Hydroelectric generating set frequency measurement method based on coded image recognition

Abstract

This invention relates to a method for measuring the frequency of hydropower units based on coded image recognition, comprising: sampling images of coded character sequences or color block sequences on the main shaft of the unit; recognizing the coded character sequences or color block sequences pointed to by a pointer in the image frame, extracting the colors of the characters or color blocks and their arrangement order along the axial direction of the unit, and converting them into a coded sequence; converting the coded sequence into the rotation angle of the main shaft of the unit; calculating the angular velocity of the main shaft of the unit based on the rotation angle of the main shaft pointed to by the pointer in adjacent image frames and the interval time between adjacent image frames; and calculating the frequency of the unit. This invention's method for measuring the frequency of hydropower units based on coded image recognition improves the accuracy of unit frequency measurement and has strong anti-interference capabilities, unaffected by electromagnetic signals from the unit and its surrounding environment.

Description

Technical Field

[0001] This invention belongs to the field of hydropower generation control, and specifically relates to a method for measuring the frequency of hydropower units based on coded image recognition. Background Technology

[0002] Currently, the frequency measurement of hydropower units mainly adopts two methods: residual pressure frequency measurement and gear disc frequency measurement. The residual pressure signal is severely distorted at low speeds, resulting in a large error in the measured frequency; moreover, after the excitation system is started, high-order harmonics are superimposed on the residual pressure signal, which are difficult to filter out using conventional hardware filtering methods.

[0003] Gear-disc frequency measurement uses a gear-disc mounted on the main shaft of a hydro-generator unit to measure speed via a speed probe. This method directly measures the turbine's rotational speed. When the main shaft rotates, it drives the gear-disc to rotate coaxially. The speed probe, fixed to a bracket, generates a step signal. The amplitude of this signal is independent of the turbine's rotational speed, while its frequency is directly proportional to the turbine's rotational speed. Gear-disc frequency measurement is affected by many factors, including the gear-disc's machining accuracy, the number of teeth, and the probe's installation distance. Improper probe installation can cause damage to the gear belt or probe, or result in inaccurate frequency measurements. Summary of the Invention

[0004] The purpose of this invention is to address the aforementioned problems by providing a method for measuring the frequency of hydropower units based on coded image recognition. This method involves spraying coded character sequences or color block sequences along the axial direction at different angular positions on the main shaft of the unit. During unit operation, an industrial camera continuously captures images of the character sequences or color block sequences on the outer surface of the main shaft. Image recognition methods are used to obtain the rotation angle of the main shaft corresponding to each image frame. By combining the time difference between the current image frame and the images before and after it, the unit frequency is calculated, achieving high-precision measurement and calculation of the unit frequency. The measurement device is easy to deploy and does not affect the normal operation of the unit. The frequency measurement process is isolated from the unit's electrical signals. The measurement results are unaffected by electromagnetic signals around the unit, exhibiting strong anti-interference capabilities.

[0005] The technical solution of the present invention is a frequency measurement method for hydropower units based on coded image recognition. The outer surface of the main shaft of the unit is divided into multiple parts at equal angles along the circumference. Each part is coded and a sequence of coded characters or color blocks is sprayed along the axial direction in the identifiable area of ​​the outer surface of the main shaft to facilitate image acquisition. A fixed pointer is set at a position on the outer surface of the main shaft, and the pointer points to the coded characters or color blocks on the outer surface of the main shaft.

[0006] The method for measuring the frequency of a hydroelectric generator unit includes the following steps:

[0007] Step 1: Use an industrial camera to target the identifiable area on the outer surface of the main shaft of the machine unit, and continuously sample images of the encoded character sequence or color block sequence of the main shaft of the machine unit;

[0008] Step 2: Recognize the coded character sequence or color block sequence pointed to by the pointer in the image frame, extract the color of the character or color block and the arrangement order of the character or color block along the unit axis, and convert it into a coded sequence;

[0009] Step 3: Based on the correspondence between the coding sequence and the partitions on the outer surface of the generator shaft, convert the coding sequence into the rotation angle of the generator shaft;

[0010] Step 4: Calculate the angular velocity of the generator shaft based on the rotation angle of the generator shaft as indicated by the pointer in adjacent image frames and the time interval between adjacent image frames;

[0011] Step 5: Calculate the frequency of the unit based on the angular velocity of the main shaft obtained in Step 4.

[0012] Preferably, a hollow baffle is provided at the coding position on the outer surface of the generator shaft, with the hollow part of the baffle aligned with the identifiable area of ​​the coding on the outer surface of the generator shaft. The baffle is used to block other objects other than the character sequence or color block sequence during image acquisition.

[0013] Preferably, the character sequence uses binary encoding 0 and 1.

[0014] Preferably, in step 1, an industrial camera with a resolution of 500fps is used to capture 500 images per second, with a frame acquisition time interval of 2ms.

[0015] Furthermore, in step 2, an edge detection algorithm is used to identify pointers and character sequences in the detected image frame, segment out the characters, and compare them with the characters in the character database to convert the character sequence at the pointer position in the image frame into an encoded sequence.

[0016] Compared with the prior art, the beneficial effects of the present invention include:

[0017] 1) The hydropower unit frequency measurement method based on coded image recognition of the present invention uses an industrial camera to collect images of character sequences or color block sequences at different angle positions on the outer surface of the main shaft of the unit. The rotation angle of the main shaft of the unit corresponding to each frame of the image is obtained by using image recognition method. The unit frequency is calculated based on the shooting time difference of the image frames, which improves the accuracy of the unit frequency measurement and has strong anti-interference ability and is not affected by electromagnetic signals of the unit and the surrounding environment.

[0018] 2) The unit frequency measurement method of the present invention is easy to implement and can be easily executed by computer program to realize automatic measurement and calculation of unit frequency.

[0019] 3) The unit frequency measurement method of the present invention calculates the unit frequency by calculating the average value of the unit major axis angle difference between adjacent image frames, which makes the unit frequency measurement results more stable and more accurate.

[0020] 4) This invention uses binary encoding 0 and 1 to encode different angular positions of the main shaft of the unit. The binary encoding contains only 2 characters, which is easy to recognize images and improves the efficiency and accuracy of the measurement and calculation of the main shaft angle of the unit.

[0021] 5) When capturing images of character sequences or color block sequences at different angles on the main shaft of the generator set, the method of the present invention uses a fixed, hollow baffle to block other objects on the main shaft of the generator set other than the character sequences or color block sequences, forming a single image background, which effectively reduces the time and difficulty of subsequent image recognition.

[0022] 6) The measuring device used in the method of the present invention only includes an industrial camera and its supporting and fixing equipment, which is easy to install at the main shaft of the hydropower unit and has low installation and construction difficulty. Attached Figure Description

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] Figure 1 This is a flowchart illustrating the frequency measurement method for hydropower units according to an embodiment of the present invention.

[0025] Figure 2 This is a schematic diagram of the binary encoding of the main shaft of the unit at different angles according to an embodiment of the present invention.

[0026] Figure 3 This is a schematic diagram illustrating the blocking effect of the hollow baffle in an embodiment of the present invention. Detailed Implementation

[0027] Example 1

[0028] In this embodiment, the outer surface of the generator set's main shaft is divided into N equal-angled sections along its circumference, where N represents the number of equal sections. Each section is encoded, and a sequence of coded characters is sprayed axially onto the identifiable area on the outer surface of the main shaft to facilitate image acquisition. A fixed pointer is positioned on the outer surface of the main shaft, pointing to the coded characters. A hollow baffle is placed on the outer surface of the main shaft, with its hollow portion aligned with the identifiable coded area. The baffle is used to block other objects besides the character sequence during image acquisition, such as... Figure 3 As shown.

[0029] In one embodiment, the character sequence uses binary encoding 0 and 1, such as Figure 2 As shown.

[0030] like Figure 1 As shown, the frequency measurement method for hydropower units based on coded image recognition includes the following steps:

[0031] Step 1: Use an industrial camera to target the identifiable area encoded on the outer surface of the main shaft of the unit, and sample the image of the encoded character sequence or color block sequence of the main shaft of the unit.

[0032] Step 2: Recognize the coded character sequence or color block sequence pointed to by the pointer in the image frame, extract the color of the character or color block and the arrangement order of the character or color block along the unit axis, and convert it into a coded sequence;

[0033] An edge detection algorithm is used to identify pointers and character sequences in the detected image frame, segment the characters, and compare them with characters in the character database. The character sequence at the pointer position in the image frame is then converted into an encoded sequence.

[0034] Step 3: Based on the correspondence between the coding sequence and the partitions on the outer surface of the generator shaft, convert the coding sequence into the rotation angle of the generator shaft.

[0035] Step 4: Calculate the angular velocity of the generator shaft based on the rotation angle of the generator shaft as indicated by the pointer in adjacent image frames and the time interval between adjacent image frames.

[0036] Step 5: Calculate the frequency of the unit based on the angular velocity of the main shaft obtained in Step 4.

[0037] In step 4, let θ(t) be the rotation angle of the main shaft of the generator corresponding to the coded character sequence or color block sequence pointed to by the pointer in the current image frame, where t represents the current time; let θ(t-1) be the rotation angle of the main shaft of the generator corresponding to the coded character sequence or color block sequence pointed to by the pointer in the previous image frame, where t-1 represents the time corresponding to the previous image frame; let Δt be the time difference between the current image frame and the previous image frame.

[0038] Calculate the angle difference of the main shaft of the generator set.

[0039] Δθ=θ(t)-θ(t-1) (1)

[0040] Determine whether Δθ>0 holds true. If Δθ≥0, calculate the angle of rotation of the unit's main shaft per unit time.

[0041] ω=Δθ / Δt(2)

[0042] If Δθ < 0, then the unit experiences a zero-crossing phenomenon in the main shaft angle from time t-1 to time t. The angle of rotation of the main shaft per unit time can be calculated.

[0043] ω=(360°+Δθ) / Δt(3)

[0044] According to the formula

[0045]

[0046] ω=360°n

[0047] achievable

[0048]

[0049] Where n represents the unit speed; f represents the unit frequency;

[0050] By combining equations (2), (3), and (4), we can obtain...

[0051]

[0052] Where p represents the number of magnetic pole pairs of the unit.

[0053] In this embodiment, a 500fps industrial camera is used, acquiring 500 images per second, with a frame acquisition interval of 2ms. The edge detection algorithm in this embodiment refers to the edge extraction algorithm disclosed in the paper "An Improved Edge Extraction Algorithm Based on Canny Algorithm" published by Zhou Fei et al. at the 4th Academic Conference on Image and Graphics Technology and Applications in 2009.

[0054] The character segmentation algorithm used in this embodiment is the character segmentation algorithm disclosed in Wang Xueying's paper "Character Segmentation Based on Boundary Features" published in the third issue of the Journal of Liaoning Teachers College in 2020.

[0055] The character sequence composed of binary codes 0 and 1 in the embodiment can be replaced with a sequence of black and white color blocks. After implementation and verification, it does not affect the accuracy of unit frequency measurement and measurement calculation efficiency of the present invention.

[0056] Example 2

[0057] Similar to Embodiment 1, in this embodiment, the outer surface of the generator shaft is divided into N equal-angled sections along the circumference, where N represents the number of equal sections of the generator shaft. Each section is encoded, and a sequence of encoded characters is sprayed axially onto the identifiable area of ​​the generator shaft's outer surface to facilitate image acquisition. A fixed pointer is positioned on the outer surface of the generator shaft, pointing to the encoded characters. A hollow baffle is positioned on the outer surface of the generator shaft, with its hollow portion aligned with the identifiable area. The baffle is used to block other objects besides the character sequence during image acquisition, such as... Figure 3 As shown.

[0058] In one embodiment, the character sequence uses binary encoding 0 and 1, such as Figure 2 As shown.

[0059] like Figure 1 As shown, the frequency measurement method for hydropower units based on coded image recognition includes the following steps:

[0060] Step 1: Use an industrial camera to target the identifiable area on the outer surface of the main shaft of the unit and sample the image of the coded character sequence or color block sequence of the main shaft of the unit.

[0061] Step 2: Recognize the coded character sequence or color block sequence pointed to by the pointer in the image frame, extract the color of the character or color block and the arrangement order of the character or color block along the unit axis, and convert it into a coded sequence;

[0062] An edge detection algorithm is used to identify pointers and character sequences in the detected image frame, segment the characters, and compare them with characters in the character database. The character sequence at the pointer position in the image frame is then converted into an encoded sequence.

[0063] Step 3: Based on the correspondence between the coding sequence and the partitions on the outer surface of the generator shaft, convert the coding sequence into the rotation angle of the generator shaft.

[0064] Step 4: Calculate the angular velocity of the generator shaft based on the rotation angle of the generator shaft as indicated by the pointer in adjacent image frames and the time interval between adjacent image frames.

[0065] Step 5: Calculate the frequency of the unit based on the angular velocity of the main shaft obtained in Step 4.

[0066] In this embodiment, the current frame and the previous four frames of images captured by the industrial camera are taken. The angle of the main axis of the unit pointed to by the pointer in the current frame and the previous four frames are calculated respectively. The difference of the main axis angle of the unit in adjacent frames is obtained and the average value is calculated. The unit frequency is calculated based on the average value of the difference of the main axis angle of the unit.

[0067] Let the angles of the generator's major axis pointed to by the pointer in the current frame and the previous four frames be θ(t), θ(t-1), θ(t-2), θ(t-3), and θ(t-4);

[0068] The calculation of the unit frequency includes the following specific steps:

[0069] 1) Calculate the difference in the main shaft angle between adjacent frames:

[0070] Δθ(t)=θ(t)-θ(t-1) (6)

[0071] Δθ(t-1)=θ(t-1)-θ(t-2) (7)

[0072] Δθ(t-2)=θ(t-2)-θ(t-3) (8)

[0073] Δθ(t-3)=θ(t-3)-θ(t-4) (9)

[0074] 2) Determine whether Δθ(t), Δθ(t-1), Δθ(t-2), and Δθ(t-3) are all greater than 0. If the calculated difference between the main axis angles of the adjacent frames is negative, then there is a zero-crossing phenomenon of the main axis angle between the two adjacent frames at the time of their capture. The calculated difference between the main axis angles of the adjacent frames needs to be corrected.

[0075] Taking Δθ(t) as an example, if Δθ(t) < 0, then the formula for correcting the result of the unit's main shaft angle difference is:

[0076] Δθ(t)=θ(t)+360°-θ(t-1) (10)

[0077] 3) Calculate the average value of the unit shaft angle difference between adjacent frames obtained in step 2);

[0078]

[0079] In the formula This represents the average value of the main shaft angle difference of the unit;

[0080] 4) The unit frequency is calculated based on the average value of the main shaft angle difference of the unit;

[0081] The angle of rotation of the unit's main shaft per unit time:

[0082]

[0083] According to the formula

[0084]

[0085] ω=360°n

[0086] achievable

[0087]

[0088] Where n represents the unit speed; f represents the unit frequency; p represents the number of magnetic pole pairs of the unit; and Δt represents the time difference between the capture of the current image frame and the previous image frame.

[0089] In this embodiment, an industrial camera with a frame rate of 500fps is used, which captures 500 images per second. The time interval between image frames is 2ms, i.e., Δt = 0.002 seconds.

[0090] The minimum angular difference Δθ is Seek N determines the resolution of the frequency measurement; the larger N is, the higher the resolution of the frequency measurement.

Claims

1. A method for frequency measurement of a hydroelectric generating unit based on coded image recognition, characterized in that, The outer surface of the main shaft of the generator set is divided into multiple parts at equal angles along the circumference. Each part is coded and the coded character sequence or color block sequence is sprayed along the axial direction in the identifiable area of ​​the outer surface of the main shaft of the generator set to facilitate image acquisition and image recognition. A fixed pointer is set on the outer surface of the generator set's main shaft, pointing to one of the coded character sequences or color block sequences on the outer surface of the generator set's main shaft; A hollow baffle is installed on the outer surface of the main shaft of the generator set. The hollow part of the baffle is aligned with the coded and identifiable area on the outer surface of the main shaft of the generator set. The baffle is used to block other objects other than the character sequence or color block sequence during the image acquisition process. The method for measuring the frequency of a hydroelectric generator unit includes the following steps: Step 1: Use an industrial camera to target the identifiable area encoded on the outer surface of the main shaft of the machine unit, and sample the image of the encoded character sequence or color block sequence of the main shaft of the machine unit; Step 2: Recognize the coded character sequence or color block sequence pointed to by the pointer in the image frame, extract the color of the character or color block and the arrangement order of the character or color block along the unit axis, and convert it into a coded sequence; Step 3: Based on the correspondence between the coding sequence and the partitions on the outer surface of the generator shaft, convert the coding sequence into the rotation angle of the generator shaft; Step 4: Calculate the angular velocity of the generator shaft based on the rotation angle of the generator shaft as indicated by the pointer in adjacent image frames and the time interval between adjacent image frames; Step 5: Calculate the frequency of the unit based on the angular velocity of the main shaft obtained in Step 4; In step 4, the rotation angle of the main shaft of the unit corresponding to the coded character sequence or color block sequence pointed to by the pointer in the current image frame is recorded as follows: θ ( t ), t This indicates the current moment; the rotation angle of the main shaft of the unit corresponding to the coded character sequence or color block sequence pointed to by the pointer in the previous image frame is... θ ( t -1), t- 1 represents the time corresponding to the previous image frame; let the time difference between the current image frame and the previous image frame be denoted as . ; Calculate the angle difference of the main shaft of the generator set. ；（1） judge Whether it is true or not, if The angle of rotation of the unit's main shaft per unit time was calculated. ；（2） like Then the unit is t- 1 hour has arrived t The generator set's main shaft angle constantly crosses zero; the angle of rotation of the main shaft per unit time is calculated. ；（3） According to the formula ， ； achievable ; in n Indicates the unit speed; f Indicates the generator unit frequency; By combining equations (2), (3), and (4), we can obtain... ；（5） in p This indicates the number of magnetic pole pairs in the generator unit.

2. The method for measuring the frequency of a hydroelectric generator unit according to claim 1, characterized in that, The character sequence is encoded in binary.

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