Operation method for wind power plant

Abstract

To suitably operate a wind power plant grid (108) of a wind power plant (105) that has lost communication with a wind power plant controller (109) and has been electrically disconnected from a utility grid (102).SOLUTION: When the wind power plant (105) is being disconnected from the utility grid (102), the wind power plant (105) causes one or more first wind turbines (111) to operate to generate power having predetermined electrical characteristics and to send the power to the wind power plant grid (108). One or more second wind turbines (112) detect the sent power (120) to identify the predetermined electrical characteristics, thereby determining that the wind power plant (105) is disconnected from the utility grid (102).SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates to a method for forming a local grid and operating in a wind farm grid for wind farms that are electrically isolated from a utility grid. More particularly, the present disclosure relates to such a wind farm grid where communication between the wind turbines and / or between the wind turbines and a wind farm controller has been lost. The present disclosure further relates to a wind farm and a wind turbine. [Background technology]

[0002] Modern wind turbines are commonly used to provide electricity to the electrical grid. This type of wind turbine typically includes a tower and a rotor disposed on the tower. The rotor typically includes a hub and a number of blades, and rotates under the influence of wind on the blades. This rotation generates a torque that is typically transferred via the rotor shaft to a generator, either directly ("direct drive" or "gearless") or using a gearbox. In this way, the generator generates electrical power that can be provided to the electrical grid.

[0003] The wind turbine hub may be rotatably coupled to the front of the nacelle. The wind turbine hub is coupled to a rotor shaft, which is rotatably mounted within the nacelle using one or more rotor shaft bearings located in a frame within the nacelle. The nacelle is a housing located on top of the wind turbine tower that may house and protect the gearbox and generator (if not located outside the nacelle), and in some wind turbines, other components such as power converters and auxiliary systems.

[0004] While the wind turbine is disconnected from the grid, some associated auxiliary systems, such as communication systems and ventilation and temperature regulation systems, may continue to operate until power is similarly exhausted, provided by auxiliary sources such as battery-based systems, supercapacitors such as uninterruptible power supplies (UPS), or diesel generators. Solar panels can also be used to provide the auxiliary power. Another way to obtain auxiliary power is to operate the wind turbine to generate a small amount of electricity, which can then be supplied to one or more auxiliary systems.

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

[0006] To transition to island mode, one or more wind turbines of the wind farm can be configured to be grid forming wind turbines. That is, when a disconnection from the electrical grid is detected, these grid forming wind turbines act as leaders and start operating in island mode first. The remaining wind turbines of the island follow the leading wind turbines, i.e., become followers or non-grid forming wind turbines. Once the island is formed, the wind turbines belonging to the island are electrically connected. For example, the island has a plurality of energized and interconnected strings, and a plurality of wind turbines are connected to each of the energized strings. In other words, a local grid is formed that electrically connects the leading and trailing wind turbines.

[0007] Non-grid forming wind turbines need to know whether the grid that is present at their terminals is the utility grid or the local grid. If the voltage registered at their terminals is provided by the utility grid and wind conditions allow, the wind turbine will try to start and inject power. However, if the wind farm is in island mode and a wind turbine is providing a voltage at its terminal that another wind turbine detects, the wind turbine should not start because the power it generates cannot be fed to the utility grid, which could lead to over-generation leading to unstable operation of the island.

[0008] During or after the islands are formed, the wind farm controller typically communicates with each wind turbine, and in particular the wind turbine controller, to indicate this, and thanks to this communication, grid following or non-grid forming wind turbines can know whether the grid present at their end is the utility grid or the local grid.

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

[0010] The present disclosure aims to enable a non-grid wind turbine to identify whether it is electrically connected to a locally formed grid or to a utility grid during and after formation of the locally formed grid, i.e. to determine whether a locally formed grid or a utility grid is present at its terminal. Throughout this disclosure, the terms "local grid" and "locally formed grid" are used interchangeably to refer to a grid formed, for example, by one or more wind turbines when a wind farm is disconnected from the utility grid, i.e., power that may be received and / or detected by other wind turbines is generated independently of the utility grid. Summary of the Invention

[0011] In one aspect of the disclosure, a method of operating a wind farm including a wind farm grid and a plurality of wind turbines connected to the wind farm grid is provided. The method comprises operating one or more first wind turbines of the plurality of wind turbines to generate electrical power having a predetermined electrical characteristic when the wind farm is disconnected from a utility grid, and supplying the electrical power having the predetermined electrical characteristic to the wind farm grid. The method further includes one or more second wind turbines of the plurality of wind turbines detecting electrical power supplied to a power grid of the wind farm and determining that the wind farm is disconnected from the utility grid by identifying the predetermined electrical characteristic.

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

[0013] In this way, the second wind turbine can quickly and reliably identify which power grid it is connected to and act accordingly. For example, if the wind turbine detects that it is electrically connected to the local grid, it can avoid injecting power into the wind farm grid. This method is particularly useful in cases where the second wind turbine does not know which power grid is present at the terminal, for example because it has lost communication with the wind farm controller and is unable to receive this information from the wind farm controller.

[0014] Throughout this disclosure, a utility grid may be understood as an electrical grid that includes an interconnected group of transmission lines and associated equipment for moving electrical energy between interconnection points of, for example, wind power plants and points that provide electrical energy to loads, such as homes, industrial plants, and other customers. In addition to one or more wind power plants, various power plants may be connected to the utility grid, such as solar power plants, hydroelectric power plants, nuclear power plants, etc. The utility grid may also be an electrical grid that is external to the wind power plants.

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

[0016] When a wind turbine is electrically disconnected from the utility grid, such as because a circuit breaker is open, it can be understood that the wind turbine is not providing or receiving power from the utility grid. 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's power grid may be energized by one or more wind turbines of the wind farm, forming a local power grid.

[0017] In a further aspect of the disclosure, a method is provided for determining whether a wind turbine has a locally formed grid at its terminal, the method including detecting, by the wind turbine, an electrical signal transmitted by another wind turbine, the method further including determining, based on the detected electrical signal, that a locally formed grid exists at the terminal of the wind turbine.

[0018] Thus, wind turbines can determine that energy is not being drawn from the utility grid, but is instead being supplied by other wind turbines.

[0019] In yet another aspect of the disclosure, a first wind turbine is provided, the first wind turbine configured to generate electrical power, e.g., a power signal or a voltage signal, having a predetermined electrical characteristic and supplying the electrical power having the predetermined electrical characteristic to a wind farm grid when the wind farm is disconnected from a utility grid, the predetermined electrical characteristic being identifiable by a second wind turbine as being different from the electrical power supplied from the utility grid to the wind farm grid.

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

[0021] In a further aspect of the present disclosure, a wind power plant is provided. The wind power plant comprises a wind power plant grid. The wind power plant further comprises one or more first wind turbines configured to generate electrical power having a predetermined electrical characteristic when the wind power plant is disconnected from the utility grid and to supply the electrical power having the predetermined electrical characteristic to the wind power plant grid. The wind power plant further comprises one or more second wind turbines configured to detect electrical power transmitted to the wind power plant grid and determine that the wind power plant is disconnected from the utility power grid by identifying the predetermined electrical characteristic. [Brief description of the drawings]

[0022] [Figure 1] 1 is a perspective view of an example wind turbine. [Diagram 2] FIG. 2 is a simplified internal view of an example nacelle of the wind turbine of FIG. 1. [Diagram 3] 1 shows a schematic diagram of an example wind power plant. [Figure 4] 1 shows a flow chart of an example of a method for operating a wind power plant. [Diagram 5] 1 shows a flow chart of an example of a method for determining whether a local grid is present at a terminal of a wind turbine. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Reference will now be made in detail to the embodiments of the present disclosure, one or more examples of which are illustrated in the drawings. Each example is provided by way of illustration only, and not by way of limitation. Indeed, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure. For example, features illustrated or described as part of one embodiment can be used with another embodiment to yield still further embodiments. Thus, it is intended that the present disclosure cover such modifications and variations as come within the scope of the appended claims and their equivalents.

[0024] FIG. 1 is a perspective view of an example of a wind turbine 10. In this example, the wind turbine 10 is a horizontal axis wind turbine. Alternatively, the wind turbine 10 may be a vertical axis wind turbine. In this example, the wind turbine 10 includes a tower 15 extending from a support system 14 on a ground 12, a nacelle 16 attached to the tower 15, and a rotor 18 coupled to the nacelle 16. The rotor 18 includes a rotatable hub 20 and at least one rotor blade 22 coupled to the hub 20 and extending outwardly from the hub 20. In this example, the rotor 18 has three rotor blades 22. In alternative embodiments, the rotor 18 includes more or less than three rotor blades 22. The tower 15 may be fabricated from tubular steel to define a cavity (not shown in FIG. 1) between the support system 14 and the nacelle 16. In alternative embodiments, the tower 15 may be any suitable type of tower having any suitable height. According to an alternative, the tower may be a hybrid tower including a concrete portion and a steel tubular portion. It may also be a partial or full lattice tower.

[0025] The rotor blades 22 are spaced apart relative to the hub 20 to rotate the rotor 18 and enable the conversion of kinetic energy from the wind into usable mechanical energy, and therefore electrical energy. The rotor blades 22 are mated to the hub 20 by coupling the blade root regions 24 to the hub 20 at a number of load transfer regions 26. The load transfer regions 26 may include hub load transfer regions and blade load transfer regions (both not shown in FIG. 1 ). Loads induced in the rotor blades 22 are transferred to the hub 20 via the load transfer regions 26.

[0026] In some examples, the rotor blades 22 may have a length ranging from about 15 meters (m) to about 90 meters (m) or more. The rotor blades 22 may have any suitable length that enables the wind turbine 10 to function as described herein. For example, non-limiting examples of blade lengths include lengths of 20 meters or less, 37 meters (m), 48.7 meters (m), 50.2 meters (m), 52.2 meters (m), or more than 91 meters (m). When wind strikes the rotor blades 22 from a wind direction 28, the rotor 18 rotates about a rotor axis 30. As the rotor blades 22 rotate and experience centrifugal forces, the rotor blades 22 also experience various forces and moments. As such, the rotor blades 22 may deflect and / or rotate from a neutral, or non-deflected, position to a deflected position.

[0027] Additionally, the pitch angles of the rotor blades 22, e.g., angles that determine the orientation of the rotor blades 22 relative to the wind direction, may be varied by a pitch system 32 to control the load and power generated by the wind turbine 10 by adjusting the angular position of at least one rotor blade 22 relative to the wind vector. A pitch axis 34 of the rotor blades 22 is shown. During operation of the wind turbine 10, the pitch system 32 may vary the pitch angles of the rotor blades 22, among other things, to reduce the angle of attack of (some of) the rotor blades, thereby facilitating reducing a rotational speed and / or facilitates a stall of the rotor 18.

[0028] In this embodiment, the blade pitch of each rotor blade 22 is individually controlled by the wind turbine controller 36 or the pitch control system 80. Alternatively, the blade pitch of all rotor blades 22 may be simultaneously controlled by these control systems.

[0029] Further, in the illustrative embodiment, as wind direction 28 changes, nacelle 16 may be yaw rotated about yaw axis 38 to position rotor blades 22 relative to wind direction 28 .

[0030] In this example, the wind turbine controller 36 is shown as being centrally located in the nacelle 16, however, the wind turbine controller 36 may be a distributed control system located throughout the wind turbine 10, on the support system 14, in 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 methods described herein. Additionally, many of the other components described herein include one or more processors. The wind turbine controller 36 may also include memory, such as one or more memory devices. As used herein, memory may include memory elements including, but not limited to, computer readable media (e.g., random access memory (RAM)), computer readable non-volatile media (e.g., flash memory), floppy disks, compact disks-read only memory (CD-ROM), magneto-optical disks (MOD), digital versatile disks (DVD), and / or other suitable memory elements.

[0031] 2 is an enlarged cross-sectional view of a portion of the 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, a hub 20 of the rotor 18 is rotatably coupled to a generator 42 disposed within the nacelle 16 by a main shaft 44, a gearbox 46, a high-speed shaft 48, and a coupling 50. In the example, the main shaft 44 is disposed at least partially coaxially with a longitudinal axis (not shown) of the nacelle 16. Rotation of the main shaft 44 drives a gearbox 46, which drives the high-speed shaft 48 by converting the relatively slow rotational motion of the rotor 18 and main shaft 44 into a relatively fast rotational motion of the high-speed shaft 48. The latter is connected, with the aid of the coupling 50, to the generator 42 for producing electrical energy. Further, a transformer 90 and / or suitable electronics, switches and / or inverters may be arranged in the nacelle 16 to convert the electrical energy generated by the generator 42 having a voltage of, for example, 400V to 1000V into electrical energy having a medium voltage (for example, 10 to 35 kV). An offshore wind turbine may have a generator voltage of, for example, 650V to 3500V, and the transformer voltage may be, for example, 30 kV to 70 kV. The electrical energy is transferred from the nacelle 16 to the tower 15 via a power cable.

[0032] 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 a 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 sensors may be configured to monitor at least one of a rotational speed of the generator 42 and a generator torque. The shaft sensors 51 and / or the generator sensors 53 may include, for example, one or more torque sensors (eg, strain gauges or pressure sensors), optical sensors, accelerometers, magnetic sensors, speed sensors and Micro-Inertial Measurement Units (MIMUs).

[0033] The gearbox 46, the generator 42 and the transformer 90 may be supported by a main support structural frame of the nacelle 16, optionally embodied as a main frame 52. The gearbox 46 may include a gearbox housing coupled to the main frame 52 by one or more torque arms 103. In an embodiment, the nacelle 16 also includes a main forward support bearing 60 and a main aft support bearing 62. Furthermore, the generator 42 may be mounted to the main frame 52 by a decoupling support means 54, particularly to prevent vibrations of the generator 42 from being introduced into the main frame 52 and thereby causing a source of noise emissions.

[0034] Optionally, the main frame 52 is configured to carry the weight of the rotor 18 and nacelle 16 components, as well as the loads caused by wind and rotational loads, and to introduce these loads into the tower 15 of the wind turbine 10. The rotor shaft 44, generator 42, gearbox 46, high speed shaft 48, coupling 50, and supports 52, and any associated fastening, support, and / or securing device, including but not limited to forward and aft support bearings 60 and 62, may be referred to as a drive train 64.

[0035] In some embodiments, the wind turbine may be a direct drive wind turbine without a gearbox 46. The generator 42 operates at the same rotational speed as the rotor 18 of a direct drive wind turbine and therefore generally has a much larger diameter than the generator used in a wind turbine with a gearbox 46 to provide a similar amount of power than a wind turbine with a gearbox.

[0036] The nacelle 16 may also include a yaw drive mechanism 56 that may be used to rotate the nacelle 16, and thereby the rotor 18, about the yaw axis 38 to control the approach or approach of the rotor blades 22 relative to the wind direction 28.

[0037] To properly position the nacelle 16 with respect to the wind direction 28, the nacelle 16 may also include at least one meteorological measurement system including a wind vane and anemometer. The meteorological measurement system 58 may provide information including the wind direction 28 and / or wind speed to the wind turbine controller 36.

[0038] In this example, pitch system 32 is disposed, at least in part, within hub 20 as a pitch assembly 66. 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 respective rotor blade 22 (shown in FIG. 1 ) for modulating the pitch angle of rotor blade 22 along pitch axis 34. Only one of the three pitch drive systems 68 is shown in FIG. 2.

[0039] In this example, pitch assembly 66 includes at least one pitch bearing 72 coupled to hub 20 and each rotor blade 22 (shown in FIG. 1 ) for rotating each rotor blade 22 about pitch axis 34. Pitch drive system 68 includes a pitch drive motor 74, a pitch drive gearbox 76, and a pitch drive pinion 78. Pitch drive motor 74 is coupled to pitch drive gearbox 76 such that pitch drive motor 74 provides a mechanical force to pitch drive gearbox 76. Pitch drive gearbox 76 is coupled to pitch drive pinion 78 such that pitch drive pinion 78 is rotated by pitch drive gearbox 76. Pitch bearing 72 is coupled to pitch drive pinion 78 such that rotation of pitch drive pinion 78 causes rotation of pitch bearing 72.

[0040] The pitch drive system 68 is coupled to the wind turbine controller 36 for adjusting the pitch angle of the rotor blades 22 in response to one or more signals from the wind turbine controller 36. In this example, the pitch drive motor 74 is any suitable motor driven by an electrical power and / or hydraulic system that enables the pitch assembly 66 to function as described herein. Alternatively, the pitch assembly 66 may include any suitable structure, configuration, arrangement, and / or components, such as, but not limited to, hydraulic cylinders, springs, and / or servo mechanisms. In certain embodiments, the pitch drive motor 74 is driven by the rotational inertia of the hub 20 and / or energy extracted from a stored energy source (not shown) that provides energy to components of the wind turbine 10.

[0041] The pitch assembly 66 may also include one or more pitch control systems 80 for controlling the pitch drive systems 68 in accordance with control signals from the wind turbine controller 36 in case of certain preferred conditions and / or upon overspeed of the rotor 18. In an example embodiment, the pitch assembly 66 includes at least one pitch control system 80 communicatively coupled to each pitch drive system 68 for controlling the pitch drive systems 68 independently from the wind turbine controller 36. In an example embodiment, the pitch control system 80 is coupled to the pitch drive systems 68 and to the sensors 70. During normal operation of the wind turbine 10, the wind turbine controller 36 may control the pitch drive systems 68 to adjust the pitch angle of the rotor blades 22.

[0042] According to an embodiment, a power generator 84, including, for example, a battery and an electrical capacitor, is disposed at or within the hub 20 and is coupled to the sensors 70, the pitch control system 80, and the pitch drive system 68 to provide a source of electrical power to these components. In this example, the power source 84 provides a continuous source of electrical power to the pitch assembly 66 during operation of the wind turbine 10. In an alternative embodiment, the power source 84 provides power to the pitch assembly 66 only during a power loss event of the wind turbine 10. A power loss event may include a loss or dip in the electrical grid, a malfunction of the electrical system of the wind turbine 10, and / or a failure of the wind turbine controller 36. During a power loss event, the generator 84 operates to provide electrical power to the pitch assembly 66 such that the pitch assembly 66 can operate during the power loss event.

[0043] In the illustrative embodiment, pitch drive system 68, sensor 70, pitch control system 80, cables, and power supply 84 are each disposed within a cavity 86 defined by an inner surface 88 of hub 20. In alternative embodiments, the components may be positioned relative to and directly or indirectly coupled to an outer surface of hub 20.

[0044] As used herein, the term "processor" is not limited to integrated circuits referred to in the art as computers, but refers broadly to controllers, microcontrollers, microcomputers, programmable logic controllers (PLCs), application specific integrated circuits, and other programmable circuitry, and these terms are used interchangeably herein.

[0045] FIG. 3 shows a schematic diagram of an example of a wind farm 105, e.g., an offshore wind farm, in which the methods 100 and 200 (shown later in this specification) may be implemented. The wind farm 105 includes a number of wind turbines 10 connected to an electrical grid 102, i.e., a utility grid 102, at points of interconnection (POI) 103. The connection between the utility grid 102 and the wind farm busbar 101 may be regulated by a switch at the POI 103. The wind turbines 10 of the wind farm may be arranged in clusters, e.g., in strings. Although a string 104 is shown in FIG. 3, other types of clusters are possible. Electrical power generated by each wind turbine 10 may be transmitted to the wind farm busbar 101 via one or more cluster busbars 106 (e.g., string busbars). Each wind turbine 10 may be connected to or disconnected from the corresponding cluster busbar 106 via one or more switches or breakers.

[0046] The wind farm 105 may comprise 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 busbar 106, for example each string busbar, may be connected or disconnected from the wind farm busbar 101 via one or more switches or breakers. In some examples, the switches or breakers may be located at the substation.

[0047] The generator 42 of the corresponding wind turbine 10 generates AC (alternating current) power, the frequency of which varies with changing wind conditions. A power converter may be provided to condition the power output from the generator 42 to be suitable for the utility grid 102, e.g., AC power having a fixed frequency. The power converter may include a machine-side converter, a line-side converter, and a DC (direct current) link (not shown) connecting the machine-side converter and the line-side converter.

[0048] The generator 42 of the wind turbine 10 may be a permanent magnet generator, in some examples, including a generator rotor and a stator carrying a plurality of permanent magnets. The permanent magnet generator may be directly driven by the wind turbine rotor 18. The generator stator may be connected to a machine-side converter, which may be configured to convert a received AC voltage to a DC voltage, which is then provided to the DC link. The line-side converter may be configured to convert a DC voltage from the DC link to a fixed-frequency AC voltage.

[0049] The line-side converter may be connected to the cluster busbar 106 via a main transformer. The main transformer may be configured to step up the voltage provided by the power converter, for example to 33 kV. The main transformer may be located in the nacelle 16 or tower 15 of the wind turbine in some examples. In other examples, the main transformer may be located in other suitable locations.

[0050] In the example of Figure 3, the main transformer may be configured to receive power from a utility grid 102. The utility grid 102 may be configured to provide power to the wind farm busbar 101 and the cluster busbar 106 during normal operation.

[0051] In the event of a loss of electrical connection with the utility grid 102, the wind farm 105, e.g., a portion of the wind farm, may enter a so-called island mode and begin operation. Throughout this 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, e.g., when the wind turbines are unable to obtain power from the utility grid. Wind turbines operating in island mode may form a local grid. For example, the wind turbines may be electrically connected, e.g., because at least one of the wind turbines is energized, e.g., a portion of the wind farm grid. In some examples, one or more wind turbines 10 may not be able to receive power from the utility grid 102 due to a missing physical connection between the wind turbines 10 and the utility grid 102, e.g., because a bus bar or some cables are damaged or broken, or for other reasons, e.g., an electrical fault.

[0052] In island mode, power to keep the auxiliary systems running, including, for example, one or more of the communications system, temperature and ventilation control system, bearing lubrication system, controller system, and navigation lights, can be obtained from an auxiliary power source other than the wind turbine or turbines whose rotors spin to generate it. The term auxiliary power source may also be referred to as an auxiliary energy storage device or auxiliary energy storage system.

[0053] The wind farm controller 109 may be communicatively coupled to the wind turbine controller 36 of the wind turbine 10 to control operation in island mode. Loss of communication with the wind farm controller 109 may cause problems such as undesirable power injection into the wind farm grid 108. Figure 3 illustrates a schematic of loss of communication between the wind farm controller 109 and the controller 36 of the second wind turbine 112.

[0054] In one aspect of the disclosure, a method 100 for operating a wind farm including a wind farm grid 108 and a plurality of wind turbines 111, 112 connected to the wind farm grid 108 is provided. The method 100 is illustrated generally in the flow chart of FIG. 4. The method includes, at block 110, operating one or more first wind turbines 111 of the plurality of wind turbines to generate electrical power having a predetermined electrical characteristic when the wind farm 105 is decoupled from the utility grid 102, and exporting the electrical power having the predetermined electrical characteristic to the wind farm grid 108. The method further includes, at block 120, determining that the wind farm 105 is decoupled from the utility grid 102 by one or more second wind turbines 112 of the plurality of wind turbines detecting the electrical power exported to the wind farm grid 108 and identifying the predetermined electrical characteristic.

[0055] Thus, detecting power with the predetermined electrical characteristics may mean that the second wind turbine 112 is electrically connected to the wind farm grid 108 and that there is a local grid at its output. On the other hand, detecting power without the 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 power from the utility grid 102. Thus, the second wind turbine 112 can distinguish which power grid is present at its terminal in a simple, effective and reliable manner. The power may be transmitted through one or more cables or bus bars 106 connecting the first wind turbine 111 and the second wind turbine 112.

[0056] The first wind turbine 111 may be a grid-forming wind turbine configured to energize the wind farm grid 108, e.g., a portion of the wind farm grid 108. For example, the grid-forming wind turbine may be configured to detect that a local grid is formed, e.g., a portion of the wind farm grid is energized. In some examples, the wind farm controller 109 may instruct the grid-forming wind turbines to this. In other examples, one or more of the grid-forming wind turbines may be configured to detect this without the wind farm controller. The second wind turbine 112 may be a non-grid-forming wind turbine. The second wind turbine may be configured to follow the instructions of the wind farm controller and the first wind turbine 111.

[0057] In some examples, if a first wind turbine is damaged or otherwise unable to assume the role of leader as a grid-forming wind turbine, a second wind turbine that was initially assigned the role of follower as a non-grid-forming wind turbine can assume the leader role instead, thus providing redundancy so that one or more second wind turbines can assume the grid-forming role if deemed necessary.

[0058] The one or more second wind turbines 112 may perform the detection and the 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, power having the predetermined electrical characteristics can be generated and supplied to the wind farm grid. This is because 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. Thus, when the wind farm is disconnected from the utility grid 102, power having the predetermined electrical characteristics can be continuously generated and supplied to the wind farm grid.

[0059] In some examples, the wind farm controller 109 may initially indicate whether the second wind turbine 112 is connected to the utility grid 102. However, if for some reason communication between the wind farm controller 109 and the second wind turbine 112 is lost, the first wind turbine 111 may (indirectly) take over the tasks of the wind farm controller such that the second wind turbine does not inject power into the wind farm grid.

[0060] It may occur that one or more of the second wind turbines maintain communication with the wind farm controller. For example, if the wind turbines are arranged in a cluster 104, e.g., in a string, it may occur that some second wind turbines in the cluster can communicate with the wind farm controller and other second wind turbines in the cluster cannot. The second wind turbines that cannot communicate with the wind farm controller may rely on power having predetermined electrical characteristics, and the second wind turbines that can communicate with the wind farm controller may receive redundant information.

[0061] The characteristics of the power can be such that the second wind turbine 112 can detect the power and not confuse it with other signals. In some examples, the second wind turbine 112 can identify that the local grid is present at the terminal after detecting power for a period of time, such as a duration that exceeds a certain threshold. In these or other examples, the second wind turbine can identify that the local grid is present at the terminal after a number of predetermined characteristics are detected, such as the predetermined characteristic being detected two, three, or more times. In other examples, one detection may be sufficient.

[0062] The predetermined electrical characteristic may include ripple. For example, the power may have a high amplitude and / or a high frequency so that the power can be distinguished from other power that the second wind turbine may receive from the utility grid. For example, the power signal may have a frequency that is different from the frequency of the utility grid 102. The predetermined electrical characteristic may, in some examples, include non-fundamental harmonics that are not present in the utility grid. In this regard, the power signal transmitted by the first wind turbine may be modulated in a particular manner so that it can be recognized by the second wind turbine.

[0063] That is, the power signal may be a voltage signal. Since the frequency and voltage of the islands should be controlled, it would be easy to transmit a voltage signal. As indicated above, the amplitude and / or frequency of the power, e.g., voltage signal, may be changed, e.g., modulated. The predetermined electrical characteristic may, in some examples, include a predetermined voltage level or a predetermined time-varying voltage level.

[0064] The predefined electrical characteristic may be a particular electrical characteristic, e.g., an electrical signature, that is known in advance by the first wind turbine 111 and the second wind turbine 112. For example, the first and second wind turbines may be configured to transmit and receive / identify power having such predefined characteristics before the first and second wind turbines, respectively, start operation for the first time, e.g., during commissioning, or may be configured earlier, e.g., in a factory.

[0065] As mentioned above, the one or more first wind turbines and the one or more second wind turbines can be arranged in one or more clusters 104, e.g., one or more strings. The wind turbines of each cluster, e.g., each string, may be connected via one or more cables 106. Such cables may be referred to as cluster busbars, array cables or offshore sea cables in some examples. The first wind turbine 111 of each cluster 104 may generate and provide power that is detected by the one or more second wind turbines 112 of that cluster 104 in some examples.

[0066] For example, each cluster 104 may be configured with one first wind turbine 111 configured to generate and supply power to the wind farm grid so that other wind turbines 112 of the corresponding cluster can detect it, such as in case of loss of communication with the wind farm controller 109. In other examples, not all clusters require a first wind turbine.

[0067] The method may further include refraining from generating power if the one or more second wind turbines identify the predetermined electrical characteristic, i.e., the one or more second wind turbines may not generate power in such a scenario, and the second wind turbines will not erroneously start up in generating mode because they correctly recognize that the utility grid 102 has not yet been restored.

[0068] In another aspect of the disclosure, a first wind turbine 111 and a second wind turbine 112 are disclosed that are configured to suitably perform one or more of the steps of the methods 100, 200 disclosed herein and generally configured to operate as described herein. 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 to supply electrical power having predetermined electrical characteristics to the wind farm grid 108 such that the predetermined electrical characteristics are identifiable by the second wind turbine as being different from electrical power supplied from the utility grid 102 to the wind farm grid 108.

[0069] The first wind turbine 111 may be further configured to generate electrical power having a second electrical characteristic when the first wind turbine 111 is connected to a utility grid. For example, the first wind turbine may not introduce ripple into the electrical power signal that it generates during normal operation of the wind turbine.

[0070] Similarly, the second wind turbine 112 is configured to detect power delivered by the first wind turbine 111 to the wind farm grid 108 having predetermined electrical characteristics and 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 comprise a control system 36 configured to perform steps of the methods described herein. The electrical power having the predetermined electrical characteristics is different from the electrical power delivered from the utility grid to the wind farm grid.

[0071] In this way, the second wind turbine 112 can distinguish whether energy is being supplied by the utility grid 102 or the first wind turbine 111, for example, if communication with the wind farm controller 109 is lost.

[0072] In some examples, the first wind turbine 111 and the second wind turbine 112 are onshore wind turbines, and in other examples, they are offshore wind turbines.

[0073] In a further aspect of the disclosure, a wind farm 105 is provided. The wind farm 105 comprises a wind farm grid 108. The wind farm further comprises one or more first wind turbines 111 configured to generate electrical power having a predetermined electrical characteristic when the wind farm is disconnected from the utility grid 102 and to supply the electrical power having the predetermined electrical characteristic to the wind farm grid 108. The wind farm further comprises one or more second wind turbines 112 configured to determine that the wind farm is disconnected from the utility grid 102 by detecting the electrical power supplied to the wind farm grid 108 and identifying the predetermined electrical characteristic.

[0074] The one or more first wind turbines 111 may be configured to continuously generate electrical power having predetermined electrical characteristics while the wind farm 105 detects that it is disconnected from the utility grid 102. The electrical power having the predetermined electrical characteristics may be generated until a connection with the utility grid 102 is restored.

[0075] The one or more second wind turbines 112 may be configured to not generate power upon detecting the presence of a local grid at that terminal.

[0076] The first wind turbines 111 may be grid forming wind turbines and the second wind turbines 112 may be non-grid forming wind turbines.

[0077] In some examples, the wind farm 105 is an onshore wind farm, and in other examples, an offshore wind farm.

[0078] The wind farm 105 may include one or more clusters 104, each of which may include a first wind turbine 111 configured to send power to one or more second wind turbines 112. The one or more clusters 104 may be arranged along a string.

[0079] The wind farm 105 may further include a wind farm controller 109 configured to communicate with the first wind turbine 111 and / or the second wind turbine 112 .

[0080] The above discussion regarding the method 100 may be combined and applied to this embodiment, and vice versa.

[0081] In a further aspect of the disclosure, a method 200 is provided for determining whether a wind turbine 112 has a grid formed locally at its end, optionally upon loss of communication with the wind farm controller 109. Method 200 is illustrated in the flow chart of Figure 5. Aspects and descriptions relating to method 100 may be combined and applied to method 200 and vice versa. The method includes detecting, by a wind turbine, an electrical signal transmitted from another wind turbine.

[0082] The method comprises, at block 210, detecting, by the wind turbine 112, an electrical signal transmitted by another wind turbine 111. The method includes, at block 220, determining that a locally formed grid is present at a terminal of the wind turbine based on the detected electrical signal.

[0083] For example, a wind farm grid 108, which is electrically isolated from the utility grid 102, may include one or more first wind turbines 111 and one or more second wind turbines 112. The first wind turbine 111 may transmit an electrical signal and the one or more second wind turbines 112 may detect the electrical signal to identify the presence of a local grid at their terminal.

[0084] The electrical signal may be detected through 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, for example the same string of wind turbines.

[0085] The electrical signal may be a signal having a different amplitude and / or frequency than other electrical signals provided by the 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.

[0086] A wind turbine can refrain from operating (producing electricity) if a locally formed grid is identified at its terminal.

[0087] Wind turbines can also generate only reactive power when a locally configured grid is identified.

[0088] The wind turbine may, for example, not receive a control signal from the wind farm controller 109 during at least a duration of the method.

[0089] Examples are used herein to disclose the teachings, including preferred embodiments, and to enable anyone of ordinary skill in the art to practice the teachings, including making and using any device or system, and performing any methods incorporated therein. The patentable scope is defined by the claims, and may include other examples that occur to those of ordinary skill in the art. Such other examples are intended to be included in the claims if they have structural elements that do not differ from the language of the claims, or if they include equivalent structural elements that do not differ substantially from the language of the claims. Aspects from the various embodiments described, and other known equivalents to each such aspect, may be mixed and matched by those of ordinary skill in the art to construct additional embodiments and techniques according to the principles of the present application. When reference signs related to the drawings are placed in parentheses in the claims, they are merely intended to improve the clarity of the claims, and should not be construed as limiting the scope of the claims. [Explanation of symbols]

[0090] 10:wind turbine 12:ground 14:support system 15:tower 16:nacelle 18:rotor 20:hub 22:rotor blade 24:blade root area 26:load transfer area 28:wind direction 30:rotor shaft 32:pitch system 34:pitch axis 36:wind turbine controller 8:yaw axis 42:generator 44:main shaft 46:gearbox 48:high speed shaft 50:coupling 51:shaft sensor 52:main frame 53:generator sensor 54:decoupling support means 56:yaw drive mechanism 58:meteorological measurement system 60:main forward support bearing 62:main aft support bearing 64:drive train 66:pitch assembly 68:pitch drive system 70:sensor 72:pitch bearing 74:pitch drive motor 76:pitch drive gearbox 78:pitch drive pinion 80:pitch control system 84: Power source / generator 86: Cavity 88: Internal surface 90: Transformer 101: Wind farm busbar 102: Utility grid 103: Torque arm / interconnect point 104: String 105: Wind farm 106: Cluster busbar 107: Substation 108: Wind farm grid 109: Wind farm controller 111: First wind turbine 112: Second wind turbine

Claims

1. A method (100) for operating a wind farm (105) comprising a wind farm grid (108) and a number of wind turbines (10) connected to the wind farm grid (108), comprising: operating (110) one or more first wind turbines (111) of the plurality of wind turbines to generate electrical power having predetermined electrical characteristics and supplying (110) the electrical power having predetermined electrical characteristics to the wind farm grid (108) when the wind farm (105) is disconnected from a utility grid (102); determining, by one or more second wind turbines (112) of the plurality of wind turbines detecting (120) power supplied to the wind farm grid (108) and identifying the predetermined electrical characteristic, that the wind farm (105) is disconnected from the utility grid (102); A method comprising:

2. 2. The method of claim 1, wherein the plurality of first wind turbines (111) are a plurality of grid-forming wind turbines configured to energize a wind farm grid (108) and the plurality of second wind turbines (112) are a plurality of non-grid-forming wind turbines.

3. The method of claim 1, wherein the detecting and determining (120) is performed after one or more second wind turbines (112) lose communication with a wind farm controller (109).

4. The method of claim 1 , wherein the predetermined electrical characteristic comprises ripple.

5. The method of claim 1 , wherein the predetermined electrical characteristic comprises a frequency that is different from a frequency of the utility grid (102).

6. The method of claim 5 , wherein the predetermined electrical characteristic comprises non-fundamental harmonics not present in the utility grid (102 ).

7. The method of claim 1 , wherein the predetermined electrical characteristic comprises a predetermined voltage level.

8. The method of claim 1 , wherein the predetermined electrical characteristic comprises a predetermined time-varying voltage level.

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

10. A first wind turbine (111), 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); The first wind turbine (111) is further configured to supply electrical power having the predetermined electrical characteristics to a wind farm grid (108), the predetermined electrical characteristics being identifiable as different from electrical power supplied by a second wind turbine (112) from the utility grid (102) to the wind farm grid (108).

11. 11. The first wind turbine of claim 10, wherein the first wind turbine (111) is further configured to generate electrical power having a second electrical characteristic when the first wind turbine (111) is connected to the utility grid (102).

12. A wind power plant (105), Wind farm grids and One or more first wind turbines (111) according to claim 10 or 11, one or more second wind turbines (112) configured to determine that the wind farm (105) is disconnected from the utility grid (102) by detecting power supplied to the wind farm grid (108) and identifying the predetermined electrical characteristic; a wind power plant (105) including

13. 13. The wind farm of claim 12, comprising one or more clusters (104), each of the clusters (104) comprising a first wind turbine (111) configured to send power to one or more second wind turbines.

14. The wind farm of claim 13, wherein one or more clusters (104) are arranged along the string.

15. The wind farm of claim 12, further comprising a wind farm controller (109) configured to communicate with the first wind turbine (111) and / or the second wind turbine (112).

Images