Wind turbine and method

Abstract

This disclosure relates to a wind turbine (10) and a method (100) for operating the wind turbine (10). A wind turbine (10) includes a power converter (104), a main transformer (105), an auxiliary transformer (107), one or more auxiliary systems (108), and a plurality of power cables (109). The power cables (109) are connected to the output side of the main transformer (105). The power converter (104) is configured to operate in an islanded mode in a pulse mode for switching the line-side converter of the power converter (104), which is different from the pulse mode used during normal operation of the wind turbine (10), and the pulse mode used during islanded mode is configured to avoid electrical resonance in the wind turbine (10).

Description

Technical Field

[0001] This disclosure relates to wind turbines, and more particularly to wind turbines configured to operate in island mode, and methods for operating wind turbines. Background Technology

[0002] Modern wind turbines are commonly used to supply electricity to the power grid. This type of wind turbine typically consists of a tower and a rotor mounted on the tower. The rotor, usually comprising a hub and multiple blades, begins to rotate under the influence of wind forces on the blades. This rotation generates torque, which is typically transmitted to a generator either directly through the rotor shaft (“direct drive” or “gearless”) or via a gearbox. The generator then produces electricity that can be supplied to the power grid.

[0003] The wind turbine hub can be rotatably coupled to the front of the nacelle. The wind turbine hub can be connected to the rotor shaft, and the rotor shaft can then be rotatably mounted in the nacelle using one or more rotor bearings arranged in a frame inside the nacelle. The nacelle is a shell located on top of the wind turbine tower that houses and protects the gearbox (if present) and generator (if not located outside the nacelle), and, depending on the wind turbine, may also house and protect additional components such as power converters and auxiliary systems.

[0004] When a wind turbine is disconnected from the power grid (public grid), some associated auxiliary systems (such as communication systems, ventilation and temperature control systems, pitch and yaw control systems, etc.) can remain operational until the power supplied by auxiliary power sources (such as battery-based systems, supercapacitors (such as uninterruptible power supplies (UPS)), or diesel generators) is also exhausted. Solar panels can also be used to provide auxiliary power.

[0005] Another way to obtain auxiliary power may involve operating wind turbines to generate a small amount of electricity and supplying that electricity to one or more auxiliary systems. This self-sufficient mode can be called "islanding mode." In islanding mode, the wind turbines are disconnected from the grid and can be operated to supply power to auxiliary systems. These auxiliary systems can be systems belonging to the power-generating wind turbine, or even systems belonging to other wind turbines or located elsewhere in the wind farm.

[0006] If the available auxiliary power is actually sufficient to restart normal operation, the wind turbine can remain in this islanded mode until it regains grid connection.

[0007] Wind turbines in a wind farm can be electrically connected together to form a current collector, or wind farm grid. Each wind turbine in the wind farm grid can include its own transformer, often referred to as the "main transformer." The main transformer steps up the voltage output from the wind turbine generator (e.g., from several hundred volts) to a higher level suitable for supplying to the wind farm grid.

[0008] Each wind turbine may also include a switching device. Typically, multiple tower cables connect the main transformer and the switching device. The tower cables may be connected to surge arresters, which protect the electrical equipment inside the wind turbine by discharging surge currents, such as those caused by lightning. The switching device may include circuit breakers, which protect the electrical equipment inside the wind turbine in the event of a fault. The switching device may also allow the wind turbine to be disconnected from the wind farm grid for maintenance purposes or, for example, during islanding mode.

[0009] However, occasional power surges have been observed in power cables. High-voltage (HV) equipment, i.e., equipment on or near the high-voltage side of the wind turbine (such as equipment on or outside the secondary side of the main transformer), may therefore be damaged. For example, one or more power cables, the HV windings of the main transformer, or surge arresters may be damaged during islanding mode. Since the electrical equipment of the wind turbine (such as its auxiliary systems) is connected to the main transformer, this equipment may also be damaged or at risk of damage during islanding mode.

[0010] This disclosure aims to avoid damage to the electrical equipment (especially HV equipment) of wind turbines during islanded operation, or to reduce the risk thereof. Summary of the Invention

[0011] In one aspect of this disclosure, a wind turbine is provided. The wind turbine includes a generator configured to generate AC power and a power converter connected to the generator. The power converter includes a machine-side converter configured to convert AC power to DC power, a DC link, and a line-side converter configured to convert DC power to AC power. The line-side converter includes a plurality of switches for converting DC power to AC power. The wind turbine also includes a main transformer and an auxiliary transformer connected to the power converter, one or more auxiliary systems connected to the auxiliary transformer, and a plurality of power cables connecting the output side of the main transformer to the power grid. The power converter is configured to operate in a first pulse mode for switching during normal operation of the wind turbine, and the power converter is also configured to operate in a second pulse mode, different from the first pulse mode, for switching during islanded operation of the wind turbine. The second pulse mode is configured to avoid electrical resonance in the wind turbine and optionally avoid electrical resonance in the plurality of power cables.

[0012] Surprisingly, the damage occurring in the wind turbines (the power cables and / or auxiliary components of the wind turbines) was primarily caused by resonances in multiple power cables. These resonances in the power cables were caused by harmonics in the pulsed modes employed during islanding. Surprisingly, the main transformer did not suppress or prevent these resonances. In some cases, additional or alternative damage may occur due to resonances, for example, in the medium-voltage (MV) power cables connecting the power converter, main transformer, and auxiliary transformer, or in the low-voltage (LV) power cables connecting the auxiliary transformer and one or more auxiliary systems.

[0013] Accordingly, wind turbines are now configured to operate in at least two different pulse modes for switching the line-side converters of the power converter: one for normal operation and one for islanded operation. Using a specific pulse mode for islanded operation allows for the avoidance or reduction of electrical resonance in power cables connected to the output side of the main transformer, and thus avoidance or reduction of damage to the high-voltage equipment of the wind turbine during islanded operation, such as damage to the HV windings of the main transformer, surge arresters, and power cables. Damage to auxiliary systems can also be avoided or reduced during islanded operation.

[0014] Throughout this disclosure, auxiliary systems are systems that support operating wind turbines, and in particular can refer to wind turbine systems or apparatuses that should still be powered, or preferably should be powered, even if the power grid is unavailable. For example, when the power grid is unavailable, it may be necessary to maintain the operation of communication systems as well as the temperature regulation and ventilation systems of the wind turbines.

[0015] Throughout this disclosure, it will be understood that a wind turbine is in operation (“normal operation”) when its rotor is driven by available wind power and rotates at a sufficiently high speed to generate electricity, a power grid is available, and the wind turbine’s generator is producing electricity that is fed into the grid. The term “normal operation” is used herein to explicitly refer to this situation and to clearly distinguish it from the operation of a wind turbine in, for example, islanded mode.

[0016] Throughout this disclosure, the term "islanded operation mode" can refer to an operating mode of a wind turbine in which the wind turbine does not receive or obtain power from the power grid, and the wind turbine is configured to operate independently of the power grid. In this mode, power can be obtained from the rotation of the wind turbine rotor and supplied to the auxiliary components of the wind turbine, particularly operational critical electrical systems, such as one or more of communication systems, temperature and ventilation control systems, bearing lubrication systems, control systems, and navigation lights.

[0017] When this disclosure refers to the fact that a wind turbine is disconnected from the power grid, it can be understood as the wind turbine neither supplying power to nor receiving power from the grid. It can refer to a situation where the wind turbine is disconnected from the power grid due to a circuit breaker being opened or other reasons. It can refer to a situation where the wind turbine is not yet operational, such as during the construction or commissioning of a wind farm. It can also refer to a situation where no power grid is available, such as during the installation and commissioning of a wind farm, or even where there may not be a power grid at all.

[0018] In another aspect of this disclosure, a method for operating a wind turbine as described herein is provided. The method includes determining that the power grid is unavailable, initiating islanded operation of the wind turbine, and switching a switch in a second pulse mode during islanded operation of the wind turbine, such that electrical resonances in the wind turbine, such as electrical resonances in multiple power cables of the tower, are avoided. For example, if electrical resonances are present, they are eliminated or at least reduced.

[0019] In another aspect of this disclosure, an offshore wind turbine is provided. The wind turbine includes a generator configured to generate an AC power signal and a power converter connected to the generator. The power converter includes a machine-side converter configured to convert the AC power signal to a DC power signal, a DC link, and a line-side converter configured to convert the DC power signal to an AC power signal. The line-side converter includes circuitry comprising a plurality of switches for converting the DC power signal to an AC power signal. The wind turbine also includes an auxiliary transformer connected to the power converter, one or more auxiliary systems connected to the auxiliary transformer, an input side of a main transformer connected to the power converter, and a plurality of tower cables configured to carry an AC power signal connected to the output side of the main transformer. The power converter is configured to operate in a first predefined pulse mode for switching during normal operation of the wind turbine, and is configured to operate in a second predefined pulse mode different from the first pulse mode for switching during islanded operation of the wind turbine, to avoid (e.g., eliminate, reduce, or prevent) resonance in the tower cables in islanded mode. Attached Figure Description

[0020] Figure 1 A perspective view of an example wind turbine is shown; Figure 2 It shows Figure 1 A simplified interior view of an example wind turbine nacelle; Figure 3 A wind turbine connected to the power grid and one or more auxiliary power sources is schematically shown; Figure 4 An example of harmonics in an AC signal generated by a power converter of a wind turbine is illustrated schematically. Figure 5An example of the impedance of a power cable is illustrated schematically; and Figure 6 A flowchart illustrating an example of a method for operating a wind turbine is shown. Detailed Implementation

[0021] 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 for explanation only and not for limitation. In fact, it will be apparent to those skilled in the art that various modifications and variations may be made to the present disclosure. For example, features shown or described as part of one embodiment may be used with another embodiment to generate yet another embodiment. Therefore, the present disclosure is intended to cover such modifications and variations that fall within the scope of the appended claims and their equivalents.

[0022] Figure 1 This is a perspective view of an example 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 the ground 12, a nacelle 16 mounted on 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 and extending outward from the hub 20. In this example, the rotor 18 has three rotor blades 22. In an alternative embodiment, the rotor 18 includes more or fewer than three rotor blades 22. The tower 15 may be made of tubular steel to define a cavity between the support system 14 and the nacelle 16. Figure 1 (Not shown in the image). In an alternative embodiment, tower 15 is any suitable type of tower with any suitable height. According to the alternative, the tower can be a hybrid tower, comprising sections made of concrete and tubular steel sections. Furthermore, the tower can be a partial or complete lattice tower.

[0023] Rotor blades 22 are spaced around hub 20 to facilitate the rotation of rotor 18, thereby enabling the conversion of kinetic energy from wind power into usable mechanical energy, and subsequently into electrical energy. Rotor blades 22 are adapted to hub 20 by coupling blade root regions 24 to hub 20 at multiple load transfer regions 26. Load transfer regions 26 may have hub load transfer regions and blade load transfer regions (neither of which are located in the hub 20 ... Figure 1 (As shown in the diagram). The load sensed by the rotor blades 22 is transmitted to the hub 20 via the load transfer area 26.

[0024] In the example, rotor blade 22 may have a length ranging from approximately 15 meters (m) to approximately 90 meters or longer. Rotor blade 22 may have any suitable length that allows the wind turbine 10 to function as described herein. For example, non-limiting examples of blade length include lengths of 20 meters or less, 37 meters, 48.7 meters, 50.2 meters, 52.2 meters, or greater than 91 meters. When wind impacts rotor blade 22 from wind direction 28, rotor 18 rotates about rotor axis 30. As rotor blade 22 rotates and is subjected to centrifugal force, rotor blade 22 is also subjected to various forces and torques. Therefore, rotor blade 22 may deflect and / or rotate from a neutral or non-deflected position to a deflected position.

[0025] Furthermore, the pitch angle of the rotor blade 22 (e.g., the angle that determines the orientation of the rotor blade 22 relative to the wind direction) can be changed by the 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. The pitch axis 34 of the rotor blade 22 is shown. During the operation of the wind turbine 10, the pitch system 32 can specifically change the pitch angle of the rotor blade 22 such that the angle of attack of (part of) the rotor blade is reduced, which is beneficial for reducing the rotational speed and / or for stopping the rotor 18.

[0026] In this example, the blade pitch of each rotor blade 22 is controlled individually by the wind turbine controller 36 or by the pitch control system 80. Alternatively, the blade pitch of all rotor blades 22 can be controlled simultaneously by the control system.

[0027] Furthermore, in this example, as the wind direction 28 changes, the yaw direction of the nacelle 16 can be rotated around the yaw axis 38 to position the rotor blades 22 relative to the wind direction 28.

[0028] In this example, the wind turbine controller 36 is shown as centralized within the nacelle 16; however, the wind turbine controller 36 may be a distributed control system distributed throughout the wind turbine 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 methods described herein. Furthermore, many 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 one or more 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 disc read-only memory (CD-ROM), magneto-optical disks (MOD), digital versatile discs (DVDs), and / or other suitable memory elements.

[0029] Figure 2 This 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 located within the nacelle 16 via a main shaft 44, a gearbox 46, a high-speed shaft 48, and a connector 50. In this example, the main shaft 44 is configured to be at least partially coaxial with the 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 latter is connected to the generator 42 for generating electrical energy with the aid of the connector 50. Furthermore, a transformer 90 and / or suitable electronics, switches, and / or inverters may be arranged in the nacelle 16 to convert electrical energy generated by the generator 42 with a voltage between, for example, 400 V and 1000 V, into electrical energy with a medium voltage (e.g., 10-35 kV). The offshore wind turbine may have a generator voltage between, for example, 650 V and 3500 V, and the transformer voltage may be between, for example, 30 kV and 70 kV. The electrical energy is conducted from the nacelle 16 to the tower 15 via power cables.

[0030] 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 loads acting on the main shaft 44 and / or the high-speed shaft 48, and the rotational speeds 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 the rotational speeds of the generator 42 and the generator torque. The shaft sensors 51 and / or generator sensors 53 may include, for example, one or more torque sensors (e.g., strain gauges or pressure sensors), optical sensors, accelerometers, magnetic sensors, velocity sensors, and micro inertial measurement units (MIMUs).

[0031] The gearbox 46, generator 42, and transformer 90 may be supported by the main support structure frame of the nacelle 16, optionally embodied in the main frame 52. The gearbox 46 may include a gearbox housing connected to the main frame 52 via one or more torque arms 103. In this example, the nacelle 16 also includes a main front support bearing 60 and a main rear support bearing 62. Furthermore, the generator 42 may be mounted to the main frame 52 via a decoupling support member 54, particularly to prevent vibrations of the generator 42 from being introduced into the main frame 52 and thus becoming a source of noise emission.

[0032] Optionally, the main frame 52 is configured to bear the weight of the components of the rotor 18 and nacelle 16, as well as all loads caused by wind and rotational loads, and further, 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 any associated fastening, support, and / or fixing devices (including, but not limited to, support members 52, and front support bearings 60 and rear support bearings 62) are sometimes referred to as the drivetrain 64.

[0033] In some examples, the wind turbine may be a direct-drive wind turbine without gearbox 46. The generator 42 operates at the same rotational speed as the rotor 18 in a direct-drive wind turbine. Therefore, they typically have a much larger diameter than the generators used in wind turbines with gearbox 46 in order to provide similar electrical power as wind turbines with gearboxes.

[0034] The nacelle 16 may also include a yaw drive mechanism 56, which can be used to rotate the nacelle 16 and thus also rotate the rotor 18 about the yaw axis 38 to control the projection of the rotor blades 22 relative to the wind direction 28.

[0035] To properly position the nacelle 16 relative to wind direction 28, the nacelle 16 may also include at least one meteorological measurement system, which may include a wind vane and an anemometer. The meteorological measurement system 58 may provide information to the wind turbine controller 36, which may include wind direction 28 and / or wind speed.

[0036] In this example, the pitch system 32 is at least partially arranged as a pitch assembly 66 in the hub 20. The 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 (e.g., Figure 1 As shown in the figure, it is used to adjust the pitch angle of the rotor blades 22 along the pitch axis 34. Figure 2 Only one of the three pitch drive systems 68 is shown in the image.

[0037] In this example, the pitch assembly 66 includes at least one pitch bearing 72, which is coupled to the hub 20 and the corresponding rotor blades 22 (e.g., Figure 1As shown in the diagram, the pitch drive system 68 is used to rotate the corresponding rotor blades 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 such 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 such that the pitch drive pinion 78 is rotated by the pitch drive gearbox 76. A pitch bearing 72 is coupled to the pitch drive pinion 78 such that rotation of the pitch drive pinion 78 causes rotation of the pitch bearing 72.

[0038] The pitch drive system 68 is coupled to the wind turbine controller 36 for adjusting the pitch angle of the rotor blades 22 upon receiving 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 electric and / or hydraulic system that enables the pitch assembly 66 to function as described herein. Alternatively, the pitch assembly 66 may include any suitable construction, configuration, arrangement, and / or components, such as, but not limited to, hydraulic cylinders, springs, and / or servo mechanisms. In some embodiments, the pitch drive motor 74 is driven by energy extracted from the rotational inertia of the hub 20 and / or from a stored energy source (not shown) that supplies energy to the components of the wind turbine 10.

[0039] The pitch assembly 66 may also include one or more pitch control systems 80 for controlling the pitch drive system 68 based on control signals from the wind turbine controller 36 under specific priority conditions and / or during rotor 18 overspeed. In this example, the pitch assembly 66 includes at least one pitch control system 80 communicatively coupled to a corresponding pitch drive system 68 for controlling the pitch drive system 68 independently of the wind turbine controller 36. In this example, the pitch control system 80 is coupled to the pitch drive system 68 and the sensor 70. During normal operation of the wind turbine 10, the wind turbine controller 36 can control the pitch drive system 68 to adjust the pitch angle of the rotor blades 22.

[0040] According to one embodiment, a generator 84, including, for example, a battery and a capacitor, is arranged at or inside the hub 20 and coupled to a sensor 70, a pitch control system 80, and a pitch drive system 68 to provide power to these components. In this example, the generator 84 provides continuous power to the pitch assembly 66 during operation of the wind turbine 10. In an alternative embodiment, the generator 84 provides power to the pitch assembly 66 only during power loss events of the wind turbine 10. Power loss events may include grid loss or decline, failure of the electrical system of the wind turbine 10, and / or failure of the wind turbine controller 36. During power loss events, in some examples, the generator 84 operates to provide power to the pitch assembly 66, enabling the pitch assembly 66 to operate during the power loss events.

[0041] In this example, the pitch drive system 68, sensor 70, pitch control system 80, cables, and power supply 84 are all located within a cavity 86 defined by the inner surface 88 of the hub 20. In an alternative embodiment, the components are positioned relative to the outer surface of the hub 20 and may be directly or indirectly coupled to the outer surface.

[0042] As used herein, the term “processor” is not limited to an integrated circuit referred to in the art as a computer, but broadly refers to controllers, microcontrollers, microcomputers, programmable logic controllers (PLCs), application-specific integrated circuits (ASICs), and other programmable circuits, and these terms are used interchangeably herein.

[0043] According to one aspect of this disclosure, a wind turbine is provided. Figure 3 An example of a wind turbine 10 in a wind farm, such as an offshore wind turbine, is illustrated schematically. The method 100 mentioned below can be implemented, for example, in the wind turbine of this example.

[0044] The wind turbine 10 includes a generator 42 configured to generate AC (alternating current) power and a power converter 104 connected to the generator 42. The power converter 104 includes a machine-side converter configured to convert AC power from the generator 42 to DC (direct current) power, a DC link, and a line-side converter configured to convert DC power to AC power. The line-side converter includes multiple switches for converting DC power to AC power.

[0045] The wind turbine also includes a main transformer 105 and an auxiliary transformer 107 connected to the power converter 104. The wind turbine also includes one or more auxiliary systems or components 108 connected to the auxiliary transformer, and multiple power cables 109 connecting the output side of the main transformer 105 to the power grid. If the main transformer 105 is located in the nacelle 16, the power cables 109 may be tower cables extending downwards from the nacelle to the wind turbine tower.

[0046] The power grid to which the cable is connected can be, in particular, the internal power grid of the wind farm, such as wind farm bus 101. In other examples, the power grid can be a public power grid.

[0047] The power converter 104 is configured to operate in a first pulse mode during normal operation of the wind turbine for switching purposes. The power converter 104 is also configured to operate in a second pulse mode, different from the first pulse mode, during islanded operation of the wind turbine for switching purposes.

[0048] The second pulse mode can be configured to avoid electrical resonance in the wind turbine, and in particular, resonance in the power cables leading to the grid. In this respect, the second pulse mode may generate more electrical losses than other optimized pulse modes, but it can, for example, avoid resonance in the power cables, thereby reducing wear and preventing damage to various components, particularly the HV components of the wind turbine.

[0049] Typically, the wind turbine 10 is connected to the wind farm bus 101 and then to the public power grid 102 via a first wind farm switch 103. All wind turbines in the wind farm (not shown) are connected to the wind farm bus 101. The connection between the power grid 102 and the wind farm bus 101 is regulated by the first wind farm switch 103.

[0050] Due to varying wind conditions, the wind turbine's generator 42 produces AC power at a variable frequency. At least one power converter 104 is provided to adjust the power output from the generator 42 to suit the power grid 102, for example, to AC power with a fixed frequency. The power converter 104 may also include a DC link connecting the machine-side and line-side converters. In some examples, one or more additional auxiliary power converters may be provided. In place of the primary power converter, or in addition to the primary power converter, the auxiliary power converter(s) may be responsible for regulating the generator torque during islanding mode.

[0051] In some examples, the wind turbine's generator 42 can be a permanent magnet generator, comprising a generator rotor and a stator carrying multiple permanent magnets. The permanent magnet generator can be directly driven by the wind turbine rotor 18. The generator's stator can be connected to a machine-side converter configured to convert received AC voltage into DC voltage, which is then supplied to a DC link. A line-side converter can be configured to convert DC voltage from the DC link into AC voltage at a fixed frequency.

[0052] Both machine-side and line-side converters can each include circuitry containing multiple switches. In some examples, the switches can be IGCTs (Integrated Gate Commutated Thyristors) or other suitable types of switches. Passing voltage through the circuit and triggering the switches can convert AC voltage to DC voltage or vice versa. The switches can have on and off states. If the switch is on, current can flow through it. If the switch is off, current is blocked from flowing through it.

[0053] Triggering a switch can be done in different ways. For example, a pulse-width modulated (PWM) signal can be used to trigger the switch in a specific way. Alternatively, a frequency-modulated (PFM) signal can be used to trigger the switch in a specific way. It is also possible to use a signal that combines the characteristics of pulse-width modulation (PWM) and pulse-frequency modulation (PFM) to trigger the switch. The rhythm or pattern of the pulses generated by the switch (i.e., when they are triggered and how long they remain in the corresponding state) will affect the resulting AC signal.

[0054] The line-side converter can be connected to the wind farm bus 101 via the main transformer 105. The main transformer 105 can be configured to step up the voltage delivered by the power converter 104, for example, to 66 kV. In some examples, the main transformer 105 can be installed inside the nacelle 16 or tower 15 of the wind turbine. Since the main transformer 105 is a step-up transformer, the side or winding of the transformer connected to the power converter 104 can be referred to as the input side, primary side, or low-voltage side, while the side or winding of the transformer connected to the power cable 109 can be referred to as the output side, secondary side, or high-voltage side. An auxiliary transformer 107 can be arranged between the input or low-voltage side of the power converter 104 and the main transformer 105.

[0055] The auxiliary transformer 107 can be configured to provide low-voltage power, such as approximately 200-400 V, to some electrical components of the wind turbine. The auxiliary transformer 107 can, for example, supply power to the auxiliary electrical system 108 of the wind turbine (e.g., a ventilation and temperature control system). The auxiliary transformer 107 can be housed within the nacelle 16 of the wind turbine and can be connected to the main transformer 105.

[0056] Wind farms may also include substations, which include, for example, wind farm transformers configured to convert power from wind farm or collector voltage into grid voltage.

[0057] If needed, one or more auxiliary power sources 84 can be provided in the wind turbine 10 to supply auxiliary power to the auxiliary electrical system 108 during islanding mode. For example, the auxiliary power source 84 can be used if, for example, the power obtained from the rotation of the rotor 18 is insufficient to keep the auxiliary electrical system 108 operational. The auxiliary power source 84 can, for example, be located within the nacelle 16. Figure 2 The diagram shows an auxiliary power supply 84 for the pitch system 32 of the blade 22. It should be understood that in other examples, this power supply may be placed in other locations, such as on the tower and in other locations.

[0058] The main transformer 105 can be configured to receive power from the grid 102 at a first voltage and power from one or more auxiliary power sources 84 at a second voltage, which is different from the first voltage, for example, lower than the first voltage. The grid 102 can be configured to supply power to the wind farm bus 101 and thus to the electrical system of the wind turbine under normal operation, and the generator 42 and (one or more) auxiliary power sources 84 can be configured to supply power to the auxiliary electrical system 108, for example, in the event of grid losses.

[0059] If the wind turbine can no longer receive power from the grid 102, the auxiliary system 108 can begin to draw power from the generator 42 and / or one or more auxiliary power sources 84. Therefore, the critical electrical components 108 of the wind turbine 10 can be powered by the auxiliary transformer 107 of the wind turbine. The auxiliary wind turbine transformer 107 converts the power received from the main transformer 105 of the wind turbine into the voltage level required by the electrical components of the wind turbine, for example, between 60 and 80 kV. If the power supplied by the generator 42 exceeds the power required by the auxiliary system 108, the auxiliary power sources 84 can also be charged.

[0060] The AC voltage generated in the converter (which then travels to and through the main transformer 105) typically includes multiple harmonics. The main transformer 105 can suppress at least some of the harmonics in the generated AC voltage signal, particularly the lowest frequency harmonics. For example, the main transformer can be equipped with a rectifier for this purpose. An electrostatic shield may optionally or additionally be located between the primary and secondary windings to act as a filter, thereby preventing potentially hazardous harmonics from propagating to the power cable 109.

[0061] The wind turbine 10 may further include a switchgear 106. A tower cable 109 connects the main transformer 105 and the switchgear 106. The switchgear may include a circuit breaker for disconnecting the wind turbine from the wind farm grid and grid 102 during islanding mode.

[0062] However, it has been surprisingly discovered that one or more HV components of the wind turbine may be damaged after the circuit breaker of switchgear 106 is triggered to disconnect the wind turbine 10 from the wind farm grid and the wind turbine enters islanded mode. In some cases, other components connected to the main transformer (such as one or more auxiliary electrical systems 108) may also be damaged.

[0063] It has been found that the main transformer 105 does not filter all harmonics of the AC signal provided by the power converter 104, and some unfiltered harmonics may cause electrical resonance, for example, in the power cable 109 of the tower. Figure 4 An example of harmonics of an AC signal generated by power converter 104 is schematically shown. The AC signal may have been generated using a first pulse mode used in the normal operation of a wind turbine. The x-axis in the figure represents frequency, and the y-axis represents the amplitude of the harmonics.

[0064] exist Figure 4 The example has already indicated the frequency range 111 that may cause resonance in the power cable 109. The power cable 109 may have a resonant frequency that falls within this frequency range 111. Figure 5 An example of the impedance of power cable 109 is shown schematically. Figure 4 The frequency range 111 of the AC signal overlaps with the frequency range 112 of the power cable, which has its resonant frequency. Therefore, since the generated AC signal includes harmonics in the frequency range 111 of the power cable 109, resonance may occur in the power cable when the AC signal reaches the power cable.

[0065] If the second pulse mode is used, the AC signal generated in the power converter may no longer include harmonics in the problematic frequency range 111. Therefore, electrical resonances in the wind turbine, and particularly in the power cable 109, can be avoided. This allows for the avoidance of damage to components on the HV side of the auxiliary electrical system 108, and avoids other possible solutions that might be more expensive or complex to implement. It also allows the auxiliary electrical system 108 to remain connected to the main transformer 105 and the power cable 109 during islanding mode.

[0066] The first and second pulse modes can be predefined pulse modes. Since the theoretical resonant frequency of the power cable can be known in advance, it can be determined within which frequency range harmonics of the AC signal generated by the power converter should not exist. Therefore, the second pulse mode can be predefined, i.e., known in advance, for example, before the wind turbine is installed. The second pulse mode (and generally any suitable pulse modes) can, for example, be included in the memory of the controller of the power converter 104. Therefore, the power converter has access to the first and second pulse modes even before the wind turbine first begins normal operation. For example, the second pulse mode can be accessible and usable during the commissioning of the wind turbine.

[0067] The second pulse mode (and, for example, a third pulse mode, see below) can differ from the first pulse mode because it causes the switch to generate pulses in different ways, such as at different rhythms. For example, the second pulse mode may cause the switch to generate pulses at different times and / or during different time periods, and in particular at one or more frequencies different from the first pulse mode. In some examples, the pulse width modulated signal used to trigger the switch in the second (or, for example, the third) pulse mode may have a different pulse width than the pulse width of the first pulse mode, for example, it may have a different pulse width.

[0068] The wind turbine 10 may also include a sensor 113 for measuring data indicating electrical resonances of harmonics in the wind turbine, particularly harmonics in multiple power cables, such as harmonics within or near the resonant frequency range of the power cables. In some examples, the sensor 113 may be a voltage sensor. In other examples, other types of sensors may be used, such as power sensors, like power analyzers.

[0069] The sensor can be configured to directly provide the harmonics of the signal. For example, the sensor can be configured to perform a Fourier transform of the voltage signal. In other examples, the signal can be processed in different devices, such as in the wind turbine controller 36 or in the controller of the power converter 104.

[0070] In some examples, sensor 113 may be positioned within the wind turbine tower. In other examples, the sensor may be positioned within switchgear 106. Sensor 113 may be positioned anywhere capable of measuring data indicating the presence or risk of electrical resonance in the wind turbine, such as in multiple power cables. For example, the presence of electrical resonance in the power cable may be detected at different locations when the power cable is electrically connected to other electrical components, such as a main transformer, power converter, auxiliary transformer, and one or more auxiliary loads.

[0071] Sensor 113 can be positioned, for example, on the HV side, such as with the power cable 109 of the tower, or with a surge arrester, or with the HV winding of the main transformer 105, and can be configured to measure data indicating harmonics in the power cable 109. Depending on which harmonics are detected, the presence of resonance or a high risk of electrical resonance can be detected. Detection of certain harmonics (e.g., harmonics close to the resonant frequency of the power cable 109) can indicate the risk of resonance.

[0072] In other examples, sensor 113 may be positioned on the medium-voltage (MV) side of the wind turbine, such as at or between the power converter 104, the primary side of the main transformer 105, and the primary side of the auxiliary transformer 107. For example, in some of these examples, the sensor (optionally a voltage sensor) may be positioned together with the power converter 104.

[0073] In other examples, sensor 113 may be positioned on the low-voltage (LV) side of the wind turbine, such as at or between the primary side of auxiliary transformer 107 and one or more auxiliary systems 108. For example, in some of these examples, a power analyzer may be positioned on the LV side.

[0074] The wind turbine 10 can be configured to detect the presence or risk of resonance, for example, by detecting certain harmonics with a sensor, and in response to this detection, the power converter 104 can be configured to change the pulse mode. In some examples, the pulse mode can be changed from a first pulse mode to a second pulse mode. In some examples, the pulse mode can be changed from either the first or second pulse mode to a third pulse mode different from the first and second pulse modes. Therefore, the wind turbine can be further configured to operate in a third pulse mode during islanded operation for switching purposes.

[0075] By setting at least one sensor 113, it is possible to check, for example, whether the signal includes harmonics that may overlap with the frequency range 112 of the power cable 109, which has its resonant frequency. If resonance or a risk of resonance is detected, the pulse pattern of the line-side converter switch can be changed to avoid or reduce the risk of resonance.

[0076] If more than one sensor 113 is provided, a sensor can be provided on one of the HV, MV, or LV sides, and another sensor 113 can be provided on the same side or the other side. For example, a first voltage sensor and a second voltage sensor can be provided on the HV side. Or in other examples, a voltage sensor can be provided on the HV side, and a power sensor can be provided on the LV side. In some examples, one or more sensors can be provided on the HV side, one or more sensors can be provided on the MV side, and one or more sensors can be provided on the LV side.

[0077] Since the resonant frequency of the power cable can be known in advance, one or more additional pulse modes may not be necessary or required in some examples. In some of these examples, one or more sensors may be provided, or one or more sensors may be omitted. When starting operation in islanded mode, the first pulse mode can be changed to the second pulse mode. However, since the resonant frequency of the power cable 109 may change as the power cable 109 or associated electronic accessories age, or, for example, when maintenance is performed on the transformer or a new component (transformer or cable) is installed, sensor 113 can help detect whether a different pulse mode should be used instead of the current pulse mode used in some of these examples. Therefore, one or more additional pulse modes can be provided, for example, stored in the memory of the power converter 104. For example, if one or more sensors detect electrical resonance or a risk of electrical resonance on the HV, MV, or LV side, the second pulse mode can be changed to the third pulse mode.

[0078] In other examples, one or more sensors 113 may be configured, and the first pulse mode may be changed to a second pulse mode once resonance or its risk is detected based on at least one sensor 113. In these examples, the wind turbine 10 may begin operating in islanded mode, and the pulse mode may remain unchanged until the risk or resonance is determined. In these examples, it may also be possible to change to an additional pulse mode, such as a third pulse mode, based on subsequent measurements from one or more sensors 113.

[0079] Depending on the location where an electrical resonance or risk of electrical resonance is detected (e.g., measured), the current pulse pattern can be changed to a different pulse pattern. For example, if an electrical resonance is detected (e.g., measured) on the LV side, the current pulse pattern can be changed to a pulse pattern specifically configured to eliminate or reduce resonance on the LV side. Although the HV, MV, and LV sides are connected, each side can be considered as a “microgrid” of the wind turbine. The spectrum can be different in each of the HV, MV, and LV sides. Pulse patterns can be set that are configured to specifically change the spectrum in one or more of these sides or internal microgrids of the wind turbine.

[0080] In another aspect of this disclosure, a method 100 for operating a wind turbine as described herein is provided. A flowchart of this method is provided in... Figure 6As shown in the diagram. The method includes, in block 110, determining that the power grid 102 is unavailable. The method also includes, in block 120, initiating islanded operation of the wind turbine 10. The method further includes, in block 130, during islanded operation of the wind turbine, switching on a switch in a second pulse mode to avoid electrical resonance in the wind turbine, particularly electrical resonance in the power cables of the tower. For example, if electrical resonance exists, it can be eliminated or at least reduced.

[0081] Therefore, when the power grid 102 is unavailable and the wind turbine is operating in an islanded mode (e.g., starting operation), i.e., generating electricity through the rotation of the wind turbine rotor 18 for its own consumption, the second pulse mode can be used to avoid or at least reduce the risk of electrical resonance.

[0082] In islanded mode, the wind turbine rotor 18 can rotate at a certain speed, causing the wind turbine generator 42 to generate electricity to power the wind turbine's auxiliary systems 108 (such as temperature control and communication systems). In some examples, the rotor 18 can rotate between 4 and 8 RPM, for example, between 5 and 7 RPM. By actively controlling the blade pitch angle of the blades 22, the rotational speed and the generated power can be maintained at desired values. The torque of the generator 42 can also be controlled, for example, using a main converter or an auxiliary converter. In some examples, the generator 42 can provide power between 100 and 300 kW in islanded operation mode.

[0083] The method can be further included by keeping the auxiliary system 108 connected to the main transformer 105 while operating the wind turbine in islanded mode. Since the risk of resonance is low or very low, it may not be necessary to disconnect the auxiliary system 108 from the main transformer 105. This avoids expensive components and the difficult methods of installing them in the wind turbine for disconnecting the auxiliary system 108 from the main transformer 105.

[0084] Before the wind turbine 10 begins operating in islanded mode, the method may further include disconnecting the wind turbine 10 from the power grid 102. For example, disconnection may include triggering a circuit breaker. The circuit breaker may be located in the switching device 106 of the wind turbine 10.

[0085] If the wind turbine 10 operates in normal mode before operating in islanded mode, the method may further include switching the switch to a first pulse mode during normal operation of the wind turbine. The first pulse mode may have features suitable for normal operation, and the second pulse mode may have features suitable for islanded operation. For example, if PWM is used to generate the first and second pulse modes, the frequency of the carrier used to generate the first pulse mode may be different from (e.g., lower than) the frequency of the carrier used to generate the second pulse mode. Typically, the pulse modes can be generated in any suitable manner known in the art.

[0086] The method may also include measuring information indicating harmonics in the wind turbine, particularly harmonics in the multiple power cables of the tower. The measured harmonics of the signal can provide information about the risk of resonance and whether the pulse pattern being used is functioning correctly. Information indicating harmonics can be measured using a voltage sensor. In some examples, voltage sensor 113 may be configured to be arranged alongside the power cables 109 of the wind turbine tower. Measuring information indicating harmonics in the power cables of the tower may be particularly suitable because resonance can occur in the power cables. However, in other examples, harmonics (and often the presence or risk of resonance) may also be measured in different locations, such as near auxiliary system 108, optionally using a power analyzer, or in power converter 104. In some examples, in addition to measuring information indicating harmonics in the multiple power cables of the tower, this information may also be measured between power converter 104 and main transformer 105.

[0087] The method may also include changing the operation of the power converter 104 to a third pulse mode in response to the detection of the presence or risk of resonance in the wind turbine 10 (e.g., in the power cable of the tower), such as in response to the detection of harmonics in the resonant frequency range of the power cable in the power cable of the tower.

[0088] As previously described, in some examples, the wind turbine 10 may begin operating in island mode and immediately change from a first pulse mode to a second pulse mode. In some of these examples, one or more sensors 113 may be additionally used to detect the presence or risk of electrical resonance in one or more of the LV, MV, or HV sides, and change to another pulse mode, such as a third pulse mode. Still in other examples, the wind turbine 10 may begin operating in island mode and use one or more sensors 113 to detect the presence or risk of electrical resonance. After detection, the first pulse mode may change to another pulse mode, such as a second pulse mode. If electrical resonance or a risk of electrical resonance is later detected, the pulse mode may again change to, for example, a third pulse mode.

[0089] Since the spectrum may differ on the HV, MV, and LV sides, depending on the location where resonance is detected (e.g., the measured location of resonance), one or another pulse mode can be selected as the new pulse mode. For example, if resonance or a risk of resonance is detected on the LV side, the current pulse mode can be changed to a specific pulse mode configured to avoid, eliminate, or reduce resonance on the LV side. However, if resonance or a risk of resonance is detected on the HV side, the current pulse mode can be changed to another pulse mode configured to avoid, eliminate, or reduce resonance on the HV side.

[0090] The details and explanations provided for this method can be applied to and combined with the aforementioned aspects of wind turbines, and vice versa.

[0091] In another aspect of this disclosure, an offshore wind turbine is provided. The details and explanations of this wind turbine can be applied to and combined with the wind turbines and methods of the foregoing aspects, and vice versa.

[0092] The wind turbine 10 includes a generator 42 configured to generate an AC power signal. The wind turbine 10 also includes a power converter 104 connected to the generator 42, the power converter 104 including a machine-side converter configured to convert the AC power signal to a DC power signal, a DC link, and a line-side converter configured to convert the DC power signal to an AC power signal. The line-side converter includes circuitry comprising a plurality of switches for converting the DC power signal to an AC power signal.

[0093] The wind turbine 10 also includes an auxiliary transformer 107 connected to the power converter 104 and one or more auxiliary systems 108 connected to the auxiliary transformer 107. The wind turbine 10 also includes a main transformer 105. The input side of the main transformer 105 is connected to the power converter 104, and the output side of the main transformer 105 is connected to a plurality of tower cables 109 configured to carry AC power signals.

[0094] The power converter 104 is configured to operate in a first predefined pulse mode for switching during normal operation of the wind turbine, and is configured to operate in a second predefined pulse mode different from the first pulse mode for switching during islanded operation of the wind turbine, in order to avoid or reduce resonance in the tower cable 109 in islanded mode.

[0095] The wind turbine 10 may also include a sensor 113 for measuring the voltage in one or more cables connected to the main transformer 105. For example, the sensor 113 may be positioned between the main transformer 105 and the auxiliary transformer 107, or between the auxiliary transformer 107 and the auxiliary system 108, or between the power converter 104 and the main transformer 105. The voltage sensor 113 may be specifically positioned with the tower cable 109 for measuring the voltage in the tower cable 109.

[0096] The voltage can indicate the presence of harmonics within a frequency range including the resonant frequency of the tower cable 109. The wind turbine can be configured to detect harmonics within a frequency range including the resonant frequency of the tower cable, and when detected, the power converter 104 can be configured to operate the wind turbine in an islanded mode, utilizing a third pulse mode different from the first and second pulse modes for switching.

[0097] This written description uses examples to disclose teachings, including preferred embodiments, and also enables any person skilled in the art to put those teachings into practice, including making and using any apparatus or system and performing any combined methods. The scope of patentability is defined by the claims and may include other examples that would occur to a person skilled in the art. Such other examples are intended to be within the scope of the claims if they 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. Based on the principles of this application, those skilled in the art can mix and match aspects from the various embodiments described, as well as other known equivalents of each such aspect, to construct additional embodiments and techniques. If reference numerals associated with the drawings are placed within brackets in the claims, they are merely intended to increase the comprehensibility of the claims and should not be construed as limiting the scope of the claims.

Claims

1. A wind turbine (10), comprising: A generator (42) configured to generate AC power; A power converter (104) is connected to the generator (42) and includes a machine-side converter configured to convert AC power to DC power, a DC link, and a line-side converter configured to convert DC power to AC power, the line-side converter including a plurality of switches for converting DC power to AC power. The main transformer (105) and auxiliary transformer (107) are connected to the power converter (104). One or more auxiliary systems (108) are connected to the auxiliary transformer (107). Multiple power cables (109) connecting the output side of the main transformer to the power grid. The power converter (104) is configured to operate in a first pulse mode during normal operation of the wind turbine (10) to switch the switch, and the power converter (104) is configured to operate in a second pulse mode different from the first pulse mode during islanded operation of the wind turbine (104) to switch the switch. The second pulse mode is configured to avoid electrical resonance in the wind turbine (10).

2. The wind turbine according to claim 1, wherein, The second pulse mode is configured to avoid electrical resonance in the plurality of power cables (109).

3. The wind turbine according to claim 1 or claim 2, wherein, The first pulse mode and the second pulse mode are predefined pulse modes.

4. The wind turbine according to any one of claims 1-3 further includes a sensor (113) for measuring data indicating electrical resonances of harmonics in the wind turbine (10), particularly in the plurality of power cables (109).

5. The wind turbine according to claim 4, wherein the sensor (113) is a voltage sensor.

6. The wind turbine according to claim 4 or claim 5, wherein, The sensor (113) is arranged together with the plurality of power cables (109) and configured to measure data indicating harmonics in the power cables (109).

7. The wind turbine according to any one of claims 4-6, wherein, The wind turbine (10) is configured to detect the presence or risk of electrical resonance using the sensor (113), and wherein the power converter (104) is configured to change the pulse mode in response to the detection.

8. The wind turbine of claim 7, further configured to operate in a third pulse mode during islanded operation of the wind turbine (10) for switching the switch, the third pulse mode being different from the first pulse mode and the second pulse mode.

9. A method (100) for operating a wind turbine according to claims 1-8, the method comprising: It is determined (110) that the power grid (102) is unavailable; Start (120) to operate the wind turbine (10) in island mode; as well as During the operation of the wind turbine (10) in island mode, the switch is switched (130) in the second pulse mode to avoid electrical resonance in the wind turbine (10).

10. The method of claim 9, further comprising maintaining the auxiliary system (108) connected to the main transformer (105) when the wind turbine (10) is operated in island mode.

11. The method according to claim 9 or claim 10, further comprising electrically disconnecting the wind turbine (10) from the power grid (102) before commencing operation in the islanded mode.

12. The method according to any one of claims 9-11, further comprising switching the switch in the first pulse mode during normal operation of the wind turbine (10).

13. The method according to any one of claims 9-12 further includes measuring information indicating harmonics in the wind turbine (10), particularly in the plurality of power cables (109).

14. The method according to claim 12 or claim 13, wherein, The information indicating harmonics is measured in the plurality of power cables (109) and optionally additionally between the power converter and the main transformer.

15. The method of claim 13 or claim 14, further comprising changing the operation of the power converter to a third pulse mode in response to detecting the presence or risk of resonance in the wind turbine (10).

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