GB2480848A

GB2480848A - Tangential electromechanical generator for wind turbine blade

Info

Publication number: GB2480848A
Application number: GB1009309A
Authority: GB
Inventors: Stephen Roberts; Adam Wasenczuk
Original assignee: Perpetuum Ltd
Current assignee: Perpetuum Ltd
Priority date: 2010-06-03
Filing date: 2010-06-03
Publication date: 2011-12-07
Also published as: GB201009309D0

Abstract

A wind turbine blade 4 has an electromechanical generator `energy harvester' 10 to supply electrical power for driving a wireless sensor node. The generator 10 comprises a movable mass 20 which reciprocates along a path L extending tangentially (circumferentially) relative to the rotational axis of the turbine. The mass moves twice during each revolution of the turbine, and because it moves tangentially, it is substantially unaffected by centrifugal force, allowing it to be installed at any required radius R along the blade. The generator may include a motion restrictor to inhibit movement of the mass until the path is nearly vertical, so that maximum energy can be extracted from the moving mass. The restrictors may comprise attractive magnets at each end of the path (figure 3). A rotary generator is also disclosed (figure 5).

Description

WIRELESS SENSOR NODE FOR WIND TURBINE

This invention relates to an electromechanical generator for a wind turbine. In particular, this invention relates to an electromechanical generator mounted on a wind turbine blade for generating electrical power for driving a wireless sensor node. The invention further relates to a self-powered wireless sensor node and to a wind blade incorporating a self-powered wireless sensor node.

Wind turbines are well known for generating electrical power by the rotation of a hub carrying a plurality of wind blades, the hub driving an electrical generator in the nacelle of the wind turbine.

There are many operational and reliability benefits to being able to measure mechanical and dynamic parameters within large wind turbine blades. Wireless sensor nodes (WSN) are attractive for this purpose because they do not require cables or slip-rings for communication with the hub. For example, cables can attract lightning strikes and slip-rings can be unreliable. To achieve truly wireless operation of the sensor nodes, energy harvesting is the only plausible method of powering these WSNs because battery changing is impractical due to access difficulties. Energy harvesting is the parasitic use of mechanical energy from a moving body to drive a local electrical generator, for example an electromechanical generator.

The present invention aims to provide an energy harvester for a wind turbine blade which has a high power output.

Accordingly, the present invention provides a wind turbine blade having an electromechanical generator mounted thereon for generating electrical power for driving a wireless sensor node, the electromechanical generator comprising a movable mass for generating electrical power by reciprocal movement along a path extending substantially tangentially relative to the rotational axis of the wind turbine blade.

The present invention further provides a wireless sensor node for a wind turbine blade, the wireless sensor node including a sensor, a wireless transmitter, and an electromechanical generator, the electromechanical generator comprising a movable mass for generating electrical power by reciprocal movement along a path under the action of an alternating gravitational force.

The present invention further provides a wind turbine blade having an electromechanical generator mounted thereon for generating electrical power for driving a wireless sensor node, the electromechanical generator comprising a rotary generator fixed to the wind turbine blade, a rotationally movable arm connected to a rotary element of the rotary generator and a mass located on the arm.

The present invention further provides a wireless sensor node for a wind turbine blade, the wireless sensor node including a sensor, a wireless transmitter, and an electromechanical generator, the electromechanical generator comprising a rotary generator, a rotationally movable arm connected to a rotary element of the rotary generator and a mass located on the arm.

The present invention further provides a method of operating a wireless sensor node for a wind turbine blade, the wireless sensor node including a sensor, a wireless transmitter, and an electromechanical generator, the electromechanical generator comprising a movable mass for generating electrical power by reciprocal movement along a path under the action of an alternating gravitational force, the method comprising moving the mass substantially tangentially during rotation of the wind turbine blade.

The present invention further provides a method of operating a wireless sensor node for a wind turbine blade, the wireless sensor node including a sensor, a wireless transmitter, and an electromechanical generator, the electromechanical generator comprising a rotary generator fixed to the wind turbine blade, a rotationally movable arm connected to a rotary element of the rotary generator and a mass located on the arm, the method comprising rotating the wind turbine blade and the rotary generator applying to the mass on the arm a rotational resistive force against gravitational force.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:-FIG. 1 is a schematic side view illustrating a wind turbine incorporating a wireless sensor node including an electromechanical generator in accordance with the invention; FIG. 2 is a schematic side view illustrating the principle of operation of a first embodiment of an electromechanical generator for a wind turbine in accordance with the invention; FIG. 3 is a schematic side view illustrating the principle of operation of a second embodiment of an electromechanical generator for a wind turbine in accordance with the invention; FIGS. 4a and 4b show a particular implementation of the electromechanical generator of FIG. 3, the generator being shown at two respective end positions; and FIG. 5 is a schematic side view illustrating the principle of operation of a third embodiment of an electromechanical generator for a wind turbine in accordance with the invention.

The inventors have determined a number of design criteria for an electromechanical energy harvester for use on a wind blade in order reliably to drive a wireless sensor node.

For example, the energy harvester should generate sufficient power for the WSN while minimising mass, volume and cost. Since the wind blade length can vary between different wind turbines, the energy harvester should operate when mounted on or within a turbine blade at a radius of between Sm and 60m from the hub axis. The energy harvester should be able to operate when the wind turbine is rotating between 7 revolutions per minute (rpm) and 12 rpm. Ideally, the energy harvester should be maintenance free and contain no parts that wear out.

In order to attempt to meet these criteria, the inventors have devised a number of embodiments of an electromechanical energy harvester for use on a wind blade.

Referring to FIG. 1, a first embodiment of a wireless sensor node an electromechanical energy harvester for use on a wind blade is schematically illustrated. The wind turbine 2 comprises a number of wind blades 4 mounted on and extending radially from a hub 6.

The hub 6 is connected to a nacelle (not shown) of known construction and the nacelle is, in turn, mounted at the top of a tower (not shown). One or more wireless sensor nodes 8 may be mounted on one or a plurality of the wind blades 4, but for clarity of illustration only one wireless sensor node 8 mounted on a single wind blade 4 is illustrated in FIG. 1.

Each wireless sensor node 8 comprises an electromechanical energy harvester 10 which generates electrical power parasitically from the rotational movement of the wind blade 4 upon which the electromechanical energy harvester 10 is mounted. The electromechanical energy harvester 10 is connected electrically to a controller 12 which is also connected to a sensor 14 and a wireless transmitter 16. The sensor 14 is adapted to sense one or more parameters, for example mechanical strain, mechanical stress, pressure, temperature, etc., and the output from the sensor 14 is processed by the controller 12 which produces a measured numerical value for the sensed parameter. The measured numerical value is transmitted to a remote location by the wireless transmitter 16, The wireless sensor node 8 is self-powered, the electromechanical energy harvester providing electrical power continuously to operate the controller 12, the sensor 14 and the wireless transmitter 16.

FIG. 2 shows the electromechanical energy harvester 10 in greater detail. The electromechanical energy harvester 10 of this embodiment uses the rotational energy of the wind turbine 2 to cause reciprocal linear movement of an electromechanical element in a tangential direction relative to the rotational movement of the wind turbine 2. This embodiment employs movement of an electromechanical element with very little radial component, i.e. in the tangential direction, which functions even when there is a large centripetal acceleration which is greater than the acceleration due to gravity, g. Energy is harvested parasitically from the cyclically inverting gravity field by allowing two gravity-forced tangential movements per cycle. This is shown pictorially in FIG. 2.

A mass 20 is located within an elongate housing 22 defining a linear cavity 24 along which the mass 20 can move reciprocally between opposed ends 26, 28 of the housing 22. The linear cavity 24 is oriented with the direction of movement L orthogonal to the radius R of the wind blade 4. The linear reciprocal movement is substantially frictionless, this being represented by bearings 25, such as roller or ball bearings, located between the mass 20 and the inner walls of the housing 22.

The mass 20 is attached to or part of a linear generator. For example, the mass 20 includes one or more magnets, and one or more electrical coils are mounted along the direction of movement L. In a system such as that shown in FIG. 2 the mass 20 moves reciprocally between its limits primarily under the action of gravity in opposite directions along the direction of movement L. As the mass 20 moves along the direction of movement L, in each direction, the moving magnetic flux from the one or more magnets is cut by the one or more electrical coils to generate an electrical current on the coil or coils which can be fed to the controller. As is known in the energy harvesting art, the alternating current is optionally rectified to produce a direct current and the direct voltage output may be regulated.

In the embodiment shown the wind turbine 2 rotates at io radians per second, in a clockwise direction. The mass 20 moves between the two end limits each time the gravity field inverts. The effect of centripetal force on the tangential movement is low.

With such clockwise movement, the mass 20 begins to move downwardly in a first direction from one end 24 to the opposite end 26 along the housing 22 just after the 6 o'clock position in a first half-cycle, and reaches the opposite end 26 during that half-cycle. Subsequently, in the next half-cycle, the mass 20 begins to move downwardly in a second direction from the end 26 to the opposite end 24 along the housing 22 just after the 12 o'clock position in a first half-cycle, and reaches the opposite end 24 during that half-cycle. The mass 20 moves in a flip-flop manner between the opposed ends 24, 26, each linear movement generating an electrical power output. For each linear tangential motion, which is substantially frictionless, the mass 20 gains velocity substantially immediately after the respective wind blade 4 has passed the vertical point, and so gains velocity with an applied force which has a vertical component which is only a fraction of the gravitational acceleration.

Although such a construction provides a useful electromechanical energy harvester 10 for some applications, such a low acceleration restricts the power output of the electromechanical energy harvester 10.

FIG. 3 shows a modification of the electromechanical energy harvester 10 of FIG. 2 which has been adapted to extract maximum electrical power output from the electromechanical energy harvester 10 as a result of such reciprocal tangential motion.

In the embodiment of FIG. 3, the movement of the mass 20 is inhibited until the mass 20 is near to the 3 o'clock and 9 o'clock positions. In this way, it can be ensured that when the mass 20 does move, the mass 20 accelerates at an acceleration which is close to the full acceleration of gravity g, and hence the electrical power output may be maximised.

FIG. 3 shows one way of achieving such inhibition or restriction of the motion until a minimum resultant threshold force acts on the mass to cause initiation of movement under the action of gravity. Referring to FIG. 3, the ends 26, 28 of the housing 22 are provided with respective end-stops 30, 32 which are made "sticky" by providing a controlled magnetic attraction between them the moving mass 20. The magnetic polarities are selected so that each end-stop 30, 32 presents a leading surface having an opposite magnetic polarity to the opposing end 34, 36 of the mass 20. The degree of magnetic attraction can readily be selected with the result that the mass 20 can be constrained so that the mass 20 only moves when gravitational force g is acting substantially along the direction of linear tangential movement, so that the movement is substantially vertically downwardly, hence imparting the greatest acceleration to the moving mass 20, and consequently generating the largest electrical power output.

The maximum energy that can be generated for each mass movement is: = igL where M is the mass of the mass, g is gravitational acceleration and L is the maximum distance of travel.

This energy is generated twice per rotation of the wind blade, so the maximum power output is: Mg Lw where w is the frequency of angular rotation in radians per second.

For a travel of LlOcm and an angular frequency of w0.733s1 (corresponding to 7rpm), the maximum possible power output is 230mW for a mass of 1kg. However this is readily scalable in both distance of travel and mass, to achieve higher power output.

The principle illustrated in FIG. 3 would in practice typically not be implemented using rollers or ball bearings, but rather a friction-free folded flexure mount for the mass would be typically employed. Such flexures require no maintenance as long at they are operated within their stress and fatigue limits. Power extraction would be achieved electromagnetically with a magnetic core attached to the mass moving relative to stationary wire coils. FIGS. 4a and 4b show this implementation schematically, but are not intended to represent a final engineered solution.

Referring to FIGS. 4a and 4b, the mass 52 is shown at respective opposed end positions of the reciprocal tangential linear motion which is along a distance L. The mass 52 is mounted on a movable carrier 54 which also carries at opposed ends 56, 58 thereof respective magnets 60, 62. The magnets 60, 62 have respective outermost faces 64, 66 of a respective selected magnetic polarity (N for magnet 60 and S for magnet 62 in the illustrated arrangement). The carrier 54 is mounted for reciprocal linear movement by two folded flexures 68, 70, each folded flexure 68, 70 fixing a respective end 56, 58 to a support 72, which in use is fixed to the wind blade 4.so that the movement of the carrier 54 is orthogonal to the elongate longitudinal direction of the wind blade 4, and therefore the radial direction of the wind blade 4 when mounted on the hub 6. Fixed magnets 74, 76 are mounted on the support 72, each opposing a respective movable magnet 60, 62.

The fixed magnets 74, 76 have respective innermost faces 78, 80 of a respective selected magnetic polarity (S for magnet 74 and N for magnet 76 in the illustrated arrangement) which is opposite to that of the opposing movable magnet 60, 62. In this way each fixed magnet 74, 76 is arranged to provide an attractive magnetic force the corresponding movable magnet 60, 62, which correspondingly provides a resistive force inhibiting the motion of the carrier 54 away from the respective end point of the direction of linear travel until a minimum threshold of a motion initiating force, which is the net gravitational force component overcoming the resistive force, has been reached.

Typically, the minimum threshold of the motion initiating force is within the range of from 0.5 to 0,9g.

The carrier 54 also supports at least one electrical power inducing magnet 82 which is mounted relative to one or more fixed electrical coils 84. Linear translational movement of the magnet 82 on the carrier 54 causes the magnetic flux of the magnet 82 to cut through the coils 84 which induces an electrical current in the coils 84 which is used to drive the wireless sensor node 8.

The motion of the magnet 82 relative to the coils 84 is in the manner of a flip-flop, with the initiation of motion being restricted at each end to provide a minimum initiation force (i.e. a "sticky" flip-flop) so that in each flip-flop half-cycle the linear motion occurs only during a predetermined central portion of the rotational half-cycle with the result that the acceleration achieved during the flip-flop motion is maximised in order to maximise the electrical power output from the interaction between the magnet element and the coil element of the electromechanical generator.

FIG. 5 illustrates a yet further embodiment of an electromechanical energy harvester according to the invention. The electromechanical energy harvester 108 of this embodiment uses the rotational energy of the electromechanical energy harvester 108 as it travels with the blade 4 to generate electrical power parasitically. The electromechanical energy harvester 108 of FIG. 5 can be used to generate electrical power in wind turbine applications where the centripetal acceleration due to the rotation of the wind blade upon which the electromechanical energy harvester is mounted is much less than the acceleration due to gravity.

In this embodiment, the electromechanical energy harvester 108 comprises a rotary generator 110 which is fixed to the wind blade 4. The rotary generator 110 comprises a known magnet/coil construction, which are relatively rotationally movable, to generate electrical power by relative rotation therebetween. A freely rotational arm 112 extends from a rotor 114 of the rotary generator 110 which has an axis of rotation 116. A mass 118 is mounted at a free end of the arm 112. In the absense of any rotation of the wind turbine 2, the mass 118 mounted on the arm 112 hangs vertically downwardly under the action of gravitational force. As the wind turbine 2 rotates at a constant angular velocity, a steady state is reached in which the mass 118 mounted on the arm 112 is inclined at an angle a to the vertical as a result of the rotary generator 110 applying a rotational force in the direction of angular motion of the wind turbine 2 as the rotary generator 110 rotates together with the wind blade 4. The electromechanical generator applies a rotational resistive force preventing the mass 118 mounted on the arm 112 from being restored to a vertical orientation solely under the action of gravity. The torque of the electromechanical generator keeps the mass 118 mounted on the arm 112 at a raised position. The angle a depends upon the torque of the electromechanical generator, and the torque varies depending upon the electrical load on the generator.

The maximum value of the angle a is 90°, i.e. the mass 118 is at the 9 o'clock position.

This occurs when the electrical load on the generator is optimised for maximum power.

For such an optimum load, the power generated by the rotation is: Pmax r ogM where r is the radius of angular motion of the mass relative to the rotational axis of the rotary generator, w is the frequency of angular rotation in radians per second, g is gravitational acceleration and M is the mass of the mass, provided that Ra2 (where R is the radius of the energy harvester relative to the hub) is significantly less than gravitational acceleration g and so the centripetal acceleration due to the rotation is much less than the acceleration due to gravity.

As an example, if R=5m and the angular velocity is 7 rpm, the centripetal acceleration is approximately 0.25g. For example, the power output can be relatively high: for r=0.lm and Mlkg, = 0.7 Watt at only 7 rpm. This embodiment has application with such short wind blades and low angular velocity. At higher wind blade lengths and rotational speeds, the centripetal acceleration is higher than g, and so the other embodiments would be employed.

Other modifications to the various embodiments of the present invention will be apparent to those skilled in the art. In particular, for each embodiment the magnet(s) may be configured to move with the coil(s) being stationary, or visa versa.

Claims

CLAIMS: 1. A wind turbine blade having an electromechanical generator mounted thereon for generating electrical power for driving a wireless sensor node, the electromechanical generator comprising a movable mass for generating electrical power by reciprocal movement along a path extending substantially tangentially relative to the rotational axis of the wind turbine blade.
2. A wind turbine blade according to claim 1 wherein the path extends substantially orthogonally to the longitudinal direction of the wind turbine blade.
3. A wind turbine blade according to claim 1 or claim 2 wherein the path is linear.
4. A wind turbine blade according to any foregoing claim wherein the movable mass includes at least one magnet and the electromechanical generator further includes at least one coil fixed to the wind turbine blade.
5. A wind turbine blade according to any foregoing claim wherein the movable mass is mounted for reciprocal movement on flexural members fixed to a support.
6. A wind turbine blade according to any foregoing claim wherein the electromechanical generator has a motion restrictor which is configured so that the movable mass is constrained against moving under the action of gravity away from ends of the path during at least a portion of a cycle of rotation of the wind turbine blade.
7. A wind turbine blade according to claim 6 wherein the motion restrictor is configured so that the movable mass is constrained against moving under the action of gravity when the wind turbine blade is at upper and lower regions of the cycle of rotation of the wind turbine blade.
8. A wind turbine blade according to any foregoing claim wherein the electromechanical generator further comprises a pair of opposed end members, each located at a respective end of the path, each end member being arranged to apply a resistive force inhibiting the motion of the mass away from the respective end member.
9. A wind turbine blade according to claim 8 wherein the end members apply a magnetic resistive force inhibiting the motion of the mass away from the respective end member.
10. A wind turbine blade according to claim 8 or claim 9 wherein the electromechanical generator has a minimum threshold of a motion initiating force for permitting the motion of the mass away from the respective end member.
11. A wind turbine blade according to claim 10 wherein the minimum threshold of the motion initiating force is within the range of from 0.5g to 0.9g, where g is gravitational acceleration.
12. A wind turbine blade according to any foregoing claim further comprising a sensor and a wireless transmitter of a wireless sensor node electrically connected to the electromechanical generator.
13. A wireless sensor node for a wind turbine blade, the wireless sensor node including a sensor, a wireless transmitter, and an electromechanical generator, the electromechanical generator comprising a movable mass for generating electrical power by reciprocal movement along a path under the action of an alternating gravitational force.
14. A wireless sensor node according to claim 13 wherein the path is linear.
15. A wireless sensor node according to claim 13 or claim 14 wherein the movable mass includes at least one magnet and the electromechanical generator further includes at least one fixed coil.
16. A wireless sensor node according to any one of claims 13 to 15 wherein the movable mass is mounted for reciprocal movement on flexural members fixed to a support.
17. A wireless sensor node according to any one of claims 13 to 16 wherein the electromechanical generator has a motion restrictor which is configured so that the movable mass is constrained against moving under the action of gravity away from ends of the path.
18. A wireless sensor node according to any one of claims 13 to 17 wherein the electromechanical generator further comprises a pair of opposed end members, each located at a respective end of the path, each end member being arranged to apply a resistive force inhibiting the motion of the mass away from the respective end member.
19. A wireless sensor node according to claim 18 wherein the end members apply a magnetic resistive force inhibiting the motion of the mass away from the respective end member.
20. A wireless sensor node according to claim 18 or claim 19 wherein the electromechanical generator has a minimum threshold of a motion initiating force for permitting the motion of the mass away from the respective end member.
21. A wireless sensor node according to claim 20 wherein the minimum threshold of the motion initiating force is within the range of from O.5g to 0.9g, where g is gravitational acceleration.
22. A wind turbine blade having an electromechanical generator mounted thereon for generating electrical power for driving a wireless sensor node, the electromechanical generator comprising a rotary generator fixed to the wind turbine blade, a rotationally movable arm connected to a rotary element of the rotary generator and a mass located on the arm.
23. A wind turbine blade according to claim 22 further comprising a sensor and a wireless transmitter of a wireless sensor node electrically connected to the electromechanical generator.
24. A wireless sensor node for a wind turbine blade, the wireless sensor node including a sensor, a wireless transmitter, and an electromechanical generator, the electromechanical generator comprising a rotary generator, a rotationally movable arm connected to a rotary element of the rotary generator and a mass located on the arm.
25. A method of operating a wireless sensor node for a wind turbine blade, the wireless sensor node including a sensor, a wireless transmitter, and an electromechanical generator, the electromechanical generator comprising a movable mass for generating electrical power by reciprocal movement along a path under the action of an alternating gravitational force, the method comprising moving the mass substantially tangentially during rotation of the wind turbine blade.
26. A method according to claim 25 wherein the path extends substantially orthogonally to the longitudinal direction of the wind turbine blade.
27. A method according to claim 25 or claim 26 wherein the path is linear.
28. A method according to any one of claims 25 to 27 further comprising constraining the movable mass against moving under the action of gravity away from ends of the path during at least a portion of a cycle of rotation of the wind turbine blade.
29. A method according to claim 28 wherein the movable mass is constrained against moving under the action of gravity when the wind turbine blade is at upper and lower regions of the cycle of rotation of the wind turbine blade.
30. A method according to claim 29 wherein the movable mass moves substantially vertically downwardly under the action of gravity when the wind turbine blade is at substantially vertically mid-point regions of the cycle of rotation of the wind turbine blade.
31, A method according to any one of claims 25 to 30 wherein the electromechanical generator further comprises a pair of opposed end members, each located at a respective end of the path, each end member being arranged to apply a resistive force inhibiting the motion of the mass away from the respective end member.
32, A method according to claim 31 wherein the end members apply a magnetic resistive force inhibiting the motion of the mass away from the respective end member.
33. A method according to claim 31 or claim 32 wherein the electromechanical generator has a minimum threshold of a motion initiating force for permitting the motion of the mass away from the respective end member.
34. A method according to claim 33 wherein the minimum threshold of the motion initiating force is within the range of from 0.5g to 0.9g, where g is gravitational acceleration.
35. A method of operating a wireless sensor node for a wind turbine blade, the wireless sensoi' node including a sensor, a wireless transmitter, and an electromechanical generator, the electromechanical generator comprising a rotary generator fixed to the wind turbine blade, a rotationally movable arm connected to a rotary element of the rotary generator and a mass located on the arm, the method comprising rotating the wind turbine blade and the rotary generator applying to the mass on the arm a rotational resistive force against gravitational force.