Method and system for evaluating fatigue load of doubly-fed wind turbine under frequency support operating condition

Abstract

This invention proposes a method and system for assessing fatigue loads on doubly-fed induction generator (DFIG) wind turbines under frequency support conditions, belonging to the field of wind turbine condition assessment technology. The method includes: acquiring the electromagnetic power output and real-time speed of the wind turbine during frequency regulation; calculating the mapping relationship between the wind turbine drivetrain torque, tower bending moment, and blade root bending moment and the electromagnetic power and real-time speed using a physical analytical model, and determining the dynamic load values; determining the weights by calculating the variance of each load and the corresponding fatigue strength within a preset time window; and constructing a wind turbine fatigue load model for fatigue load assessment based on the dynamic load values ​​and corresponding weights. This invention can calculate the impact of changes in the active power output of the wind turbine on the mechanical side load of the wind turbine, achieving online and accurate assessment of the fatigue load of DFIG wind turbines.

Description

Technical Field

[0001] This invention belongs to the field of wind turbine condition assessment technology, and particularly relates to a method and system for assessing fatigue loads of doubly fed wind turbines under frequency support conditions. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] With the global energy structure transformation, new energy sources, primarily wind turbines, are being integrated into the power grid in large quantities, leading to a decrease in the overall system inertia and a reduction in the system's ability to resist disturbances. This necessitates frequency support for wind turbines. Traditional wind turbine load studies only consider fatigue loads under normal operating conditions. Due to the relatively low frequency and duration of frequency support triggering, its impact on fatigue loads is generally not considered in traditional evaluation methods. However, with the increasing penetration rate of wind power, providing frequency support to the grid has become a common requirement for high-proportion wind power systems, and the frequency and duration of wind power providing frequency support to the grid are both showing an upward trend. Under these circumstances, it is necessary to consider the frequency support condition in the fatigue load evaluation process to obtain more accurate evaluation results.

[0004] Currently, the assessment of fatigue loads on wind turbines mainly relies on dynamic simulation software such as Bladed and FAST. However, these load assessment methods have the following technical drawbacks: (1) Existing dynamic simulation software generates the load time history of each component and calculates the equivalent fatigue load by reproducing the entire physical process of the unit operation in the computer. Although the accuracy is high, the calculation time is long, the resource requirements are large, and it is essentially an offline testing tool that cannot be integrated into the wind turbine main control system as a real-time variable. Furthermore, the physical logic inside the software is not transparent to the user, lacks intuitive analytical mathematical expressions, cannot provide feedback for the unit in operation, and is difficult to use for load optimization control.

[0005] (2) Existing load assessments focus on aerodynamic mechanical loads, but cannot determine the impact of wind turbine active power output changes on mechanical loads when the wind turbine is frequency supported, especially the load changes caused by torque changes due to frequency regulation. Therefore, the assessment results are not ideal. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, this invention provides a method and system for evaluating the fatigue load of doubly-fed wind turbine generators under frequency support conditions. This method can calculate the impact of changes in the active power output of the wind turbine on the mechanical side load of the wind turbine, and achieve online and accurate evaluation of the fatigue load of the doubly-fed wind turbine generator.

[0007] To achieve the above objectives, one or more embodiments of the present invention provide the following technical solutions: The first aspect of this invention provides a method for evaluating the fatigue load of a doubly fed wind turbine under frequency support conditions.

[0008] The fatigue load assessment method for doubly-fed wind turbines under frequency support conditions includes: When the grid frequency fluctuation exceeds the preset dead zone, the electromagnetic power and real-time speed of the wind turbine output are obtained; The mapping relationship between the wind turbine drive train torque, tower bending moment, and blade root bending moment and the obtained electromagnetic power and real-time speed is calculated using a physical analytical model, and the dynamic load value is determined; wherein, the wind turbine drive train torque is calculated using a drive train dual-mass block model; Within a preset time window, the statistical variances of the wind turbine drive chain torque, tower bending moment, and blade root bending moment are calculated respectively, and the weights are determined based on the fatigue strength corresponding to each load variance. A fatigue load model for wind turbines is constructed based on the dynamic load values ​​and corresponding weights, and a fatigue load assessment is performed based on the fatigue load model for wind turbines.

[0009] Furthermore, when the grid frequency fluctuation exceeds the preset dead zone, the wind turbine participates in frequency regulation under integrated inertia control and MPPT control, and combines the frequency regulation power generated in real time under integrated inertia control and MPPT control into electromagnetic power, which is transmitted to the rotor-side controller for frequency regulation control; wherein, the integrated inertia control includes virtual inertia control and droop control.

[0010] Furthermore, the acquisition of the electromagnetic power includes: when the fan participates in frequency modulation, acquiring the frequency modulation power of the fan under virtual inertia control; and combining the frequency modulation power under virtual inertia control with the power of the fan under MPPT control to obtain the electromagnetic power.

[0011] Furthermore, in the dual-mass block model of the transmission chain, the wind turbine and the low-speed shaft are equivalent to one mass block, and the gearbox, the high-speed shaft, and the generator are equivalent to another mass block. The two mass blocks are connected by a shaft with stiffness and damping. The dynamic equation corresponding to the dual-mass block model of the transmission chain is expressed as: ; in, , These are the moments of inertia of the wind turbine and the generator, respectively. This is the equivalent damping of the transmission chain shaft system. This is the equivalent stiffness of the transmission chain shaft system. , and These are the angular displacements of the wind turbine, generator, and drive chain shafts, respectively. , and These represent the torques of the wind turbine, generator, and drivetrain shafts, respectively. N This refers to the gearbox transmission ratio; For wind turbine angular acceleration, For the generator angular acceleration, ω represents the angular velocity of the transmission chain shaft system.

[0012] Furthermore, the calculation of the blade root bending moment includes: decomposing the resultant force generated by the airflow into two directions, normal force and tangential force, on the blade element micro-element at a preset distance from the blade root; determining the integral expression of the micro-element moment along the lever arm under the action of the normal force at the blade root according to the blade element theory; determining the normal force on the micro-element segment according to the aerodynamic formula; and substituting the normal force on the micro-element segment into the integral expression of the micro-element moment to calculate the blade root bending moment.

[0013] Furthermore, the weights are determined based on the fatigue strength corresponding to each load variance, including using the statistical variance of the load time series as a measure of fatigue strength.

[0014] Furthermore, the wind turbine fatigue load model has a weighted L2 norm property, that is, the equivalent fatigue load magnitude is directly linearly weighted by the dynamic load values ​​corresponding to the wind turbine drive chain torque, tower bending moment and blade root bending moment.

[0015] The second aspect of the present invention provides a fatigue load assessment system for doubly fed wind turbine generators under frequency support conditions.

[0016] A fatigue load assessment system for doubly-fed wind turbines under frequency support conditions includes: The data acquisition module is configured to acquire the electromagnetic power and real-time speed of the wind turbine when the power grid frequency fluctuation exceeds the preset dead zone. The load calculation module is configured to: calculate the mapping relationship between the wind turbine drive chain torque, tower bending moment, and blade root bending moment and the obtained electromagnetic power and real-time speed through a physical analytical model, and determine the dynamic load value; wherein, the wind turbine drive chain torque is calculated through a drive chain dual-mass block model; The weight calculation module is configured to: calculate the statistical variances of the wind turbine drive chain torque, tower bending moment and blade root bending moment within a preset time window, and determine the weights based on the fatigue strength corresponding to each load variance; The fatigue load assessment module is configured to: construct a wind turbine fatigue load model based on the dynamic load value and corresponding weights, and perform fatigue load assessment based on the wind turbine fatigue load model.

[0017] A third aspect of the present invention provides a computer-readable storage medium having a program stored thereon, which, when executed by a processor, implements the steps in the fatigue load assessment method for doubly-fed wind turbine generators under frequency support conditions as described in the first aspect of the present invention.

[0018] The fourth aspect of the present invention provides an electronic device, including a memory, a processor, and a program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps in the fatigue load assessment method for doubly-fed wind turbines under frequency support conditions as described in the first aspect of the present invention.

[0019] The above one or more technical solutions have the following beneficial effects: (1) This invention abandons the path of relying on high-fidelity dynamic simulation software such as Bladed and FAST for offline load simulation in the prior art. By establishing a closed analytical mapping relationship from easily measurable electrical quantities such as electromagnetic power and rotational speed to key mechanical loads such as transmission chain torque, tower bending moment, and blade root bending moment, the load calculation no longer depends on complex full physical process reproduction and huge computing resources. This model can be directly integrated into the wind turbine main control system as a real-time variable to realize online fatigue load assessment. At the same time, due to the analytical nature of the model, it can provide real-time load feedback for the operating unit, laying a technical foundation for subsequent load optimization control and active life management, and overcoming the defects of existing simulation software being "black box"-like, offline, and difficult to use for real-time control.

[0020] (2) This invention is specifically designed for the operation scenario of wind turbines participating in grid frequency support. When acquiring electromagnetic power, it explicitly considers frequency regulation-related power components such as virtual inertia control and droop control, and accurately maps the rapid changes in electromagnetic power caused by frequency regulation to mechanical loads such as transmission chain torque, tower bending moment, and blade root bending moment through physical mechanisms such as the transmission chain dual-mass block model. As a result, this invention can quantitatively capture the additional fatigue damage to the mechanical transmission system and structural components caused by sudden changes in active power output during frequency support, especially the load impact caused by dynamic torque changes induced by frequency regulation. Compared with the existing technology that only evaluates conventional aerodynamic loads, this invention significantly improves the accuracy of fatigue load assessment for wind turbines participating in grid frequency regulation, providing a more realistic and reliable basis for the structural safety assessment and life prediction of wind turbines in high-proportion wind power systems.

[0021] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0022] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0023] Figure 1 This is a flowchart of the fatigue load assessment method for a doubly fed wind turbine under frequency support conditions in Embodiment 1 of the present invention.

[0024] Figure 2 This is a schematic diagram of the process of the fan participating in frequency regulation in Embodiment 1 of the present invention.

[0025] Figure 3 This is a schematic diagram of the dual-mass block model of the transmission chain in Embodiment 1 of the present invention. Detailed Implementation

[0026] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0027] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations of the present invention.

[0028] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0029] The overall approach of this invention is as follows: This invention provides a fatigue load assessment method for doubly-fed induction generator (DFIG) wind turbines considering frequency support conditions. This method abandons the high-fidelity simulation approach commonly used in existing technologies, and instead establishes a simplified dynamic load model from electrical-side electromagnetic power and speed to mechanical-side loads. Based on the dynamic variance of the loads of the three key components of the wind turbine, a weighted aggregation is performed to ultimately synthesize an equivalent fatigue load model with clear physical meaning and suitable for practical calculations. Specifically, this invention proposes the following two key technologies: 1) A model was established that does not rely on high-fidelity dynamic simulation software and calculates the wind turbine load by only using the electromagnetic power and speed signals obtained in real time by the wind turbine controller in the scenario where the wind turbine participates in the system frequency regulation.

[0030] 2) When constructing the fatigue load of the wind turbine, a method is introduced that can adapt to different operating states of the unit. It uses the "weighted second norm" theory and the weighted aggregation equivalent fatigue load model of the wind turbine based on the size of the key torque variance of the wind turbine. This makes the equivalent model more realistically reflect the size of the fatigue load of the whole unit.

[0031] Example 1 This embodiment discloses a method for evaluating the fatigue load of a doubly fed wind turbine under frequency support conditions.

[0032] like Figure 1 As shown, the fatigue load assessment method for doubly-fed wind turbines under frequency support conditions includes: Step S1: When the grid frequency fluctuation exceeds the preset dead zone, obtain the electromagnetic power and real-time speed of the wind turbine output; Step S2: Calculate the mapping relationship between the wind turbine drive chain torque, tower bending moment, and blade root bending moment and the obtained electromagnetic power and real-time rotational speed using a physical analytical model, and determine the dynamic load value; wherein, the wind turbine drive chain torque is calculated using a drive chain dual-mass block model; Step S3: Within a preset time window, calculate the statistical variances of the wind turbine drive chain torque, tower bending moment, and blade root bending moment, and determine the weights based on the fatigue strength corresponding to each load variance. Step S4: Construct a wind turbine fatigue load model based on the dynamic load value and corresponding weights, and perform fatigue load evaluation based on the wind turbine fatigue load model.

[0033] Based on the above process, this invention can calculate the impact of changes in the active power output of the wind turbine on the mechanical side load of the wind turbine, achieving online and accurate assessment of the fatigue load of the doubly-fed induction generator (DFIG) wind turbine. To facilitate understanding of the technical solution of this invention, the specific implementation methods of this invention will be further explained and described below.

[0034] In step S1, when the grid frequency fluctuation exceeds the preset dead zone, the electromagnetic power and real-time speed of the wind turbine output are obtained.

[0035] The system determines whether the current grid frequency fluctuation is within the specified dead zone. If it exceeds the normal dead zone, the wind turbine participates in system frequency regulation and outputs regulated power under integrated inertia control. and the power under the MPPT control of the wind turbine The electromagnetic power output by the fan is generated by the summation. Simultaneously, the real-time rotational speed of the fan is measured. As a preferred implementation, a frequency deviation of less than 0.1 Hz or a frequency change rate of less than 0.1 Hz / s can be considered the normal dead zone range.

[0036] In the specific implementation process, the mechanical power of the wind turbine Represented as: (1) in, R The radius of the wind turbine blade; v Wind speed; Indicates air density, Indicates the tip speed ratio of the fan blades. This indicates the pitch angle of the wind turbine blades. The wind energy utilization coefficient is expressed as follows: (2) Furthermore, the real-time electromagnetic power of the wind turbine participating in system frequency regulation Represented as: (3) like Figure 2 As shown, electromagnetic power The frequency modulation power is obtained by combining the real-time generated power under integrated inertia control and MPPT control, and is then transmitted to the rotor-side controller for frequency modulation control. Integrated inertia control includes virtual inertia control and droop control. In the virtual inertia control process, a virtual inertia coefficient is introduced. Simulate inertia response; during droop control, introduce droop control coefficient. Simulates a single frequency modulation.

[0037] In step S2, the wind turbine drive train torque, tower bending moment, and blade root bending moment are calculated using a physical analytical model, along with the electromagnetic power obtained in step S1. The mapping relationship between the wind turbine and real-time rotational speed is established, and the dynamic load value is determined. The torque of the wind turbine drivetrain is calculated using a dual-mass block model of the drivetrain. Specifically, this can be achieved through the following methods: 1) Calculation of wind turbine drive chain torque.

[0038] To better reflect the torsional dynamic characteristics of the transmission chain shaft system while maintaining computational accuracy, this invention employs the following... Figure 3 The transmission chain dual-mass model shown depicts the wind turbine and low-speed shaft as one mass block, and the gearbox, high-speed shaft, and generator as another mass block. The two mass blocks are connected by a rigid... and damping The shaft is connected. Because the shaft is elastic, the two are not exactly the same in a transient state. This difference produces the transmission chain torque, which is denoted here as transmission chain torque.

[0039] The dynamic equations corresponding to the dual-mass model of the transmission chain are expressed as follows: (4) in, , These are the moments of inertia of the wind turbine and the generator, respectively. This is the equivalent damping of the transmission chain shaft system. This is the equivalent stiffness of the transmission chain shaft system. , and These are the angular displacements of the wind turbine, generator, and drive chain shafts, respectively. , and These represent the torques of the wind turbine, generator, and drivetrain shafts, respectively. N This refers to the gearbox transmission ratio; For wind turbine angular acceleration, For the generator angular acceleration, ω represents the angular velocity of the transmission chain shaft system.

[0040] Selecting the high-speed shaft generator rotor dynamics equation and the low-speed shaft wind turbine rotor dynamics equation from equation (4), we can obtain the following: (5) in, The generator's angular velocity, ω is the angular velocity of the wind turbine.

[0041] Rewrite the high-speed axleside equations as about Format: (6) in, for The differential derivative form of .

[0042] The low-speed axle side equation is written as about Format: (7) Further conjunctive equations: (8) Cross-multiply equation (8) and combine the contents of equation (8) with the cross-multiplication of equation (8). The terms are moved to the same side to get: (9) From the above formula, the torque of the wind turbine drive train shaft system can be derived as follows: (10) In the formula: (11) (12) in, Electromagnetic power output by the fan This refers to the mechanical power of the wind turbine.

[0043] Substituting equations (11) and (12) into equation (10), we can obtain the transmission chain torque. The expression is: (13) 2) Tower bending moment calculation.

[0044] In the tower direction, the wind turbine bears the tower bending moment. It can be represented as: (14) in, The tower height; The aerodynamic thrust acting on the tower is specifically expressed as: (15) In the formula, The thrust coefficient of the wind turbine and the wind energy utilization coefficient Similarly, the specific details can be obtained by looking up a table.

[0045] in, and The following relationship exists: (16) Combining equations (1), (14), and (15), we get: (17) Eliminate equation (5) ,have to: (18) Multiply both sides of equation (18) And satisfying the equality relationship in equation (12), it can be simplified to: (19) Substituting equation (19) into the tower bending moment expression (17), we get: (20) in, This represents the thrust coefficient of the wind turbine.

[0046] 3) Calculation of leaf root bending moment.

[0047] The calculation of blade root bending moment includes: decomposing the resultant force generated by the airflow into two directions, normal force and tangential force, on a blade element micro-element at a predetermined distance from the blade root; determining the integral expression of the micro-element moment along the lever arm under the action of the normal force at the blade root according to blade element theory; determining the normal force on the micro-element segment according to aerodynamic formulas; and substituting the normal force on the micro-element segment into the integral expression of the micro-element moment to calculate the blade root bending moment. Specifically, this can be achieved through the following methods: The aerodynamic force generated by each small segment of the blade is amplified through the "lever arm" (the distance of that segment from the blade root), accumulating to form a huge bending moment at the blade root. If we consider each blade element segment of the wind turbine blade as a two-dimensional airfoil, assuming that the aerodynamics between blade elements are independent, then each blade element segment of the wind turbine blade... Above, the resultant force generated by the airflow can be decomposed into two directions: Normal force (mainly contributed by lift): generates flapping moment, causing the blade to bend towards the tower, and is the largest source of load on the blade.

[0048] Tangential force: parallel to the plane of rotation, generating driving torque and mechanical power.

[0049] Based on this, according to the leaf element theory, the total waving moment at the leaf root It is normal force Along the lever arm Integral of the infinitesimal torque: (twenty one) in, The lever arm refers to the distance between the center of the leaf root and the currently calculated leaf element; It is a micro segment Normal force on the surface, This refers to the length of the wind turbine blades.

[0050] According to aerodynamic formulas, It can be represented as: (twenty two) in, It is the normal force coefficient. The angle of entry; and These are the lift coefficient and drag coefficient, which can be found in the airfoil aerodynamic data handbook. It is the length of the leaf string. The velocity of the leaf element airflow.

[0051] Substituting equation (22) into equation (21), we get: (twenty three) The wind turbine rotates, generating a tangential force that produces mechanical power. for (twenty four) for: (25) for: (26) Combining equations (26) and (21), we obtain the relationship between the blade root bending moment and the mechanical power: (27) Combining equations (19) and (27), we get: (28) in, This is the tangential force coefficient.

[0052] In step S3, within a preset time window The statistical variances of three load signals—wind turbine drive chain torque, tower bending moment, and blade root bending moment—are calculated separately. The weights are determined based on the fatigue strength corresponding to each load variance. In other words, the magnitude of the variance directly reflects the degree of load fluctuation of the corresponding component, and the weight of each load variance is the proportion of the total variance of the three.

[0053] After obtaining the analytical expressions for the transmission chain torque, tower bending moment, and blade root bending moment of the wind turbine, a unified index is needed to characterize the overall fatigue level of the turbine. Since the dynamic characteristics and fatigue contributions of the loads borne by different components vary significantly, using fixed weights or simple superposition will fail to accurately reflect the true fatigue state of the wind turbine under complex operating conditions. Therefore, this invention proposes a variance-based weighting method to achieve adaptive weight assignment.

[0054] Fatigue damage in wind turbines is essentially caused by irregular fluctuations in load, and the variance of the load signal can effectively reflect the intensity of these fluctuations. Therefore, using the statistical variance of the load time series as a measure of fatigue strength has clear physical significance.

[0055] In the time window Within, the magnitude of their variances are defined as follows: (29) in, The magnitude of the torque variance in the transmission chain. The magnitude of the tower bending moment variance. This represents the variance of the leaf root bending moment. This represents the variance used to calculate the torque of the transmission chain. This represents the variance of the calculated tower bending moment. This represents the variance of the calculated leaf root bending moment; the larger the variance, the more severe the load fluctuation, the greater its contribution to fatigue damage, and the greater its corresponding weight.

[0056] To achieve a unified characterization of fatigue loads across multiple components, a weighting coefficient for each component is defined as the proportion of its variance in the total variance, i.e.: (30) (31) In step S4, a wind turbine fatigue load model is constructed based on the dynamic load value and corresponding weights, and a fatigue load assessment is performed based on the wind turbine fatigue load model.

[0057] A weighted 2-norm form is adopted to uniformly characterize multi-source fatigue loads. This form is derived from the norm definition in the weighted inner product space and possesses favorable mathematical properties such as positive definiteness, homogeneity, and trigonometric inequalities. Furthermore, its square-weighted summation structure is consistent with the fatigue damage accumulation mechanism, thus ensuring the physical rationality and engineering interpretability of the model.

[0058] The weighted 2-norm method used in this paper is essentially equivalent to mapping multi-source loads to a weighted inner product space and achieving a unified metric through norm operations. Its physical meaning corresponds to the weighted distribution and aggregation of structural fatigue loads among different components.

[0059] After obtaining the weights of each key component in equation (31), the equivalent fatigue load index of the whole machine is constructed based on the weighted L2 norm property: (32) in, This is the equivalent fatigue load of the transmission chain. The equivalent fatigue load of the tower, The equivalent fatigue load of the leaf root bending moment is calculated using the rainflow counting method and the linear fatigue damage accumulation theory. , and These are the weighting coefficients for the transmission chain torque, tower bending moment, and blade root bending moment, respectively.

[0060] Based on the above formula, the weights of each key component directly participate in the linear weighting, and the equivalent fatigue load is expressed in the form of a weighted sum of squares. This avoids the physical distortion problem caused by linear superposition and achieves a good balance between the physical meaning and engineering practicality of the constructed equivalent fatigue load index.

[0061] The method provided by this invention achieves the following technological breakthroughs compared to existing technologies: 1) A dual-drive strategy combining physics and data. Considering the wind turbine's role in system frequency regulation and its provision of frequency support, a fatigue load modeling scheme for wind turbines integrating physical mechanism modeling and statistical data features was designed. At the physical mechanism level, based on the dual-mass block dynamic model of the wind turbine drivetrain, an analytical relationship was established from measurable electrical quantities such as generator electromagnetic power and speed to drivetrain torque. Furthermore, the functional expressions of tower bending moment and blade root bending moment with the unit's operating state were derived, achieving unified analytical modeling of key structural loads. At the data-driven level, statistical variance of the load time series was introduced to quantitatively characterize the dynamic fluctuation characteristics of the loads of each key component, reflecting the weight of different structural components in the fatigue load.

[0062] 2) Variance-based weighted aggregation strategy. The load variance dynamically reflects the fluctuation intensity of each component, and the "weighted L2 norm" theory characterizes the "cumulative effect" of the load, avoiding physical distortion caused by linear superposition. Based on the adaptive weights of each load variance, the loads of multiple key components are uniformly mapped to a single equivalent fatigue load index. Furthermore, the weights of different structural components in the total fatigue index are adjusted according to the load variance, realizing the transformation from "local fatigue assessment" to "whole-machine fatigue characterization," thus improving the model's sensitivity and robustness.

[0063] 3) Mathematical Model of Fatigue Load for Doubly Fed Induction Generator (DFIG) Wind Turbines. Addressing the impact of rapid changes in active power output on mechanical loads during frequency regulation, this model introduces a dynamic analytical model driven by electromagnetic power. This model maps the changes in active power output to mechanical loads through the transmission chain dynamics equations, achieving multi-domain coupled modeling of electrical, mechanical, and structural aspects. This overcomes the limitation of traditional methods that only focus on aerodynamic loads and neglect the frequency support conditions of the wind turbine, thereby improving the accuracy of fatigue load assessment under frequency regulation conditions.

[0064] Example 2 This embodiment discloses a fatigue load assessment system for doubly fed wind turbines under frequency support conditions.

[0065] A fatigue load assessment system for doubly-fed wind turbines under frequency support conditions includes: The data acquisition module is configured to acquire the electromagnetic power and real-time speed of the wind turbine when the power grid frequency fluctuation exceeds the preset dead zone. The load calculation module is configured to: calculate the mapping relationship between the wind turbine drive chain torque, tower bending moment, and blade root bending moment and the obtained electromagnetic power and real-time speed through a physical analytical model, and determine the dynamic load value; wherein, the wind turbine drive chain torque is calculated through a drive chain dual-mass block model; The weight calculation module is configured to: calculate the statistical variances of the wind turbine drive chain torque, tower bending moment and blade root bending moment within a preset time window, and determine the weights based on the fatigue strength corresponding to each load variance; The fatigue load assessment module is configured to: construct a wind turbine fatigue load model based on the dynamic load value and corresponding weights, and perform fatigue load assessment based on the wind turbine fatigue load model.

[0066] Example 3 The purpose of this embodiment is to provide a computer-readable storage medium.

[0067] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps in the fatigue load assessment method for doubly-fed wind turbines under frequency support conditions as described in Embodiment 1 of this disclosure.

[0068] Example 4 The purpose of this embodiment is to provide an electronic device.

[0069] An electronic device includes a memory, a processor, and a program stored in the memory and executable on the processor. When the processor executes the program, it implements the steps in the fatigue load assessment method for doubly-fed wind turbines under frequency support conditions as described in Embodiment 1 of this disclosure.

[0070] The steps and methods involved in the apparatuses of Embodiments 2, 3, and 4 above correspond to those in Embodiment 1. For specific implementation details, please refer to the relevant description section of Embodiment 1. The term "computer-readable storage medium" should be understood as a single medium or multiple media including one or more instruction sets; it should also be understood as including any medium capable of storing, encoding, or carrying an instruction set for execution by a processor and enabling the processor to perform any of the methods in this invention.

[0071] Those skilled in the art will understand that the modules or steps of the present invention described above can be implemented using general-purpose computer devices. Optionally, they can be implemented using computer-executable program code, thereby allowing them to be stored in a storage device for execution by a computer device, or they can be fabricated as separate integrated circuit modules, or multiple modules or steps can be fabricated as a single integrated circuit module. The present invention is not limited to any particular combination of hardware and software.

[0072] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for fatigue load assessment of a doubly-fed wind turbine in frequency support operating condition, characterized in that, include: When the grid frequency fluctuation exceeds the preset dead zone, the electromagnetic power and real-time speed of the wind turbine output are obtained; The mapping relationship between the wind turbine drive train torque, tower bending moment, and blade root bending moment and the obtained electromagnetic power and real-time speed is calculated using a physical analytical model, and the dynamic load value is determined; wherein, the wind turbine drive train torque is calculated using a drive train dual-mass block model; Within a preset time window, the statistical variances of the wind turbine drive chain torque, tower bending moment, and blade root bending moment are calculated respectively, and the weights are determined based on the fatigue strength corresponding to each load variance. A fatigue load model for wind turbines is constructed based on the dynamic load values ​​and corresponding weights, and a fatigue load assessment is performed based on the fatigue load model for wind turbines.

2. The method of assessing fatigue loads of a doubly-fed wind turbine in a frequency support operating condition according to claim 1, characterized in that, When the grid frequency fluctuation exceeds the preset dead zone, the wind turbine participates in frequency regulation under integrated inertia control and MPPT control, and combines the frequency regulation power generated in real time under integrated inertia control and MPPT control into electromagnetic power, which is transmitted to the rotor-side controller for frequency regulation control; wherein, the integrated inertia control includes virtual inertia control and droop control.

3. The method of assessing fatigue loads of a doubly-fed wind turbine in frequency support operating conditions according to claim 1, characterized in that, The acquisition of electromagnetic power includes: when the fan participates in frequency modulation, acquiring the frequency modulation power of the fan under virtual inertia control; and combining the frequency modulation power under virtual inertia control with the power of the fan under MPPT control to obtain electromagnetic power.

4. The method of assessing fatigue loads of a doubly-fed wind turbine in a frequency support operating condition according to claim 1, characterized in that, The dual-mass block model of the transmission chain equates the wind turbine and low-speed shaft to one mass block, and the gearbox, high-speed shaft, and generator to another mass block. The two mass blocks are connected by a shaft with stiffness and damping. The dynamic equations corresponding to the dual-mass block model of the transmission chain are expressed as follows: ； wherein, , Iw, Ig, Idare the moment of inertia of the wind rotor, the generator and the drive train respectively, Cidis the equivalent damping of the drive train shafting, Kdis the equivalent stiffness of the drive train shafting, , and are the angular displacements of the wind rotor, the generator and the drive train respectively, , and are the torques of the wind rotor, the generator and the drive train respectively, N is the gear box transmission ratio; is the angular acceleration of the wind rotor, is the angular acceleration of the generator, is the angular velocity of the drive train.

5. The method of assessing fatigue loads of a doubly-fed wind turbine in frequency support operating conditions according to claim 1, characterized in that, The calculation of the blade root bending moment includes: decomposing the resultant force generated by the airflow into two directions, normal force and tangential force, on the blade element micro-element at a preset distance from the blade root; determining the integral expression of the micro-element moment along the lever arm under the action of the normal force at the blade root according to the blade element theory; determining the normal force on the micro-element segment according to the aerodynamic formula; and substituting the normal force on the micro-element segment into the integral expression of the micro-element moment to calculate the blade root bending moment.

6. The method of assessing fatigue loads of a doubly-fed wind turbine in frequency support operating conditions according to claim 1, characterized in that, The weights are determined based on the fatigue strength corresponding to each load variance, including using the statistical variance of the load time series as a measure of fatigue strength.

7. The method of assessing fatigue loads of a doubly-fed wind turbine in frequency support operating conditions according to claim 1, characterized in that, The fatigue load model of the wind turbine has the property of weighted L2, that is, the magnitude of the equivalent fatigue load directly participates in the linear weighting through the dynamic load values ​​corresponding to the wind turbine drive chain torque, tower bending moment and blade root bending moment.

8. A system for evaluating fatigue loads of a doubly-fed wind turbine in a frequency support operating condition, characterized in that include: The data acquisition module is configured to acquire the electromagnetic power and real-time speed of the wind turbine when the power grid frequency fluctuation exceeds the preset dead zone. The load calculation module is configured to: calculate the mapping relationship between the wind turbine drive chain torque, tower bending moment, and blade root bending moment and the obtained electromagnetic power and real-time speed through a physical analytical model, and determine the dynamic load value; wherein, the wind turbine drive chain torque is calculated through a drive chain dual-mass block model; The weight calculation module is configured to: calculate the statistical variances of the wind turbine drive chain torque, tower bending moment and blade root bending moment within a preset time window, and determine the weights based on the fatigue strength corresponding to each load variance; The fatigue load assessment module is configured to: construct a wind turbine fatigue load model based on the dynamic load value and corresponding weights, and perform fatigue load assessment based on the wind turbine fatigue load model.

9. A computer-readable storage medium having stored thereon a program, characterized in that, When executed by the processor, the program implements the steps in the fatigue load assessment method for doubly fed wind turbine generators under frequency support conditions as described in any one of claims 1-7.

10. An electronic device comprising a memory, a processor, and a program stored in the memory and capable of running on the processor, characterized by When the processor executes the program, it implements the steps in the fatigue load assessment method for doubly-fed wind turbine generators under frequency support conditions as described in any one of claims 1-7.

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