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Title:
ENERGY HARVESTING BUOY
Document Type and Number:
WIPO Patent Application WO/2018/164583
Kind Code:
A1
Abstract:
Energy harvesting buoy (10) comprising a float (11) and a wave energy converter (20), wherein the wave energy converter (20) comprises a translator (40) provided helically shaped permanent magnets (42), wherein the translator (40) is arranged movable in a sleeve (30) extending vertically in the float (11), and a generator unit (50) fixed in the float (11) comprising a rotor assembly (60) enclosing the translator (40) and at least one stator assembly (70) enclosing the rotor assembly (60), wherein the helically shaped permanent magnets (42) of the translator (40) transfer linear force from a relative linear movement between the float (11) and translator (40) into a torque working on the rotor assembly (60) inducing a current in the stator assembly (70).

Inventors:
WESTBY TOV (NO)
SKOTTE ASBJÖRN (NO)
Application Number:
PCT/NO2018/050065
Publication Date:
September 13, 2018
Filing Date:
March 09, 2018
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
WESTBY TOV (NO)
SKOTTE ASBJOERN (NO)
International Classes:
F03B13/20; H02K49/10; H02K7/06
Foreign References:
US20100109329A12010-05-06
GB2463102A2010-03-10
US8866328B12014-10-21
US20100327595A12010-12-30
CN103199651A2013-07-10
CA2753055A12010-08-26
GB2461792A2010-01-20
Other References:
TECHLER, L: "Could Magnetic Gears Make Wind Turbines Say Goodbye to Mechanical Gearboxes?", MACHINE DESIGN, 14 June 2014 (2014-06-14), XP055560252, Retrieved from the Internet [retrieved on 20180615]
Attorney, Agent or Firm:
CURO AS (NO)
Download PDF:
Claims:
Claims

1. Energy harvesting buoy (10) comprising a float (11) and a wave energy converter (20), characterized in that the wave energy converter (20) comprises a translator (40) provided helically shaped permanent magnets (42), wherein the translator (40) is arranged movable in a sleeve (30) extending vertically in the float (11), and a generator unit (50) fixed in the float (11) comprising a rotor assembly (60) enclosing the translator (40) and at least one stator assembly (70) enclosing the rotor assembly (60), wherein the helically shaped permanent magnets (42) of the translator (40) transfer linear force from a relative linear movement between the float (11) and translator (40) into a torque working on the rotor assembly (60) inducing a current in the stator assembly (70).

2. Energy harvesting buoy (10) according to claim 1, characterized in that the translator (40) is formed by an elongated sleeve (41) and that the helically shaped permanent magnets (42) are arranged at an outer surface thereof and enclosed by a protective sleeve or coating (43).

3. Energy harvesting buoy (10) according to claim 1, characterized in that the generator unit (50) comprising a housing (51) accommodating the rotor assembly (60) rotatably therein and the stator assembly (70) fixed therein.

4. Energy harvesting buoy (10) according to claim 3, characterized in that the rotor assembly (60) is formed by a mainly cylinder-shaped rotator sleeve (61) provided with at least one circumferentially extending set of permanent magnets (62a-b) on an outer surface thereof. 5. Energy harvesting buoy (10) according to claim 3, characterized in that the stator assembly (70) comprises at least one stator (71a-b) arranged enclosing the at least one set of permanent magnets (62a-b) of the rotor assembly (60) in circumferential direction with a gap therebetween.

6. Energy harvesting buoy (10) according to claim 1, characterized in that translator (40) at lower end is arranged to a submerged retaining device (200) exterior of the float (11) arranged for retaining the translator (40) linearly when the float (11) moves due to passing waves.

7. Energy harvesting buoy (10) according to claim 6, characterized in that the submerged device is formed by at least one submerged drag plate (200) which is connected to the translator (40) by means of a shaft (110) extending out of the float (11) and a drag plate connecting rod (201) arranged to lower end of the shaft (110) at one end and the at least one submerged drag plate (200) at the other end.

8. Energy harvesting buoy (10) according to claim 7, characterized in that the retaining device (200) includes a number of drag plates (200) distributed in longitudinal direction of the drag plate connection rod (201).

9. Energy harvesting buoy (10) according to claim 7, characterized in that further it comprises a spring assembly (120) arranged between a seat (122) at upper part of the shaft (110) and lower part of the sleeve (30) extending vertically in the float (11) or an extension (12) of the float (11).

10. Energy harvesting buoy (10) according to claim 6, characterized that a support structure (800) exhibiting an elongated shape extending from the float (11) and down in the water adapted for accommodating the submerged retaining device (200).

11. Energy harvesting buoy (10) according to claim 10, characterized in that the support structure (800) is an elongated cylinder-shaped grid or cylinder (810) of composite or steel.

12. Energy harvesting buoy (10) according to claim 11, characterized in that the elongated cylinder (810) is provided numerous holes or openings (811) allowing water to flow in and out of the cylinder (810).

13. Energy harvesting buoy (10) according to claim 1, characterized in that further comprising a control unit (400) arranged to convert harvested alternating phase current to DC current for storage in an energy storage (300) arranged in the float (11) and/or transfer to shore via cable.

14. Energy harvesting buoy (10) according to claim 13, characterized in that the control unit (400) is provided with a battery management system.

15. Energy harvesting buoy (10) according to claim 13, characterized in that it further is provided with a light tower (500) with a LED marking light (501) powered by the energy storage (300).

16. Energy harvesting buoy (10) according to claim 1, characterized in that it further is provided with anchoring means (700) for arranging the energy harvesting buoy (10) movably to a fixed structure (600).

Description:
Energy harvesting buoy

The present invention is related to an energy harvesting buoy, according to the preamble of claim 1.

The present invention is especially related to an energy harvesting buoy utilizing a translator in the form of a magnetic lead screw for transferring linear force from a relative movement between the translator and a float into a torque working on a rotor assembly of a generator unit for producing electric energy.

Background Many concepts has been proposed for todays wave energy converters, however they almost all suffer from poor efficiency, low shear force or structural problems regarding storm protection etc.

E.g. today, many hours of service is spend on ocean marking lights, for either fish farms or normal boat traffic. The service include change of batteries for powering the LED marking light, which is done by technicians using a service vessel for each buoy. The process of changing batteries is expensive and time consuming why other technologies are investigated.

One of these new technologies is the idea of having a LED marking buoy which is self-powered, which should minimize the requirement for servicing. Until now, the most popular technology for self-powering marking buoys is Photo-Voltaic (PV) panels. However one drawback using PV panels for ocean buoys is problems with salt crystalizing on top of the panels, which decrease the efficiency of the panels dramatically.

Further in polar areas, where there are long periods with polar night where the PV panels will produce any electricity.

Further, the use of PV panels will not be able to produce electricity at night hours.

Further, at tube and research buoys, weather data buoys or similar which are provided with power demanding communication means for transferring data, as well as power demanding, this will require very large batteries to be able to provide the required power, especially at polar areas.

Further, these solutions are not capable of providing sufficient energy that the harvested energy can be used to power other consumers at e.g. fish farms. There is accordingly a need for an energy harvesting buoy which is capable of harvesting energy from waves requiring minimal maintenance, hereunder an energy harvesting buoy having few movable parts.

There is further a need for an energy harvesting buoy reducing the need for re-installation of batteries during the specified lifetime.

There is a need for an energy harvesting buoy having higher efficiency than prior art solutions.

It is further a need for providing an energy harvesting buoy capable of withstanding forces from big waves passing the energy harvesting buoy without damaging parts of the wave energy converter.

Objects

The main object of the present invention is to provide an energy harvesting buoy partly or entirely solving the above mentioned drawbacks of prior art solutions and mentioned needs.

An object of the present invention is to provide an energy harvesting buoy having low installation and operating costs, as well as requiring minimal maintenance.

An object of the present invention is to provide an energy harvesting buoy arranged to withstand big waves.

It is further an object of the present invention to provide an energy harvesting buoy having few movable parts.

An object of the present invention is to provide an energy harvesting buoy where there is no contact between force transferring parts.

It is an object of the present invention to provide an energy harvesting buoy where there is minimal friction between moving parts.

An object of the present invention is to provide an energy harvesting buoy providing higher efficiency compared to prior art solutions.

An object of the present invention is to provide an energy harvesting buoy which does not require a connection to the seabed for harvesting energy from a passing wave. An object of the present invention is to provide an energy harvesting buoy which does not include polluting fluids, such as hydraulic oil or similar, which can constitute a risk for the environment at breakdown.

Further objects of the present invention will appear from the following description, claims and attached drawings.

The invention

An energy harvesting buoy according to the present invention is disclosed in claim 1. Preferable features of the energy harvesting buoy are disclosed in the dependent claims. The present invention provides an energy harvesting buoy comprising a float having positive buoyancy and a wave energy converter which converts linear movement of the buoy due to passing waves into electricity. According to the present invention a core component in the wave energy converter is a translator in the form of a magnetic lead screw and a generator unit.

According to the present invention the wave energy converter is located approximately in the center of a float, and arranged to convert the slow linear movement of the waves into a fast rotating movement of a rotor assembly in the generator unit, which makes it possible to extract energy using a standard rotary generator.

According to the present invention the wave energy converter comprises a translator arranged movable in a vertically arranged sleeve in the float, which translator is provided with helically shaped and radially magnetized permanent magnets. Accordingly, the translator exhibits a magnetic thread instead of a mechanical thread.

The generator unit of an energy harvesting buoy according to the present invention is formed by a rotor assembly and a stator assembly accommodated in a housing fixed in relation to the movement of the translator. The rotor assembly is formed by a rotor sleeve enclosing the translator and further arranged rotatably in the housing, which rotor sleeve is provided with at least one set of permanent magnets arranged in circumferential direction thereof. Accordingly, the rotor assembly constitutes a rotor for both the translator and generator unit. The stator assembly is formed by at least one stator formed by coils and back iron arranged to enclose the set(s) of permanent magnets of the rotor assembly with a gap therebeteween.

The mentioned translator is further arranged to a submerged retaining device exterior of the float which enables the translator to be retained linearly when the buoy moves due to passing waves. Accordingly, the submerged retaining device tends to keep the translator stationary while the float moves due to an incoming wave. In other words the submerged retaining device provides a counterweight for the translator. The submerged retaining device can e.g. be formed by at least one submerged drag plate or similar, but the translator can also be anchored to the seabed by means of a wire. The great advantage with using a submerged drag plate compared with an anchoring wire to the seabed is that there will be no need for adjusting for low tide and high tide.

According to a further embodiment of the energy harvesting buoy according to the present invention it further comprises a support structure exhibiting an elongated shape extending from the float and down in the water adapted for accommodating the submerged retaining device. According to the present invention the support structure is an elongated cylinder-shaped grid or cylinder of composite or steel. In the case the support structure is an elongated cylinder, the elongated cylinder is provided numerous holes or openings allowing water to flow in and out of the cylinder.

The energy harvesting buoy according to the present invention is able to produce energy by that the relative movement between buoy and translator results in rotation of the rotor assembly of the generator unit. When the rotor assembly of the generator unit rotates, the permanent magnets of the rotor assembly induce a current in the generator assembly resulting in an AC current which is feed to a control unit.

Accordingly, relative linear movement between the buoy and translator results in rotation of the rotor assembly with a speed determined by the lead of the translator and the input linear velocity. In the present invention the translator uses helically shaped permanent magnets in order to transfer the linear force of the translator/buoy into a torque working on the rotor assembly.

The control unit for an energy harvesting buoy according to the present invention can be arranged for rectifying the generated current by that it is provided with rectifying means, such as an AC frequency converter, and further control the damping profile of the generator assembly. According to the present invention the rectified DC current can be transferred to an energy storage arranged in the float or transferred to shore via a cable. In an alternative embodiment the generated AC current is transferred to shore via a cable and further processes at shore side, such as rectified.

A great advantage with the present invention is that by using permanent magnets to transfer the linear force allows the wave energy converter slip one or more pole pairs if the force applied to the translator exceeds the force of the translator is designed for, i.e. the maximum force the translator is capable of transferring. This is a considerable advantage over prior art mechanical geared systems, as any big waves will not damage the translator and/or the generator unit of the wave energy converter. Accordingly, in the present invention will be capable of withstanding high forces from big waves due to this built-in force protection. A further advantage with the present invention is that by using a magnetic lead screw for transferring linear forces to torque on the rotor assembly there are not contact between the force transferring parts, thereby minimizing friction and increasing efficiency of the energy harvesting buoy.

It is further an advantage with the present invention, compared to prior art solutions, that the energy harvesting buoy according to the present invention does not include polluting fluids, such as hydraulic oil or similar, which can constitute a risk for the environment at breakdown. The energy harvesting buoy according to the present invention only contains magnets and electronics which do not constitute a danger for the environment.

Further preferable features and advantageous details of the present invention will appear from the following example description, claims and attached drawings.

Example

The present invention will below be described in further detail with references to the attached drawings, where: Fig. 1 is a principle drawing of an energy harvesting buoy according to the present invention, Fig. 2 is a principle drawing showing details of translator and generator unit, Fig. 3 is an exploded principle drawing of a generator unit 50 according to the present invention, Fig. 4 is a principle drawing of an energy harvesting buoy according to an alternative embodiment,

Fig. 5 is a principle drawing of an energy harvesting buoy according to another alternative embodiment, Fig. 6a-b are principle drawings of an energy harvesting buoy according to another alternative embodiment, and

Fig. 7 is a principle drawing of a number of energy harvesting buoys according to the present invention forming a plant or farm.

Reference is now made to Figure 1 which is a principle drawing of an energy harvesting buoy 10 according to the present invention. The energy harvesting buoy 10 is formed by a float 11 having positive buoyancy such that it floats at the water surface. The energy harvesting buoy 10 according to the present invention further includes a wave energy converter 20 that is based on a magnetic lead screw (MLS) as a core component. The wave energy converter 20 according to the present invention consist of a translator 40 in the form of a magnetic lead screw and a generator unit 50, wherein the translator 40 is arranged movable in a sleeve 30 extending vertically in the float 11, and wherein the generator unit 50 is arranged in a fixed position in the sleeve 30.

Reference is also made to Figure 2 which is a cross-sectional principle drawing showing details of the translator 40 and generator unit 50. The translator 40 according to the present invention is formed by an elongated translator sleeve 41, which at outer surface thereof is provided with helically shaped and radially magnetized permanent magnets 42 which is enclosed by a protective sleeve or coating 43. The magnetic orientation is such that there is provided a magnetic north and south pole on the translator sleeve 41. The permanent magnets 42 are preferably neodymium magnets, preferably sintered NDFeB magnets. In the shown example there are formed two magnet threads with a lead of e.g. at least 10 mm/revolution of the two magnetic threads, and e.g. 9 magnets per revolution. The dimension and shape of the magnets will be dependent of desired properties and is not limited to the examples given above. In the shown example the magnetizing direction will be upwards. In an alternative embodiment the translator 40 is provide with one thread of magnets. Reference is further also made Figure 3 showing an exploded principle drawing of a generator unit 50 according to the present invention adapted to be arranged in the float 11.

The generator unit 50 is formed by a housing 51 accommodating a rotor assembly 60 and a stator assembly 70. The rotor assembly 60 according to the present invention formed by a mainly cylinder-shaped rotator sleeve 61 exhibiting an inner diameter corresponding to the outer diameter of a inner sealing tube 90, which is arranged for accommodating the translator 40. The rotor sleeve 61 in the shown example is provided with two circumferentially extending sets of permanent magnets 62a- b at an outer surface thereof, spaced apart in the longitudinal direction of the sleeve 61. In an alternative embodiment the rotor sleeve 61 can be provided with only one set of permanent magnets.

The generator unit 50 further comprises a stator assembly 70 formed by two stators 71a-b formed by windings 72 and back iron 73 spaced apart in longitudinal direction of the generator unit 50 by means of a stator distance spacer ring 74 such that the two stators 71a-b are arranged over respective sets of permanent magnets 62a-b of the rotor assembly 60 and enclose these in circumferential direction with a gap therebetween. The stator assembly 70 can further comprise upper or lower distance rings 75 for positioning the stator assembly 70 and fixation of the stator assembly 70 in relation to the generator housing 51. In an alternative embodiment where the rotor assembly only is provided with one sets of permanent magnets, the stator assembly only includes one stator.

The rotor assembly 60 is further arranged rotatable in a generator housing 51 by means of ball bearings 80a-b and ball bearing end shield 81a-b arranged at upper and lower side thereof, respectively.

The generator housing 51 is further provided with sealing means at upper and lower side thereof, e.g. in the form of a sealing plate 91 arranged to the inner sealing tube 90 and a sealing plate 92 arranged to the ball bearing end shield 81a at lower side.

To the upper and lower ends of the generator unit 50 is further arranged linear bearings 100 and linear bearing housing 101, adapted for accommodation of the translator 40.

Accordingly, the components of the generator unit 50 are securely encapsulated in the housing 51 protecting the components of the generator unit 50 from water. By means of the above described embodiment it is possible to seal the generator unit 50 without using rotary or linear seals, which for a given period would wear down. In the present invention all seals are stationary, which means that the life-time is improved significant.

Reference is again made to Figure 1. The translator 40 is further at the lower end arranged to a shaft 110 extending out of the float 11 for connection to a submerged retaining device 200 exterior of the float 11 in the form of submerged drag plate via a drag plate connecting rod 201. The submerged drag plate 200 is preferable from an upper surface thereof provided with anti- rotating fins 202 arranged in connection with the drag plate connecting rod 201. The submerged drag plate 200 is e.g. a mainly circular disk providing a counterweight for the translator 40, such that translator 40 is retained linearly in the water when the float 11 moves due to passing waves.

Accordingly, relative linear movement between the float 11 and translator 40 will result in movement of the translator 40 in relation to the generator unit 50, which by means of the interaction of the helically shaped permanent magnets 42 of the translator 40 and permanent magnets 62a-b of the rotor assembly 60 will transfer the linear force of the translator 40 into a torque working on the rotor assembly 60 of the generator unit 50, inducing a current in the stator assembly 70.

In connection with the shaft 110 is preferably arranged a spring assembly 120, comprising at least one spring 121, arranged between a seat 122 at upper part of the shaft 110 and lower part of the sleeve 30 extending vertically in the float 11. If required the float 11 can be provided with a cylinder-shaped extension 12 extending from the sleeve 30 to provide the required stroke length. In such cases the mentioned spring assembly 120 can be arranged at lower part of this extension 12, as e.g. shown in Figure 1.

The spring assembly 120 will ensure that the translator 40 moves to zero (initial) position. The spring assembly 120 will only be active at half of the length of the stroke of submerged drag plate 200 downwards until the spring assembly 120 counteract this force. This ensures that the translator 40 is always located at the center of the full stroke which enables the energy harvesting buoy 10 to harvest energy in both up and down movement when a wave hits the energy harvesting buoy 10.

The energy harvesting buoy 10 can further be provided with an energy storage 300 in the form of one or more batteries and/or be arranged for transferring harvested energy to shore by means by means of a cable as AC or DC voltage/current. The energy harvesting buoy 10 is preferably provided with a control unit 400 arranged to convert the harvested alternating phase current to DC current for storage in the energy storage 300 and/or for transfer to shore via a cable. For rectifying the AC current to DC current the control unit 400 can e.g. be provided with an AC frequency converter. The control unit 400 will further typically be provided with means and/or software for controlling the damping profile of the generator assembly 50. The control unit 400 will in an embodiment where the energy harvesting buoy 10 is provided with an energy storage 300 preferably be provided with a battery management system for controlling the battery charge current.

For monitoring the electrical position of the rotor assembly 50, the energy harvesting buoy 10 can be provided with one or more hall effect sensors 401, as shown in Figure 2.

The energy harvesting buoy 10 can further be provided with a light tower 500 with a LED marking light 501 powered by the energy storage 300. Marking light 501 will usually be required for buoys 10 arranged in sea.

The energy harvesting buoy 10 according to the present invention will typically be movably anchored to a fixed structure 600, such as a pram of a quay, fish farm structure, or similar by means of anchoring means 700, e.g. as shown in Figure 1. In the shown example the anchoring means 700 comprises a pair of connecting arms 701a-b extending between the fixed structure 600 and the float 11, wherein the arms 701a-b are rotatably connected to the float 11 by means of diametrically couplings 702a-b at one side, respectively, and to couplings 703a-b spaced apart on the fixed structure 600, respectively. For reinforcement of the anchoring structure the arms 701a- b in connection with the couplings 703a-b are connected by a rod 704.

By means of the anchoring means 700 the energy harvesting buoy 10 will be held in position in the sea, as well as the energy harvesting buoy 10 can be tilted up from the sea and stored on the fixed structure 600 in case of storm or harsh weather conditions which otherwise could risk damaging the energy harvesting buoy 10. Especially in areas where ice is a problem this would be appreciated.

Reference is now made to Figure 4 showing an alternative embodiment of the energy harvesting buoy 10 according to the present invention, where the energy harvesting buoy 10 comprises a support structure 800 for the submerged drag plate 200. The support structure 800 is formed by an elongated cylinder-shaped grid of composite or steel where the submerged drag plate 200 is arranged movable in longitudinal direction of the elongated cylinder-shaped grid, and wherein the support structure 800 has an extension in longitudinal direction thereof having a longer extension than the stroke of the submerged drag plate 200. The support structure 800 can e.g. be fixed to the couplings 702a-b of the float 11 or by other suitable means attached to the float 11. In this way the support structure 800 will increase the structural strength of the submerged drag plate 200 structure and protect the submerged drag plate structure 200 from underwater forces or objects in the water which could bend and damage the submerged drag plate 200 structure. It will further ensure a stable longitudinal structure for the submerged drag plate 200 structure.

Reference is now made to Figure 5 showing another embodiment of the submerged drag plate 200 structure, where the energy harvesting buoy 10 is provided with a number of submerged drag plates 200 distributed along the longitudinal direction of the drag plate connecting rod 201. The submerged drag plates 200 can further exhibit different shape and size.

Reference is now made to Figures 6a and 6b showing further embodiments of the energy harvesting buoy 10 according to the present invention. In the embodiments shown in Figures 6a-b the support structure 800 for the submerged drag plate structure 200 is formed by a mainly elongated cylinder 810 of composite or steel provided with numerous holes or openings 811 for allowing water to flow in and out of the cylinder 810. The submerged drag plates 200 in this embodiment are further adapted to be positioned inside the elongated cylinder 810. In the shown embodiment in Figure 6b is further shown an embodiment where the submerged drag plates 200 exhibit a different size.

By means of that the elongated cylinder 810 is provided with a sufficient number of holes 811 and/or with sufficient size, the required retaining force is achieved. The elongated cylinder 810 can further be integrated into the float 11, e.g. by a casting process casting the float 11 and cylinder 810 as one unit.

The above mentioned embodiments can be combined to alternative embodiments within the scope of the attached claims. A typical area of use of the present invention are as a ocean marking light, for either fish farms or normal boat traffic, where the energy harvesting buoy 10 will be self-powered with minimized requirement for servicing.

The energy harvesting buoy 10 according to the present invention can also be positioned and connected to other buoys, such as research buoys, for powering them. Another typical area of use is using the energy harvesting buoy 10 as energy harvesting units for fish farms or in shore close areas where a number of such energy harvesting buoys 10, as shown in Figure 7, can provide a small scale amount of environmentally friendly energy for e.g. charging of electrical vehicles or boats or be a supplement for ordinary energy production. The energy harvesting buoy 10 according to the present invention will also be usable in remote areas where no infrastructure is built to provide enough energy for a small community, such as island communities, where the solution shown in Figure 7 can be used.