7. A method according to any one of Technical Solutions 1-6, wherein the predetermined electrical characteristic includes a predetermined voltage level.

[0031] Technical Solution 8. A method according to any one of Technical Solutions 1-7, wherein the predetermined electrical characteristic includes a predetermined time-varying voltage level.

[0032] Technical Solution 9. The method according to any one of Technical Solutions 1-8 further includes the one or more second wind turbines (112) avoiding generating electrical power when the one or more second wind turbines (112) identify the predetermined electrical characteristics.

[0033] Technical solution 10. A first wind turbine (111), wherein:

[0034] The first wind turbine (111) is configured to generate electrical power having predetermined electrical characteristics when the wind farm (105) is disconnected from the utility grid (102), and wherein:

[0035] The first wind turbine (111) is further configured to deliver the electric power having the predetermined electrical characteristic to a wind farm grid (108), such that the predetermined electrical characteristic is identifiable by the second wind turbine (112) as being different from the electric power delivered to the wind farm grid (108) by the utility grid (102).

[0036] Technical Solution 11. A first wind turbine according to Technical Solution 10, wherein the first wind turbine (111) is further configured to generate electric power having second electrical characteristics when the first wind turbine (111) is connected to the utility grid (102).

[0037] Technical Solution 12. A wind farm (105), comprising:

[0038] Wind farm power grid;

[0039] One or more of the first wind turbines (111) according to technical solution 10 or 11, and further comprising

[0040] One or more second wind turbines (112) are configured to detect the electrical power delivered to the wind farm grid (108) and determine that the wind farm (105) is disconnected from the utility grid (102) by identifying the predetermined electrical characteristic.

[0041] Technical Solution 13. The wind farm according to Technical Solution 12 comprises one or more clusters (104), wherein each of the clusters (104) comprises a first wind turbine (111) configured to generate electrical power to one or more second wind turbines.

[0042] Technical Solution 14. A wind farm according to Technical Solution 13, wherein the one or more clusters (104) are arranged along a string.

[0043] Technical Solution 15. The wind farm according to any one of Technical Solutions 12-15 further includes a wind farm controller (109) configured to communicate with the first wind turbine (111) and / or the second wind turbine (112). BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 illustrates a perspective view of one example of a wind turbine;

[0045] Figure 2 Graphics Figure 1 A simplified interior view of an example of a nacelle of a wind turbine;

[0046] Figure 3 schematically illustrates an example of a wind farm;

[0047] Figure 4 a flow chart illustrating an example of a method of operating a wind farm; and

[0048] Figure 5 A flow chart showing an example of a method for determining whether a wind turbine has a local grid present at its terminals. DETAILED DESCRIPTION

[0049] Reference will now be made in detail to embodiments of the present disclosure, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation only and not as a limitation. In fact, it will be apparent to those skilled in the art that various modifications and variations may be made in the present disclosure. For example, a feature illustrated or described as part of one embodiment may be used together with another embodiment to produce yet another embodiment. Therefore, it is intended that the present disclosure covers such modifications and variations and their equivalents as fall within the scope of the appended claims.

[0050] Figure 1 1 is a perspective view of an example of a wind turbine 10. In this example, wind turbine 10 is a horizontal-axis wind turbine. Alternatively, wind turbine 10 may be a vertical-axis wind turbine. In this example, wind turbine 10 includes a tower 15 extending from a support system 14 on the ground 12, a nacelle 16 mounted on tower 15, and a rotor 18 coupled to nacelle 16. Rotor 18 includes a rotatable hub 20 and at least one rotor blade 22 connected to hub 20 and extending outwardly from hub 20. In this example, rotor 18 has three rotor blades 22. In alternative embodiments, rotor 18 includes more or less than three rotor blades 22. Tower 15 may be fabricated from tubular steel to define a cavity (not shown) between support system 14 and nacelle 16. Figure 1). In alternative embodiments, the tower 15 is any suitable type of tower having any suitable height. According to an alternative, the tower may be a hybrid tower including a portion made of concrete and a tubular steel portion. Furthermore, the tower may be a partial lattice tower or a full lattice tower.

[0051] Rotor blades 22 are spaced about hub 20 to facilitate rotating rotor 18 to enable kinetic energy to be converted from the wind into usable mechanical energy and subsequently into electrical energy. Rotor blades 22 are mated to hub 20 by coupling blade root regions 24 to hub 20 at a plurality of load transfer regions 26. Load transfer regions 26 may have hub load transfer regions and blade load transfer regions (neither of which is present in the hub load transfer region). Figure 1 The loads induced to the rotor blades 22 are transferred to the hub 20 via the load transfer region 26 .

[0052] In an example, rotor blades 22 may have a length varying from about 15 meters (m) to about 90 meters or more. Rotor blades 22 may have any suitable length that enables wind turbine 10 to function as described herein. For example, non-limiting examples of blade lengths include 20 meters or less, 37 meters, 48.7 meters, 50.2 meters, 52.2 meters, or a length greater than 91 meters. When wind strikes rotor blades 22 from wind direction 28, rotor 18 rotates about rotor axis 30. When rotor blades 22 are rotated and subjected to centrifugal forces, rotor blades 22 are also subjected to various forces and moments. As such, rotor blades 22 may deflect and / or rotate from a neutral position or a non-deflected position to a deflected position.

[0053] In addition, the pitch angle of rotor blades 22 (e.g., an angle that determines the orientation of rotor blades 22 relative to the wind direction) may be varied by pitch system 32 to control the load and power generated by wind turbine 10 by adjusting the angular position of at least one rotor blade 22 relative to the wind vector. A pitch axis 34 is shown for rotor blades 22. During operation of wind turbine 10, pitch system 32 may specifically vary the pitch angle of rotor blades 22 such that the angle of attack of (portions of) the rotor blades is reduced, which may facilitate reducing the rotational speed of rotor 18 and / or facilitating stalling of rotor 18.

[0054] In this example, blade pitch of each rotor blade 22 is individually controlled by wind turbine controller 36 or pitch control system 80. Alternatively, blade pitch for all rotor blades 22 may be controlled simultaneously by the control system.

[0055] Furthermore, in this example, as wind direction 28 changes, the yaw orientation of nacelle 16 may be rotated about yaw axis 38 to position rotor blades 22 relative to wind direction 28 .

[0056] In this example, the wind turbine controller 36 is shown as being centralized within the nacelle 16, however, the wind turbine controller 36 may be a distributed control system distributed throughout the wind turbines 10 on the support system 14, within the wind farm and / or at a remote control center. The wind turbine controller 36 may include one or more processors configured to perform one or more steps of the method described herein. In addition, many other components described herein include one or more processors. The wind turbine controller 36 may also include a memory, such as one or more storage devices. As used herein, a memory may include (multiple) storage elements, including but not limited to computer-readable media (e.g., random access memory (RAM)), computer-readable non-volatile media (e.g., flash memory), a floppy disk, a compact disk read-only memory (CD-ROM), a magneto-optical disk (MOD), a digital versatile disk (DVD), and / or other suitable storage elements.

[0057] Figure 2 1 is an enlarged cross-sectional view of a portion of a wind turbine 10. In this example, the wind turbine 10 includes a nacelle 16 and a rotor 18 rotatably coupled to the nacelle 16. More specifically, the hub 20 of the rotor 18 is rotatably coupled to a generator 42 positioned within the nacelle 16 via a main shaft 44, a gearbox 46, a high-speed shaft 48, and a coupling 50. In this example, the main shaft 44 is disposed at least partially coaxial with a longitudinal axis (not shown) of the nacelle 16. The rotation of the main shaft 44 drives the gearbox 46, which in turn drives the high-speed shaft 48 by converting the relatively slow rotational motion of the rotor 18 and the main shaft 44 into a relatively fast rotational motion of the high-speed shaft 48. The high-speed shaft 48 is connected to the generator 42 by means of the coupling 50 to generate electrical energy. Furthermore, a transformer 90 and / or suitable electronics, switches and / or inverters may be arranged in the nacelle 16 in order to convert the electrical energy generated by the generator 42, for example, with a voltage between 400 V and 1000 V, into electrical energy with a medium voltage (e.g., 10-35 kV). An offshore wind turbine may have a generator voltage, for example, between 650 V and 3500 V, and a transformer voltage, for example, between 30 kV and 70 kV. The electrical energy is conducted from the nacelle 16 to the tower 15 via a power cable.

[0058] In some examples, the wind turbine 10 may include one or more shaft sensors 51. The shaft sensors may be configured to monitor at least one of the torque load acting on the main shaft 44 and / or the high-speed shaft 48 and the rotational speed of the shafts 44, 48. In some examples, the wind turbine 10 may include one or more generator sensors 53. The generator sensor may be configured to monitor at least one of the rotational speed of the generator 42 and the generator torque. The shaft sensor 51 and / or the generator sensor 53 may include, for example, one or more torque sensors (e.g., strain gauges or pressure sensors), optical sensors, accelerometers, magnetic sensors, speed sensors, and micro inertial measurement units (MIMUs).

[0059] The gearbox 46, the generator 42 and the transformer 90 may be supported by a main support structural frame of the nacelle 16, which is optionally implemented as a main frame 52. The gearbox 46 may include a gearbox housing connected to the main frame 52 by one or more torque arms 103. In this example, the nacelle 16 also includes a front main support bearing 60 and a rear main support bearing 62. In addition, the generator 42 may be mounted to the main frame 52 by a separate support device 54, in particular in order to prevent vibrations of the generator 42 from being introduced into the main frame 52 and thereby causing a source of noise emission.

[0060] Optionally, main frame 52 is configured to carry all loads caused by the weight of components of rotor 18 and nacelle 16 and by wind and rotational loads, and further configured to introduce these loads into tower 15 of wind turbine 10. Rotor shaft 44, generator 42, gearbox 46, high speed shaft 48, coupling 50, and any associated fastening, supporting, and / or fixing devices (including but not limited to bracket 52 and front and rear support bearings 60, 62) are sometimes referred to as drive train 64.

[0061] In some examples, the wind turbine may be a direct drive wind turbine without a gearbox 46. In a direct drive wind turbine, the generator 42 operates at the same rotational speed as the rotor 18. Therefore, they typically have a much larger diameter than generators used in wind turbines with a gearbox 46 to provide a similar amount of power as a wind turbine with a gearbox.

[0062] The nacelle 16 may also include a yaw drive mechanism 56 that may be used to rotate the nacelle 16 , and thereby also the rotor 18 , about the yaw axis 38 to control the viewing angle of the rotor blades 22 relative to the wind direction 28 .

[0063] To properly position nacelle 16 relative to wind direction 28, nacelle 16 may also include at least one meteorological measurement system, which may include a wind vane and anemometer. Meteorological measurement system 58 may provide wind turbine controller 36 with information that may include wind direction 28 and / or wind speed.

[0064] In this example, pitch system 32 is arranged at least in part as a pitch assembly 66 in hub 20. Pitch assembly 66 includes one or more pitch drive systems 68 and at least one sensor 70. Each pitch drive system 68 is coupled to a corresponding rotor blade 22 (at Figure 1 ), for modulating the pitch angle of the rotor blades 22 along the pitch axis 34. Figure 2 Only one of three pitch drive systems 68 is shown.

[0065] In this example, pitch assembly 66 includes at least one pitch bearing 72 coupled to hub 20 and a corresponding rotor blade 22 (at Figure 1 34 ), for rotating the corresponding rotor blade 22 about the pitch axis 34. The pitch drive system 68 includes a pitch drive motor 74, a pitch drive gearbox 76, and a pitch drive pinion 78. The pitch drive motor 74 is coupled to the pitch drive gearbox 76 so that the pitch drive motor 74 applies a mechanical force to the pitch drive gearbox 76. The pitch drive gearbox 76 is coupled to the pitch drive pinion 78 so that the pitch drive pinion 78 is rotated by the pitch drive gearbox 76. The pitch bearing 72 is coupled to the pitch drive pinion 78 so that rotation of the pitch drive pinion 78 causes rotation of the pitch bearing 72.

[0066] Pitch drive system 68 is coupled to wind turbine controller 36 for adjusting the pitch angle of rotor blades 22 upon receipt of one or more signals from wind turbine controller 36. In this example, pitch drive motor 74 is any suitable motor driven by electrical power and / or a hydraulic system that enables pitch assembly 66 to function as described herein. Alternatively, pitch assembly 66 may include any suitable structure, construction, arrangement, and / or components, such as, but not limited to, a hydraulic cylinder, a spring, and / or a servo mechanism. In certain embodiments, pitch drive motor 74 is driven by energy extracted from the rotational inertia of hub 20 and / or a stored energy source (not shown) that supplies energy to components of wind turbine 10.

[0067] Pitch assembly 66 may also include one or more pitch control systems 80 for controlling pitch drive system 68 according to control signals from wind turbine controller 36 in the event of certain priority conditions and / or during overspeed of rotor 18. In this example, pitch assembly 66 includes at least one pitch control system 80 communicatively coupled to a corresponding pitch drive system 68 for controlling pitch drive system 68 independently of wind turbine controller 36. In this example, pitch control system 80 is coupled to pitch drive system 68 and sensor 70. During normal operation of wind turbine 10, wind turbine controller 36 may control pitch drive system 68 to adjust the pitch angle of rotor blades 22.

[0068] According to one embodiment, a power generator 84, for example including a battery and a capacitor, is disposed at or within the hub 20 and is coupled to the sensor 70, the pitch control system 80, and the pitch drive system 68 to provide a power source to these components. In this example, the power generator 84 provides a continuous power source to the pitch assembly 66 during operation of the wind turbine 10. In an alternative embodiment, the power generator 84 provides power to the pitch assembly 66 only during an electrical power loss event of the wind turbine 10. The electrical power loss event may include a grid loss or voltage dip, a fault in the electrical system of the wind turbine 10, and / or a failure of the wind turbine controller 36. During the electrical power loss event, the power generator 84 operates to provide electrical power to the pitch assembly 66 so that the pitch assembly 66 can operate during the electrical power loss event.

[0069] In this example, pitch drive system 68, sensor 70, pitch control system 80, cables, and power generator 84 are each positioned within a cavity 86 defined by an inner surface 88 of hub 20. In an alternative embodiment, the components are positioned relative to an outer surface of hub 20 and may be coupled directly or indirectly to the outer surface.

[0070] As used herein, the term "processor" is not limited to the integrated circuits known in the art as computers, but refers broadly to controllers, microcontrollers, microcomputers, programmable logic controllers (PLCs), application specific integrated circuits, and other programmable circuits, and these terms are used interchangeably herein.

[0071] Figure 3An example of a wind farm 105 is schematically illustrated, such as an offshore wind farm, in which the methods 100 and 200 (illustrated later herein) may be implemented. The wind farm 105 comprises a plurality of wind turbines 10 connected to a power grid 102 (i.e., a utility grid 102) at a point of interconnection (POI) 103. The connection between the utility grid 102 and a wind farm bus 101 may be regulated by a switch at the POI 103. The wind turbines 10 of the wind farm may be arranged in clusters, such as strings. The strings 104 are arranged in a plurality of wind turbines 10 connected to a power grid 102 (i.e., a utility grid 102). The connection between the utility grid 102 and a wind farm bus 101 may be regulated by a switch at the POI 103. The wind turbines 10 of the wind farm may be arranged in clusters, such as strings. The strings 104 may be arranged in a plurality of wind turbines 10 connected to a power grid 102 (i.e., a utility grid 102). Figure 3 , but other types of clusters are possible. The electrical power generated by each wind turbine 10 may be transferred to the wind farm bus 101 via one or more cluster buses 106 (e.g., string buses). Each wind turbine 10 may be connected to or disconnected from the corresponding cluster bus 106 via one or more switches or circuit breakers.

[0072] The wind farm 105 may include a substation 107 including, for example, a wind farm transformer configured to convert power from a wind farm voltage to a utility grid voltage. Each cluster bus 106 (e.g., each string bus) may be connected to or disconnected from the wind farm bus 101 via one or more switches or circuit breakers. In some examples, the switches or circuit breakers may be arranged at the substation.

[0073] The generator 42 of the corresponding wind turbine 10 generates AC (alternating current) power of variable frequency due to different wind conditions. A power converter may be provided for adjusting the power output from the generator 42 to a power output suitable for the utility grid 102, for example, to AC power with a fixed frequency. The power converter may include a machine-side converter, a line-side converter, and a DC (direct current) link connecting the machine-side converter and the line-side converter (not shown).

[0074] In some examples, the generator 42 of the wind turbine 10 may be a permanent magnet generator including a generator rotor carrying a plurality of permanent magnets and a stator. The permanent magnet generator may be directly driven by the wind turbine rotor 18. The stator of the generator may be connected to a machine-side converter, which may be configured to convert the received AC voltage into a DC voltage and then transmit the DC voltage to the DC link. The line-side converter may be configured to convert the DC voltage from the DC link into a fixed frequency AC voltage.

[0075] The line side converter may be connected to the cluster bus 106 via a main transformer. The main transformer may be configured to step up the voltage delivered by the power converter, for example to 33 kV. In some examples, the main transformer may be installed in the nacelle 16 or tower 15 of the wind turbine. In other examples, the main transformer may be arranged at other suitable locations.

[0076] exist Figure 3 In the example of , the main transformer may be configured to receive electric power from utility grid 102. Utility grid 102 may be configured to provide electric power to wind farm bus 101 and cluster bus 106 in normal operation.

[0077] If the electrical connection to the utility grid 102 is lost, the wind farm 105 (e.g., part of the wind farm) may enter and begin operating in a so-called island mode. Throughout the present disclosure, the term "island mode" may refer to an operating mode in which one or more wind turbines 10 are configured to operate independently of the utility grid 102, for example when the wind turbine cannot obtain electrical power from the utility grid. Wind turbines operating in island mode may form a local grid. For example, these wind turbines may be electrically connected between them because at least one of them has energized, for example, part of the wind farm grid. In some examples, one or more wind turbines 10 may not be able to receive electrical power from the utility grid 102 due to the fact that the physical connection between the wind turbine 10 and the utility grid 102 is missing, for example because a busbar or some cables are damaged or broken, or other reasons such as electrical failures may prevent the wind turbine 10 from obtaining electrical power from the utility grid 102.

[0078] In the island mode, in addition to the electric power for maintaining the normal operation of auxiliary systems obtained from one or more wind turbines whose rotors rotate to generate electric power, the electric power for maintaining the normal operation of auxiliary systems can also be obtained from auxiliary power sources, including, for example, one or more of a communication system, a temperature and ventilation adjustment system, a bearing lubrication system, a controller system, and a navigation light or other system. The term "auxiliary power source(s)" may also be referred to as auxiliary energy storage device(s) or auxiliary energy storage system(s).

[0079] The wind farm controller 109 is communicatively coupled to the wind turbine controllers 36 of the wind turbines 10 for controlling their operation in the island mode. If communication with the wind farm controller 109 is lost, problems such as injection of undesired power into the wind farm grid 108 may arise. Figure 3 It is schematically illustrated how the communication between the wind farm controller 109 and the controller 36 of the second wind turbine 112 is lost.

[0080] In one aspect of the present disclosure, a method 100 for operating a wind farm is provided, the wind farm comprising a wind farm grid 108 and a plurality of wind turbines 111, 112 connected to the wind farm grid 108. The method 100 is schematically illustrated in Figure 4The method includes, at box 110, when the wind farm 105 is disconnected from the utility grid 102, operating one or more first wind turbines 111 of the plurality of wind turbines to generate electric power having predetermined electrical characteristics, and delivering the electric power having the predetermined electrical characteristics to the wind farm grid 108. The method also includes, at box 120, one or more second wind turbines 112 of the plurality of wind turbines detecting the electric power delivered to the wind farm grid 108, and determining that the wind farm 105 is disconnected from the utility grid 102 by identifying the predetermined electrical characteristics.

[0081] Thus, detecting electric power with predetermined electrical characteristics may mean that the second wind turbine 112 is electrically connected to the wind farm grid 108 and that a local grid exists at their output. Conversely, detecting electric power without predetermined electrical characteristics may mean that the second wind turbine is electrically connected to the utility grid 102 and that the second wind turbine may receive electric power from the utility grid 102. Thus, the second wind turbine 112 may distinguish which grid is present at their terminals in a simple, efficient and reliable manner. The electric power may be emitted via one or more cables or busbars 106 connecting the first wind turbine 111 to the second wind turbine 112.

[0082] The first wind turbine 111 may be a grid-building wind turbine configured to energize the wind farm grid 108 (e.g., a portion of the wind farm grid 108). For example, the grid-building wind turbine may be configured to detect a local grid to be formed, such as a portion of the wind farm grid to be energized. In some examples, the wind farm controller 109 may indicate this to the grid-building wind turbine. In other examples, one or more grid-building wind turbines may be configured to detect this without the wind farm controller. The second wind turbine 112 may be a non-grid-building wind turbine. The second wind turbine may be configured to follow the instructions of the wind farm controller and the first wind turbine 111.

[0083] In some examples, if the first wind turbine is unable to perform the leading role as a grid-building wind turbine, for example because it is damaged, a second wind turbine that was initially assigned the follower role of a non-grid-building wind turbine may take over the leading role. That is, redundancy may be provided such that one or more second wind turbines may take over the grid-building role if deemed necessary.

[0084] The one or more second wind turbines 112 may perform the detection and determination after losing communication with the wind farm controller 109. Regardless of whether the one or more first wind turbines 111 and / or the one or more second wind turbines 112 have lost communication with the wind farm controller 109, electric power with predetermined electrical characteristics may be generated and delivered to the wind farm grid. This is due to the fact that the first wind turbine 111 may not know whether the one or more second wind turbines 112 have lost communication with the wind farm controller. Therefore, once the wind farm has been disconnected from the utility grid 102, electric power with predetermined electrical characteristics may be continuously generated and delivered to the wind farm grid.

[0085] In some examples, wind farm controller 109 may initially indicate to second wind turbines 112 whether they are connected to utility grid 102. However, if communication between wind farm controller 109 and second wind turbines 112 is lost for any reason, first wind turbine 111 may (indirectly) assume the role of wind farm controller such that the second wind turbine does not inject electrical power into the wind farm grid.

[0086] It may happen that one or more second wind turbines may be in communication with the wind farm controller. For example, if the wind turbines are arranged in a cluster 104, such as in a string, it may happen that some second wind turbines in the cluster may be in communication with the wind farm controller, while some other second wind turbines in the cluster may not be. Second wind turbines that are not able to communicate with the wind farm controller may rely on electrical power having predetermined electrical characteristics, while in some examples, second wind turbines that are still able to communicate with the wind farm controller may receive redundant information.

[0087] The characteristics of the electric power may enable second wind turbine 112 to detect it and not confuse it with other signals. In some examples, second wind turbines 112 may recognize that the local grid is present at their terminals after they have detected the electric power for a certain period of time (e.g., having a duration above a certain threshold). In these or other examples, the second wind turbines may recognize that the local grid is present at their terminals after they have detected a certain number of predetermined characteristics (e.g., having detected the predetermined characteristics two, three, or more times). In other examples, a single detection may be sufficient.

[0088] The predetermined electrical characteristic may include ripple. For example, the electrical power may have a high amplitude and / or a high frequency so that it can be distinguished from other electrical power that the second wind turbine may receive from the utility grid. For example, the signal of the electrical power may have a frequency that is different from the frequency of the utility grid 102. In some examples, the predetermined electrical characteristic may include non-fundamental harmonics that are not present in the utility grid. In this regard, the electrical power signal emitted by the first wind turbine may be modulated in a particular manner so that it can be recognized by the second wind turbine.

[0089] The predetermined electrical characteristic may include a voltage, i.e., the electrical power signal may be a voltage signal. Since the frequency and voltage of the island should be controlled, it may be easy to issue a voltage signal. As indicated above, the amplitude and / or frequency of the electrical power (e.g., voltage signal) may be modified, e.g., modulated. In some examples, the predetermined electrical characteristic may include a predetermined voltage level or a predetermined time-varying voltage level.

[0090] The predetermined electrical characteristic may be a specific electrical characteristic, such as an electronic signature, known in advance by the first wind turbine 111 and the second wind turbine 112. For example, the first wind turbine and the second wind turbine may be configured to respectively emit and receive / recognize electrical power having such predetermined characteristics before the first wind turbine and the second wind turbine begin their operation for the first time, for example, they may be configured during commissioning or even before (e.g., in a factory).

[0091] As previously mentioned, one or more first wind turbines and one or more second wind turbines may be arranged into one or more clusters 104, for example, arranged into one or more strings. Each wind turbine of each cluster (e.g., each string) may be connected by one or more cables 106. In some examples, such cables may be referred to as cluster busbars, array cables, or offshore cables. In some examples, the first wind turbine 111 of each cluster 104 may generate and transmit electrical power to be detected by one or more second wind turbines 112 of the cluster 104.

[0092] For example, each cluster 104 may include a first wind turbine 111 configured to generate and deliver electrical power to the wind farm grid so that, for example, other wind turbines 112 of the corresponding cluster can detect the electrical power if communication with the wind farm controller 109 is lost. In other examples, not all clusters require a first wind turbine.

[0093] The method may also include the one or more second wind turbines refraining from generating power when the one or more second wind turbines identify the predetermined electrical characteristic. That is, in this case, the one or more second wind turbines may not generate power. Since the second wind turbines correctly identify that the utility grid 102 has not been restored, they will not accidentally start in a power generation mode.

[0094] In another aspect of the present disclosure, a first wind turbine 111 and a second wind turbine 112 are disclosed, which are configured to appropriately perform one or more steps of the methods 100, 200 disclosed herein and operate substantially as described herein. The first wind turbine 111 is configured to generate electric power having predetermined electrical characteristics when the wind farm 105 is disconnected from the utility grid 102, and to deliver the electric power having the predetermined electrical characteristics to the wind farm grid 108, so that the predetermined electrical characteristics can be identified by the second wind turbine as being different from the electric power delivered by the utility grid 102 to the wind farm grid 108.

[0095] First wind turbine 111 may also be configured to generate electrical power having a second electrical characteristic when first wind turbine 111 is connected to the utility grid.For example, first wind turbine may not introduce ripple into a power signal it generates during normal operation of the wind turbine.

[0096] Likewise, the second wind turbine 112 is configured to detect the electric power having the predetermined electrical characteristics delivered to the wind farm grid 108 by the first wind turbine 111, and to determine that the wind farm 105 is disconnected from the utility grid 102 by identifying the predetermined electrical characteristics. The first wind turbine 111 and the second wind turbine 112 may include a control system 36 configured to perform the steps of the method described herein. The electric power having the predetermined electrical characteristics is different from the electric power delivered to the wind farm grid by the utility grid.

[0097] In this manner, second wind turbine 112 may identify whether energy is being provided by utility grid 102 or by first wind turbine 111 , for example, if communication with wind farm controller 109 is lost.

[0098] In some examples, first wind turbine 111 and second wind turbine 112 may be onshore wind turbines, while in other examples they may be offshore wind turbines.

[0099] In a further aspect of the present disclosure, a wind farm 105 is provided. The wind farm 105 includes a wind farm grid 108. The wind farm also includes one or more first wind turbines 111 configured to generate electric power having predetermined electrical characteristics when the wind farm is disconnected from the utility grid 102, and to deliver the electric power having the predetermined electrical characteristics to the wind farm grid 108. The wind farm also includes one or more second wind turbines 112 configured to detect the electric power delivered to the wind farm grid 108, and to determine that the wind farm is disconnected from the utility grid 102 by identifying the predetermined electrical characteristics.

[0100] One or more first wind turbines 111 may be configured to generate electrical power having predetermined electrical characteristics in a continuous manner when they detect that their wind farm 105 is disconnected from utility grid 102. Electrical power having predetermined electrical characteristics may be generated until connection to utility grid 102 is regained.

[0101] One or more second wind turbines 112 may be configured to not produce power when they detect that a local grid is present at their terminals.

[0102] The first wind turbine 111 may be a grid-capable wind turbine and the second wind turbine 112 may be a non-grid-capable wind turbine.

[0103] In some examples, wind farm 105 may be an onshore wind farm, while in other examples, the wind farm may be an offshore wind farm.

[0104] Wind farm 105 may include one or more clusters 104, and each of the clusters may include a first wind turbine 111 configured to generate electrical power to one or more second wind turbines 112. One or more clusters 104 may be arranged along a string.

[0105] Wind farm 105 may further include a wind farm controller 109 configured to communicate with first wind turbine 111 and / or second wind turbine 112 .

[0106] The previous explanations regarding the method 100 may be combined and applied to this aspect, and vice versa.

[0107] In a further aspect of the present disclosure, a method 200 is provided for determining whether a wind turbine 112 has a locally formed grid present at its terminals, optionally when communication with the wind farm controller 109 is lost. The method 200 is Figure 5The aspects and explanations about the method 100 can be combined and applied to the method 200, and vice versa. The method includes detecting, by a wind turbine, an electrical signal emitted by another wind turbine.

[0108] The method includes, at block 210, detecting, by the wind turbine 112, an electrical signal emitted by another wind turbine 111. The method includes, at block 220, identifying that a locally formed grid is present at terminals of the wind turbine based on the detected electrical signal.

[0109] For example, wind farm grid 108 electrically disconnected from utility grid 102 may include one or more first wind turbines 111 and one or more second wind turbines 112. First wind turbine 111 may emit an electrical signal, and one or more second wind turbines 112 may detect the electrical signal and recognize that a local grid exists at their terminals.

[0110] The electrical signal may be detected via a cable or busbar 106 connecting the two wind turbines 111, 112. The two wind turbines may belong to the same cluster 104 of wind turbines, eg to the same string of wind turbines.

[0111] The electrical signal may be a signal having an amplitude and / or frequency that is different from other electrical signals provided by utility grid 102 when the wind turbine is connected to the utility grid. The electrical signal may be a modulated signal, such as a modulated voltage signal.

[0112] When a locally formed grid is identified at the terminals of a wind turbine, the wind turbine may refrain from operating (generating electrical power).

[0113] When recognizing a locally formed grid, the wind turbines may only generate reactive power.

[0114] For example, during at least the duration of the method, the wind turbine may not receive control signals from the wind farm controller 109 .

[0115] This written description uses examples including preferred embodiments to disclose teachings, and also enables any person skilled in the art to practice the teachings, including making and using any device or system and performing any combined methods. The patentable scope is defined by the claims and may include other examples that occur to those skilled in the art. If such other examples have structural elements that are not different from the literal language of the claims, or if they 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. A person of ordinary skill in the art may mix and match aspects from the various embodiments described and other known equivalents of each such aspect to construct additional embodiments and techniques according to the principles of the present application. If reference marks associated with the drawings are placed in brackets in the claims, they are merely intended to increase the understandability of the claims and should not be interpreted as limiting the scope of the claims.

Claims

1. A method (100) for operating a wind farm (105), the wind farm (105) comprising a wind farm grid (108) and a plurality of wind turbines (10) connected to the wind farm grid (108), the method include: When the wind farm (105) is disconnected from the utility grid (102), operating (110) one or more first wind turbines (111) of the plurality of wind turbines to generate electric power having predetermined electrical characteristics, and delivering the electric power having the predetermined electrical characteristics to the wind farm grid (108); and One or more second wind turbines (112) of the plurality of wind turbines detect (120) the electrical power delivered to the wind farm grid (108) and determine that the wind farm (105) is disconnected from the utility grid (102) by identifying the predetermined electrical characteristic.

2. The method according to claim 1, in, The first wind turbine (111) is a grid-enabled wind turbine configured to energize the wind farm grid (108), and wherein the second wind turbine (112) is a non-grid-enabled wind turbine.

3. The method according to claim 1 or claim 2, in, The one or more second wind turbines (112) perform the detecting and the determining (120) after losing communication with the wind farm controller (109).

4. The method according to any one of claims 1 to 3, in, The predetermined electrical characteristic includes a ripple.

5. The method according to any one of claims 1 to 4, in, The predetermined electrical characteristic includes a frequency different from a frequency of the utility grid (102).

6. The method according to any one of claims 1 to 5, in, The predetermined electrical characteristics include non-fundamental harmonics not present in the utility grid (102).

7. The method according to any one of claims 1 to 6, in, The predetermined electrical characteristic includes a predetermined voltage level.

8. The method according to any one of claims 1 to 7, in, The predetermined electrical characteristic comprises a predetermined time-varying voltage level.

9. The method of any one of claims 1-8, further comprising refraining from generating electrical power by the one or more second wind turbines (112) when the one or more second wind turbines (112) identify the predetermined electrical characteristic.

10. A first wind turbine (111), in, The first wind turbine (111) is configured to generate electrical power having predetermined electrical characteristics when the wind farm (105) is disconnected from the utility grid (102), and wherein: The first wind turbine (111) is further configured to deliver the electric power having the predetermined electrical characteristic to a wind farm grid (108), such that the predetermined electrical characteristic is identifiable by the second wind turbine (112) as being different from the electric power delivered to the wind farm grid (108) by the utility grid (102).

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