Method for calculating frequency sensitivity of wind turbine drive train fatigue loads

Abstract

The application discloses a kind of wind turbine transmission chain fatigue load to the calculation method of system frequency sensitivity, belong to wind turbine technical field, specific scheme includes the following steps: step one, first determine the relationship between the frequency deviation standard value of wind turbine participating in primary frequency modulation and primary frequency modulation power reference value;Step two, establish wind turbine state space equation based on wind wheel speed and pitch angle;Step three, the relationship between the fluctuation ΔT s (t+1) of low-speed shaft torque and the active power reference value ΔP W_ref that double-fed wind turbine needs to adjust participating in frequency modulation;Step four, the sensitivity of transmission chain fatigue load to system frequency is solved

Description

Technical Field

[0001] This invention belongs to the field of wind turbine technology, specifically relating to a method for calculating the frequency sensitivity of a doubly fed wind turbine transmission chain fatigue load. Background Technology

[0002] With the increasing application of renewable energy sources (such as wind and solar power) in power systems, primary frequency regulation of wind turbines has become more critical. Due to the uncertainty and intermittency of renewable energy, power system frequencies may fluctuate more frequently. Therefore, it is necessary to study how to effectively manage the primary frequency regulation of wind turbines to ensure the stability of the power system. Wind energy is an unstable resource, and wind speed fluctuates over time. This means that wind turbines need to adjust their output power to meet the needs of the power system when wind speed changes. This frequent power adjustment can generate additional fatigue loads on wind turbine components, such as blades, bearings, and generators. After primary frequency regulation, the generator torque of wind turbines will change more frequently, which will have a serious impact on their fatigue loads. Therefore, fatigue loads often need to be considered when formulating primary frequency regulation methods. One prerequisite for developing a frequency regulation method that considers fatigue loads is to clarify the relationship between the fatigue load of wind turbines and the system frequency deviation, that is, the sensitivity of fatigue loads to the system frequency, and then suppress fatigue loads. Summary of the Invention

[0003] The purpose of this invention is to provide a method for calculating the sensitivity of the fatigue load of the transmission chain of a doubly fed wind turbine to the system frequency, so as to calculate the sensitivity of the fatigue load of the transmission chain of the doubly fed wind turbine to the system frequency when participating in primary frequency regulation, and thus to suppress the fatigue load of the wind turbine under primary frequency regulation.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] The frequency regulation method primarily addressed in this invention is a method that directly schedules the active power of wind turbines by responding to the per-unit value of the system frequency deviation. Therefore, the reference power of a doubly-fed induction generator (DFIG) wind turbine can be expressed by the following formula:

[0006] ΔP W_ref =G C (s)Δf (1)

[0007] In the formula: Δf is the per-unit value of the power system frequency deviation, G C (s) is the transfer function of the frequency regulation method used in the actual application of doubly-fed wind turbine units, ΔP W_ref The active power reference value that needs to be adjusted for doubly-fed wind turbine units participating in frequency regulation;

[0008] The fatigue load on the transmission chain of the doubly-fed induction generator (DFIG) of this invention is expressed as the partial derivative of the low-speed shaft torque fluctuation with respect to the frequency deviation per unit value, and is denoted as... Where ΔT s (t+1) represents the fluctuation of the low-speed shaft torque at the next moment, i.e., ΔT. s (t+1)=ΔT s (t+t s )-ΔT s (t), where t represents time, t s Indicates the sampling period.

[0009] Furthermore, The calculation method consists of three steps:

[0010] S1 establishes the state-space equations for the wind turbine based on the rotor speed and pitch angle;

[0011] S2 establishes the low-speed shaft torque fluctuation ΔT s (t+1) and the active power reference value ΔP that needs to be adjusted for the doubly-fed wind turbine units participating in frequency regulation. W_ref Relationship;

[0012] S3 solution

[0013] Furthermore, in step S1, the state-space equation model of the wind turbine based on the rotor speed and pitch angle is as follows:

[0014]

[0015] in:

[0016] x=[Δω r ,Δθ] T

[0017]

[0018]

[0019]

[0020] Where, ω r θ is the rotor speed (rad / s); θ is the blade pitch angle; v is the wind speed (m / s); J t It is the equivalent inertia (kg·m2); T r It is aerodynamic torque; η g It is the gearbox speed ratio; k P and k I It is the proportional gain and integral gain of the PI-based pitch controller.

[0021] The discretized model of equation (2) is as follows:

[0022] x(t+1)=Hx(t)+IΔP W_ref +J (3)

[0023] in:

[0024]

[0025] Where t represents time; t s The sampling period is denoted by ; e is the natural base.

[0026] Step S2 mentions establishing the low-speed shaft torque fluctuation ΔT s (t+1) and the active power reference value ΔP that needs to be adjusted for the doubly-fed wind turbine units participating in frequency regulation. W_ref The relationship is implemented as follows:

[0027] ΔT s (t+1)=aΔP W_ref +b (4)

[0028] in:

[0029]

[0030]

[0031] Among them, J g It is the generator inertia (kg·m) 2 );T g It is the generator torque, in Nm.

[0032] In step S3, The solution result is:

[0033]

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] Reduced fatigue load: Traditional wind turbines are susceptible to high-frequency fatigue loads under fluctuations in wind force and frequency, leading to wear and damage to components. The method of this invention can more effectively reduce the fatigue load of wind turbines by accurately calculating the frequency sensitivity of fatigue load, thereby extending the life of key components and reducing maintenance costs.

[0036] Improved primary frequency regulation performance: The method of this invention can be applied to the primary frequency regulation method of wind turbine generators, which is crucial for ensuring the stability and performance of the system. By reducing fatigue load, the primary frequency regulation performance of wind turbine generators can be improved, unnecessary frequency fluctuations can be reduced, and the quality of power output can be improved.

[0037] Enhanced sustainability: Reducing fatigue loads helps improve the sustainability of wind turbines, lowers operating and maintenance costs, and extends system lifespan. This is crucial for reducing reliance on non-renewable energy sources and promoting the sustainable development of green energy.

[0038] Greater economic benefits: Lower maintenance costs, improved performance, and sustainability mean greater economic benefits. The method of this invention will help improve the competitiveness of wind turbines and reduce the cost of electricity production, thereby making renewable energy more attractive. Attached Figure Description

[0039] Figure 1 A flowchart illustrating a method for calculating the frequency sensitivity of a doubly fed wind turbine transmission chain to fatigue load.

[0040] Figure 2 This is a partially enlarged view of the comparison curve between the transmission chain torque calculated by this invention and the actual measured transmission chain torque. Detailed Implementation

[0041] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some embodiments of the invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0042] Example 1:

[0043] The calculation of the fatigue load on the drivetrain of a doubly-fed induction generator (DFIG) wind turbine and its impact on system frequency sensitivity aims to assess the influence of wind turbine frequency regulation on the fatigue load of the drivetrain and to contribute to the suppression of fatigue loads caused by frequency regulation. For DFIG wind turbines participating in grid frequency regulation, the fatigue load on the drivetrain is mainly assessed through fluctuations in low-speed shaft torque. Therefore, by establishing the relationship between low-speed shaft torque fluctuations and the per-unit value of power system frequency deviation, the fatigue load on the DFIG drivetrain and its impact on system frequency sensitivity are solved.

[0044] A method for calculating the frequency sensitivity of a doubly-fed wind turbine drive train due to fatigue load includes the following steps:

[0045] Step 1: First, determine the relationship between the primary frequency regulation power reference value and the per-unit value of the frequency deviation when the wind turbine participates in primary frequency regulation. The specific calculation formula is as follows:

[0046] ΔP W_ref =G C (s)Δf (1)

[0047] In the formula: Δf is the per-unit value of the power system frequency deviation; G C (s) is the transfer function of the frequency regulation method used in the actual application of doubly-fed wind turbines, G C (s) is a constant or variable constant, taking values ​​from 20pu or 5pu to 100pu for the gain; ΔP W_ref The active power reference value that needs to be adjusted for doubly-fed wind turbine units participating in frequency regulation;

[0048] Step 2: Establish the state-space equations of the wind turbine based on the rotor speed and blade pitch angle:

[0049]

[0050] in:

[0051] x=[Δω r ,Δθ] T

[0052]

[0053]

[0054]

[0055] Where, ω r θ is the rotor speed, rad / s; θ is the blade pitch angle; v is the wind speed, m / s; J t It is the equivalent inertia, kg·m 2 ;T r It is aerodynamic torque; η g It is the gearbox speed ratio; k P and k I It is the proportional gain and integral gain of the PI-based pitch controller;

[0056] Discretizing equation (2) yields the following discretized formula:

[0057] x(t+1)=Hx(t)+IΔP W_ref +J (3)

[0058] in:

[0059]

[0060] Where t represents time; t s The sampling period is e; e is the natural base.

[0061] Step 3: Establish the low-speed shaft torque fluctuation ΔT s (t+1) and the active power reference value ΔP that needs to be adjusted for the doubly-fed wind turbine units participating in frequency regulation. W_ref Relationship:

[0062] ΔT s (t+1)=aΔP W_ref +b (4)

[0063] in:

[0064]

[0065]

[0066] Among them, J g It is the generator inertia, kg·m 2 ;T g It is the generator torque, in Nm.

[0067] Taking the wind turbine parameters shown in Table 1 as an example, the active power reference value ΔP is used... W_ref Calculate the transmission chain torque ΔT s (t+1) and the actual measured ΔT s The results of the comparison are as follows Figure 2 As shown.

[0068] Table 3 Wind Turbine Parameters

[0069]

[0070]

[0071] Step 4: Solve for the sensitivity of the transmission chain fatigue load to the system frequency:

[0072]

[0073] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for calculating the frequency sensitivity of a wind turbine drivetrain to fatigue load, characterized in that: The sensitivity is expressed as the partial derivative of the low-speed shaft torque fluctuation with respect to the frequency deviation per unit value, and is denoted as... The calculation method includes the following steps: Step 1: First, determine the relationship between the primary frequency regulation power reference value and the per-unit value of the frequency deviation when the wind turbine participates in primary frequency regulation. The specific calculation formula is as follows: ΔP W_ref =G C (s)Δf (1) In the formula: Δf is the per-unit value of the power system frequency deviation, G C (s) is the transfer function of the frequency regulation method used in the actual application of doubly-fed wind turbine units, ΔP W_ref The active power reference value that needs to be adjusted for doubly-fed wind turbine units participating in frequency regulation; Step 2: Establish the state-space equations of the wind turbine based on the rotor speed and pitch angle; Step 3: Establish the low-speed shaft torque fluctuation ΔT s (t+1) and the active power reference value ΔP that needs to be adjusted for the doubly-fed wind turbine units participating in frequency regulation. W_ref Relationship; Step 4: Solve for the sensitivity of the transmission chain fatigue load to the system frequency.

2. The method for calculating the frequency sensitivity of a wind turbine drive train fatigue load to a system according to claim 1, characterized in that: Step 2: Establish the state-space equations of the wind turbine based on the rotor speed and blade pitch angle: in: x=[See r ,Dth] T Where, ω r θ is the rotor speed, rad / s; θ is the blade pitch angle; v is the wind speed, m / s; J t It is the equivalent inertia, kg·m 2 ;T r It is aerodynamic torque; η g It is the gearbox speed ratio; k P and k I It is the proportional gain and integral gain of the PI-based pitch controller; Discretizing equation (2) yields the following discretized formula: x(t+1)=Hx(t)+IΔP W_ref +J (3) in: Where t represents time; t s The sampling period is denoted by ; e is the natural base.

3. The method for calculating the frequency sensitivity of a wind turbine drivetrain fatigue load according to claim 2, characterized in that: In step three, the fluctuation ΔT of the low-speed shaft torque is established. s (t+1) and the active power reference value ΔP that needs to be adjusted for the doubly-fed wind turbine units participating in frequency regulation. W_ref Relationship: ΔT s (t+1)=aΔP W_ref +b (4) in: Among them, J g It is the generator inertia, kg·m 2 ;T g It is the generator torque, in Nm.

4. The method for calculating the frequency sensitivity of a wind turbine drive train fatigue load according to claim 3, characterized in that: In step four, the sensitivity of the transmission chain fatigue load to the system frequency is calculated:

5. The method for calculating the frequency sensitivity of a wind turbine drive train fatigue load according to claim 1, characterized in that: In step one, G C (s) is a constant or variable constant, with a value ranging from 20pu or 5pu to 100pu of gain.

6. The method for calculating the frequency sensitivity of a wind turbine drive train fatigue load according to claim 1, characterized in that: In step three, the ΔT s (t+1) represents the fluctuation of the low-speed shaft torque at the next moment, i.e., ΔT. s (t+1)=ΔT s (t+t s )-ΔT s (t).

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