Complete machine frequency calculation method for wind turbine generator

Abstract

The invention discloses a wind turbine generator complete machine frequency calculation method which comprises the following steps: S1, modeling and parameterizing a wind turbine generator, simplifying a machine head into a mass point, simplifying a foundation into a spring, simplifying a tower tube into a beam unit (E, I, t), and establishing a single-degree-of-freedom vibration model of the wind turbine generator by taking a tower bottom as an origin of coordinates, a horizontal direction as an x axis and a vertical direction as a z axis; s2, according to the material mechanics cantilever beam theory, a displacement equation of the thrust F in the x direction of the tower top and all the sections of the tower drum is established; s3, solving a potential energy coefficient R and a kinetic energy coefficient Q of the system at a balance position; s4, establishing a system free vibration equation according to an energy method; and S5, substituting the vibration motion relation, and calculating the first-order inherent frequency value of the whole wind turbine. The method can quickly and accurately calculate the first-order inherent frequency of the whole machine, and is high in precision.

Description

Technical Field

[0001] The invention relates to the technical field of wind turbine generator sets, and in particular to a method for calculating the whole frequency of a wind turbine generator set. Background Art

[0002] As the main force to deal with ecological and environmental pollution and climate change, wind power has gradually gained universal consensus and has been vigorously developed by countries around the world. As the competition in the wind power market becomes increasingly fierce, structural design needs to comprehensively consider structural safety and economy. Wind power tower design generally includes both straight and conical structures. Each tower section is divided into several sections. The diameter and wall thickness of each section are customized according to the actual limit load.

[0003] The use of refined finite element models can accurately obtain the fundamental frequency of wind turbine towers, but the modeling workload is extremely large and is not suitable for simplified and fast calculations in the early design of towers. The current analytical method is relatively simple and does not consider the foundation stiffness, the variable stiffness characteristics of the tower section, the head mass and the center of gravity position. The calculation accuracy is not high and it is difficult to meet the actual needs of the project. Summary of the invention

[0004] The object of the present invention is to provide a method for calculating the whole machine frequency of a wind turbine generator set in order to solve the above-mentioned problems, so as to quickly and accurately calculate the first-order natural frequency of the whole machine.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A method for calculating the frequency of a wind turbine generator system comprises the following steps:

[0007] S1: Model and parameterize the wind turbine, simplify the head to a mass point, the foundation to a spring, and the tower to a beam unit (E, I, t). Take the tower bottom as the coordinate origin, the horizontal direction as the x-axis, and the vertical direction as the z-axis to establish a single-degree-of-freedom vibration model of the wind turbine;

[0008] S2: Based on the cantilever beam theory of material mechanics, establish the displacement equation of the thrust F on the top of the tower in the x direction and each section of the tower;

[0009] S3: Calculate the potential energy coefficient R and kinetic energy coefficient Q of the system at equilibrium position;

[0010] S4: According to the energy method, the free vibration equation of the system is established;

[0011] S5: Substitute the vibration motion relationship to calculate the first-order natural frequency value of the wind turbine unit.

[0012] Alternatively, in S1, a rectangular coordinate system is established with the tower bottom as the origin, the horizontal direction as the x-axis, and the vertical direction as the z-axis; the nose is simplified to a mass point with a mass of m h, the center of gravity coordinates of the nose are P(0, H h ), the foundation is simplified to a spring with bending stiffness k d According to the number of tower sections, the tower is simplified into k beam units, and the elastic modulus of the i-th tower section is E i , the section moment of inertia is I i , establish a single degree of freedom vibration model of the wind turbine.

[0013] Alternatively, the moment of inertia of the cylinder section can be expressed as:

[0014]

[0015] Alternatively, in S2, a thrust F is applied to the top of the tower in the x direction, and the displacement of each section of the tower is u i According to the cantilever beam theory of material mechanics, the relationship between F and each section u of the tower is established. i The displacement equation.

[0016] Alternatively, the displacement equation is as follows: i =PiF

[0017]

[0018] Alternatively, in S3, the system potential energy is composed of the potential energy of the tower at the equilibrium position after bending deformation and the potential energy of the foundation spring at the equilibrium position after bending deformation; the system kinetic energy is composed of the kinetic energy of each tower section at the equilibrium position and the kinetic energy of the nose at the equilibrium position.

[0019] Alternatively, the potential energy calculation formula is:

[0020]

[0021] Further:

[0022]

[0023] Among them, m i is the mass of the cylinder, ρ is the material density, t i is the thickness of the tube section, H t is the tower height. Alternatively, the kinetic energy calculation formula is:

[0024]

[0025] Further:

[0026]

[0027] in:

[0028]

[0029]

[0030] Where Q is the tower kinetic energy coefficient, m i is the mass of the cylinder, ρ is the material density, t i is the thickness of the tube section, H t is the tower height.

[0031] Alternatively, in S3, the kinetic energy calculation formula is:

[0032]

[0033] Further:

[0034]

[0035] Alternatively, in S4, according to the energy method (PE) max =(KE) max , establish the free vibration equation of the system.

[0036]

[0037] Alternatively, in S5, consider the kinematic relationship Calculate the first-order natural frequency value of the wind turbine.

[0038]

[0039] Further,

[0040]

[0041] or,

[0042]

[0043] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0044] The present invention provides a method for calculating the whole-machine frequency of a wind turbine set. For a given wind turbine tower structure, the foundation stiffness, tower height, cross-sectional dimensions, wall thickness, segmented material parameters, head mass, and center of gravity position and other parameters can be arbitrarily changed to quickly obtain the first-order prestressed natural frequency value of the bending vibration of the wind turbine tower, thereby solving the current problem that it is difficult to quickly and accurately calculate the first-order natural frequency of the whole machine for a wind turbine set with given different foundation stiffness, tower height, cross-sectional dimensions, wall thickness, segmented material parameters, head mass, and center of gravity position parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The present invention will now be described by way of example with reference to the accompanying drawings, in which:

[0046] Figure 1 is a flow chart of this method.

[0047] Figure 2 It is a modeled and parameterized schematic diagram of the actual wind turbine structure;

[0048] Figure 3 It is a schematic diagram of the deformation of the simplified model of the unit under the action of thrust F;

[0049] Figure 4 It is the tower structure data.

[0050] Figure 5 It is a schematic diagram of the tower cross section and parameters.

[0051] Figure 6 3 is a coordinate diagram of the equivalent inertia moment of each tower section in the embodiment.

[0052] Figure 7 It is the mass coordinate diagram of each tower section in the embodiment. DETAILED DESCRIPTION

[0053] The present invention will be described in detail below in conjunction with the accompanying drawings.

[0054] All features disclosed in this specification, or steps in all methods or processes disclosed, except mutually exclusive features and / or steps, can be combined in any manner.

[0055] Any feature disclosed in this specification, unless otherwise stated, can be replaced by other equivalent or alternative features with similar purposes. That is, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0056] A method for calculating the frequency of a wind turbine generator system, such as Figure 1-7 As shown, the following steps are included:

[0057] S1: Model and parameterize the wind turbine, simplify the head to a mass point, the foundation to a spring, and the tower to a beam unit (E, I, t). Take the tower bottom as the coordinate origin, the horizontal direction as the x-axis, and the vertical direction as the z-axis to establish a single-degree-of-freedom vibration model of the wind turbine;

[0058] S2: Based on the cantilever beam theory of material mechanics, establish the displacement equation of the thrust F on the top of the tower in the x direction and each section of the tower;

[0059] S3: Find the potential energy and kinetic energy of the system at equilibrium;

[0060] S4: According to the energy method, the free vibration equation of the system is established;

[0061] S5: Substitute the vibration motion relationship to calculate the first-order natural frequency value of the wind turbine unit.

[0062] Specifically, S1 simplifies the complex actual structure into a mathematical model that is easy to analyze, and simplifies the nose into a mass point, so that the mass of the nose can be considered without considering its shape and size. The foundation is simplified to a spring, so that the support and elastic characteristics of the foundation on the tower can be simulated. The tower is simplified to a beam unit, and the elastic modulus E, length I and cross-sectional area t are used to describe the mechanical characteristics of the tower. A coordinate system is established with the bottom of the tower as the origin, the horizontal direction as the x-axis, and the vertical direction as the z-axis, so that the vibration of the tower in the horizontal and vertical directions can be described. S2 uses the cantilever beam theory in material mechanics to establish the displacement equation when the top of the tower is subjected to a thrust F in the x-direction, which can describe the displacement of each section of the tower under the action of the thrust. S3 At the equilibrium position, the potential energy and kinetic energy of the system can be expressed in the form of coefficients R and Q. The potential energy coefficient R is related to the elastic characteristics and displacement of the tower, and the kinetic energy coefficient Q is related to the mass and speed of the nose. S4 Based on the principle of conservation of the total mechanical energy (potential energy + kinetic energy) of the system, the free vibration equation of the system is established by combining the potential energy and kinetic energy coefficients. S5 substitutes the vibration motion relationship into the free vibration equation and solves the eigenvalue problem of the equation, where the eigenvalue is the natural frequency of the system, and the first-order natural frequency value of the entire wind turbine can be obtained.

[0063] By simplifying the model, the calculation process can be carried out quickly without sacrificing too much accuracy. At the same time, the fundamental frequency of the wind turbine tower is calculated by considering factors such as foundation stiffness, variable stiffness characteristics of the tower section, head mass and center of gravity position, which can more accurately simulate the actual working state of the tower, thereby improving the accuracy of the fundamental frequency calculation and better meeting the actual needs of the project.

[0064] As another specific implementation, Figure 2 As shown in S1, the tower bottom is taken as the origin, the horizontal direction is the x-axis, and the vertical direction is the z-axis to establish a rectangular coordinate system; the head is simplified as a mass point with a mass of m h , the center of gravity coordinates of the nose are P(0,H h ), the foundation is simplified to a spring with bending stiffness k d According to the number of tower sections, the tower is simplified into k beam units, and the elastic modulus of the i-th tower section is E i , the section moment of inertia is I i , establish a single degree of freedom vibration model of the wind turbine.

[0065] As another specific implementation, since the tower has a constant cross-section tower and a variable cross-section tower, the top diameter d of the i-th tower section is i+1 , bottom diameter d i , thickness t i , the moment of inertia of the cylinder section is expressed as:

[0066]

[0067] As another specific implementation, Figure 3 As shown in S2, the thrust F in the x direction acts on the top of the tower, and the displacement of each section of the tower is u i According to the cantilever beam theory of material mechanics, the relationship between F and each section u of the tower is established. i The displacement equation.

[0068] The displacement equation is as follows: i =P i F

[0069]

[0070] As another specific implementation, in S3, the system potential energy is composed of the potential energy of the tower at the equilibrium position after bending deformation and the potential energy of the base spring at the equilibrium position after bending deformation; the system kinetic energy is composed of the kinetic energy of each tower section at the equilibrium position and the kinetic energy of the nose at the equilibrium position.

[0071] As another specific implementation, the potential energy calculation formula is:

[0072]

[0073] Further:

[0074]

[0075] Where R is the system potential energy coefficient, m i is the mass of the cylinder, ρ is the material density, t i is the thickness of the tube section, H t is the tower height.

[0076] As another specific implementation, the kinetic energy calculation formula is:

[0077]

[0078] Further:

[0079]

[0080] in:

[0081]

[0082] Where Q is the tower kinetic energy coefficient, m i is the mass of the cylinder, ρ is the material density, t i is the thickness of the tube section, H t is the tower height.

[0083] As another simplified algorithm, in S3, the kinetic energy calculation formula is:

[0084]

[0085] Further:

[0086]

[0087]

[0088] As another specific implementation, in S4, according to the energy method (PE) max =(KE) max , establish the free vibration equation of the system:

[0089] As another specific implementation, in S5, considering the motion relationship Calculate the first-order natural frequency value of the wind turbine.

[0090]

[0091] Further,

[0092]

[0093] or,

[0094]

[0095] Example

[0096] The total mass of the tower structure is m t =300t, tower height H t =117.3m, divided into five sections, the first and fourth sections are straight sections, the rest are conical sections, the number of tower sections is 46, the elastic modulus of the tower is E=2.1×10 11 Pa, density is ρ = 7850 kg / m 3 , tower structure data such as Figure 4 As shown. The total mass of the head is m h =300t, head center of gravity height H t =117.3m. Foundation bending stiffness k d =6×10 10 kNm / rad.

[0097] Tower cross section and parameters such as Figure 5 As shown, calculate the equivalent moment of inertia of each tower section:

[0098]

[0099] Specific results such as Figure 6 shown.

[0100] Calculate the mass of each tower section:

[0101]

[0102] Specific results such as Figure 7 shown.

[0103] Calculate the potential energy coefficient R and kinetic energy coefficient Q of the system at equilibrium position respectively.

[0104]

[0105] Calculate the first-order natural frequency value of the wind turbine:

[0106]

[0107] Conclusion: The first-order prestressed natural frequency of the wind turbine tower structure is 0.2017Hz when the finite element model is established using ANSYS software. The error between the present invention and the finite element calculation result is 0.049%. This embodiment considers the foundation stiffness, the cross-sectional data of the tower, the mass and position of the head, and obtains the natural frequency value of the wind turbine tower structure by the energy method. This method is applicable to wind turbine tower structures with different foundation stiffness, tower height, cross-sectional size, wall thickness, segmented material parameters, head mass and center of gravity position.

[0108] The present invention is not limited to the above-mentioned specific embodiments, but extends to any new features or any new combination disclosed in this specification, as well as any new method or process steps or any new combination disclosed.

Claims

1. A method for calculating the frequency of a wind turbine generator set, characterized in that: The following steps are involved: S1: Model and parameterize the wind turbine, simplify the head to a mass point, the foundation to a spring, and the tower to a beam unit (E, I, t). Take the tower bottom as the coordinate origin, the horizontal direction as the x-axis, and the vertical direction as the z-axis to establish a single-degree-of-freedom vibration model of the wind turbine; S2: Based on the cantilever beam theory of material mechanics, establish the displacement equation of the thrust F on the top of the tower in the x direction and each section of the tower; S3: Calculate the potential energy coefficient R and kinetic energy coefficient Q of the system at equilibrium position; S4: According to the energy method, the free vibration equation of the system is established; S5: Substitute the vibration motion relationship to calculate the first-order natural frequency value of the wind turbine unit.

2. The method for calculating the frequency of a wind turbine generator system according to claim 1, wherein: In S1, a rectangular coordinate system is established with the tower bottom as the origin, the horizontal direction as the x-axis, and the vertical direction as the z-axis; the nose is simplified to a mass point with a mass of m h , the center of gravity coordinates of the nose are P(0,H h ), the foundation is simplified to a spring with bending stiffness k d According to the number of tower sections, the tower is simplified into k beam units, and the elastic modulus of the i-th tower section is E i , the section moment of inertia is I i , establish a single degree of freedom vibration model of the wind turbine.

3. The method for calculating the frequency of a wind turbine generator system according to claim 2, wherein: The moment of inertia of the cylinder section is expressed as:

4. The method for calculating the frequency of a wind turbine generator system according to claim 3, wherein: In S2, the x-direction thrust F is applied to the top of the tower, and the displacement of each section of the tower is u i According to the cantilever beam theory of material mechanics, the relationship between F and each section u of the tower is established. i The displacement equation.

5. The method for calculating the frequency of a wind turbine generator system according to claim 4, characterized in that: The displacement equation is as follows: u i =P i F 6. The method for calculating the frequency of a wind turbine generator system according to claim 5, characterized in that: In S3, the system potential energy is composed of the potential energy of the tower at the equilibrium position after bending deformation and the potential energy of the foundation spring at the equilibrium position after bending deformation; the system kinetic energy is composed of the kinetic energy of each tower section at the equilibrium position and the kinetic energy of the nose at the equilibrium position.

7. The method for calculating the frequency of a wind turbine generator system according to claim 6, wherein: The potential energy calculation formula is: Further: Among them, m i is the mass of the cylinder, ρ is the material density, t i is the thickness of the tube section, H t is the tower height.

8. The method for calculating the frequency of a wind turbine generator system according to claim 7, characterized in that: The formula for calculating kinetic energy is: Further: in: Alternatively, in S3, the kinetic energy calculation formula is: Further: Where Q is the tower kinetic energy coefficient, m i is the mass of the cylinder, ρ is the material density, t i is the thickness of the tube section, H t is the tower height.

9. The method for calculating the frequency of a wind turbine generator set according to claim 8, characterized in that: In S4, according to the energy method (PE) max =(KE) max , establish the free vibration equation of the system:

10. The method for calculating the frequency of a wind turbine generator system according to claim 9, characterized in that: In S5, consider the motion relationship Calculate the first-order natural frequency value of the wind turbine:

Images