FI130969B1

FI130969B1 - Vertical axis wind turbine with self-adaptive blades based on wind conditions.

Info

Publication number: FI130969B1
Application number: FI20237120A
Authority: FI
Inventors: Seyyedjavad Hosseininia
Original assignee: Amertat Energy Oy
Priority date: 2023-06-21
Filing date: 2023-06-21
Publication date: 2024-06-24
Also published as: FI20237120A1

Abstract

Disclosed is a drag-type vertical axis wind turbine with self-adaptive blades based on wind conditions. In the state-of-the-art development, a vertical axis wind turbine adaptable to harsh climate which is capable of maximizing driving force and minimizing resistance forces as well as maintenance, has not been proposed. Current disclosure comprises a plurality of magnetic and mechanical brakes to control the blades yaw angle of the first group of turbine blades (5) in different situations. The present construction reduces resistive forces caused by blades (5) in negative wind direction and increases the generated power by exposing the blades to wind in positive wind direction. Furthermore, the disclosure includes a plurality of coils (10) in the blade magnetic brakes that activate and change the angle of attack of blades in the storm conditions, as well as a magnetic rotor brake that makes the turbine capable of generating electricity safely in storm conditions.

Description

Vertical axis wind turbine with self-adaptive blades based on wind con- ditions

FIELD OF THE INVENTION

The present invention relates generally to the technical field of wind power generation, and more particularly, to a drag-type vertical axis wind turbine com- prised of self-adaptive blades based on wind conditions.

BACKGROUND TO THE INVENTION

When the wind flows into a turbine, the emerging forces turn a shaft and gen- erate the necessary kinetic energy for producing electrical power. In general, wind turbines are split up into horizontal axis and vertical axis types. In both types, the blades are the most effective components that may have a fixed shape and size. Thus, the blades may not be efficient enough to perform well in a wide variety of weather conditions and the generated power may be limited due to the resistance forces engendered by the shape of the blades.

When wind flows into an under-operation drag-type vertical axis wind turbine, the moving direction of some blades is aligned with the wind direction (positive wind direction) which generate driving forces. Also, the moving direction of some other blades is opposite (negative wind direction), which generate resis- tive forces that substantially affect the generated power by the turbine.

CN201635921 has been disclosed with the purpose of adjusting the deflection of the blades and consequently the speed of the turbine in different wind con- ditions. The deflection of the blades is controlled by following causes; (I) adopt- ing centrifugal force generated by a counterweight, (II) a bracket connected to the end of the blades which holds a plate and pins for positioning an arc- shaped blade in different angles, and (III) a return spring for pulling back the counterweight.

The model has many mechanical parts (e.g., spring, gear, pins, bracket, etc) to control the speed and the condition of the blades in start-up, normal and high-speed operations. Nevertheless, in starting conditions the turbine acts same as a regular drag-type turbine and the resistance force still affects the performance significantly.

With the aim of adjusting the blade deflection and consequently reducing the resistance forces generated by the blades in the negative wind direction, a mechanism that takes advantage of timing shafts has been proposed in

US10539115 (B1). The disclosed model comprises many moving mechanical components such as sliding parts, timing parts, springs and etc. The power generator system faces frequent maintenance requirements and an elevated risk of damage, particularly in harsh climate environments, due to the intercon- nection of numerous mechanical components.

In CN101634277 (A), a lift-type vertical axis wind turbine has been disclosed with the purpose of controlling the yaw angle of the blade as well as improving the start-up speed. The disclosure makes use of centrifugal forces generated by a pendulum control mechanism, and the lift force emerged from the influ- ence of the wind force on the blade surface, to control the yaw angle of the blade. The pendulum control mechanism comprises of a blade, counterweight and pendulum rod. The disclosure presents some different versions of the pen- dulum control mechanism, although the principle is similar in all of them. In the — description of the invention, it has been stated that the centrifugal force and the lift force are opposite with respect to the blade rotating center and under the action of the two forces, the blade swings as far as the two moments are balanced. technically, this means that part of the driving force consumes to overcome the centrifugal force generated by the center of mass and make the — blade balanced.

It as well has been mentioned that adjusting the counterweight of the pendu- lum mechanism and debugging is troublesome and should be done while the turbine is under operation. However, for one of the presented versions it is affordable only in mass production. Therefore, adjusting the center of mass is very challenging which significantly affects the yaw angle and performance of the lift-type vertical axis turbines.

The disclosure adopts a spring element positioned between the blade and the pendulum rod to change the center of mass, destroy the yaw angle and limit the speed of the turbine in storm conditions. As the spring should be hard enough to be activated at high speed, it has a tendency to move back quickly after activation (when speed decrees a bit). This would happen frequently in storm conditions that increases the risk of damage significantly.

Despite continuous development of the vertical axis wind turbines, a structure; (1) capable of maximizing driving force in the low-speed wind, (II) minimizing resistance force, (III) adaptable enough with harsh climate environments, and (IV) affordable in manufacturing, has not been proposed yet.

The start-up performance is another important characteristic of the turbine, on which the resistance force significantly influences. Therefore, the resistance force should be considered the most, when designing a new type of vertical- axis wind turbine. Actually, the resistance forces have been progressively con- sidered in the development of vertical axis wind turbines. However, due to the slow progress, the techniques are neither mature yet nor compatible with harsh climate environments and wind conditions.

PURPOSE OF THE INVENTION

The present invention takes advantage of an integration of the centrifugal force generated by the blades’ center of mass, the wind force that emerged on their surfaces, and the magnetic forces engendered on the blades brake, to adjust the yaw angle of the blades and consequently the angle of attack in different wind conditions. Furthermore, in stormy conditions, a magnetic brake utilizes centrifugal force to get activated and restrict the speed of the rotor. This safety mean allows the turbine to operate securely even during storm conditions. In the proposed vertical axis wind turbine, the blade yaw angle control mecha- nism has been simplified and the moving pairs (e.g., gears, sliding and timing components) have been eliminated in order to enhance the adaptability to harsh climate environment. This innovative design brings about enhancement in several key aspects, revolutionizing the performance of vertical axis wind turbines. Notably, it greatly enhances adaptability to harsh climate environ- ments, ensuring optimal functionality even in the face of challenging climate conditions. Moreover, it swiftly adjust the blade yaw abgle to sudden changes in wind direction, thereby maximizing energy capture. Furthermore, this design boosts the start-up speed of the vertical axis wind turbines, enabling them to initiate power generation more rapidly, it optimizes the generated torque, re- sulting in increased efficiency and overall power output, and it takes advantage of a safety brake to be able to operate even in storm conditions, ensuring the suitability of the design for the residential areas.

DESCRIPTION OF THE INVENTION

The present invention has been devised to solve the problems mentioned in the background to the invention. The main objectives of the present invention are; (I) mitigating the resistance forces generated by the blades in the negative wind direction, (II) increasing the generated power in low-speed wind, (III)

improving the start-up characteristic, (IV) enabling the turbine to be operated safely even in storm conditions, making it ideal for residential areas, and (V) facilitating the turbine's agility in swiftly adapting to sudden changes in wind directions.

In order to achieve the above mentioned objectives, the present invention takes advantage of the following distinguishing characteristics and technical solutions.

The drag-type vertical axis wind turbine according to the invention comprises a turbine shaft configured to be coupled to an electric power generator, at least — two turbine blade brackets for connecting turbine blades to the turbine shaft, a first group of turbine blades comprising at least two turbine blades connected to the turbine shaft by means of one or more of said at least two turbine blade brackets at equal radial distances from the turbine shaft, each turbine blade being attached to a respective turbine blade bracket rotatably about a rotation — axis that is parallel to the axial direction of the turbine shaft, a first stopper element and a second stopper element for each turbine blade of the first group of turbine blades for limiting rotational movement of the respective turbine blade about said rotation axis between a first position and a second position, wherein in the first position the turbine blade is positioned to generate driving force to rotate the wind turbine and in the second position the turbine blade is positioned to minimize the force resisting the rotation of the wind turbine. The wind turbine comprises for each turbine blade of said first group of turbine blades a magnetic brake for braking the rotational movement of said turbine blade as the turbine blade approaches the first position and/or the second po- sition, the magnetic brake comprising at least one magnet and at least one conductive element, the rotational movement of the turbine blade about the rotation axis being configured to move said at least one magnet and said at least one conductive element relative to each other to induce electric current in said at least one conductive element.

The conductive element(s) of the magnetic brake can be made of, for instance, aluminium, aluminium alloy or some other paramagnetic material. The current induced in the conductive element creates a magnetic field resisting the rota- tional movement of the turbine blade. This ensures smooth deceleration, as the turbine blade approaches the first position or the second position.

The magnet of the magnetic brake may be attached to the turbine blade and the conductive element may be attached to a turbine blade bracket. The magnetic brake may comprise a first conductive element, where current is in- duced as the turbine blade approaches the first position, and a second con- ductive element, where current is induced as the turbine blade approaches the second position. Each conductive element may extend over a certain angular 5 range, such as 10-55 degrees. Two braking regions are thus defined. Each braking region could also be formed by two or more conductive elements. Al- ternatively, the turbine blade could be provided with a conductive element, and one or more magnets could be attached to a turbine blade bracket close to the first position and/or the second position. The magnet or magnets could be ar- ranged close to the first position and second position to extend over a certain angular range to define a first braking region and a second braking region, respectively. In each braking region, a single magnet or a plurality of magnets distributed over the braking region could be provided.

The first embodiment of the present invention is a vertical axis wind turbine comprising a turbine shaft that conveys the generated kinetic energy to the electric power generator, a plurality of turbine blade brackets that connect the first group of blades (outer blades) to the turbine haft, a plurality of blade rota- tion axis assembled on the blade brackets and allow the blades to swing, a plurality of first group of turbine blades installed on their rotation axis, a plurality of blade magnetic and mechanical brakes, a plurality of blades’ first and sec- ond stoppers that limit the movement of each blade of first group of turbine blades around its rotation axis, and a plurality of second group of turbine blades (inner blades).

According to an embodiment of the invention, the wind turbine may comprise a plurality of weights installed on the blades of the first group of blades.

According to an embodiment of the invention, the wind turbine may comprise a magnetic rotor brake.

In the second embodiment of the present invention, the second group of tur- bine blades are connected to the turbine shaft radially toward the first group of turbine blades. These blades amplify the power output of the turbine and facil- itate the yaw angle adjustment of the first group of turbine blades. The first group of turbine blades, that can have any shape, can be assembled on the blade rotation axis along the length in a way that the turbine blade is divided by the rotation axis into a smaller portion and a larger portion. The larger por- tion locates inward to the center of the rotor and the smaller portion locates outward, when the blade is near the first stopper and is generating driving force. To adjust the center of mass of the blade of the first group of turbine blades with a distance to the rotation axis of the blade, but not on the larger portion of the blade, the smaller portion is provided with one or more weights such that the mass of the smaller portion is greater than the mass of the larger portion. Thus, when the turbine rotates, the first group of turbine blades swing smoothly and prevents any swift movement. The smaller portion of the blades may be reinforced using some additional fins in order to increase the drag force. Moreover, this design ensures the accumulation of a larger amount of snow on the smaller portion of the blade during freezing conditions, effectively preventing any significant change in the adjusted center of mass of the blade.

To achieve a simpler rotor structure, the blades can be connected to the blade brackets, through the rotation axis, from the middle side, forming an upper and lower portion of the blade that simplifies the overall design.

In the third embodiment of the present invention, the turbine may comprise upper and lower blade brackets and the first group of turbine blades may be connected to the blade brackets through their two ends. In addition, the first group of turbine blades may be connected to the rotation axis through the edge along the length and a counterbalance may be connected to the rotation axis in order to adjust the center of mass of the blade.

In the fourth embodiment of the present invention, the first group of turbine blades could be positioned freely between the first and second stoppers when the turbine is in the stationary state. Once the wind blows into the turbine, some blades located in the positive wind direction swing toward the center of the turbine, push the first stopper, and generate driving torque in the turbine. On the other hand, the blades located in the negative wind direction swing outward of the center of the turbine to get the no resistance orientation in the second position near the second stopper.

In the fifth embodiment of the invention, each one of the first group of turbine blade comprises a magnetic brake. The magnetic brake comprises three parts and each part covers 10-55 degrees of blade movement around its rotation axis. Those parts are (|) a first braking region, (II) a second braking region, and (III) a coil. The first braking region which is connected to the first stopper and/or blade bracket, is a conductive element. The appearance of the magnet, which is connected to the first group of turbine blades, close to the first braking re- gion, induces an electric current within the conductive element. By moving the magnet, the induced current in the conductive element causes a magnetic field which acts as a brake and causes a smooth deceleration in the blade move- ments. This prevents any impact on the first stopper. The coil operates in non- braking state in normal condition due to the open circuit of the coil. However, during storm conditions, a switch that may take advantage of centrifugal force, connect both ends of each coil and effectively create a closed circuit and put the coil in a braking state. As the result of induced electric current in the closed circuit coil by being close to the magnet of the blade, the engendered magnetic fields cause a contactless brake. This way the movement of the blade around its rotation axis undergoes slower changes that increases the resistive force in — the negative wind direction, ensuring a limited speed of the turbine in storm conditions. The coilis notan essential part of the magnetic brake, but the mag- netic brake could comprise only the first and second braking regions, which can be arranged apart from each other to provide a non-braking region in- between. The second braking region of the magnetic brake is a conductive component (as like as the first braking region) and acts as a brake when the blade is getting closer to the second stopper (the position of no resistance).

Alternatively, an electromagnetic brake which is connected to the blade rota- tion axis can be utilized to control the blade movement around its rotation axis in different conditions. The wind turbine can be configured to supply electric current into the electromagnetic brake (coil). When a storm happens and the rotation speed of the wind turbine exceeds a predetermined limit, the electro- magnetic brake gets activated. The limit of the rotation speed of the wind tur- bine may vary depending on the size of the turbine, however, the equivalent speed of a storm can be set as the limit.

In the sixth embodiment of the invention, each one of the first group of turbine blades comprises a mechanical brake in which there is a cam connected to the blade rotation axis and is controlled using a cam follower. Due to the spe- cial design of the cam, the cam follower limits the rotational movement of the cam when the blade is near the first stopper or the second stopper, ensuring no impact between blades and stoppers. Moreover, the cam follower is pro- vided with a spring to hold it continuously on the cam surface and ensure a smooth movement in the cam follower.

In the seventh embodiment of the invention, the wind turbine comprises a mag- netic rotor brake, that regulates the turbine's rotation speed in storm condi- tions. The magnetic rotor brake comprises one or more magnets and a con- ductive element which is a disk in the design of the drawings. Each magnet is connected to the turbine shaft through an arm and fastening means. The arm is keeping back from the conductive element using a spring. When a storm happens, the speed of the rotor exceeds a certain level and the centrifugal force engendered on the magnet and its arm overcome the force of the spring, the arm unfolds and lets the magnet to be very close to the conductive element.

The turbine's rotational movement facilitates the relative motion between the magnets and the conductive element. The induced current and the engen- dered magnetic fields within the conductive element, configures a contactless brake due to the movement of the magnet very close to the conductive ele- ment. Alternatively, this brake can be electromagnetic brake in some design of the turbine or even a friction brake.

LIST OF THE FIGURES

The accompanying drawings are used to illustrate the embodiments, methods, operations, and other aspects of the invention. In different examples of the figures the elements may not be drawn to scale, and some components may be designed as a single one. Moreover, some components may not be shown in many examples and some other components may be shown multiple times.

In the following, various embodiments will be described thoroughly in accord- ance with the attached drawings. The drawings are provided to illustrate, not limit, the scope and operation of the present invention in which:

Figure 1 illustrates a general perspective of the invention under operation when the first turbine blades in the positive wind direction generate driving force and the first turbine blades in the negative wind direction swing between first and second stoppers to mitigate the resistance force, in accordance with at least one embodiment;

Figure 2 illustrates the top view of the invention, in accordance with at least one embodiment;

Figure 3 illustrates a general perspective of the first group of turbine blades, a blade bracket, magnetic brake and mechanical brake in accordance with at least one embodiment;

Figure 4 illustrates a top view of the first group of turbine blades, a blade bracket, magnetic brake and mechanical brake in accordance with at least one embodiment;

Figure 5-1 illustrates a general perspective of the mechanical brake of the first group of turbine blades, in accordance with at least one embodiment;

Figure 5-2 illustrates the top view of the mechanical brake of the first group of turbine blades, in accordance with at least one embodiment;

Figure 6-1 illustrates a general perspective of the rotor magnetic brake, in ac- cordance with at least one embodiment; and

Figure 6-2 illustrates the top view of the rotor magnetic brake, in accordance with at least one embodiment.

DETAILED DESCRIPTION OF THE INVENTION

In this section, the present invention has been illustrated in detail, and various embodiments have been clarified with reference to the accompanying draw- ings. Furthermore, it should be noted that the provided illustrations and em- bodiments with respect to the figures are merely for explanatory purposes and the mechanisms and their function may extend beyond the illustrated embod- iments. — Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

As used herein, unless the context clearly dictates otherwise, the singular is intended to include the plural as well, furthermore, it is to be understood that when the terms "comprising" and/or "including" are used in this specification, it indicates that there are features, steps, operations, devices, components and/or combinations thereof. In the claims, the terms “first”, “second”, and so forth are to be interpreted merely as ordinal designations; they shall not be limited in themselves.

In this invention, terms such as "upper", "lower", "left", "right", "front", "rear", "vertical", "horizontal", "side", "bottom", "position", "direction", etc. The orienta- tion or positional relationship is based on the orientation or positional relation- ship shown in the drawings, and is only a relational word determined for the convenience of describing the structural relationship of each component or el- ement of the present invention, and does not specifically refer to any compo- nent or element in the present invention, and should not be construed as a reference to the present invention.

A general perspective of the invention in accordance with one embodiment has been shown in figure (1) on which the turbine is under operation. The drag- type vertical axis wind turbine with self-adaptive blades includes a turbine shaft 1, a plurality of second turbine blades 6, a plurality of turbine blade brackets 4,

a plurality of first turbine blades 5, a plurality of weights 7 (shown and explained in figure 1), a plurality of rotation axis 16 of the first group of turbine blades, a plurality of blade magnetic brakes, a plurality of blades’ first stoppers (stopper elements) 14 and second stoppers (stopper elements) 15 (shown and ex- plained in figure 4), a plurality of blade mechanical brakes (shown and ex- plained in figure 5), and a turbine brake (shown and explained in figure 6).

The turbine comprises at least 2 blades of first group of turbine blades and least 2 blades of second group of turbine blades, but preferably 5-9. Each blade of the first group of turbine blades is accompanied by weights 7, a blade rotation axis 16, a magnetic brake and a mechanical brake. In no-wind situa- tions, when the turbine is in a stationary state, the yaw angle of the first group of turbine blades is freely set between the first stopper 14 and the second stopper 15. The second turbine blades 6 are fixed.

Figure (3) and (4) show a blade of the first group of turbine blades that is ac- companied with blade brackets 4, an upper portion and a lower portion of the blade 5, a blade mechanical brake 13, an upper and a lower weight 7. Further- more, the blade magnetic brake includes magnets 12 attached on the first group of turbine blades, a first and second stopper 14 and 15, a first and sec- ond braking region 11 and 9. The blade bracket 4 connects the blade of the first group of turbine blades to turbine shaft 1 through fastening means and component 2. The upper and lower portions of the blade 5 are connected to the blade bracket 4 through the blade rotation shaft 16. Instead of the blades 5 comprising upper and lower portions, each blade 5 could comprise a single portion arranged between an upper blade bracket and a lower blade bracket.

The weights 7 (shown in figure 3) are installed on the lower and upper portions of the first group of turbine blades 5. The weights make the smaller portion of the blade heavier than the larger portion to adjust the center of mass of the blade on the smaller portion with a distance to the blade rotation axis. When the turbine is under operation, the smaller portion of the blade is subject to a centrifugal force due to the weights 7. In addition, the blade is subject to the wind force, and under the action of those two forces, the blade movement is smooth and any harsh impact with first stopper 14 and second stopper 15 is prevented. The turbine blades 5 could be attached to the blade brackets 4 from vertical edges such that the whole turbine blade 5 is on one side of the blade rotation axis 16.

Once the wind blows into the turbine, the first group of the turbine blades 5 start swinging to adjust a proper position based on the wind direction and the position of the blade with respect to the turbine shaft 1. Thus, the operational state of the turbine, shown in figure (1 and 2), happens. In operational condi- tions, the turbine includes one or more blades of the first group of turbine blades 5 exposed to wind (in the positive wind direction), that are located in the first braking region 11 and push the first stopper 14 and generate driving torque in the turbine. On the other side (in the negative wind direction) there are one or more blades of the first group of the turbine blades 5 that are posi- tioned align to the wind direction in the second braking region 9 close to the second stopper 15.

While the first group of turbine blades 5 move in the negative wind direction, the resultant of the wind force on the blade swings it around the rotation axis 16. This enables the blade to get closer to the second stopper 15 and set a — position with less resistance force in the negative wind direction nearby the position P-3 in figure (2). Then, when the turbine rotates and the wind force as the main force affecting the blades, gradually rotates the blade of the first group of turbine blades 5 around its rotation axis 16 until the blade approaches the first braking region 11 nearby the position P-2 in figure (2). In that position, the blade magnet 12 pushes the first stopper 14 and generates driving force. The driving force generation continues after P-1 to near P-4 where the wind force decreases a lot and the centrifugal force of the weights 7 controls the blade movement. In position P-4, the second group of turbine blades 6, which are connected to the turbine shaft 1 through a pipe 3, prevent wind from blowing into the blade of the first group of turbine blade 5, ensuring a smooth move- ment of the blade around position P-4. Also, the centrifugal force engendered on the first group of turbine blades 5 prevents any impact on the second stop- per 15 before the position P-3, where again the wind force controls the blade.

The blade magnetic brake is illustrated in figures (3 and 4) in accordance with atleast one embodiment of the invention. The rotation shafts 16 allow the first group of turbine blades 5 to swing freely between the first stoppers 14 and the second stoppers 15. The first and second stoppers 14 and 15, the first and second braking region 11 and 9, as well as the coil 10 are installed on the blade bracket 4 together as a single component, and magnets 12 are installed on the lower portion and the upper portion of the blade 5. These components configure the blade magnetic brake. According to the figure (2), while the turbine is under operation, the first group of the turbine blades 5 are continu- ously swinging around their rotation axis. In the position P-1 the magnet 12 locates in the first braking region 11 and induces electric current in the con- ductive element of the first braking region 11 and causes magnetic fields which affect the magnetic fields of the magnet 12 and the blade 5 approaches the first stopper 14 with a smooth deceleration. While the blade is getting closer to the first stopper 14, the blade also adopts the mechanical brake as well as a repulsion between the magnet 12 and a magnet or conductive element in the first stopper 14 to further prevent any impact. — After position P-4, when the blade is moving away from the first braking region 11, the magnet is passing the coil 10. In normal condition the coil is an open circuit and does not affect the blade movement. However, in storm condition a switch connects two ends of the coil 10 and as the result, the coil is a closed circuit. Therefore, when the blade is passing the coil, the magnet 12 induces current and causes magnetic fields in the coil 10 which act as a brake for the blade. This slows down the movement of the blade and increases the re- sistance in the negative wind direction. After the coil 10, the magnet 12 ap- proaches the second braking region 9 and induces current in the conductive element of the second braking region 9 and causes magnetic fields which af- fect the magnetic fields of the magnet 12 and the blade approaches the second stopper 15 with a smooth deceleration. While the blade is getting closer to the second stopper 15, the blade again adopts the mechanical brake and a repul- sion between the magnet 12 and a magnet or conductive element in the sec- ond stopper 15 to further prevent any impact. The conductive elements can be made of, for instance, aluminium or aluminium alloy or some other paramag- netic material. In the embodiment of the figures, the conductive elements are arranged in arc-shape. Each conductive element extends over a certain angle, such as 10-55 degrees to define the first and second braking regions 11, 9.

Preferably, each of the first and second braking regions extend over an angle of 15-30 degrees. This allows ensuring smooth deceleration of the rotation of the blades 5, but also quick rotation of the blade 5 as the blade 5 moves from power-generation side to return side and vice versa. Instead of attaching the magnet 12 to the blade 5 and the conductive elements and the coil 10 to the blade bracket 4, the conductive elements and the coil 10 could be attached to the blade 5 and the magnet 12 or a plurality of magnets to the blade bracket 4.

The mechanical brake of the first group of turbine blades is illustrated in figures (5-1 and 5-2) in accordance with at least one embodiment of the invention. The mechanical brake comprises an upper plate 17 and a lower plate 18 which connect the mechanical brake to the blade bracket 4, the rotation axis 16, a cam 20, a cam follower 21, a cam follower arm 19, a cam follower spring 22, and housing of the mechanical brake 13. The components 17, 18 and 13 act as housing of the mechanical brake to isolate the brake component. In opera- tional conditions of the wind turbine, the first group of turbine blades 5 rotate — using rotation axis 16. The rotation axis is connected to the housing of the mechanical brake using bearings. Inside the component 13, the cam 20 is fixed on the rotation axis 16 and the cam follower 21 is holding on the cam surface using its arm 19 and spring 22. While the blade is in the first braking region 11 and the second braking region 9, the special design of the cam affects the cam follower, and their interaction incrementally increases the force between them and decreases the rotational speed of the cam. The mechanical brake pro- vides an additional braking effect, but the wind turbine could be implemented even without the mechanical brakes.

The magnetic rotor brake is illustrated in figures (6-1 and 6-2) in accordance with at least one embodiment of the invention. The magnetic rotor brake com- prises a rotor shaft 1, a turbine holder flange 24, a conductive element 23 which is fixed, magnets 25, magnet arms 27, arm fastening components 26, and springs 28. In the magnetic rotor brake only the conductive element 23 is fixed and all other components that are connected to the turbine shaft rotate together with the turbine. This provides a relative movement between the mag- net 25 and the conductive element 23.

In normal operation of the turbine the spring 28 holds the arm 27 back, and consequently the magnet 25 which is connected to the arm 27 is away from the conductive element 23. Once a storm happens and the rotational speed of the turbine exceeds a certain level, the engendered centrifugal forces on the magnet 25 and arm 27 overcome the force of the spring 28. This unfolds the arm 27 and consequently the magnet 25 gets closer to the conductive element 23 and the magnetic rotor brake gets activated. When the magnet 25 is very close to the conductive element 23, it induces electric current and causes mag- netic fields within the conductive element 23. The magnetic fields affect each other and act as a brake and limit the rotational speed of the turbine. Therefore,

the turbine is capable of generating power safely in storm conditions. The con- ductive element 23 of the magnetic rotor brake can be made of, for instance, aluminium, aluminium alloy, or other paramagnetic material.

The brake continues being activated during the storm conditions due to the relative movement of the magnet 25 and the conductive element 23 and con- tinuous magnetic fields generation. When storm subsides, the centrifugal force of the magnet 25 and its arm 27 decreases below the force of the spring. Then, the arm 27 gets pulled back by the spring 28 and the magnetic rotor brake gets deactivated. The magnetic rotor brake could also be implemented by providing one or more stationary magnets and a conductive element rotating with the turbine shaft. The magnetic rotor brake could also be activated by some other means than the springs and centrifugal force. For instance, the wind turbine could be provided with an electromagnet that is configured to switch the mag- netic rotor brake to a braking state when the rotation speed of the turbine ex- ceeds a predetermined limit. The magnetic rotor brake provides advantageous non-contact braking in storm conditions. However, the rotation speed of the turbine could be limited by some other means.

Claims

CLAIMS:

1. A drag-type vertical axis wind turbine comprising - a turbine shaft (1) configured to be coupled to an electric power gen- erator, - at least two turbine blade brackets (4) for connecting turbine blades to the turbine shaft, - a first group of turbine blades (5) comprising at least two turbine blades connected to the turbine shaft (1) by means of one or more of said at least two turbine blade brackets at equal radial distances from the turbine shaft (1), each turbine blade (5) being attached to a re- spective turbine blade bracket rotatably about a rotation axis (16) that is parallel to the axial direction of the turbine shaft, - a first stopper element (14) and a second stopper element (15) for each turbine blade of the first group of turbine blades (5) for limiting rotational movement of the respective turbine blade about said rota- tion axis (16) between a first position and a second position, wherein in the first position the turbine blade is positioned to generate driving force to rotate the wind turbine and in the second position the turbine blade is positioned to minimize the force resisting the rotation of the wind turbine, characterized in that the wind turbine comprises for each turbine blade of said first group of turbine blades (5) a magnetic brake for braking the rotational movement of said turbine blade as the turbine blade ap- proaches the first position and/or the second position, the magnetic brake comprising at least one magnet and at least one conductive element, the rotational movement of the turbine blade about the rotation axis (16) be- ing configured to move said at least one magnet and said at least one conductive element relative to each other to induce electric current in said at least one conductive element.

2. A wind turbine according to claim 1, wherein the magnetic brake has a first braking region (11) configured to brake the turbine blade as the tur- bine blade (5) approaches the first position and a second braking region (9) configured to brake the turbine blade (5) as the turbine blade ap- proaches the second position, each of the first braking region and the second braking region extending over an angle of 10-55 degrees, pref- erably over an angle of 15-30 degrees.

3. A wind turbine according to claim 1 or 2, wherein the first braking region (11) and the second braking region (9) are arranged apart from each other.

4. A wind turbine according to any of claims 1-3, wherein said at least one magnet (12) is attached to the turbine blade (5) and said at least one conductive element is attached to the turbine blade bracket.

5. A wind turbine according to any of the preceding claims, wherein the magnetic brake comprises a first conductive element (11) arranged such that electric current is induced in the first conductive element as the tur- bine blade (5) approaches the first position, and a second conductive el- ement (9) arranged such that electric current is induced in the second conductive element as the turbine blade (5) approaches the second po- sition.

6. A wind turbine according to any of the preceding claims, wherein the tur- bine blade (5) is provided with a magnet (12) and the turbine blade bracket (4) is provided with one or more magnets arranged such that at least one of the magnets of the turbine blade bracket repels the magnet of the turbine blade as the turbine blade approaches the first position and/or the second position to prevent the turbine blade from hitting the first stopper element (14) or the second stopper element (15).

7. A wind turbine according to any of the preceding claims, wherein the wind turbine comprises for each turbine blade of said first group of turbine blades (5) a mechanical brake for braking the rotational movement of said turbine blade as the turbine blade approaches the first position and/or the second position, the mechanical brake comprising a cam (20) attached to the turbine blade (5) such that the cam rotates with the turbine blade as the turbine blade rotates about the rotation axis (16), and a cam fol- lower (21) attached to the turbine blade bracket and biased by means of a spring (22) against the cam such that the cam brakes the turbine blade

(5) as the turbine blade approaches the first position and/or the second position.

8. Awind turbine according to any of the preceding claims, wherein the wind turbine comprises for each turbine blade of said first group of turbine blades (5) a coil (10) that can be selectively set into a non-braking state or a braking state, and a magnet arranged such that the rotational move- ment of the turbine blade (5) about the rotation axis (16) moves the mag- net and the coil relative to each other, and in the braking state of the coll the coil and the magnet are configured to interact such that the turbine blade is further braked as it approaches the second position.

9. A wind turbine according to claim 8, wherein in the non-braking state the coil (10) forms part of an open electrical circuit and in the braking state the coil forms part of a closed electrical circuit, and the wind turbine com- prises a switch that is configured to close said electrical circuit when the rotation speed of the wind turbine exceeds a predetermined limit.

10. A wind turbine according to claim 8, wherein the coil (10) forms part of an electromagnet, and the wind turbine is configured to supply electric cur- rent into the coil when the rotation speed of the wind turbine exceeds a predetermined limit to switch the coil to the braking state.

11. Awind turbine according to any of the preceding claims, wherein the wind turbine comprises a magnetic rotor brake for controlling the rotation speed of the wind turbine, the magnetic rotor brake comprising at least one magnet (25) and at least one conductive element (23), the rotational movement of the turbine being configured to move said at least one mag- net and said at least one conductive element relative to each other to induce electric current in said at least one conductive element, and said at least one magnet and said at least one conductive element are config- ured to approach each other when the rotation speed of the turbine in- creases and/or exceeds a predetermined limit.

12. A wind turbine according to claim 11, wherein the magnetic rotor brake comprises at least one arm (27) and a magnet (25) attached to the arm, the arm being pivotably attached to the turbine shaft and spring-biased such that centrifugal force caused by the rotational movement of turbine moves the magnet closer to the conductive element (23).

13. A wind turbine according to any of the preceding claims, wherein the ro- tation axis (16) of each turbine blade of said first group of turbine blades (5) is offset from the middle axis of the plane of the turbine blade.

14. A wind turbine according to claim 13, wherein the turbine blade (5) is divided by the rotation axis (16) of the turbine blade into a smaller portion and a larger portion, and the smaller portion is provided with one or more weights (7) such that the mass of the smaller portion is greater than the mass of the larger portion.

15. A wind turbine according to any of the preceding claims, wherein the wind turbine comprises a second group of turbine blades (6) comprising at least two turbine blades, wherein the turbine blades of the second group of turbine blades are arranged radially inwards of the first group of turbine blades (5).