Wind turbine yaw system with variable frequency drive and electronic switch

Abstract

The invention provides a yaw system for a wind turbine. The wind turbine includes a tower and a nacelle atop the tower. The yaw system includes a yaw ring, a plurality of motors for driving rotation of the nacelle relative to the tower, and a variable frequency drive for driving the plurality of motors. The yaw system includes a plurality of sensors, each sensor associated with a respective motor, and each sensor for measuring an operating parameter of the respective motor. The yaw system includes an electronic switch configured to receive, from each of the sensors, a sensor signal indicative of the measured operating parameter. The electronic switch is controllable to select a sensor signal of the plurality of sensor signals for receipt by the variable frequency driver. The variable frequency driver is configured to drive the plurality of motors based on a selected one of the plurality of sensor signals.

Description

Technical Field

[0001] The present invention relates to a yaw system for a wind turbine, and more particularly to a yaw system comprising: a frequency converter for driving an electric motor to rotate the nacelle of the wind turbine relative to the tower of the wind turbine; and an electronic switch for receiving a plurality of sensor signals indicating operation of the electric motor and for selecting one of the sensor signals to provide to the frequency converter. Background Technology

[0002] Wind turbines known in the art have a tower supporting a nacelle and a rotor with multiple rotor blades. A yaw system is known to be incorporated into wind turbines to control the rotation of the nacelle relative to the tower. Typically, yaw control is implemented to keep the rotor plane, defined by the rotor and rotor blades, perpendicular to the direction of the oncoming wind in order to maximize energy capture.

[0003] In known arrangements, multiple electric motors are provided to drive the rotation of the nacelle relative to the tower. Additionally, multiple variable frequency drives (VFDs) are provided to drive the rotation of the motors. For example, each motor may have its own dedicated VFD. In this arrangement, each VFD can receive sensor signals indicating the speed or other operating parameters of the motor controlled by the corresponding VFD. As part of a feedback control loop, the VFD uses these sensor signals to adjust its output frequency to control the motor according to the desired speed or torque.

[0004] To provide a more compact yaw system arrangement, it may be desirable to provide fewer VFDs than the number of motors in the yaw system, such that each VFD drives multiple motors. In this regard, the most compact solution is to provide a yaw system with a single VFD driving each motor of the yaw system.

[0005] Problems may arise with arrangements where each VFD drives multiple motors. This is because each VFD may only be able to receive a single sensor signal. Therefore, when multiple motors are to be controlled by a VFD, the VFD may not be able to receive sensor signals, such as speed signals, from all the motors to be controlled.

[0006] This invention was conceived in this context. Summary of the Invention

[0007] According to one aspect of the invention, a yaw system for a wind turbine is provided, the wind turbine including a tower and a nacelle located atop the tower. The yaw system includes: a yaw ring configured to allow rotation of the nacelle relative to the tower; and a plurality of electric motors configured to drive the rotation of the nacelle relative to the tower. The yaw system includes a frequency converter driver configured to drive the plurality of electric motors. The yaw system includes a plurality of sensors, each of which is associated with a corresponding electric motor, and each of which is configured to measure operating parameters of the corresponding electric motor. The yaw system includes an electronic switch configured to receive a sensor signal from each of the plurality of sensors, the sensor signal indicating the measured operating parameters of the corresponding electric motor. The electronic switch can be controlled to select a sensor signal from the plurality of sensor signals for reception by the frequency converter driver. The frequency converter driver is configured to drive the plurality of electric motors based on the selected sensor signal from the plurality of sensor signals.

[0008] The electronic switch can be a solid-state switch.

[0009] Each of the plurality of sensors may be an encoder. Alternatively, each of the plurality of sensors may be a solver.

[0010] The measured operating parameter for each of the plurality of motors can be the rotational speed or position of the shaft of the respective motor.

[0011] According to one aspect of the present invention, a control system is provided, the control system including the yaw system as described above. The control system may include a controller configured to: control the variable frequency drive to drive the plurality of motors; and control the electronic switch to select one of the plurality of sensor signals to be received by the variable frequency drive.

[0012] The controller can be configured to control the variable frequency drive to adjust the frequency of the input power supply to the variable frequency drive based on a selected sensor signal from the plurality of sensor signals, so as to control the plurality of motors to be driven at a desired shaft rotation speed as part of a closed feedback loop.

[0013] The controller can be configured to detect whether the sensor is faulty, wherein a selected sensor signal from the plurality of sensor signals is received from the sensor. The controller can be configured to, upon detection, send a control signal to control the electronic switch to select a different sensor signal from the plurality of sensor signals to be received by the frequency converter. The frequency converter can be configured to drive the plurality of motors based on the selected different sensor signal from the plurality of sensor signals.

[0014] The controller can be configured to determine that a sensor is faulty if a selected sensor signal from the plurality of sensor signals stops being received by the electronic switch.

[0015] The selected sensor signal in the sensor signals may be received from a first sensor among the plurality of sensors. The controller may be configured to perform a maintenance check on the first sensor based on the selected sensor signal in the sensor signals. The controller may be configured to: (i) control the electronic switch to select different sensor signals from different sensors among the plurality of sensors for reception by the frequency converter; and (ii) perform a maintenance check on another sensor based on the selected different sensor signal in the sensor signals. The controller may be configured to repeat steps (i) and (ii) for different sensors among the plurality of sensors until a maintenance check for each of the plurality of sensors has been performed.

[0016] The yaw system may include a circuit breaker that can be controlled to selectively provide electrical connection between the input power supply and the plurality of motors. The circuit breaker may be arranged in parallel with the variable frequency drive. The controller may be configured to detect whether the variable frequency drive cannot be controlled to drive the plurality of motors. The controller may be configured to send a control signal to control the circuit breaker to provide electrical connection between the input power supply and the plurality of motors when this is detected.

[0017] According to another aspect of the present invention, a wind turbine is provided, the wind turbine including the yaw system as described above. According to another aspect of the present invention, a wind turbine is provided, the wind turbine including the control system as described above.

[0018] According to another aspect of the invention, a method is provided for controlling a yaw system for a wind turbine, the wind turbine including a tower and a nacelle located on top of the tower. The yaw system includes: a plurality of electric motors for driving rotation of the nacelle relative to the tower; and a variable frequency drive for driving the electric motors. The method includes: for each of the plurality of electric motors, measuring operating parameters of that motor using a corresponding sensor. The method includes: receiving a sensor signal from each of the plurality of sensors at an electronic switch of the yaw system, the sensor signal indicating the measured operating parameters of the corresponding motor. The method includes: selecting a sensor signal from the plurality of sensor signals received from the sensors at the electronic switch, and transmitting the selected sensor signal to the variable frequency drive. The method includes: controlling the variable frequency drive to drive the plurality of electric motors based on the selected sensor signal received via the electronic switch.

[0019] The method may include: detecting whether the sensor is faulty, wherein the selected sensor signal is received from the sensor. The method may include: upon detection, selecting a different sensor signal from the plurality of sensor signals received from the sensor at an electronic switch, and transmitting the selected different sensor signal to the variable frequency drive. The method may include: controlling the variable frequency drive to drive the plurality of motors based on the selected different sensor signals received via the electronic switch.

[0020] The selected sensor signal in the sensor signals may be received from a first sensor among the plurality of sensors. The method may include performing a maintenance check on the first sensor based on the selected sensor signal in the sensor signals. The method may include: (i) controlling the electronic switch to select different sensor signals from different sensors among the plurality of sensors for reception by the frequency converter; and (ii) performing a maintenance check on another sensor based on the selected different sensor signals in the sensor signals. The method may include repeating steps (i) and (ii) for different sensors among the plurality of sensors until a maintenance check has been performed for each of the plurality of sensors.

[0021] According to another aspect of the present invention, a non-transitory computer-readable storage medium is provided, on which instructions are stored, which, when executed by one or more processors, cause the one or more processors to perform the method defined above. Attached Figure Description

[0022] Examples of the invention will now be described with reference to the accompanying drawings, in which:

[0023] Figure 1 This is a schematic diagram of a wind turbine according to an example of the present invention;

[0024] Figure 2 yes Figure 1 A schematic top view of a wind turbine, showing how the nacelle of a wind turbine can rotate the yaw angle based on the direction of the wind;

[0025] Figure 3 yes Figure 1 A schematic diagram of the yaw system of a wind turbine, which is used to rotate the nacelle. Figure 2 The yaw angle indicated in the middle;

[0026] Figure 4 The illustration shows, based on the example, Figure 3 The components of the yaw system include multiple electric motors and dedicated frequency converters for each respective electric motor;

[0027] Figure 5 The illustrations show different examples. Figure 3 The components of the yaw system include multiple electric motors and a single variable frequency drive for driving each electric motor;

[0028] Figure 6 The illustrations show different examples. Figure 3 The components of the yaw system include multiple electric motors and multiple frequency converters, each frequency converter being used to drive multiple electric motors;

[0029] Figure 7 schematically shown Figure 5 Multiple electric motors and a single variable frequency drive, multiple sensors (each sensor associated with a corresponding electric motor), and electronic switches between the sensors and the variable frequency drive; and,

[0030] Figure 8 schematically shown Figure 5 Multiple motors and a single frequency converter, as well as circuit breakers arranged in parallel with the frequency converter. Detailed Implementation

[0031] Figure 1An example of a wind turbine 10 is illustrated schematically. The wind turbine 10 includes a tower 102, a nacelle 103 disposed at the apex or top of the tower 102, and a rotor 104 operatively coupled to a generator housed within the nacelle 103. In addition to the generator, the nacelle 103 houses other components necessary for converting wind energy into electrical energy, as well as various components required for operating, controlling, and optimizing the performance of the wind turbine 10. The rotor 104 of the wind turbine 10 includes a central hub 105 and three rotor blades 106 projecting outward from the central hub 105.

[0032] The rotor 104 and rotor blades 106 rotate about the rotor axis and define the rotor plane. In particular, wind impacting the rotor blades 106 drives the rotation of the rotor 104 and rotor blades 106, thereby capturing wind energy that can be converted into electrical energy, for example, for supplying to the power grid.

[0033] The wind turbine 10 includes a yaw system ( Figure 1 (Not shown in the image), which is used to rotate the nacelle 103 (including the rotor 104 and rotor blades 106) relative to the tower 102 about a defined yaw axis of the wind turbine 10. This is in Figure 2 The diagram illustrates that, Figure 2 This is a top view of the wind turbine 10. Specifically, Figure 2 The nacelle 103 is schematically shown relative to the tower 102 along with the rotor 104 and rotor blades 106. Figure 2 (Not shown in the image) Rotation yaw angle 201.

[0034] Typically, the yaw system is operated to drive the rotation of the nacelle 103 or maintain the position of the nacelle 103 such that the rotor axis 202 is aligned with the wind direction 203, or equivalently, such that the rotor plane 204 is perpendicular to the wind direction 203. This operation typically allows the wind turbine 10 to maximize the energy captured by the wind passing over it. This can be referred to as headwind control. As the wind direction 203 changes, based on input from a wind direction sensor, the yaw system causes the nacelle 103 to rotate about the yaw axis as appropriate.

[0035] Figure 3 A side view of an example of components of the yaw system 30 of the wind turbine 10 is shown. The yaw system 30 includes a yaw ring 301. In the described example, the yaw ring 301 is fixed to the top of the tower 102; however, in different examples, the yaw ring may alternatively be fixed to the nacelle 103, adjacent to the top of the tower.

[0036] The yaw system 30 includes multiple electric motors or yaw motors 302, one of which is in Figure 3As shown in the illustration. In the described example, the motor 302 is fixed to the nacelle 103 (adjacent to the tower top); however, in different examples, the motor may alternatively be fixed to the tower top. Each motor 302 includes an electric brake and is connected to a corresponding yaw gear 303. When the motor 302 is driven, the corresponding yaw gear 303 is driven and engages the yaw ring 301 to cause rotation of the nacelle 103 relative to the tower 102. In this regard, a bearing 304 is disposed between the tower top and the nacelle 103 to allow / permit relative rotation between them.

[0037] Electric motors can be driven in different ways. In an example of the invention, the yaw system 30 is provided with one or more variable frequency drives (VFDs) for driving the electric motor. A VFD is an alternating current (AC) motor drive that controls the speed and torque of the motor by changing the frequency of the input power supply. A VFD can have both AC and DC (direct current) power supplies. The use of a VFD allows for greater flexibility in motor control. For example, the use of a VFD allows for gradual increases / decreases in torque / power / speed, thereby increasing the wind turbine's ability to handle certain load conditions. The use of a VFD can be particularly beneficial in larger wind turbines.

[0038] Figure 4 A top view schematically illustrating components of an example yaw system 30 is shown. Multiple electric motors 302 are arranged around and adjacent to the periphery of a yaw ring 301. In the example shown, the yaw system 30 includes 18 electric motors 302; however, it should be understood that any suitable number of electric motors can be provided, for example, depending on the size of the wind turbine. The number of electric motors can typically be between 6 and 20. For example, the electric motors can be synchronous motors or asynchronous motors.

[0039] exist Figure 4 In the example shown, the yaw system 30 includes a plurality of VFDs 41. Specifically, in the example shown, each of the plurality of motors 302 is controlled / driven by a dedicated VFD 41. That is, in the example shown, an equal number of VFDs 41 and motors 302 are provided, i.e., 18 in this example. Each VFD 41 is communicatively connected to a corresponding motor 302, i.e., each VFD 41 is electrically connected to a corresponding motor 302 via connection 42. Note that... Figure 4 Only some connections 42 are shown. The arrangement of providing a dedicated VFD to control each motor can be considered relatively simple to implement.

[0040] Each VFD 41 is connected (electrically) to the input power supply. Figure 4(Not shown in the image). When VFD 41 is supplied with power from the input power source, VFD 41 is configured to control (e.g., drive) the corresponding motor 302 to rotate at a desired speed or with a desired torque. In this way, motor 302 is controlled to rotate nacelle 103 relative to tower 102 by a yaw angle via engagement with yaw ring 301, or to maintain nacelle 103 in a yaw position relative to tower 102.

[0041] although Figure 4 Not shown, but the yaw system 30 also includes multiple sensors, each associated with a corresponding one of the motors 302. The yaw system 30 also includes an electronic switch positioned between the VFD 41 in the circuit and the sensor, and used to receive sensor signals from each sensor. This will be discussed in more detail below.

[0042] The wind turbine 10 includes an (advanced) wind turbine controller for controlling various control systems of the wind turbine 10, such as a pitch control system, a generator speed control system, etc. In the described example, the wind turbine controller is configured to control a yaw system 30. Specifically, the wind turbine controller can request or require the yaw system to perform yaw to achieve a specific yaw angle of the nacelle 103, for example, to maximize power generation. The yaw system 30 may include a yaw controller 305 for implementing requests from the wind turbine controller (in... Figure 2 (Illustrated schematically). Specifically, the yaw controller 305 can define one or more operating parameters in the form of setpoints for speed, torque, power, etc. The yaw system 30 may also include one or more VFD controllers (not shown), each VFD controller being associated with one or more corresponding VFDs 41. The VFD controllers (one or more) can use the setpoints of the yaw controller 305 to power the VFDs 41, for example by controlling voltage or current, to control the components of the yaw system 30 to rotate clockwise, rotate counterclockwise, stop rotating, apply mechanical braking, or apply torque in order to control the movement of the nacelle 103 about the yaw axis as required by headwind control.

[0043] The yaw controller 305 can take the form of any suitable computing device, such as one or more functional units or modules implemented on one or more computer processors. Such functional units can be provided by suitable software running on any suitable computing substrate using conventional or custom processors and memory. One or more functional units can use a common computing substrate (e.g., they can run on the same server) or separate substrates, or one or two functional units can be distributed among multiple computing devices. The computer memory can store instructions for performing methods executed by the controller (e.g., controlling the yaw system in a desired manner), and the processor can execute the stored instructions to perform the methods.

[0044] Figure 5 A schematic top view of components of a yaw system 30 according to another example is shown. The yaw system 30 includes a plurality of motors 302 (specifically, 18 motors) arranged around and adjacent to a yaw ring 301. However, with... Figure 4 The examples are different, in Figure 5 In the example, the yaw system 30 includes only a single VFD 51. The single VFD 51 is electrically connected to each of a plurality of motors 302 via a connection 52. Note that... Figure 5 Not all connections are shown in Figure 52. VFD 51 is connected to the communication ground (electrical connection) to the input power supply. Figure 5 (Not shown in the image). When VFD 51 is supplied with power from the input power source, VFD 51 is configured to control (e.g., drive) the corresponding motor 302 to rotate at a desired speed or with a desired torque. The arrangement of providing a single VFD to control each motor can be considered a relatively cost-effective and compact solution. Although a single VFD 51 can be larger than one of the dedicated VFDs 41, significant space savings still exist due to having only a single VFD unit.

[0045] although Figure 5 As not shown, the yaw system 30 also includes multiple sensors, each associated with a corresponding one of the motors 302. The yaw system 30 also includes an electronic switch located between the VFD 51 and the sensors in the circuit, and used to receive sensor signals from each sensor. This will be discussed in more detail below.

[0046] Figure 6 A schematic top view of components of a yaw system 30 according to another example is shown. The yaw system 30 includes a plurality of motors 302 (specifically, 18 motors) arranged around and adjacent to a yaw ring 301. Figure 6 In the example, the yaw system 30 includes multiple VFDs 61. However, compared to... Figure 4The examples are different, in Figure 6 In the example, each of the VFDs 61 is electrically connected to a plurality of motors 302 via connection 62. Note that... Figure 6 Not all connections 62 are shown. There are fewer VFDs 61 than motors 302. In the example shown, there are 4 VFDs 61 (and 18 motors 302). Each VFD 61 is communicatively connected (electrically connected) to the input power supply. Figure 6 (Not shown in the image).

[0047] As described above, each VFD is used to control the rotation of the motor. Specifically, the VFD can receive sensor signals indicating the speed or other operating parameters of the motor controlled by the VFD. Then, as part of a feedback control loop, the VFD can use these sensor signals to adjust its output frequency to control the motor according to the desired speed or torque.

[0048] It is possible to have an arrangement where each VFD drives multiple motors (e.g.) Figure 5 The arrangement shown presents operational issues. This is because each VFD may be able to receive only a single sensor signal. Therefore, when multiple motors are to be controlled by a VFD, the VFD cannot receive sensor signals, such as speed signals, from all the motors to be controlled.

[0049] Therefore, the present invention is advantageous because it provides an arrangement that allows a VFD to control the speed or torque of an electric motor based on a desired speed or torque in a wind turbine yaw system, in which the VFD controls the speed or torque of multiple electric motors. The arrangement of the present invention is also advantageous because it provides increased redundancy compared to previous arrangements and allows monitoring of the operation of the components of the arrangement as part of a maintenance procedure. The means of achieving these benefits are described below.

[0050] Figure 7 The components of a yaw system 30 are schematically shown in an example where each VFD of the yaw system drives multiple motors, wherein the yaw system includes one or more VFDs. Figure 7 The example shown specifically involves Figure 5 The yaw system 30 shown includes a single VFD 51 electrically connected to each of a plurality of motors 302 and used to drive the plurality of motors 302. Figure 7 Only each of the four motors 302 is shown in the diagram.

[0051] Figure 7The yaw system 30 also includes a plurality of sensors 71. Each of the sensors 71 is associated with a corresponding one of the motors 302. Each sensor 71 is configured to measure operating parameters associated with the operation of the corresponding motor 302. Each of the sensors 71 may be an encoder or a decoder. The operating parameters to be measured using the sensors 71 may be the rotational speed of the corresponding motor 302, the position of the shaft of the corresponding motor 302, and / or the direction of rotation of the shaft of the corresponding motor 302.

[0052] Figure 7 The yaw system 30 also includes an electronic switch 72. Switch 72 is located between the VFD 51 and the sensor 71 in the circuit. Switch 72 is configured to receive sensor signals 73 from each of the plurality of sensors 71. Each sensor signal 73 indicates a measured operating parameter of the corresponding motor 302, such as shaft rotation speed.

[0053] The specific VFD 51 used is capable of receiving only a single sensor signal. The electronic switch 72 is advantageously controllable to select one of a plurality of sensor signals 73 received from sensor 71 for reception by VFD 51. The electronic switch 72 is configured to direct / send the selected sensor signal 73 to VFD 51 as selected signal 74. VFD 51 is configured to control / drive a plurality of motors 302 based on the selected signal 74 from the plurality of sensor signals 73.

[0054] The yaw controller 305 can be used to control the VFD 51 to drive / control the motors 302. Specifically, the yaw controller 305 or the VFD controller can be configured to control the VFD 51 to adjust the frequency of the input power supply 65 to the VFD 51 based on a selected sensor signal 74, so as part of a closed feedback loop, that each of the motors 302 is driven at a desired shaft rotation speed. The yaw controller 305 can also be used to control the electronic switch 72 to select which received sensor signal 73 is provided to the VFD 51. The controller 205 and the yaw system 30 can be collectively referred to as the control system of the wind turbine 10. In an alternative example, the VFD and / or the electronic switch can act as controllers to control their own and / or each other's operation. For example, the electronic switch can be configured to monitor received sensor signals and determine / select which sensor signal is provided to the VFD.

[0055] In the described example, the electronic switch is a solid-state switch. This type of switch is an electronic switching device with no moving parts that is switched on or off when an external voltage is applied to its control terminals. This type of switch is advantageous because it is fast and reliable in coupling and decoupling signals. It should be understood that different types of electronic switches can be used in different examples. The type of switch deployed can depend on the type of sensor used to measure the motor's operating parameters.

[0056] During normal operation of the yaw system 30, a single signal indicating operation of only one of the motors 302 is sufficient to enable the VFD 51 to perform closed-loop feedback control to control each motor 302. In one example, one of a plurality of sensors 71 can be considered the default sensor, wherein the electronic switch 72 selects the sensor signal 73 associated with the default sensor 71 to be provided to the VFD 51 during normal operation. In another example, the electronic switch 72 can be controlled to switch between different received sensor signals 73, for example, in a cyclic or periodic manner, such that the VFD receives sensor signals from different motors among the motors at different times.

[0057] The yaw system 30, including the electronic switch 72, is advantageous because it introduces a degree of redundancy into the system. Specifically, if a motor 302 or sensor 71 associated with a sensor signal 73 selected by the electronic switch 72 to be provided to the VFD 51 fails or is faulty, the electronic switch 72 can select a different sensor signal 73 associated with a correctly operating motor 302 and sensor 71 to provide to the VFD 51, ensuring continuous operation of the yaw system. For example, the yaw controller 305 can be configured to detect a fault in one of the sensors 71, or that the motor 302 is not operating as expected. In this case, the yaw controller 305 can be configured to control the electronic switch 72 to select one of the sensor signals 73 not associated with the faulty / failed sensor 71 or motor 302. In one example, the yaw controller 305 can be configured to determine that one of the sensors 71 is faulty if the electronic switch 72 stops receiving the corresponding signal 73 from the sensor 71, i.e., communication is lost. In this way, a failure of one or more motors 302 or sensors 71 will not affect the operation of the VFD 51. This added redundancy in the yaw system can be referenced to a previous arrangement in which one VFD controls multiple motors, but in which a sensor signal associated with one of the motors is directly fed to the VFD, i.e., without an electronic switch. It is important to note that if none of the sensor signals 73 to be received by the electronic switch 72 are detected to be available, the VFD 51 can be controlled to operate according to an open feedback loop (rather than a closed feedback loop), i.e., determining the frequency output used to control the motor 302, where this determination is not based on any sensor signal 73.

[0058] It should be noted that each motor has a dedicated VFD arrangement (such as...) Figure 4 The advantage of the example shown is that the operation of each motor, as well as the brakes and gears of the yaw system, can be monitored using sensor signals that indicate the operating parameters of the corresponding motor for feedback control, received by the respective dedicated VFD. For example, the sensor signals can be analyzed to ensure that the actual shaft rotation speed of the motor matches the shaft rotation speed controlled by the VFD.

[0059] In an arrangement where one VFD controls multiple motors and the VFD performs feedback control based on the measured operating parameter signals of only one motor (such as...), Figure 5 and Figure 6As shown in the arrangement, one problem is that it is more difficult to perform maintenance checks on all the motors, brakes, gears, etc., of the yaw system. Another benefit of the yaw system 30, which includes the electronic switch 72 described herein, is that checks can be performed to ensure that all motors and sensors are operating correctly. Similar to the above, this benefit can be apparent, for example, relative to the previous arrangement, in which one VFD controls multiple motors, but in the previous arrangement, the sensor signal associated with one of the motors was directly fed to the VFD, i.e., without an electronic switch.

[0060] When it is desired, for example, to perform maintenance checks periodically, the wind turbine controller can be configured to control the electronic switch 72 to cycle through each of a plurality of received sensor signals 73 to become a selected signal 74 to be sent to the VFD 51. For the first of the received sensor signals 73 that is the selected signal 74, the controller 205 can be configured to perform a maintenance check on the sensor 71 associated with the first of the sensor signals 73. This may involve analyzing the sensor signals 73 to detect any potential problems. For example, if the electronic switch 72 does not receive a signal 73, i.e., the sensor signal is unavailable, this may indicate that the associated sensor 71 is faulty or that communication between the sensor 71 and the switch 72 has been lost. If the sensor signal 73 indicates that the measured operating parameters are outside the expected operating range, this may indicate a fault in the corresponding motor 302 or a fault in the associated sensor 71. The controller 205 can be configured to repeat this process for each sensor signal 73 input to the electronic switch 72. If a problem is detected with one of the sensor signals 73 during a maintenance check, various appropriate actions can be taken. For example, controller 205 can issue an alarm to the operator indicating that maintenance or investigation is required. Controller 205 can control electronic switch 72 to prevent the selection of sensor signals 73 associated with the fault until the fault has been investigated and repaired. Maintenance checks can alternatively be performed or initiated by yaw controller 305 or one or more dedicated (internal) VFD controllers, or by a combination of wind turbine controller, yaw controller 305, and one or more VFD controllers.

[0061] It should be understood that a yaw system with electronic switches can be implemented in a yaw system where one or more VFDs each control multiple motors, the electronic switches receiving multiple sensor signals indicative of corresponding operation of the multiple motors and selecting sensor signals from the received sensor signals to be provided to the VFD. This includes Figure 5 The arrangement shown (where a single VFD controls each motor of the yaw system) and such Figure 6The arrangement (where multiple VFDs each control multiple motors, for example, a yaw system including 2 VFDs and 18 motors, where each VFD controls 9 motors).

[0062] refer to Figure 8 In an example of the present invention, the yaw system 30 may optionally further include a circuit breaker 83. Figure 8 The example shown specifically involves Figure 5 The yaw system 30 shown includes a single VFD 51 electrically connected to and used to drive each of a plurality of motors 302, and the yaw system 30 includes an electronic switch 72.

[0063] Circuit breaker 83 can be actuated to disconnect or close the electrical connection between input power supply 65 and motor 302. Circuit breaker 83 is arranged in parallel with VFD 51. That is, VFD 51 and circuit breaker 83 are located on different branches 54a, 54b of the electrical connection between input power supply 65 and motor 302.

[0064] In the described example, circuit breaker 83 is a direct-on-line (DOL) contactor. The DOL allows bypass branch 54b to be connected, enabling full-line voltage to be applied immediately via bypass branch 54b, thus allowing starting under full load. Other types of contactors may be used. In some examples, the circuit breaker may be, for example, a molded case circuit breaker. DOL 83 allows motor 302 to start under full load by applying full-line voltage to the motor terminals. A DOL starter may be used if the high inrush current of starting the motor will not cause an excessive voltage drop in the power supply circuit.

[0065] When VFD 51 is electrically connected to the input power supply 65 and the motor 302, causing VFD 51 to control the operation of the motor 302, the circuit breaker 83 is tripped or disconnected. That is, in this case, current does not flow from the input power supply 65 to the motor 302 via circuit branch 54b.

[0066] When VFD 51 cannot control the operation of motor 302, circuit breaker 83 can be actuated to close or open, allowing current to flow from input power supply 65 to motor 302 via circuit branch 54b. VFD 51 can then be shunted out of the circuit. In this way, when VFD 51 cannot be used to control motor 302, motor 302 remains operational thanks to branch 54b and circuit breaker 83. Specifically, while providing power via branch 54b may not allow for this level of control over the operation of motor 302 compared to when VFD 51 is operational, circuit breaker 83 is a relatively simple and cost-effective way to ensure that motor 302 remains operational at least until the problem affecting the operation of VFD 51 can be resolved. In addition to the controllable circuit breaker allowing current to flow via bypass branch 54b, the system also includes controllable electrical contacts to shunt VFD 51 into / out of the circuit as needed, as described above.

[0067] Therefore, circuit breaker 83 can selectively provide electrical connection between input power supply 65 and multiple motors 302. In particular, circuit breaker 83 can provide electrical connection when VFD 51 cannot be controlled, for example, due to a fault associated with VFD 51 or a loss of connection associated with VFD 51.

[0068] Depending on the specific reason why VFD 51 cannot be used to control motor 302, VFD 51 may be disconnected from input power supply 65 and / or motor 302, for example, before circuit breaker 83 closes to complete the circuit.

[0069] The wind turbine controller can be configured to request a specific yaw angle, for example, to maximize wind turbine power generation. The yaw controller 305 (or yaw motor controller) of the wind turbine 10 can then fulfill this request from the wind turbine controller. A VFD controller can also be provided to control the VFD 51. The yaw controller 305 and the VFD controller can be part of the yaw system 30. Specifically, the yaw controller 305 controls the operation of the VFD 51, for example, to adjust the output frequency according to the desired rotational speed of the motor 302. This can be done directly or through the VFD controller. In some examples, the controller 205 is configured to control the actuation of the circuit breaker 83 between an open and closed position. For example, the yaw controller 305 can be configured to detect that the VFD 51 cannot be controlled to drive multiple motors 302. The detection can be performed in any suitable manner. For example, the yaw controller 305 can be configured to receive signals with status updates from the VFD 51, such as Controller Area Network (CAN) signals, where one such update could be that the VFD 51 has failed or is unavailable for another reason. Alternatively, the yaw controller 305 can be configured to monitor the movement of the motor 302 or the nacelle 103 when the yaw controller 305 sends a control signal to the VFD 51 to operate in a certain way (e.g., to rotate the nacelle 103 in a particular direction). If the yaw controller detects that the motor 302 or the nacelle 103 is not responding, the yaw controller 305 can determine that a connection has been lost or that the VFD 51 is faulty. Upon detecting that the VFD 51 cannot be controlled to drive multiple motors 302, the controller 205 can be configured to send a control signal to control the circuit breaker 83 to provide an electrical connection between the input power supply 65 and the multiple motors 302.

[0070] In different examples, circuit breaker 83 can be configured to automatically close to provide an electrical connection between VFD 51 and the multiple motors 302 when VFD 51 cannot provide the input power 65. For example, circuit breaker 83 can receive signals from sensors indicating a fault in VFD 51 or that an electrical connection in branch 54a has been lost; upon receiving such a signal, circuit breaker 83 is configured to automatically close to complete the circuit through branch 54b.

[0071] It should be understood that providing a circuit breaker arranged in parallel with the VFD for the yaw system can be achieved in each of the following ways: Figure 4 The yaw system, in which each motor has a dedicated VFD; Figure 5 The yaw system, wherein a single VFD controls all the motors of the yaw system; and Figure 6The yaw system comprises multiple VFDs, each controlling multiple motors. Circuit breakers can be provided for all or only some of the VFDs in the yaw system in parallel. In the example where electronic switch 62 is provided, circuit breaker 83 can also be provided as part of the same arrangement.

[0072] In all these cases, providing a circuit breaker advantageously increases the redundancy of the yaw drive system when one or more VFDs are not operating. However, it should also be understood that providing a circuit breaker is particularly advantageous in yaw systems with fewer VFDs, because in such systems, the failure of one VFD has a greater impact on the operation of the yaw system. That is, the more motors a particular VFD controls, the more motors may be unable to be driven in the event of a VFD failure. Furthermore, it should be understood that in… Figure 5 In the example shown (where a single VFD controls all motors in the yaw system), providing a circuit breaker is most advantageous. This is because if the single VFD 51 cannot be used to control motor 302, the yaw system 30 will be inoperable without a backup circuit breaker. This helps to avoid wind turbine downtime and minimize power generation losses.

[0073] Using circuit breakers or contactors in this manner is a relatively cost-effective and robust way to add redundancy to a wind turbine yaw system. Furthermore, existing wind turbines can be retrofitted to include any necessary / missing components to provide an arrangement with one or more VFDs arranged in parallel with one or more circuit breakers. Retrofitting may involve incorporating one or more VFDs into the existing arrangement and / or incorporating one or more circuit breakers into the existing system. Retrofitting may also involve removing certain components, such as one or more VFDs. Increasing the redundancy and reliability of wind turbines in this way can extend the life of major, difficult-to-replace components of the wind turbine, such as yaw rings and main shafts.

[0074] Many modifications may be made to the described examples without departing from the scope of the appended claims.

Claims

1. A yaw system for a wind turbine, the wind turbine comprising a tower and a nacelle located on top of the tower, the yaw system comprising: a yaw ring configured to allow rotation of the nacelle relative to the tower; a plurality of electric motors configured to drive rotation of the nacelle relative to the tower; a variable frequency drive configured to drive the plurality of electric motors; a plurality of sensors, wherein each of the sensors is associated with a respective one of the electric motors, wherein each of the sensors is configured to measure an operating parameter of the respective electric motor; and an electronic switch configured to receive a sensor signal from each of the plurality of sensors, the sensor signal being indicative of the measured operating parameter of the respective electric motor, wherein the electronic switch is controllable to select a sensor signal of the plurality of sensor signals to be received by the variable frequency drive, wherein the variable frequency drive is configured to drive the plurality of electric motors based on the selected sensor signal of the plurality of sensor signals.

2. The yaw system of claim 1, wherein, The electronic switch is a solid state switch.

3. The yaw system of claim 1 or 2, wherein: each of the plurality of sensors is an encoder; or each of the plurality of sensors is a resolver.

4. The yaw system according to any of the preceding claims, wherein, The measured operating parameter of each of the plurality of electric motors is a rotational speed or a position of a shaft of the respective electric motor.

5. A control system comprising the yaw system of any of the preceding claims, the control system comprising a controller configured to: control the variable frequency drive to drive the plurality of electric motors; and control the electronic switch to select the sensor signal of the plurality of sensor signals to be received by the variable frequency drive.

6. The control system of claim 5, wherein, The controller is configured to control the variable frequency drive to adjust a frequency of an input power supply to the variable frequency drive based on the selected sensor signal of the plurality of sensor signals in order to control the plurality of electric motors to be driven at a desired shaft rotational speed as part of a closed feedback loop.

7. The control system of claim 5 or 6, wherein, The controller is configured to: detect whether a sensor from which the selected sensor signal of the plurality of sensor signals is received has a fault; and upon detection, send a control signal to control the electronic switch to select a different sensor signal of the plurality of sensor signals to be received by the variable frequency drive, wherein the variable frequency drive is configured to drive the plurality of electric motors based on the selected different sensor signal of the plurality of sensor signals. The controller is configured to determine that the sensor has a fault if the selected sensor signal of the plurality of sensor signals stops being received by the electronic switch.

8. The control system of claim 7, wherein, ​ 9. The control system of any one of claims 5 to 8, wherein, The selected one of the sensor signals is received from a first one of the plurality of sensors, wherein the controller is configured to perform a maintenance check of the first sensor based on the selected one of the sensor signals, wherein the controller is configured to: (i) control the electronic switch to select a different one of the sensor signals received from a different one of the plurality of sensors for receipt by the variable frequency drive; and (ii) perform a maintenance check of the other sensor based on the selected different one of the sensor signals, wherein the controller is configured to repeat steps (i) and (ii) for different ones of the plurality of sensors until a maintenance check has been performed for each of the plurality of sensors.

10. The control system of any one of claims 5 to 9, wherein, The yaw system comprises a circuit breaker controllable to selectively provide an electrical connection between an input power supply and the plurality of electric motors, wherein the circuit breaker is arranged in parallel with the variable frequency drive, wherein the controller is configured to: detect that the variable frequency drive cannot be controlled to drive the plurality of electric motors; and upon detection, send a control signal to control the circuit breaker to provide the electrical connection between the input power supply and the plurality of electric motors.

11. A wind turbine comprising a yaw system according to any one of claims 1 to 4, or comprising a control system according to any one of claims 5 to 10.

12. A method of controlling a yaw system for a wind turbine, the wind turbine comprising a tower and a nacelle located on top of the tower, the yaw system comprising: a plurality of electric motors for driving rotation of the nacelle relative to the tower; and a variable frequency drive for driving the electric motors, The method comprises: for each of the plurality of electric motors, measuring an operating parameter of the respective electric motor using a respective sensor; receiving, at an electronic switch of the yaw system, a sensor signal from each of the plurality of sensors, the sensor signal being indicative of the measured operating parameter of the respective electric motor; selecting, at the electronic switch, a sensor signal from the plurality of sensor signals received from the sensors, and passing the selected sensor signal to the variable frequency drive; and controlling the variable frequency drive to drive the plurality of electric motors based on the selected sensor signal received via the electronic switch.

13. The method of claim 12, the method comprising: detecting that the sensor from which the selected sensor signal is received has failed; upon detection, selecting, at the electronic switch, a different one of the plurality of sensor signals received from the sensor, and passing the selected different sensor signal to the variable frequency drive; and controlling the variable frequency drive to drive the plurality of electric motors based on the selected different sensor signal received via the electronic switch. ​ 14. The method of claim 12 or 13, wherein, The selected one of the sensor signals is received from a first sensor of the plurality of sensors, and the method comprises performing a maintenance check of the first sensor based on the selected one of the sensor signals, The method further comprises: (i) controlling the electronic switch to select a different one of the sensor signals received from a different one of the plurality of sensors for receipt by the variable frequency drive; (ii) performing a maintenance check of the other sensor based on the selected different one of the sensor signals; and, Steps (i) and (ii) are repeated for different ones of the plurality of sensors until a maintenance check has been performed on each of the plurality of sensors.

15. A non-transitory computer-readable storage medium having stored thereon instructions which, when executed by one or more processors, cause the one or more processors to perform the method of any one of claims 12 to 14.

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