A rocking rotor for use in a wave power plant

Abstract

The present invention relates to a rocking rotor for use in a wave power plant, the rocking rotor comprising a buoyant body being rotatably connected to a frame construction, the buoyant body being interconnected to the frame construction via a first rotational joint, the buoyant body being configured to, in response to an incoming wave, perform a rocking motion about a first rotational axis, an energy extractor having a first end, a second end and a frame-side rotational center, the energy extractor having a first connector at the first end and a second connector at the frame-side rotational center, wherein the first connector rotatably connects the first end of the energy extractor to the buoyant body at a first position via a third rotational joint, and wherein the second connector rotatably interconnects the frame-side rotational center of the energy extractor to the frame construction via a second rotational joint, the frame-side rotational center of the energy extractor being configured to rotate about a second rotational axis.

Description

[0001] A ROCKING ROTOR FOR USE IN A WAVE POWER PLANT

[0002] Technical field

[0003] The present invention relates to a rocking rotor for use in a wave power plant, a wave power plant using said rocking rotor, and use of a rocking rotor in a wave power plant.

[0004] Background

[0005] Extracting the energy of waves continue to be a field with much development as waves are more predictable and reliable than solar or wind energy, and they could power hard-to-reach locations, like coastal communities and remote islands. Wave power plants are realized in various ways, with some wave power plants utilizing rocking rotors as the method of energy extraction. Rocking rotors provide an alternating movement substantially in a vertical direction as a response to impacting waves. The vertical movement is transformed into a rotational movement when the rocking rotor is mounted to a frame placed in a location horizontally displaced with respect to the centre of gravity of the rocking rotor.

[0006] Wave power plants intended for off-shore use face the problem that they need to be able to cope with very harsh marine conditions, i.e. a salty environment, that will increase corrosion, and weather conditions that challenges engineering solutions, through extreme temperature differences and extreme mechanical stress on the construction. Further, the off-shore location may make regular service and maintenance difficult and costly. Yet further, in order to obtain an acceptable energy harvest, relative to the investment of locating and maintaining the wave power plant in such hostile environments, wave power plants will need to be rather large structures. As the structure rise in size, larger requirements for the drive train of the wave power plant are introduced. The drive trains available in the art for large wave power plants are either complex and require intensive maintenance or labour when exchanging components, or are inefficient and introduces losses to the energy harvest. Thus, there is need for a simple, sturdy, stable, and easily replaceable solution for energy harvesting on such wave energy plants in order to maintain scalability in large dimensions. Additionally, the energy harvesting mechanism needs to be as efficient as possible to ensure as high yield as possible for the wave power plant.

[0007] Summary

[0008] In view of the above, it is an object of the present invention to provide an improved rocking rotor for use in a wave power plant, a wave power plant comprising one or more of said rocking rotors, and use of said rocking rotor in a wave power plant.

[0009] According to a first aspect, a rocking rotor for use in a wave power plant is provided. The rocking rotor comprises a buoyant body being rotatably connected to a frame construction, the buoyant body being interconnected to the frame construction via a first rotational joint, the buoyant body being configured to, in response to an incoming wave, perform a rocking motion about a first rotational axis. The rocking rotor comprises an energy extractor having a first end, a second end and a frameside rotational center. The energy extractor may have a first connector at the first end and a second connector at the frame-side rotational center. The first connector may rotatably connect the first end of the energy extractor to the buoyant body at a first position via a third rotational joint. The second connector may rotatably interconnect the frame-side rotational center of the energy extractor to the frame construction via a second rotational joint. The frame-side rotational center being configured to rotate about a second rotational axis. The first rotational axis and the second rotational axis may be different rotational axes.

[0010] The energy extractor may rotatably interconnect the frame construction and the buoyant body.

[0011] It is an advantage to provide an energy extractor having the first connector at the first end and the second connector at the frame-side rotational center being configured so that the first connector rotatably interconnects the first end of the energy extractor to the buoyant body at the first position via a third rotational joint and the second connector rotatably interconnects the frame-side rotational center of the energy extractor to the frame construction via the second rotational joint in that the energy extractor may translate the rotational movement into linear movement for harvesting energy from the rocking rotor, replacing the known drivetrain solutions, alleviating at least some of the disadvantages of the drivetrain solutions, particularly as the energy extractor may be mechanically less complex.

[0012] It may be an advantage to have the first connector rotatably connect the first end of the energy extractor to the buoyant body at a first position via a third rotational joint, in that service access for the energy extractor is available above sea level. A defect energy extractor may therefore be easily reachable for replacement or repair on site.

[0013] The rocking rotor for use in a wave power plant may be during operation, have a rotational movement in relation to a frame construction of the wave power plant. The rocking rotor may be rotating in a rocking manner, so that it rotates in a first direction and a second direction during operation. The rocking rotor will thus typically not operate by rotating in one direction only. The rocking rotor may be rotating about the first rotational axis.

[0014] The buoyant body being a part of the rocking rotor is configured to be buoyant when immersed in water. The buoyancy of the buoyant body may be achieved in various ways available to the skilled person, such as by having a hollow body filled with a buoyancy material. The buoyancy material may be a material with a density lower than the water the buoyant body is configured to be immersed in. The buoyancy material may for example be a gas, such as air, it may be rubber, plastic, Styrofoam, etc., or any combination of the above. The buoyancy material may fill the hollow body in full or in part. The buoyancy material may be a single material. The buoyancy material may comprise a plurality of materials. The buoyant body may additionally comprise a ballast. The ballast may comprise one or more ballast materials having a similar or higher density than the density of the water. The ballast material may be a single material. The ballast material may comprise a plurality of materials. The ballast material may comprise water, concrete, stone, iron, etc. The buoyant body is interconnected to the frame construction via the first rotational joint, the buoyant body being configured to rotate about a first rotational axis. The first rotational joint may be a mechanical connection which enables the buoyant body of the rocking rotor to rotate relative to the frame construction. The first rotational joint may be any type of mechanical connection which allow a rotary movement. Examples of such mechanical joints may be revolute joints, pin joints, hinge joints, pivot joints, cylindrical joints, but may also be more advanced joints, such as ball joints, or bearings, such as ball bearings.

[0015] The buoyant body of the rocking rotor facilitates the rotation of the rocking rotor. The buoyant body, when positioned in the operational position in a water body, rocks around the first rotational axis in response to incoming waves.

[0016] In some embodiments, the width of the buoyant body is between 1 meter and 10 meter, such as between 2 meter and 5 meter, such as between 3 meter and 4,5 meter, such as at least 2 meter, such as at least 3 meter, such as 4,5 meter in diameter.

[0017] The energy extractor may be configured for enabling conversion of wave energy to another form, such as electrical energy, hydraulic energy, air pressure, or any other suitable form which may be stored, consumed or converted into an energy form for consumption or distribution.

[0018] The energy extractor may have a first connector at the first end and a second connector at the frame-side rotational center. The first connector may form an interface between the buoyant body and the energy extractor. The first connector may be any component suitable for rotatably coupling the energy extractor to the buoyant body. The second connector may form an interface between the frame structure and the energy extractor. The second connector may be any component suitable for coupling the energy extractor to the second rotational joint. The first connector and the second connector may be any connector, such as an eye connector, such as any connector suitable to connect to any one of revolute joints, pin joints, pivot joints, hinge joints, cylindrical joints, such as configured to connect to any one of ball joints, bearings, such as ball bearings, etc. The first connector and / or the second connector may form a part of the first rotational joint and the second rotational joint, respectively.

[0019] The energy extractor may rotatably connect the first end of the energy extractor to a first position on the buoyant body via the third rotational joint. The first position is a fixed position on the buoyant body.

[0020] In some embodiments, the length of the energy extractor corresponds to the size of the buoyant body. The length of the energy extractor may be between half the width of the buoyant body and the width of the buoyant body, such as between 1 meter and 10 meter, such as between 2 meter and 5 meter, such as between 3 meter and 4,5 meter, such as at least 2 meter, such as at least 3 meter, such as 2 meter.

[0021] The frame-side rotational center may be the frame-side center of rotation of the energy extractor. The second connector is arranged at the frame-side rotational center of the energy extractor. The frame-side rotational center may be positioned along the length of the energy extractor. The frame-side rotational center may be positioned at the second end of the energy extractor. The frame-side rotational center may be positioned closer to the first rotational joint, and thus closer to the frame-side, than to the third rotational joint.

[0022] The second rotational joint may be a mechanical connection which enables the energy extractor of the rocking rotor to rotate around the frame construction where the second rotational joint is arranged. The second rotational joint may be any type of mechanical connection which allow a rotary movement. Examples of such mechanical joints may be revolute joints, pin joints, hinge joints, pivot joints, cylindrical joints, but may also be more advanced joints, such as ball joints, or bearings, such as ball bearings.

[0023] The first end of the energy extractor is configured to rotate about a third rotational axis, and the frame-side rotational center of the energy extractor is configured to rotate about a second rotational axis, whereby a movement, such as a telescopic movement, of the energy extractor is obtained.

[0024] Having a first connector rotatably connecting the first end of the energy extractor to the first position of the buoyant body and the second connector rotatably connecting the energy connector to the frame construction facilitates a combined linear and rotational movement of the energy extractor driven by the buoyant body.

[0025] Facilitating a rotational movement of the energy extractor driven by the buoyant body may improve the design possibilities of the energy extractor, so the energy extractor may be designed to achieve an increased energy conversion.

[0026] The second end of the energy extractor may thus rotate about the second rotational axis different from the first rotational axis of the buoyant body which the first connector of the energy extractor is connected to, allows the first end of the energy extractor to follow the first rotational axis while the second connector of the energy extractor is having a frame-side rotational center at the second rotational axis. The claimed configuration of the energy extractor enables the energy extractor to have a change of length during rotation. This change of length may be understood as a linear displacement of the energy extractor, which may be harnessed in order to produce energy, such as electrical energy, such as piezo electric energy, or magnetic energy, or inducted energy, but may also be harnessed to produce hydraulic energy or any other type of energy achievable by a medium with a linear displacement. The first end comprising the first connector may be configured to move independent of the movement of the frame-side rotational center, which may allow the linear displacement of the exergy extractor to be a linear motion of the first end compared to the remainder of the energy extractor.

[0027] In an embodiment of the invention, the frame-side rotational center is arranged at the second end of the energy extractor. The second end of the energy extractor may be the end of the energy extractor closest to the first rotational joint. The first end of the energy extractor may be the end furthest away from the first rotational joint. Arranging the frame-side rotational center at the second end of the energy extractor allows a full range of motion of the energy extractor to be between the first connector and the second connector.

[0028] In an embodiment of the invention, a displacement between the first rotational joint and the second rotational joint is smaller than a distance between the first connector and the first rotational joint.

[0029] In an embodiment of the invention, the first rotational axis and the second rotational axis are parallel. This may allow the energy extractor to receive a larger portion of force in a direction between the first connector and the second connector. Having a larger portion of the force in a direction between the first connector and the second connector, such as the total amount of force, allows for an increased energy yield, as the larger portion generates a linear displacement in the same direction.

[0030] If, as an example, the first rotational axis and the second rotational axis were not parallel, a portion of the force applied on the energy extractor may be applied in a direction different from the direction between the first connector and the second connector, which could result in an increased friction loss of the energy extractor during operation of the rocking rotor.

[0031] In an embodiment of the invention, a first distance from the third rotational joint to the second rotational joint is different from a second distance from the third rotational joint to the first rotational joint.

[0032] In an embodiment of the invention, the first distance is smaller than the second distance. Hereby, the energy extractor may rotate within an area protected by the buoyant body and the frame construction. The buoyant body is configured for receiving continuous impacts from incoming waves, as is also the case with the frame construction. Having the energy extractor arranged and rotating within the beforementioned area may minimize the impact of incoming waves on the energy extractor. Furthermore, having the energy extractor arranged and rotating within the beforementioned area may minimize the risk of foreign objects, such as drifting objects, including drift wood or a loose container, hitting the energy extractor. Therefore, the design of the energy extractor may be less influenced by the risk of impact.

[0033] The energy extractor may comprise two members. The two members may be joined by a prismatic joint. The energy extractor comprising two members may be configured to perform a telescopic movement.

[0034] The energy extractor may comprise a hollow body, the hollow body being connected to the second connector, and a piston arranged in the hollow body and being connected to the first connector. The energy extractor may thus have a high- pressure side port and low-pressure side port. The hollow body may be connected to the frame structure and the piston may be connected to the buoyant body, or vice versa.

[0035] In an embodiment of the invention, the energy extractor is a hydraulic cylinder.

[0036] During operation, the rocking motion of the rocking rotor caused by the rising and falling motion of incoming waves, may extend and retract the piston.

[0037] In an embodiment of the invention, the energy extractor further comprises an energy conservator, such as for example an energy conservator configured for storing and releasing energy which may assist the rotation of the rocking rotor. An example of such energy conservator may be a spring, a pneumatic cylinder, a hydraulic cylinder, a cylinder comprising a piston with a magnet with a first magnetic field direction and a hollow body comprising a magnet with a second magnetic field direction, wherein the first- and second magnetic field directions of the respective magnets are different, such as 180 degrees different, such as in opposite directions, but may also be so as the first magnetic field direction and the second magnetic field direction of the respective magnets are the same, or any combination thereof with a third magnet comprising a third magnetic field direction. The energy conservator may for example provide a boosting force in the rotational direction of the rocking rotor, which may help overcome initial inertia of the rocking rotor, such as a mass inertia of the buoyant body. The energy conservator may be a spring.

[0038] The energy conservator may be a pneumatic cylinder.

[0039] In an embodiment of the invention, the energy conservator is configured to be pretensioned. By pre-tensioning the energy conservator, the boosting force may be controlled and configured. By configuring the boosting force, a customized setup can be implemented for each individual site in which the rocking rotor is installed, e.g. in view of the wave pattern in a particular site.

[0040] In an embodiment of the invention, the rocking rotor, in its operational position being immersed in water, has an equilibrium state, in which equilibrium state the first rotational joint, the second rotational joint and the third rotational joint are aligned along an equilibrium axis.

[0041] The equilibrium state may be a resting position for the rocking rotor. For example, so that the rocking rotor immersed in still water will not be rotating out of the equilibrium state. The equilibrium state may for example be understood as the situation wherein the center of gravity and the center of buoyancy of the rocking rotor are on a same vertical line perpendicular to the water in which the rocking rotor is immersed.

[0042] The center of gravity may be adjusted by the use of ballasts in or on the buoyant body of the rocking rotor.

[0043] It may be an advantage to have an equilibrium state in which the first rotational joint, the second rotational joint and the third rotational joint are aligned along an equilibrium axis, in that the energy extractor may generate an equal amount of energy regardless of which direction the rocking rotor moves away from the equilibrium axis.

[0044] It may be an advantage to have an equilibrium state in which the first rotational joint, the second rotational joint and the third rotational joint are aligned along an equilibrium axis, in that a length of the energy extractor may be reduced.

[0045] It may be an advantage to have an equilibrium state in which the first rotational joint, the second rotational joint and the third rotational joint are aligned along an equilibrium axis, in that such a configuration may allow the energy extractor to operate both in a downstroke and upstroke rotation of the rocking rotor.

[0046] It may be an advantage to have an equilibrium state in which the first rotational joint, the second rotational joint and the third rotational joint are aligned along an equilibrium axis, in that the linear movement of the energy extractor may be reversed when passing the equilibrium axis during the rocking motion. The energy extractor may be extended at both sides of the equilibrium axis.

[0047] It may be an advantage to have an equilibrium state in which the first rotational joint, the second rotational joint and the third rotational joint are aligned along an equilibrium axis, and wherein the energy extractor has a minimum length in the equilibrium state.

[0048] In some embodiments, the energy extractor is configured so as to have a minimum length in the equilibrium state, wherein the energy extractor is configured to be extended when the rocking rotor is moved out the equilibrium state.

[0049] The buoyant body may have any shape being suitable for performing a rocking motion when being positioned partly sub-merged in water, such as when being immersed in water in the operational position. The buoyant body may have an egglike shape with a pointed top, the buoyant body may have a triangular shape, having a pointed top. For example, the buoyant body may have a triangular shape having two convex sides and one concave side, the two convex sides meeting in a pointed top. The concave side being configured to be submerged in water in an equilibrium position of the rocking rotor, when the rocking rotor is positioned in its operational position immersed in water. The rocking rotor may be configured so that the concave side of the shell of the buoyant body may tangentially touch the water surface, when the rocking rotor is placed in the operational position in the water.

[0050] In some embodiments, the buoyant body is configured so that an axis through the pointed top and the first rotational joint will form an angle below 90 degrees, such as between 30 degrees and 70 degrees, such as between 40 degrees and 50 degrees, such as an angle of 45 degrees, with respect to a horizontal surface of the water (when quiet) in which the rocking rotor is configured to be immersed, when the rocking rotor is in the equilibrium position or state.

[0051] In an embodiment of the invention, the energy conservator is configured to be pretensioned to have a maximum tension in the equilibrium state. Hereby, the release of the boosting force may be facilitated in both the downstroke and upstroke rotation of the rocking rotor.

[0052] In an embodiment of the invention, the rocking rotor is configured to, in response to an incoming wave, perform a rocking motion about the first rotational axis by moving in a first direction away from the equilibrium, moving in a second direction back through the equilibrium state and away from the equilibrium state in the second direction.

[0053] According to a second aspect a wave power plant is provided. The wave power plant comprises a rocking rotor according to the first aspect and any embodiments related thereto and a pressure circuit, wherein the pressure circuit is connected the energy extractor.

[0054] The pressure circuit and said pressure circuit connected to the energy extractor, may enable the energy extractor to convert the linear displacement of the energy extractor during rotation of the rocking rotor to a flow of a medium in the pressure circuit. The medium in the pressure circuit may be a fluid, such as water or oil, such as hydraulic oil, but may also be air.

[0055] In an embodiment of the invention, the rocking rotor is a rocking rotor according to any one of the embodiments related to the first aspect comprising an energy extractor, wherein the energy extractor is further connected to the pressure circuit via the high-pressure side port and the low-pressure side port, wherein the high- pressure side port is connected to a high-pressure side of the pressure circuit and the low-pressure side port is connected to a low-pressure side port of the pressure circuit.

[0056] Having a pressure circuit and having said pressure circuit connected to the high- and low-pressure side port of the energy extractor, enables the pressure of the medium of the pressure circuit to be controlled by the energy extractor. The high- and low- pressure side port of the energy extractor may be arranged at fixed positions on either side of a piston of the energy extractor.

[0057] It may be an advantage of having a high- and low-pressure side port of the energy extractor arranged at fixed positions on either side of a piston of the energy extractor, such as the first end for the high-pressure side port and the second end for the low-pressure side port, as this may enable the use of a pressure circuit designed for a uniform flow direction. The uniform flow direction may be facilitated by the energy extractor without the need for a switching system that switches the flow direction of the medium in the pressure circuit during rotation. This in turn may lower the overall complexity of the wave power plant.

[0058] The position of the high-pressure side port and the second end for the low-pressure side port may also be switched depending on a rotational direction of the rocking rotor, that is depending on the direction in which the rocking rotor rotates. As an example, the high-pressure side port may be arranged at the first end of the energy extractor and the low-pressure side port may be arranged at the second end of the energy extractor as long as the energy extractor is extended during rotation, and switch locations when the energy extractor is compressed during rotation. It may also be so as the low-pressure side port may be arranged at the first end of the energy extractor and the high-pressure side port may be arranged at the second end of the energy extractor as long as the energy extractor is extended during rotation, and switch locations when the energy extractor is compressed during rotation.

[0059] The pressure circuit may comprise a valve station. The valve station may be controlled based on the rotational direction of the rocking rotor. By controlling a valve station of the wave power plant based on the rotational direction of a rocking rotor connected to said wave power plant, an increased flexibility of the pressure system may be facilitated. Hereby, the pressure differences inside the pressure circuit may be improved.

[0060] The valve station may be configured to switch between the high-pressure side and the low-pressure side for each high-pressure side port and low-pressure side port based on the rotational direction of the rocking rotor. By switching between the high-pressure side and the low-pressure side for each high-pressure side port and low-pressure side port based on the rotational direction of the rocking rotor, an improved pressure distribution of the pressure circuit may be facilitated, as the switching of the high-pressure side and low-pressure side allows the rocking rotor to rotate towards the high-pressure side of the pressure circuit during multiple stages of operation.

[0061] Switching the position of the high-pressure side port and low-pressure side port depending on the rotational position of the rocking rotor allows for an increased energy yield from the rocking rotor.

[0062] In an embodiment of the invention, the pressure circuit further comprises a one-way valve configured for maintaining a flow direction of the pressure circuit. The oneway valve may be part of a valve station comprising at least the one-way valve and at least one additional controllable valve.

[0063] The pressure circuit comprising a one-way valve configured for maintaining a flow direction of the pressure circuit may allow for maintaining a same flow direction of the medium in the pressure circuit. Furthermore, having a pressure circuit comprising a one-way valve configured for maintaining a same flow direction of the pressure circuit may limit backflow of the medium in the pressure circuit during operation. Additionally, having a uniform flow direction of the pressure circuit, or limiting backflow in the pressure circuit, may allow for an efficient pressure circuit design of low complexity.

[0064] In an embodiment of the invention, the high-pressure side port is arranged in the first end of the energy extractor and the low-pressure side port is arranged in the second end of the energy extractor.

[0065] In an embodiment of the invention, the wave power plant further comprises one or more additional rocking rotors according to the first aspect and any embodiments related thereon, wherein the energy extractor of the rocking rotor and the one or more additional rocking rotors are connected via the pressure circuit.The one or more additional rocking rotors may be connected to a same frame construction.

[0066] In some embodiments, having the energy extractor of the rocking rotor and the one or more additional rocking rotors connected via the pressure circuit enables the plurality of rocking rotors to provide energy to a common pressure circuit. An advantage of having a common pressure circuit may include that the flow of a medium in the pressure circuit is more even, in that the individual rocking rotors may be in a downstroke or upstroke independently and in different times compared to each other. The energy extractors of the rocking rotors may be coupled in series, and ultimately to the pressure circuit, but may also be coupled in parallel. It is an advantage to couple the energy extractors in series, in that a higher pressure can be achieved in the pressure circuit, in addition to having a system comprising fewer components.

[0067] In an embodiment of the invention, the energy extractor of the rocking rotor and the one or more additional rocking rotors are connected in parallel via the pressure circuit. In that the energy extractor of each rocking rotor is connected in parallel allows the energy extractors of each rocking rotor to receive an even pressure. Each energy extractor may therefore be designed identical regardless of order in the pressure circuit and regardless of which rocking rotor of the wave power plant the energy extractor is installed in. Having a single design for an energy extractor for the wave power plant allows for easy replacement and maintenance, in addition to fewer requirements to spare part stocks.

[0068] Additionally, a system wherein the energy extractors were connected in series, would require the energy extractors to receive higher and higher pressures depending on their position in the series connection.

[0069] In an embodiment of the invention, the pressure circuit further comprises a pressure accumulator tank. Hereby, the pressure circuit may be enabled to improve pressure stability, so as a more even pressure is in place during operation of the wave power plant.

[0070] Additionally, having the pressure circuit comprising an accumulator tank allows the pressure circuit to use the accumulator tank as a backup pressure supplier, in case one or more rocking rotors are unable to operate.

[0071] In an embodiment of the invention, the wave power plant further comprises a pressure driven motor. The pressure driven motor may be a hydraulic motor.

[0072] In an embodiment of the invention, the wave power plant further comprises an energy generating unit, wherein the energy extractor is configured for generating a pressure difference in the pressure circuit.The energy generating unit may be configured for generating energy based on the pressure difference. In that the wave power plant comprises an energy generating unit configured for generating energy based on the pressure difference generated by the energy extractor may allow utilization of wave energy generated by the wave energy plant. The energy generating unit may be driven by the pressure driven motor. The pressure driven motor may in turn be driven by the pressure difference generated by the energy extractor. In an embodiment of the invention, the energy generating unit is an electric generator, and the energy generated is electrical energy.

[0073] Having the energy generated by the energy unit as electrical energy allows for storage and export of electrical energy to an electrical grid. Furthermore, electric energy is a common energy used for consumption by end users and can be implemented with various systems in order to convert said electric energy to other types of energy, such as heating.

[0074] The wave power plant may be placed in open waters, such as in the open sea away from docks and harbors.

[0075] The wave power plant may be a floating wave power plant.

[0076] The wave power plant may be a floating wave power plant moored to a buoy, wherein the buoy is anchored to a sea bed.

[0077] According to a third aspect use of a rocking rotor according to the first aspect and any embodiments related thereon, in a wave power plant is provided.

[0078] Using a rocking rotor according to the first aspect and any embodiments related thereon in a wave power plant allows for simple energy extraction of energy found in incoming waves. The rocking rotor comprises few components, which is beneficial when considering service life of said rocking rotor.

[0079] A further scope of applicability will become apparent from the detailed description given below. However, it should be understood that the detailed description and specific examples are given by way of illustration only.

[0080] It is to be understood that the terminology used herein is for purpose of describing particular embodiments only, and is not intended to be limiting. It must be noted that, as used in the specification and the appended claim, the articles "a", "an," "the," and "said" are intended to mean that there are one or more of the elements unless the context clearly dictates otherwise. Thus, for example, reference to "a unit" or "the unit" may include several devices, and the like. Furthermore, the words "comprising", "including", "containing" and similar wordings do not exclude other elements or steps.

[0081] Brief description of the drawings

[0082] The above and other aspects will now be described in more detail, with reference to appended figures. The figures should not be considered limiting; instead they are used for explaining and understanding.

[0083] As illustrated in the figures, the sizes of layers and regions may be exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures. Like reference numerals refer to like elements throughout.

[0084] Fig. 1 illustrates a rocking rotor connected to a frame construction as per the invention,

[0085] Fig. 2 illustrates a perspective of a rocking rotor connected to a frame construction according to the invention,

[0086] Fig. 3 illustrates a rocking rotor connected to a frame construction as per the invention in an upstroke position, wherein the first- and second rotational axis of the rocking rotor is shown,

[0087] Fig. 4 illustrates a rocking rotor connected to a frame construction as per the invention in an upstroke position,

[0088] Fig. 5 illustrates a rocking rotor and an energy extractor, wherein the energy extractor is shown in various rotational positions,

[0089] Fig. 6 is a perspective representation of a plurality of rocking rotors, Fig. 7a is an illustration of a rocking rotor with and without ballast, and the effect of said ballast on the equilibrium state of the rocking rotor,

[0090] Fig. 7b is an illustration of the rocking rotors of Fig. 7a, wherein a center of gravity is depicted, and a rotational pattern for each rocking rotor is illustrated,

[0091] Fig. 8 is an illustration of a pressure circuit diagram connected to the energy extractor.

[0092] Detailed description

[0093] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms.

[0094] Fig. 1 illustrates a rocking rotor 1 comprising a buoyant body 2. The buoyant body 2 is rotatably connected to a frame construction 3 via a first rotational joint 4. The rocking rotor 1 further comprises an energy extractor 6 with a first end 7 and a second end 8. The first end 7 of the energy extractor 6 is rotatably connected to a first position 11 of the buoyant body 2 at a third rotational joint 18 via a first connector 9. The energy extractor 6 is further rotatably connected to the frame construction 3 at a second rotational joint 12 via a second connector 10. The position on the energy extractor 6 which is connected to the second rotational joint 12 is called a frame-side rotational center. The rocking rotor 1 is further illustrated as comprising a second end 8 of the energy extractor 6 opposite of the first end 7. The second end 8 may extend beyond the frame-side rotational center of the energy extractor 6, but may also be arranged so as the second connector 10 is arranged at the second end 8. The energy extractor 6 illustrated in Fig. 1 is shown as comprising a frame-side rotational center arranged between the first end 7 and the second end 8.

[0095] Having the energy extractor 6 rotatably connected by a first connector 9 to a first position 11 of the buoyant body 2 rotating about the first rotational joint 4 via a third rotational joint 18 and rotatably connected by a second connector 10 to the frame construction 3 via a second rotational joint 12 enables the energy extractor 6 to follow two different rotational axes. The rocking rotor 1 is configured so that the two rotational axes are different, which enables the energy extractor 6 to have a linear displacement, such as a telescopic movement, during rotation of the rocking rotor 1. The two rotational axes, namely the first rotational axis 5 and the second rotational axis 13, are described in more detail in Fig. 3

[0096] Fig. 2 is a perspective view of the rocking rotor 1 illustrated in Fig. 1. Fig. 2 illustrates a rocking rotor 1 comprising a buoyant body 2. The buoyant body 2 is rotatably connected to a frame construction 3 via a first rotational joint 4. The rocking rotor 1 further comprises an energy extractor 6 with a first end 7 and a second end 8. The first end 7 of the energy extractor 6 is rotatably connected to a first position 11 of the buoyant body 2 at a third rotational joint 18 via a first connector 9. The energy extractor 6 is further rotatably connected to the frame construction 3 at a second rotational joint 12 via a second connector 10, wherein the second connector 10 is arranged at a second end 8 of the energy extractor 6. The position on the energy extractor 6 which is connected to the second rotational joint 12 is called a frameside rotational center. The rocking rotor 1 is further illustrated as comprising a second end 8 of the energy extractor 6 opposite of the first end 7, wherein the frame-side rotational center of the energy extractor 6 is illustrated as being arranged at the second end 8 of the energy extractor 6. The energy extractor 6 is further illustrated as comprising a high-pressure port 14 and a low-pressure port 15, wherein the high-pressure port 14 and low-pressure port 15 are arranged at opposite ends of the energy extractor 6. The high-pressure port 14 and the low- pressure port 15 are further illustrated as being connected to individual cables 16. The cables 16 may be further connected to a system (not shown) for harvesting energy, such as a system comprising a pressure circuit and a generator (not shown), wherein the cables 16 are hydraulic cables 16.

[0097] Fig. 3 illustrates a rocking rotor 1 comprising a buoyant body 2. The buoyant body 2 is rotatably connected to a frame construction 3 via a first rotational joint 4. The rocking rotor 1 further comprises an energy extractor 6 with a first end 7 and a second end 8. The first end 7 of the energy extractor 6 is rotatably connected to a first position 11 of the buoyant body 2 at a third rotational joint 18 via a first connector 9. The energy extractor 6 is further rotatably connected to the frame construction 3 at a second rotational joint 12 via a second connector 10, wherein the second connector 10 is arranged at a second end 8 of the energy extractor 6. The position on the energy extractor 6 which is connected to the second rotational joint 12 is called a frame-side rotational center. The rocking rotor 1 is further illustrated as comprising a second end 8 of the energy extractor 6 opposite of the first end 7. The frame-side rotational center of the energy extractor 6 is illustrated as being arranged at the second end 8 of the energy extractor 6, wherein the frame-side rotational center of the energy extractor 6 is illustrated as being arranged at the second end 8 of the energy extractor 6.

[0098] During rotation of the rocking rotor 1, the buoyant body 2 is rotating about a first rotational axis 5 via the first rotational joint 4. The energy extractor 6 is rotating about first rotational joint 4 at a first end 7 of the energy extractor 6 and the second rotational joint 12 at a second end 8 of the energy extractor 6, wherein the second end 8 of the energy extractor 6 rotates in a second rotational axis 13, and the first end 7 of the energy extractor 6 follows the first rotational axis 5. The first end 7 of the energy extractor 6 follows the first rotational axis 5, due to the first end 7 being rotatably connected to a first position 11 of the buoyant body 2 at a third rotational joint 18 via a first connector 9. When the first rotational axis 5 and the second rotational axis 13 are different, a distance D occurs between the first rotational axis 5 and the second rotational axis 13. When a respective center of rotation for the first rotational axis 5 and for the second rotational axis 13 are different, the distance D will vary during rotation of the rocking rotor 1. Having the distance D vary between the first rotational axis 5 and the second rotational axis 13 during rotation results in a linear displacement of the energy extractor 6, as the first end 7 of the energy extractor 6 follows the first rotational axis 5 and the second end 8 follows the second rotational axis 13 while the distance D varies during rotation of the rocking rotor 1. The linear displacement of the energy extractor 6 during rotation of the rocking rotor 1 is illustrated in an upstroke position of the rocking rotor 1 in Fig. 4. Fig. 4 illustrates a rocking rotor 1 comprising a buoyant body 2. The buoyant body 2 is rotatably connected to a frame construction 3 via the first rotational joint 4. The rocking rotor 1 further comprises an energy extractor 6 with a first end 7 and a second end 8. The first end 7 of the energy extractor 6 is rotatably connected to a first position 11 of the buoyant body 2 at a third rotational joint 18 via a first connector 9. The energy extractor 6 is further rotatably connected to the frame construction 3 at a second rotational joint 12 via a second connector 10, wherein the second connector 10 is arranged at a second end 8 of the energy extractor 6. The position on the energy extractor 6 which is connected to the second rotational joint 12 is called a frame-side rotational center. Thus, the frame-side rotational center of the energy extractor 6 is arranged at the second end 8 of the energy extractor 6. The energy extractor 6 is illustrated in a cross-section view, wherein the first end 7 is illustrated as a piston 17 which is freely moving from the remainder of the energy extractor 6. It can be seen from Fig. 4, that the piston 17 is moving away from the second end 8 as the energy extractor 6 is extended during rotation of the rocking rotor 1. When the piston 17 moves away from the second end 8 of the energy extractor 6, a hollow room of the energy extractor 6 above the piston 17 is compressed, and pressure of a medium inside may be increased. Likewise, when the piston 17 moves away from the second end 8 of the energy extractor 6, a hollow room of the energy extractor 6 below the piston 17 is compressed, and pressure of a medium inside may be decreased. This change of pressure for the respective medium inside the respective hollow room of the energy extractor 6 on either side of the piston 17 enables harvesting energy by a system (not shown) configured for converting the pressure change of the medium inside the energy extractor 6. An illustration of the linear displacement of the energy extractor 6 during rotation of the rocking rotor 1 is shown in Fig. 5.

[0099] Fig. 5 illustrates a rocking rotor 1 comprising a buoyant body 2. The buoyant body 2 is rotatably connected to a frame construction 3 via a first rotational joint 4. The rocking rotor 1 further comprises an energy extractor 6 with a first end 7 and a second end 8. The first end 7 of the energy extractor 6 is rotatably connected to a first position 11 of the buoyant body 2 at a third rotational joint 18 via a first connector 9. The energy extractor 6 is further rotatably connected to the frame construction 3 at a second rotational joint 12 via a second connector 10, wherein the second connector 10 is arranged at a second end 8 of the energy extractor 6. The position on the energy extractor 6 which is connected to the second rotational joint 12 is called a frame-side rotational center. Thus, the frame-side rotational center of the energy extractor 6 is arranged at the second end 8 of the energy extractor 6. The linear displacement of energy extractor 6 is further disclosed in various extended states, namely a partial upstroke extended state 6', a fully upstroke extended state 6”, a partial downstroke extended state 6'”, and a fully downstroke extended state 6'”', which all may occur during rotation of the rocking rotor 1. Starting from the equilibrium state of the rocking rotor 1, the energy extractor 6 may, in an upstroke rotation, reach the partial upstroke extended state 6' and continue to the fully upstroke extended state 6”, given that the rocking rotor 1 rotates sufficiently for the energy extractor 6 to reach the fully upstroke extended state 6”. Subsequently, when the incoming wave that rotates the rocking rotor 1 passes the rocking rotor 1, the rocking rotor 1 may rotate downwards and the energy extractor 6 reach the partial upstroke extended state 6' if starting from the fully upstroke extended state 6”, or the position of the energy extractor 6 in the equilibrium state if the energy extractor 6 was at a partial upstroke extended state 6' by the time the incoming wave passes. The rocking rotor 1 may continue its downwards rotation, wherein the energy extractor 6 may reach a partial downstroke extended state 6'” and may, given that no incoming waves reverse the rotation of the rocking rotor 1, continue to a fully downstroke extended state 6””.

[0100] It can be derived from the various extended states 6', 6”, 6'”, 6”” of the energy extractor 6, that the first end 7 is moved by the buoyant body 2 and follows the first rotational axis 5, resulting in the first end 7 extending out of the remainder of the energy extractor 6 which rotates about the second rotational axis 13 and the distance D increases in a telescopic movement.

[0101] Fig. 6 illustrates a rocking rotor 1 comprising a buoyant body 2. The buoyant body 2 is rotatably connected to a frame construction 3 via a first rotational joint 4. The rocking rotor 1 further comprises an energy extractor 6 with a first end 7 and a second end 8. The first end 7 of the energy extractor 6 is rotatably connected to a first position 11 of the buoyant body 2 at a third rotational joint 18 via a first connector 9. The energy extractor 6 is further rotatably connected to the frame construction 3 at a second rotational joint 12 via a second connector 10, wherein the second connector 10 is arranged at a second end 8 of the energy extractor 6. The position on the energy extractor 6 which is connected to the second rotational joint 12 is called a frame-side rotational center. The rocking rotor 1 is further illustrated as comprising a second end 8 of the energy extractor 6 opposite of the first end 7. Furthermore, Fig.6 illustrates two additional rocking rotors 1' identical to the rocking rotor 1, wherein all rocking rotors 1, 1' are rotatably connected to the same frame construction 3.

[0102] Fig. 7a illustrates a rocking rotor 1 comprising a buoyant body 2 and a rocking rotor comprising a buoyant body 2, wherein said buoyant body 2 further comprises a ballast 20. The two rocking rotors 1 are depicted as showing the equilibrium state of each rocking rotor 1 when arranged in water 22. It can be derived from Fig. 7a, that a ballast 20 arranged inside the buoyant body 2 of a rocking rotor 1 changes the equilibrium state of said rocking rotor 1. The rocking rotor 1 comprising the buoyant body 2 with the ballast 20 is illustrated as having an equilibrium state which is 45 degrees downwards rotated, compared to the rocking rotor 1 comprising the buoyant body 2 without the ballast 20.

[0103] Fig. 7b illustrates the two rocking rotors 1 from Fig. 7a, wherein a Center of Gravity 21 of each rocking rotor is depicted. One with a centralized center of gravity, and one with an off-set center of gravity. Fig. 7b further illustrates a range of motion of each rocking rotor 1 when subjected to a wave from a wave direction 19. The range of motion is illustrated namely as partial upstroke rotation states 2', a fully upstroke rotation state 2”, partial downstroke rotation states 2'”, and a fully downstroke rotation state 2"" . During rotation, the rocking rotor 1 without a ballast 20 may have a center of gravity 21 resulting in the rocking rotor 2 having a substantial vertical equilibrium state. The rocking rotor 1 without a ballast 20 may therefore rotate to a partial upstroke rotation state 2', and possibly all the way to the fully upstroke rotation state 2”, when impacted by a wave with the wave direction 19. When the wave passes the rocking rotor 1 with a centralized center of gravity 21, the rocking rotor 1 may, if the wave rotated the rocking rotor to the fully upstroke rotation state 2”, rotate in a downstroke movement towards the partial upstroke rotation states 2' and continue to the initial state of the rocking rotor 1, namely the equilibrium state. If the wave did not rotate the rocking rotor to the fully upstroke rotation state 2”, but only to one of the partial upstroke rotation states 2”, the rocking rotor 1 would rotate in a downstroke movement towards the initial state of the rocking rotor 1, namely the equilibrium state. The rocking rotor 1 may even in both cases, due to inertia, continue towards the partial downstroke states 2'”, and if said inertia is sufficiently high for the rocking rotor 1, continue towards the fully downstroke state 2"" . A new incoming wave with the wave direction 19 may stop and even reverse the rotation of the rocking rotor 1.

[0104] In the case of a rocking rotor 1 with an off-set center of gravity, the rocking rotor may have a center of gravity 21 resulting in the rocking rotor 2 having an equilibrium state different from a substantial vertical position, such as between 70 degrees and 30 degrees, such as 45 degrees. The rocking rotor 1 with a ballast 20 may therefore rotate to a partial upstroke rotation state 2', and possibly all the way to the fully upstroke rotation state 2”, when impacted by a wave with the wave direction 19. When the wave passes the rocking rotor 1, the rocking rotor 1 may, if the wave rotated the rocking rotor to the fully upstroke rotation state 2”, rotate in a downstroke movement towards the partial upstroke rotation states 2' and continue to the initial state of the rocking rotor 1, namely the equilibrium state. If the wave did not rotate the rocking rotor to the fully upstroke rotation state 2”, but only to one of the partial upstroke rotation states 2" , the rocking rotor 1 would rotate in a downstroke movement towards the initial state of the rocking rotor 1, namely the equilibrium state. The rocking rotor 1 may even in both cases, due to gravity and inertia, continue towards the partial downstroke states 2"' , and if said inertia and / or gravitational force are sufficiently high for the rocking rotor 1, continue towards the fully downstroke state 2"" . A new incoming wave with the wave direction 19 may stop and even reverse the rotation of the rocking rotor 1

[0105] Fig. 8 illustrates a generic example of a pressure circuit connected to an energy extractor 6. The energy extractor 6 is illustrated as comprising a piston 17, a high- pressure port 14, and a low-pressure port 15, and a pressure circuit. The pressure circuit comprises a hydraulic motor 27 driving a generator 25 via a drive axle 28 and may further comprise an optional pressure accumulator tank 24 connected to a high-pressure side of the pressure circuit. The components of the pressure circuit are connected via cable 16, which also may be pipes, such that the hydraulic motor 27 is connected to the energy extractor 6 at two pressure levels, namely to a high- pressure port 14 and a low-pressure port 15. An optional pressure accumulator tank 24 is illustrated as connected to the cable 16, wherein the pressure accumulator tank 24 is configured for maintaining a steady flow of a flow medium inside the pressure circuit. The flow between the energy extractor 6 and the hydraulic motor 27 may be controlled by a valve station comprising one or more valves, such as at least a one-way valve. This valve station may be arranged between the hydraulic motor 27 and the energy extractor 6, but may also be arranged inside of the hydraulic motor 27. During operation, the energy extractor 6 creates a flow of a flow medium of the pressure circuit, which drives the hydraulic motor 27. The hydraulic motor 27 converts the energy received from the energy extractor 6 to mechanical energy, which is used to drive the generator 25. The hydraulic motor 27 may drive the generator by use of a drive axle 28, but may also use other means for driving the generator 25, such as a chain.

[0106] As explained in the embodiments of the invention, the pressure accumulator tank 24 facilitates an even pressure to the generator 25. The accumulator tank 24 is therefore an optional component which only further improves the invention, as the energy extractor 6, alone or in combination with a valve station, may ensure that a high-pressure side of the pressure circuit may remain a high-pressure side during operation.

[0107] The person skilled in the art realizes that the present invention by no means is limited to what is explicitly described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

[0108] For example, the energy extractor could utilize the linear displacement by having a linear electromagnetic generator or piezoelectric generator instead of the piston in order to harvest energy. As a further example, the pressure circuit described in Fig. 8 may have a valve station which is controlled based on a rotational direction of the rocking rotor. This may enable the energy extractor to switch between a high-pressure side and low- pressure side for each high-pressure side port and low-pressure side port.

[0109] Additionally, variations can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

[0110] References

[0111] 1 Rocking rotor

[0112] 1' Additional rocking rotor

[0113] 2 Buoyant body

[0114] 2' Partial upstroke rotation state

[0115] 2” Fully upstroke rotation state

[0116] 2'” Partial downstroke rotation state

[0117] 2'”' Fully downstroke rotation state

[0118] 3 Frame construction

[0119] 4 First rotational joint

[0120] 5 First rotational axis

[0121] 6 Energy extractor

[0122] 6' Partial upstroke extended state

[0123] 6" Fully upstroke extended state

[0124] 6"' Partial downstroke extended state

[0125] 6"" Fully downstroke extended state

[0126] 7 First end

[0127] 8 Second end

[0128] 9 First connector

[0129] 10 Second connector

[0130] 11 First position

[0131] 12 Second rotational joint

[0132] 13 Second rotational axis

[0133] 14 High-pressure port

[0134] 15 Low-pressure port

[0135] 16 Cable

[0136] 17 Piston

[0137] 18 Third rotational joint

[0138] 19 Wave direction

[0139] 20 Ballast

[0140] 21 Center of Gravity

[0141] 22 Water 23 One-way valve

[0142] 23' First additional one-way valve

[0143] 23” Second additional one-way valve

[0144] 24 Pressure accumulator tank

[0145] 25 Generator

[0146] 26 First control valve

[0147] 26' Second control valve

[0148] 27 Hydraulic motor

[0149] 28 Drive axle

Claims

29CLAIMS1. A rocking rotor for use in a wave power plant, the rocking rotor comprising a buoyant body being rotatably connected to a frame construction, the buoyant body being interconnected to the frame construction via a first rotational joint, the buoyant body being configured to, in response to an incoming wave, perform a rocking motion about a first rotational axis, an energy extractor having a first end, a second end and a frame-side rotational center, the energy extractor having a first connector at the first end and a second connector at the frame-side rotational center, wherein the first connector rotatably connects the first end of the energy extractor to the buoyant body at a first position via a third rotational joint, and wherein the second connector rotatably interconnects the frame-side rotational center of the energy extractor to the frame construction via a second rotational joint, the frameside rotational center of the energy extractor being configured to rotate about a second rotational axis.

2. A rocking rotor according to claim 1, wherein the frame-side rotational center is arranged at the second end of the energy extractor.

3. A rocking rotor according to claim 1 or 2, wherein a first distance from the third rotational joint to the second rotational joint is different from a second distance from the first position to the first rotational joint, wherein the first distance is smaller than the second distance.

4. A rocking rotor according to any of the previous claims, wherein the first rotational axis and the second rotational axis are parallel.

5. A rocking rotor according to any of the previous claims, wherein the energy extractor comprises a hollow body, the hollow body being connected to the second connector,30 a piston arranged in the hollow body and being connected to the first connector, the energy extractor having a high-pressure side port and low-pressure side port.

6. A rocking rotor according to any of the previous claims, wherein the rocking rotor, in its operational position being immersed in water, has an equilibrium state, in which equilibrium state the first rotational joint, the second rotational joint and the third rotational joint are aligned along an equilibrium axis.

7. A rocking rotor according to claim 6, wherein the rocking rotor is configured to, in response to an incoming wave, perform a rocking motion about the first rotational axis by moving in a first direction away from the equilibrium, moving in a second direction back through the equilibrium state and away from the equilibrium state in the second direction.

8. A rocking rotor according to any of the previous claims, wherein the energy extractor is a hydraulic cylinder.

9. A wave power plant comprising; a rocking rotor according to any one of the claims 1-8, a pressure circuit, wherein the pressure circuit is connected the energy extractor.

10. The wave power plant according to claim 9, the rocking rotor is a rocking rotor according to any one of the claims 5- 8, wherein the energy extractor is further connected to the pressure circuit via the high-pressure side port and the low-pressure side port, wherein the high-pressure side port is connected to a high- pressure side of the pressure circuit and the low-pressure side port is connected to a low-pressure side port of the pressure circuit.

11. The wave power plant according to claim 9 or 10, wherein the pressure circuit further comprises a one-way valve configured for maintaining a flow direction of the pressure circuit.

12. The wave power plant according to any one of the claims 10-11, wherein the high-pressure side port is arranged in the first end of the energy extractor and the low-pressure side port is arranged in the second end of the energy extractor.

13. The wave power plant according to any one of the claims 10-12, further comprising one or more additional rocking rotors according to any one of the claims 1-8, wherein the energy extractor of the rocking rotor and the one or more additional rocking rotors are connected via the pressure circuit.

14. The wave power plant according to claim 13, wherein the energy extractor of the rocking rotor and the one or more additional rocking rotors are connected in parallel via the pressure circuit.

15. The wave power plant according to any one of the claims 9-14, wherein the pressure circuit further comprises a pressure accumulator tank.

16. The wave power plant according to any one of the claims 9-15, further comprising an energy generating unit, wherein the energy extractor is configured for generating a pressure difference in the pressure circuit, and wherein the energy generating unit is configured for generating energy based on the pressure difference.

17. The wave power plant according to claim 16, wherein the energy generating unit is an electric generator, and wherein the energy based on the pressure difference is electrical energy.

18. The wave power plant according to claim 17, wherein the wave power plant further comprises a hydraulic motor, wherein the electric generator is driven by the hydraulic motor.

19. The wave power plant according to any one of the claims 9-18, wherein the pressure circuit further comprises a valve station, the valve station being controlled based on a rotational direction of the rocking rotor.

20. The wave power plant according to claim 19 and any one of the claims 10-18, wherein the valve station is configured to switch between the high-pressure side and the low-pressure side for each high-pressure side port and low-pressure side port based on the rotational direction of the rocking rotor.

21. Use of a rocking rotor according to any one of the claims 1-8 in a wave power plant.

22. The use according to claim 21, wherein the wave power plant is a wave power plant according to any one of the claims 9 to 20.

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