Obstacle warning system

Abstract

A method of operating an obstacle warning system (4) for a wind turbine facility (2) comprises operating a radar system (14) to obtain scan data of an area around the facility (2); analyzing the scan data to identify a pair of signals, the pair of signals comprising a first signal corresponding to a first location (34) and a second signal corresponding to a second location (32), the first location (34) being spaced apart from the second location (32); comparing the first signal and the second signal to determine a value indicative of a performance of the radar system (14) for an area comprising the second location (32); and activating the warning system (4) if the value is below a threshold value.

Description

Technical Field

[0001] The present invention relates to obstacle warning systems for fixed installations such as wind turbine installations. In particular, the present invention relates to systems configured to avoid collisions by activating warning lights or other alarms when a nearby aircraft is detected using a radar system, also known as obstacle collision avoidance systems. Background Art

[0002] To comply with national and international regulations, structures of a certain height that pose a potential obstacle to aircraft may be required to use warning lights at night to alert nearby aircraft to the structure's presence, thereby reducing the risk of aircraft colliding with the structure. Such structures may include facilities such as wind turbine installations (also known as "wind farms" or "wind parks") that include one or more wind turbines.

[0003] However, permanent nighttime lighting can lead to light pollution, which can be problematic in areas where dark night skies are desirable, such as those with nearby populations or observatories. Wind turbine lighting can also be harmful to local wildlife, which may be attracted to the lights.

[0004] Therefore, it is desirable to limit lighting used for warning purposes to situations where aircraft are nearby, thereby meeting regulatory requirements while also reducing light pollution. To this end, known obstacle warning systems use radar (radio detection and ranging) systems to detect nearby aircraft and activate warning lights when an aircraft enters a regulatory "warning zone" around the facility. For example, such a warning zone may cover an area with a radius of 4 to 6 kilometers around the facility. When no aircraft are detected within the warning zone, the warning lights may be turned off.

[0005] However, in some cases, such as due to a malfunction or when unfavorable weather conditions prevail, the range of the radar signal may be reduced. This creates the possibility that the radar system will not detect the aircraft before it enters the warning zone.

[0006] The present invention has been designed under this background. Summary of the Invention

[0007] One aspect of the present invention provides a method of operating an obstacle warning system for a wind turbine installation. The method includes: operating a radar system to obtain scan data of an area surrounding the installation; analyzing the scan data to identify a pair of signals, the pair of signals including a first signal corresponding to a first location and a second signal corresponding to a second location, the first location being spaced apart from the second location; comparing the first signal and the second signal to determine a value indicating the performance of the radar system for an area including the second location; and activating the warning system if the value is below a threshold.

[0008] Comparing a pair of signals that correspond to known locations and therefore have expected characteristics relative to each other enables the identification of changes in radar system performance. For example, under ideal conditions, there may be a known and expected difference between the power of the first signal and the power of the second signal, in which case a change in this power difference indicates a change in radar system performance.

[0009] If the value indicating radar system performance falls below a threshold, this may mean that the radar system cannot be relied upon to detect incoming hazards, such as aircraft, before they enter the warning zone surrounding the facility. By automatically activating the warning system in such circumstances, a warning is provided to any such hazards that may be present, even though they may not be detected, thereby reducing the risk of collision.

[0010] The first signal and the second signal relate to respective known geographic locations in the area surrounding the facility, for example, as indicated by the respective directions of origin of the first and second signals. Note that these signals may not actually originate from the intended corresponding locations, for example, if there is interference or obstruction, such as rain or other precipitation, that reflects the signals back toward the radar system before they reach the intended location. This can be discerned to some extent from the characteristics of the signals, for example, if the power difference between the signals is smaller than typical.

[0011] Although the first location is spaced apart from the second location, typically these locations are close together and at similar distances from the radar system.

[0012] The first position may define a baseline position, in which case the first signal defines the baseline signal. Correspondingly, the second position may define a reference position, in which case the second signal defines the reference signal.

[0013] The method may comprise comparing the respective strengths of the pair of signals.

[0014] The value indicative of radar system performance can represent a signal-to-noise ratio of the pair of signals. In this regard, the first location can be selected such that the first signal represents the noise floor near the second location, while the second location can be selected based on the signal from that location having higher power under normal conditions, for example due to the presence of a reflective feature at the second location. In this case, comparing the second signal with the first signal enables calculation of the signal-to-noise ratio of the pair of signals. A decrease in the signal-to-noise ratio of the pair of signals indicates a corresponding decrease in radar system performance, for example due to the signals containing increased clutter levels.

[0015] The threshold may define a noise level. For example, if a signal-to-noise ratio of the pair of signals is determined, this ratio may be compared to a threshold signal-to-noise ratio value to evaluate the performance of the radar system.

[0016] The method may include identifying and comparing a plurality of pairs of signals in the scan data, each pair of signals including a respective first signal and a respective second signal corresponding to a respective first location and a second location. Each first signal in the plurality of pairs of signals may be associated with a different location within an area surrounding the facility.

[0017] The method may include evaluating the performance of the radar system. Evaluating the performance of the radar system may include estimating the range of the radar system, for example, in which case the value indicative of the performance of the radar system may represent the estimated range of the radar system. Alternatively or additionally, evaluating the performance of the radar system may include estimating a loss factor.

[0018] Analyzing the scan data may include comparing the scan data to calibration data.

[0019] The method may be preceded by a calibration routine, the calibration routine comprising operating the radar system to obtain calibration scan data for an area surrounding the facility. The calibration scan data comprises data relating to a first location and a second location.

[0020] The calibration routine may include analyzing the calibration scan data to identify a reference feature, whereby the position of the reference feature defines the second position. The reference feature may be a highly reflective feature, such as a building or a geographical feature. Similarly, the calibration routine may include analyzing the calibration scan data to identify the first position.

[0021] During the calibration routine, the signal received from the second location may have a higher power than the signal received from the first location. In this regard, the calibration routine may include identifying the first location and the second location based on the strength of the signal received by the radar system from these locations. The signal strength may be monitored over a specified period of time to assess signal stability, in which case only locations where sufficiently stable signals are received may be selected as the first location and / or the second location.

[0022] Activating the warning system may include operating a warning light, and optionally a plurality of lights. Operating a light may include causing the light to flash.

[0023] Separately from the result of the comparison of the value indicative of the performance of the radar system with the threshold value, the method may include activating a warning system if the scanning data indicates the presence of an aircraft in the area surrounding the installation.

[0024] The warning system may be configured to alert the aircraft to the presence of the facility.

[0025] Another aspect of the present invention provides a method for calibrating an obstacle warning system for a wind turbine installation. The method includes operating a radar system to obtain calibration scan data for an area surrounding the installation; and analyzing the calibration scan data to identify a pair of signals, the pair comprising a first signal corresponding to a first location and a second signal corresponding to a second location, the first location being spaced apart from but in close proximity to the second location. The second signal has a higher power than the first signal. The strengths of the first and second signals may be monitored over a predetermined period of time, in which case the first and second signals may be identified based on sufficiently stable signal strengths. The first signal may represent the noise floor at the second location.

[0026] Another aspect of the present invention provides an obstacle warning system for a wind turbine installation. The system includes a radar system configured to obtain scanning data of an area surrounding the installation; a warning device; and a control system. The control system is configured to: analyze the scanning data to identify a pair of signals, the pair of signals including a first signal corresponding to a first location and a second signal corresponding to a second location, the first location being spaced apart from the second location; compare the first signal and the second signal to determine a value indicating the performance of the radar system for the area including the second location; and activate the warning device if the value is below a threshold.

[0027] Another aspect of the present invention provides a controller or control system for an obstacle warning system for a wind turbine installation. The control system is configured to: analyze scanning data obtained by a radar system to identify a pair of signals, the pair of signals including a first signal corresponding to a first location and a second signal corresponding to a second location, the first location being spaced apart from the second location; compare the first signal and the second signal to determine a value indicating the performance of the radar system for an area including the second location; and generate a control signal if the value is below a threshold, the control signal being configured to activate the warning device.

[0028] It will be appreciated that preferred and / or optional features of each aspect of the present invention may also be incorporated into other aspects of the present invention, either alone or in appropriate combinations. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] For a more complete understanding of the present invention, the invention will now be described, by way of example only, with reference to the following drawings in which like features are assigned like reference numerals, and in which:

[0030] Figure 1 is a schematic diagram of a wind power plant including an obstacle warning system according to an embodiment of the present invention;

[0031] Figure 2 yes Figure 1 a schematic diagram of a portion of the warning system;

[0032] Figure 3 yes Figure 1 Schematic diagram of a wind farm in an example operating scenario;

[0033] Figure 4 yes Figure 1 Schematic diagram of a wind power plant in another operating scenario;

[0034] Figure 5 The present invention is a diagram showing a method for debugging Figure 1 A flow chart of a method for a warning system for a wind power plant; and

[0035] Figure 6 is a diagram illustrating an embodiment of the present invention for operating Figure 1 Flowchart of a method of a warning system. DETAILED DESCRIPTION

[0036] Generally speaking, embodiments of the present invention provide an obstacle warning system and associated warning method for a fixed facility, such as a wind turbine facility, configured to identify scenarios in which there is a possibility that an aircraft or other hazard may enter a warning zone defined around the facility without being detected. In this regard, such a warning system can be configured to enable detection based on the quality of a signal received by an associated radar system used to detect hazards near the facility. For example, the signal quality can be evaluated relative to a corresponding noise floor level.

[0037] In some embodiments, if the radar system receives a signal indicating that the radar system's performance is degraded and below a threshold level, the warning system can operate in a fail-safe mode, automatically activating the warning system, such as by triggering a flashing warning light visible to nearby aircraft, in the event that the radar system cannot reliably determine whether a hazard has entered the warning zone. By automatically activating the alert when degradation of the radar system's performance is detected, aircraft are prevented from being unalerted of the facility's presence. Conversely, automatically activating the warning only when radar performance is assessed to be degraded minimizes any additional contribution to light pollution.

[0038] The radar system's performance may include its current scan range in all directions around the facility, which defines the area the radar is currently able to effectively scan. Scan range degradation may occur due to a number of possible factors. If degradation is suspected, the warning system may trigger a warning if the scan range or area is assessed to be insufficient to cover the entire warning zone, such that a hazard may have entered the area undetected.

[0039] More generally, embodiments of the present invention also allow the performance of fixed radar systems or other scanning systems to be assessed in a passive manner and performance degradation to be detected without additional hardware requirements.

[0040] As described in more detail below, the quality of radar signals and degradation of radar system performance can be evaluated by calibrating the system using landmarks and other reference features in the area scanned by the system, so that changes in performance can be detected. For example, the signal received from the known location of a landmark (which can be referred to as a "reference area" or "signal area") can be compared with the signal from a nearby area (which can be referred to as a "baseline area" or "noise area") with a corresponding baseline noise level at the geographic location representing the landmark. This comparison allows the performance of the radar system to be evaluated for the landmark location, for example, by determining the noise level in the signal received from the corresponding geographic area. An increase in noise can then indicate a decrease in the system's scan range, as described in more detail below.

[0041] Thus, the baseline area defines a first location and the location of the landmark defines a second location, such that signals received from the first location and the second location can be compared to provide an indication of the performance of the radar system.

[0042] To provide context for the present invention, Figure 1 An exemplary onshore wind turbine installation or "wind farm" 2 is shown in which an obstacle warning system 4 according to an embodiment of the present invention has been implemented. Warning system 4 defines an obstacle collision avoidance system configured to reduce the risk of collision between an aircraft and wind farm 2. However, it will be appreciated that obstacle warning systems according to the present invention may be applied to various other types of fixed installations in a range of locations.

[0043] The wind farm 2 comprises a plurality of wind turbine generators 6 arranged in a circular array. In this simplified example, the wind turbine generators 6 are typical horizontal axis wind turbines, which are well known in the art and therefore will not be described in detail here.

[0044] The warning system 4 comprises a set of warning devices in the form of warning lights 8 which, when illuminated, serve to warn nearby aircraft of the presence of the wind farm 2. In this example, each warning light 8 is positioned on a respective one of the wind turbine generators 6. Figure 2 As more clearly shown, in this example, each warning light 8 is mounted to a nacelle 9 of the wind turbine generator 6. The lights 8 may also be supported on other parts of the wind turbine generator, or supported spaced apart from the wind turbine generator 6, such as on a dedicated pole.

[0045] Warning system 4 also includes a control system configured to operate warning lights 8 to illuminate the lights when an aircraft is or may be in the vicinity of wind farm 2, thereby alerting the aircraft to the presence of wind farm 2 so that the aircraft can take evasive maneuvers if necessary. For example, illuminating lights 8 may require activating flashing of lights 8.

[0046] In this example, the control system is implemented to define Figure 2 The control unit is a controller 10 schematically shown in FIG, which has an input 11 for receiving input data, a processor 12 for analyzing the input data and generating control signals, and an output 13 for issuing the control signals. The control system can be configured in a more distributed configuration involving multiple control units in other devices.

[0047] The warning system 4 also includes a radar system 14 that is operable to detect incoming aircraft or other hazards, thereby providing input data required by the controller 10 to operate the warning lights 8. Communications between the controller 10 and the radar system 14 and between the controller 10 and the warning lights 8 are performed by Figure 2 A suitable network is provided as depicted by the dashed line in FIG. For example, the network may be a Modbus network. Thus, input terminal 11 of controller 10 receives input data in the form of scan data from radar system 14. This scan data is analyzed by processor 12 to generate appropriate control commands. Controller 10 then issues control commands to warning light 8 via output terminal 13 to control the operation of warning light 8.

[0048] The radar system 14 is mounted on an upright column 15 which is centrally located between the wind turbine generators 6. Figure 1 In the simplified example shown, radar system 14 has a single radar device, but in other examples, radar system 14 may include one or more distributed radar devices, which may be arranged, for example, on multiple separate poles or on one or more of wind turbine generators 6 .

[0049] Radar system 14 is operable to transmit and receive signals throughout an ideal coverage area 16, which represents the maximum possible operating range of radar system 14 under ideal conditions. The outer boundary of ideal coverage area 16 may be referred to as ideal range boundary 17. In the example shown, mast 15 is positioned so that radar system 14 is arranged such that ideal coverage area 16 is generally hemispherical in shape and centered on mast 15 and wind turbine generator 6. However, it should be noted that ideal coverage area 16 may have different shapes in practice. For example, radar system 14 may be configured to scan a full circle in the azimuth plane while simultaneously scanning an angular range of, for example, 45° in the vertical plane. This results in an ideal coverage area that is generally annular in shape, having a triangular cross-section in the vertical plane, and defining a cone of silence above radar system 14.

[0050] A continuous warning boundary 18 is defined around the wind farm 2, and the area bounded by the warning boundary 18 defines a warning zone 20. The warning zone 20 represents the area around the wind farm 2 within which aircraft should be warned of the presence of the wind turbine generators 6, as may be required by local regulations. Therefore, when an aircraft enters the warning zone 20, the warning light 8 is illuminated.

[0051] In the example shown, warning zone 20 is substantially cylindrical, defining an upright axis centrally located relative to wind farm 2. In this simplified example, warning zone 20 extends upward from the ground surrounding wind farm 2 to define a generally planar boundary ceiling 22 and generally tubular boundary sides 24. For example, boundary ceiling 22 may be approximately 300 meters above the ground, and boundary sides 24 may have a radius of 4 to 6 km. Warning zone 20 may, in practice, take various other forms.

[0052] Radar system 14 is configured so that ideal coverage area 16 completely surrounds warning zone 20, while also allowing for a safety margin. That is, when ideal conditions prevail, radar system 14 has a scan range sufficient to detect aircraft at any location on warning boundary 18. Controller 10 is configured so that when radar system 14 detects an aircraft within warning zone 20, warning light 8 is illuminated.

[0053] However, radar conditions are not always ideal, and suboptimal conditions may result in degradation in the performance of radar system 14. For example, such degradation may be caused by adverse weather conditions and / or damage or malfunction of radar system 14, and may manifest as a reduction in the scanning or monitoring range of radar system 14. In other words, when conditions are less than ideal, the actual coverage area effectively scanned by radar system 14 may deviate from the ideal coverage area 16.

[0054] To account for the fact that the actual coverage area may be smaller than the ideal coverage area 16, the controller 10 is configured such that the warning light 8 is illuminated when any portion of the warning zone 20 is determined to extend outside the actual coverage area of ​​the radar system 14. In this manner, a fail-safe mode of operating the warning system 4 is provided that ensures that warning regulations are met even when the radar system 14 is unable to detect an aircraft within the warning zone 20 due to degradation effects.

[0055] in this regard, Figure 3 A scenario is shown where, due to degradation in the performance of the radar system 14 , an aircraft 30 may pass into the warning zone 20 without being detected. Figure 3 Warning boundary 18 is shown as a solid line surrounding wind farm 2, and range boundary 26, representing the actual range of radar system 14, is shown as a dashed line. Thus, the area within range boundary 26 defines the actual coverage area 27 of radar system 14, also referred to as the "scan area." In this example, range boundary 26 extends beyond warning boundary 18 at most angles relative to the center of warning zone 20, but curves radially inward in the lower left portion of the illustration away from ideal coverage area 16, thereby crossing warning boundary 18 and extending within warning zone 20. This represents a reduction in the range of radar system 14 in this area.

[0056] This range reduction can be caused by a range of factors, including environmental and internal factors, and in this example, is due to an area of ​​heavy rainfall 28. Rainfall 28 acts as environmental clutter that interferes with and degrades the radar signal, both by absorbing and thereby attenuating the signal, and by reflecting the signal back to radar system 14 before reaching warning boundary 18 and thereby creating clutter in the signal received by radar system 14, which clutter may mimic expected real reflected signals from features in ideal coverage area 16 and may therefore be misinterpreted by radar system 14. Thus, although radar system 14 may receive a strong signal from an area of ​​rainfall 28, the signal will be primarily due to reflections from the rain, rather than reflections from other features in or outside of the rain.

[0057] It should be noted that various other conditions may have similar degrading effects on the performance of radar system 14, including other types of precipitation (such as snow or hail), airborne dust, fog or low cloud cover, and varying humidity or temperature. Furthermore, damage, aging, or failure of components of radar system 14 may cause performance degradation, as may the accumulation of snow, ice, or debris on the components.

[0058] Therefore, the signals received by radar system 14 emanating from an area of ​​rainfall 28 are characterized by high noise, such that features at that location may be indistinguishable from the noise and clutter generated by the rain.

[0059] in this regard, Figure 3 The aircraft 30 depicted in FIG is traveling through an area of ​​heavy rain 28 such that the rain effectively masks the aircraft 30 from the radar system 14. This is indicated by the aircraft 30 in FIG. Figure 3 The fact that the aircraft 30 is within the warning zone 20 but outside the range boundary 26 represents that the aircraft 30 has therefore entered the warning zone 20 without being detected.

[0060] However, in this example, the pilot of the aircraft 30 is still alerted to the presence of the wind farm 2 because the warning lights 8 are flashing, having been activated as a precautionary measure when degradation of the performance of the radar system 14 was detected, as will now be explained.

[0061] In this regard, controller 10 utilizes the calibration data and landmarks in scanning area 27 as reference features to determine the current performance of radar system 14 and, in turn, whether warning light 8 should be illuminated as a precautionary measure. Figure 3 , which in this example is a large building that is highly reflective with respect to signals transmitted and received by radar system 14, such that radar system 14 receives a strong, low-noise return signal from a location corresponding to landmark 32 under normal conditions. Thus, the location of landmark 32 defines a reference location or "signal region" for evaluating the performance of radar system 14. Furthermore, the signal reflected from the location of landmark 32 defines a "reference signal."

[0062] A "noise region," "baseline location," or baseline area 34 is defined near landmark 32. Baseline area 34 does not contain particularly reflective features such that the signal received by radar system 14 from that location can be considered a "noise signal" representing the baseline noise of radar system 14, or the "noise floor" for that geographic region of scan area 27. Thus, baseline area 34 is selected to be as close as possible to landmark 32 so that it represents the baseline level of noise expected at the location of landmark 32. In this regard, the baseline level of noise varies with location and, in particular, tends to increase with distance from radar system 14.

[0063] Thus, the baseline region 34 provides a reference by which to determine the quality of the signal received from the known location of the landmark 32, and in particular, to quantify the noise in the landmark signal and verify the source of the signal. For example, the signal received from the baseline region 34 can be used as a reference for determining the power-over-noise level, which can be expressed as a signal-to-noise ratio (SNR), for the signal received from the location of the landmark 32. As described above, while a strong signal may be received from the location of the landmark 32, this may be due to clutter caused by rain rather than a true, expected reflection from the landmark 32 itself. Thus, the "noise signal" received from the corresponding baseline region 34 provides a means by which to evaluate what is shown in the signal from the landmark location.

[0064] More specifically, since the power of the signal received from the baseline region 34 represents the noise in that region, the SNR of a pair of signals associated with the landmark 32 and the baseline region 34 can be defined as:

[0065]

[0066] On top, P r is the signal power of the signal from the location of the landmark, P n is the signal power of the signal received from baseline area 34. Although SNR values ​​are determined for signal pairs, these SNR values ​​also indicate the SNR of the signal received from the location of landmark 32. More generally, the SNR values ​​provide an indication of the performance of radar system 14 at a geographic area containing an associated pair of locations (i.e., landmark 32 and corresponding baseline area 34).

[0067] It is worth noting that using the signal received from the baseline region 34 as the noise reference takes into account variations in the baseline noise level. Such variations may be widespread, such as caused by changes in humidity or temperature, or may be more local in nature. Figure 3 In the scenario shown in , patches of rain 28 will increase the noise in the signals received from both landmark 32 and baseline area 34, tending to increase the power of the signal received from baseline area 34 while the power of the signal received from landmark 32, which in any case would be expected to be relatively strong due to reflections from landmark 32, remains relatively unchanged. In this scenario, the SNR calculated for this pair of signals will decrease, so that the reference provided by baseline area 34 enables quantification of the noise level in the signal from landmark 32. In effect, this approach allows controller 10 to verify the source of the reflected signal received by radar system 14, determining in this example that radar system 14 is detecting rain rather than landmark 32.

[0068] Thus, landmark 32 and baseline region 34 form a location pair whose relationship between signals can be used to determine the quality of the signal received from landmark 32 and, therefore, the performance of radar system 14 .

[0069] It should be noted that the extent to which the range of the radar system 14 is reduced by an area of ​​rain 28 depends on the intensity of the rain. Thus, in other circumstances, rain may reduce the range of the radar system 14 to a lesser extent, such that the warning zone 20 remains within the scanning area 27. In such circumstances, the warning light 8 would typically not be automatically activated, since any aircraft entering the warning zone 20 would be expected to be detected despite the slight degradation in radar system performance.

[0070] Conversely, it is also possible that the signals from landmark 32 and baseline area 34 are completely blocked by rain or other sources of interference. In this case, the signals received by radar system 14 from the locations of landmark 32 and baseline area 34, or at least from directions corresponding to those locations, will be very similar because each signal will have reflected from the clutter-generating obstruction (e.g., rain) before reaching the intended location.

[0071] Figure 4 An alternative schematic diagram of wind farm 2 is shown to reveal other possible location pairs including landmarks 32 and associated baseline areas 34 .

[0072] Each landmark 32 defines a highly reflective reference feature and, therefore, can be easily identified by the radar system 14 under ideal conditions. These features include geographical features such as hills or peaks, as well as man-made landmarks such as buildings, silos, and communication towers, and, for example, overhead power lines. Under ideal conditions, strong reflected signals are expected to be received from these features, making the location of the landmark 32 represent a "reference area" or "signal area."

[0073] For each position pair, a corresponding baseline region 34 provides a reference by which to quantify the noise in the signal received by the radar system 14 from the landmark 32, or at least the scanning direction corresponding to the landmark 32. In this example, each baseline region 34 is located near its corresponding landmark 32, and therefore at a similar distance from the radar system 14, to represent the noise floor at that distance. In this regard, and as described above, each baseline region 34 is selected based on the noise floor of the indicative radar system 14, such that the baseline region defines a "noise region." This may be due to a lack of reflective features in the region, such as in the case of a flat ground region. As Figure 4 As shown, the baseline region 34 may represent a noise floor due to being hidden behind geographic or topographical features, such as mountains, that obstruct signals returning from the baseline region.

[0074] therefore, Figure 4The peaks shown in FIG can be used as landmarks to define reference features, while the space immediately behind each peak serves as baseline area 34. These spaces are good choices for baseline area 34 because they will be "hidden" from radar signals due to the terrain elevation. However, in the example shown, buildings exist directly adjacent to each peak, and these buildings serve as landmarks 32.

[0075] Thus, each position pair defines a pair of known positions having corresponding radar scan directions from which, in use, the radar system 14 receives signals having characteristics that can be analyzed and compared to assess the performance of the radar system 14 .

[0076] Figure 4 The effect of rain on the signal received from one of the pairs, including landmark 32 and baseline region 34, is also graphically illustrated, as the SNR for that pair drops dramatically when rain begins. As the SNR decreases, clutter begins to dominate the signals received from landmark 32 and baseline region 34, making it increasingly difficult to confidently distinguish true features within the signal from landmark 32. By extension, when the SNR at warning boundary 18 falls below a threshold, it becomes impossible to detect aircraft 30 with the desired confidence.

[0077] As can be seen above, the range of radar system 14 can be evaluated by comparing the signals received by radar system 14 for each position pair to assess the noise level in the signals received from various regions of scan area 27. The signal corresponding to the position of landmark 32 exhibits relatively high noise, and thus the relatively low SNR of the associated signal pair, then indicates degradation in the performance of radar system 14 in that portion of scan area 27.

[0078] In this regard, under ideal conditions, the SNR for a position pair is expected to be high. If the SNR decreases such that the calculated ratio approaches 1 as the difference in strength of the signals received from the two positions decreases, this indicates that the performance of the radar system 14 is degraded.

[0079] More specifically, the power P of the reflected signal received by the radar system 14 r The distance (R) to the reflection source can be related using the following standard equation:

[0080]

[0081] In the above, for a fixed radar system with constant transmitter power and gain and effective aperture, most variables are constant, allowing a simplified version of the formula on the right, where a constant "K" is introduced to represent those variables. The theoretical maximum range (R) of the radar system 14 is then max ) can refer to the received minimum power P that can be detected by the radar system 14r min The reflected signal is estimated as follows:

[0082]

[0083] This means that P r_min represents the sensitivity of the radar system 14, which depends on the system noise level. Therefore, considering the detection threshold, the target detectable reflected signal must be above the noise floor (i.e., from the noise area (P n ) the power of the received signal), the detection threshold can be defined as a factor "X" of the noise floor. Therefore, P r_min The value of corresponds to the minimum SNR of the radar system 14:

[0084]

[0085] Equation (2) represents the fourth-order decay of the received power with distance from the source (i.e., radar system 14) to the target. This only takes into account free space path loss and does not take into account atmospheric attenuation or losses due to errors and uncertainties in signal processing. To account for these losses, a loss factor (L) can be introduced to represent the attenuation of the radar pulse, thereby simulating any type of degradation in the performance of the radar system due to internal or external effects. The loss factor can be defined as the ratio of the reflected signal power under ideal conditions to the current reflected signal power, which can be expressed as follows:

[0086]

[0087] Using this loss factor, the maximum range under lossy conditions (R loss ):

[0088]

[0089] Substituting (2) into (5) and defining the attenuation factor α as the inverse of the loss factor, the final simplified formula for the actual range of the radar system 14 is obtained:

[0090]

[0091] Therefore, the maximum range of the radar system 14 decreases in proportion to the fourth root of the decrease in the SNR value of the position pair. At the same time, it is observed that under lossy conditions with high clutter, the SNR of the position pair tends to 1, while under low noise conditions, the SNR can generally be expressed in terms of the attenuation factor and the measured noise NT as follows:

[0092]

[0093] It should be noted that the measured noise may be substantially equal to the signal P received from the associated baseline region 34. n The intensity of R is thus provided above as a method for estimating the real-time range of a scanning system based on the loss factor L. Therefore, the value of the loss factor can be calculated to correspond to the value of loss The situation when the range required to reach the warning boundary 18 is consistent. This value can then be used to set a unique threshold for the SNR of each position pair to activate the warning system. In this regard, it should be noted that the SNR of each position pair will be different under ideal conditions, which mainly depends on the distance of the position pair from the radar system 14.

[0094] To evaluate the performance of the radar system 14 in this manner, first use Figure 5 36 to calibrate the system. The calibration routine 36 may be performed, for example, at commissioning before installing the wind turbine 6 to ensure that the warning system 4 is functional before the wind turbine 6 is in place. Optionally, the calibration routine 36 may be repeated after commissioning to check for changes in calibration, for example periodically at regular intervals.

[0095] Calibration routine 36 involves operating radar system 14 to acquire raw data by scanning an ideal coverage area 16 around wind farm 2 under ideal conditions (see step 38). In this regard, scanning area 16 requires transmitting radar signals and then collecting reflections of those signals, also known as echo signals. Radar signals may be partially or completely reflected by reflective media located within ideal coverage area 16. The echo signals are received by radar system 14 and compiled into scan data, which is transmitted to controller 10. The scan data includes data indicating the intensity of each received echo signal and the origin direction of the echo signal, which in turn indicates the location where the signal was emitted under ideal conditions. Therefore, the location of any reflective media in the scan area can be determined from the associated scan data.

[0096] The controller 10 is then operated to analyze the scan data to identify echo signals having characteristics that are stable over a specified period of time and, therefore, indicative of a fixed reflective feature (see step 40). Of these stable echo signals, each echo signal having an intensity above a threshold is identified as having emanated from a corresponding fixed and highly reflective medium, which is the landmark 32 defining the reference feature described above. In other words, the controller 10 is operated to analyze the scan data to identify landmarks 32 that will serve as reference features within the desired coverage area 16 in the future.

[0097] Accordingly, a stable echo signal having an intensity below the threshold is determined to represent a baseline level of background noise in the relevant region of the scanning area (ie, the baseline region 34 ).

[0098] After identifying the candidate landmarks 32 and baseline regions 34, the controller 10 then identifies a suitable pair of locations, namely, a pair of landmarks and baseline regions 34 that are within a maximum separation distance from each other, such that the baseline region 34 represents the baseline noise at its corresponding landmark 32 to enable calculation of a meaningful SNR between the two.

[0099] Once the position pairs have been defined, the controller 10 calibrates each position pair by determining the SNR relationship of the pair's corresponding signals under ideal conditions (see step 42 ).

[0100] Controller 10 then defines a corresponding power threshold for each position pair (see step 44), assuming the SNR for each position pair is calibrated under ideal conditions. More specifically, in this example, an SNR threshold is defined for each position pair. For example, the SNR threshold for each position pair can be calculated using a loss factor (or attenuation factor) corresponding to the scan range required to reach the warning boundary. Each SNR threshold is calculated such that a drop in the SNR from the ideal SNR to a value below the SNR threshold corresponds to a reduction in the range of radar system 14 in the direction corresponding to the associated portion of scan area 27 to the point where it cannot reliably detect aircraft entering warning zone 20 in that portion. Each SNR threshold is calculated to take into account the distance of the position pair from warning boundary 18.

[0101] In other words, each SNR threshold defines a trigger for activating the warning light 18 if the measured SNR at any pair of locations is below the corresponding threshold.

[0102] The SNR threshold for each position pair can be dynamically adjusted to account for variations in the expected ideal SNR at different times of day and in different seasons, again taking note of the effects of environmental conditions including temperature, wind, and humidity on the radar signal even under otherwise ideal conditions.

[0103] With the SNR threshold defined, the calibration routine 36 is then complete and the system 4 is alerted to be ready for operation.

[0104] Go to Figure 6 , shows a warning process 50 that is continuously performed by the warning system 4 after calibration and commissioning to achieve calibration to activate the warning light 8 when degradation of the performance of the radar system 14 is detected. Generally speaking, this involves operating the warning system 4 to compare the real-time value of the SNR at each position pair with the corresponding SNR threshold value.

[0105] Thus, the warning process 50 begins by operating the radar system 14 to acquire scan data (see step 52), which entails sending and receiving radar signals across the scan area 27 around the wind farm 2 in the same manner as the calibration routine 36 described above, although not necessarily under ideal conditions. The controller 10 then analyzes the scan data to identify return signals received from known locations of landmarks 32 and corresponding pairs of baseline areas 34, and calculates the actual SNR for each pair of signals (see step 54).

[0106] The controller 10 then compares the calculated actual SNR for each position pair with the corresponding SNR threshold defined for the associated position pair (see step 56 ).

[0107] If the actual SNR is lower than the corresponding SNR threshold at any position pair, the controller 10 initiates a safety mode in which a precautionary alert is generated. Specifically, the warning light 8 is activated to flash, thereby providing a warning to any aircraft 30 that may have entered the warning zone 20 without being detected (see step 58).

[0108] The warning process 50 continues to iterate in safe mode until the calculated SNR value of the signal at each position pair is above the corresponding SNR threshold. At this point, the warning system 4 exits safe mode because the radar system 14 is again considered capable of detecting any aircraft that may enter the warning zone 20 at any point on the warning boundary 18 (see step 60).

[0109] From the above we can see that Figure 6 The warning process 50 shown can be used to Figure 3 Warning lights 8 are automatically activated in the illustrated operational scenario in which the operating range of radar system 14 is reduced due to an area of ​​rain 28 in an area of ​​warning zone 20 that an aircraft 30 is entering undetected. In this manner, warning system 4 provides warnings to aircraft 30 even when aircraft 30 is not detected, while maintaining the ability to deactivate warning lights 8 at other times to reduce light pollution.

[0110] It will be appreciated by those skilled in the art that modifications may be made to the specific embodiments described above without departing from the inventive concept defined by the claims.

[0111] For example, in some embodiments, upon detection of degraded radar performance, only a subset of warning lights may be activated. Specifically, if analysis of scan data reveals a localized degradation of radar range in a particular direction, only the warning lights proximate the area of ​​reduced range may be activated.

[0112] Furthermore, other thresholds may be defined as an alternative to the threshold SNR value for a position pair, for example a threshold for the strength or power of the received signal, or a threshold for the difference in strength in the signals for a position pair.

[0113] Furthermore, although the embodiments of the present invention described above utilize a baseline position representing the noise floor and a reference position from which a stronger reflection is received, in principle, any pair of positions from which signals of different strengths are received under ideal conditions can be used to evaluate the performance of the radar system.

Claims

1. A method of operating an obstacle warning system (4) for a wind turbine installation (2), the method comprising: operating a radar system (14) to obtain scanning data of an area surrounding the facility (2); analyzing the scan data to identify a pair of signals, the pair of signals including a first signal corresponding to a first location (34) and a second signal corresponding to a second location (32), the first location (34) being spaced apart from the second location (32); comparing the first signal and the second signal to determine a value indicative of the performance of the radar system (14) for an area including the second location (32); and If the value is below a threshold, the warning system (4) is activated.

2. The method according to claim 1, comprising: The respective intensities of the pair of signals are compared.

3. The method according to claim 1 or claim 2, wherein: The value represents the signal-to-noise ratio of the pair of signals.

4. A method according to any one of the preceding claims, wherein The threshold defines the noise level.

5. The method according to any one of the preceding claims, comprising: A plurality of pairs of signals in the scan data are identified and compared, each pair of signals comprising a corresponding first signal and a second signal.

6. The method according to claim 5, wherein: Each first signal is associated with a different location (34) within the area surrounding the facility (2).

7. The method according to any one of the preceding claims, comprising: The performance of the radar system (14) is evaluated.

8. The method according to claim 7, wherein: Evaluating the performance of the radar system (14) includes estimating the range of the radar system (14).

9. The method according to claim 7 or claim 8, wherein: Evaluating the performance of the radar system (14) includes estimating a loss factor.

10. A method according to any one of the preceding claims, wherein Analyzing the scan data includes comparing the scan data to calibration data.

11. The method according to any one of the preceding claims, wherein the method is preceded by a calibration routine, the calibration routine comprising: The radar system (14) is operated to obtain calibration scan data of an area surrounding the facility (2), wherein the calibration scan data includes data associated with the first location (34) and the second location (32).

12. The method according to claim 11, wherein The calibration routine includes analyzing the calibration scan data to identify a reference feature (32), and wherein the position of the reference feature (32) defines the second position (32).

13. The method according to claim 11 or claim 12, wherein: The calibration routine includes analyzing the calibration scan data to identify the first position (34).

14. The method according to any one of claims 11 to 13, wherein The signal received from the second location (32) during the calibration routine has a higher power than the signal received from the first location (34).

15. The method according to claim 14, comprising: The first location (34) and the second location (32) are identified based on strengths of signals received by the radar system (14) from the first location (34) and the second location (32).

16. The method according to claim 14 or claim 15, comprising: monitoring the strength of the signal over a specified period of time; And if the strength of each corresponding signal is sufficiently stable, the first position (34) and the second position (32) are identified.

17. A method according to any one of the preceding claims, wherein Activating the warning system (4) includes operating a warning light (8).

18. The method according to any one of the preceding claims, comprising: If the scanning data indicates the presence of an aircraft (30) in the area surrounding the facility (2), the warning system (4) is activated.

19. A method according to any one of the preceding claims, wherein The warning system (4) is configured to warn an aircraft of the presence of the facility (2).

20. A method of calibrating an obstacle warning system (4) for a wind turbine installation (2), the method comprising: operating a radar system (14) to obtain calibrated scan data of an area surrounding the facility (2); and The calibration scan data is analyzed to identify a pair of signals, the pair of signals comprising a first signal corresponding to a first location (34) and a second signal corresponding to a second location (32), the first location (34) being spaced apart from but in close proximity to the second location (32), wherein the second signal has a higher power than the first signal.

21. An obstacle warning system (4) for a wind turbine installation (2), the system (4) comprising: a radar system (14) configured to obtain scanning data of an area surrounding the facility (2); Warning device (8); and A control system (10), wherein the control system (10) is configured to: analyzing the scan data to identify a pair of signals, the pair of signals including a first signal corresponding to a first location (34) and a second signal corresponding to a second location (32), the first location (34) being spaced apart from the second location (32); comparing the first signal and the second signal to determine a value indicative of the performance of the radar system (14) for an area including the second location (32); and If the value is below a threshold value, the warning device (8) is activated.

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