Wind turbine of low wind speeds

Abstract

Horizontal axis W/T of low wind speeds of propeller type, bearing a main rotor of three blades (1), while in the space between two successive blades (1) and diametrically opposite to the third, an additional 4th blade (2) also of propeller type but of significantly longer length, is interposed. This additional blade (2) is not permanently coupled but selectively engaged in the system of the W/T at low wind speeds, contributing to the startup and enhancing the energy production. The blade (2) bears diametrically opposite a counterweight (15) to balance the forces developed, and rotates in a plane parallel to the main rotor. The coupling of the blade (2) is preferably made at the stand-by state or at low wind speed operation of the W/T, while the uncoupling will be performed during operating state and at the rated power. The blade (2) after uncoupling, gets in vertical position and remains immobilized attached to the tower.

Claims

1. A horizontal axis wind turbine of propeller type comprising: a horizontal main shaft (4); a main rotor comprising a first hub and three first blades (1) arranged around the hub, the main rotor being permanently fixed to the main shaft (4); and an additional rotor comprising a second hub (13) and fourth blade (2) of longer length than a length of each of the three first blades (1), the second hub (13) surrounding the main shaft (4), the additional rotor being configured for being selectively coupled to the main rotor, the main and additional rotors both being configured to rotate in parallel planes to each other, in a same direction of rotation, and coaxially with the main shaft (4); wherein, the fourth blade (2) of the additional rotor is configured for being positioned between two successive blades of the main rotor and diametrically opposite to the third blade of the main rotor, when the main and additional rotors are coupled; wherein the fourth blade (2) is configured for remaining in a stand-by position when the additional rotor is uncoupled from main rotor, stopped and stored in a vertical orientation.

2. The horizontal axis wind turbine according to claim 1, wherein the additional rotor comprises a counterweight (15) disposed diametrically opposite to the fourth blade (2), the counterweight (15) being more compact than the fourth blade (2).

3. The horizontal axis wind turbine according to claim 2, wherein the counterweight (15) comprises a telescopic mechanism (16) configured to move the counterweight (15) toward and away from the main shaft (4) during a rotation of the additional rotor to control the rotation of the additional rotor.

4. The horizontal axis wind turbine according to claim 1, wherein the additional rotor comprises a control system of active pitch or passive stall type or of a combination thereof.

5. The horizontal axis wind turbine according to claim 1, wherein; the horizontal axis wind turbine comprises two arms (14) fixedly joined to and extending radially away from the main shaft (4), the two arms (14) being disposed symmetrically to each other about the main shaft (4); the additional rotor comprises at the second hub (13) two pistons (10) that are disposed symmetrically to each other about a center of the second hub (13) and lie parallel to an axis of the main shaft (4), the pistons (10) being configured to move parallel to the axis of the main shaft (4); the pistons (10) are configured to engage with the arms (14) by being moved toward the arms (14) and contacting respective sides of the two arms (14), thereby transmitting a rotational torque from the additional rotor to the main shaft (4) and coupling the additional rotor to the main rotor; the pistons (10) are configured to disengage from the arms (14) by being retracted into the second hub, thereby uncoupling the additional rotor from the main rotor.

6. The horizontal axis wind turbine according to claim 1, wherein the additional rotor comprises an independent brake system (17).

7. The horizontal axis wind turbine according to claim 1, wherein the additional rotor is joined to and rotatably mounted around a hollow cylindrical protrusion (11) of a nacelle (8) that surrounds the main shaft (4).

8. The horizontal axis wind turbine according to claim 1, wherein the additional blade (2) is fixed, rotatable mounded, and directly supported onto the main shaft (4).

9. The horizontal axis wind turbine according to claim 1, further comprising two separate generators: a smaller one for startup, and a larger one for operation at rated power.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1. Shows a view of the W/T of the present invention with an additional fourth blade.

(2) FIG. 2. Shows a side view A of the W/T of FIG. 1.

(3) FIG. 3. Shows the side view A with a detail of a mounting proposal of the additional fourth blade of FIG. 1.

(4) FIG. 3a shows the section A-A of FIG. 1 with a variation of the mounting proposal of the additional fourth blade on to the shaft of the W/T.

(5) FIG. 4. Shows the section B-B of the shaft of the W/T with the detail of the coupling of the additional fourth blade to the system. FIG. 4a. Shows a section of a variation of the way to connect the additional fourth blade directly onto the main shaft of the W/T.

(6) FIG. 5. Shows the power curves of Power vs. Wind Speed of a three bladed W/T with an additional fourth blade. Both are equipped with power control system (active pitch control).

(7) FIG. 6. Shows the power curves of Power vs. Wind Speed of a conventional W/T with an additional fourth blade. Both are equipped with passive power control system (Stall control).

DETAILED DESCRIPTION OF THE INVENTION

(8) It is known that a conventional W/T does not rotate at low wind speeds: speeds VV.sub.c and in particular for V3,5-4,5 m/sec, where V.sub.c is the cut-in speed, the speed at startup. The reason is the several kinds of losses that must be overcome by the rotational torque of the wind, since a substantial part of the wind energy potential is left unexploited.

(9) It is also known that the power output of the W/T is proportional to the third power of wind speed V on the surface area A of the rotor: N=f(V.sup.3*A), and as a consequence, proportional to the square of the rotor diameter D: N=f(V.sup.3*D.sub.2), since A=D.sup.2/4.

(10) FIGS. 1, 2, 3 show the views of a conventional horizontal axis W/T with: three conventional blades 1 of propeller type of radius R.sub.1 and diameter D.sub.1, the hub 7, the nacelle 8 with the mechanisms, the yaw system 9, the tower 3, the shaft 4 of rotation, the gearbox 18, the disc brake, the generator, etc. The W/T cooperates with the new additional fourth blade 2 of diameter D.sub.2 and radius R.sub.2.

(11) The additional fourth blade 2 is preferably mounded and fixed around a hollow cylindrical protrusion 11 of the nacelle 8 that surrounds the main shaft 4. The hub 13 of the blade 2 and the bearings 12 between the protrusion 11 and the hub 13 are also shown, while the main shaft 4 of the W/T is rotated supported by the bearings 5.

(12) The blade 2 is equipped preferably with systems for the regulation, stabilization and optimization of the power output, based preferably: a) on the continuous altering of the direction of the blade airfoil (pitch angle/angle of attack) relative to the direction of the wind (active pitch control), or b) on the simpler passive system of the air flow detachment (passive stall control) wherein the blade is mounded onto the hub, fixedly twisted, and its profile may display different pitch angles from the root towards the tip, or c) a combination of a) +b). The above control systems operate independently from those used by the blades 1, with which the blade 2 cooperates with.

(13) Consequently the cross-section in the root of the blade 2 may be circular in most of the versions and may be mounted also in a circular flange-seat 6 which enables the smooth rotation of the blade 2 around its longitudinal axis, in order to alter continuously the pitch angle of the airfoil, the magnitude of the desired detachment of the flow, etc.

(14) FIG. 4 shows the cross-section B-B of the shaft of the W/T, with the necessary counterweight 15, in order for the blade-counterweight system to be statically and dynamically balanced. The coupling of the additional fourth blade 2 in the system is preferably activated at the stand-by or at low speed of the W/T, while the blade 2 is preferably at stand-by position and vertically attached along the tower 3.

(15) In this position and being attached along the tower 3, remains the blade 2 during of its uncoupling, in order not to be affected by the wind and to avoid the development of rotational torques, or wind pressures, that enhance the development of additional drag and overloads the whole system of the W/T.

(16) The vertical position of the additional fourth blade 2 is preferably succeeded by moving of the counterweight 15 towards the center of rotation and towards the main shaft 4 and the hub 13 of the additional fourth blade 2. This movement (contraction of the telescopic system), can also preferably be activated by switching off of the hydraulic mechanism of the telescopic system 16. Similarly the above process could be performed by means of a motor-gear unit with toothed rack and pinion (not designed), which alters the balance of the blade 2-counterweight 15, while the center of gravity is moved away from the shaft 4 of the W/T towards the blade 2.

(17) With this movement of the center of gravity, the blade 2 acts as a pendulum in descending oscillation and is driven and stabilized at a vertical position along the tower 3. This action is enhanced by: a) proper position (pitch angle) of the airfoil of blade 2 relative to the direction of the wind by the active pitch control (if any) and b) an independent braking system.

(18) The coupling could be also performed by an electromechanical rotation device, but it will be more easily achieved by the following procedure: On the outer surface (periphery), on the left and right side of the blade's hub 13, there are two parallel and preferably hydraulic pistons 10. Both pistons 10 lay in a plane passing through the axis 4.

(19) Upon activation of the hydraulic system, the piston/bolts 10 are forwarded to the direction of the main rotor 1 right and left (from both sides) of the shaft 4. Between blade 2 and main rotor 1 are built-in two radial arms 14 which extend diametrically opposite, and are firmly connected to each other. The arms 14 are also fixedly connected with the shaft 4 by means of splines 14b.

(20) The rotational direction of both, the main rotor of the W/T and the additional fourth blade 2 are the same, while the additional fourth blade 2 due to its larger diameter on one hand, and due to classical behavior as monopteros-single blade on the other, rotates faster than the main rotor 1. Thus, the two piston 10 being activated in projected position, always touch and press at the same point of the inner concave surface 14a the two arms 14, transferring the rotational torque always in the same direction, that of the system.

(21) It is obvious that if the imaginary diameter that joins the two arms 14 is fixed and vertical on one of the conventional blades 1, then the additional fourth blade 2 will always be coupled automatically and symmetrically in the space between the two others.

(22) The uncoupling takes place with the W/T in operation. By the deactivation of the hydraulic/bolt 10, that retracts, the arms 14 do not transmit torque on the shaft 4, while at the same time the hydraulic telescopic mechanism 16 of the counterweight 15 is deactivated and retracted, whereby the center of gravity of the system blade 2-counterweight 15 will be disturbed, blade 2 acts as a pendulum and moves gradually in the stabilized vertical position at the front of the tower 3.

(23) This procedure is supported by the proper position of the pitch angle of the airfoil of the blade 2 relatively to the direction of the wind (by active pitch control), if any, or by an independent electromechanical brake system in FIG. 3a.

(24) FIG. 4a shows in section a variation of a direct support of the blade 2 on the shaft 4 of the W/T, with the detail of the coupling-uncoupling system by means of the pistons 10 and the arms 14.

(25) FIG. 5. shows the power curves of Power vs. Wind Speed of the W/T of the FIGS. 1, 2, 3. The magnitudes of the power output in these diagrams are dimensionless and are illustrated qualitative as a percentage of the rated one.

(26) The curve (N) (or N/N.sub.1, as a percentage of the rated power N.sub.1) refers to a conventional W/T conventionally dimensioned for a particular region according to the particular wind data, with three conventional blades 1 of diameter D.sub.1. The W/T itself is equipped with a regulation & control power system by altering the pitch angle pitch control, while the additional fourth blade 2 is not yet coupled to the W/T system.

(27) The curve therefore follows the known simplified form of the straight lines A.sub.1C.sub.1 & C.sub.1C.sub.F1 and the W/T starts to rotate and to operate at the point A.sub.1. The startup point A.sub.1 corresponds to a relatively high speed, the cut-in speed V.sub.c1 (of 3.5-4.5 m/sec) since it must overcome the startup losses that correspond to the particular dimensioning of a conventional W/T with the rated power of N.sub.1.

(28) At the breaking point C.sub.1, which corresponds to the speed V.sub.R1 (rated output speed of the rated power of the conventional W/T) the control and protection system active pitch control will keep the rated power output N.sub.1 constant until the maximum cut-out speed V.sub.F of interruption, which corresponds to point C.sub.F1, wherein the W/T for safety and security reasons will be switched off.

(29) By coupling of the additional fourth blade 2 of significantly larger diameter D.sub.2, the new power curve (N.sub.2) (dashed line) is created resulting logically to a higher rated power output N.sub.2 (or N.sub.2/N.sub.1, as a percentage of the rated power N.sub.1 of the basic main W/T).

(30) Note that in this case the structural and functional elements of the system of the conventional W/T, will not be reinforced, meaning that they will be not dimensioned to a higher class that corresponds to the greater diameter D.sub.2. In this case we consider that the blade 2 is also equipped with an independent system of altering and adjusting the pitch angle (active pitch control).

(31) By coupling of the blade 2 we note that: a) the new power output of the new system W/T (new rated power N.sub.2, or N.sub.2/N1) illustrated with a dashed line, is significantly increased, b) the rotation starts at significantly lower wind speeds V.sub.c2, (V.sub.c2<V.sub.c1=3.5 to 4.5 m/sec), c) the increase of the Power vs. Wind Speed is of significantly steeper inclination (exponential), and d) the annual energy production, which is the goal, is clearly greater. The reasons, besides the obvious advantage of the larger diameter D.sub.2, are numerous:

(32) By coupling of the blade 2 in the system of a W/T conventionally dimensioned based on the (smaller) diameter D.sub.1, namely lighter, it is evident that the certainly stronger torque transmitted by the blade 2 will cause the startup of rotation already at the point A.sub.2, i.e. at much lower cut-in speeds V.sub.c2, (V.sub.c2<V.sub.c1).

(33) The above is obvious, since: a) the elements of the W/T: gearbox, generator, etc., have not been particularly reinforced, and therefore the startup losses are kept low, and b) the blade 2 is equipped by independent control and adjustment systems of the pitch angle i.e.

(34) active pitch control, which is activated already from the start of the coupling, so that the blade 2 is adjusted at the appropriate pitch angle giving to the system augmented torque.

(35) Regarding the inclination of the new power curve (N.sub.2) (or N.sub.2/N.sub.1), this will follow a clearly steeper (exponential) increase, since due to a priori conventional (lighter) dimensioning based on the rotor diameter D.sub.1, the structure is lighter, if this relays on the new data (diameter D.sub.2). Normally the new power curve should follow its own independent course, and in simplified form, the lines A.sub.2A.sub.3C.sub.2-C.sub.2C.sub.F2.

(36) In reality, however, the power output cannot exceed, for safety and protection reasons, the rated power N.sub.1 (or N.sub.1/N.sub.1) of the conventional W/T, due to its a priori conventional (lighter) dimensioning.

(37) For this reason, at the point A.sub.3 where the new power curve (N.sub.2) meets the rated power of the basic curve N.sub.1 (or N.sub.1/N.sub.1), the independent active pitch control system of the blade 2 will keep constant the new power output at the level of N.sub.1, and so the highest power output will be limited and equal to the rated N.sub.1, and the new curve will follow the course (approximately straight line) A.sub.3C.sub.1 of the conventional W/T. After reaching the point C.sub.1 the blade 2 is no longer needed and will be disconnected, as the production with the rated power N.sub.1 by the conventional W/T has already started.

(38) The point A.sub.3 corresponds to wind speed V.sub.RA, which is clearly lower than the speed V.sub.R1 (rated output speed) of point C.sub.1, from where production of the rated power starts, limiting at the same time for safety and operational reasons the power output of the conventional W/T. Therefore, reaching the rated power N.sub.1 of the new system of the W/T, starts much earlier (point A.sub.3), and at lower cut-in speeds, ensuring greater annual energy production.

(39) FIG. 6 shows the power curves also of a W/T of FIGS. 1, 2, 3, with and without additional fourth blade 2 both equipped with passive (stall control) system. Blade 2 also with passive power regulation, is the simpler and cheaper version of the new invention, and cooperates perfectly with a conventional W/T of the same also simple regulation technology (stall control).

(40) The power output in these diagrams is also a dimensionless value, and is shown qualitative as a percentage of the rated power. The solid line curve relates to the conventional W/T from FIG. 1, 2, 3, without the additional fourth blade 2 been coupled.

(41) It is clear that after the coupling of the blade 2, the new power curve (N.sub.22) (dashed line & new rated power N.sub.22/N.sub.1) , shows a clearly steep (exponential) increase almost similar to that of (N.sub.2) in FIG. 5, since despite the fact that blade 2 is not equipped with active pitch control system, the passive system Stall control, is equally effective.

(42) The new power curve, along with the operation of the new W/T system, starts at the point A.sub.22, i.e. at lower cut-in speeds (which are clearly lower than V.sub.c1 of the corresponding point A.sub.1) and follows its own independent course by following the simplified straight line A.sub.22A.sub.32 with a rated power N.sub.22, clearly greater than the conventional N.sub.1 one.

(43) In reality, however, for safety and stability reasons of the conventional W/T, it cannot exceed much over the power output N.sub.1 (or N.sub.1/N.sub.1), due to its a priori conventional (lighter) dimensioning. Thus, from the point A.sub.32, the power output will slightly exceed N.sub.1 and blade 2 will be uncoupled from the system of the W/T just before the point C.sub.1, from which both the production of the rated power and at the same time the power limitation of the conventional W/T, by means of the control system of its own blades 1, will start.

(44) We note that the slight increase in the power output after the breaking point A.sub.32 and its decline just after (curve A.sub.32:C.sub.1) is a general feature of the W/T system with passive power regulation stall control, in contrast to the active pitch control systems, wherein the rated power is continuously adjustable and is kept constant. We also state, that a generator 10%-20% stronger than the conventional one, could offer a great advantage in this transitional phase, namely in the interval between point A.sub.32 and point C.sub.1, without burdening substantially the overall cost.

(45) Therefore, reaching of the rated power output N.sub.1 of the new W/T system, starts much earlier (from the point A.sub.32 instead of point C.sub.1) and at lower cut-in speeds, ensuring greater annual energy production.

(46) The cut-out speed V.sub.F is the same for all alternatives and power output curves: (N.sub.1), (N.sub.2) & (N.sub.22), of the FIGS. 5, 6, and therefore constitutes the common limit of the operation of all of them.

(47) Comparing also the above power curves (N.sub.1) , (N.sub.2) & (N.sub.22), of FIGS. 5, 6 for a given wind potential, it is shown that the total annual energy production: P.sub.1, P.sub.2 & P.sub.22, corresponding to the above power outputs, is graded as follows: P.sub.1<P.sub.22<P.sub.2, with the energy of P.sub.2, corresponding to a blade 2 with the independent active pitch control, to be the greatest. The reason is that the control process of this system is continuous aiming for both the protection as well as the optimization of the efficiency.

(48) In particular cases, where the wind potential of the region is in general low, the contribution of the blade 2 is particularly vital, since: a) the startup of the operation is at significantly lower (V.sub.c2) cut-in speeds (V.sub.c2<V.sub.c1), and blade 2 remains most of the year coupled into the W/T increasing significantly the energy production, reducing rapidly the time for the amortization of the additional investment, b) without any issue for the other structural elements of the W/T system, the generator of the system could be sized at least 20% stronger, with a clear and immediate increase in annual energy production, and c) it enables the development and the electrification of particularly lowlands, where however there is typically the biggest concentration for demand of energy.

(49) In another version of the W/T, the system could be equipped with two independent generators: a very small one, almost 50% of the conventional size, for the startup, and another approximately 120% of the conventional respectively, for the rated operation. The generators are connected to the system successively. Such a variation would increase the production, since it would clearly prolong the operational time of the blade 2 in the system, and would also increase the rated power of the conventional W/T, since the additional fourth blade 2 offers immediate and significant increase in torque to the shaft of the W/T. In another variation, the blade 2 has a structure of laminated synthetic fibers, enabling at high wind speeds the automatic passive twisting and bending of the blade, altering simultaneously both the pitch angle as well as its diameter, under the action of the wind pressure (aeroelastic effect). Not designed.

(50) The blade 2 could also bear special aerodynamic serrated elements (flaps, or tips-vanes) mounted at the airflow breakaway edge, or a plurality of aerodynamic protrusions of small height fixed perpendicular at the blade 2, and on to the outer convex surface of it, selectively creating low turbulence eddy currents (vortex generators) delaying the detachment of airflow and increasing the driving forces. Not designed.

(51) In order to protect the whole structure, besides other safety systems, an interruption of the power supply uncouples and disconnects the blade 2 and switches-off the hydraulic system of the telescopic mechanism 16 of the counterweight 15, which retracts automatically the mechanism 16, stopping gradually but quickly the blade 2 driving and immobilizing it to its initial vertical stand-by position.

(52) In another variation, the coupling of the blade 2 in the system of the W/T can be done also with very different ways and means, such as by electromagnetic coupling, etc. Not designed.

(53) In another variation, the conventional rotor could bear only two diametrically opposite conventional blades 1, so that the two additional blades should either: a) be two independent and identical, diametrically opposite aligned and arranged, rotating in two parallel planes (clock hands) in the coupling phase, while both go down and will remain parallel to each other along the tower 3 in the phase of uncoupling, or b) to be permanently and diametrically opposite connected to each other (one body). Not designed.

(54) It is obvious that new variations could be created with combinations of the aforementioned.