A laser radar scanning path planning method for wind farm wake measurement

Abstract

The application discloses a laser radar scanning path planning method for wind farm wake measurement, which is based on the wind measurement principle of laser radar scanning, wind farm unit distribution and natural wind fluctuation characteristics, and comprises four steps of determining a laser radar installation position, determining a laser radar scanning angle range, determining a laser radar scanning angle interval and determining a continuous repeated measurement number, so that the contradiction between the measured wake field information amount and the measurement accuracy can be well balanced, and the method can be used for guiding the scheme design and implementation of the laser radar scanning measurement of the wind farm wake. The method is applicable to both land and sea wind farms.

Description

Technical Field

[0001] This invention belongs to the field of wind farm technology and relates to a method for measuring wind farm wakes. More specifically, it relates to a laser radar scanning path optimization method for measuring wind farm wakes, which can better balance the contradiction between the amount of information in the measured wake field and the measurement accuracy. It can be used to guide the design and implementation of laser radar scanning measurement schemes for wind farm wakes. Background Technology

[0002] The wake effect of wind turbines leads to power loss and increased fatigue load in downstream units, affecting the overall operational efficiency of the wind farm. A clear understanding of the wake characteristics of wind turbines can optimize turbine layout and improve wind energy resource utilization during the initial planning and construction phases of a wind farm; it can also guide the development of wake control technologies during wind farm operation to reduce wake losses and increase power generation.

[0003] In recent years, the study of wind turbine wake characteristics has received widespread attention from academia and industry. Methods for studying wind turbine wake characteristics include analytical models, high-precision numerical simulations, wind tunnel tests, and field measurements. Due to significant differences in wind environments and turbine layouts at different wind farms, and with the rapid development of lidar technology, field measurements based on lidar scanning wind measurement technology have become an important means of studying wind farm wake characteristics.

[0004] LiDAR (LiDAR) wind measurement technology emits laser signals and receives the echo signals reflected by aerogel particles in the air. Utilizing the Doppler frequency shift principle, it obtains the speed at which the aerogel particles move with the wind as wind speed. The laser probe is then mounted on an angle-controlled pan-tilt unit to scan and measure wind speed, thus obtaining the wind speed field within a spatial range. As can be seen from the above principle, the wind speed field obtained by lidar scanning is not the wind speed distribution at a single moment, but rather a stitched image of wind speeds at different moments within the scanning period. However, natural wind has strong fluctuations, and the wind speed field formed by stitching together wind speeds from different moments has a certain degree of distortion. If the scanning period is too short, sufficient spatial resolution or a sufficiently large wake field cannot be obtained; if the scanning period is too long, the measured wake field will have a large error. Therefore, it is necessary to plan an appropriate scanning path, balancing the information content of the wake field and measurement accuracy, to achieve the expected measurement purpose. Summary of the Invention

[0005] (I) The technical problem to be solved by the present invention

[0006] To address the aforementioned shortcomings and deficiencies of existing technologies, this invention, based on the principles of lidar measurement, wind farm turbine distribution, and natural wind fluctuation characteristics, comprehensively analyzes four dimensions: lidar installation location, scanning angle range, scanning angle interval, and number of consecutive repeated measurements. It proposes a lidar scanning path planning method for wind farm wake measurement. The measurement error caused by natural wind fluctuations within the scanning period essentially comprises two sources: one is the error caused by the change in average wind speed over time, which increases with time; the other is the error caused by natural wind turbulence, which remains essentially constant over time and can be reduced through continuous repeated measurements and averaging. Therefore, the lidar scanning path planning method for wind farm wake measurement proposed in this invention can effectively balance the contradiction between the amount of wake field information measured and the measurement accuracy, and can be used to guide the design and implementation of lidar scanning measurement schemes for wind farm wakes.

[0007] (II) The technical solution adopted by the present invention to solve its technical problem

[0008] A lidar scanning path planning method for wind farm wake measurement, characterized in that the method includes at least the following steps:

[0009] SS1. Determine the installation location of the lidar.

[0010] First, based on the historical wind direction data of the wind farm, determine the prevailing wind direction, and then install the lidar at the upwind or downwind position of the wind farm according to the prevailing wind direction.

[0011] Secondly, based on the on-site installation conditions of the wind farm, and taking the principle of maximizing the number of wind turbine units within the range of the lidar measurement, the vertical height of the lidar probe should be set near the center height of the wind turbine hub, while avoiding installation near obstacles that block the laser beam as much as possible.

[0012] SS2. Determine the scanning angle range of the lidar.

[0013] The scanning angle of a lidar includes the pitch angle in the vertical plane and the azimuth angle in the horizontal plane. If the lidar is installed at the same height as the center of the wind turbine hub, the pitch angle of the lidar in the vertical plane is 0 degrees. If the wind farm does not have the conditions to install the lidar at the same height as the center of the wind turbine hub, the pitch angle of the lidar in the vertical plane needs to be determined based on the horizontal and vertical distances between the measured turbine and the lidar, so that the measurement result of the lidar is the wind speed at the height of the measured turbine hub.

[0014] Under the premise that the azimuth angle range of the lidar is set to not exceed ±60° of the prevailing wind direction, the scanning angle range is further reduced according to the distribution of wind farm units and the range of obstacle blocking area, so as to shorten the scanning cycle of lidar and reduce the error caused by wind speed fluctuation within the scanning cycle, and finally obtain the scanning angle range γ of lidar.

[0015] SS3. Determine the lidar scanning angle interval

[0016] Based on the installation location of the lidar and the distribution location of the wind farm units, the maximum distance L between the lidar and the units is calculated. The lidar scanning angle interval should ensure that there are at least 3 data points within the sweep diameter D of the wind turbine of the unit farthest from the lidar. The lidar scanning angle interval α is calculated using α=arctan(D / 2L).

[0017] SS4. Determine the number of consecutive repeated measurements

[0018] Repeated measurements can reduce the error caused by natural wind turbulence, but they also increase the error caused by the change in average wind speed over time. Therefore, it is necessary to determine the number of repeated measurements that minimizes the error. The specific method is as follows:

[0019] SS41. Based on the historical wind speed data v(t) and historical wind direction data θ(t) of the measured wind farm, the data is averaged according to different consecutive repeated measurements n to obtain new wind speed data v. n (t), wind direction data θ n (t), and then the new wind speed data v n (t), wind direction data θ n (t) Calculate the pulsation error within a fixed time interval to obtain the variation law ε of wind speed pulsation error with the number of consecutive repeated measurements. v′ =f v (n) and the variation law of wind direction pulsation error with the number of consecutive repeated measurements ε θ′ =f θ (n);

[0020] SS42. Average wind speed data is obtained by averaging the historical wind speed v(t) and historical wind direction data θ(t) of the measured wind farm at fixed time intervals. Average wind direction data Then, using the initial value of the average wind speed respectively Initial value of average wind direction Based on this, calculate the average wind speed data. Average wind direction data Error that changes over time

[0021] SS43. Based on the time interval Δt of the lidar scanning measurement, the number of consecutive repeated measurements n, and the number of scanning angles i, the wind speed v(i,n) at different scanning angles i caused by natural wind fluctuations is calculated using the following formula.

[0022]

[0023] Among them, g v (Δt·n·i)=g v (t) represents the average wind speed data. Error that varies over time, g θ (Δt·n·i)=g θ (t) represents the average wind direction data. Errors that change over time;

[0024] SS44. Calculate the total error of scanning measurement under different consecutive repeated measurements n. in Given the total number of scanning angles, find the number of consecutive repeated measurements that minimize the overall error.

[0025] Preferably, in step SS1, the lidar is suitable to be installed upwind or downwind of the wind farm because the angle between the lidar beam and the incoming flow direction is smaller when the lidar is upwind or downwind, resulting in higher measurement accuracy.

[0026] Preferably, in step SS2, the scanning angle range should not exceed ±60° of the prevailing wind direction. This is because the wind speed measured by the lidar is the component of the actual wind speed in the direction of the laser beam. Actual measurements show that the measurement results exceeding this angle range have a large error and should not be used. With the improvement of lidar measurement technology, this angle range may increase.

[0027] Preferably, in step SS2, the scanning angle range is further appropriately reduced within this range based on the distribution of wind farm turbines and the range of obstacle-blocked areas. This means that the scanning angle range may include areas without turbines or areas blocked by obstacles. The scanning angles corresponding to these invalid areas can be removed to shorten the scanning cycle and improve measurement accuracy.

[0028] Preferably, in step SS1, a wind rose diagram for one year is obtained based on the historical wind direction data of the measured wind farm, and the prevailing wind direction of the measured wind farm is determined based on the wind rose diagram.

[0029] Preferably, in step SS3, taking into account the pointing accuracy of the lidar, the minimum scanning angle interval of the lidar should not be less than 0.5°.

[0030] Preferably, in step SS4, the fixed time interval is approximately 10 minutes.

[0031] (III) Significant technical effects of the present invention compared with the prior art

[0032] This invention presents a lidar scanning path planning method for wind farm wake measurement. Starting from the lidar scanning wind measurement principle, wind farm turbine distribution, and natural wind fluctuation characteristics, it proposes a lidar scanning path planning method that balances measurement information volume and measurement accuracy, following four steps: determining the lidar installation location, determining the lidar scanning angle range, determining the lidar scanning angle interval, and determining the number of consecutive repeated measurements. This method can provide scientific guidance for the design of lidar scanning measurement schemes for wind farm wakes. This method is applicable to both onshore and offshore wind farms. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of a lidar scanning wind measurement scheme;

[0034] Figure 2 The diagram shows the historical wind speed and direction data of the wind farm, where (a) is a diagram showing the change of wind speed over time, and (b) is a diagram showing the change of wind direction over time.

[0035] Figure 3 The diagram shows the variation of wind speed and direction pulsation error with the number of consecutive repeated measurements. (a) shows the variation of wind speed pulsation error with the average number of measurements, and (b) shows the variation of wind direction pulsation error with the average number of measurements.

[0036] Figure 4 The diagrams show the errors caused by the change in average wind speed and direction over time. (a) shows the error caused by the change in wind speed over time, and (b) shows the error caused by the change in wind direction over time.

[0037] Figure 5 This is a schematic diagram illustrating how the overall error of scanning measurement changes with the number of consecutive repeated measurements.

[0038] The meanings of the reference numerals in the attached figures are as follows:

[0039] 1-Prevailing wind direction, 2-LiDAR, 3-Wind turbine. Detailed Implementation

[0040] To make the objectives and technical solutions of this invention clearer, specific implementation examples are provided below, along with reference to the accompanying drawings, to further illustrate the invention in detail. In the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The described embodiments are some, but not all, embodiments of this invention, and are intended to explain the invention, not to limit it. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0041] This example applies to a 5x5 array arrangement of offshore wind farms, such as... Figure 1 As shown, the spacing between each wind turbine 3 in the wind farm is 1000 meters, the rotor diameter D = 160 meters, the hub center height is 120 meters, and the radial measurement distance Lr of the lidar 2 is 6000 meters. According to the lidar scanning path planning method proposed in this invention, the wind farm wake measurement scheme can be designed with the following steps:

[0042] 1. Determine the installation location of the lidar

[0043] Based on the historical wind direction data of the wind farm, a wind rose diagram for the past year was obtained, and the prevailing wind direction 1 was determined to be north-northwest. Since there are no other platforms at sea available for installing lidar, lidar 2 was installed on the top platform of the nacelle of the last row of wind turbines downwind. The location of lidar 2 was determined based on the principle of maximizing the number of wind turbines within the lidar's measurement range.

[0044] 2. Determine the scanning angle range of the lidar.

[0045] Since the lidar is installed on the top platform of the cabin, approximately at the same height as the wheel hub center, the scanning pitch angle is 0°. The azimuth angle range is extended by 60° clockwise and counterclockwise with the prevailing wind direction as the center, resulting in an azimuth angle range γ = 120°.

[0046] SS3 determines the scanning angle interval of the lidar.

[0047] Based on the installation location of the lidar and the distribution location of the wind farm units, the maximum distance between the lidar and the units was calculated to be L = 5000 meters. The angle interval was set so that the wind turbine of the unit farthest from the lidar swept at least 3 data points within a diameter D = 100 meters. The angle interval was calculated to be α = arctan(D / 2L) = 0.92°. In order to make the azimuth range an integer multiple of the angle interval, the final angle interval was set to 1°.

[0048] 4. Determine the number of consecutive repeated measurements

[0049] Repeated measurements can reduce the error caused by natural wind turbulence, but they also increase the error caused by the change in average wind speed over time. Therefore, it is necessary to determine the number of repeated measurements that minimizes the error. The specific method is as follows:

[0050] 4.1 Based on the historical wind speed and direction data v(t), θ(t) of the wind farm, such as Figure 2 As shown, the new wind speed and direction data v are obtained by averaging the data according to different consecutive repeated measurements n. n (t),θ n (t), and then for v n(t),θ n (t) Calculate the pulsation error within 10 minutes to obtain the variation law ε of wind speed and wind direction pulsation error with the number of consecutive repeated measurements. v′ =f v (n), ε θ′ =f θ (n), such as Figure 3 As shown;

[0051] 4.2 Average wind speed and direction data are obtained by averaging the historical wind speed and direction data v(t) and θ(t) over a 10-minute period. Then, using the initial values ​​as a baseline, the average wind speed and direction are calculated. Error that changes over time like Figure 4 As shown;

[0052] 4.3 Based on the time interval Δt = 1 (s) of the lidar scanning measurement, the number of consecutive repeated measurements n, and the number of scanning angles i, the wind speed at different scanning angles i caused by natural wind fluctuations is calculated according to the following formula.

[0053]

[0054] 4.4 Calculation of the total error of scanning measurement under different consecutive repeated measurements n like Figure 5 As shown, where Given the total number of scanning angles, the number of consecutive repeated measurements to find the minimum overall error is 5.

[0055] The above examples of lidar scanning measurement schemes for wind farm wakes are summarized as follows: The lidar is installed on the top platform of the nacelle of the last row of downwind units, with a constant pitch angle of 0° and an azimuth angle within ±60° of the prevailing wind direction. The scanning angle interval is 0°, and the cumulative time for each angle measurement and laser scanning movement is 1 second. The number of consecutive measurements is 5, so it takes 10 minutes to complete one wind farm wake scanning measurement.

[0056] The above description is merely one embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the scope of the present invention should be included within the scope of the present invention.

Claims

1. A lidar scanning path planning method for wind farm wake measurement, characterized in that, The method includes at least the following steps: SS1. Determine the installation location of the lidar. First, based on the historical wind direction data of the wind farm, determine the prevailing wind direction, and then install the lidar at the upwind or downwind position of the wind farm according to the prevailing wind direction. Secondly, based on the on-site installation conditions of the wind farm, and taking the principle of maximizing the number of wind turbine units within the range of the lidar measurement distance, the vertical height of the lidar probe is set near the center height of the wind turbine hub, while avoiding installation near obstacles that block the laser beam. SS2. Determine the scanning angle range of the lidar. The scanning angle of a lidar includes the pitch angle in the vertical plane and the azimuth angle in the horizontal plane. If the lidar is installed at the same height as the center of the wind turbine hub, the pitch angle of the lidar in the vertical plane is 0 degrees. If the wind farm does not have the conditions to install the lidar at the same height as the center of the wind turbine hub, the pitch angle of the lidar in the vertical plane needs to be determined based on the horizontal and vertical distances between the measured turbine and the lidar, so that the measurement result of the lidar is the wind speed at the height of the measured turbine hub. With the azimuth angle range of the lidar set to not exceed ±60° of the prevailing wind direction, the scanning angle range is further reduced based on the distribution of wind farm turbines and the extent of obstacle obstruction. This shortens the lidar's scanning cycle and reduces errors caused by wind speed fluctuations within the scanning cycle, ultimately yielding the lidar's scanning angle range. ; SS3. Determine the lidar scanning angle interval. Based on the installation location of the lidar and the distribution location of the wind farm turbines, the maximum distance between the lidar and the turbines is calculated. The scanning angle interval of the lidar should be such that the sweep diameter of the wind turbine rotor furthest from the lidar is... There are at least 3 data points within the range, and the LiDAR scanning angle interval is [missing information]. use Calculated; SS4. Determine the number of consecutive repeated measurements. The specific steps to determine the number of consecutive repeated measurements that minimize the overall error of the scanning measurement are as follows: SS41. Based on the historical wind speed data of the wind farm measured. Historical wind direction data According to different consecutive repeated measurements The average data is then processed to obtain new wind speed data. Wind direction data This leads to new wind speed data. Wind direction data The fluctuation error within a fixed time interval was calculated to obtain the variation law of wind speed fluctuation error with the number of consecutive repeated measurements. and the variation law of wind direction pulsation error with the number of consecutive repeated measurements ; SS42. Historical wind speed data for the measured wind farm Historical wind direction data Average wind speed data is obtained by averaging at fixed time intervals. Average wind direction data Then, using the initial value of the average wind speed respectively Initial value of average wind direction Based on this, average wind speed data were calculated separately. Average wind direction data Error that changes over time , ; SS43. Based on the time interval measured by lidar scanning. Number of consecutive repeated measurements Scanning angle number The different scanning angle numbers caused by natural wind fluctuations are calculated according to the following formula. wind speed : ,in, Average wind speed data Error that varies over time. Average wind direction data Errors that change over time; SS44. Calculate the number of consecutive repeated measurements. Total error of scanning measurement ,in Given the total number of scanning angles, find the number of consecutive repeated measurements that minimize the overall error.

2. The lidar scanning path planning method according to claim 1, characterized in that: In step SS1, a wind rose diagram for one year is obtained based on the historical wind direction data of the measured wind farm, and the prevailing wind direction of the measured wind farm is determined based on the wind rose diagram.

3. The lidar scanning path planning method according to claim 1, characterized in that: In step SS3, taking into account the pointing accuracy of the lidar, the minimum scanning angle interval of the lidar is not less than 0.5°.

4. The lidar scanning path planning method according to claim 1, characterized in that: In step SS4, the fixed time interval is 10 minutes.

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