Double-variable-pitch blade for restraining flutter instability and control method of double-variable-pitch blade

Abstract

The invention discloses a double-variable-pitch blade for inhibiting flutter instability and a control method thereof, the double-variable-pitch blade comprises a blade base part, a blade tip part, a blade base part variable-pitch driver and a blade tip part variable-pitch driver, and a PI fuzzy control algorithm is adopted to actively control the pitch angle of the blade tip part. The method comprises the following steps: establishing wind driven generator structure models corresponding to different blade tip lengths; optimal control parameters during active control of the blade tip pitch angle under each wind driven generator structure model are solved, and optimal wind driven generator structure models corresponding to different blade tip lengths are obtained; and comparing different wind driven generator blade tip torsion response values to determine an optimal wind driven generator structure model with the minimum response, wherein a blade tip length value corresponding to the model is a final blade tip length optimal value. The system has the advantages of high operability, convenience in maintenance, good control effect and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of blades and blade control, and in particular to a double-pitch blade for suppressing flutter instability and a control method thereof. Background Art

[0002] In order to meet the development needs of the world's wind energy industry, and to optimize the efficiency and cost of wind power generation and improve the market competitiveness of wind power, the continuous increase in the capacity of wind turbines, the enlargement of their sizes, and the slenderness of their blades have become an inevitable development trend. However, with the development of large-scale wind turbines, the aeroelastic stability of wind turbine blades has become more and more prominent, especially the classic flutter instability of blades, which not only affects the working performance of wind turbines and produces aerodynamic noise, but also significantly reduces the fatigue life of blades. More seriously, it will lead to direct fracture and damage of blades, causing huge losses to wind power systems. Existing literature studies have shown that for the next generation of wind turbines above 10 megawatts, the theoretical calculated value of their flutter critical speed is equal to or even less than the rated speed. Therefore, the flutter instability problem of wind turbine blades will become one of the key issues restricting the development of the next generation of wind turbines.

[0003] At present, the solutions to the flutter instability problem of wind turbines are mainly divided into two categories: First, aerodynamic measures, the basic principle of which is to improve the aerodynamic load of the blade by changing the aerodynamic shape of the wind turbine blade section, thereby improving the aeroelastic stability of the blade. Common practices include the use of trailing edge flap blades with active control systems, or the installation of micro spoilers with actively controlled lengths at the tail of the blade. However, flutter occurs during the airflow attachment stage of the blade, and the critical condition for flutter is related to the slope of the aerodynamic lift coefficient of the blade section. Relevant experiments have shown that the effect of changing the slope of the lift coefficient of the blade section through aerodynamic measures is very limited, so the effect of suppressing flutter through aerodynamic measures is not ideal. Second, structural measures, the basic principle of which is to improve the structural aeroelastic stability by changing the structural characteristics of the blade, such as using composite materials to change the degree of bending-torsion coupling of the blade; or changing the cross-section type of the blade ply material to change the relative position of the cross-section center of gravity, aerodynamic center and shear center; or adding damping materials in the blade to improve the structural damping of the blade itself. However, relevant studies have shown that increasing the bending-torsion coupling of blades can increase the critical speed of structural flutter to a certain extent, but it will also cause static instability of the blades. At the same time, the method of changing the relative positions of the center of gravity, aerodynamic center and shear center of the section by changing the blade ply material and cross-sectional shape to increase the critical speed of flutter of wind turbines is only applicable to small household wind turbines, and is not applicable to commercial wind turbines with blade lengths of tens of meters. Although the method of adding a damping layer to the blade can increase the structural damping of the blade and is beneficial to the flutter suppression of the blade, relevant studies have shown that the increase of the damping layer will reduce the structural stiffness of the blade. In summary, the existing flutter control measures cannot achieve adaptive control, and the control effect is very limited. The increase in the critical speed of flutter is less than 15%, which cannot meet the future safety design standards of wind turbines. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a double variable pitch blade for suppressing flutter instability and a control method thereof which has strong operability, high flutter suppression efficiency, low cost and strong maintainability.

[0005] In order to solve the above technical problems, the technical solution proposed by the present invention is: A double-pitch blade for suppressing flutter instability, comprising a blade base, a blade tip, a blade base pitch driver for adjusting a blade base pitch angle, and a blade tip pitch driver for adjusting a blade tip pitch angle, wherein the blade base is rotatably connected to a hub via a blade base pitch bearing, the blade base pitch driver is disposed in the hub and connected to the blade base pitch bearing; the blade tip pitch driver is disposed at the blade base, and the blade tip is connected to the blade tip pitch driver; The PI fuzzy control algorithm is used to adjust the pitch angle of the blade tip. Active control is performed, in which the torsion angle at the tip of the blade is used as the feedback quantity, and the pitch angle at the tip of the blade is Determined by the following formula: , in, is the angular velocity of the blade tip pitch angle, Indicates time, is the tip twist angle of the blade base, is the angular velocity of the torsion angle at the tip of the blade base, is the proportionality constant, is the constant of integration, is the response time of the control.

[0006] As a further improvement of the above technical solution, the blade base pitch drive is connected to a driving gear, the blade base pitch bearing is provided with an inner gear ring, and the driving gear is meshed with the inner gear ring.

[0007] As a further improvement of the above technical solution, the blade tip pitch drive is connected to a blade tip transmission shaft, and the blade tip is fixedly connected to the blade tip transmission shaft.

[0008] As a further improvement of the above technical solution, the blade tip pitch drive is arranged at the shear center of the top cross section of the blade base, and the blade tip transmission shaft is fixedly connected to the shear center of the bottom cross section of the blade tip.

[0009] As a further improvement of the above technical solution, the blade tip transmission shaft is made of alloy material.

[0010] As a further improvement of the above technical solution, the top cross section of the blade base and the bottom cross section of the blade tip are sealed with alloy material.

[0011] As a further improvement of the above technical solution, the blade base pitch bearing is made of alloy structural steel.

[0012] A control method for a double pitch blade for suppressing flutter instability as described above determines the optimal value of the blade tip length according to the following steps: Establish the wind turbine structure model corresponding to different blade tip lengths; Solve the pitch angle of the blade tip under each wind turbine structure model The optimal control parameters during active control are used to obtain the optimal wind turbine structure model corresponding to different blade tip lengths, wherein the optimal control parameters include the optimal blade tip length and the optimal blade tip transmission shaft position parameters; The tip twist response values ​​of different wind turbines are compared to determine the optimal wind turbine structure model with the minimum response. The blade tip length value corresponding to the optimal wind turbine structure model with the minimum response is the final optimal blade tip length value.

[0013] As a further improvement of the above technical solution: the establishment of a wind turbine structural model corresponding to different blade tip lengths includes: first establishing a three-dimensional refined shell unit numerical model of the wind turbine blade through finite element software based on the original three-dimensional structural data of the wind turbine blade, and then establishing a three-dimensional beam unit model of the wind turbine blade corresponding to different blade tip lengths and blade tip drive shaft positions based on the three-dimensional refined shell unit numerical model of the wind turbine blade.

[0014] Compared with the prior art, the advantages of the present invention are: When the blade torsional flutter occurs, the present invention uses a PI fuzzy control algorithm to actively control the blade tip pitch angle. Under the control of the active control strategy of the blade tip, the blade tip variable pitch driver automatically adjusts the blade tip pitch angle to the target value, thereby changing the aerodynamic load of the blade tip. The torque generated by the combined force of the blade tip load is transmitted to the blade base by the transmission shaft. The torque inhibits the torsional deformation of the blade base, thereby inhibiting the blade flutter and achieving the best blade flutter suppression effect. The present invention has strong operability and does not need to change the internal structure of the blade; at the same time, it has strong maintainability, and the maintenance personnel only need to replace the shorter blade tip without repairing the entire blade; at the same time, the present invention has good control effect, low manufacturing cost, and good versatility. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will be described in more detail below based on embodiments and with reference to the accompanying drawings, wherein: Figure 1 It is a schematic diagram of the three-dimensional structure of the double variable pitch blades for suppressing flutter instability according to the present invention installed on a wind turbine.

[0016] Figure 2 It is a schematic diagram of the three-dimensional structure of the double variable pitch blade for suppressing flutter instability according to the present invention.

[0017] Figure 3 It is an enlarged view of the blade base pitch structure of the present invention.

[0018] Figure 4 It is a schematic diagram of the main structure of the present invention.

[0019] Figure 5 for Figure 4 Schematic diagram of the AA section.

[0020] Figure 6 It is a schematic diagram of the structure of the blade tip.

[0021] Figure 7 It is a schematic diagram of the calculation process of the optimal values ​​of the blade tip length and the blade tip transmission shaft position.

[0022] The symbols in the figure represent: 1. Hub; 2. Blade base pitch drive; 3. Blade base pitch bearing; 4. Blade base bottom; 5. Driving gear; 6. Blade base; 7. Blade tip pitch drive; 8. Blade base top; 9. Blade tip drive shaft; 10. Blade tip bottom; 11. Blade tip; 12. Blade tip top; 13. Nacelle; 14. Yaw bearing; 15. Tower. DETAILED DESCRIPTION

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereby.

[0024] like Figures 1 to 7 As shown, the double pitch blade for suppressing flutter instability of this embodiment includes a blade base 6, a blade tip 11, a blade base pitch drive 2 for adjusting the pitch angle of the blade base 6, and a blade tip pitch drive 7 for adjusting the pitch angle of the blade tip 11. The blade base 6 is connected to the hub 1 through a blade base pitch bearing 3, and the hub 1 is installed at the front end of a nacelle 13, and the nacelle 13 is installed on the top of a tower 15 through a yaw bearing 14; the blade base pitch drive 2 is arranged in the hub 1, the blade tip pitch drive 7 is arranged at the blade base 6, and the blade tip 11 is connected to the blade tip pitch drive 7.

[0025] See Figure 5 In this embodiment, the double-pitch blade includes two parts: a blade base 6 and a blade tip 11, and the two parts are connected by a blade tip drive shaft 9. The two parts are independently pitched, the blade base 6 is pitched by a blade base pitch driver 2 installed in the hub 1, and the blade tip 11 is pitched by a blade tip pitch driver 7 installed at the junction of the blade base 6 and the blade tip 11. The blade tip pitch driver 7 provides damping for blade torsion, thereby suppressing flutter, and has a simple structure and reliable transmission. In the double-pitch blade for suppressing flutter instability of this embodiment, when torsional flutter occurs in the blade, the blade tip pitch driver 7 adjusts the blade tip pitch angle under the control of the active control strategy of the blade tip 11. To the target value, the aerodynamic load of the blade tip 11 is changed, and the torque generated by the combined force of the load on the blade tip 11 is transmitted to the blade base 6, which inhibits the torsional deformation of the blade base 6, thereby inhibiting the flutter of the blade. The double-pitch blade for suppressing flutter instability of this embodiment has strong operability and does not need to change the internal structure of the blade; at the same time, it has strong maintainability, and the maintenance personnel only need to replace the shorter blade tip 11, and do not need to repair the entire blade; at the same time, the present invention has good control effect, low manufacturing cost, and good versatility.

[0026] See Figure 3 In this embodiment, the blade base pitch drive 2 is connected to a driving gear 5, and the blade base pitch bearing 3 is provided with an inner gear ring (not shown in the figure), and the driving gear 5 is meshed with the inner gear ring. When the blade base pitch drive 2 drives the driving gear 5 to rotate, the driving gear 5 drives the inner gear ring to rotate, thereby realizing the rotation of the blade base pitch bearing 3, and the blade base 6 rotates with the blade base pitch bearing 3, thereby adjusting the blade base pitch angle To the target value, the structure is simple and the transmission is reliable. Active control strategy of blade base 6 and target value of blade base pitch angle It can be determined according to the design manual of different wind turbine models.

[0027] See Figure 2 and Figure 4 In this embodiment, the blade tip pitch driver 7 is connected to the blade tip transmission shaft 9, and the blade tip 11 is fixedly connected to the blade tip transmission shaft 9. Under the control of the blade tip active control strategy, the blade tip pitch driver 7 drives the blade tip 11 to rotate through the blade tip transmission shaft 9 to adjust the blade tip pitch angle. To the target value, simple structure and reliable transmission.

[0028] As a preferred embodiment, the blade tip pitch drive 7 is arranged at the shear center of the cross section of the top end 8 of the blade base, and the blade tip transmission shaft 9 is fixedly connected to the shear center of the cross section of the bottom end 10 of the blade tip. Figure 4 The top end 8 of the blade base is the end of the blade base 6 away from the hub 1, and correspondingly, the bottom end 4 of the blade base is the end of the blade base 6 close to the hub 1. The bottom end 10 of the blade tip is the end of the blade tip 11 close to the blade base 6, and correspondingly, the top end 12 of the blade tip is the end of the blade tip 11 away from the blade base 6.

[0029] As a preferred embodiment, the blade tip transmission shaft 9 is made of alloy material to meet the strength and stiffness requirements.

[0030] As a preferred embodiment, the cross section of the top end 8 of the blade base and the cross section of the bottom end 10 of the blade tip are sealed with alloy material to meet the strength and stiffness requirements while preventing airflow from entering the inside of the blade base 6 and the blade tip 11.

[0031] As a preferred embodiment, the blade base pitch bearing 3 is made of alloy structural steel to meet the requirements of strength, rigidity and durability.

[0032] Furthermore, the PI control algorithm is used to adjust the blade tip pitch angle Active control is performed, in which the torsion angle of the top 8 of the blade base is used as the feedback quantity, and the pitch angle of the blade tip is Determined by the following formula: , in, is the angular velocity of the blade tip pitch angle, Indicates time, is the torsion angle at the top of the blade base, is the angular velocity of the torsion angle at the tip 8 of the blade base, is the proportionality constant, is the constant of integration, and The optimal value is determined by the ITAE (Integral of Timed Absolute Error) criterion, where , G represents the control gain, represents the integral constant (in actual situations, the specific controller device used at the blade tip has a recommended value range for this parameter). According to the blade control target (such as minimizing the torsional vibration angle of the blade tip), a numerical optimization algorithm (such as a genetic algorithm) is used to search for the optimal value within the recommended value range. is the response time of the control.

[0033] In this embodiment, according to the original data of the three-dimensional structure of the wind turbine blade, a three-dimensional refined shell unit numerical model (or solid unit model, considering the amount of model calculation, it is recommended to use shell unit modeling) of the wind turbine blade is first established through finite element software (such as Ansys, etc.). The model suggests considering the ply structure of the glass fiber inside the blade. Subsequently, based on the three-dimensional refined shell unit numerical model of the wind turbine blade, a three-dimensional beam unit model of the wind turbine blade corresponding to different blade tip lengths and blade tip transmission shaft positions is established (Timushenko beam unit or Euler beam unit can be used).

[0034] See Figure 6In this embodiment, for the blade tip 11, it is assumed that the cross-section elastic center coincides with the shear center, and the elastic center is assumed to be on the cross-section chord, that is, on the y2 axis. The blade tip 11 selects Nt typical sections according to the actual blade structure (it is recommended to select a section every 1 meter along the blade length). The typical blade cross section is evenly divided into n equal parts along the chord length, a total of n+1 points, and these n+1 points contain the cross-section elastic center.

[0035] See Figure 7 ,Specific steps: First, a three-dimensional refined shell unit or solid unit model of a wind turbine blade is established based on general finite element software, and the length of the blade base 6 and the blade tip 11 is preliminarily determined according to the actual blade structure (the length of the blade base 6 is represented by Lb, the length of the blade tip 11 is represented by Lt, and the total length of the blade L=Lb+Lt). Considering the actual manufacturing installation and control effect, the value range of Lt (the parameter to be optimized) is generally controlled to be 1%-9% of the total length of the blade L. Then, the blade base 6 selects Nb typical sections according to the actual blade structure. The bending stiffness of the two elastic principal axes (xy) of each typical section with the elastic center of the section as the origin is calculated by the blade airfoil section stiffness calculation software. Secondly, the blade tip 11 selects Nt typical sections according to the actual blade structure, and divides the typical blade section into n equal parts along the chord length, with a total of n+1 points, and these n+1 points contain the elastic center of the section. When the blade tip transmission shaft 9 is installed at one of these n+1 points, the bending and torsional stiffness of each part of the blade tip are different. Therefore, it is necessary to calculate the bending stiffness of the two elastic principal axes (xy) of each typical section centered on these n+1 points through the blade airfoil section stiffness calculation software, and a total of Nt* (n+1) groups of bending stiffness are calculated. At this time, the blade tip transmission shaft 9 is installed at n+1 different tip shaft positions as the second parameter to be optimized. Finally, a three-dimensional beam unit model of the wind turbine blade is established based on the calculation results of the stiffness of each section of the blade base 6 and the blade tip 11, and the blade tip active control strategy is coupled (i.e., considering the target pitch angle of the blade tip 11 formula).

[0036] Afterwards, through numerical simulation, it is calculated that in a variety of (N*(n+1)) working conditions coupled with N different blade tip lengths (the range of values ​​is 1%-9% of the total blade length L) and n+1 different blade tip drive shaft 9 positions, that is, when studying the optimal control parameters of the blade tip 11 length, the relative position of the blade tip drive shaft 9 is controlled to change in sequence within the range of 1%-9% of the total blade length L. Finally, according to the blade tip torsion response time history curve calculated by the simulation software, the blade tip torsion response amplitude after the model is installed at the blade tip drive shaft 9 at n+1 calculation points is obtained, and the working condition with the minimum blade tip torsion response is found. The blade tip length and blade tip drive shaft 9 position used in this working condition are the optimal parameters.

[0037] Taking DTU10MW wind turbine as an example, at the original flutter critical speed (Ω cr / r=1.57), the optimal parameters (blade tip length) were found in 99 working conditions with 9 different blade tip lengths and 11 different blade tip drive shaft positions coupled by the above method. Lt / L =3.3%, blade tip transmission shaft 9 position ct / c =45%), and the tip torsion response amplitude of the fan blade designed with the optimal parameters is only 3.8% of the original blade amplitude. , the optimal value can be searched within the recommended value range of wind turbine design to optimize the design.

[0038] The working principle of the double variable pitch blade for suppressing flutter instability of the present invention is as follows: When the blade torsional flutter occurs, the PI fuzzy control algorithm is used to actively control the blade tip pitch angle. Under the control of the active control strategy of the blade tip 11, the blade tip pitch driver 7 automatically adjusts the blade tip pitch angle through the blade tip transmission shaft 9. To the target value, the aerodynamic load of the blade tip 11 is changed, and the torque generated by the combined force of the blade tip 11 load is transmitted to the blade base 6 through the blade tip transmission shaft 9. The torque inhibits the torsional deformation of the blade base 6, thereby inhibiting the blade flutter and achieving the best blade flutter suppression effect. The wind turbine structure model corresponding to different blade tip 11 lengths is established by numerical simulation, and the optimal control parameters of the active control strategy of the blade tip 11 under each model are obtained based on the optimal control algorithm. The model with the minimum response is determined by comparing the torsional response values ​​of the blade tip 11 of different wind turbines, and the corresponding blade tip 11 length value is the optimal value.

[0039] Although the present invention has been described with reference to preferred embodiments, various modifications may be made thereto and parts thereof may be replaced by equivalents without departing from the scope of the present invention. In particular, the various technical features mentioned in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A double variable pitch blade for suppressing flutter instability, characterized in that: The blade base comprises a blade tip, a blade base pitch drive for adjusting the blade base pitch angle, and a blade tip pitch drive for adjusting the blade tip pitch angle, wherein the blade base is rotatably connected to the hub via a blade base pitch bearing, the blade base pitch drive is arranged in the hub and connected to the blade base pitch bearing; the blade tip pitch drive is arranged at the blade base, and the blade tip is connected to the blade tip pitch drive; The PI fuzzy control algorithm is used to adjust the pitch angle of the blade tip. Active control is performed, in which the torsion angle at the tip of the blade is used as the feedback quantity, and the pitch angle at the tip of the blade is Determined by the following formula: ， in, is the angular velocity of the blade tip pitch angle, Indicates time, is the tip twist angle of the blade base, is the angular velocity of the torsion angle at the tip of the blade base, is the proportionality constant, is the constant of integration, is the response time of the control.

2. The double variable pitch blade for suppressing flutter instability according to claim 1, characterized in that: The blade base pitch drive is connected with a driving gear, the blade base pitch bearing is provided with an inner gear ring, and the driving gear is meshed with the inner gear ring.

3. The double variable pitch blade for suppressing flutter instability according to claim 1, characterized in that: The blade tip pitch driver is connected to a blade tip transmission shaft, and the blade tip is fixedly connected to the blade tip transmission shaft.

4. The double variable pitch blade for suppressing flutter instability according to claim 3, characterized in that: The blade tip pitch drive is arranged at the shear center of the top cross section of the blade base, and the blade tip transmission shaft is fixedly connected to the shear center of the bottom cross section of the blade tip.

5. The double variable pitch blade for suppressing flutter instability according to claim 3, characterized in that: The blade tip transmission shaft is made of alloy material.

6. The double variable pitch blade for suppressing flutter instability according to claim 4, characterized in that: The top end section of the blade base and the bottom end section of the blade tip are sealed with alloy material.

7. The double variable pitch blade for suppressing flutter instability according to claim 1, characterized in that: The blade base pitch bearing is made of alloy structural steel.

8. A control method for a double pitch blade for suppressing flutter instability according to any one of claims 1 to 7, characterized in that: Follow the steps below to determine the optimum blade tip length: Establish the wind turbine structure model corresponding to different blade tip lengths; Solve the pitch angle of the blade tip under each wind turbine structure model The optimal control parameters during active control are used to obtain the optimal wind turbine structure model corresponding to different blade tip lengths, wherein the optimal control parameters include the optimal blade tip length and the optimal blade tip transmission shaft position parameters; The tip twist response values ​​of different wind turbines are compared to determine the optimal wind turbine structure model with the minimum response. The blade tip length value corresponding to the optimal wind turbine structure model with the minimum response is the final optimal blade tip length value.

9. The control method for double pitch blades for suppressing flutter instability according to claim 8, characterized in that: The method of establishing a wind turbine structure model corresponding to different blade tip lengths includes: first establishing a three-dimensional refined shell unit numerical model of the wind turbine blade through finite element software according to the original three-dimensional structural data of the wind turbine blade, and then establishing a three-dimensional beam unit model of the wind turbine blade corresponding to different blade tip lengths and blade tip transmission shaft positions based on the three-dimensional refined shell unit numerical model of the wind turbine blade.

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