Double-oil-cylinder hydraulic variable pitch mechanism and design method thereof

Abstract

The invention discloses a double-oil-cylinder hydraulic variable-pitch mechanism and a design method thereof.The method comprises the following steps that S1, the working space size range and the installation size range of the variable-pitch mechanism are obtained, and acting force arms of two variable-pitch oil cylinders are obtained according to the position relation of the two variable-pitch oil cylinders in the variable-pitch mechanism; s2, according to the working state of the system, the effective areas corresponding to the two variable-pitch oil cylinders during propeller opening and feathering are obtained; and S3, verifying the rationality of the arrangement parameters of the variable-pitch mechanism and the specifications of the oil cylinders. The two variable-pitch oil cylinders are designed into different reasonable specifications, so that the opening and feathering torque formed by the variable-pitch mechanism is matched with the opening and feathering load of a fan, the redundancy of the variable-pitch capacity of the variable-pitch mechanism is reduced, the optimal variable-pitch mechanism arrangement parameters and the optimal oil cylinder specifications and dimensions within a limited range are obtained, and the optimal variable-pitch mechanism arrangement parameters and the optimal oil cylinder specifications and dimensions within the limited range are obtained. Under the condition that the variable pitch requirement is met, the purpose of achieving the optimal comprehensive cost of the variable pitch system is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of wind power pitch drive, and particularly relates to a double-cylinder hydraulic pitch mechanism and a design method thereof. Background Art

[0002] The included angle between the chord line of the blade of a wind turbine and the wind wheel rotation plane is called the pitch angle. The pitch operation is to change the size of the pitch angle so that it varies within the range of 0° to 90°. The process of gradually decreasing the pitch angle is called the open-pitch operation, and the process of gradually increasing the pitch angle is called the feathering operation;

[0003] The pitch system of a wind turbine needs to meet all pitch load conditions. The current pitch loads have the following characteristics: the maximum open-pitch load at the same pitch angle is greater than the maximum feathering load; the pitch load gradually decreases as the pitch angle increases, but it will still maintain 30% - 40% of the maximum pitch load near the 90° pitch angle position;

[0004] The existing hydraulic pitch technologies all arrange the oil cylinders in a central symmetry manner with the pitch rotation center of the blade. During the pitch operation, the two pitch oil cylinders extend or retract simultaneously, and the force arms of the two pitch oil cylinders are the same at any pitch angle and change together with the pitch operation;

[0005] The hydraulic pitch system is a crank-link mechanism. Whether it adopts a double-cylinder symmetric arrangement or a single-cylinder arrangement, the resultant force arm of the oil cylinder on the blade rotation changes linearly. When designing the oil cylinder arrangement, it will be designed so that the resultant force arm is the smallest at the 90° pitch angle position. Due to the pitch load characteristics, the change slope of the oil cylinder resultant force arm - pitch angle is much greater than the change slope of the maximum pitch load - pitch angle. Therefore, when designing the existing hydraulic pitch system, in order to meet the maximum pitch load at any pitch angle, the hydraulic system needs to consider a relatively high working pressure, which brings poor economy;

[0006] At the same time, the hydraulic pitch system generally uses a high-pressure accumulator as the emergency feathering power source to meet the load of any condition under the power-off condition. Since the existing hydraulic pitch technology requires a relatively high minimum working pressure within the entire pitch angle change range, the high-pressure accumulator needs to be designed with a relatively large volume to ensure that when the internal hydraulic oil volume of the accumulator changes to meet the emergency feathering operation, the minimum working pressure of the accumulator meets the working pressure of the maximum feathering load, which results in low utilization rate of the accumulator and poor system economy; Summary of the Invention

[0007] The object of the present invention is to overcome the defects of the prior art and provide a dual-cylinder hydraulic pitch mechanism and its design method. The two pitch cylinders are designed into reasonable different specifications according to the pitch load and feathering load of the wind turbine and the layout parameters, so that the pitch moment and feathering moment formed by the pitch mechanism match the pitch load and feathering load of the wind turbine, reducing the redundancy of the pitch capacity of the pitch mechanism, obtaining the optimal pitch mechanism layout parameters and cylinder specifications within a limited range, and achieving the optimal comprehensive cost of the pitch system while meeting the pitch requirements.

[0008] The object of the present invention is achieved by the following technical solutions:

[0009] A dual-cylinder hydraulic pitch mechanism includes a hub and blades provided on the hub, and further includes two pitch cylinders axially symmetrically installed on the same side of the blade. Both ends of the pitch cylinder are respectively connected to the hub and the blade, and the pitch cylinder is also connected to a power source. The specifications of the two pitch cylinders are different.

[0010] In one embodiment, the hub is connected to the blade through a pitch bearing. The pitch bearing includes an outer bearing ring connected to the hub and an inner bearing ring connected to the blade.

[0011] In one embodiment, both ends of the pitch cylinder are respectively connected to the hub and the blade through pins.

[0012] In one embodiment, the power source is a hydraulic system connected to the pitch cylinder.

[0013] The present invention also provides a design method for a dual-cylinder hydraulic pitch mechanism, including the following steps:

[0014] Step S1: Obtain the working space size range and installation size range of the pitch mechanism, and obtain the acting arms of the two pitch cylinders according to the positional relationship between the two pitch cylinders in the pitch mechanism.

[0015] Step S2: Obtain the effective areas corresponding to the two pitch cylinders during pitch and feathering according to the system working state.

[0016] Step S3: Verify the rationality of the pitch mechanism layout parameters and cylinder specifications.

[0017] In one embodiment, in step S1, the two pitch cylinders in the pitch mechanism are installed on the same side of the blade in an axially symmetric manner, and the axis of symmetry of the two pitch cylinders passes through the rotation center of the blade pitch rotation.

[0018] In one embodiment, in step S1, the calculation method of the acting arms of the two pitch cylinders is as follows:

[0019]

[0020] Among them,

[0021]

[0022] In the above formula,

[0023]

[0024] r < R;

[0025] δ n = λ n - λ;

[0026] Among them, R is the distance from the installation point at the cylinder end of the pitch cylinder to the rotation center of the blade; B is the distance from the installation point at the cylinder barrel end of the pitch cylinder to the symmetry axis; r is the distance from the installation point at the rod end of the pitch cylinder to the rotation center of the blade; λ is the initial installation angle of the pitch system; λ n is the installation angle of the system when the pitch angle is n°; γ is the total pitch angle range of the wind power main engine; δ n is the total amount of angle change of the pitch system; θ n1 is the included angle formed by the axis of one of the pitch cylinders and the line connecting the installation point at the cylinder end and the rotation center of the blade at the pitch angle n°; θ n2 is the included angle formed by the axis of the other pitch cylinder and the line connecting the installation point at the cylinder end and the rotation center of the blade at the pitch angle n°; β n1 is the included angle formed by the line connecting the rotation center of the blade and the installation point at the cylinder end of one of the cylinders and the line connecting the installation point at the rod end of the cylinder; β n2 is the included angle formed by the line connecting the rotation center of the blade and the installation point at the cylinder end of the other cylinder and the line connecting the installation point at the rod end of the cylinder.

[0027] In one embodiment, in step S2, the system working states include a differential condition and a non-differential condition;

[0028] Under the differential condition,

[0029] A s1 = d 1 2 π / 4

[0030] A s2 = (D 2 2 - d 2 2 ) * π / 4;

[0031] Under the non-differential condition,

[0032] A s1 = D 1 2 π / 4

[0033] A s2 (D 2 2 - d 2 2 ) * π / 4;

[0034] Wherein, D 1 and d 1 are respectively the cylinder diameter and the rod diameter of one of the pitch cylinders, D 2 and d 2 are respectively the cylinder diameter and the rod diameter of the other pitch cylinder; A k1 and A k2 are respectively the effective opening pitch areas of the two pitch cylinders; A s1 and A s2 are respectively the effective feathering areas of the two pitch cylinders.

[0035] In one embodiment, in step S3, the opening pitch driving torque and the feathering driving torque provided by the pitch mechanism at any pitch angle are respectively greater than the opening pitch load and the feathering load at the corresponding angle.

[0036] In one embodiment, in step S3, the verification formula is:

[0037] M nk = P(A k1 L n1 + A k2 L n2 ) > M fk

[0038] M ns = P(A s1 L n1 + A s2 L n2 ) > M fs ;

[0039] Wherein, P is the effective working pressure of the system, M nk is the opening pitch driving torque provided by the pitch mechanism at any pitch angle, M ns is the feathering driving torque provided by the pitch mechanism at any pitch angle, M fk is the opening pitch load at the corresponding angle, M fs is the feathering load at the corresponding angle.

[0040] The beneficial effects of the present invention are as follows:

[0041] (1) Use oil cylinders of different specifications and sizes to match the load of pitching the blades open and pitching them closed, so that the pitching ability of the system highly coincides with the pitching load of the wind turbine, reducing the redundancy of the pitching ability of the system, thereby reducing the cost of the pitching system and achieving high economy of the pitching system;

[0042] (2) The change in the pitching force arm within the full pitch angle range of the pitching mechanism is small, and the force arm at a large pitch angle is still large enough. Therefore, only a relatively low pressure is required for pitching drive, that is, the minimum working pressure of the high-pressure accumulator is reduced, thereby reducing the volume requirement of the high-pressure accumulator, which stores the energy for emergency blade pitching, and improving the volume utilization rate of the high-pressure accumulator. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The present invention will be described in more detail below based on embodiments and with reference to the drawings. Among them:

[0044] Figure 1 It shows a schematic diagram of the cylinder arrangement of the pitching mechanism of the pitching technology used by existing manufacturers in the background art;

[0045] Figure 2 It shows a schematic diagram of the structure of the pitching mechanism of the present invention at one extreme position of the pitching action;

[0046] Figure 3 It shows a schematic diagram of the structure of the pitching mechanism of the present invention at another extreme position of the pitching action;

[0047] In the drawings, the same components are denoted by the same reference numerals. The drawings are not drawn to actual scale.

[0048] REFERENCE NUMERALS:

[0049] 1 - Hub, 2 - Blade, 3 - First pitching oil cylinder, 4 - Pin shaft, 5 - Second pitching oil cylinder, 6 - Inner ring of pitching bearing, 7 - Outer ring of pitching bearing. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0050] The present invention will be further described below with reference to the drawings.

[0051] Embodiment 1

[0052] The present invention provides a design method for a double - cylinder hydraulic pitching mechanism, including the following steps:

[0053] Step S1, obtain the working space size range and installation size range of the pitching mechanism, and obtain the acting force arms of the two pitching oil cylinders in the pitching mechanism according to the positional relationship between the two pitching oil cylinders;

[0054] Among them, the positional relationship between the two pitch cylinders in the pitch mechanism is installed on the same side of the blade in an axisymmetric manner, and the axis of symmetry of the two pitch cylinders passes through the rotation center of the blade pitch rotation;

[0055] The calculation method of the force arms of the two pitch cylinders is as follows:

[0056]

[0057] Among them,

[0058]

[0059] In the above formula,

[0060]

[0061] r < R;

[0062] δ n = λ n - λ;

[0063] Among them, R is the distance from the installation point of the cylinder end of the pitch cylinder to the rotation center of the blade; B is the distance from the installation point of the cylinder barrel end of the pitch cylinder to the axis of symmetry; r is the distance from the installation point of the rod end of the pitch cylinder to the rotation center of the blade; λ is the initial installation angle of the pitch system; λ n is the system installation angle when the pitch angle is n°; γ is the total pitch angle range of the wind power main engine; δ n is the total amount of angle change of the pitch system; θ n1 is the angle formed by the axis of one of the pitch cylinders and the line connecting the installation point of the cylinder end and the rotation center of the blade at the pitch angle n°, θ n2 is the angle formed by the axis of the other pitch cylinder and the line connecting the installation point of the cylinder end and the rotation center of the blade at the pitch angle n°; β n1 is the angle formed by the line connecting the rotation center of the blade and the installation point of one cylinder end and the line connecting the rod end of the cylinder; β n2 is the angle formed by the line connecting the rotation center of the blade and the installation point of the other cylinder end and the line connecting the rod end of the cylinder;

[0064] Step S2, according to the system working state, obtain the effective areas corresponding to the two pitch cylinders during blade opening and feathering;

[0065] Among them, the system working state includes differential working conditions and non-differential working conditions;

[0066] Under differential working conditions,

[0067] A s1= d 1 2 π / 4

[0068] A s2 = (D 2 2 - d 2 2 ) * π / 4;

[0069] Under non - differential conditions,

[0070] A s1 = D 1 2 π / 4

[0071] A s2 = (D 2 2 - d 2 2 ) * π / 4;

[0072] Wherein, D 1 and d 1 are respectively the cylinder diameter and the rod diameter of one of the pitch cylinders, and D 2 and d 2 are respectively the cylinder diameter and the rod diameter of the other pitch cylinder; A k1 and A k2 are respectively the effective opening - pitch areas of the two pitch cylinders; A s1 and A s2 are respectively the effective feathering - pitch areas of the two pitch cylinders.

[0073] Step S3, verify the rationality of the pitch mechanism layout parameters and the cylinder specifications, that is, the opening - pitch driving torque and the feathering - pitch driving torque provided by the pitch mechanism at any pitch angle are respectively greater than the opening - pitch load and the feathering - pitch load at the corresponding angle;

[0074] Wherein, the verification formula is:

[0075] M nk = P(A k1 L n1 + A k2 L n2 ) > M fk

[0076] M ns = P(A s1 L n1 + A s2 L n2 ) > M fs ;

[0077] Wherein, P is the effective working pressure of the system, Mnk The opening pitch driving torque provided by the pitch mechanism at any pitch angle, M ns The feathering driving torque provided by the pitch mechanism at any pitch angle, M fk The opening pitch load corresponding to the angle, M fs The feathering load corresponding to the angle.

[0078] It should be noted that in this embodiment, cylinders of different specifications and sizes are adopted to match the opening pitch and feathering loads of the pitch, so that the pitch capacity of the system is highly consistent with the pitch load of the wind turbine, reducing the redundancy of the pitch capacity of the system, thereby reducing the cost of the pitch system and achieving high economy of the pitch system. At the same time, the change amount of the pitch moment arm within the full pitch angle range of the pitch mechanism is small, and the moment arm at the large pitch angle is still large enough. Therefore, only a lower pressure is required for pitch drive, that is, the minimum working pressure of the high-pressure accumulator is reduced, thereby reducing the volume requirement of the high-pressure accumulator as a storage for emergency feathering energy and improving the volume utilization rate of the high-pressure accumulator;

[0079] Embodiment 2

[0080] The present invention also provides a double-cylinder hydraulic pitch mechanism, as Figure 2 and Figure 3 shown, including a hub 1, on which a blade 2 is connected through a pitch bearing. The pitch bearing is composed of an inner bearing ring 6 and an outer bearing ring 7. The outer bearing ring 7 of the pitch bearing is connected to the hub 1, and the inner bearing ring 6 of the pitch bearing is connected to the blade 2. The cylinder ends of a first pitch cylinder 3 and a second pitch cylinder 5 are connected to the hub 1 through a pin shaft 4, and the rod ends of the first pitch cylinder 3 and the second pitch cylinder 5 are connected to the blade 2 through a pin shaft 4;

[0081] It should be noted that, as Figure 2 and Figure 3 shown, through the connection of the pitch bearing, the blade 2 and the hub 1 can rotate relative to each other to realize the pitch movement of the wind turbine. The first pitch cylinder 3 and the second pitch cylinder 5 extend and retract the cylinders respectively through the power oil source provided by the hydraulic system, thereby driving the blade 2 to rotate clockwise; conversely, when the first pitch cylinder 3 and the second pitch cylinder 5 retract and extend the cylinders respectively through the power oil source provided by the hydraulic system, thereby driving the blade 2 to rotate counterclockwise. The clockwise rotation and counterclockwise rotation of the blade 2 are both pitch movements, and the difference lies in whether it is opening pitch or feathering;

[0082] As Figure 2As shown in the figure, at this time, the first pitch cylinder 3 is in the extended state. The pitch cylinder is close to the rotation center of the pitch movement of the blade, and its lever arm is the smallest; while the second pitch cylinder 5 is in the contracted state. The pitch cylinder is far from the rotation center of the pitch movement of the blade, and its lever arm is large. In this state, according to the torque formula, it can be obtained that whether it is the blade opening action or the feathering action, when the hydraulic system provides the same pressure oil, when the effective action area of the cylinder provided by the second pitch cylinder 5 is smaller than that of the first pitch cylinder 3, it can still provide the same or even greater pitch torque;

[0083] As Figure 3 shown in the figure, at this time, the first pitch cylinder 3 is in the contracted state. The pitch cylinder is far from the rotation center of the pitch movement of the blade, and its lever arm is large; while the second pitch cylinder 5 is in the extended state. The pitch cylinder is close to the rotation center of the pitch movement of the blade, and its lever arm is the smallest. In this state, according to the torque formula, it can be obtained that whether it is the blade opening action or the feathering action, when the hydraulic system provides the same pressure oil, when the effective action area of the cylinder provided by the first pitch cylinder 3 is smaller than that of the second pitch cylinder 5, it can still provide the same or even greater pitch torque;

[0084] That is, since the specifications of the first pitch cylinder 3 and the second pitch cylinder 5 are different, it can be realized that in the hydraulic pitch system, whether it is differential or non-differential, the effective action area of the cylinder corresponding to the blade opening or feathering is different, and thus the pitch ability is also different. Accordingly, the cylinder specifications are adjusted to a state where the blade opening and feathering capabilities match the blade opening and feathering loads of the wind turbine;

[0085] Embodiment 3

[0086] As Figures 1 to 3 shown in the figure, in this embodiment, a specific design method of a double-cylinder hydraulic pitch mechanism is provided. The two pitch cylinders in the pitch mechanism are installed on the same side of the blade in an axisymmetric manner, that is, the ends of the two pitch cylinders connected to the hub are close to each other on the same side of the blade, and the axis of symmetry of the two pitch cylinders passes through the rotation center of the blade pitch rotation;

[0087] First, determine the value range of R according to the structure of the wind turbine mainframe, and initially select R as the maximum value within the range. Take r as 2 / 3R, B as 1 / 5R, and γ as -5. The two pitch cylinders are installed on the same side in an axisymmetric manner, and the axis of symmetry passes through the rotation center of the blade pitch rotation. First, obtain the acting lever arms L n3 and L n5 ;

[0088]

[0089] where θ n5 、θ n3are respectively the angles formed by the axes of the second pitch cylinder 5 and the first pitch cylinder 3 and the connecting line between the cylinder end mounting point and the blade rotation center when the pitch angle is n°; R is the distance from the cylinder end mounting point to the blade rotation center;

[0090]

[0091] In the above formula

[0092]

[0093] wherein, R is the distance from the cylinder end mounting point to the blade rotation center; B is the distance from the cylinder barrel end mounting point to the symmetry axis; r is the distance from the cylinder rod end mounting point to the blade rotation center, r < R; λ is the initial installation angle of the pitch system; λ n is the system installation angle when the pitch angle is n°; γ is the total pitch angle range of the wind power main engine; δ n is the total amount of angle change of the pitch system, δ n = λ n - λ; β n5 , β n3 are respectively the angles formed by the connection between the blade rotation center and the cylinder end mounting point and the connection line with the cylinder rod end mounting point;

[0094] According to the specified system effective working pressure P, the pitch opening driving torque M nk provided by the pitch mechanism at any pitch angle and the feathering driving torque M ns must be respectively greater than the pitch opening load M fk and the feathering load M fs , that is, the rationality of the selected pitch mechanism layout parameters and cylinder specifications is verified by the following formula:

[0095] M nk = P(A k5 L n5 + A k3 L n3 ) > M fk

[0096] M ns = P(A s5 L n5 + A s3 L n3 ) > M fs ;

[0097] A k5 , A k3 are respectively the effective pitch opening areas of the second pitch cylinder 5 and the first pitch cylinder 3; A s5 , A s3 are respectively the effective feathering acting areas of the second pitch cylinder 5 and the first pitch cylinder 3;

[0098] Among them, the value ranges of R, r, B, and γ are all restricted by the structure of the wind turbine mainframe. At the initial stage of design, according to the restrictions of the pitch structure on the layout parameters, R can be selected as the maximum value within the range, r is taken as 2 / 3R, B is taken as 1 / 5R, and γ is taken as -5. Thus, the required cylinder specifications of the system are calculated by trial;

[0099] According to the working state of the system (differential or non-differential working), the effective pitch-opening areas A k5 and A k3 of the second pitch cylinder 5 and the first pitch cylinder 3 during pitch opening are respectively:

[0100] For the differential working condition:

[0101] For the non-differential working condition:

[0102] The effective pitch-closing acting areas A s5 and A s3 of the second pitch cylinder 5 and the first pitch cylinder 3 during pitch closing are respectively:

[0103] For the differential working condition:

[0104] For the non-differential working condition:

[0105] In the above formulas, D 5 and d 5 , D 3 and d 3 are respectively the cylinder diameter and rod diameter of the second pitch cylinder 5, and the cylinder diameter and rod diameter of the first pitch cylinder 3;

[0106] After calculating the cylinder specifications, round the cylinder specifications according to the national recommended standards, and then reverse-calculate and optimize the values of R, r, B, and γ from the rounded cylinders. At the same time, the cylinder specifications can also be adjusted in real time according to the calculation results;

[0107] With the goal of achieving the optimal comprehensive cost of the pitch system under the condition of meeting the pitch requirements, and taking the wind turbine mainframe parameters and the relevant parameters of the cylinders and accumulators as boundary conditions for planning and solving, the optimal pitch mechanism layout parameters within the range will be obtained, so that the pitch-opening and pitch-closing torques formed by the pitch mechanism match the pitch-opening and pitch-closing loads of the wind turbine, and the redundancy of the pitch capacity of the pitch mechanism is reduced;

[0108] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by the terms "upper", "lower", "bottom", "top", "front", "rear", "inner", "outer", "left", "right", etc. are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention.

[0109] Although the present invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed, as long as they do not depart from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the different dependent claims and the features herein can be combined in a manner different from that described in the original claims. It should also be understood that the features described in connection with a single embodiment can be used in other embodiments.

Claims

1. A double-cylinder hydraulic pitch mechanism, characterized in that: It includes a wheel hub and blades arranged on the wheel hub, and also includes two variable pitch cylinders axially symmetrically installed on the same side of the blades, the two ends of the variable pitch cylinders are respectively connected to the wheel hub and the blades, the variable pitch cylinders are also connected to a power source, and the specifications of the two variable pitch cylinders are different.

2. A dual-cylinder hydraulic pitch mechanism according to claim 1, characterized in that: The hub is connected to the blade via a variable pitch bearing, and the variable pitch bearing comprises an outer bearing ring connected to the hub and an inner bearing ring connected to the blade.

3. A dual-cylinder hydraulic pitch mechanism according to claim 2, characterized in that: Both ends of the pitch cylinder are connected to the hub and the blade respectively through pins.

4. A dual-cylinder hydraulic pitch mechanism according to claim 1, characterized in that: The power source is a hydraulic system connected to the pitch cylinder.

5. A design method for a dual-cylinder hydraulic pitch mechanism, characterized in that: The steps include: Step S1, obtaining a working space size range and an installation size range of the pitch mechanism, and obtaining the force arms of the two pitch cylinders according to the positional relationship between the two pitch cylinders in the pitch mechanism; Step S2, according to the system working state, obtain the effective areas corresponding to the two pitch cylinders when the propellers are opened and the propellers are feathered; Step S3: verifying the rationality of the pitch mechanism layout parameters and the cylinder specifications.

6. The design method of a dual-cylinder hydraulic pitch mechanism according to claim 5 is characterized in that: In step S1, two pitch cylinders in the pitch mechanism are installed on the same side of the blade in an axisymmetric manner, and the symmetry axes of the two pitch cylinders pass through the rotation center of the blade pitch rotation.

7. The design method of a dual-cylinder hydraulic pitch mechanism according to claim 6 is characterized in that: In step S1, the force arms of the two pitch cylinders are calculated as follows: in, In the above formula, r<R； d n =λ n -l; Where R is the distance from the mounting point of the pitch cylinder end to the blade rotation center; B is the distance from the mounting point of the pitch cylinder barrel end to the symmetry axis; r is the distance from the mounting point of the pitch cylinder rod end to the blade rotation center; λ is the initial installation angle of the pitch system; λ n is the system installation angle when the pitch angle is n°; γ is the total variable pitch angle range of the wind turbine; δ n is the total angle change of the pitch system; θ n1 is the angle between the axis of one of the pitch cylinders and the line connecting the cylinder end mounting point and the blade rotation center at the pitch angle n°, θ n2 β is the angle between the axis of another pitch cylinder and the line connecting the cylinder end mounting point and the blade rotation center at the pitch angle n°; n1 β is the angle between the blade rotation center and the line connecting one of the cylinder end mounting points and the line connecting the propeller blade rotation center and the cylinder rod end mounting point. n2 It is the angle formed by the line connecting the blade rotation center and the mounting point of the cylinder end of another cylinder and the line connecting the blade rotation center and the mounting point of the cylinder rod end.

8. The design method of a dual-cylinder hydraulic pitch mechanism according to claim 7 is characterized in that: In step S2, the system operating state includes a differential operating state and a non-differential operating state; In differential operation, In non-differential conditions, Wherein, D1 and d1 are the cylinder diameter and rod diameter of one pitch cylinder, respectively, and D2 and d2 are the cylinder diameter and rod diameter of the other pitch cylinder, respectively; A k1 and A k2 are the effective opening areas of the two pitch cylinders; A s1 and A s2 They are the effective feathering areas of the two pitch cylinders respectively.

9. The design method of a dual-cylinder hydraulic pitch mechanism according to claim 8, characterized in that: In step S3, the propeller opening drive torque and the propeller feathering drive torque provided by the pitch mechanism at any pitch angle are respectively greater than the propeller opening load and the propeller feathering load at the corresponding angles.

10. The design method of a dual-cylinder hydraulic pitch mechanism according to claim 9, characterized in that: In step S3, the verification formula is: M nk =P(A k1 L n1 +A k2 L n2 )>M fk M ns =P(A s1 L n1 +A s2 L n2 )>M fs ; Among them, P is the effective working pressure of the system, M nk M is the propeller drive torque provided by the pitch mechanism at any pitch angle. ns M is the feathering drive torque provided by the pitch mechanism at any pitch angle. fk is the propeller load at the corresponding angle, M fs is the feathering load at the corresponding angle.

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