Detecting properties of a moving object at a wind turbine site using a beam forming arrangement of leaky feeders

Field of Invention

The present invention relates to wind turbines. More specifi cally, the present invention relates to an apparatus for de tecting properties of a target object at a wind turbine site. The present invention further relates to a wind turbine com prising such apparatus and to a method of detecting proper ties of a target object at a wind turbine site.

Art Background

In the above defined technical field, systems are known, which comprise a plurality of radar units operatively config ured to emit and receive radar signals. The radar units are typically mounted on and around the wind turbine tower, the radar units being positioned so as to measure reflections of an emitted radar signal from the turbine blade. A processing unit is configured to receive measurement data from the radar unit and to determine, by analysis of Doppler shift, time of flight, phase and amplitude in received radar signals rela tive to transmitted signals due to movement of the blade to wards or away from the turbine tower, the velocity of the blade in the direction towards or away from the turbine tow er. This permits calculation of the trajectory and, in par ticular, the absolute speed and position of the blade.

Using radar units to measure blade position based on the Dop pler Effect is for example described in EP 2864632 and per mits to avoid the installation of other types of sensors on the blades or nacelle of the wind turbine. This reduces manu facturing and maintenance costs of the wind turbine, since sensors positioned on the tower are easier to replace in the field . However, such a solution is not yet optimal considering that for rotating objects, like the rotor blades or the nacelles, installation of a plurality of radar units is required.

A single radar unit may in fact be used but only for detect ing the passage of the blade at a single location. At least two radar units (horizontally mounted) are required for fol lowing the position of the blade around the nacelle yawing. One radar unit is able to detect the revolution of the blade at a specific position. More than two single radar units may be used for improving redundancy, resolution and confidence of the detection. However, this further increases costs and the need for software resources. Each radar unit requires a dedicated processing unit for analyzing the signals and de riving the position and speed of the blade.

Attempts using leaky feeders arranged e.g. around the wind turbine tower have been made but suffer from at least the drawback that the radiation pattern from a leaky feeder is neither very well defined nor controllable. Thus, a reasona ble signal to noise ratio requires the use of very strong signals and thus significant amounts of power and energy. Furthermore, it is not possible to vary radiation pattern in order to e.g. optimize and/or vary the direction of the emit ted signal.

There may thus be a need for an improved way of efficiently detecting properties of a target object, such as a rotating rotor blade of a wind turbine, in a flexible manner.

Summary of the Invention

This need may be met by the subject-matter according to the independent claims. Advantageous embodiments of the present invention are set forth in the dependent claims. According to a first aspect of the present invention, an ap paratus for detecting one or more properties of a target ob ject at a wind turbine site is provided. The apparatus com prises (a) a leaky feeder arrangement comprising a plurality of parallel leaky feeders, (b) a transmitter coupled to the leaky feeder arrangement and configured to supply individual first radar signals to a group of leaky feeders in the leaky feeder arrangement, the individual first radar signals being configured to form a first radar signal beam in a predeter mined direction relative to the leaky feeder arrangement, (c) a receiver coupled to the leaky feeder arrangement and con figured to receive a second radar signal from the leaky feed er arrangement, wherein the second radar signal is reflected from the target object when the first radar signal beam hits the target object, and (d) a processing unit configured to analyse a first signal corresponding to the first radar sig nals and a second signal corresponding to the second radar signal in order to determine the one or more properties of the moving object.

This aspect of the invention is based on the idea that paral lel leaky feeders in a leaky feeder arrangement are supplied with individual signals (first radar signals) in such a way that the corresponding emitted (leaked) radar signals combine to form a radar signal beam in a predetermined direction. In other words, the group of leaky feeders is capable of beam forming. Thereby, energy consumption can be kept low as the irradiated energy is concentrated in the desired direction, and the direction can be chosen and varied in dependency on the circumstances and tasks to be carried out.

According to an embodiment of the invention, the transmitter is configured to generate the individual first radar signals by applying individual phase shifts to the first signal or by applying an amplitude modulation to the first signal.

By supplying individually phase shifted versions of the first signal to each leaky feeder in the group, the signals propa- gating along the parallel leaky feeders in the group will have different phases and thus be delayed relative to each other, such that a beam is formed in the predetermined direc tion .

A similar beam forming effect can be achieved by applying am plitude modulation to the first signal.

According to a further embodiment of the invention, the leaky feeders in the group of leaky feeders are arranged with a predetermined distance between neighbouring leaky feeders.

In other words, the radial distance between any pair of neighbouring leaky feeders in the group is the same.

According to a further embodiment of the invention, each leaky feeder in the leaky feeder arrangement comprises a plu rality of leaky sections at corresponding positions in the longitudinal direction of the leaky feeders.

In other words, each leaky feeder comprises a plurality of leaky sections (for leaking or emitting the respective indi vidual first radar signals and/or for receiving the reflected second radar signal) and these leaky sections are located at corresponding positions in the sense that a line perpendicu lar to the longitudinal direction of the parallel leaky feed ers will pass through a leaky section of each leaky feeder.

According to a further embodiment of the invention, the leaky feeder arrangement comprises at least one leaky feeder which is not part of the group of leaky feeders and configured to receive the second radar signal.

In this embodiment, the second radar signal (i.e. the radar signal reflected from the target object) is received by a leaky feeder in the leaky feeder arrangement, which is not part of the group that emits the phase shifted first radar signals forming the first radar signal beam. According to a further embodiment of the invention, the leaky feeder arrangement comprises a further group of leaky feeders which are not part of the group of leaky feeders and config ured to receive the second radar signal.

In this embodiment, the second radar signal (i.e. the radar signal reflected from the target object) is received by a further group of leaky feeders which are not part of the group of leaky feeders that transmit the first radar signals.

According to a further embodiment of the invention, the re ceiver is configured to apply individual phase shifts to the second radar signal received by the leaky feeders in the fur ther group of leaky feeders, thereby forming a second radar signal beam in a further predetermined direction relative to the leaky feeder arrangement.

In other words, the receiver uses the leaky feeders in the further group to perform beam forming with regard to the re ceived (second) radar signal. This is advantageous in that it allows the apparatus to configure independent transmitting and receiving beams and thereby to adapt to changing blade properties, such as bending under variable loading conditions and resulting changes in the reflection angle at the blade.

By determining the change in receiving beam direction needed to obtain maximum signal strength of the received signal, a current bending state of the rotor blade can e.g. be deter mined .

According to a further embodiment of the invention, at least one leaky feeder in the group of leaky feeders is configured to receive the second radar signal.

In this embodiment, the second radar signal (i.e. the radar signal reflected from the target object) is received by a leaky feeder in the leaky feeder arrangement, which is also part of the group that emits the phase shifted first radar signals forming the first radar signal beam.

According to a further embodiment of the invention, each leaky feeder in the leaky feeder arrangement is a leaky coax ial cable or a leaky waveguide.

A coaxial leaky cable may in particular be suitable in imple mentations where the first and second radar signals are RF signals. A leaky waveguide or a leaky stripline may in par ticular be suitable for embodiments where the first and sec ond radar signals have higher frequencies.

According to a further embodiment of the invention, the leaky feeder arrangement is configured to form an arc or loop, e.g. around a wind turbine tower.

Thereby, by arranging the at least one leaky feeder in a suitable height (e.g. corresponding to the height in which a particular rotor blade section, such as a tip or mid section passes), reflections from the rotor blade will be received for any yaw angle (which may be set in dependency of the wind direction) .

According to a further embodiment of the invention, the tar get object is a moving object of a wind turbine or a moving object external to a wind turbine.

A moving object of a wind turbine may in particular be a ro tor blade or the nacelle. External objects may e.g. be birds or waves (in case of off shore installations) .

According to a further embodiment of the invention, the mov ing object is a wind turbine rotor blade, and the one or more properties comprise one or more of a rotor blade position, a rotor blade speed, a rotor blade distance from tower, a rotor blade size, a rotor blade soiling state, and structural changes inside the rotor blade. In other words, the properties span from parameters relating to spatial position and movement of the blade to analysis of the rotor blade surface geometry and properties (which chang es in case of soiling) .

As can be seen, the apparatus may also be used to detect oth er objects, such as birds, bats, ice, intruders, and sea waves, i.e. for the detection of height, direction and speed of waves in offshore applications.

According to a further embodiment of the invention, the transmitter is configured to vary the predetermined direction during operation in order to scan a predetermined region.

Thereby, a surface section of a rotor blade may e.g. be ana lysed.

According to a second aspect of the invention, a wind turbine is provided. The wind turbine comprises an apparatus accord ing to the first aspect or any of above embodiments, wherein leaky feeder arrangement is arranged at a tower or a nacelle of the wind turbine.

This aspect is essentially based on the same idea as the first aspect discussed above.

The leaky feeder arrangement may be geometrically configured as an arc around the tower. In particular, the leaky feeder arrangement may be geometrically configured as a loop (or part/segment of a loop) surrounding the tower of the wind turbine. Thereby, by arranging the at least one leaky feeder in a suitable height (e.g. corresponding to the height in which a particular rotor blade section, such as a tip or mid section passes), reflections from the rotor blade will be re ceived for any yaw angle (which may be set in dependency of the wind direction) . According to a third aspect of the invention, a method of de tecting one or more properties of a target object at a wind turbine site is provided. The method comprises (a) providing a leaky feeder arrangement comprising a plurality of parallel leaky feeders, (b) supplying individual first radar signals to a group of leaky feeders in the leaky feeder arrangement, the individual first radar signals being configured to form a first radar signal beam in a predetermined direction relative to the leaky feeder arrangement, (c) receiving a second radar signal from the leaky feeder arrangement, wherein the second radar signal is reflected from the target object when the first radar signal beam hits the target object, and (d) ana lysing a first signal corresponding to the first radar sig nals and a second signal corresponding to the second radar signal in order to determine the one or more properties of the moving object.

This aspect is essentially based on the same idea as the first aspect discussed above.

Brief Description of the Drawings

The aspects defined above and further aspects of the present invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to the examples of embodiment. The invention will be described in more detail hereinafter with reference to examples of embodi ment but to which the invention is not limited.

Figure 1 shows a schematic section of a wind turbine utiliz ing embodiments of the present invention.

Figure 2 shows a group of parallel leaky feeders of an appa ratus according to an exemplary embodiment of the present in vention .

Figure 3 shows the group of parallel leaky feeders depicted in Figure 2 when mounted on a wind turbine tower. Figure 4 illustrates the principle of beam forming with the group of leaky feeders shown in Figure 2 and Figure 3 in ac cordance with an exemplary embodiment of the present inven tion .

Detailed Description

The illustrations in the drawings are schematic. It is noted that in different figures, similar or identical elements are provided with the same reference numerals or with reference numerals which differ only within the first digit.

Figure 1 shows a partial cross-sectional view of a wind tur bine 1 utilizing an apparatus 10 for detecting properties of rotor blade 4 of the wind turbine in accordance with the in vention .

More specifically, the wind turbine 1 comprises a tower 2, which is mounted on a non-depicted fundament. A nacelle 3 is arranged on top of the tower 2. In between the tower 2 and the nacelle 3, a yaw angle adjustment device (not shown) is provided, which is capable of rotating the nacelle around a vertical yaw axis Z. The wind turbine 1 further comprises a wind rotor 5 having one or more rotor blades 4 (in the per spective of Figure 1 only two blades 4 are visible) . The wind rotor 5 is rotatable around a rotational axis Y. In general, when not differently specified, the terms axial, radial and circumferential in the following are made with reference to the rotational axis Y. The rotor blades 4 extend radially with respect to the rotational axis Y. The wind turbine 1 comprises an electric generator 6 having a stator 11 and a rotor 12. The rotor 12 is rotatable with respect to the sta tor 11 about the rotational axis Y to generate electrical power. The electric generator 6 and the generation of elec trical power through the present invention is not a specific object of the present invention and will therefore not be de scribed in further detail. Figure 1 further shows an apparatus 10 according to the pre sent invention. The apparatus 10 comprises a leaky feeder ar rangement 20 mounted at the tower 2, and a transmitter 30 and a receiver 40 coupled to the leaky feeder arrangement 20. The transmitter 30 is configured to supply first radar signals to the leaky feeder arrangement 20 while the receiver 40 is con figured to receive a second radar signal from the leaky feed er arrangement 20, e.g. a radar signal reflected from the ro tor blade 4 when the first radar signals hit the rotor blade 4. The apparatus further comprises a processing unit (not shown) configured to analyse a first signal corresponding to the first radar signals and a second signal corresponding to the second radar signal in order to determine one or more properties of the target object, e.g. in this case the rotor blade 4.

Figure 2 shows an example of the leaky feeder arrangement 20 in more detail. As shown, the leaky feeder arrangement com prises a group of parallel leaky feeders 21, 22, 23. The first leaky feeder 21 comprises leaky sections 211, 212, 213, the second leaky feeder 22 comprises leaky sections 221, 222, 223, and the third leaky feeder 23 comprises leaky sections 231, 232, 233. The leaky sections 211, 221, 231 are posi tioned above each other in the drawing, i.e. in such a way that a line perpendicular to the longitudinal or axial direc tion of the leaky feeders 21, 22, 23 and extending through any of the leaky sections 211, 221, 231 will also extend through the other two leaky sections. Leaky sections 212,

222, 232 are positioned above each other in the same sense, as are leaky sections 213, 223, 233. The distance between each pair of neighbouring leaky feeders, i.e. between leaky feeders 21 and 22 and between leaky feeders 22 and 23, is equal to D. All three leaky feeders 21, 22, 23 are coupled to transmitter 30 which is configured to supply an individual first radar signal to each leaky feeder 21, 22, 23. The leaky feeders 21, 22, 23 may in particular be leaky coaxial cables, leaky waveguides or leaky striplines. Figure 3 shows the group of parallel leaky feeders 21, 22, 23 depicted in Figure 2 as mounted on the wind turbine tower 2 in Figure 1. Each leaky feeder 21, 22, 23 forms an arc or a loop around at least a part of the tower circumference at a height where a tip section of rotor blade 4 passes by, such that the leaky feeders 21, 22, 23 can emit first radar sig nals away from the tower around at least a part of, prefera bly around the entire circumference of the tower 2 and there by detect the rotor blade 4 for many or all possible yaw an gles (corresponding to wind directions) . Although Figure 3 only shows leaky feeders 21, 22, 23 at one side of the tower 2, it is preferable that the leaky feeders 21, 22, 23 sur round the entire circumference of the tower, such that first radar signals can be emitted towards the rotor blade for any given yaw angle between 0° and 360°. In other words, the leaky feeders 21, 22, 23 will emit first radar signals around the entire circumference of the tower 2, such that the direc tional characteristic of the leaky feeder arrangement 20 has the shape of a torus or donut which is focussed in a specific elevation angle.

Figure 4 illustrates the principle of beam forming with the group of leaky feeders 21, 22, 23 shown in Figure 2 and Fig ure 3 in accordance with an exemplary embodiment of the pre sent invention. Here, the individual first radar signals sup plied to neighbouring leaky feeders in the group of leaky feeders 21, 22, 23 are phase shifted by a certain amount Df. In other words, the phase of the first radar signal supplied to leaky feeder 21 is lagging the phase of the first radar signal supplied to leaky feeder 22 by the amount Df. Similar ly, the phase of the first radar signal supplied to leaky feeder 22 is also lagging the phase of the first radar signal supplied to leaky feeder 23 by the amount Df. If more than three leaky feeders are used, this will continue such that the phase between any pair of neighbouring leaky feeder sig nals differ by the same amount Df. As shown in Figure 4, this causes a plane wave front W to propagate in the direction in- dicated by arrow P. The angle between the direction of propa gation P and the direction A (which is perpendicular to the leaky feeder arrangement) is indicated as v. With knowledge of the distance D between the leaky feeders 21, 22, 23, a de sired value of the angle v can be obtained by choosing the value of the phase shift Df as

D sin v

Af = 2p l where l is the wavelength of the signal.

By varying the phase shift Df rapidly, a surface (e.g of a rotor blade or another target object) can be scanned.

The leaky feeder arrangement 20 also comprises at least one leaky feeder for receiving the reflected signal which is pro cessed by a processing unit (not shown) together with the first signal in order to obtain the desired properties of the target object. The receiving leaky feeder may be a separate leaky feeder or one (or more) of the leaky feeders 21, 22, 23 used to transmit the phase shifted signals. Alternatively, a further group of leaky feeders may be provided to receive the reflected signal. In this case, the receiver 40 may further be configured to apply individual phase shifts to the re ceived signals in order to also form a receiving beam.

As shown in Figure 3, each leaky feeder 21, 22, 23 comprises a plurality of slots that allow the corresponding first radar signal to leak out of the leaky feeder along its entire length and towards the target object, e.g. rotor blade 4. The slots may, according to possible embodiments, be regularly distributed along the length of the leaky feeder 21, 22, 23. According to other possible embodiments of the present inven tion, the leaky feeders 21, 22, 23 are a normal coaxial cable with low optical coverage of the outside conductor (mesh or slots/apertures), which also leaks electromagnetic waves. The leaky feeders 20 may be provided with a heating system (not shown) in case severe over icing conditions are possi ble. Heating may be provided by air flowing between inside and outside conductors or by electrical current which runs in inner or outer conductors of the leaky feeders 20.

The first radar signal may, according to possible embodi ments, be an electromagnetic radar signal or an ultrasonic radar signal. In case of an electromagnetic radar signal, the leaky feeders 20 are preferably configured as leaky coaxial cables. According to other embodiments, particularly where the first radar signal 100 is an electromagnetic signal of higher frequency, the leaky feeders 20 are preferably config ured as leaky waveguides.

In general, according to different embodiments of the present invention, the first radar signal may be of any frequency, provided that it can be transmitted to the target object and be reflected by the same.

When the first radar signal beam W impinges on or hits the rotor blade 4, a reflected second radar signal is transmitted towards the leaky feeder arrangement 20. The plurality of slots of one or more of the leaky feeders in the arrangement 20 allow the second radar signal to leak into the correspond ing leaky feeder (s) and propagate towards the receiver 40.

The processing unit (not shown) may e.g. determine the posi tion and/or the speed of rotor blade 4 by analysing a first signal corresponding to the first radar signals (i.e. the transmitted radar signal beam W) and a second signal corre sponding to the second radar signal (i.e. the reflected radar signal) . The processing unit generates the first signal and transmits it to the transmitter 30 (e.g. via an optical link) . The processing unit receives the second signal from the receiver 40 (e.g. via an optical link) . Thereby, a closed loop is formed that allows precise determination of the posi tion and/or speed of rotor blade 4. The processing unit analyses the first signal (corresponding to first radar signal beam) and the second signal (corre sponding to the second radar signal) for determining the po sition, speed, direction and size of the target object. Ac cording to known (radar) principles with regard to amplitude, phase, Doppler effect and ToF (Time of Flight) , the pro cessing unit is able to compare the first signal and the sec ond signal caused by a moving object and consequently to de termine the speed and/or position and/or direction and/or size of such object. The position of such object may be an angle with respect to a rotational axis or the three- dimensional position with respect to a system of Cartesian axes .

According to other embodiments of the present invention, the target object is the nacelle 2 for the detection of the posi tion of the nacelle about the vertical yaw axis Z.

According to other embodiments of the present invention, oth er target objects may be detected in an area comprising a wind turbine 1, for example animals or intruders or changing waves (in offshore applications) . In such embodiments, the leaky feeder arrangement 20 and associated electronics

(transmitter 30, receiver 40, and processing unit) may not be located on the wind turbine tower 2, but instead on another structural element, possibly external to the wind turbine 1, such as a support structure or transition element.

It should be noted that the term "comprising" does not ex clude other elements or steps and "a" or "an" does not ex clude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be con strued as limiting the scope of the claims.