Wind turbine generator blade multi-section load estimation method based on blade root load

Abstract

The invention provides a wind turbine generator blade multi-section load estimation method based on blade root load, which comprises the following steps: acquiring blade design parameters and operation parameters of a wind turbine generator, and calculating blade static load based on the blade design parameters; constructing a blade dynamic model based on the static load, and obtaining a blade modal state equation according to the blade dynamic model; carrying out order reduction processing on the blade modal state equation, and correcting the blade modal state equation after order reduction by adopting Kalman filtering based on the operation parameters to obtain a displacement equation of each section of the blade; and estimating the load of each section of the blade based on the displacement equation of each section of the blade. The problems that in the prior art, wind turbine generator blade data are difficult to measure, and load estimation is inaccurate are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of wind power generation, and in particular to a method for estimating multi-section loads of wind turbine blades based on blade root loads. Background Art

[0002] In order to meet the requirements of the grid parity policy for the wind power industry, the design and development of wind turbines are constantly breaking through the original design methods and design boundaries in order to achieve improved product performance and reduced costs. Under the background of rapid development of the industry and product technology, if the load status of key components such as blades and towers of wind turbines is grasped in real time during service, accurate evaluation of the performance and status of the unit can be achieved, thereby avoiding abnormal fatigue over-limit or extreme overload events, and guiding life calculation and unit operation optimization.

[0003] Traditional component fatigue life prediction based on measured results requires the participation of direct sensor signals, and is not feasible for mass production due to cost and installation conditions. Component fatigue life prediction based on digital simulation models uses wind conditions to perform fatigue life fitting assessment. However, due to limited data dimensions and deviations in on-site wind condition measurements, it cannot accurately reflect component fatigue loads for actual working conditions that exceed the design. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a method for estimating multi-section loads of wind turbine blades based on blade root loads, which solves the problems of difficult data measurement and inaccurate load estimation of wind turbine blades in the prior art.

[0005] According to an embodiment of the present invention, a method for estimating multi-section loads of a wind turbine blade based on blade root loads comprises:

[0006] Obtain blade design parameters and operating parameters of the wind turbine, and calculate the blade static load based on the blade design parameters;

[0007] A blade dynamics model is constructed based on static loads, and the blade modal state equation is obtained according to the blade dynamics model;

[0008] The blade modal state equation is reduced in order, and based on the operating parameters, the Kalman filter is used to correct the reduced blade modal state equation to obtain the displacement equation of each section of the blade;

[0009] Based on the displacement equations of each blade section, the load on each blade section is estimated.

[0010] Preferably, the blade parameters include the blade cross-sectional chord length and the cross-sectional inflow angle;

[0011] The operating parameters include blade root bending moment load.

[0012] Preferably, the blade static load includes aerodynamic load and gravity load;

[0013] The blade element momentum theory method is used to solve the aerodynamic load and gravity load.

[0014] Preferably, the method for obtaining the blade modal state equation is as follows:

[0015] The blade is discretized into multiple beam elements using the finite element method, and each beam element is numbered;

[0016] Connect the beam elements end to end according to the numbers and establish the blade dynamics model;

[0017] The mass and stiffness matrix of each beam element are obtained according to the blade dynamics model, and the aerodynamic load and gravity load are equivalently converted into node loads using the finite element method.

[0018] Based on the mass and stiffness matrices of each beam element and the node loads, the blade dynamic state equation is obtained;

[0019] The blade dynamic state equation is transformed into a characteristic form to obtain the blade modal state equation.

[0020] Preferably, the blade dynamics model is as follows:

[0021]

[0022]

[0023] X e =[d1φ1d2φ2] T

[0024] Among them, ρ e is the mass density of the beam element, l is the length of the beam element, E is the Young's modulus, I is the section moment of inertia of the beam element, d1 and φ1 are the translational and rotational displacements of node 1, respectively, and d2 and φ2 are the translational and rotational displacements of node 2, respectively.

[0025] Preferably, the blade modal state equation is as follows:

[0026]

[0027] in, is the system damping, and are the diagonal element values ​​of the modal mass matrix and the modal stiffness matrix, respectively. is the displacement vector.

[0028] Preferably, the system damping includes aerodynamic damping and structural damping, the aerodynamic damping is obtained when calculating the aerodynamic load, and the structural damping is a constant value.

[0029] Preferably, the steps for obtaining the displacement estimation equation of each section of the blade are as follows:

[0030] The blade modal state equation is reduced to a third-order differential equation and converted into a state-space expression, and then the blade root bending moment load is used as the output of the state-space expression;

[0031] The state space expression is transformed into a discrete space expression, and the discrete space expression is corrected by using Kalman filtering to obtain the displacement estimation equation of each section of the blade.

[0032] Preferably, based on the displacement equations of each blade section, the bending moment equations of each blade section can be obtained:

[0033]

[0034] Among them, M i is the bending moment at the ith node, X(k)=[X1(k)...X i (k)...X N (k)] T is the translational displacement of each node of the blade, k is the stiffness of the beam element;

[0035] The moment equation is differentiated to obtain the load estimation equation for each section of the blade, and the load estimation equation is used to estimate the load on each section of the blade.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The present invention establishes a blade dynamics model, calculates the static load of the blade in actual operation according to the blade design parameters, adopts the Kalman filter algorithm to correct the blade motion state estimation result using the measured value of the blade root bending moment load, and finally realizes accurate estimation of the motion state and load level of multiple sections of the blade under the condition of limited cross-section measurement of the blade load, thereby solving the problems of difficult comprehensive measurement and inaccurate estimation. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a load estimation flow chart of an embodiment of the present invention.

[0039] Figure 2 This is a diagram of a finite unit method discrete blade model according to an embodiment of the present invention. DETAILED DESCRIPTION

[0040] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0041] like Figure 1 As shown, the embodiment of the present invention proposes a method for estimating multi-section loads of a wind turbine blade based on blade root loads, comprising:

[0042] Obtain blade design parameters and operating parameters of the wind turbine, and calculate the blade static load based on the blade design parameters;

[0043] The blade parameters include the blade section chord length and the section inflow angle;

[0044] Based on the blade element momentum theory BEM, the aerodynamic thrust per unit length of the blade in the direction perpendicular to the rotor surface and in the direction of the rotating tangent is shown as follows:

[0045]

[0046] Where ρ is the air density, W is the cross-sectional relative wind speed, c is the chord length of the blade cross section, is the cross-sectional inflow angle, C L and C D are the cross-sectional lift and drag coefficients respectively.

[0047] In the relative wind speed calculation, the exponential model shown in the following formula is used to calculate the free stream wind speed at other heights based on the hub center wind speed.

[0048]

[0049] Among them, V(z0,t) is the wind speed at the center height of the hub, and z is the height of the blade section at time t during the rotation process.

[0050] The gravity acting on the blades changes periodically with the rotor attitude angle θ during the rotation of the rotor. Considering the transmission chain elevation angle x and the rotor cone angle β, the gravity components along the three directions of the rotor coordinate system are shown in the following equations.

[0051]

[0052] Where m is the mass per unit length of the blade and g is the acceleration due to gravity.

[0053] A blade dynamics model is constructed based on static loads, and the blade modal state equation is obtained according to the blade dynamics model;

[0054] The finite unit method is used to discretize the blade into n beam elements to solve the problem of comprehensive measurement difficulties. Figure 2 As shown. Adjacent beam units are connected end to end and share node displacements. Each node considers two degrees of freedom, translation and rotation. Structural dynamic equations are established according to the two directions of the wind wheel out of the plane and in the plane, that is, the flapping and swinging directions of the blades. Among them, the mass matrix, stiffness matrix and corresponding displacement vector of a single beam unit are shown by the following three formulas:

[0055]

[0056]

[0057] X e =[d1φ1d2φ2] T

[0058] Among them, ρ e is the unit mass density, l is the unit length, E is Young's modulus, I is the unit section moment of inertia, d1 and φ1 are the translational and rotational displacements of node 1, d2 and φ2 are the translational and rotational displacements of node 2, respectively.

[0059] The unit mass and stiffness matrix of each beam are obtained in turn, and then assembled in sequence to obtain the dynamic equation shown in the following formula.

[0060]

[0061] Among them, f(t) is the node load after equivalent transformation of aerodynamic load and gravity load. According to the above formula, the characteristic equation is solved to obtain the characteristic angular frequency ω1 and the characteristic vector Φ i (i=1,2,…,N), based on the transformation relationship between the node displacement vector and the modal displacement vector X(t)=Φξ(t), the blade modal displacement equation is obtained:

[0062]

[0063] in, and are the modal mass matrix and the modal stiffness matrix, respectively. is the displacement vector. and is a diagonal matrix, and the diagonal elements are and For the i-th order mode, introduce system damping The state equation of the i-th order model can be written as shown in the following form:

[0064]

[0065] Among them, the system damping It is mainly composed of two parts: pneumatic damping and structural damping. The pneumatic damping is C D In , the structural damping can be defined as a constant value.

[0066] The blade modal state equation is reduced in order, and based on the operating parameters, the Kalman filter is used to correct the reduced blade modal state equation to obtain the displacement equation of each section of the blade;

[0067] The operating parameters include the blade root bending moment load, which can be accurately measured through actual operation.

[0068] Based on the blade dynamics analysis, usually the first three modes in a single direction can meet the accuracy requirements, so the blade modal displacement equation can be reduced to a set of third-order differential equations.

[0069] The Kalman filter algorithm is used to correct the blade motion state estimation result using the measured value of the blade root bending moment load to improve the estimation accuracy. First, the reduced-order differential equations need to be transformed into the state space expression shown in equation (1), and the blade root bending moment load is used as the output variable The output equation is shown in formula (2).

[0070]

[0071]

[0072] in, is the displacement of each section of the blade, which is a state quantity, x is the state vector, u is the input vector, w is the input interference (or process noise) vector, A, B, and G are the state matrix, input matrix, and input interference matrix, respectively. is the measurable output variable, H is the output matrix, and v is the measurement noise. The expressions of x, A, B, and G are as follows.

[0073] x=[ξ T ξ T ] T

[0074]

[0075]

[0076]

[0077] Equations (1) and (2) are continuous state space expressions in the time domain. To facilitate simulation calculation and control, they need to be converted into discrete expressions, as shown below.

[0078] x k+1 =Φ k x k +Γ k u k +γ k w k

[0079]

[0080] Among them, x k=x(kΔt), Δt is the time step. For the above formula, the discrete linear Kalman filter can be used to improve the estimation accuracy of the state quantity of the state equation. The corrected discrete state equation is shown in formula (3). Kalman gain matrix K k As shown in formula (4). The deviation between the estimated value and the true value of the state quantity is defined as the estimation error, and the error covariance matrix P k As shown in formula (5).

[0081]

[0082]

[0083]

[0084] Based on the displacement equations of each blade section, the load on each blade section is estimated.

[0085] Based on the revised Substitute into matrix X e The translation displacement of each node of the blade is obtained as follows: X(k)=[X1(k)...X i (k)...X N (k)] T , the bending moment at the node can be obtained by the following formula, where k is the stiffness of the beam element:

[0086]

[0087] Then the bending moment equation is differentiated to obtain the load estimation equation for each section of the blade, and the load estimation equation is used to estimate the load on each section of the blade.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for estimating multi-section loads of wind turbine blades based on blade root loads, characterized in that: include: Obtain blade design parameters and operating parameters of the wind turbine, and calculate the blade static load based on the blade design parameters; A blade dynamics model is constructed based on static loads, and the blade modal state equation is obtained according to the blade dynamics model; The blade modal state equation is reduced in order, and based on the operating parameters, the Kalman filter is used to correct the reduced blade modal state equation to obtain the displacement equation of each section of the blade; Based on the displacement equations of each blade section, the load on each blade section is estimated.

2. A method for estimating multi-section loads of wind turbine blades based on blade root loads as claimed in claim 1, characterized in that: The blade parameters include the blade section chord length and the section inflow angle; The operating parameters include blade root bending moment load.

3. The method for estimating multi-section loads of a wind turbine blade based on blade root loads according to claim 1, characterized in that: The static load of the blade includes aerodynamic load and gravity load; The blade element momentum theory method is used to solve the aerodynamic load and gravity load.

4. The method for estimating multi-section loads of a wind turbine blade based on blade root loads according to claim 1, characterized in that: The method to obtain the blade modal state equation is as follows: The blade is discretized into multiple beam elements using the finite element method, and each beam element is numbered; Connect the beam elements end to end according to the numbers and establish the blade dynamics model; The mass and stiffness matrix of each beam element are obtained according to the blade dynamics model, and the aerodynamic load and gravity load are equivalently converted into node loads using the finite element method. Based on the mass and stiffness matrices of each beam element and the node loads, the blade dynamic state equation is obtained; The blade dynamic state equation is transformed into a characteristic form to obtain the blade modal state equation.

5. The method for estimating multi-section loads of a wind turbine blade based on blade root loads according to claim 1, characterized in that: The blade dynamics model is as follows: X e =[d1φ1d2φ2] T Among them, ρ e is the mass density of the beam element, l is the length of the beam element, E is the Young's modulus, I is the section moment of inertia of the beam element, d1 and φ1 are the translational and rotational displacements of node 1, respectively, and d2 and φ2 are the translational and rotational displacements of node 2, respectively.

6. The method for estimating multi-section loads of a wind turbine blade based on blade root loads according to claim 1, characterized in that: The blade modal state equation is as follows: in, is the system damping, and are the diagonal element values ​​of the modal mass matrix and the modal stiffness matrix, respectively. is the displacement vector.

7. A method for estimating multi-section loads of a wind turbine blade based on blade root loads as claimed in claim 6, characterized in that: The system damping includes pneumatic damping and structural damping. The pneumatic damping is obtained when calculating the pneumatic load, and the structural damping is a constant value.

8. The method for estimating multi-section loads of a wind turbine blade based on blade root loads according to claim 1, characterized in that: The steps to obtain the displacement estimation equation of each section of the blade are as follows: The blade modal state equation is reduced to a third-order differential equation and converted into a state-space expression, and then the blade root bending moment load is used as the output of the state-space expression; The state space expression is transformed into a discrete space expression, and the discrete space expression is corrected by using Kalman filtering to obtain the displacement estimation equation of each section of the blade.

9. A method for estimating multi-section loads of a wind turbine blade based on blade root loads as claimed in claim 8, characterized in that: Based on the displacement equations of each blade section, the bending moment equations of each blade section can be obtained: Among them, M i is the bending moment at the ith node, X(k)=[X1(k)...X i (k)...X N (k)] T is the translational displacement of each node of the blade, k is the stiffness of the beam element; The moment equation is differentiated to obtain the load estimation equation for each section of the blade, and the load estimation equation is used to estimate the load on each section of the blade.

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