Blade strain detection method and system based on hybrid fiber grating sensor

Abstract

The invention provides a blade strain detection method based on a hybrid fiber bragg grating sensor, and relates to the field of fan blade strain detection, and the method comprises the steps: enabling a strain fiber bragg grating sensor and a temperature fiber bragg grating sensor to be connected in series in a fan blade; light emitted by the laser enters the strain fiber grating sensor and the temperature fiber grating sensor; calculating the center wavelength of the strain fiber grating sensor at the moment t; angle information of the fan blade, a temperature value measured by a temperature fiber grating sensor and an initial parameter are obtained; constructing a strain correction algorithm; correcting the initial wavelength of the strain fiber grating sensor according to the initial parameter, the temperature value, the angle information and a strain correction algorithm; and calculating the strain value of the strain fiber grating sensor through the corrected initial wavelength of the strain fiber grating sensor. By correcting the initial wavelength of the strain fiber bragg grating sensor, the problem of cross sensitivity of the fiber bragg grating to strain and temperature is solved, and the measurement precision is improved.

Description

Technical Field

[0001] The present application relates to the field of wind turbine blade strain detection, and in particular to a blade strain detection method and system based on a hybrid fiber grating sensor. Background Art

[0002] In order to solve the energy crisis and ease global energy pressure, sustainable development, clean and pollution-free new energy is particularly important. Wind energy, as a clean and renewable energy, has the advantages of environmental protection, cleanliness, wide distribution and large reserves compared with traditional energy, which can effectively ease the energy crisis. China is rich in wind resources, and wind power generation has also developed rapidly in my country.

[0003] The wind turbine blades are the most critical part of the wind turbine. The damage of the blades will directly affect the stable operation of the wind turbine. It is necessary to monitor their strain in real time. The wind turbine blades are the most critical part of the wind turbine. Their cost accounts for about 15% to 20% of the total cost of the wind turbine. [1,2] Its damage will directly affect the smooth operation of the wind turbine, so it is necessary to monitor its status.

[0004] Existing monitoring methods include ultrasonic detection, image recognition, noise analysis, etc., which are indirect detection methods that reflect structural defects by detecting changes in other environmental parameters caused by deformation. [3] However, since the indirect detection method is subject to many external interference factors and is not sensitive to the early damage signal characteristics before the blade defects occur, the detection effect of this type of method is not ideal. Compared with the indirect detection method, direct detection of blade strain can more quickly and accurately reflect the operating status of the blade.

[0005] When a wind turbine blade is damaged, its deformation, stress, strain, temperature, and material properties will change significantly. The blade strain can be detected to reflect the damage of the blade, so that the blade can be maintained in time to avoid major accidents. Therefore, stable and reliable wind turbine blade strain detection technology is of great significance to the stable development of the wind power industry.

[0006] Fiber Bragg grating (FBG) sensors have excellent properties that cannot be replaced by traditional electrical sensors, such as strong anti-electromagnetic interference ability, low loss, suitable for long-distance transmission, corrosion resistance, small size, and high detection sensitivity. They have been widely used in civil engineering, aviation, shipping, electricity, petroleum, building structure health monitoring, complex mechanical system dynamic monitoring and other fields. [4,5] In addition, due to its light structure, high signal-to-noise ratio, and strong reusability, FBG has been successfully applied to strain monitoring of various structures. [6] .

[0007] Matveenko et al.[7] proposed a method of quoting strain values ​​between FBG sensors at different positions and conducted tensile tests on glass fiber specimens to achieve a rough judgment of the damage location. Jin et al. [8] The relationship between the wavelength shift of fiber Bragg grating and the crack extension length was studied, and the crack extension of aluminum alloy plate was monitored by fiber Bragg grating reflection spectrum. Yu et al. [9] Aiming at the problem of low-speed collision location, a FBG sensor network was constructed. Based on the skewness and steepness of the signal time series, a reliable method was provided to determine the collision location of carbon fiber composite panels. Alvarez et al.

[10] Combined with fiber Bragg grating detection technology, a damage diagnosis method based on strain field pattern recognition was proposed, and it was tested on the wing and achieved good results.

[0008] Existing deformation detection of wind turbine blades mostly only uses deformation-sensitive stress fiber Bragg grating sensors to perform stress detection on wind turbine blades. When the wind turbine blades are in different operating states, the detection error is relatively large. Summary of the invention

[0009] The purpose of the present invention is to solve the problems mentioned in the above background technology and to provide a blade strain detection method and system based on a hybrid fiber grating sensor that can accurately detect blade strain data in any state of a wind turbine.

[0010] The above-mentioned purpose of the present application is achieved through the following technical solutions:

[0011] S1: a strain fiber Bragg grating sensor and a temperature fiber Bragg grating sensor are arranged in series inside a fan blade; a laser is used to emit light incident on the strain fiber Bragg grating sensor and the temperature fiber Bragg grating sensor;

[0012] S2: Obtain the optical signal reflected by the strain fiber Bragg grating sensor and convert the optical signal into an electrical signal, and calculate the central wavelength λ of the strain fiber Bragg grating sensor at time t by combining the FBG demodulation algorithm. t ; Obtain the angle information of the fan blades and the temperature value T measured by the temperature fiber Bragg grating sensor t , and initial parameters;

[0013] S3: construct strain correction algorithm;

[0014] S4: Based on the initial parameters, the temperature value T t , angle information and strain correction algorithm to correct the initial wavelength λ0 of the strain fiber Bragg grating sensor;

[0015] S5: Calculate the strain value of the strain fiber Bragg grating sensor through the corrected initial wavelength λ0 of the strain fiber Bragg grating sensor, and the strain value is the strain detection result of the fan blade.

[0016] Optionally, the calculation formula of the FBG demodulation algorithm is as follows:

[0017]

[0018] Among them, λ t represents the central wavelength of the strain fiber Bragg grating sensor at time t; e -λ s Indicates that the output wavelength of the laser in one scanning cycle changes from λ s Increases linearly to λ e The difference between t It indicates the number of pulse signals input to the laser at time t; N indicates that there are N synchronization pulses in a scanning cycle. The synchronization pulse is used to record the number of wavelength changes. Every time the synchronization pulse outputs a falling edge signal, the wavelength of the laser increases by one step.

[0019] Optionally, the temperature T of the temperature fiber Bragg grating sensor at time t t The calculation formula is as follows:

[0020] T t =f T (λ T )

[0021] f T (λ T )=A*λ T *λ T +B*λ T +C

[0022] Among them, A, B, C represent the function f t The parameters are obtained from the temperature wavelength fitting curve of the temperature fiber Bragg grating; λ T represents the central wavelength of the temperature fiber Bragg grating sensor at temperature T; f T (λ T ) represents a quadratic function of the central wavelength.

[0023] Optionally, the strain correction algorithm is as follows:

[0024]

[0025]

[0026] Where λ0 is the initial wavelength of the strained fiber Bragg grating in the naturally straightened state, at which the strain value is zero; T trepresents the temperature measured by the fiber Bragg grating sensor at time t; abs represents the absolute value; N λ Used to determine whether the change in the fan wavelength is caused by stress; 0.008*N λ represents the effect of temperature on the central wavelength of the fiber Bragg grating sensor, N λ is a positive integer; g(t) is the angle information of the fan blade; g′(t) is the angular velocity, N g is the empirical value, g′(t)>N g Indicates that the fan is in a stopped state, ε t Represents the strain value measured by the strain fiber Bragg grating sensor.

[0027] Optionally, step S4 specifically includes:

[0028] Obtain angle information through the angle sensor of the fan blade and determine the differential value of the angle sensor to time; determine the working state of the fan according to the size of the differential value;

[0029] According to the working state of the fan and the temperature T at time t measured by the temperature fiber Bragg grating sensor t , the initial wavelength λ0 of the strain fiber grating sensor is corrected by the strain correction algorithm.

[0030] A blade strain detection system based on a hybrid fiber Bragg grating sensor, comprising: a fiber Bragg grating data acquisition module, an analog-to-digital conversion module, a main control module, an angle sensor, a communication module and a cloud control interface;

[0031] Fiber Bragg grating data acquisition module, analog-to-digital conversion module, main control module, angle sensor, communication module and cloud control interface;

[0032] The fiber grating data acquisition module is connected to the analog-to-digital conversion module; the angle sensor and the analog-to-digital conversion module are connected to the main control module; the main control module is connected to the communication module; and the communication module is connected to the cloud control interface;

[0033] The fiber Bragg grating data acquisition module is used to convert the collected optical signals into electrical signals;

[0034] The analog-to-digital conversion module converts the analog electrical signal into a digital signal and sends it to the main control module. After the FBG demodulation algorithm, the central wavelength of the strain fiber Bragg grating sensor and the temperature value of the temperature fiber Bragg grating sensor are obtained;

[0035] The main control module is used to obtain the angle information of the angle sensor, judge the operating status of the fan through the angle information and temperature value, and correct the central wavelength of the strain fiber Bragg grating sensor;

[0036] The main control module is also used to calculate the strain value of the strain fiber Bragg grating sensor through the corrected initial wavelength of the strain fiber Bragg grating sensor;

[0037] The main control module packages the calculated strain values ​​and sends them to the cloud control interface through the communication module to complete the collection of the entire strain data.

[0038] Optionally, the fiber Bragg grating data acquisition module includes: a laser, a beam splitter, a circulator, an optical fiber, a photodetector, and a circuit switching module;

[0039] The chip types of the main control module include: FPGA chip and ARM chip;

[0040] The laser is connected to the beam splitter; the beam splitter is connected to the circulator; the circulator is connected to three optical fibers; eight fiber grating sensors are embedded in each optical fiber, including two temperature grating sensors respectively arranged at the two ends of the grating, and six strain grating sensors are arranged in the middle of the two temperature gratings; the circulator is connected to the photodetector, and the photodetector is connected to the circuit switching module;

[0041] The laser uses an adjustable laser; the laser is used to emit laser, which is divided into three beams by a beam splitter and enters three circulators respectively, and then enters the fiber grating sensor after passing through the circulator; the light equal to the central wavelength of the fiber grating sensor will be reflected back and enter the photodetector through the circulator; the photodetector converts the optical signal into an electrical signal, which is input into the analog-to-digital conversion module in sequence through the circuit switching module.

[0042] An electronic device comprises a processor, a memory, a user interface and a network interface, wherein the memory is used to store instructions, the user interface and the network interface are used to communicate with other devices, and the processor is used to execute the instructions stored in the memory so that the electronic device executes a blade strain detection method based on a hybrid fiber grating sensor.

[0043] A computer-readable storage medium stores instructions. When the instructions are executed, a blade strain detection method based on a hybrid fiber grating sensor is performed.

[0044] The beneficial effects of the technical solution provided by this application are:

[0045] According to the real-time rotation angle information of the fan blades, the operating status of the fan blades is determined; a more accurate strain correction algorithm is constructed; the temperature value measured by the temperature fiber Bragg grating sensor is obtained; the initial wavelength of the strain fiber Bragg grating sensor is corrected through the strain correction algorithm, temperature value and the determined operating status, and the actual strain value of the corresponding position of the strain fiber Bragg grating sensor is calculated through the corrected initial wavelength. This solves the problem that the fiber Bragg grating is cross-sensitive to strain and temperature, reducing the limited measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The present application will be further described below with reference to the accompanying drawings and embodiments, in which:

[0047] Figure 1 is a step diagram of a blade strain detection method based on a hybrid fiber grating sensor in an embodiment of the present application;

[0048] Figure 2 is a curve diagram of the FBG strain variation over time in the fan shutdown state of the blade strain detection method based on the hybrid fiber grating sensor in the embodiment of the present application;

[0049] Figure 3 is a graph of the FBG strain variation over time in the blade strain detection method based on the hybrid fiber grating sensor in the embodiment of the present application under the operation state of the wind turbine;

[0050] Figure 4 It is a fiber Bragg grating structure and principle diagram of a blade strain detection method based on a hybrid fiber Bragg grating sensor in an embodiment of the present application;

[0051] Figure 5 is a temperature wavelength fitting curve diagram of the temperature grating in the blade strain detection method based on the hybrid fiber grating sensor in the embodiment of the present application;

[0052] Figure 6 It is a structural block diagram of a fan blade strain monitoring system based on a blade strain detection system of a hybrid fiber grating sensor in an embodiment of the present application;

[0053] Figure 7 Schematic diagram of FBG distribution of a blade strain detection system based on a hybrid fiber grating sensor in an embodiment of the present application;

[0054] Figure 8 This is a monitoring data diagram of a fan blade stopping operation according to a blade strain detection method based on a hybrid fiber grating sensor in an embodiment of the present application;

[0055] Fig. 9 It is a wind turbine blade monitoring data diagram of a blade strain detection method based on a hybrid fiber grating sensor in an embodiment of the present application;

[0056] Fig.10 It is a force distribution diagram of a wind turbine blade according to a blade strain detection method based on a hybrid fiber grating sensor in an embodiment of the present application;

[0057] Fig.11 It is a schematic diagram of the electronic device structure of the blade strain detection method based on the hybrid fiber grating sensor in the embodiment of the present application. DETAILED DESCRIPTION

[0058] In order to have a clearer understanding of the technical features, purposes and effects of the present application, the specific implementation methods of the present application are now described in detail with reference to the accompanying drawings.

[0059] An embodiment of the present application provides a blade strain detection method based on a hybrid fiber grating sensor.

[0060] Please refer to Figure 1 , Figure 1 : is a step diagram of a blade strain detection method based on a hybrid fiber grating sensor in an embodiment of the present application, comprising:

[0061] S1: a strain fiber Bragg grating sensor and a temperature fiber Bragg grating sensor are arranged in series inside a fan blade; a laser is used to emit light incident on the strain fiber Bragg grating sensor and the temperature fiber Bragg grating sensor;

[0062] S2: Obtain the optical signal reflected by the strain fiber Bragg grating sensor and convert the optical signal into an electrical signal, and calculate the central wavelength λ of the strain fiber Bragg grating sensor at time t by combining the FBG demodulation algorithm. t ; Obtain the angle information of the fan blades and the temperature value T measured by the temperature fiber Bragg grating sensor t , and initial parameters;

[0063] S3: construct strain correction algorithm;

[0064] S4: Based on the initial parameters, the temperature value T t , angle information and strain correction algorithm to correct the initial wavelength λ0 of the strain fiber Bragg grating sensor;

[0065] S5: Calculate the strain value of the strain fiber Bragg grating sensor through the corrected initial wavelength λ0 of the strain fiber Bragg grating sensor, and the strain value is the strain detection result of the fan blade.

[0066] Specifically, the temperature compensation principle of the fiber Bragg grating method [11,12]Two gratings are connected in series inside the fiber Bragg grating strain gauge, one is the strain grating, which is tightly fixed on the structure, and its wavelength is affected by both strain and temperature; the other is the temperature grating, whose wavelength is only affected by temperature and is used for temperature compensation. The conventional temperature compensation scheme of the series temperature grating performs temperature compensation on the strain grating, which is simple and fast. When the fan is in operation, temperature is not the main influencing factor and the measured stress value is more accurate. When the fan is stopped, temperature has a greater impact on the measured stress value. Due to the cross-sensitivity of the fiber Bragg grating to strain and temperature, the measurement accuracy is limited, resulting in the temperature compensation scheme of the series temperature grating. When the fan is stopped, it is unable to accurately detect the strain data of the blades; therefore, the angle information is introduced to judge the operating state of the fan blades. Under different operating states of the fan blades, the corresponding correction method is used to correct the initial wavelength of the strain fiber Bragg grating sensor.

[0067] The calculation formula of the FBG demodulation algorithm is as follows:

[0068]

[0069] Among them, λ t represents the central wavelength of the strain fiber Bragg grating sensor at time t; e -λ s Indicates that the output wavelength of the laser in one scanning cycle changes from λ s Increases linearly to λ e The difference between t It indicates the number of pulse signals input to the laser at time t; N indicates that there are N synchronization pulses in a scanning cycle. The synchronization pulse is used to record the number of wavelength changes. Every time the synchronization pulse outputs a falling edge signal, the wavelength of the laser increases by one step.

[0070] The temperature T of the temperature fiber Bragg grating sensor at time t t The calculation formula is as follows:

[0071] T t =f T (λ T )

[0072] f T (λ T )=A*λ T *λ T +B*λ T +C

[0073] Among them, A, B, C represent the function f t The parameters are obtained from the temperature wavelength fitting curve of the temperature fiber Bragg grating; λ T represents the central wavelength of the temperature fiber Bragg grating sensor at temperature T; f T (λ T) represents a quadratic function of the central wavelength.

[0074] The strain correction algorithm is as follows:

[0075]

[0076]

[0077] Where λ0 is the initial wavelength of the strained fiber Bragg grating in the naturally straightened state, at which the strain value is zero; T t represents the temperature measured by the fiber Bragg grating sensor at time t; abs represents the absolute value; N λ Used to determine whether the change in the fan wavelength is caused by stress; 0.008*N λ represents the effect of temperature on the central wavelength of the fiber Bragg grating sensor, N λ is a positive integer; g(t) is the angle information of the fan blade; g′(t) is the angular velocity, N g is the empirical value, g′(t)>N g Indicates that the fan is in a stopped state, ε t Represents the strain value measured by the strain fiber Bragg grating sensor.

[0078] Step S4 specifically includes:

[0079] Obtain angle information through the angle sensor of the fan blade and determine the differential value of the angle sensor to time; determine the working state of the fan according to the size of the differential value;

[0080] According to the working state of the fan and the temperature T at time t measured by the temperature fiber Bragg grating sensor t , the initial wavelength λ0 of the strain fiber grating sensor is corrected by the strain correction algorithm.

[0081] Specifically, when broadband light is transmitted in a fiber Bragg grating, the incident light that meets the conditions will be reflected back by the fiber Bragg grating, and the reflected wavelength of the light must satisfy the fiber equation:

[0082] λ B =2n eff Λ (1)

[0083] Among them, λ B is the central wavelength of the Bragg grating, n eff is the effective refractive index of the fiber Bragg grating, Λ is the grating period of the fiber Bragg grating;

[0084] Taking the differentiation on both sides of the fiber equation, we can obtain:

[0085] Δλ B =2Δn eff Λ+2n effΔΛ (2)

[0086] Fiber effective refractive index n eff It will change with the change of temperature due to the thermo-optic effect, and it will also change with the change of longitudinal strain due to the elastic-optic effect. At the same time, due to the change of the optical fiber length l due to the thermal expansion effect, the grating period Λ will also change accordingly, so n eff and Λ are functions of temperature T and fiber length l, and we get:

[0087]

[0088]

[0089] Substituting formula (3) and (4) into formula (2), the formula for the central wavelength of fiber Bragg grating sensing when strain and temperature change is derived:

[0090]

[0091] The sensing principle can be expressed by formula (6), as follows:

[0092] Δλ B =λ B (K T ΔT+K ε Δε) (6)

[0093] Among them, K T is the temperature sensitivity of the fiber Bragg grating, K ε is the strain sensitivity of the fiber Bragg grating, Δε is the strain of the fiber Bragg grating sensor, and ΔT is the temperature change;

[0094] Assume that at time t0, the fiber Bragg grating sensor is in a naturally straightened state, the strain is 0, the initial wavelength of the fiber Bragg grating sensor is λ0, and the temperature at this time is T0; Assume that at time t, the central wavelength of the fiber Bragg grating sensor is λ t , temperature is T t , the strain value is ε t , according to formula (6):

[0095] λ t -λ0=λ0[K T (T t -T0)+K ε ε t ] (7)

[0096] According to formula (7), the strain calculation formula of the fiber Bragg grating sensor at time t can be calculated as:

[0097]

[0098] Among them, KT and K ε is the factory parameter of the fiber Bragg grating, and its size is determined by the material of the fiber Bragg grating; λ0 and T0 are the parameters obtained when the fiber Bragg grating leaves the factory; ε t is the strain value of the strain fiber Bragg grating sensor corresponding to the position of the fan blade.

[0099] A blade strain detection system based on a hybrid fiber Bragg grating sensor, comprising: a fiber Bragg grating data acquisition module, an analog-to-digital conversion module, a main control module, an angle sensor, a communication module and a cloud control interface;

[0100] The fiber grating data acquisition module is connected to the analog-to-digital conversion module; the angle sensor and the analog-to-digital conversion module are connected to the main control module; the main control module is connected to the communication module; and the communication module is connected to the cloud control interface;

[0101] The fiber Bragg grating data acquisition module is used to convert the collected optical signals into electrical signals;

[0102] The analog-to-digital conversion module converts the analog electrical signal into a digital signal and sends it to the main control module. After the FBG demodulation algorithm, the central wavelength of the strain fiber Bragg grating sensor and the temperature value of the temperature fiber Bragg grating sensor are obtained;

[0103] The main control module is used to obtain the angle information of the angle sensor, judge the operating status of the fan through the angle information and temperature value, and correct the central wavelength of the strain fiber Bragg grating sensor;

[0104] The main control module is also used to calculate the strain value of the strain fiber Bragg grating sensor through the corrected initial wavelength of the strain fiber Bragg grating sensor;

[0105] The main control module packages the calculated strain values ​​and sends them to the cloud control interface through the communication module to complete the collection of the entire strain data.

[0106] The fiber grating data acquisition module includes: a laser, a beam splitter, a circulator, an optical fiber, a photoelectric detector, and a circuit switching module;

[0107] The chip types of the main control module include: FPGA chip and ARM chip;

[0108] The laser is connected to the beam splitter; the beam splitter is connected to the circulator; the circulator is connected to three optical fibers; eight fiber grating sensors are embedded in each optical fiber, including two temperature grating sensors respectively arranged at the two ends of the grating, and six strain grating sensors are arranged in the middle of the two temperature gratings; the circulator is connected to the photodetector, and the photodetector is connected to the circuit switching module;

[0109] The laser uses an adjustable laser; the laser is used to emit laser, which is divided into three beams by a beam splitter and enters three circulators respectively, and then enters the fiber grating sensor after passing through the circulator; the light equal to the central wavelength of the fiber grating sensor will be reflected back and enter the photodetector through the circulator; the photodetector converts the optical signal into an electrical signal, which is input into the analog-to-digital conversion module in sequence through the circuit switching module.

[0110] The central wavelengths of all fiber Bragg grating sensors used in this application are measured at 22°C, i.e., T0 = 22°C. FBGX_0 and FBGX_7 are the wavelengths of the temperature gratings, and the others are the wavelengths of the strain gratings. The initial central wavelength λ0 of each fiber Bragg grating sensor can be obtained by looking up the table. K can be obtained based on the factory parameters of the selected fiber Bragg grating model. ε ≈0.78×10 -6 nm / uε,K T ≈1.1×10 -2 nm / uε.

[0111] Specifically, Figure 4 As shown in Figure 1, the fiber Bragg grating acts like a bandpass filter, which can reflect and transmit light of a specific wavelength. Changes in external measured variables (such as strain, temperature, etc.) can cause the axial deformation of the fiber Bragg grating, thereby causing the wavelength of its reflected light to shift.

[0112] Specifically, the effect of temperature change on the central wavelength of FBG is as follows: Figure 2 It is a curve chart of FBG strain change over time when the wind turbine is stopped. It can be seen from the figure that the data with strain change below 10με is mainly caused by temperature change, wavelength measurement error and slow swing of wind turbine blades, while the others are mainly caused by blade rotation. Figure 3 It is a curve diagram of the FBG strain change over time when the wind turbine is running. At this time, the strain change is greater than 200με, which is much greater than the FBG strain change when the wind turbine is stopped.

[0113] Since the change in ambient temperature is a very slow process, the amount of change each time is very small, and its impact on the central wavelength of the strain grating is accumulated over time. When the fan is running, the strain change of the blades is an instantaneous process, the amount of change each time is large, and it will return to its original state immediately. However, when the fan is stopped, it will rotate slowly due to the influence of the wind. At this time, the change in the central wavelength of the FBG caused by the free rotation of the blades may be superimposed on the change in the central wavelength caused by temperature. Therefore, how to distinguish from the tiny wavelength changes whether it is the temperature change or the free rotation of the blades that causes the change in the central wavelength of the FBG is the primary problem to be solved in this application.

[0114] Specifically, the light generated by the laser is divided into three beams by a beam splitter and enters three circulators respectively, and then enters the fiber grating sensor after passing through the circulator; the light with the same central wavelength as the fiber grating sensor will be reflected back and enter the photodetector through the circulator; the photodetector converts the optical signal into an electrical signal, which is sequentially input to the analog-to-digital conversion module through the circuit switching module, and the analog-to-digital conversion module converts the analog electrical signal into a digital signal and sends it to the main control module, and the corresponding wavelength data of the fiber grating sensor is obtained after the demodulation algorithm;

[0115] The FPGA sends the demodulated wavelength data to the ARM processor through the SPI bus. The ARM processor finally packages the data and sends it to the cloud control interface through the 4G communication module to complete the entire data collection.

[0116] Specifically, the fan blade is the most critical part of the wind turbine. The damage of the blade will directly affect the smooth operation of the wind turbine. It is very necessary to monitor its strain in real time. This application designs a blade strain detection system based on a hybrid fiber grating sensor and applies it to the strain monitoring of wind turbine blades. At the same time, in view of the fact that the strain of the fan blade is affected by temperature, this application points out the problems existing in the use of traditional temperature correction methods on fan blades. On this basis, improvements are made, and the angle data of the real-time rotation of the fan blade is combined to construct a strain correction algorithm, which has achieved good results in the strain monitoring of wind turbine blades.

[0117] The verification results are as follows: The data of the fan stopping operation within a period of time was collected, such as Figure 8 As shown in the figure. When the rotation angle of the wind turbine blade changes slightly, as the temperature drops, the blade strain without the temperature correction algorithm will change due to the temperature. However, the strain data using the strain correction algorithm remains unchanged, indicating that our algorithm model can well correct the influence of temperature on the FBG center wavelength.

[0118] In order to further verify the algorithm, the wind turbine blade monitoring data was collected continuously for about 12 hours, such as Fig. 9 As shown in the figure, it can be seen that the fan is in operation for more than 6 hours, and in the shutdown and natural swing state for more than 5 hours. Fig. 9 From the second and third figures, we can see that the strain does not shift with the change of temperature, which shows that the temperature correction algorithm does play a corrective role. From the analysis of the natural swing of the fan during shutdown, the strain returns to near 0 at this time, and changes periodically with the natural swing of the blades. It can be further analyzed that the strain correction algorithm of this application can perform temperature correction well, and there is no strain shift.

[0119] For example, if Figure 7As shown, 8 FBG sensors are installed on a fan blade, the six in the middle are strain fiber Bragg grating sensors, and the two on the left and right are temperature fiber Bragg grating sensors; the two on the left and right are temperature fiber Bragg grating sensors, and the average value can be taken, which is the temperature inside the fan blade;

[0120] In order to analyze the internal force distribution of the blade, the strain data of 6 strain fiber Bragg grating sensors on a single blade were collected and the following graph was drawn after filtering and data fitting: Fig.10 The curve of the strain of the wind turbine blades changing with time is shown in the figure. It can be seen from the figure that the waveforms of the four groups of data FBG1, FBG3, FBG4, and FBG6 are very similar, and the vibration amplitude is very obvious. On the contrary, the vibration amplitude of FBG2 and FBG5 is very small. Combined with the distribution of FBG on the wind turbine blades in the previous section, it can be seen that FBG1, FBG3, FBG4, and FBG6 are all pasted horizontally inside the blades, while FBG2 and FBG5 are pasted vertically. Therefore, we can analyze that the blades are mainly subjected to lateral forces when the wind turbine is running. From the FBG vibration amplitude data in the figure, it can be seen that the amplitudes of FBG1, FBG3, FBG4, and FBG6 are increasing, indicating that the closer the wind turbine blades are to the top of the blades, the more obvious the deformation of the blades.

[0121] [1][D]Du, Ying, et al. "Damage detection techniques for wind turbineblades: A review." Mechanical Systems and Signal Processing141(2020):106445.

[0122] [2][E]Malekimoghadam, Reza, Stefan Krause, and Steffen Czichon. "Acritical review on the structural health monitoring methods of the compositewind turbine blades." Proceedings of 1st International Conference on Structural Damage Modelling and Assessment. Springer, Singapore, 2021.

[0123] [3][A] Hu Yanping, Dai Juchuan, Liu Deshun. Research status and development trend of large wind turbine blades[J]. Journal of Mechanical Engineering, 2013, 49(20): 140-151

[0124] [4][B]Wang, Lei, Dong Sheng Li, and Jin Ping Ou. "Fiber Bragg grating temperature sensor system on a twin - deck continuous rigid frame bridge for long term monitoring." Advanced Materials Research. Vol. 148. Trans Tech Publications Ltd, 2011.

[0125] [5][C]Jiang Desheng, He Wei. Application overview of fiber Bragg grating sensors [J]. Journal of Optoelectronics·Laser, 2002(04):420 - 430.

[0126] [6][F]Soman, Rohan, et al. "A two - step guided waves based damage localization technique using optical fiber sensors." Sensors 20.20(2020):5804.

[0127] [7][G]Matveenko, Valerii, Natalia Kosheleva, and Grigorii Serovaev. "Damage detection algorithm based on using surface mounted fiber - optic sensors on Bragg gratings." Procedia Structural Integrity 18(2019):12 - 19.

[0128] [8][H]Jin, Xin, Shenfang Yuan, and Jian Chen. "On crack propagation monitoring by using reflection spectra of AFBG and UFBG sensors." Sensors and Actuators A:Physical 285(2019):491 - 500.

[0129] [9][I]Wang,Bingkai,et al."Location Determination of Impact on theWind Turbine Blade Surface Based on the FBG and the Time Difference."Sensors21.1(2021):232.

[0130]

[10] [J]Alvarez-Montoya,Joham,Alejandro Carvajal-Castrillón,and JuliánSierra-Pérez."In-flight and wireless damage detection in a UAV composite wingusing fiber optic sensors and strain field pattern recognition."MechanicalSystems and Signal Processing 136(2020):106526.

[0131]

[11] Zhu,Hong-Hu,et al."An optical fibre monitoring system forevaluating the performance of a soil nailed slope."Smart Structures andSystems 9.5(2012):393-410.

[0132]

[12] Weng,Xiaolin,et al."Experimental investigation of pavementbehavior after embankment widening using a fiber optic sensor network."Structural Health Monitoring 14.1(2015):46-56.

[0133] It should be noted that: when the device provided in the above embodiment realizes its function, only the division of the above functional modules is used as an example. In actual application, the above functions can be assigned to different functional modules as needed, that is, the internal structure of the device is divided into different functional modules to complete all or part of the functions described above. In addition, the device and method embodiments provided in the above embodiment belong to the same concept, and the specific implementation process is detailed in the method embodiment, which will not be repeated here.

[0134] The present application also discloses an electronic device. Fig.11 , Fig.11 The electronic device 500 may include: at least one processor 501 , at least one network interface 504 , a user interface 503 , a memory 505 , and at least one communication bus 502 .

[0135] The communication bus 502 is used to realize the connection and communication between these components.

[0136] The user interface 503 may include a display screen (Display) and a camera (Camera), and the optional user interface 503 may also include a standard wired interface and a wireless interface.

[0137] The network interface 504 may optionally include a standard wired interface or a wireless interface (such as a WI-FI interface).

[0138] Among them, the processor 501 may include one or more processing cores. The processor 501 uses various interfaces and lines to connect various parts in the entire server, and executes various functions of the server and processes data by running or executing instructions, programs, code sets or instruction sets stored in the memory 505, and calling data stored in the memory 505. Optionally, the processor 501 can be implemented in at least one hardware form of digital signal processing (Digital Signal Processing, DSP), field programmable gate array (Field-Programmable Gate Array, FPGA), and programmable logic array (Programmable Logic Array, PLA). The processor 501 can integrate one or a combination of a central processing unit (Central Processing Unit, CPU), a graphics processing unit (Graphics Processing Unit, GPU) and a modem. Among them, the CPU mainly processes the operating system, user interface and application programs; the GPU is responsible for rendering and drawing the content to be displayed on the display screen; the modem is used to process wireless communications. It can be understood that the above-mentioned modem may not be integrated into the processor 501, and it can be implemented separately through a chip.

[0139] The memory 505 may include a random access memory (Random Access Memory, RAM) or a read-only memory (Read-Only Memory).

[0140] Optionally, the memory 505 includes a non-transitory computer-readable storage medium. The memory 505 can be used to store instructions, programs, codes, code sets or instruction sets. The memory 505 may include a program storage area and a data storage area, wherein the program storage area may store instructions for implementing an operating system, instructions for at least one function (such as a touch function, a sound playback function, an image playback function, etc.), instructions for implementing the above-mentioned various method embodiments, etc.; the data storage area may store data involved in the above-mentioned various method embodiments, etc. The memory 505 optionally also includes but is not limited to at least one storage device located away from the aforementioned processor 501. Refer to Fig.11 The memory 505 as a computer storage medium may include an operating system, a network communication module, a user interface module, and an application program of a blade strain detection method based on a hybrid fiber grating sensor.

[0141] exist Fig.11In the electronic device 500 shown, the user interface 503 is mainly used to provide an input interface for the user and obtain the data input by the user; and the processor 501 can be used to call the application program stored in the memory 505 for a blade strain detection method based on a hybrid fiber grating sensor. When executed by one or more processors 501, the electronic device 500 executes one or more methods in the above-mentioned embodiments. It should be noted that for the aforementioned method embodiments, for the sake of simple description, they are all expressed as a series of action combinations, but those skilled in the art should be aware that the present application is not limited to the described order of actions, because according to the present application, certain steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily required for the present application.

[0142] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0143] In the several implementation modes provided in this application, it should be understood that the disclosed devices can be implemented in other ways. For example, the device embodiments described above are only schematic, such as the division of units, which is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed includes but is not limited to indirect coupling or communication connection of devices or units through some service interfaces, including but not limited to electrical or other forms.

[0144] The units described as separate components include but are not limited to, or may not be physically separated, and the components shown as units include but are not limited to, or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0145] In addition, each functional unit in each embodiment of the present application can be integrated into a processing unit, including but not limited to each unit being physically present separately, or two or more units can be integrated into one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of software functional units.

[0146] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent commodity, it can be stored in a computer-readable memory. Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product, which is stored in a memory and includes several instructions for a computer device (which can be a personal computer, server or network device, etc.) to execute all or part of the steps of the various embodiments of the present application. The aforementioned memory includes: various media that can store program codes, such as USB flash drives, mobile hard drives, magnetic disks or optical disks.

[0147] The above are only exemplary embodiments of the present disclosure and cannot be used to limit the scope of the present disclosure. That is, any equivalent changes and modifications made according to the teachings of the present disclosure are still within the scope of the present disclosure. After considering the disclosure of the specification and practice, those skilled in the art will easily think of other embodiments of the present disclosure.

[0148] This application is intended to cover any variation, use or adaptation of the present disclosure, which follows the general principles of the present disclosure and includes common knowledge or customary technical means in the art not described in the present disclosure. The description and examples are to be regarded as exemplary only, and the scope and spirit of the present disclosure are defined by the claims.

Claims

1. A blade strain detection method based on a hybrid fiber grating sensor, characterized in that: The method comprises the following steps: S1: a strain fiber Bragg grating sensor and a temperature fiber Bragg grating sensor are arranged in series inside a fan blade; a laser is used to emit light incident on the strain fiber Bragg grating sensor and the temperature fiber Bragg grating sensor; S2: Obtain the optical signal reflected by the strain fiber Bragg grating sensor and convert the optical signal into an electrical signal, and calculate the central wavelength λ of the strain fiber Bragg grating sensor at time t by combining the FBG demodulation algorithm. t ; Obtain the angle information of the fan blades and the temperature value T measured by the temperature fiber Bragg grating sensor t , and initial parameters; S3: construct strain correction algorithm; S4: Based on the initial parameters, the temperature value T t , angle information and strain correction algorithm to correct the initial wavelength λ0 of the strain fiber Bragg grating sensor; S5: Calculate the strain value of the strain fiber Bragg grating sensor through the corrected initial wavelength λ0 of the strain fiber Bragg grating sensor, and the strain value is the strain detection result of the fan blade.

2. A blade strain detection method based on hybrid fiber grating sensor as claimed in claim 1, characterized in that: The calculation formula of the FBG demodulation algorithm is as follows: Among them, λ t represents the central wavelength of the strain fiber Bragg grating sensor at time t; e -λ s Indicates that the output wavelength of the laser in one scanning cycle changes from λ s Increases linearly to λ e The difference between t It indicates the number of pulse signals input to the laser at time t; N indicates that there are N synchronization pulses in a scanning cycle. The synchronization pulse is used to record the number of wavelength changes. Every time the synchronization pulse outputs a falling edge signal, the wavelength of the laser increases by one step.

3. A blade strain detection method based on hybrid fiber grating sensor as claimed in claim 1, characterized in that: The temperature T of the temperature fiber Bragg grating sensor at time t t The calculation formula is as follows: T t =f T (l T ) f T (l T )=A*λ T *l T +B*λ T +C Among them, A, B, C represent the function f t The parameters are obtained from the temperature wavelength fitting curve of the temperature fiber Bragg grating; λ T represents the central wavelength of the temperature fiber Bragg grating sensor at temperature T; f T (λ T ) represents a quadratic function of the central wavelength.

4. A blade strain detection method based on hybrid fiber grating sensor as claimed in claim 1, characterized in that: The strain correction algorithm is as follows: Where λ0 is the initial wavelength of the strained fiber Bragg grating in the naturally straightened state, at which the strain value is zero; T t represents the temperature measured by the fiber Bragg grating sensor at time t; abs represents the absolute value; N λ Used to determine whether the change in the fan wavelength is caused by stress; 0.008*N λ represents the effect of temperature on the central wavelength of the fiber Bragg grating sensor, N λ is a positive integer; g(t) is the angle information of the fan blade; g′(t) is the angular velocity, N g is an empirical value, g′(t)>N g Indicates that the fan is in a stopped state, ε t Represents the strain value measured by the strain fiber Bragg grating sensor.

5. The blade strain detection method based on hybrid fiber grating sensor according to claim 1, characterized in that: Step S4 specifically includes: Obtain angle information through the angle sensor of the fan blade and determine the differential value of the angle sensor to time; determine the working state of the fan according to the size of the differential value; According to the working state of the fan and the temperature T at time t measured by the temperature fiber Bragg grating sensor t , the initial wavelength λ0 of the strain fiber grating sensor is corrected by the strain correction algorithm.

6. A blade strain detection system based on hybrid fiber grating sensor, characterized in that: include: Fiber Bragg grating data acquisition module, analog-to-digital conversion module, main control module, angle sensor, communication module and cloud control interface; The fiber grating data acquisition module is connected to the analog-to-digital conversion module; the angle sensor and the analog-to-digital conversion module are connected to the main control module; the main control module is connected to the communication module; and the communication module is connected to the cloud control interface; The fiber Bragg grating data acquisition module is used to convert the collected optical signals into electrical signals; The analog-to-digital conversion module converts the analog electrical signal into a digital signal and sends it to the main control module. After the FBG demodulation algorithm, the central wavelength of the strain fiber Bragg grating sensor and the temperature value of the temperature fiber Bragg grating sensor are obtained; The main control module is used to obtain the angle information of the angle sensor, judge the operating status of the fan through the angle information and temperature value, and correct the central wavelength of the strain fiber Bragg grating sensor; The main control module is also used to calculate the strain value of the strain fiber Bragg grating sensor through the corrected initial wavelength of the strain fiber Bragg grating sensor; The main control module packages the calculated strain values ​​and sends them to the cloud control interface through the communication module to complete the collection of the entire strain data.

7. A blade strain detection system based on hybrid fiber Bragg grating sensor as claimed in claim 6, characterized in that: The fiber grating data acquisition module includes: a laser, a beam splitter, a circulator, an optical fiber, a photoelectric detector, and a circuit switching module; The chip types of the main control module include: FPGA chip and ARM chip; The laser is connected to the beam splitter; the beam splitter is connected to the circulator; the circulator is connected to three optical fibers; eight fiber grating sensors are embedded in each optical fiber, including two temperature grating sensors respectively arranged at the two ends of the grating, and six strain grating sensors are arranged in the middle of the two temperature gratings; the circulator is connected to the photodetector, and the photodetector is connected to the circuit switching module; The laser uses an adjustable laser; the laser is used to emit laser, which is divided into three beams by a beam splitter and enters three circulators respectively, and then enters the fiber grating sensor after passing through the circulator; the light equal to the central wavelength of the fiber grating sensor will be reflected back and enter the photodetector through the circulator; the photodetector converts the optical signal into an electrical signal, which is input into the analog-to-digital conversion module in sequence through the circuit switching module.

8. An electronic device, characterized in that: The electronic device (500) comprises a processor (501), a memory (505), a user interface (503) and a network interface (504), wherein the memory (505) is used to store instructions, the user interface (503) and the network interface (504) are used to communicate with other devices, and the processor (501) is used to execute the instructions stored in the memory (505) so that the electronic device (500) executes the method according to any one of claims 1 to 5.

9. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores instructions, and when the instructions are executed, the method steps according to any one of claims 1 to 5 are performed.

Images