WO2012111022A1

WO2012111022A1 - Speed control of wind turbine by implying drag using centrifugal control

Info

Publication number: WO2012111022A1
Application number: PCT/IN2012/000082
Authority: WO
Inventors: Rajagopal Raghunathan VALAGAM
Original assignee: Valagam Rajagopal Raghunathan
Priority date: 2011-02-14
Filing date: 2012-02-03
Publication date: 2012-08-23

Abstract

According to an aspect of the present invention, there is provided a system for controlling the rotational speed of the wind turbine by means of drag device. The wind turbine develops stresses and undesirable noise while slowing down its speed by means of existing braking. The present invention comprises of drag device pivoted at the arms which is held in no drag position by the tension spring as long as the turbine operates within the ratedspeed. While the turbine exceeds the rated speed, the centrifugal force corresponding to that speed exceeds the designed value of spring which causes it to lose the tension over the drag device. The created drag force retards the rotation of the turbine and brings the rotational speed under control. The drag device is brought back to no drag position as the centrifugal force is within the designed value of spring.

Description

TITLE OF THE INVENTION: SPEED CONTROL OF WIND TURBINE BY IMPLYING DRAG USING CENTRIFUGAL CONTROL

FIELD OF THE INVENTION

This invention relates to the wind turbine with unique method of rotational speed control. When the wind turbine is rotated by the approaching wind, its rotational speed should be in control for the safety of the system. The existing wind turbine employs the braking system by means of control systems which creates sudden imbalance on the system which is also not reliable for the safety of the turbine. The turbines rely on passive mechanisms such as furling and/or blade flutter to Control the rotational speed. These passive methods cause high mechanical stresses and undesirable noise. One method to reduce the stresses and noise is to control the rotational speed of the rotor. The present invention employs drag device to bring the rotational speed of the turbine while it exceeds the rated value. The drag device is lifted by means of centrifugal force corresponding to the maximum rotational speed which controls the rotation of the turbine and brings it within the desired limit which is economical and safe than existing systems.

BACKGROUND AND PRIOR ART OF THE INVENTION As energy demands around the world increase, the need for a renewable energy sources that will not harm the environment has been increased. Wind energy conversion is a fast-growing interdisciplinary field that encompasses many different branches of engineering and science. The wind energy market has grown because of the environmental advantages of harnessing a clean and inexhaustible energy source. However, there are still many unsolved challenges in expanding wind power.

Wind energy is increasingly recognized as a viable option for complementing and even replacing other types of energy resources. However, the control of the operation of a wind turbine is often very sensitive because a wind turbine is typically exposed to ever changing ambient conditions which may cause extreme mechanical stresses to the structure of the turbine.ln case of any failure of network near the wind turbine, it makes impossible for the generator of the wind turbine to export the produced electrical power. The result is an increasing of the rotational speed of the rotor of the wind turbine with the risk of a dangerous over speed situation.

While the turbine exceeds its rated speed due to cyclones and other above said factors it needs to be slowed down for the safety of the system and also to generate continuous power from the turbine. With system of controlling the rotational speed of the turbine by means of braking mechanism which is practiced in the industry creates imbalance to the system. The turbines rely on passive mechanisms such as furling and/or blade flutter to control the rotational speed. These passive methods cause high mechanical stresses and undesirable noise. Most small wind turbines have a passive mechanical method of speed control. The turbines either furl their rotor out of the wind and/or the blades flutter to reduce the rotor performance. When a turbine's passive speed control begins to operate, the performance of the turbine can be greatly reduced while the mechanical stresses increase.

A few patents are typical of the known prior art attempting to improve the methods of controlling the rotational speed of the wind turbine. For example, U.S Pat. No. 2010/0140941 to Per Egedal discloses a method in which the wind turbine is impeded to export electrical power to an electricity network being connected to the wind turbine. It contains rotational speed controlling device for controlling the rotational speed by means of computer program controls.

While U.S Pat. No: 2007/0269311 to Raymond Browning discloses a method for controlling the rotational speed of rotor. The system included awind turbine having a rotor having airfoils having an orientation relative to the wind and a rotationalaxis. It includes a structure supporting the wind turbine above ground and it is coupled to the ground. The structure has first portion closer to the wind turbine and a second portion farther from the wind turbine. The first portion will move farther in response to the wind acting across the structure than said second portion causing the turbine rotational axis tilt. Themethod includes tilting the rotor rotational axis about an angle and varying the angle in response to changes of the wind force.

But none of the prior art documents disclose a method of controlling the rotational speed of the turbine which is simple, economical and easy to install and also minimizes the stresses and noise developing while controlling the speed.

SUMMARY OF THE INVENTION According to aspect of the present invention, there is provided a system for controlling the rotational speed of the turbine with the aid of the drag device for the safety of the system. The drag device pivoted with the arm is held in tensioncorresponding to the rated rotational speed by means of spring. The spring keeps the drag device in no drag position as long as the rotational speed is within the rated value and when the speed exceeds the rated value, the drag device is lifted since the centrifugal force goes beyond the value of the rated speed. So, the rotational speed of the turbine is brought down by the drag force. The stresses and noise generate while slowing down the turbine is reduced and thereby the systems proves to be the economical and safe method of controlling the rotational speed of the turbine. The drag device pivoted to the arm is broughtback to the no drag position by the tension exerted by the spring.

OBJECT OF THE INVENTION

It is an object of the invention to provide aneconomical, simple and safe method of controlling the rotational speed of the wind turbine.

It is an object of the invention to provide a drag device through which the rotational speed is controlled by means of drag force.

It is an object of the invention to provide a method of controlling the speed of the wind turbine with elimination of stresses and undesirable noise that will generate while controlling the rotation of turbine. It is an object of the invention to provide a spring for holding the drag device in no drag position as long as the rotational speed falls within the rated speed and to the drag position when needed.

It is yet another object of the invention to create the drag force generated by the difference in velocity and pressure between the drag device and the air.

STATEMENT OF THE INVENTION

The system for controlling the rotational speed of the wind turbine with the aid of drag device comprising of:

A. The airfoil blade (1 ) for generating the power from the approaching wind.

B. The drag device (2) for creating the drag force to control the rotation of the turbine.

C. The Bob (3) for activating the drag device by means of centrifugal force from the wind.

D. The sliding arm (4) for tilting the drag device about an axis by means of Bob.

E. The roller wheel (5) held in point contact with the drag device to have a smooth relative motion with the drag device.

F. The arm (6) for connecting the airfoil blade operably with the rotor for structural support of the blade.

G. The spring (7) for holding the drag device and releasing it when needed.

H. The arm fixture (8) for securing the arm with the rotor.

I. The rotor (9) for transmitting the power from the airfoil blade to the motor.

While the rotational speed of the turbine exceeds the rated value, the rotational speed of the turbine needs to be controlled for the safety of the turbine. When the brakes are applied it creates sudden imbalance with stresses and undesirable noise develop at the structures which is not acceptable. The present invention utilizes drag device installed at the arm to control the speed by means of drag force. The drag device is operated by means of spring which brings the device to drag position and back to the no drag position as the speed is controlled and thereby it accounts for economic and safe control of rotational speed. NO DRAG POSITION:

The turbine is designed to operate at rated speed above which the safety of the turbine is at risk. When the rotational speed of the turbine goes beyond the rated speed due to heavy storm or due to imbalance in the system it has to be controlled to have control over it. The drag device installed at the arm in the present invention is kept in position by the tension as long as the speed falls within the rated value. So, while rotation the drag device does not resist the air approaching it thereby it does not create any drag which is said to be No-Drag position.

DRAG POSITION:

While the turbine goes beyond the rated speed, the spring which is designed to corresponding tension of the centrifugal force at the rated speed loses its tension over the drag device which lifts it to a certain degree and thereby it creates drag due to the difference of velocity between the drag device and air by resisting the air approaching it which is said to be drag position.

DRAG:

Drag is a mechanical force. It is generated by the interaction and contact of a solid body with a fluid (liquid or gas). For drag to be generated, the solid body must be in contact with the fluid. If there is no fluid, there is no drag. Drag is generated by the difference in velocity between the solid object and the fluid. There must be motion between the object and the fluid. If there is no motion, there is no drag. It makes no difference whether the object moves through a static fluid or whether the fluid moves past a static solid object.

WORKING CONDITIONS: The present invention of controlling the rotational speed of the wind turbine by means of drag device comprises of two modes of operation

A. No Drag condition

B. Drag condition

NO DRAG CONDITION:

As shown in Fig. 1, 1(a) the drag device installed on the arm and secured in no drag by means of tension spring which is operably connected to Bob. When the turbine operates at rated speed, the position of the drag device remains in the no drag state by means of tension spring which is designed to withstand the force corresponding to the rated speed. So, the air approaching the drag device passes over it smoothly as long as the speed falls within the rated value. DRAG CONDITION:

As shown in Fig .2, 2(a) while the rotational speed of the turbine exceeds the rated speed, the spring loses its tension over the drag device and the bob lifts the drag device by means of sliding arm. The lifted drag device resists the approaching air and thereby a difference of velocity and pressure is created between the drag device and the air which creates a drag to control the rotation of turbine.

The method of controlling the rotational speed of wind turbine by means of drag device comprises of:

A. The drag device (2) is pivoted at the arm for creating the drag force to control the rotation of the turbine.

B. The turbine is operated for generating the power from the approaching wind.

C. The drag device (2) is held in no drag position by means of tension spring

(7)designed to withstand the force of the rated speed.

D. The spring(7) loses its tension while the turbine exceeds the rated speed. E. The bob(3) tilts or lifts the drag device(2) by means of sliding arm(4)attached to the arm(6).

F. The drag device(2) resists the approaching air and creates a velocity and pressure difference between the drag device(2) and the air.

G. Drag is created and the rotational speed of the turbine is brought under control.

H. The spring(7) brings back the drag device (2) to no drag position.

BRIEF DESCRIPTION OF THE DRAWINGS Fig.1 illustrates the drag device pivoted at the arm by means of tension spring at no drag condition.

Fig.2 illustrates the drag device pivoted at the arm by means of tension spring at drag condition.

Fig.3 illustrates an alternative embodiment in which two profiled plates pivoted at the arm by means of tension spring for controlling the rotational speed of the turbine.

Fig.4 illustrates a block diagram showing the steps involved in controlling the rotational speed of the turbine by means of drag device.

DETAILED DESCRIPTION OF THE DRAWINGS

The other and further features, advantages, and benefits of the invention will become apparent in the following description taken in conjunction with the following drawings. It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory but are not to be restrictive of the invention. The accompanying drawings which are incorporated in and constitute a part of this invention, illustrate one of the embodiments of the invention, and together with the description, serve to explain the principles of the invention in general terms. Like numerals refer to like parts throughout the disclosure. It was with knowledge of the foregoing state of the technology that the present invention has been conceived and is now reduced to practice. Fig.1& 1(a) illustrates the drag device pivoted at the arm by means of tension spring at no drag condition. The drag device(2) is pivoted at the arm(6) and is held in no drag position by the tension spring(7) which is designed to withstand the force corresponding to the rated rotational speed.The bob(3) along with the sliding arm(4) is attached to the arm(6) with roller wheel(5) is in contact with the drag device(2). The drag device(2) is maintainedin the ground or no drag position as long as the rotational speed fallswithin the rated speed and the air approaching it passes over smoothly and the drag device(2) does not resists the air and thereby no drag is induced at this position, Meanwhile the power is generated from the rotation of the turbine by the approaching wind.

Fig.2& 2(a) illustrates the drag device pivoted at the arm by means of tension spring at drag condition. The spring(7) which is holding the drag device(2) in place is designed to withstand the force corresponding to the rated speed and while the turbine goes beyond the rated speed the centrifugal force exceeds the rated value and thereby the spring(7) loses its tension over the drag device(2). So, the rotation of turbine causes the bob(3) to tilt which lifts the drag device(2) by means of sliding arm(4) and the roller wheel(5) held in contact with the drag device(2). As soon as the drag device(2) is tilted or turned by certain degree, it resists the approaching air and difference of velocity and pressure is created between the drag device (2) and the air. So, a drag force is created which retards the rotational speed of the turbine.

Fig.3 illustrates an alternative embodiment in which two profiled plates pivoted at the arm by means of tension spring for controlling the rotational speed of the turbine. An alternative to the above said concept is suggested in which two profiled plates are pivoted to the arm and held in no drag position by means of spring as like the above concept. So, when the turbine rotates within the rated speed, the approaching air passes over the plates smoothly and when the rotational speed exceeds the rated value, the spring loses its tension over the plates and thereby the bob tilts or lifts the plates by means of sliding arm. So, drag force is created which slows down the rotation of turbine. Fig.4 illustrates a block diagram showing the steps involved in controlling the rotational speed of the turbine by means of drag device.

A. The drag device(2) is pivoted at the arm for creating the drag force to control the rotation of the turbine.

B. The turbine is operated for generating the power from the approaching wind.

C. The drag device(2) is held in place by means of tension spring(7) designed to withstand the force of the rated speed.

D. The spring(7) loses its tension while the turbine exceeds the rated speed.

E. The bob(3) tilts or lifts the drag device by means of sliding arm(4) attached to the arm(6).

H. The spring(7) brings back the drag device(2) to no drag position. The operation of controlling the rotational speed of the turbine by means of drag device installed at the arm is as follows:

When the rotational speed of the turbine exceeds the rated speed, it needs to be controlled to have a continuouspower generation and for the safety of the system.While applying brakes to control the rotation of the turbine, it develops stresses on the structure due to sudden imbalance which is also unsafe. Also, it generates so much of undesirable noise during its operation. So, the present invention utilizes the drag force to control the rotation of the turbine by means of drag device(2). The drag device(2) is pivoted at the arms(6) of the turbine which is held in no drag position by the tension spring(7). The spring(7) is designed to withstand maximum centrifugal force corresponding to the rated rotational speed of the turbine. So, the drag device(2) is held in no drag position as long as the turbine operates within the rated speed and while the turbine is in rotation the air passes over the drag device(2) smoothly. When the rotational speed of the turbine goes beyond the rated speed, the centrifugal force corresponding to that speed exceeds the rated value of the spring(7). So, the spring(7) loses its tension over the drag device(2) and the bob(3) attached to the arm(6) tilts or lifts the drag device(2) by means of sliding arm(4) and roller wheel(5). As soon as the drag device(2) is tilted or lifted, it resists the approaching air thereby it creates a pressure and velocity difference between the dragdevice (2) and air.So, a drag force is created which retards the rotation of the turbine and thereby the speed is brought under control which causes the spring(7) to bring back the drag device(2) to the no drag position since the centrifugal force is brought under the designed value of the spring(7).

It will be obvious to a person skilled in the art that with the advance of technology, the basic idea of the invention can be implemented in a plurality of ways. The invention and its embodiments are thus not restricted to the above examples but may vary within the scope of the claims.

Further the above-described embodiments of the present invention are intended to be examples only. Alterations, modifications and variations may be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined solely by the claims appended hereto.

Claims

CLAIMS:

1. A system for controlling the rotational speed of the wind turbine with the aid of drag device comprising of:

A. The airfoil blade(1) for generating the power from the approaching wind.

B. The drag device(2) for creating the drag force to control the rotation of the turbine;.

C. The Bob(3) for activating the drag device by means of centrifugal force from the wind;.

D. The sliding arm(4) for tilting the drag device about an axis by means of Bob;.

E. The roller wheel(5) held in point contact with the drag device to have a smooth relative motion with the drag device;.

F. The arm(6) for connecting the airfoil blade operably with the hub for structural support of the blade;.

G. The spring(7) for holding the drag device and releasing it when needed;.

H. The arm fixture(8) for securing the arm with the rotor.

I. The rotor(9) for transmitting the power from the airfoil blade to the motor;.

2. The system as claimed in claim 1 wherein the airfoil blade(1) is fixed to the arm(6) for generating power from the wind asthe turbine rotates.

3. The system as claimed in claim 1 wherein the drag device(2) is pivoted to the arm(6) for controlling the rotational speed of the turbine.

4. The system as claimed in claim 1 wherein the spring(7)anchored to the arm(6) to hold the drag device (2) in no drag position and to the drag position when needed.

5. The system as claimed in claim 1 wherein the bob(3) activates the drag device(2) to drag position and vice versa.

6. The system as claimed in claim 1 wherein the arm(6) for connecting the airfoil blade(1) with the rotor(9) acting as structural support to the blades(1 ).

7. The system as claimed in claim 1 wherein the rotor(9) for transmitting the power from the airfoil blades(1 ) to the motor.

8. The system as claimed in claim 3 wherein the drag device(2)creates drag force while the rotational speed of. the turbine exceeds the rated speed.

9. The system as claimed in claim 4 wherein the spring(7) holding the drag device(2) is designed to withstand the centrifugal force corresponding to the rated speed of the turbine.

10. The system as claimed in claim 4 wherein the spring(7) loses it tension as soon as the rotational speed exceeds the rated speed.

11. The system as claimed in claim 8 wherein the drag device(2) creates a drag by the pressure and velocity difference between the drag device(2) and the air medium.

12. The system as claimed in claim 3 where in the drag device(2) retards the rotational speed of the turbine by means of drag force and thereby bringing the system under control.

13. The system as claimed in claim 3 where in the method of controlling the rotational speed of the turbine minimizes the development of stresses and noise.

14. A method of controlling the rotational speed of wind turbine by means of drag device as claimed in claim 1 comprises of:

A. Pivoting the drag device(2) at the arm (6) for creating the drag force to control the rotation of the turbine;

B. Operating the turbine for generating the power from the approaching wind;. C. Holding the drag device(2) in place by means of tension spring(7) designed to withstand the force of the rated speed.

D. Said spring(7) losing its tension while the turbine exceeds the rated speed.

E. Tilting or lifting the drag device using the bob(3)by means of sliding arm(4) attached to the arm (6).

F. Resisting of approaching air by the drag device(2) there by creating a velocity and pressure difference between the drag device(2) and the air.

G. Using drag createdto bring under control the rotational speed of the turbine is brought under control.

H. After which, the spring(7) brings back the drag device(2) to no drag position.

15. The system of controlling the rotational speed of wind turbine by means of drag device as claimed in claim 1 and methodsubstantially as claimed in claim 14, as herein described with respect to the accompanying drawings.