CABLE-STAYED BLADE STRUCTURE FOR VARIABLE SPEED WIND TURBINES

Abstract

The present invention presents a structure for a set of cable-stayed blades for variable-speed wind turbines with the aim of manufacturing low-cost, large-capacity wind turbines with blades of up to 200 meters long, do not rotate to change the tilt of the wing, insulated from turbine shaft, the structure includes the steel tube at the center of the central hub for affixing the blade set onto the head of the wind turbine shaft, a tower to extend the turbine vertical axis for mounting stay cables which are fastened to the axial bearing blade frame, the blade body consists of a triangular prismatic frame with two rear-framing tubes parallel to each other to form the baselines for mounting blade surface sheets which can be furl/unfurled, the blades can be disassembled and placed into containers to be transported to the base of the turbine tower for assembly.

Claims

1. The structure of cable-stayed blade set for variable speed wind turbines includes: athe central hub at the center of the blade set: the steel tubes (2) at the center of the central hub for affixing the blade set onto the head (1) of the wind turbine shaft, the steel tubes (2) consist of 3 layers, the middle layer is made of an insulating material between the blades and turbine shaft to prevent lightning strikes for the turbine, the steel tubes (2) are connected to the blade-mounting pads (4) by connecting-steel bars (3), the blade mounting pads (4) form a regular polygonal prismatic blade-mounting truss frame, the turbine blades are mounted onto the central hub by affixing the blade-mounting pads (4) to the blade-root flanges (9); the steel tubes (5) are affixed at the intersection points of the front edge of the blade mounting pads (4) and reaching upwards to the front of the turbine to form a cable-stayed tower, the steel tubes (5) converge at the flange (6) at the top of the cable-stayed tower; the flange (6) on the top of the cable-stayed tower is used for mounting the stay cables (8), an anemometer (7) is attached to the front of the flange (6), bthe body of the turbine blade has a truss structure that consists of the following components: the blade-root flange (9) is where the framing-metal tubes (10); (11); (12) are mounted, these tubes are linked together by connecting-metal tubes (13), forming the base prismatic frame of the blades, the centerlines of the rear rotating framing tube (10) and front rotating framing tube (11) are made to be parallel to each other, forming a plane perpendicular to the horizontal plane and the wind direction when rotating, they serve as the baselines for the fabrication and assembly of the blade components, the front framing tubes (12) are placed on the front side of the blades, equidistant from the two framing tubes (10) and (11), from the middle of the blade, the framing tube (12) is placed in decreasing distances to the plane containing the center lines of the two framing tubes (10) and (11). on the rear side of the two framing tubes (10) and (11), there are blade-cross tubes (14) that are of the same length as the blade width, and buffer pads (24) to attach the tubes (14) to the front rotating frame tube (11), and the bars (23) to connect the tubes (14) to the rear rotating frame tube (10), the turbine blade frame is made into segments with length and width suitable to be shipped by containers and assembled at the base of the turbine mast, cthe stay cables to bear turbine axial thrust for blades: each blade may have 1 or more stay cables (8), the blade hub (18) is made of 3 steel tubes fixed onto 3 framing tubes (10), (11), and (12) to prevent sagging of the stay cables, on the top of the hub, there is a supporting frame (19) to support the stay cables, the cables (20) connect the blades to enhance their rigidity, dthe wind turbine blade surface consists of: the outer edge behind the two ends of the blade-cross tubes (14) are fitted with pairs of blade sliders (15) along the length of each blade cell to carry the blade surface sheet (16), the blade surface sheet (16) is made into waveform, so it does not sag across the surface when operating and easy to be rolled up, the blade surface sheet is slid on the two sliders (15) to fold or unfold, the blade surface sheet is divided into many cells, the round cladding pads (17) are to reduce wind resistance of the slider when the blade is rolled up, the sliding of the blade surface sheet is operated by the dual-shaft unit (21). The dual-shaft unit (21) is operated by an electric motor controlled by a blade sensor to furl and unfurl the blade surface according to wind speeds, the blade surface is rolled or unrolled on the blade furling shaft (22) by an electric motor controlled by the blade furling/unfurling sensor, the blade furling shaft (22) is made to rotate synchronously with the blade-surface-stretching-cable shaft so that the blade surface is always straightened up during the furling/unfurling process. to prevent sagging of the blades, the blade-stretching bars (25) are installed under the blade surface by the clamps (27) for stretching the anti-sagging cables (26) to prevent sagging of the blade surface, eThe way to calculate the thickness n (or n) of the buffer pads (24) and the length p (or p) of the bar (23) to install the blade-surface-cross tubes (14) at the position of the blade surface angle of inclination ?.sub.i: the distance between the center lines of the framing tubes (11) and (10) is taken as m (m), in the horizontal direction, the distance from the framing tube (11) to the tube (14) is taken as n (m), then the distance between the framing tube (10) to the tube (14) at each position i in the horizontal direction is calculated as p=m cot ?.sub.i+n (m), in the direction perpendicular to the tube (14), the distance from the framing tube (11) to the tube (14) is taken as n (m), then the distance between the framing tube (10) to the tube (14) at each position i in the horizontal direction is calculated as p=m cot ?.sub.i+n (m),

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] FIG. 1 demonstrates overall design of one blade of the cable-stayed blade structure for variable-speed wind turbines: 1turbine shaft; 2steel tube; 3connecting steel bars; 4blade mounting pad; 5central-hub-extending steels tubes; 6central-hub-head flange for affixing stay cables; 7anemometer, 8stay cables; 9blade-root flange; 10, 11, 12steel tubes forming base structure for blade frame; 13steel tubes connecting the steel tubes 10, 11, 12 to form the blade frame; 14blade-cross tubes for mounting sliders; 15sliders on blade surface; 16blade surface; 17round cladding panels for sliders; 18 cable-supporting hub; 19cable-support frame; 20blade-connecting cables; 21blade furling/unfurling dual shaft; 22blade surface-furling shaft; 23support bars for blade-cross tubes 14 connected to rear-framing steel tubes.

[0047] FIG. 2 shows the arrangement of blades for an 8-bladed wind turbine with blade length of 100 m and turbine tower measuring at 110 m; 18stay-cable-supporting hub; 20blade-connecting cables.

[0048] FIG. 3 shows the cross section of a blade. 10, 11, 12framing-steel tubes; 13steel tubes connecting the steel tubes 10, 11, 12 to form the blade frame; 14blade-cross tubes for mounting sliders; 15sliders on blade surface; 16corrugated metal sheet for making blade surface; 17round cladding panels for sliders; 23support bar for the blade-cross bars 14 connected to rear framing steel tubes; 24buffer pads between the blade-cross tubes 14 and the front framing steel tube 11; 25bars for securing and stretching anti-sagging cables on the back of the blade surface; 26anti-sagging cables; 27clamps for mounting bars for securing and stretching anti-deflection cables 25; D-Dblade section below base frame.

DETAILED DESCRIPTION OF THE INVENTION

[0049] This section presents a detailed description of the invention of cable-stayed blades for variable-speed wind turbines. The description consists of the preferred implementation plan accompanied with drawings to illustrate. The cable-stayed blade structure is particularly suitable to be applied for wind turbines with variable rotational speeds, whose blade surface is made of thin sheets, making it possible to produce wind turbine blades with very large area in order to manufacture wind turbines with very large capacity.

[0050] 1. The structure of the cable-stayed blades for variable-speed wind turbines includes: [0051] aThe central hub is in the exact center of the set of blades.

[0052] In the center of the central hub, there are the steel tubes 2 for attaching the blades onto the head of shaft 1 of the wind turbine.

[0053] The steel tubes 2 are connected to the blade mounting pads 4 by connecting-steel bars 3.

[0054] The steel tubes (2) consist of 3 layers, the middle layer is made of an insulating material between the blades and turbine shaft to prevent lightning strikes for the turbine,

[0055] The blade mounting pads 4 form a regular polygonal prismatic blade mounting truss.

[0056] The turbine blades are fastened to the central hub by having the blade mounting pads 4 fitted with blade-root flanges 9. The height along the steel tubes 2 of the blade-mounting pads is greater than the height of the blades and the width of the blade-mounting pads is equal to that of the turbine blades. The number of blade-mounting pads 4 is equal to the number of blades.

[0057] Steel tubes 5 are installed at the point of intersection of the front edges of the blade-mounting pads 4 and reach toward the front of the turbine to form a cable-stayed tower. The steel tubes 5 converge at the flange 6 on top of the cable-stayed tower.

[0058] The flange 6 on top of cable-stayed tower is for mounting stay cables 8. The front side of flange 6 is fitted with the anemometer 7 so wind speeds will be measured more accurately than if the anemometer were placed on the top of the turbine, providing wind speed and wind direction values for the controllers. (FIG. 1). [0059] bThe body of the wind turbine blades has a truss frame structure to increase rigidity and reduce the weight of the blades. It consists of the following components:

[0060] The blade-root flanges 9 are the starting points of the metal tubes 10, 11 and 12 forming the base prism-shaped frame for the blades. The tubes are made to taper towards the blade tip to reduce weight.

[0061] The centerlines of the metal tubes 10 and 11 are made to be parallel to each other, forming a plane perpendicular to the horizontal section and wind direction. The distance between the centerlines is equal to less than 90% of the blade width. The centerlines of the two framing tubes 10 and 11 are fixed and do not change when the turbine is in operation. It is easy to locate the position of the centerlines when assembling the turbine blades at the foot of the turbine mast. They serve as the baselines for the fabrication and assembly of the blade components.

[0062] The framing tubes 10, 11 and 12 are linked together by the connecting-metal tubes 13 forming the prismatic frame of the blades which has a very good bearing capacity for mounting the blade surface structures.

[0063] The tube 11 is the front-rotating framing tube because it is placed near the front edge of the blades, and as the turbine rotates, the wind touches the front edge of the blades and exits at the rear edge of the blades. The tube 10 which is positioned near the rear edge of the blades is called the rear-rotating framing tube. The front framing tube 12 is on the front side of the blades.

[0064] The framing tube 12 is equidistant from the two framing tubes 10 and 11. From the middle of the blade, the framing 12 tube is made to be in gradually reduced distance from the plane containing the centerlines of the framing tubes 10 and 11 until the distance is only 0.2 m to 0.5 m at the tip of the blade.

[0065] Behind the framing tubes 10 and 11, there are the blade-cross tubes 14 whose length is equal to the width of the blade. The buffer pads 24 are to connect the tubes 14 to the front framing tube 11. The bars 23 are to connect the tube 14 to the rear framing tube 10. The bars 23 may include 2 or 3 bars to secure the tube 14 onto the framing tube 10. The tubes 14 are positioned approximately 1.5 m to 2 m apart from each other.

[0066] The turbine blade frame is fabricated in segments with length and width suitable for shipping by containers and assembled at the base of the turbine mast (FIG. 1). [0067] cStay cable system:

[0068] The stay cables 8 stretch from the flanges 6 down to the blade-framing steel tubes 12 of blade body to withstand turbine axial thrust for turbine blades. Each blade can have 1 or more stay cables 8.

[0069] Each blade has triangular pyramid-shaped hubs mounted on the blade body. Each hub is made from 3 steel tubes 18. The 3 feet of the blade-hub are fixed on three framing tubes 10; 11; 12 to prevent sagging for the stay cables.

[0070] On the top of the blade hub, there is the supporting frame 19 to support the stay cables. There may be 1 or more blade hubs if the blades are very long, or no hubs when the turbine blades are shorter than 60 m.

[0071] The cables 20 connect the blades to increase their rigidity. (FIG. 1) [0072] dWind turbine blade surface:

[0073] The outer edges behind the two ends of the blade-cross tubes 14 are fitted with pairs of blade surface sliders 15 along the length of each blade cell to carry the blade surface sheet 16, thus the inclination level of the blades will be nearly the same as the inclination level the blade-cross tubes 14.

[0074] The sliders 15, if not made round, will be covered by the round panels 17 to reduce wind resistance when the blade surface is rolled up.

[0075] The blade surface sheets 16 are made to be corrugated (FIG. 3; D-D) to prevent sagging across the blades and make it easy to be rolled up. The blade surface sheets can be made of metal or composite materials. The side with wide ridges and small grooves is turned to the front side of the blade surface.

[0076] The blade surface sheet is slid on two slider 15 to fold or unfold. The sliding trip of the blade surface sheet is operated by the dual shaft set 21. The dual shaft set 21 is operated by an electric motor controlled by the blade furling/unfurling sensor based on wind speeds.

[0077] The blade surface sheet is furled up or unfurled on the blade furling shaft 22 by an electric motor also controlled by the blade furling/unfurling sensor according to wind speeds. The blade furling shaft (22) is made to rotate synchronously with the blade-surface-stretching-cable shaft so that the blade surface is always straightened up during the furling/unfurling process. The blade surface is divided into many cells measuring at 20 m long each to ensure easy furling/unfurling.

[0078] To prevent sagging of the blade surface, the cable-stretching 25 are installed under the blade surface by the clamps 27 for stretching under-the-blade-surface support cables and to prevent sagging of the blade surface. (FIG. 3). [0079] eThe way to calculate the thickness n (or n) of the buffer pads (24) and the length p (or p) of the bar (23) to install the blade-surface-cross tubes (14) at the position of the blade surface angle of inclination ?.sub.i.

[0080] The angle of inclination of tube 14 at each position is the angle of inclination ?.sub.i of the blade surface and the wind direction at each position i along the length of the blade according. The distance between the two centerlines of the framing tube 11 and 10 is taken as m (m).

[0081] If in the horizontal direction, the distance from the framing tube 11 to the tube 14 is taken as n (m), then the distance between the framing tube 10 and the tube 14 at each position i in the horizontal direction will be calculated as:

p=m cot ?.sub.i+n (m).

[0082] If in the direction perpendicular to the tube 14, the distance from the framing tube 11 to the tube 14 is taken as n (m), then the distance between the framing tube 10 and the tube 14 at each position i in the horizontal direction can be calculated p=m cot ?.sub.i+n (m).

[0083] Then the buffer pads 24 and the bars 23 will have length measurements at each blade position to be mass-produced for each type of wind turbines.

[0084] 2 The inclination levels of variable-speed wind turbine blades are determined as follows: [0085] First, choose the wind speed v.sub.C at which the turbine has the maximum capacity; [0086] Second, choose blade length and blade-tip linear velocity to calculate maximum turbine rotational speed ?.sub.max; [0087] Third, find the angle of inclination ?.sub.i of the blade surface at a position whose distance from the center of rotation is taken as r.sub.i, by using the parameters including: length r.sub.i, wind speed for maximum power v.sub.C, maximum rotational speed ?.sub.max; choose k.sub.i=1, take the angles ?.sub.i with magnitudes less than 89? and put into the equation reduced from the power function of bladed wind turbines:

[00007]$A_i={\left[k_i{v}_C-r_i{?}_{\max }\cot {?}_i\right]}^2\cos {?}_i{\sin }^2{?}_i$

[0088] Tabulating the value of A.sub.i, we will find the values of ?.sub.i corresponding to d.sub.i at which A.sub.i reaches the maximum value. These ?.sub.i values are chosen as the angles of inclination to manufacture the inclination level of the blade at a position a distance d.sub.i away from the center of the rotational axis.

[0089] The tilt surface formed by lines lying across the blade, a distance r.sub.i from the center of rotation, inclined to the wind direction at an angle ?.sub.i is the twisting level of the wind turbine blade surface. The angle of inclination of the blades remains unchanged while the turbine is in operation.

[0090] The turbine blade elements can still capture wind energy when the wind speeds in the sweep area vary by up to 6 m/s, so the turbine blades only need to be shorter than the mast by more than 5 m.

[0091] The allowed margins of error of the angle of inclination of the blades in the manufacture and installation processes is 1.sup.0.3 greater or 1.sup.0.6 less than the calculated angle of inclination so the turbine capacity is no more than 5% less than the maximum capacity. This is explained by the power graphs of the blade element as its tilt angle changes.

[0092] When the wind speed is greater than the wind speed v.sub.C where the power is the highest, the blade is partly furled up so that the capacity does not exceed the maximum capacity. When the turbine stops working dud to excessive wind, the entire blade surface is furled up.

[0093] The power to run the controllers can be obtained from the turbine when there are no thunderstorms or from a small wind turbine mounted on the main turbine blades to ensure insulation of the blades.

Implementation Example

[0094] Fabrication of a variable speed wind turbine with maximum generating capacity of 3.5 MW at a wind speed of 20 m/s in the delta region. [0095] The turbine mast is 110 m high; the mast body's diameter is about 20 m. To turn the blades to the direction of the wind, the top of the mast is made into a circular track; the turbine base rotates around the central axis; the top of the base where the turbine blades are attached is mounted on the guide wheels running in circular direction on the mast-top track. [0096] There are 8 blades, each measuring at 101 m long and 6 m, 4 of which have an area covering 92% of blade length, and 4 having an area covering 60% of blade length. [0097] The blades have a cable-stayed frame structure. The central hub is 30 m long, with an 8-sided-regular-prism blade mounting frame truss; the blade-mounting pads measure 6 m wide by 5 m high; the core tube of the central hub is 3 m in diameter and 5 m long; each blade has 2 blade hubs 40 m from the central hub and 35 m from each other; the blades with 92 m-long blade surface sheets have 5 pairs of stay cables, and the blades with 60 m-long blade surface sheets have 4 pairs of stay cables.

[0098] The maximum force acting on the turbine blades when the wind reaches 25 m/s for the turbine to stop working is 270 N/m.sup.2 of the blade. This is when the turbine furls up the blades and stops working. This force is used to calculate the tension of the stay cables.

[0099] The axial force at wind speed of 20 m/s is 150 N/m.sup.2 and is used to calculate the mast head thrust.

[0100] The blade surface is made of corrugated metal sheets; each blade cell is less than 20 m long. The long blades whose surface sheet covers their entire length have 4 cells, and the short ones have 3 cells.

[0101] The capacity is stabilized when the wind speed exceeds the highest level by rolling up some blade cells. The turbine is protected in windstorms by furling up the entire blade surface.

[0102] The start-up wind speed is 4 m/s; the wind speed for the highest capacity is 20 m/s; the maximum wind speed for the turbine to stop operating is 25 m/s.

[0103] Inclination angles with respect to the wind direction at different positions of the blade surface at a wind speed of 20 m/s are as follows:

TABLE-US-00001 Distance to turbine shaft (m). Blade angle of inclination (??) 8 64.05 10 65.95 12 67.7 14 69.3 16 70.7 18 72.05 20 73.15 22 74.15 24 75.05 26 75.95 28 76.7 30 77.35 32 78.05 34 78.65 36 79.2 38 79.7 40 80.155 42 80.55 44 80.95 46 81.3 48 81.6 50 81.9 52 82.2 54 82.45 56 82.7 58 82.95 60 83.15 62 83.35 64 83.55 66 83.75 68 83.95 70 84.1 72 84.25 74 84.4 76 84.55 78 84.7 80 84.85 82 84.95 84 85.05 86 85.15 88 85.25 90 85.35 92 85.45 94 85.55 96 85.65 98 85.75 100 85.8

[0104] Turbine power capacity obtained at different wind speeds:

TABLE-US-00002 Wind speed v (m/s) Power capacity P (KW) 4 28 5 52 6 92 7 144 8 220 9 312 10 428 11 572 12 740 13 944 14 1176 15 1448 16 1760 17 2112 18 2504 19 2948 20 3440

POSSIBILITIES FOR INDUSTRIAL APPLICATION

[0105] Since the blades are fabricated to be non-rotating for variable speed wind turbines, the blades can be manufactured in very large lengths, possibly up to 200 m.

[0106] The blades only need to be about 10 m shorter than the turbine mast. With the height of today's cranes, it is possible to manufacture and install wind turbines with blades up to 200 m long, with a rotational speed of 0.5 rad/s (less than 5 rpm), to create wind turbines with very large capacity.

[0107] The blades are made into sections with maximum length of no more than 12 m and maximum width of 2.5 m, which are suitable to be transported by containers to the foot of the turbine tower mast and assembled very easily.

[0108] The installation is not difficult because the accuracy level required is not too high. The calibration to achieve an error factor for the blade inclination angle of no more than 0.5 degree is easy to get with available measuring tools.

BENEFITS BROUGHT ABOUT BY THE INVENTION

[0109] Produce wind turbines with a power capacity of up to 10 MW when the blades are nearly 200 m long.

[0110] Reduce wind power prices by 4 or 5 times compared current prices with new investments.

[0111] Renovate current wind turbines to increase the actual capacity by 3 to 4 times