Patent Publication Number: US-2021164440-A1

Title: Wind turbine and method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to European Application No. 19212309.9, having a filing date of Nov. 28, 2019, the entire contents of which are hereby incorporated by reference. 
     FIELD OF TECHNOLOGY 
     The following relates to a wind turbine and to a method for preventing failure of a pitch bearing of a rotor blade of the wind turbine. 
     BACKGROUND 
     Modern wind turbine rotor blades are built from fiber-reinforced plastics. A rotor blade typically comprises an airfoil having a rounded leading edge and a sharp trailing edge. The rotor blade is connected with its blade root to a hub of the wind turbine. The hub is supported in a nacelle and the nacelle is attached to an end of a tower of the wind turbine. The rotor blades are supported at or in the hub by pitch bearings. The pitch bearings, a pitch angle of the rotor blades can be changed. 
     During long periods of operation, the power needs not to be adjusted by pitching the rotor blade. This means that the pitch bearing will be static. During this period, the load on the rotor blade will be highly dynamic which can cause false brinelling and fretting corrosion on the raceway of the pitch bearing unless the pitch bearing is moved to a new location which allows lubricant to get onto the contact surface. Accordingly, stand still marks can occur after a given time period. This time period will depend on many factors like load level, temperature, lubrication condition, water content and so on. 
     To avoid this issue, the pitch bearing can be pitched with a certain pattern which has proven to remove the risk completely under all circumstances and/or running conditions. This pattern is based on experience and tests. However, when the rotor blade is pitched away from the optimal power position, there will be a loss of energy. This has to be avoided. 
     SUMMARY 
     An aspect relates to providing an improved wind turbine. 
     Accordingly, a wind turbine is provided. The wind turbine comprises a hub, rotor blades, wherein each rotor blade is rotatably supported at or in the hub by a pitch bearing, a pitch control device for changing a pitch angle of the rotor blades, and a measurement system for capturing a sensor signal in or at the pitch bearing and for changing the pitch angle by the pitch control device as a function of the sensor signal to prevent failure of the pitch bearing due to a lack of lubrication, wherein the sensor signal represents a change in vibration, noise and/or temperature in or at the pitch bearing. 
     Due to the fact that the pitch angle can be changed as a function of the sensor signal, lubrication of the pitch bearing is ensured throughout the lifespan of the pitch bearing. Unnecessary pitch movements can be prevented. This reduces energy loss. Also, damage of the pitch bearing due to a lack of lubrication can be prevented. 
     The hub is rotatably supported at a nacelle of the wind turbine. The number of rotor blades is arbitrary. For example, there are provided three rotor blades. The pitch bearing is part of the wind turbine. Each rotor blade has a pitch bearing. The pitch angle is an angle that is changed when the rotor blade is rotated around a middle axis of the pitch bearing. The pitch angles of the rotor blades can be changed independently. The pitch bearing can be a rolling bearing, a ball bearing or a plain bearing. Any bearing can be used. 
     The pitch control device can comprise an actuator to pitch the rotor blades. Each rotor blade can have its own actuator. The actuator can be an electric or hydraulic motor. “Capturing” the sensor signal in this context means that the measurement system is capable of generating the sensor signal by one sensor or a plurality of sensors. Changing the pitch angle as a “function” of the sensor signal in this context means that the pitch angle is changed when the sensor signal changes when the sensor signal indicates that vibration, noise, temperature and/or another suitable parameter in or at the pitch bearing changes, and/or increases. “Vibration” includes oscillations and vibrations. “Noise” or “sound” can also include oscillations and vibrations, audible oscillations and vibrations. 
     The sensor signal is preferably an indirect sensor signal. “Indirect” in this context means that not the lubrication itself is measured, but the consequences of a weak lubrication, namely a change in vibration, noise and/or temperature. In contrast to that can be seen direct sensor signals. “Direct” in this context means that the lubrication itself is qualified. This can for example be done by measuring capacitance and/or resistance of the pitch bearing. Accordingly, any other indirect sensor signal can also be used to evaluate the status of the pitch bearing. Preferably, indirect sensor signals are used. However, direct sensor signals are not excluded and can also be used, but are less preferred. No measurement method is excluded. 
     “Failure” in this context includes stand still marks, false brinelling and fretting corrosion on the raceway of the pitch bearing and/or any other potential damage of the pitch bearing that can be caused by weak lubrication. In particular, “failure” includes stand still failure. 
     According to an embodiment, the measurement system comprises a controller and at least one sensor which is coupled to the controller. 
     The number of sensors is arbitrary. For example, each rotor blade and/or each pitch bearing comprises one or more sensors. The sensors can comprise temperature sensors, sound transducers or the like. 
     According to a further embodiment, the sensor is arranged in or at the hub and/or the sensor is arranged in or at the blades. 
     The sensor can also be arranged in or at the pitch bearing. The hub can have a plurality of sensors. Also, each blade can have one sensor or more than one sensor. 
     According to a further embodiment, the wind turbine further comprises a memory that is coupled to the controller, wherein the sensor signal is stored in the memory. 
     Threshold values can be stored in the memory. The sensor signal can be compared with the threshold values. When the sensor signal significantly deviates from the threshold values, the pitch angle can be changed, for example. 
     According to a further embodiment, the measurement system compares the sensor signal to an initial level and/or an initial pattern of the sensor signal, wherein when a final level and/or a final pattern of the sensor signal deviates from the initial level and/or the initial pattern, the pitch control device is controlled to change the pitch angle. 
     “Initial” in this context means a sensor signal which is captured under normal operation conditions. This means, when no pitch movement is needed. “Final” in this context means a sensor signal which is captured under critical operation conditions. This means, when a pitch movement is needed to prevent damage of the pitch bearing due to weak lubrication. A “pattern” in this context means the progress of the sensor signal over a predetermined time slot. Hence, the “pattern” can be a curve displaying the sensor signal over time. 
     Furthermore, a method for preventing failure of a pitch bearing of a rotor blade of a wind turbine due to a lack of lubrication is provided. The method comprises the steps of: a) capturing a sensor signal in or at the pitch bearing by a measurement system, wherein the sensor signal represents a change in vibration, noise and/or temperature in or at the pitch bearing, and b) changing the pitch angle by a pitch control device as a function of the sensor signal to prevent failure of the pitch bearing due to a lack of lubrication. 
     In step b), the pitch angle is changed when the sensor signal indicates that the lubrication is weak. This can result in an increase in vibration, noise and/or temperature. 
     According to an embodiment, in or before step b), the sensor signal is compared with an initial level and/or an initial pattern of the sensor signal, wherein the pitch angle is changed by the pitch control device when a final level and/or a final pattern deviates from the initial level and/or the initial pattern. 
     “Deviate” in this context means that the final level and/or the final pattern has a significantly different value than the initial level and/or the initial pattern. “Significantly different” in this context can mean that the value of the final level and/or the final pattern differs from the initial level and/or the initial pattern in a distinctive factor. This factor can for example be 0.5 to 5 or the like. The factor can be chosen as needed. “Initial” in this context means a sensor signal which is captured under normal operation conditions. This means, when no pitch movement is needed. 
     “Final” in this context means a sensor signal which is captured under critical operation conditions. This means, when a pitch movement is needed to prevent damage of the pitch bearing due to weak lubrication. A “pattern” in this context means the progress of the sensor signal over a predetermined time slot. Hence, the “pattern” can be a curve displaying the sensor signal over time. 
     According to a further embodiment, the pitch angle is changed when the final level and/or the final pattern is higher than the initial level and/or the initial pattern. 
     “Higher” in this context means that the final level has a higher value that the initial level. The pitch angle can also be changed when the final level and/or the final pattern is lower than the initial level and/or the initial pattern. “Lower” in this context means that the final level has a smaller value that the initial level. 
     According to a further embodiment, the level and/or the pattern are measured throughout the operation of the wind turbine. 
     In this way, a continuous control of the pitch bearing over the lifetime thereof is possible. 
     According to a further embodiment, the pattern is a function of the sensor signal over time. 
     For example, the pattern is a function of the oscillation in Hertz over the time in milliseconds. However, the pattern can also be a function of the temperature in Degree Celsius over the time in milliseconds. 
     Further possible implementations or alternative solutions of embodiments of the invention also encompass combinations—that are not explicitly mentioned herein—of features described above or below with regard to the embodiments. The person skilled in the art may also add individual or isolated aspects and features to the most basic form of embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION 
       Some of the embodiments will be described in detail, with references to the following Figures, wherein like designations denote like members, wherein: 
         FIG. 1  shows a perspective view of a wind turbine according to one embodiment; 
         FIG. 2  shows a perspective view of a wind turbine rotor blade according to one embodiment; 
         FIG. 3  shows a cross-sectional view of the wind turbine according to  FIG. 1 ; 
         FIG. 4  shows a diagram displaying a sensor signal over time; and 
         FIG. 5  shows a block diagram of one embodiment of a method for preventing failure of a pitch bearing of the rotor blade according to  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a wind turbine  1  according to one embodiment. 
     The wind turbine  1  comprises a rotor  2  connected to a generator (not shown) arranged inside a nacelle  3 . The nacelle  3  is arranged at the upper end of a tower  4  of the wind turbine  1 . The tower  4  has a plurality of tower sections that are arranged on top of each other. The tower  4  can be named wind turbine tower. 
     The rotor  2  comprises three rotor blades  5 . The rotor blades  5  are connected to a hub  6  of the wind turbine  1 . Rotors  2  of this kind may have diameters ranging from, for example,  30  to  160  meters or even more. The rotor blades  5  are subjected to high wind loads. At the same time, the rotor blades  5  need to be lightweight. For these reasons, rotor blades  5  in modern wind turbines  1  are manufactured from fiber-reinforced composite materials. Therein, glass fibers are generally preferred over carbon fibers for cost reasons. Oftentimes, glass fibers in the form of unidirectional fiber mats are used. 
       FIG. 2  shows a rotor blade  5  according to one embodiment. 
     The rotor blade  5  comprises an aerodynamically designed portion  7 , which is shaped for optimum exploitation of the wind energy and a blade root  8  for connecting the rotor blade  5  to the hub  6 . 
       FIG. 3  shows a cross-sectional view of the wind turbine  1 . 
     As can be seen from  FIG. 3 , the nacelle  3  encases a generator  9  that is coupled to the rotor  2  to transfer the wind energy into electric energy. The nacelle  3  also encases a controller  10  and a memory  11 . The controller  10  is coupled to the generator  9 . Control of the power output of the wind turbine  1  requires the possibility to rotate the rotor blades  5 . Therefore, each rotor blades  5  is supported by a blade bearing or pitch bearing  12  connecting the blade root  8  of the rotor blade  5  to the hub  6 . In the following only one rotor blade  5  will be referred to. 
     The pitching of the rotor blade  5  is done by a pitch control device  13 . The pitch control device  13  can be part of the hub  6  and/or can be arranged inside the hub  6 . The pitch control device  13  can have an electric or hydraulic motor to pitch the rotor blade  5 . The pitch control device  13  is coupled to the controller  10 . 
     During long periods of operation, the power needs not to be adjusted by pitching the rotor blade  5 . This means that the pitch bearing  12  will be static. During this period, the load on the rotor blade  5  will be highly dynamic which can cause false brinelling and fretting corrosion on the raceway of the pitch bearing  12  unless the pitch bearing  12  is moved to a new location which allows lubricant to get onto the contact surface. Accordingly, stand still marks can occur after a given time period. This time period will depend on many factors like load level, temperature, lubrication condition, water content and so on. 
     To avoid this issue, the pitch bearing  12  can be pitched with a certain pattern which has proven to remove the risk completely under all circumstances and/or running conditions. This pattern is based on experience and tests. However, when the rotor blade  5  is pitched away from the optimal power position, there will be a loss of energy. This has to be avoided. 
     Accordingly, the wind turbine  1  has one or more sensors  14 ,  15  sensing vibration and/or noise(sound) from one or more pitch bearings  12 . For example, the sensor  14  is arranged at or inside the pitch bearing  12  or at or inside the rotor blade  5 . The sensor  15  can be placed inside the hub  6 . The number of sensors  14 ,  15  is arbitrary. Each rotor blade  5  and/or each pitch bearing  12  can comprise several sensors  14 ,  15 . The sensors  14 ,  15  are in communication with the controller  10  and the pitch control device  13 . The data received by the controller  10  is stored in the memory  11 . As shown in  FIG. 3 , the controller  10  may also be in communication with the generator  9 . 
     The controller  10  together with the sensors  14 ,  15  forms a measurement system  16  which is suitable for determining when a pitch movement of the rotor blade  5  or the pitch bearing  12  is required to avoid stand still issues. In this way, the pitch cycle strategy can go to the limit and thereby energy loss can be minimized. In other words, the amount of pitching can be reduced. The measurement system  16  initiates a pitching movement based on the sensor signals from the sensors  14 ,  15 . Unnecessary pitching is avoided. 
     This may for example be done by measuring, by one or more sensors  14 ,  15 , specific vibration and/or sound and/or noise curves and/or patterns and/or levels (e.g. mean values or similar) of the pitch bearing  12  during operation of the wind turbine  1 . Hence, when the vibration and/or sound and/or noise curves and/or patterns and/or levels of the pitch bearing  12  reach one or more specific curves and/or patterns and/or levels, the pitch bearing  12  is activated by the pitch control device  13  and moved to a chosen pitch angle, whereby the pitch bearing  12  is lubricated. 
     Any movements and/or vibrations and/or sound and/or noise from the rotating hub  6  with the rotor blades  5  and/or related movements and/or vibrations of the tower  4  and/or sound and/or noise of other mechanical induced movements and/or vibrations and/or sound and/or noise from the wind turbine  1 , e.g. from a gear or the generator  9 , may be reflected in the pitch bearing  12 . Depending on the level of lubrication inside the pitch bearing  12  and/or when false brinelling or fretting corrosion has occurred or is just about to occur, the pitch bearing  12  may vibrate and/or make a sound and/or noise in one or more specific curves and/or patterns and/or having specific levels. 
     In a further example of an embodiment of the wind turbine  1 , besides movements and/or vibrations and/or sound and/or noise sensor measurements, the sensor measurements may also comprise temperature measurements of the pitch bearing  12 . Preferably, local temperature changes close to the raceway of the pitch bearing  12  are measured and/or monitored. These temperature changes may occur when the contact zone is no longer lubricated and more frictional energy is therefore deposited into the contact zone as heat. This may be done by one or more sensors  14 ,  15  placed in or near the raceway and/or by a sensor in a ball or roller of the pitch bearing  12 . 
     Alternatively, besides measuring levels and/or curves and/or patterns, also peak, local maximum, values of the specific measuring signals may be measured to give an indication if stand still marks is about to happen or has happened and the controller  10  may thereby activate the pitch control device  13  to make the rotor blade  5  pitch or move to a specific angle to ensure lubrication in the pitch bearing  12 . 
       FIG. 4  shows a diagram where a sensor signal f, the frequency in Hertz [Hz], is displayed over time t in milliseconds [ms]. 
     As can be seen from  FIG. 4 , different levels L 1 , L 2  and/or different patterns P 1 , P 2  are measured and evaluated by the measurement system  16  indicating a specific level of lubrication inside the pitch bearing  12  and/or that false brinelling or fretting corrosion has occurred or is just about to occur in the pitch bearing  12 . A “pattern” in this context means the progress of the sensor signal f over a predetermined time slot. Hence, the “pattern” is a curve. 
     For example, a pitching movement can be necessary when the sensor signal f increases from level L 1  to level L 2  and/or when pattern P 1  of the sensor signal f switches to pattern P 2  of the sensor signal f. L 1  and P 1  indicate normal operation conditions, whereas L 2  and P 2  indicate the need for a pitch movement. Any radical change in the level L 1  and/or the pattern P 1  can require a pitch movement. 
     In  FIG. 4 , the sensor signal f means measured frequency and/or vibration levels L 1 , L 2  and/or patterns P 1 , P 2  or curves. However, the sensor signal f could as well be sound and/or noise and/or temperature levels and patterns or curves. When the specific level L 2  or pattern P 2  or curve is evaluated by the controller  10  as being critical, that means low lubrication and/or false brinelling or fretting corrosion indication or similar, the pitch bearing  12  may be activated by the pitch control device  13  and moved for a specific pitch angle. This pitch angle can be 1° or more or less. 
     Some degree of pitch activity is needed to avoid stand still issues. Therefore, the full potential of savings will not be achievable. However, the pitching could be reduced to a minimum, which would release some additional energy production. 
       FIG. 5  shows a block diagram of one embodiment of a method for preventing failure of the pitch bearing  12 . 
     “Failure” in this context includes stand still marks, false brinelling and fretting corrosion on the raceway of the pitch bearing  12  and/or any other potential damage of the pitch bearing  12  that can be caused by weak lubrication. In particular, “failure” includes stand still failure. 
     In an initial step S 1 , the sensor signal f is captured in or at the pitch bearing  12  by the measurement system  16 . The sensor signal f represents a change in vibration, noise and/or temperature in or at the pitch bearing  12 . In a step S 2 , the pitch angle is changed by the pitch control device  13  as a function of the sensor signal f to prevent failure of the pitch bearing  12  by reason of a lack of lubrication. 
     In or before step S 2 , the sensor signal f is compared with an initial level L 1  and/or an initial pattern P 1  of the sensor signal f, wherein the pitch angle is changed by the pitch control device  13  when a final level L 2  and/or a final pattern P 2  deviates from the initial level L 1  and/or the initial pattern L 1 . “Initial” in this context means a sensor signal f which is captured under normal operation conditions. This means, when no pitch movement is needed. “Final” in this context means a sensor signal f which is captured under critical operation conditions. This means, when a pitch movement is needed to prevent damage of the pitch bearing  12 . 
     The pitch angle is changed when the final level L 2  and/or the final pattern P 2  is higher than the initial level L 1  and/or the initial pattern P 1 . “Higher” in this context means that the final level L 2  has a higher value that the initial level L 1 . 
     Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention. 
     For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements. The mention of a “unit” or a “module” does not preclude the use of more than one unit or module.