Embodiments of the present invention are generally related to controlling and/or regulating or monitoring the operation of wind turbines. Embodiments are in particular related to devices and methods including a strain and vibration measuring system.
Wind turbines are subjected to a complex control or regulation, which may be required, for example, by changing operational conditions. Furthermore, measurements are necessary for monitoring the state of a wind turbine. Due to the conditions linked with the operation of a wind turbine, for example, temperature variations, weather and meteorological conditions, but also in particular strongly varying wind conditions, as well as due the multitude of safety measures prescribed by law, monitoring and the sensors necessary for monitoring are subjected to a plurality of constraints.
Rotor blades may be equipped with strain sensors, acceleration sensors or further sensors in order to detect blade loads, accelerations or further physical measurement parameters. The document US 2009/0246019 describes a measurement system comprised of four strain sensors in the blade root for ice detection. The document WO 2017/000960 A1 describes a method for measuring the load of a wind turbine and a wind energy plant for such a load measurement. Load sensors are configured to measure a mechanical deformation of the root end of the blade. Load sensors may be optical strain gauges such as e.g. fiber Bragg gratings. A triaxial acceleration sensor for blade state monitoring is described in WO 1999/057435.
In monitoring operational states of wind turbines, a plurality of sensors is used. Strain measurements for measuring the bending of a rotor blade, acceleration measurements for measuring an acceleration of the rotor blade, or other parameters may be measured, for example. One group of sensors seeming to promise success for further applications, are fiber optic sensors. It is therefore desirable to further improve measurements for monitoring a wind turbine with fiber optic sensors.
In general, it is therefore desirable to enable improvements in controlling and monitoring in sensors for a rotor blade of a wind turbine, in rotor blades for wind turbines, and in wind turbines themselves.
According to one embodiment, an assembly for monitoring and/or controlling a wind turbine is provided. The assembly for monitoring and/or controlling a wind turbine includes an arrangement of at least two strain sensors, in particular three strain sensors, which detects blade bending moments of a rotor blade of a wind turbine in at least two different spatial directions; a first fiber optic vibration sensor for detecting vibrations of the rotor blade in a first spatial direction; and at least one second fiber optic vibration sensor for detecting vibrations of the rotor in a second spatial direction, which differs from the first spatial direction.
According to a further embodiment, a method for monitoring and/or controlling a wind turbine is provided The method includes measuring vibrations of a rotor blade of the wind turbine in two different spatial directions, wherein the measuring of vibrations is performed by means of at least two fiber optic vibration sensors; measuring bending moments of the rotor blade of the wind turbine in at least two different spatial directions; and monitoring and/or controlling the wind turbine based on the vibrations in the two different spatial directions of the measurement of vibrations, and the bending moments in the at least two different spatial directions of the measurement of bending moments.
Exemplary embodiments are shown in the drawings and explained in more detail in the description below. In the drawings:
In the drawings, identical reference numerals denote identical or functionally identical components or steps.
Hereinafter, more detailed reference is made to various embodiments of the invention, with one or more examples being illustrated in the drawings.
Wind turbines can be monitored and regulated by measurement technological systems in the rotor blades. Hereby, one or more of the following applications may be implemented: individual pitch control of a rotor blade, buoyancy optimization of a rotor blade, load regulation of a rotor blade or the wind turbine, load measurement on a rotor blade or the wind turbine, determination of the state of components of the wind turbine, for example, determination of the state of a rotor blade, ice detection, lifetime estimation of components of the wind turbine, for example, a rotor blade, regulation based on wind fields, regulation based on trailing effects of the rotor, regulation based on loads, regulation of the wind turbine with respect to adjacent wind turbines, predictive maintenance, tower clearance measurement, peak load switch-off, and detection of imbalance.
Embodiments of the present invention are related to a combination of strain and vibration sensors in the rotor blade of a wind turbine. Here, it is possible to obtain a complete image on the blade load and vibration of a rotor blade of a wind turbine, wherein an optimized relationship between redundancy of components and material usage (CoO=cost of ownership) can be achieved. Furthermore, there is the option of new applications for optimizing wind turbines.
According to further embodiments, the vibration sensors may preferably be arranged in an area radially directed outward, i.e. toward the blade tip. The vibration sensors can be provided, for example, at a radial position in the area of the outer 80% to the outer 60% of the radius of a rotor blade of the wind turbine, as shown by the area 107 in
According to embodiments described herein, an arrangement of sensors in an area facing the blade tip is in particular enabled by the use of fiber optic sensors, for example, fiber optic vibration sensors. Fiber optic sensors can be provided without electrical components. This allows to avoid that a lightning strike takes place directly into electronic components and/or cables or signal cables for electronic components. Even in case of conducting a lightning strike via an arrester, i.e. in case of controlled conducting to ground potential, a damage in cables or signal cables by the currents generated by induction can be prevented. According to embodiments described herein, fiber optic vibration sensors are preferably used as will be explained in more detail with reference to
According to some embodiments, which can be combined with other embodiments, the vibration sensors (110/112) are fiber optic vibration sensors. For fiber optic vibration sensors, an optical signal is transmitted to the evaluation unit 114 by means of a light guide 212, for example, an optical fiber. In a fiber optic vibration sensor, the sensor element itself can be provided outside an optical fiber. As an alternative to this, the actual sensor element can be provided inside an optical fiber, for example, in the form of a fiber Bragg grating, in a fiber optic vibration sensor. This will be described in detail with reference to
The embodiments and applications mentioned above may be enabled by a combination of strain sensors and vibration sensors in the rotor blade. According to embodiments described herein, three strain sensors and two vibration sensors are used as is illustrated in
The use of three strain sensors allows redundancy and thus increased safety against failures to be realized. According to embodiments described herein, it is moreover possible to use temperature-compensated strain sensors, in particular temperature-compensated fiber optic strain sensors. The use of temperature-compensated strain sensors allows the temperature influence on the determination of the blade bending moments to be minimized. Fiber optic strain sensors moreover enable high reliability of the blade bending moment determination due to their high peak load resistance and steady load resistance.
Vibration sensors in the rotor blade allow vibrations of the rotor blade to be determined, and thus applications, e.g. for blade state monitoring or ice detection, to be realized. The use of passive fiber optic sensors enables blade vibration without influence by electromagnetic fields or high electrical currents, such as e.g. lightning flashes, to be measured reliably.
The combination of measuring strain and vibration in the rotor blade enables the applications mentioned above. Moreover, the combination of the signals allows a more extensive view to be gained on the state and the operation of the wind turbine, whereby further applications may result. A complete view on the blade load and vibration of a rotor blade of a wind turbine can be provided. The result will be the option of realizing new applications for optimizing wind turbines. Embodiments of the present invention are related to the combination presented here of strain and vibration sensors in the rotor blade of a wind turbine. The use of two vibration sensors and three strain sensors allows a favorable relationship between material expenditure and redundancy to be provided.
According to some of the embodiments described herein, vibration sensors, in particular fiber optic vibration sensors, may be configured to measure a shift of vibration frequency. For example, a vibration sensor may not refer to absolute accelerations or measurements in frequency ranges. This may take place in the scope of an evaluation or by a corresponding analysis of optical fibers of a fiber optic vibration sensor, for example. According to further embodiments, vibration sensors may cover a frequency range from 0.1 Hz up to higher frequencies. A high-pass filter may be used, for example, in order to filter absolute accelerations occurring due to the rotation of the rotor from the signal.
According to some embodiments described herein, which can be combined with other embodiments, fiber optic vibration sensors and/or strain sensors enable measurements for monitoring the applications described herein. Furthermore, the fiber optic sensors allow risks in case of lightning strike to be reduced, and an optical transmission can reduce the maintenance expenditure.
In general, the blade bending moments can be determined by two strain sensors, for example, in the flapping direction and swing direction. According to the IEC 61400-13 standard, the blade strains are determined by means of four strain sensors. If the survival probabilities of a strain sensor are regarded statistically, three strain sensors will result in a significant increase of the survival probability of the entire system as compared to a system with two strain sensors. A further increase of the survival probability of the entire system by four sensors, however, is correspondingly low. An arrangement 120 of three strain sensors for determining blade bending moments of a rotor blade of a wind turbine thus offers a similarly high survival probability of the entire system for determining blade bending moments at reduced material expenditure and thus reduced CoO. At the same time, three strain sensors allow the centripetal forces and constant components of temperature effects to be compensated for. According to typical embodiments, the strain sensors may be fiber optic strain sensors. Moreover, it is possible to use temperature-compensated fiber optic sensors.
The embodiments and applications described above can be enabled by a combination of strain sensors and vibration sensors. According to some embodiments described herein, two strain sensors can also be used as shown in
According to some embodiments, and as illustrated in
According to embodiments described herein, and as illustrated in
λB=2·nk·Λ.
In this case, nk is the effective refractive index of the basic mode of the core of the optical fiber, and Λ is the spatial grating period (modulation period) of the fiber Bragg grating 506.
A spectral width given by the full width at half maximum of the reflection response depends on the expansion of the fiber Bragg grating 506 along the sensor fiber. Due to the effect of the fiber Bragg grating 506, light propagation within the sensor fiber or the light guide 212, for example, is dependent on forces, moments and mechanical tensions and temperatures applied to the sensor fiber, i.e. the optical fiber, and in particular the fiber Bragg grating 506 within the sensor fiber.
As shown in
In a case, where the electromagnetic radiation 14 or the primary light is irradiated in a wide spectral range, a transmission minimum will result in the transmitted light 16 at the place of the Bragg wavelength. In the reflected light, a reflection maximum will result at this place. Detecting and evaluating the intensities of the transmission minimum or the reflection maximum, or of intensities in corresponding wavelength ranges, will generate a signal, which can be evaluated with respect to the length change of the optical fiber or the light guide 112 and is thus indicative of the forces or vibrations.
The fiber optic sensor element 610 such as a fiber Bragg grating (FBG) or an optical resonator, for example, is integrated into a sensor fiber or optically coupled to the sensor fiber. The light reflected from the fiber optic sensor elements is in turn guided via the fiber coupler 604, which guides the light via the transmission fiber 605 to a beam splitter 606. The beam splitter 606 splits the reflected light for detection by means of a first detector 607 and a second detector 608. On this occasion, the signal detected on the second detector 608 is first filtered by means of an optical edge filter 609.
The edge filter 609 allows a shift of the Bragg wavelength at the FBG or a wavelength change due to the optical resonator to be detected. In general, a measurement system as illustrated in
In particular when several FBGs are used, additional optical filter means (not shown) may be provided for filtering the optical signal or secondary light. An optical filter means 609 or additional optical filter means may comprise an optical filter selected from the group consisting of a thin film filter, a fiber Bragg grating, an LPG, an arrayed waveguide grating (AWG), an Echelle grating, a grating array, a prism, an interferometer and any combination thereof.
A further aspect in monitoring wind turbines, which can be combined with other embodiments and aspects described herein, but which is also provided independently of further embodiments, aspects and details, is an improved method for monitoring and controlling and/or regulating a wind turbine by means of vibration sensors and strain sensors, in particular fiber optic vibration sensors and fiber optic strain sensors. One or more of the following applications may be implemented: individual pitch control of a rotor blade, buoyancy optimization of a rotor blade, load regulation of a rotor blade or the wind turbine, load measurement on a rotor blade or the wind turbine, determination of the state of components of the wind turbine, for example, determination of the state of a rotor blade, ice detection, lifetime estimation of components of the wind turbine, for example, a rotor blade, regulation based on wind fields, regulation based on trailing effects of the rotor, regulation of the wind turbine based on loads, regulation of the wind turbine with respect to adjacent wind turbines, predictive maintenance, tower clearance measurement, peak load switch-off, and detection of imbalance. According to such an aspect or such an embodiment, a method for monitoring or controlling and/or regulating a wind turbine is provided. The method for monitoring a wind turbine includes measuring vibrations with two vibration sensors in two spatial directions and measuring bending moments in at least two different spatial directions, for example, three different spatial directions (see reference numeral 702 in
Although the present invention has been described above on the basis of typical embodiments, it is not restricted thereto but can be modified in a number of ways. The invention is not restricted to the mentioned options of application either.
Number | Date | Country | Kind |
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10 2017 115 927.4 | Jul 2017 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2018/069033 | 7/12/2018 | WO | 00 |