Blade assembly and mast for wind power plant

Abstract

A blade assembly (1) for connection to a mast (5) of a wind turbine. The blade assembly includes: a main blade (10) including a main attachment portion (12) configured to be attached to a mast (5) and a main airfoil (16) protruding from the main attachment portion; and a double-wing blade (20) connected to the main blade. The double-wing blade extends between a first connection (22) and a second connection (24) connected to the main blade. The double-wing blade includes a double-wing airfoil (26) located between the first connection portion and the second connection portion. The blade assembly also includes a main strut (30) configured to be connected between the main blade and the mast. The utility model further provides the mast of the wind power plant.

Description

Technical Field

[0001] The utility model relates to a blade assembly for connecting to a mast of a wind turbine. The blade assembly is configured to be attached to the mast to transfer energy to the wind turbine. The blade assembly includes a main blade and a main airfoil. The main blade includes a main attachment portion configured to be attached to the mast, and the main airfoil projects from the main attachment portion. The blade assembly further includes a biplane blade connected to the main blade. The biplane blade extends between a first connection portion and a second connection portion connected to the main blade. The biplane blade includes a biplane airfoil located between the first connection portion and the second connection portion.

[0002] The utility model further relates to a mast of a wind power plant including the blade assembly and the use of the blade assembly. Background Art

[0003] Wind power plants use blade assemblies connected to masts to transfer rotational energy to turbines. The rotational energy can be transferred directly to the turbine, such as in a horizontal axis wind turbine (HAWT), or alternatively, the rotational energy can be transferred to the turbine through the mast, such as in a vertical axis wind turbine (VAWT).

[0004] During the use of blade assemblies in wind power plants, the blade assemblies are subjected to large forces and torques. To improve the efficiency of wind power plants, it is desirable to arrange the blade assemblies to have a longer length. However, this results in the blade assemblies being subjected to large forces and torques. To withstand these forces and torques, various special materials are usually used to manufacture the blade assemblies, such as fiber-reinforced polymers, carbon fibers, etc. Although these materials provide high strength, their problem is that they are expensive and will significantly increase the total cost of wind power plants.

[0005] It is preferable to use relatively low-cost materials, such as aluminum alloys or wood, to provide the structural strength of the blade assembly.

[0006] US2014363303A1 discloses a wind turbine blade having a biplane portion. Summary of the Utility Model

[0007] The object of the present utility model is to provide an improved blade assembly for a wind power plant. Specifically, the first object of the present utility model is to provide an improved blade assembly that can use relatively low-cost construction materials, such as aluminum alloy or wood or a combination thereof. The second object of the present utility model is to provide an improved blade assembly that can be configured to have a longer length compared to the blade assemblies of the prior art. The third object of the present utility model is to provide an improved blade assembly that is suitable for connection to a horizontal axis wind turbine (HAWT).

[0008] These objects are achieved by a blade assembly for connection to a mast of a wind turbine, wherein the blade assembly is configured to be attached to the mast. The blade assembly comprises:

[0009] - a main blade, which includes a main attachment portion configured to be attached to the mast and a main airfoil protruding from the main attachment portion, and

[0010] - a double-wing blade connected to the main blade, wherein the double-wing blade extends between a first connection portion and a second connection portion connected to the main blade, wherein the double-wing blade includes a double-wing airfoil located between the first connection portion and the second connection portion, and

[0011] - a main strut configured to connect between the main blade and the mast.

[0012] The main blade has the function of a main absorber that uses the main airfoil to absorb energy from the wind. The main blade defines the total length of the blade assembly. The double-wing blade is connected to the main blade through the first connection portion and the second connection portion. The double-wing blade has the function of a secondary absorber that uses the double-wing airfoil to absorb energy from the wind. The main blade and the double-wing airfoil together absorb energy from the wind.

[0013] The double-wing blade also has the function of providing structural stability to the main blade. The structural stability of the main blade is further improved by the main strut extending between the main blade and the mast. The main function of the main strut is to absorb the thrust received by the main blade. The double-wing blade and the main strut together improve the structural stability of the main blade.

[0014] Through the configuration of the blade assembly, the structural stability of the blade assembly is generally improved, which enables the use of relatively low-cost materials, such as aluminum alloy or wood or a combination thereof. Alternatively, special materials such as fiber-reinforced polymers, carbon fibers, etc. can be used to further increase the length of the blade assembly compared to the blade assemblies of the prior art.

[0015] According to an embodiment of the present invention, the main attachment portion is configured to be attached to a first portion of the mast, and the main strut is configured to be connected to a second portion of the mast, wherein the first portion and the second portion of the mast are spaced apart from each other by a certain distance. By arranging the attachment of the main blade to the mast and the attachment of the main strut to the mast to be separated from each other, the stability of the blade assembly is improved.

[0016] According to an embodiment of the present invention, the main blade includes a tip portion, and a first connecting portion and a second connecting portion where the double-wing blade is connected to the main blade are located between the tip portion where the main attachment portion is connected to the main blade. The main blade extends from the main attachment portion to the tip portion. By connecting the double-wing blade between the main attachment portion and the tip portion, the structural stability of the blade assembly is improved.

[0017] According to an embodiment of the present invention, the first connecting portion where the double-wing blade is connected to the main blade is located near the main attachment portion.

[0018] According to an embodiment of the present invention, the second connecting portion where the double-wing blade is connected to the main blade is located near the tip portion of the main blade.

[0019] According to an embodiment of the present invention, the double-wing blade is shorter than the main blade, and the length of the double-wing blade between the first connecting portion and the second connecting portion accounts for 30% to 70% of the length of the main blade, preferably 40% to 60% of the length of the main blade. The main function of the double-wing blade is to support the main blade, and for this purpose, it is sufficient for the double-wing blade to be shorter than the main blade.

[0020] According to an embodiment of the present invention, the double-wing blade is provided as an intermediate blade centered relative to the main blade.

[0021] According to an embodiment of the present invention, the second connecting portion where the double-wing blade is connected to the main blade is positioned at a distance from the main attachment portion that includes between one-third and two-thirds of the length of the main blade, preferably half of the length of the main blade. The main function of the double-wing blade is to support the main blade, and therefore, preferably, the second connecting portion is located at an intermediate blade at a distance from the tip portion.

[0022] According to an embodiment of the present invention, the double-wing blade includes a first portion that extends from the first connecting portion and away from the main blade, such that a first space is formed between the first portion and the main blade, and a first portion of the double-wing airfoil is arranged on the first portion.

[0023] According to an embodiment of the present utility model, the double-wing blade includes a second portion that extends from the second connecting portion and away from the main blade, such that a second space is formed between the second portion and the main blade, wherein the second portion of the double-wing airfoil is disposed on the second portion.

[0024] According to an embodiment of the present utility model, the chord line of the first portion of the double-wing airfoil is greater than the chord line of the second portion of the double-wing airfoil.

[0025] According to an embodiment of the present utility model, the chord line of the second portion of the double-wing airfoil is greater than the chord line of the first portion of the double-wing airfoil.

[0026] According to an embodiment of the present utility model, the blade assembly further includes a secondary strut that is connected between the main blade and the double-wing blade. The secondary strut extending between the main blade and the double-wing blade improves the structural stability of the connection between the main blade and the double-wing blade. The main function of the secondary strut is to absorb the thrust between the main blade and the double-wing blade.

[0027] According to an embodiment of the present utility model, the double-wing blade includes a connecting portion where the first portion and the second portion of the double-wing blade are connected, and wherein the secondary strut is connected to the connecting portion. By connecting the secondary strut to the connecting portion between the first portion and the second portion of the double-wing blade, the structural stability of the double-wing blade is improved.

[0028] According to an embodiment of the present utility model, the connecting portion between the first portion and the second portion of the double-wing blade is positioned further away from the main blade compared to the first portion and the second portion of the double-wing blade.

[0029] According to an embodiment of the present utility model, the main strut is connected to the main blade at an angle within a + / - 25-degree range perpendicular to the extension of the main blade, preferably at an angle within a + / - 10-degree range perpendicular to the extension of the main blade.

[0030] According to an embodiment of the present utility model, the secondary strut is connected to the double-wing blade at an angle within a + / - 25-degree range perpendicular to the extension of the double-wing blade, preferably at an angle within a + / - 10-degree range perpendicular to the extension of the double-wing blade.

[0031] According to an embodiment of the present utility model, the chord line of the airfoil of the double-wing blade is smaller than the chord line of the airfoil of the main blade. The main function of the double-wing blade is to support the main blade, and thus preferably, the chord line of the airfoil of the double-wing blade is smaller than the chord line of the airfoil of the main blade. Therefore, the main blade serves as the main absorber of energy from the wind.

[0032] According to an embodiment of the present invention, the chord line of the airfoil of the double-wing blade is within the range of 10% to 50% of the chord line of the airfoil of the main blade, preferably within the range of 20% to 30% of the chord line of the airfoil of the main blade.

[0033] According to an embodiment of the present invention, the secondary strut includes at least one beam, and the at least one beam is arranged in a streamlined shape with respect to the displacement direction of the blade assembly. By means of the streamlined arrangement structure of the at least one beam, the resistance of the secondary strut to the rotation of the blade assembly is reduced.

[0034] According to an embodiment of the present invention, the secondary strut includes two or more connected beams, and these beams extend between different positions of the main blade and the double-wing blade. By arranging the secondary strut to have two or more beams, the structural stability of the connection between the main blade and the double-wing blade is improved.

[0035] According to an embodiment of the present invention, the main attachment portion of the main blade includes two separate attachment portions, and the two attachment portions are configured to form an attachment portion with the mast.

[0036] According to an embodiment of the present invention, the connection portion of the main strut includes two separate attachment portions, and the two attachment portions are configured to form an attachment portion with the mast.

[0037] According to an embodiment of the present invention, the main blade and the double-wing blade mainly include one of aluminum and wood, or a combination of aluminum and wood.

[0038] According to an embodiment of the present invention, the tip portion of the main blade includes a leading edge, and the leading edge includes a layer of one of steel, titanium, and aluminum or a layer of a composition of steel, titanium, and aluminum.

[0039] According to an embodiment of the present invention, at least one of the main blade and the double-wing blade includes a beam assembly and an aerodynamic shell. The beam assembly is preferably a box-shaped beam assembly, and the aerodynamic shell is fixed to the beam assembly. The beam assembly has the function of providing main structural stability for the main blade and / or the double-wing blade. The aerodynamic shell has the function of forming the main airfoil and / or the double-wing airfoil.

[0040] According to an embodiment of the present invention, the aerodynamic shell includes a core and an inner layer and an outer layer attached to the core. The core mainly includes one of a bio-derived composition (preferably wood), a para-aramid synthetic fiber composition, or an aluminum honeycomb structure, a metal foam, and a polymer foam (preferably mainly including divinycells), and the inner layer and the outer layer mainly include aluminum alloy sheets.

[0041] According to an embodiment of the present utility model, the core, the inner layer and the outer layer are joined together by an adhesive (preferably epoxy resin).

[0042] According to an embodiment of the present utility model, the aluminum alloy sheets of the inner layer and the outer layer are joined by friction stir welding. Friction stir welding is particularly suitable for joining rigid sheets of aluminum alloy.

[0043] According to an embodiment of the present utility model, the beam assembly includes the following beams: the beams mainly comprise aluminum alloy.

[0044] According to an embodiment of the present utility model, the main blade, the double-wing blade, the main strut and the secondary strut are made of separate elements.

[0045] According to an embodiment of the present utility model, the beam assemblies of the main blade and the double-wing blade are joined together by friction stir welding.

[0046] According to an embodiment of the present utility model, at least one of the main blade and the double-wing blade includes a leading edge along its extension, wherein the leading edge includes a reinforcing layer of one or a combination of steel, titanium and aluminum. By providing a reinforcing outer layer at the leading edge, the corrosion problem at the leading edge is reduced. According to an embodiment, the outer layer on the core at the leading edge - for example in the form of an aluminum alloy layer - can partially or completely replace the outer layer.

[0047] According to an embodiment of the present utility model, the blade assembly includes a pin joint configured to: during the assembly of the blade assembly, hold the main blade, the double-wing blade, the main strut and the secondary strut rotatably attached at their respective attachment parts. By means of the pin joint, the assembly of the blade assembly is facilitated.

[0048] According to an embodiment of the present utility model, the blade assembly includes a locking device configured to lock the pin joint to prevent its rotation after the assembly of the blade assembly is completed. By means of the locking device, a permanent connection of the main blade, the double-wing blade, the main strut and the secondary strut is established.

[0049] The object of the present utility model is also achieved by a mast of a wind power plant including a blade assembly according to any of the above embodiments.

[0050] The object of the present utility model is also achieved by the use of a blade assembly according to any of the above embodiments. Description of the Drawings

[0051] Embodiments of the present utility model will now be described by way of example only with reference to the following drawings, in which:

[0052] Figure 1a A schematic diagram of a blade assembly according to an embodiment of the present utility model is disclosed,

[0053] Figure 1b Schematic diagram of a blade assembly according to another embodiment of the present utility model is disclosed.

[0054] Figure 1c Schematic diagram of a blade assembly according to yet another embodiment of the present utility model is disclosed.

[0055] Figure 2 Embodiments of a main blade, a double-wing blade, and a main strut as separate elements are disclosed.

[0056] Figure 3 Cross-section of a main blade according to an embodiment of the present utility model is disclosed.

[0057] Figure 4 Schematic diagram of a blade assembly according to another embodiment of the present utility model is disclosed. Detailed embodiments

[0058] Figures 1a to 1c Schematic diagram of a blade assembly 1 according to an embodiment of the present utility model is disclosed. The blade assembly 1 is shown as being connected to a mast 5 of a wind power plant.

[0059] The blade assembly 1 includes a main blade 10, and the main blade 10 includes a main attachment portion 12 that attaches the main blade 10 to the mast 5. The main blade 10 extends from the main attachment portion 12 to a tip portion 14. The main blade 10 includes a main airfoil 16 located between the main attachment portion 12 and the tip portion 14. The main airfoil 16 can be disposed entirely or partially between the main attachment portion 12 and the tip portion 14.

[0060] The blade assembly 1 further includes a double-wing blade 20 connected to the main blade 10. The double-wing blade 20 includes a first connection portion 22 and a second connection portion 24 connected to the main blade 10. The double-wing blade 20 further includes a double-wing airfoil 26 located between the first connection portion 22 and the second connection portion 24.

[0061] Preferably, the chord line of the double-wing airfoil 26 of the double-wing blade 20 is smaller than the chord line of the main airfoil 16 of the main blade 10. Preferably, the chord line of the double-wing airfoil 26 of the double-wing blade 20 is in the range of 10% to 50% of the chord line of the main airfoil 16 of the main blade 10, preferably in the range of 20% to 30% of the chord line of the main airfoil 16 of the main blade 10.

[0062] The blade assembly 1 further includes a main strut 30 extending from the mast 5 to the main blade 10. The main strut 30 includes a first main strut connection portion 32 connecting the main strut 30 to the mast 5 and a second main strut connection portion 34 connecting the main strut 30 to the main blade 10. The main blade 10 is connected to a first portion 12a of the mast 5 through a main attachment portion 12. The main strut 30 is connected to a second portion 32a of the mast 5 through the main strut connection portion 32. In the disclosed embodiment, the first portion 12a of the mast 5 and the second portion 32a of the mast 5 are positioned separately from each other. However, it should be understood that the first portion 12a of the mast 5 and the second portion 32a of the mast 5 may be arranged adjacent to each other.

[0063] The blade assembly 1 further includes a secondary strut 40 connected between the main blade 10 and the bi-wing blade 20. The secondary strut 40 includes a first secondary strut connection portion 42 connecting the secondary strut 40 to the main blade 10 and a second secondary strut connection portion 44 connecting the secondary strut 40 to the bi-wing blade 20. In Figures 1a to 1c the disclosed embodiment, the main strut 30 and the secondary strut 40 are separate elements. However, it should be understood that the main strut 30 and the secondary strut 40 may be formed by combined elements.

[0064] In the disclosed embodiment, the bi-wing blade 20 is shorter than the main blade 10. Preferably, the length of the bi-wing blade 20 between the first connection portion 22 and the second connection portion 24 occupies 30% to 70%, preferably 40% to 60% of the length of the main blade 10.

[0065] The bi-wing blade 20 includes a first portion 20a extending from the first connection portion 22 and away from the main blade 10 such that a first space 28a is formed between the first portion 20a and the main blade 10. The first portion 26a of the bi-wing airfoil 26 is arranged on the first portion 20a.

[0066] Correspondingly, the bi-wing blade 20 includes a second portion 20b extending from the second connection portion 24 and away from the main blade 10 such that a second space 28b is formed between the second portion 20b and the main blade 10. The second portion 26b of the bi-wing airfoil 26 is arranged on the second portion 20b.

[0067] The bi-wing blade 20 further includes a connecting portion 29 where the first portion 20a and the second portion 20b of the bi-wing blade 20 are connected. In the disclosed embodiment, the secondary strut 40 is connected to the connecting portion 29. In the disclosed embodiment, the first portion 20a and the second portion 20b of the bi-wing blade 20 have similar lengths. However, it should be understood that the first portion 20a and the second portion 20b of the bi-wing blade 20 may have different lengths.

[0068] In the disclosed embodiments, the connecting portion 29 between the first portion 20a and the second portion 20b of the double-wing blade 20 is farther from the main blade 10 than the first portion 20a and the second portion 20b of the double-wing blade 20. Accordingly, the connecting portion 29 forms the tip of the double-wing blade 20.

[0069] In the disclosed embodiments, the main strut 30 is connected to the intermediate blade of the main blade 10 through the second main strut connecting portion 34. The double-wing blade 20 is preferably arranged to extend symmetrically with respect to the position of the intermediate blade. It should be understood that the double-wing blade 20 can be arranged alternately. For example, the first connecting portion 22 of the double-wing blade 20 and the main blade 10 can be positioned adjacent to the main attachment portion 12 of the main blade 10. Correspondingly, the second connecting portion 24 where the double-wing blade 20 is connected to the main blade 10 can be positioned adjacent to the tip 14 of the main blade 10.

[0070] In the disclosed embodiments, the main strut 30 is connected through the second main strut connecting portion 34 substantially perpendicular to the extension of the main blade 10. However, it should be understood that the main strut 30 can be connected to the main blade 10 at an angle within the range of + / - 25 degrees perpendicular to the extension of the main blade 10, and preferably can be connected to the main blade 10 at an angle within the range of + / - 10 degrees perpendicular to the extension of the main blade 10.

[0071] In the disclosed embodiments, the secondary strut 40 is connected at the connecting portion 29 substantially perpendicular to the double-wing blade 20 through the second secondary strut connecting portion 44. However, it should be understood that the secondary strut 40 can be connected to the double-wing blade 20 at an angle within the range of + / - 25 degrees perpendicular to the extension of the double-wing blade 20, and preferably can be connected to the double-wing blade 20 at an angle within the range of + / - 10 degrees perpendicular to the extension of the double-wing blade 20.

[0072] According to an embodiment of the present invention, the secondary strut 40 includes at least one beam, and the beam is arranged in a streamlined shape with respect to the displacement direction of the blade assembly 1. In the disclosed embodiments, a single beam indicating the strut of the secondary strut 40 is shown. However, it should be understood that the secondary strut 40 can include two or more beams extending and connecting between different positions of the main blade 10 and the double-wing blade 20.

[0073] Reference Figure 1b , additional embodiments of the present invention are disclosed. Figure 1b The embodiments in Figure 1a are different from the embodiments in

[0074] Reference Figure 1c discloses another embodiment of the present utility model. The difference between the present utility model and the embodiments in Figure 1a and Figure 1b is that the blade assembly 1 lacks the secondary strut 40. The main blade 10 further bends and extends, while the double-wing blade 20 extends substantially straight.

[0075] Reference Figure 2 discloses an embodiment of the main blade 10, the double-wing blade 20, and the main strut 30 as independent elements. It should be understood that the element represented as touching the strut 30 in Figure 2 can simultaneously perform the functions of the main strut 30 and the secondary strut 40.

[0076] In the disclosed embodiment, the main attachment portion 12 of the main blade 10 includes two attachment portions 13a, 13b that are separated from each other. The two attachment portions 13a, 13b are configured to form an attachment portion with the mast 5.

[0077] Correspondingly, the main strut connection portion 32 of the main strut 30 includes two attachment portions 33a, 33b that are separated from each other. The two attachment portions 33a, 33b are configured to be an attachment portion with the mast 5.

[0078] According to an embodiment of the present utility model, the main blade 10 and the double-wing blade 20 mainly include one of aluminum and wood, or a combination thereof. The combination of wood and aluminum provides structural strength to the blade assembly 1.

[0079] According to an embodiment of the present utility model, the tip portion 14 of the main blade 10 includes a leading edge, and the leading edge includes one or a combination of a steel layer, a titanium layer, and an aluminum layer.

[0080] Reference Figure 3 discloses a cross-section of the main blade 10 according to an embodiment of the present utility model. The corresponding embodiment is applicable to the double-wing blade 20. The main blade 10 includes a beam assembly 50 and an aerodynamic housing 52 fixed to the beam assembly 40. The beam assembly 50 is preferably a box-shaped beam assembly.

[0081] The aerodynamic housing 52 includes a layered structure, and the layered structure includes a core 60 and an inner layer 62 and an outer layer 64 attached to the core 60. The core 60, the inner layer 62, and the outer layer 64 are preferably bonded together with an adhesive, preferably with epoxy resin. The inner layer 62 and the outer layer 64 are preferably aluminum alloy sheets joined together by friction stir welding.

[0082] According to an embodiment of the present invention, the core 60 mainly comprises a bio-derived composition preferably wood, a honeycomb structure of an aramid synthetic fiber composition or aluminum, metal foam and polymer foam, preferably mainly comprising divinycells. The inner layer 62 and the outer layer 64 mainly comprise aluminum alloy sheets.

[0083] Reference Figure 4 , a schematic illustration of a blade assembly 1 according to another embodiment of the present invention is disclosed. The blade assembly 1 includes a pin joint 70 configured to rotatably attach the main blade 10, the double-wing blade 20, the main strut 30 and the secondary strut 40 at their respective attachment portions during the assembly of the blade assembly 1.

[0084] According to an embodiment of the present invention, the blade assembly 1 includes a locking device configured to lock the pin joint 70 against rotation after the assembly of the blade assembly 1 is completed. The locking device is not shown in the figure.

[0085] It should be noted that the above embodiments illustrate rather than limit the present invention, and those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims.

[0086] For example, it should be understood that the features and embodiments related to the structure of the beam assembly 50 and the pneumatic housing 52 can be applied independently of the features related to the structural configuration of the blade assembly 1.

Claims

1. A blade assembly for connection to a mast (5) of a wind turbine, wherein, The blade assembly (1) is configured to be attached to the mast (5), wherein the blade assembly (1) comprises: - a main blade (10), the main blade (10) including a main attachment portion (12) configured to be attached to the mast (5) and a main airfoil (16) protruding from the main attachment portion (12), - a bi-wing blade (20), the bi-wing blade (20) being connected to the main blade (10), wherein the bi-wing blade (20) extends between a first connection portion (22) and a second connection portion (24) connected to the main blade (10), wherein the bi-wing blade (20) includes a bi-wing airfoil (26) located between the first connection portion (22) and the second connection portion (24), characterized in that the blade assembly (1) further includes a main strut (30), the main strut (30) being configured to be connected between the main blade (10) and the mast (5).

2. The blade assembly according to claim 1, wherein The main attachment portion (12) is configured to be attached to a first portion of the mast (5), and the main strut (30) is configured to be connected to a second portion of the mast (5), wherein the first portion and the second portion of the mast (5) are spaced apart from each other by a distance.

3. The blade assembly according to claim 1 or 2, characterized in that The main blade (10) includes a tip portion (14), and wherein the first connection portion (22) and the second connection portion (24) of the bi-wing blade (20) connected to the main blade (10) are located between the main attachment portion (12) and the tip portion (14) of the main blade (10).

4. The blade assembly according to claim 1 or 2, characterized in that, The first connection portion (22) of the bi-wing blade (20) connected to the main blade (10) is located near the main attachment portion (12).

5. The blade assembly according to claim 3, wherein The second connection portion (24) of the bi-wing blade (20) connected to the main blade (10) is located near the tip portion (14) of the main blade (10).

6. The blade assembly according to claim 1 or 2, characterized in that The bi-wing blade (20) is shorter than the main blade (10), wherein the length of the bi-wing blade (20) between the first connection portion (22) and the second connection portion (24) accounts for 30% to 70% of the length of the main blade (10).

7. The blade assembly according to claim 1 or 2, characterized in that, The bi-wing blade (20) is arranged as an intermediate blade centered relative to the main blade (10).

8. The blade assembly according to claim 1 or 2, characterized in that, The bi-wing blade (20) includes a first portion extending from the first connection portion (22) and away from the main blade (10), such that a first space (28a) is formed between the first portion of the bi-wing blade (20) and the main blade (10), wherein a first portion of the bi-wing airfoil (26) is arranged on the first portion of the bi-wing blade (20).

9. The blade assembly according to claim 8, characterized in that, The bi-wing blade (20) includes a second portion extending from the second connection portion (24) and away from the main blade (10), such that a second space (28b) is formed between the second portion of the bi-wing blade (20) and the main blade (10), wherein a second portion of the bi-wing airfoil (26) is arranged on the second portion of the bi-wing blade (20).

10. The blade assembly according to claim 9, wherein, The chord of the first part of the double-wing airfoil (26) is larger than the chord of the second part of the double-wing airfoil (26).

11. The blade assembly according to claim 9, characterized in that, The chord of the second part of the double-wing airfoil (26) is larger than the chord of the first part of the double-wing airfoil (26).

12. The blade assembly according to claim 9, wherein, The blade assembly (1) further includes a secondary strut (40) connected between the main blade (10) and the double-wing blade (20).

13. The blade assembly according to claim 12, wherein, The double-wing blade (20) includes a connecting portion (29), where the first part and the second part of the double-wing blade (20) are connected at the connecting portion (29), and wherein the secondary strut (40) is connected to the connecting portion (29).

14. The blade assembly according to claim 13, wherein Compared with the first part and the second part of the double-wing blade (20), the connecting portion (29) between the first part and the second part of the double-wing blade (20) is farther from the main blade (10).

15. The blade assembly according to claim 1 or 2, characterized in that, The main strut (30) is connected to the main blade (10) at an angle within a range of + / - 25 degrees perpendicular to the extension of the main blade (10).

16. The blade assembly according to claim 12, wherein, The secondary strut (40) is connected to the double-wing blade (20) at an angle within a range of + / - 25 degrees perpendicular to the extension of the double-wing blade (20).

17. The blade assembly according to claim 1 or 2, characterized in that, The chord of the double-wing airfoil (26) of the double-wing blade (20) is smaller than the chord of the main airfoil (16) of the main blade (10).

18. The blade assembly according to claim 17, wherein The chord of the double-wing airfoil (26) of the double-wing blade (20) is within the range of 10% to 50% of the chord of the main airfoil (16) of the main blade (10).

19. The blade assembly according to claim 12, characterized in that, The secondary strut (40) includes at least one beam arranged in a streamlined manner with respect to the displacement direction of the blade assembly (1).

20. The blade assembly according to claim 12, characterized in that, The secondary strut (40) includes two or more connected beams extending between different positions of the main blade (10) and the double-wing blade (20).

21. The blade assembly according to claim 1 or 2, characterized in that, The main attachment portion (12) of the main blade (10) includes two attachment portions separated from each other, and the two attachment portions are configured to form an attachment portion with the mast (5).

22. The blade assembly according to claim 1 or 2, characterized in that, The connecting portion of the main strut (30) includes two attachment portions separated from each other, and the two attachment portions are configured to form an attachment portion with the mast (5).

23. The blade assembly according to claim 1 or 2, characterized in that, The main blade (10) and the double-wing blade (20) include one of aluminum and wood, or a combination of aluminum and wood.

24. The blade assembly according to claim 1 or 2, characterized in that, The tip portion (14) of the main blade (10) includes a leading edge, and the leading edge of the main blade (10) includes a layer of one of steel, titanium, and aluminum, or the leading edge of the main blade (10) includes a layer of a composition of steel, titanium, and aluminum.

25. The blade assembly according to claim 1 or 2, characterized in that, At least one of the main blade (10) and the double-wing blade (20) includes a beam assembly (50) and an aerodynamic housing (52) fixed to the beam assembly (50).

26. The blade assembly according to claim 25, characterized in that, The pneumatic housing includes a core (60) and an inner layer (62) and an outer layer (64) attached to the core (60), wherein the core (60) includes one of the following: a bio-derived composition, a metal foam, and a polymer foam, and wherein the inner layer (62) and the outer layer (64) include aluminum alloy sheets.

27. The blade assembly according to claim 26, characterized in that, The core (60), the inner layer (62), and the outer layer (64) are bonded together with an adhesive.

28. The blade assembly according to claim 26, characterized in that The aluminum alloy sheets of the inner layer (62) and the outer layer (64) have been joined together by friction stir welding.

29. The blade assembly according to claim 26, wherein, The beam assembly (50) includes: a beam including aluminum alloy.

30. The blade assembly according to claim 12, wherein, The main blade (10), the double-wing blade (20), the main strut (30), and the secondary strut (40) are made of separate elements.

31. The blade assembly according to claim 25, wherein, The beam assemblies (50) of the main blade (10) and the double-wing blade (20) have been joined together by friction stir welding.

32. The blade assembly according to claim 1 or 2, characterized in that, The double-wing blade (20) includes a leading edge along its extension, wherein the leading edge of the double-wing blade (20) includes a layer of one of steel, titanium, and aluminum, or the leading edge of the double-wing blade (20) includes a layer of a composition of steel, titanium, and aluminum.

33. The blade assembly according to claim 12, wherein, The blade assembly (1) includes a pin joint (70) configured to rotatably attach the main blade (10), the double-wing blade (20), the main strut (30), and the secondary strut (40) at their respective attachment locations during assembly of the blade assembly (1).

34. The blade assembly according to claim 33, characterized in that, The blade assembly (1) includes a locking device configured to lock the pin joint (70) to prevent rotation after completion of the assembly of the blade assembly (1).

35. The blade assembly according to claim 1 or 2, characterized in that, The length of the double-wing blade (20) between the first connection portion (22) and the second connection portion (24) is 40% to 60% of the length of the main blade (10).

36. The blade assembly according to claim 1 or 2, characterized in that, The main strut (30) is connected to the main blade (10) at an angle within a range of + / - 10 degrees perpendicular to the extension of the main blade (10).

37. The blade assembly according to claim 12, wherein, The secondary strut (40) is connected to the double-wing blade (20) at an angle within a range of + / - 10 degrees perpendicular to the extension of the double-wing blade (20).

38. The blade assembly according to claim 17, wherein, The chord of the double-wing airfoil (26) of the double-wing blade (20) is within a range of 20% to 30% of the chord of the main airfoil (16) of the main blade (10).

39. The blade assembly according to claim 25, wherein, The beam assembly (50) is a box-shaped beam assembly.

40. The blade assembly according to claim 26, wherein, The core (60) includes wood.

41. The blade assembly according to claim 26, wherein, The core (60) includes a honeycomb structure of a para-aramid synthetic fiber composition or a honeycomb structure of aluminum.

42. The blade assembly according to claim 26, wherein, The core (60) includes vinyl foam.

43. The blade assembly according to claim 27, wherein, The adhesive is an epoxy resin.

44. Mast of a wind power plant, characterized in that, The mast (5) includes the blade assembly (1) according to any one of claims 1 to 43.

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