A decoupling control method for biaxial fatigue loading of fan blades

Abstract

The present invention relates to a decoupling control method for biaxial fatigue loading of wind turbine blades, comprising: applying a certain amplitude excitation to the blades by a vibration device; collecting raw signals during blade motion; decomposing the horizontal raw signals using a decoupling method to obtain horizontal flapping signal components and horizontal shimmy signal components; decomposing the vertical raw signals using a decoupling method to obtain vertical flapping signal components and vertical shimmy signal components; the vibration device selecting the horizontal shimmy signal component as a feedback signal to apply closed-loop loading to the blades in the horizontal direction; and the vibration device selecting the vertical flapping signal component as a feedback signal to apply closed-loop loading to the blades in the vertical direction. During the closed-loop loading process, the vibration device applies excitation when the feedback signal reaches a maximum value, with the excitation frequency approaching the frequency of the feedback signal. Compared with existing technologies, the present invention can effectively increase the fixed frequency of blade motion and shorten fatigue testing time.

Description

Technical Field

[0001] The present invention relates to the field of fatigue testing of fan blades, and in particular to a decoupling control method for biaxial fatigue loading of fan blades. Background Art

[0002] Before mass production, wind turbine blades typically undergo full-scale static and fatigue testing. During fatigue testing, blades are subjected to millions of fatigue vibrations in both the flapping and shimmying directions, with the vibration frequency corresponding to the first-order natural frequency in each direction. As blades grow larger, their natural frequencies decrease. To ensure that blades withstand loads more consistent with actual operating conditions, a growing number of testing institutions and researchers are conducting research on biaxial fatigue testing of blades. Biaxial testing, which involves simultaneous fatigue vibration of blades in both the flapping and shimmying directions, can significantly reduce testing time and better reflect the evolution of blade damage. For example, Chinese utility model patent publication number CN 212110522 U proposes a wind turbine blade fatigue testing system designed to reduce testing costs and improve loading accuracy during blade fatigue testing. However, existing biaxial loading tests still significantly reduce the blade's natural frequency due to the heavy weight of the blade and inertial excitation device, resulting in extended fatigue testing time and increased testing difficulty. Summary of the Invention

[0003] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a biaxial fatigue loading decoupling control method for fan blades.

[0004] The purpose of the present invention can be achieved by the following technical solutions:

[0005] A method for decoupling control of biaxial fatigue loading of fan blades, comprising the following steps:

[0006] S1. The excitation device applies a certain amplitude excitation to the blade in the horizontal and vertical directions to make the blade respond;

[0007] S2, collecting horizontal original signals and vertical original signals when the blade moves;

[0008] S3. Decomposing the horizontal original signal by a decoupling method to obtain a horizontal waving signal component signal and a horizontal shimmy signal component signal; decomposing the vertical original signal by a decoupling method to obtain a vertical waving signal component signal and a vertical shimmy signal component signal;

[0009] S4. The excitation device selects the horizontal swing signal component signal as a first feedback signal, and the excitation device performs closed-loop loading on the blade in the horizontal direction based on the first feedback signal; the excitation device selects the vertical flapping signal component signal as a second feedback signal, and the excitation device performs closed-loop loading on the blade in the vertical direction based on the second feedback signal;

[0010] During the closed-loop loading process, the excitation device applies excitation when the feedback signal reaches its maximum value, and the excitation frequency is close to the frequency of the feedback signal.

[0011] Furthermore, in step S4, when the feedback signal reaches a minimum value, the excitation is reduced to a certain value, and the value of the excitation remains unchanged during the process of the feedback signal changing from minimum to maximum, so as to keep the loading cable of the excitation device in a taut state.

[0012] Furthermore, the excitation device adopts a traction-type loading device, including a blade clamp, a motor, a drum, a loading cable and a pulley set. The drum is connected to the output shaft of the motor, one end of the loading cable is wound on the drum, and the other end passes through its corresponding pulley set and is connected to the side of the blade clamp.

[0013] Furthermore, the horizontal original signal and the vertical original signal of the blade movement are collected by strain gauges or distance measuring instruments, and the strain gauges are set at the main beam positions of the PS surface and SS surface of the blade, as well as the leading and trailing edge positions.

[0014] Furthermore, in step S3, the decoupling method adopts Fourier transform.

[0015] Furthermore, the horizontal original signal and the vertical original signal of the blade movement are collected by an encoder inside the vibration device.

[0016] Furthermore, in step S3, the decoupling method adopts function fitting, and the selected fitting function is a simple harmonic signal function.

[0017] Furthermore, in step S4, the excitation application time of the excitation device is ahead of the feedback signal by a certain phase.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. This invention collects raw signals from blades in motion, performs decoupling analysis, and then selects the appropriate decomposed signal as feedback to achieve closed-loop control of the blades. By tracking the blade's natural frequencies in the flapping and shimmying directions, excitation is applied at the peak of the motion, minimizing the output power of the excitation device. Since the excitation device is not mounted on the blades, the blade test frequency is effectively increased, shortening fatigue testing time.

[0020] 2. The original signal can be collected by strain gauges and distance measuring instruments, and the signal can be decoupled by Fourier transform, which makes the calculation convenient and fast.

[0021] 3. The original signal can also be collected directly using the encoder that comes with the excitation device, and the signal can be decoupled in conjunction with the fitting function algorithm. There is no need to set up additional measuring devices on the blade, which is more convenient to use.

[0022] 4. The excitation application of the excitation device has a certain advance phase, which is used to overcome the signal lag and the slight communication lag in the excitation device controller, and improve the accuracy of the excitation loading. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a structural schematic diagram of the present invention.

[0024] Figure 2 It is a schematic diagram illustrating parameters of parts on the cross section of the blade in the present invention.

[0025] Figure 3 Schematic diagram of the general trajectory of the two-axis vibration of the blade of the present invention.

[0026] FIG4 is a schematic diagram of a decoupling control method using amplitude or strain as the original signal in the present invention.

[0027] Figure 5 Schematic diagram of the decoupling control method using the encoder as the original signal in the present invention. DETAILED DESCRIPTION

[0028] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0029] like Figure 1 As shown, this embodiment provides a decoupling control method for biaxial fatigue loading of fan blades, comprising the following steps:

[0030] Step S1: The excitation device applies a certain amplitude to the blade in the horizontal and vertical directions, causing the blade to produce a visible response. The combined motion in these two directions produces a complex spatial trajectory in the rectangular coordinate system. This combined motion generates raw signals such as strain and displacement.

[0031] Step S2: collecting the original signals in the horizontal direction and the original signals in the vertical direction when the blade moves, that is, the horizontal original signal and the vertical original signal.

[0032] Step S3: Decompose the horizontal original signal by an appropriate decoupling method to obtain a horizontal waving signal component signal and a horizontal swing signal component signal; decompose the vertical original signal by an appropriate decoupling method to obtain a vertical waving signal component signal and a vertical swing signal component signal.

[0033] Step S4: The excitation device selects the horizontal swing signal component signal as the first feedback signal, and the excitation device performs closed-loop loading on the horizontal direction of the blade based on the first feedback signal; the excitation device selects the vertical swing signal component signal as the second feedback signal, and the excitation device performs closed-loop loading on the vertical direction of the blade based on the second feedback signal, thereby realizing blade resonant frequency tracking to ensure that the blade is always in a resonant state.

[0034] During closed-loop loading, the excitation device applies excitation when the feedback signal reaches its maximum value (the blade reaches its highest point in the flapping or shimmying direction), and the excitation frequency is close to the frequency of the feedback signal. When the feedback signal reaches its minimum value (the blade reaches its lowest point in the flapping or shimmying direction), the excitation is reduced to a certain value. This value remains unchanged during the transition of the feedback signal from minimum to maximum (i.e., blade rebound), and is used to maintain the tension of the excitation device's loading cable. When the excitation device performs closed-loop control based on the feedback signal, the feedback signal has been filtered, and the signal will have a certain lag. Since the controller also has a slight communication lag, when performing closed-loop control, the excitation device needs to output the excitation at a certain phase advance. The value of the advance phase needs to be determined based on the filtering algorithm and controller used.

[0035] In this embodiment, the excitation device adopts a traction-type loading device, which specifically includes a blade clamp, a motor, a drum, a loading cable and a pulley set. The blade clamp is clamped on the blade; the motor, drum, loading cable and pulley set each have two sets, the drum is connected to the output shaft of the motor, one end of the loading cable is wound on the drum, and the other end passes through its corresponding pulley set and is connected to the blade clamp. The two sets of combinations are connected to the blade clamp from the left and right sides or the upper and lower sides of the loading cable, respectively, to realize the excitation loading of the blade by the excitation device. Since the installation position of the excitation device is fixed, when the blade moves in space, the angle between the loading cable and the blade will continue to change. In order to ensure that the blade can reach the target amplitude, the excitation device can compensate and adjust the phase of the excitation applied to the blade according to the vibration trajectory of the blade.

[0036] In this embodiment, the appropriate decoupling method may be Fourier transform or function fitting. For an original signal composed of two signal components with different frequencies in the swing and shimmy directions, Fourier transform can be selected to obtain the amplitude-frequency characteristics and phase-frequency characteristics of each signal component, and then the variation pattern of the signal components can be obtained. In addition to Fourier transform, function fitting can also be used to obtain the variation pattern of the signal components. Among them, when using the function fitting method, it is necessary to select a suitable function and initial value. The following will specifically expand on the two decoupling methods:

[0037] 1. Using Fourier Transform

[0038] Fourier transform is applicable to the original signals collected by strain gauges and distance measuring instruments. Figure 2 As shown, strain gauges are typically attached to the main beams (PS-SC and SS-SC) and leading and trailing edges of the blade's PS and SS surfaces. Raw signals are obtained through numerical conversion of the strain gauges. A distance measuring instrument is placed directly on the side of the blade to directly obtain the raw signal.

[0039] Due to the structure of the blade itself, there will be a certain deflection angle, resulting in the blade vibration direction is not vertical or horizontal. That is, the blade's flapping or swinging direction is not consistent with the vertical or horizontal direction in the rectangular coordinate system, and the two directions form a certain angle. In the uniaxial test, the blade vibrates along the flapping and swinging directions, rather than the vertical and horizontal directions. In the biaxial fatigue test, combined with the deflection angle of the blade structure, it can be seen that its motion trajectory is as follows Figure 3 As shown, the blade trajectory is related to the vibration frequency and phase difference of the blade in the flapping and shimmying directions.

[0040] First, the excitation device is used to apply initial excitation to the blade in the horizontal and vertical directions. The blade will produce an initial trajectory, and the horizontal original signal measured by the rangefinder ( Figure 4a (shown as ) is the amplitude signal component of the blade's own flapping direction amplitude in the horizontal direction, that is, the horizontal flapping signal component ( Figure 4b ) and the amplitude signal component of the blade's own swing amplitude in the horizontal direction, that is, the horizontal swing signal component ( Figure 4c ). Similarly, the vertical amplitude raw signal measured by the rangefinder is also the superposition of the vertical flapping signal component and the vertical shimmy signal component. The blade's own flapping and shimmy amplitudes should satisfy Formula 1, while their respective horizontal amplitude signal components satisfy Formula 2. The horizontal amplitude raw signal measured by the rangefinder satisfies Formula 3.

[0041] Formula 1:

[0042]

[0043] in, and They are the self-flapping response and the self-shimmying response; and are the amplitudes of the blade in flapping and shimmying directions, respectively; and are the vibration frequencies of the blade in flapping and shimmying directions, respectively; and are the initial phase angles of blade vibration in flapping and shimmying directions, respectively.

[0044] Formula 2:

[0045]

[0046] in, and are the horizontal flapping signal component and the horizontal shimmy signal component respectively; and are the angles between the flapping or swinging direction of the blade and the vertical or horizontal direction in the rectangular coordinate system.

[0047] Formula 3:

[0048]

[0049] in, is the collected horizontal original signal.

[0050] Taking the original horizontal signal as an example, the measured original horizontal signal By performing filtering and Fourier transform, the horizontal waving signal component and the horizontal shimmy signal component in the original signal can be separated, that is, Formula 2.

[0051] Since the original signal in the horizontal direction is mainly composed of the swing vibration of the blade, the horizontal swing signal component is selected This signal serves as the feedback signal for the closed-loop control of the horizontal vibration excitation equipment. Similarly, the control process for the vertical exciter follows a similar process, requiring only the corresponding parameters to be modified. The vertical flapping signal component, separated from the vertical raw signal, is selected as the feedback signal for the closed-loop control of the vertical vibration excitation equipment. The exciter in each direction performs closed-loop control of the blade based on the feedback signal in that direction.

[0052] 2. Using function fitting

[0053] Function fitting is applicable to the raw data collected by the encoder inside the vibration device. The main process of the dual-axis decoupling control strategy is as follows:

[0054] First, the blades are initially excited using excitation equipment installed in the vertical and horizontal directions. The blades will generate an initial trajectory. Figure 5The original signal example of the encoder value in the horizontal direction is shown. The original signal in each direction is related to the blade's vertical amplitude, horizontal amplitude, and the initial installation position of the exciter in each direction, that is, it satisfies Formula 4:

[0055]

[0056] in, and They are the original acquisition signals of the encoder in the horizontal and vertical directions respectively; is the vertical original signal, is the horizontal original signal, satisfying Formula 5; and These are the initial installation positions of the vibrators in the horizontal and vertical directions, respectively.

[0057] Formula 5:

[0058]

[0059] in, and The vertical flapping signal component and the vertical shimmy signal component are respectively. That is, to satisfy Formula 6:

[0060]

[0061]

[0062] The acquired signals of the encoder in the horizontal and swinging directions are shown in Formula 4, which needs to be decoupled. Due to the complexity of the waveform of the acquired signal, a specified function fitting can be performed according to its rules. Since Formula 4 also contains and , we need to first solve and According to formula 4, when the acquisition signals of the two encoders and the initial installation position of the exciter are known, the equation about and For a quadratic equation with two variables, we can eliminate unreasonable solutions according to the actual situation and get and The law of change over time. At this time, according to Formula 5 and Formula 6, and There are two frequencies and The frequency is selected as and The simple harmonic signal is the fitting function, and the amplitude and initial phase of the fitting function are changed to match the value obtained by formula 4 as much as possible. and The law is followed, and finally the amplitude, frequency and initial phase difference of the two simple harmonic signals with the highest fitting are obtained.

[0063] When using encoders to collect signals for load control, it is necessary to obtain signals from both encoders at the same time. Further, the signal components of the blade's own flapping and shimmying directions in the horizontal and vertical directions can be obtained by joint solution. Select the vertical flapping signal component As the feedback signal for the closed-loop control of the vertical excitation equipment, the horizontal swing signal component is selected As the feedback signal for the closed-loop control of the horizontal vibration equipment, the vibrators in each direction perform closed-loop control on the blades according to the feedback signal in that direction.

[0064] The above describes in detail the preferred embodiments of the present invention. It should be understood that those skilled in the art can make numerous modifications and variations based on the concepts of the present invention without inventive effort. Therefore, any technical solutions that can be derived by those skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art should be within the scope of protection defined by the claims.

Claims

1. A biaxial fatigue loading decoupling control method for fan blades, characterized in that: The following steps are involved: S1. The excitation device applies a certain amplitude excitation to the blade in the horizontal and vertical directions to make the blade respond; S2, collecting horizontal original signals and vertical original signals when the blade moves; S3. Decomposing the horizontal original signal by a decoupling method to obtain a horizontal waving signal component signal and a horizontal shimmy signal component; Decomposing the vertical original signal by the decoupling method, the vertical flapping signal component and the vertical shimmy signal component are obtained; S4. The excitation device selects the horizontal swing signal component signal as a first feedback signal, and the excitation device performs closed-loop loading on the blade in the horizontal direction based on the first feedback signal; the excitation device selects the vertical flapping signal component signal as a second feedback signal, and the excitation device performs closed-loop loading on the blade in the vertical direction based on the second feedback signal; During the closed-loop loading process, the excitation device applies excitation when the feedback signal reaches a maximum value, and the excitation frequency is close to the frequency of the feedback signal; when the feedback signal reaches a maximum value, the excitation device applies excitation when the blade reaches the highest point in the flapping or shimmying direction; In step S4, when the feedback signal reaches a minimum value, the excitation is reduced to a certain value. The excitation value remains unchanged during the process of the feedback signal changing from minimum to maximum, so as to keep the loading cable of the excitation device in a taut state. When the feedback signal reaches a minimum value, the blade reaches the lowest point in the flapping or shimmying direction. The horizontal and vertical raw signals of the blade motion are collected by strain gauges or distance measuring instruments. The strain gauges are set at the main beam positions of the PS and SS surfaces of the blade, as well as the leading and trailing edges; the distance measuring instrument is set on one side of the blade; The horizontal original signal is decomposed by the decoupling method, and the formula is: in, and They are the self-flapping response and the self-shimmying response; and are the amplitudes of the blade in flapping and shimmying directions, respectively; and are the vibration frequencies of the blade in flapping and shimmying directions, respectively; and are the initial phase angles of vibration in the blade flapping and shimmying directions, respectively; in, and are the horizontal flapping signal component and the horizontal shimmy signal component respectively; and They are the angles between the flapping or swinging direction of the blade and the vertical or horizontal direction in the rectangular coordinate system. Due to the structure of the blade itself, there is a certain deflection angle, and the vibration direction of the blade is not vertical or horizontal, that is, the flapping or swinging direction of the blade is not consistent with the vertical or horizontal direction in the rectangular coordinate system, and the two directions form a certain angle.

2. A fan blade biaxial fatigue loading decoupling control method according to claim 1, characterized in that: The excitation device adopts a traction-type loading device, including a blade clamp, a motor, a drum, a loading cable and a pulley set. The drum is connected to the output shaft of the motor. One end of the loading cable is wound on the drum, and the other end passes through its corresponding pulley set and is connected to the side of the blade clamp.

3. A fan blade biaxial fatigue loading decoupling control method according to claim 1, characterized in that: In step S3, the decoupling method adopts Fourier transform.

4. A fan blade biaxial fatigue loading decoupling control method according to claim 1, characterized in that: In step S4, the excitation application time of the excitation device is ahead of the feedback signal by a certain phase.

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