Power extraction device for wave energy converter, and wave energy converter equipped with power extraction device

Abstract

The power take-off for a point absorption type wave energy converter comprises: a cylinder (1) adapted to be attached to a floating device and having a first upper end and a second lower end; a piston (5) arranged to reciprocate inside the cylinder (1) and having a piston rod (6) adapted to be attached to a mooring; at least one penstock (13) arranged parallel to the cylinder (1) and having a first lower end in fluid communication with the second end of the cylinder (1) through a first opening and a second upper end with a second opening; a housing (16) arranged above the first end of the cylinder (1) and having a hydraulic fluid supply to the second end of the cylinder (1) through the second opening; a housing (16) fluidly communicating with the pipe (13) and with a first end of the cylinder (1) through a third opening in the bottom of the housing (16), whereby the cylinder (1), the at least one penstock (13), and the housing (16) together form a closed loop of working fluid in the power take-off device; and a water turbine (4) disposed inside the housing (16), wherein the working fluid entering the housing (16) from the at least one penstock (13) through the second opening is oriented to rotate the water turbine (4) and drive a generator (15) connected to the water turbine (4). A wave energy converter comprising such a power take-off device is also disclosed.

Description

Technical Field

[0001] The present disclosure relates generally to a power take-off (PTO) device for extracting energy from waves, and more particularly to those used in point-absorbing type wave energy converters (WECs).

Background Art

[0002] The vast power in ocean waves is known as a potential source of extracting electrical energy. Examples of wave energy converters for harnessing this potential are disclosed, for example, in International Publication No. WO 98 / 20253, European Patent No. 0265594, International Publication No. WO 2009 / 093988, US Patent Application Publication No. US 2004 / 160060, UK Patent Application Publication No. GB 2472055, US Patent No. 5701740, and International Publication No. WO 2017 / 217919.

[0003] However, one potential problem in power take-off devices known in the art is that they utilize seawater drawn into a cylinder as a working fluid, pump it through a water pressure pipe from the cylinder to a hydraulic turbine, and then return it to the sea. Such a solution has several drawbacks in that the salt-laden seawater is quite corrosive to the components of the PTO system, reducing the lifespan of the PTO system and / or requiring component replacement. Adding additives such as conditioners, lubricants, and corrosion inhibitors does not alleviate this problem in the long term because the additives will be washed away by the seawater passing through the PTO. Additionally, such additives, as well as particles from within the system, seals, metals, bearings, and leaks, will be released from the upper openings of the cylinder or turbine housing, which can cause pollution of the surrounding seawater over time. Manufacturing all components from a more corrosion-resistant material such as stainless steel could be an alternative, but this is not practical due to the severe difficulties associated with electrolytic corrosion of the various components, as well as the associated high metal costs.

[0004] Furthermore, the intake of seawater can lead contaminants and / or debris, as well as marine organisms, to enter the system through the opening of the cylinder. This may result in the adhesion of scale, dirt, and the accumulation of residues inside the cylinder, and the cylinder requires regular cleaning. Additionally, protective means will be needed to protect marine organisms from strong and intermittent underwater suction. Preventive improvement measures to overcome these obstacles include high-capacity filtration and cleaning utilities at both the water inlet and outlet. Such high-capacity filtration / cleaning systems increase the manufacturing and repair costs of the PTO system because they increase the weight and reduce the technical performance.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Summary of the Invention

Problems to be Solved by the Invention

[0006] Therefore, there is a need for an improved power take-off device to overcome the above-mentioned defects and disadvantages.

Means for Solving the Problems

[0007] The object of the present disclosure is to provide a solution to the problems outlined above. This object is achieved in a first aspect of the invention. There, a power take-off device is provided for a point-absorbing type wave energy converter. The power take-off device is adapted to be mounted on a floating device and comprises a cylinder having a first upper end and a second lower end; a piston having a piston rod arranged to reciprocate inside the cylinder and adapted to be mounted on a mooring facility; at least one hydraulic pipe having a first lower end arranged parallel to the cylinder and in fluid communication with the second end of the cylinder via a first opening, and a second upper end including a second opening; a housing arranged above the first end of the cylinder and in fluid communication with the hydraulic pipe via the second opening; and a hydraulic turbine arranged inside the housing and through which the working fluid entering the housing from at least one hydraulic pipe via the second opening is directed to rotate the hydraulic turbine and drive a generator connected to the hydraulic turbine. The working fluid present at the second end of the cylinder below the piston enters at least one hydraulic pipe through the first opening during the downward stroke of the piston relative to the cylinder and exits at least one hydraulic pipe through the second opening. The housing is in fluid communication with the first end of the cylinder via a third opening at the bottom of the housing, whereby the cylinder, at least one hydraulic pipe, and the housing together form a closed loop for the working fluid of the power take-off device. The power take-off device further comprises at least one forward conduit having at least one one-way valve. The one-way valve is arranged to allow the working fluid to pass only in the direction from the first end of the cylinder above the piston to the second end of the cylinder below the piston via at least one forward conduit during the upward stroke of the piston relative to the cylinder.

[0008] The device according to the present disclosure provides a closed loop containing a working fluid within the power take-off device. Due to the reciprocating up-and-down motion of the piston with respect to the cylinder, the working fluid is sent by a pump into at least one hydraulic pipe and further directed towards a hydraulic turbine to rotate and generate electrical energy. Thereafter, the working fluid falls inside the housing towards the first upper end of the cylinder under the influence of gravity to complete the closed loop. As a result, the internal components of the PTO system are not exposed to seawater containing corrosive salts and biological organisms. This prevents or minimizes component fouling and degradation, similarly reduces the need for repair and maintenance, and extends the life of the PTO system. The new PTO device eliminates the need for filtration / washing and protection against corrosion, thereby ensuring long-term maintained performance. Furthermore, the closed system ensures that the working fluid and any particles present therein, such as those generated from wear of internal components, are not released into the surrounding environment and do not contaminate the surrounding environment. In this way, an environmentally friendly and improved solution for harnessing wave energy is realized. Additionally, this closed system provides improved protection for marine wildlife in that the risk of strong underwater suction is eliminated.

[0009] Other advantages of the PTO device according to the present disclosure over other marine energy devices include, for example, a large lifting force made possible by combining with a rectangular float in a WEC system, easily converting slow wave motion with well-proven repetition in a hydroelectric power plant into a high-speed rotational motion of the generator, an easy method of latching at the wave bottom, and a non-resonant behavior that avoids the very complex tuning of the resonant concept of regular waves.

[0010] In one embodiment, at least one forward conduit is arranged on the piston. This solution eliminates additional pipes outside the cylinder and provides a compact configuration of the power take-off device. Alternatively, at least one forward conduit consists of a return pipe arranged outside the cylinder.

[0011] In one embodiment, the power take-off device further comprises a regulator unit disposed in fluid communication with a closed loop formed by a cylinder, a hydraulic pipe, and a housing. The regulator unit is arranged to replenish the working fluid in the closed loop of the power take-off device, monitor the working fluid, clean the working fluid, and / or add an additive to the working fluid to reduce friction and / or corrosion of the power take-off device. Preferably, the regulator unit comprises a fluid analysis chamber, a mixing chamber, a filter, a waste chamber, and / or an additive chamber. The regulator unit realizes improved performance of the power take-off device in terms of providing an optimal working fluid in which lubricants and / or corrosion inhibitors reduce the frequency of maintenance and thereby the cost. Continuous monitoring of the state of the power take-off device can be carried out. Cleaning or replenishment of the working fluid is performed as necessary to ensure optimal operating conditions for the power take-off device.

[0012] In one embodiment, the power take-off device further comprises a flywheel arranged to rotate coaxially with the rotating shaft of the hydraulic turbine. The hydraulic turbine and the flywheel are separated by a partition inside the housing. The flywheel rotates with the hydraulic turbine and is arranged to store rotational energy, thereby maintaining the rotation of the hydraulic turbine during the upward stroke of the piston. That is, when the floating device of the wave energy converter moves downward with the wave, the working fluid does not act on the hydraulic turbine.

[0013] In one embodiment, the power take-off device further comprises a pressure tank disposed between the hydraulic turbine and at least one hydraulic pipe. The pressure tank is arranged to provide the working fluid delivered to the hydraulic turbine at a substantially constant and continuous pressure. By providing the pressure tank, a substantially continuous flow of the working fluid at a substantially constant pressure is provided, enabling it to act on the hydraulic turbine, thereby reducing the weight of the flywheel or the exhaust of the flywheel.

[0014] In one embodiment, the generator is arranged to rotate the hydraulic turbine to control the rotational speed of the hydraulic turbine when the working fluid does not rotate the hydraulic turbine. When the working fluid does not exit the penstock to drive the hydraulic turbine, for example, during the falling stage of the wave, by operating the generator as a motor to rotate the hydraulic turbine, it becomes possible to maintain an optimal level of the RPM of the hydraulic turbine with respect to the speed of the working fluid hitting the moving blades of the hydraulic turbine, thereby reducing energy losses and achieving a higher power conversion efficiency.

[0015] In one embodiment, the power extraction device further comprises at least one valve. This valve is arranged in at least one penstock and is configured to allow the working fluid to pass only in the direction from the first lower end to the second upper end of at least one penstock. For example, by providing a one-way valve in at least one penstock, it is possible to prevent the working fluid from returning to the cylinder during the upward stroke of the piston. This directional flow is ensured by an electrically / hydraulically / pneumatically or otherwise actuated valve. This valve closes when the floating body moves downward with the wave and opens when the flow is in the desired upward direction with respect to the nozzle. This valve may also be combined with the nozzle and is often a spear valve.

[0016] In one embodiment, the power extraction device further comprises at least one penstock and at least one first bypass conduit arranged to be in fluid communication with the first end of the housing or cylinder below the hydraulic turbine. The at least one first bypass conduit comprises a first relief valve. The first relief valve is configured to open at a predetermined pressure and allow the working fluid to pass from at least one penstock, through at least one first bypass conduit, to the first end of the housing or cylinder below the hydraulic turbine.

[0017] In one embodiment, the power extraction device further comprises at least one second bypass conduit having a first lower end fluidly communicating with a second end of the cylinder and a second upper end fluidly communicating with a housing below the hydraulic turbine or a first end of the cylinder. The at least one second bypass conduit comprises a second relief valve. The second relief valve opens at a predetermined pressure and is configured to allow the working fluid to pass from a second end in the cylinder below the piston, through the at least one second bypass conduit, to a housing below the hydraulic turbine or a first end of the cylinder above the piston. Optionally, the at least one second bypass conduit is disposed on the piston, thereby providing a small bypass solution.

[0018] At one or more positions along the closed loop system, by providing a bypass conduit in fluid communication with various components associated with the relief valve, redundant protection of the power extraction device is achieved against increased pressure when the flow of the working fluid is obstructed or blocked. This fail - safe mechanism ensures that the components of the power extraction device are not damaged by the continuous up - and - down movement of the piston caused by the incoming waves.

[0019] In one embodiment, the power extraction device further comprises a cylinder partition wall that divides the second end of the cylinder into two spaces. The partition wall comprises an opening with a high - pressure seal surrounding the piston rod, and the bottom wall of the cylinder comprises an opening with a low - pressure seal surrounding the piston rod. The lower space is in fluid communication with the first end of the cylinder via at least one bypass conduit, allowing the working fluid to pass in the direction from the lower space of the cylinder to the first end. By partitioning the second lower end of the cylinder and providing high - and low - pressure seals around the piston rod, the possibility of leakage to the surrounding water is further minimized, and similarly, the life of the high - pressure seal is extended.

[0020] In one embodiment, the piston rod comprises a first section mounted to the piston from above, a second section disposed outside the cylinder parallel to the first section, and a third section joined to the first and second sections above the cylinder. The cylinder comprises a pair of sliding joints arranged such that the cylinder can slide along the second section of the piston rod. In an alternative configuration of the piston rod mounted to the piston from above, the cylinder no longer requires a seal at its lower end, ensuring that the working fluid cannot escape from the closed-loop system and, conversely, that seawater cannot enter the closed-loop system. The advantage of this configuration is that the sealing portion between the cylinder and the piston rod can be arranged without direct contact with seawater by having a portion of the piston that extends upward into the cylinder.

[0021] In one embodiment, the piston rod is configured to be mounted to a separate marine structure, such as the leg of an oilfield drilling device. This enables the wave energy converter to utilize pre-existing facilities. The water depth at the location of the facilities is not critical, as the piston rod will be substantially fixed to the seabed via a fixture on the marine structure. This fixture for the piston rod to a separate marine structure is possible for both conventional downward-facing piston rods and the new reverse configuration using the upward-facing piston rod described above.

[0022] In a second aspect of the present disclosure, there is provided a point-absorbing type wave energy converter comprising a floating device and a power take-off device according to the first aspect.

[0023] In a third aspect of the present disclosure, there is provided the use of a power take-off device according to the first aspect in a point-absorbing type wave energy converter for generating electrical energy from the wave power of a body of water.

[0024] In one embodiment, the generator is used to rotate the hydraulic turbine such that when the working fluid does not rotate the hydraulic turbine, the rotational speed of the hydraulic turbine is controlled. By controlling the rotational speed of the hydraulic turbine by the generator acting as a motor, it becomes possible to maintain an optimal level of the RPM of the hydraulic turbine with respect to the speed of the working fluid hitting the moving blades of the hydraulic turbine, thereby reducing energy losses and achieving a greater power conversion efficiency.

[0025] Next, the present invention will be described as an example with reference to the accompanying drawings.

Brief Description of the Drawings

[0026]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Modes for Carrying Out the Invention

[0027] The following presents a detailed description of a power take-off device for a point-absorbing type wave energy converter according to the present disclosure. In the drawings, the same reference numerals throughout several views indicate the same or corresponding elements. These drawings are for illustrative purposes only, and it is to be understood that they do not impose any limitation or restriction on the scope of the present disclosure.

[0028] The power take-off device according to the present disclosure operates according to the same or similar principles as those disclosed in the above-mentioned International Publication No. 2017 / 217919, the content of which is incorporated herein by reference. Hereinafter, "power take-off (device)" and its abbreviation "PTO", as well as "wave energy converter" and its abbreviation "WEC" are used interchangeably.

[0029] Referring now to FIG. 1, a power take-off device according to one embodiment of the present disclosure is illustrated. This PTO includes four main components, as well as several auxiliary / optional components, and monitoring / sensing devices known in the art to ensure the function and safety of the device. The main components include a piston-cylinder device including a piston 5 and a piston rod 6 arranged to reciprocate inside a cylinder 1; one or more hydraulic pipes 13 arranged parallel to the cylinder 1; a housing 16 arranged above the upper end of the cylinder 1; and a hydraulic turbine 4 arranged inside the housing 16. The cylinder 1, at least one hydraulic pipe 13, and the housing 16 are arranged in fluid communication with each other to form a closed loop for the working fluid. This working fluid flows through the PTO in response to the up and down movement of a floating device (not shown) to which the PTO can be attached in ocean waves.

[0030] Referring to FIG. 9, an example of a point absorption type wave energy converter incorporating a power take-off device according to the present disclosure is shown. The cylinder 1 can be connected via a bearing 3 to a floating device or platform 66 such that the PTO is substantially vertically oriented regardless of the orientation of the floating platform by the waves. This can be achieved by a swivel connection that allows rotation about one or two substantially horizontal axes independent of each other for a swivel motion generally applicable to freely floating devices. However, other fixations of the cylinder 1 in a more fixed structure or frame are also applicable, for example, where the cylinder and the floating body are fixed together as one unit or by other means for the hydraulic power creating the lifting force. One exemplary floating device that can be used with the power take-off device of the present disclosure is disclosed in International Publication No. WO 2017 / 160216, which is incorporated herein by reference. Other shapes of the floating device are also encompassed by the present disclosure.

[0031] There is a piston 5 inside the cylinder 1. The piston 5 preferably has piston rings (not shown) suitable for operating with a selected cylinder material. Since the up and down stroke of the piston 5 relative to the cylinder 1 generally changes direction every 2 to 8 seconds and the speed is further 0.5 to 1.5 meters per second, the piston rings do not need to provide a perfect seal. This is because the volume and speed of the working fluid are hardly affected by a slight compression leakage. In one embodiment, the piston 5 comprises one or more front conduits formed therein. Each of these front conduits has a one-way valve 17 disposed therein or connected thereto, and when the piston 5 moves upward relative to the cylinder 1, allows the working fluid to pass through the front conduit via the volume of the stationary working fluid present at the upper end of the cylinder 1 above the piston 5. When the piston 5 moves in the opposite direction, the valve 17 closes, thereby creating compression at the lower end in the cylinder 1. The valve 17 can be positioned on the piston itself, or above or below the piston. A spring is also loaded to support the closure. This / these valve 17 may also incorporate a safety pressure valve, whereby when a specific pressure is exceeded, the working fluid will pass upward through the piston 5.

[0032] The piston 5 is connected to a piston rod 6, which slides within a bushing at the lower end of the cylinder 1 and extends downward out of the cylinder 1 through an opening in the cylinder 1. One purpose of this bushing is to stabilize the piston rod 6 in the center of the cylinder 1. It also includes a scrape ring for keeping the piston rod 6 clean, as well as a compression ring / high-pressure seal 51 closest to the inside of the cylinder 1 for preventing the working fluid from leaking into the surrounding sea.

[0033] As can be seen in Fig. 1, the hydraulic pipe 13 is arranged parallel to the cylinder 1 and is in fluid communication with the inside of the cylinder 1 through a first lower opening at the lower end of the cylinder 1. The hydraulic pipe 13 extends along the cylinder 1 towards the upper end of the cylinder 1 and reaches its apex at a second upper opening that proceeds into the housing 16, establishing fluid communication therebetween. The housing 16 is shown in more detail in Fig. 8. At least one spear valve 12, or another valve with a similar cut-off / on, and / or adjustment function, is in some cases combined with a separate pressure relief valve 7 or is combined into one and is arranged at the upper opening of the hydraulic pipe 13. The pressure relief valve 7 may be a drum, ball, or solenoid valve driven by electricity, hydraulics, or pneumatics. Additionally, or alternatively, a one-way valve 11 is arranged in the hydraulic pipe 13. The spear valve 12 is directed towards the hydraulic turbine 4 within the housing 16 and guides the flow of the working fluid to drive the hydraulic turbine 4. The valves 7, 12 open when the specific pressure required for the optimal operation of the hydraulic turbine 4 is obtained. Thus, the working fluid flows out of the spear valve 12 at high speed and strikes the moving blades or impact blades of the hydraulic turbine 4, driving the hydraulic turbine 4 at an optimal speed.

[0034] It is possible and recommended to provide a pressure relief valve 24 in the top section of the hydraulic pipe 13 leading into the bypass conduit. The bypass conduit is in the form of a pressure relief pipe 20 of the hydraulic pipe and leads from the hydraulic pipe 13 to the housing 16 below the hydraulic turbine 4 or directly into the upper end of the cylinder 1. When the spear valve 12 is blocked, the increased pressure within the hydraulic pipe 13 can be effectively bypassed around the spear valve 12 through the pressure relief pipe 20 of the hydraulic pipe and released by directly discharging the working fluid into the housing 16 or the cylinder 1.

[0035] Preferably, the RPMs of the hydraulic turbine 4, the flywheel 14, and the generator 15, which are preferably arranged coaxially, are adjusted by the load drawn to the power grid or other receiving units (e.g., an assembly for hydrogen generation located on board a ship, or a battery storage on board a ship or on land, or a nearby floating device, or on land, etc.) such that the speed and RPM of the working fluid are in a preferred ratio. In a simpler but less effective way, the PTO system can also function using only the check valve 11 arranged within or along the hydraulic pipe 13 and using the nozzle holes fixed at the second upper opening of the hydraulic pipe 13. Thus, although it cannot fully latch at the wave trough, it is possible to generate a significant pressure through the resistance of the nozzle and deliver a similarly high power output. However, the performance of the cut-off / on function will result in a higher output in many wave conditions.

[0036] In another embodiment, the adjustment to fully match the continuous rotation and RPM of the common axis of the hydraulic turbine 4 and the flywheel 14 (and in some cases the generator 15 as well) to the pressure and thus the speed of the working fluid hitting the hydraulic turbine 4 can use the flow of current from the battery or the power grid. The generator 15 will instead act as a motor during this stage to rotate the hydraulic turbine 14. In this solution, there is no delivery of electricity to the power grid during the stage when the wave is descending, but it involves more than approximately 10 units in the array of wave energy converters and does not affect the stable delivery of current to the power grid. This is because the power becomes uniform using a larger number of WEC units. The advantage of this consists in that the optimal RPM from the turbine is directly related to the peripheral speed of the turbine. For example, a Pelton turbine requires a speed of the working fluid twice that of the moving blade for the best efficiency.

[0037] By having a smaller flywheel, or eliminating the flywheel if possible, the RPM can be adjusted to match the next incoming wave. Since all incoming waves have a specific height, there is an optimal draft of the floating body, either before releasing the latching or without latching, in terms of the size of the nozzle holes in the spear valve. By measuring the height of the incoming waves, the RPM can be quickly adjusted to match the predicted pressure and velocity of the working fluid, and the efficiency of the turbine can be improved. To achieve the optimal output, the measuring device, installed on the side of the floating device or on a remote buoy or the seabed, can measure the closest incoming wave to adjust the perfect setting for each and every wave, rather than the average wave.

[0038] The housing 16 is disposed above the cylinder 1 and is in fluid communication with the upper end of the cylinder 1 through a third opening at the bottom of the housing 16. Thereby, the working fluid will fall into the cylinder 1 under the influence of gravity. The internal space of the cylinder 1, at least one hydraulic pipe 13, and the housing 16 together form a closed-loop system for the circulation of the working fluid therein. Preferably, the housing 16 is liquid-tight in at least the surface area that will normally be in contact with the working fluid to prevent leakage. As can be seen in FIG. 1, the housing 16 is preferably tapered downwardly towards the upper end of the cylinder 1 to allow the working fluid to flow in. This configuration also allows for accommodating equipment that is larger than the diameter of the cylinder 1 in the housing 16.

[0039] Above the cylinder 1 inside the housing 16, a hydraulic turbine 4 is preferably mounted, which operates on the Pelton wheel / turbine type or a similar principle, such as a Turgo turbine. Alternatively, a reaction turbine, such as a Francis turbine or a similar underwater turbine, can be used, which only requires slightly raising the housing 16 and can increase the height of the wet section under the housing partition 18 that acts like a split floor section. In other words, with a Pelton turbine, the height of the working fluid is around the height of the top of the cylinder 1, and with a Francis turbine, the height of the working fluid is around the height of the wheel of the hydraulic turbine. Alternatively, a turbine driving a hydraulic pump would seem reasonable. The Pelton turbine has the advantages of being able to work with water without being completely submerged and providing excellent performance over a wide range of pressures and flow rates.

[0040] In operation, when the floating device starts to move downward, the pressure and the flow of the working fluid in the hydraulic pipe 13 become zero. If a one-way valve 11 is installed at the upper end of the hydraulic pipe 13, it will close, and similarly, if a drum / ball / solenoid valve 7 is installed, it will also close. If the flow is opened and closed only by the spear valve 12, the spear valve will close. Since there are several options mentioned for closing the flow of the working fluid, the main purpose is to actually avoid the reverse flow of the volume of the working fluid when the floating device descends, which can be achieved in several ways as described above. When the floating device descends, the piston 5 starts to move upward relative to the cylinder 1. A one-way valve 17, which can also be loaded with a spring, opens above or below the piston 5, allowing the working fluid to pass through the piston 5 from top to bottom. The height of the working fluid is kept almost constant when the piston 5 moves only through the working fluid in this way. Since the other valves are closed, in addition to keeping the working fluid at almost the same position, suction occurs below the piston 5. Note also the description with reference to FIG. 2, which outlined an alternative method of piping the working fluid flow but with the same effect.

[0041] The check valve 11 in the hydraulic pipe can be omitted. This is because the closing of the spear valve 12 or the drum / ball / solenoid valve 7 has a similar effect. Similarly, it is possible to operate the system to control the flow by having only the check valve 11 without the drum / ball / solenoid valve 7 or by closing the spear valve 12. If this solution is used, either the fixed or adjustable opening of the spear valve 12 will increase the pressure of the system even if it cannot be latched as described below.

[0042] At the end of the descent of the floating device, i.e., at the wave trough, the piston 5 will be at its uppermost position at the end of its upward stroke. The cylinder 1 will always be filled with the working fluid, so the piston 5 will move upward relative to the working fluid while the floating device is descending. In the case of an alternative solution with the outer return pipe 19, as will be described below with reference to FIG. 2, the cylinder 1 will also always be filled with the working fluid above and below the piston 5, but the working fluid will move from the top of the piston 5 downward below the piston 5 during the downward stage due to the suction created by the relative upward stroke of the piston 5.

[0043] Subsequently, when the floating device moves upward with the waves, the cylinder 1 moves with it, while the piston 5 remains stationary. Most of the working fluid around the piston 5 also remains stationary. The moving working fluid is the compressed working fluid that is squeezed out from at least one opening in the lower part of the cylinder 1. When the spear valve 12 and / or the drum valve 7 are opened and the working fluid can flow, it enters at least one hydraulic pipe 13, is pressed upward through the hydraulic pipe 13, and is guided towards the hydraulic turbine 4. In other words, most of the working fluid remains stationary relative to the surrounding working fluid, meaning that only a small amount of energy is extracted for this operation. One or more one-way valves 17 may be present on the piston 5 itself and / or on the return pipe 19. It is also conceivable to arrange at least one hydraulic pipe 13 inside the cylinder 1, but in that case, the piston 5 has to be redesigned.

[0044] After the working fluid hits the hydraulic turbine 4, the working fluid will freely fall into the cylinder 1 through a third opening between the housing 16 and the upper end of the cylinder 1, keeping the height of the working fluid relatively constant, and is further assisted by the suction created by the piston 5 moving downward relative to the cylinder 1. The same amount of working fluid that is pressed out from the lower end of the cylinder 1 enters the closed loop by this principle and returns into the upper end of the cylinder 1.

[0045] The lifespan of a normal hydraulic power device is longer than 30 years. By using seawater as the working fluid, slightly different grades of stainless steel have to be used to avoid pitting corrosion of the moving blades of the hydraulic turbine 4 and other components. Adding 2% molybdenum is a common method. Otherwise, off-the-shelf turbine concepts can be used.

[0046] However, since the present disclosure proposes a closed system, fresh water with some additives, if possible, is a more suitable working fluid than seawater, but both are possible. Thus, the working fluid used does not corrode the components of the PTO so much as to extend its life and / or reduce the frequency of maintenance inspections and repairs, and keeps the operation of the PTO under optimal conditions. In addition to providing a small closed-loop system, another reason for mounting the hydraulic turbine 4 directly above the cylinder 1 is to avoid having any flexible pipes with a more limited life and to directly utilize the working fluid pressure to reduce power losses. Thus, the hydraulic pipe 13 is preferably made of a rigid material so as to withstand the high pressure of the working fluid.

[0047] The materials of the cylinder 1, the piston 5, the one-way valve 17 of the piston, and the piston rod 6 can be several options, such as, for example, a metal or a polymer composite material provided with reinforcing fibers. Steel or aluminum combined with a composite material is one alternative because it becomes robust and thin with respect to weight. In that case, the assembly and setting also become easier because it is lighter. However, a massive material such as steel, which has holes drilled inside for hole correction and is bent downward on the outside to conform to local stresses as well, is also a useful option.

[0048] Next, referring to FIG. 2, another embodiment is shown, where at least one forward conduit with a one-way valve 17 is replaced with a return pipe 19 on the piston 5. The return pipe 19 extends from the upper end to the lower end of the cylinder 1, is provided with a one-way valve 17, and prevents the working fluid from flowing to the division. In FIG. 2, an optional pressure relief valve 21 is positioned on the piston 5, but one or more pressure relief valves 8 can be positioned in the pressure relief pipe 9 as shown in FIG. 1 to complement each other. The principle of the pressure relief valve 21 can be combined with the one-way valve 17 arranged on the piston 5, the same valve, or adjacent to each other. By designing the floating body such that the actual volume of air in the water and the maximum lifting force are equal to the maximum load of the PTO and the floating body, it will act as a safety valve by itself. In other words, the floating body will sink into the water if any of the above-mentioned relief valves do not open, thereby avoiding structural damage to the floating body or the PTO. Since it is extremely important to survive a storm, a known solution is to force the WEC to sink into the water when a storm occurs. This can be achieved by disabling the pressure relief valves 21 / 24 to a certain closed position, and then closing the valves 7 or 12 as in normal operation at the bottom of the wave, but not opening at a specific pressure as normal. This keeps the floating body mainly submerged in the higher part of the wave motion, thereby avoiding the greater lateral wave power of the wave. To accommodate this option, it is desirable to extend the distance between the upper part of the floating body and the lower part of the housing 16.

[0049] Next, referring to FIG. 3, between the water pressure pipe 13 and the hydraulic turbine 4, a pressure tank 40 arranged to be in fluid communication with the closed loop of the power extraction device is shown. More specifically, in this embodiment, before acting on the hydraulic turbine 4 through the spear valve 12, the working fluid proceeds from the water pressure pipe 13 into the pressure tank 40. The purpose of the pressure tank 40 is to provide a substantially continuous and constant pressure of the working fluid delivered to the hydraulic turbine 4 in order to maintain the rotation of the hydraulic turbine 4. For this purpose, the pressure tank 40 includes a gas / air chamber 45 with a piston or diaphragm 41 that separates air from the working fluid. Alternatively, the piston or diaphragm 41 may be absent, and the line 41 in FIG. 4 simply represents the height of the working fluid. The gas / air pressure sensor 42 continuously monitors the pressure and gives a signal if the pressure is too high or too low, whereby replenishment or discharge can be carried out via the gas / air replenishment cap 44 as necessary. The water height / diaphragm sensor 43 gives a signal when the height of the working fluid reaches this height, whereupon the signal starts the closing of the valve 46 (e.g., a solenoid valve), whereby the gas cannot escape and instead waits for the accumulation of another pressure in a new cycle.

[0050] Next, referring to FIG. 4, in order to minimize the loss of the working fluid to the surrounding seawater, it is conceivable to have a low-pressure section below the cylinder 1 and accumulate all the working fluid that leaks through the upper high-pressure seal portion 51. For this purpose, the lower end portion of the cylinder 1 is divided into two spaces by a cylinder partition wall 53. The cylinder partition wall 53 has a through-opening for the piston rod 6, where a high-pressure seal portion 51 is installed to provide a seal against the piston rod 6. Below the cylinder partition wall 53, a lower space 50 is created and fluidly communicates with the upper end portion of the cylinder 1 or the housing 16 through at least one pressure relief pipe 9 formed by a pipe extending externally along the cylinder 1. The bottom wall of the cylinder 1 has a through-opening for the piston rod 6, where a low-pressure seal portion 52 is installed. All the working fluid that leaks into the lower space 50 through the high-pressure seal portion 51 through at least one pressure relief pipe 9 will be conveyed to the upper end portion of the cylinder 1. In this way, any potential slight leakage of the working fluid to the outside environment will be further reduced.

[0051] Additionally, in FIG. 4, a regulator unit 30 is shown, which is located on the right side of the figure and connected to the hydraulic pipe 13. However, the regulator unit 30 can be installed anywhere that fluidly communicates with the closed loop of the PTO and enables interaction with the working fluid as described below.

[0052] Next, referring to FIG. 5, the regulator unit 30 is shown in more detail. The regulator unit 30 includes a fluid analysis chamber 31, a mixing chamber 32, a filter 33, a waste chamber 34, and an additive chamber 35. In the fluid analysis chamber 31, one or more sensors (not shown) are provided to analyze the state of the working fluid, such as transparency / turbidity, chemical composition, presence and size of solids, etc. The mixing chamber 32 is in fluid communication with the additive chamber 35 that contains additives such as lubricants, corrosion inhibitors, or other media to improve the operation of the PTO. The additives can be added to the working fluid as needed before entering the closed loop of the PTO and mixed with the working fluid in the mixing chamber 32.

[0053] Furthermore, the regulator unit 30 includes a waste chamber 34 for separating solid particles, which may result from wear of the PTO components for example, from the hydraulic fluid. The hydraulic fluid is pumped into the disposal chamber 34 via a separate conduit (not shown) with a check valve, and returned to the closed loop via a filter 33, ensuring that debris remains in the waste chamber 34.

[0054] Presumably, since the hydraulic fluid is somewhat lost over time, the regulator unit 30 is configured to replenish the hydraulic fluid. The hydraulic fluid height sensor 22 at the upper part of the cylinder 1 is activated when the height of the hydraulic fluid falls below a specific height, and then the regulator unit 30 will replenish the hydraulic fluid with water and / or fluid as needed. Rainwater can also be used as a replenishment source. Alternatively, a small electric pump can supply fluid in the upper region of the cylinder 1.

[0055] In the vicinity of the inlet and outlet of the regulator unit 30, a fairing or partition can be provided. The fairing or partition extends into the hydraulic pipe 13, creating an automatic flow through the regulator unit 30 by diverting some of the hydraulic fluid from the hydraulic pipe 13.

[0056] In some embodiments, the regulator unit 30 may further comprise means for communicating with, for example, an external control station located on land, and means for monitoring one or more WEC units. Preferably, the communication is effected through a wireless connection established between the WEC unit and a control station known in the art, or by means of an Internet fiber cable incorporated in a submarine electrical cable leading to land. The regulator unit 30 may also comprise means for generating an alarm and / or sending a signal indicating that repair is necessary to the control station, for example when the working fluid is contaminated, when the additive runs out, when the waste chamber 34 is full, when the height of the working fluid becomes too low, when any valve is blocked or malfunctioning, or in other conceivable situations regarding the function of the power take-off device, the closed loop, or any component. Suitable sensors (e.g., pressure, height of the working fluid, etc.) may be used to determine when an appropriate predetermined threshold is exceeded and an alarm is initiated.

[0057] To counter the horizontal movement of the floating device, the piston rod 6 is directly connected at its lower end to the U-joint 23. The principle of the U-joint 23 is the same as that of any socket wrench set or an automotive propeller shaft. Other flexible solutions may equally well be used. When the PTO involves only vertical movement and is attached to the frame or the like, a rigid connection is appropriate. The U-joint or ball joint 23 is similarly connected to the suction anchor / suction wing / pile / mooring weight 10 on the seabed. Alternatively, a screw or rod may be drilled and fixed to the seabed rock. However, other methods for fixing the piston rod 6 to the seabed are conceivable to counter the relative movement between the piston 5 and the cylinder 1 due to waves, and they fall within the scope of the present disclosure.

[0058] The rotational movement of the floating device 66 due to the change in the direction of the wave also creates a similar rotational movement of the cylinder 1 when the floating body is not round. The piston ring and piston 5 (connected to a substantial fixed piston rod 6 mounted on the seabed) can also rotate inside the cylinder 1 because the friction is reduced by the combined vertical movement. A solution for promoting the rotation between the piston 5 and the cylinder 1 is envisioned to reduce the load and wear in the PTO. For example, the piston 5 may be provided with bearings to facilitate rotation relative to the cylinder 1. Another alternative is to introduce a rotary joint above or below the U-shaped joint 23.

[0059] Referring next to FIG. 6, another embodiment is shown. There, the piston rod 6 comprises a first section 61 attached to the piston 5 and extending into the cylinder 1 from above, a second section 62 disposed outside the cylinder 1 and parallel to the first section, and a third section 63 joining the first and second sections 61, 62 above the cylinder 1. To accommodate the first section 61 of the piston rod 6, the housing 16 is designed in an offset configuration with inclined walls, whereby the axis of rotation of the hydraulic turbine 4 is positioned eccentrically with respect to the longitudinal axis of the cylinder 1. The dashed line in FIG. 6 represents the floating device 66, on which the power take-off device of the present disclosure is mounted to form a WEC unit. The floating device 66 can have various shapes, and one example of a suitable floating device is disclosed in International Publication No. WO 2017 / 160216, which is incorporated herein by reference in its entirety.

[0060] Next, referring to FIG. 7, the PTO housing 16 as seen from above is shown. In this figure, only the third section 63 of the piston rod 6 located above the cylinder 1 and the housing 16 is visible. The misaligned positions of the components for converting wave power into electrical energy, namely the hydraulic turbine 4, the flywheel 14, and the generator 15, are visualized on the right side of FIG. 7. In the actual application of the PTO, the components will be covered with a suitable cover to prevent water from entering. In this reverse configuration of the piston rod 6, the housing 16 is provided with a feed-through opening such that the first section 61 enters the cylinder 1 from above.

[0061] The second section 62 of the piston rod 6 can be adapted to be attached to the seabed by a suitable connection 65, for example, via a suction anchor / suction vane / pile / mooring weight 10, or indirectly via the above-mentioned joint 23 and / or mooring equipment, at its lower end. The connection 65 at the lower end may be directly hammered into the seabed or may be connected to the second section 62 next as a suction anchor, pile, or weight. The cylinder 1 is provided with a pair of sliding connections 64 that are longitudinally spaced apart on the outer surface of the cylinder 1 and are connected to the second section 62 of the piston rod 6, enabling the cylinder 1 to slide along the second section 62 of the piston rod 6. In an alternative configuration of the piston rod 6 attached to the piston 5 from above, the cylinder 1 no longer requires a sealing portion at the lower end, ensuring that the working fluid cannot escape from the closed-loop system into the surrounding water and that seawater cannot enter the closed-loop system.

[0062] In an alternative embodiment, instead of having a WEC unit mounted on the seabed, the piston rod 6 can be mounted on a separate marine structure, such as the leg of an oilfield drilling rig submerged, for example, below the sea surface. This solution has the advantage of improving the PTO and making it available for use on existing marine facilities, regardless of the water depth at the location of the facility. This is because oilfield drilling and similar suitable marine structures involve a huge weight and the draft remains substantially unchanged relative to the seabed. In the reverse configuration of the piston rod 6 as described in relation to FIG. 6 above, the second section 62 of the piston rod 6 will then be mounted parallel and rigidly to the leg of the oilfield drilling at that time.

[0063] The spear valve 12, which controls the pressure and flow of the working fluid hitting the moving blades of the hydraulic turbine 4, needs to be slightly strengthened if it is to be closed or adjusted in all wave cycles, because the number of movements will be more than in conventional use. A separate valve immediately before the spear valve 12 may also be an option to reduce wear and tear of the standard spear valve. This may be, for example, a drum or ball valve 7, a solenoid valve, or other solutions that can open and close the flow of the working fluid at a specific pressure. This valve 7 can be operated, for example, electrically, hydraulically, or pneumatically. The hydraulic turbine 4 can operate using fixed nozzles instead of an adjustable spear valve, especially if it has a plurality of nozzles. Thus, the hydraulic turbine 4 can use a separate valve 7 to admit the pressurized working fluid into the inlet conduit provided around the hydraulic turbine 4.

[0064] For further delicate tuning and system optimization, the opening area of the spear valve 12 is adjusted to fit the size of all incoming waves and can be adjusted even during the upward movement of the waves. The latter is for achieving a ratio that brings the velocity of the working fluid as close as possible to twice the velocity in the moving blades of the hydraulic turbine. To obtain the maximum output, the spear valve 12 or the drum valve 7 will maintain the locking of the system as if it were hydraulically locked when the waves are at their lowest. When the waves rise, the floating device continues to be stationary, whereby the floating device is partially or completely submerged, capturing a large amount of air under water to increase buoyancy and thereby increasing the pressure applied to the working fluid. The higher the waves, the greater the draft of the floating device becomes possible, for example, up to 3 meters is achievable in many areas. The pressure sensors 64 in the lower section of the cylinder 1 and in the upper section of the penstock 13 provide information to the control system. When the desired pressure for the relevant wave height is achieved, the drum valve 7 or the spear valve 12 opens, releasing the high-pressure working fluid to the hydraulic turbine 4 and at the same time enabling the floating device to rise upward. This procedure is called latching and, contrary to other ocean solutions, is realized in a very simple way with this concept. For simpler and smaller WEC units, they can also operate using a fixed nozzle, without the drum valve 7 or the pressure sensor 64, but with lower efficiency.

[0065] The hydraulic turbine 4 is connected to the generator 15, preferably by a vertical shaft installed in the housing 16 at the top of the cylinder 1, or by a horizontal shaft with a drive shaft connected to the generator in a floating device. In the case of a horizontal shaft, the connection may preferably be a propeller shaft. An optional flywheel 14 can be installed in relation to the hydraulic turbine 4 and the generator 15. The optimum pressure of the working fluid coming from the penstock 13 will depend on the size and lifting force of the floating platform, the wave height and wave speed, the diameter of the cylinder 1, the internal flow resistance, as well as the resistance in the flywheel 14 and the generator 15. Since the working fluid will act on the turbine 4 with a large force during each undulation movement, the generator 15 will receive rather rapid accelerating forces even if attenuated by the flywheel 14. This can be attenuated by a torsional or torque coupling between the hydraulic turbine 4 and the generator 15, similar to the solution in wind power applications. If a solution with the generator 15 in a floating device is selected, since this can move in various patterns relative to the cylinder 1, a flexible connection to the generator 15 is required. This is achieved by a propeller shaft having a U-joint at both ends or near both ends. Preferably, splines are provided in the intermediate region. In this way, the U-joint can cope with the frequent and larger movements of the waves hitting the long side of the rectangular platform, while the splines will handle the smaller movements when the waves move the platform from the short side. Similar to the concept used in wind power applications, a torsional or torque coupling related to the propeller shaft can be set.

[0066] As an asymmetric unit, it is also perfectly reasonable to have a horizontal-axis turbine, a flywheel, and a generator all positioned in the housing 16 above the cylinder 1. The advantages of this configuration are that it does not require a drive shaft, the noise generated by swirling the working fluid in the housing 16 is sometimes less, and similarly the losses due to water turbulence are sometimes less. It is desirable to divide the housing 16 into a wet section for the hydraulic turbine 4 and a dry section for the generator 15 and the control system. This is achieved by a vertical housing partition (not shown).

[0067] The option of using a vertical-axis turbine (with the impeller wheel positioned horizontally) and a hydraulic turbine 4 positioned directly above the top of the cylinder 1 where water falls directly into the cylinder 1 is a smaller solution, referring to FIG. 1. The hydraulic turbine 4 can have one or more nozzles, as well as one or more impeller wheels. In this embodiment, the generator 15 can be positioned directly on top of the hydraulic turbine 4. In this setup, the flywheel 14 can be a practical solution directly below the lower impeller wheel and on top of the generator 15, or between them. The housing 16 is divided into a wet section for the hydraulic turbine 4 and a dry section for the generator 15 and the control system. This is achieved by a horizontal housing partition 18 as shown in FIG. 1. It is also conceivable to have two or more turbine wheels 4, and even those with different diameters and different blade sizes, to adapt to changing wave heights and thereby further improve efficiency.

[0068] The outside of the cylinder 1 and the platform can be coated with an antifouling paint. The dark inside of the cylinder 1 attracts less growing organisms. Competent consultants in the field state that this is hardly or only slightly a problem since organisms are generally attracted to brighter areas. Since the working fluid is in constant motion, any major difficulties in this area are significantly reduced. First, additives can be added to the working fluid to avoid this problem and further reduce friction, thereby reducing wear of the components. The additives are preferably environmentally friendly in case of any possible leakage. A possible treatment using a ceramic coating further surely contributes to reducing the organisms attracted to the cylinder 1 wall.

[0069] Nevertheless, the piston 5 has upper and lower scrape rings and can remove / it is desirable to remove residues that can grow on the cylinder wall. The stroke length in normal operation is considerably shorter than the maximum length, and the residues in the upper and lower regions may need to be cleaned periodically. This can be done by releasing the joint 23 and moving the piston up and down its full length. Releasing one or more anchor lines will also pull the piston 5 to the lower position and thus to the lower section of the cylinder 1. Another option is to attach additional scrape pistons of low height but the same diameter to the upper region and possibly also to the lower region and move them towards the center from time to time.

[0070] To clean the piston rod 6, a feasible solution is to attach a movable brush around the piston rod. The movable brush is driven upward by buoyancy and downward by its own weight or a line through the wheel of the weight 10 and then upward to the floating device. It is also possible to move it circularly as well as up and down using pressurized air, pressurized water, or an electric motor. A fifth option is a movable high-pressure water nozzle or a robot operated from the outside by a diver or from remote control on the ship.

[0071] The electricity that powers the system can be taken from the generator 15 and supplied to the system via a converter connected to the battery. Alternatively, since the periods without wind at sea are extremely short, small and simple wind or solar units can supply sufficient power to the battery. Reverse current from the power distribution network is also possible.

[0072] In any technical system, there is a risk of component failure or deformation. In addition to the pressure relief valves 8, 21, 24 described above, it may or is desirable to set up more safety components. These may include explosive cartridges or weaknesses to break and release the piston rod 6 or bearing connection in the event of a sudden stop of the piston and / or in the event of valve blockage or malfunction. Similar solutions can also be applied to some mooring chains so that the platform can be moved laterally from its position, thereby avoiding excessive component collisions when deformation or parts stop moving. Similarly, the control is characterized by attenuating the pressure via the pressure relief valves 8, 21, 24 to avoid exceeding the maximum pressure bar or to completely attenuate the pressure in the event of some defined malfunctions. Alarm sensors connected to the fire suppressant system, as well as bilge pumps, would be similarly applicable. Without listing all options, similar safety settings in ships and aviation are required, especially in larger and more expensive versions of this platform and power extraction concept.

[0073] A preferred embodiment of the power extraction device in a point absorption type wave energy converter has been disclosed above. However, those skilled in the art should understand that it can be varied within the scope of the appended claims without departing from the idea of the present invention.

[0074] All alternative embodiments, or parts of embodiments, described above can be freely combined or used separately from each other without departing from the idea of the present invention, as long as the combination is not contradictory.

Explanation of reference numerals

[0075] 1 cylinder 3 Bearings for connecting to the floating body 4 Hydraulic turbine 5 Piston 6 Piston rod 7 Drum / ball / solenoid valve 8 Pressure relief valve for the cylinder 9 Pressure relief pipe 10 Seabed, weight, suction anchor, or pile 11 One-way valve 12 Spira valve 13 Hydraulic pipe 14 Flywheel 15 Generator 16 Housing 17 Piston one-way valve 18 Housing partition (partition floor between the wet section and the dry section) 19 Interactive return pipe 20 Pressure relief pipe for the hydraulic pipe 21 Pressure relief valve for the piston 22 Height sensor for the working fluid 23 U-joint / ball joint 24 Pressure relief valve for the hydraulic pipe 25 Upper pressure sensor 26 Lower pressure sensor 30 Regulator unit 31 Fluid analysis chamber 32 Mixing chamber 33 Filter 34 Waste chamber 35 Additive chamber 40 Pressure tank 41 Piston / membrane, or height of the working fluid 42 Gas / air pressure sensor 43 Water height sensor 44 Gas / air filling cap 45 Gas / air chamber 46 Solenoid / valve closure 50 Low-pressure chamber 51 High-pressure bushing / sealing part 52 Low-pressure bushing / sealing part 53 Cylinder partition wall 61 First section of the piston rod 62 Second section of the piston rod 63 Third section of the piston rod 64 Sliding connection part 65 Connecting part 66 Floating device

Claims

Claim 1 A power extraction device in a point absorption type wave energy converter, a cylinder (1) adapted to be mounted on a floating device and having a first upper end and a second lower end; a piston (5) arranged to reciprocate inside the cylinder (1) and adapted to be mounted on a mooring facility, having a piston rod (6); at least one hydraulic pipe (13) arranged parallel to the cylinder (1) and having a first lower end in fluid communication with the second end of the cylinder (1) through a first opening therebetween, and a second upper end including a second opening; a housing (16) arranged above the first end of the cylinder (1) and in fluid communication with the hydraulic pipe (13) through the second opening; a hydraulic turbine (4) arranged inside the housing (16), wherein the working fluid entering the housing (16) from at least one of the hydraulic pipes (13) through the second opening is directed to rotate the hydraulic turbine (4) to drive a generator (15) connected to the hydraulic turbine (4); comprising in response to a downward stroke of the piston (5) relative to the cylinder (1), the working fluid present at the second end of the cylinder (1) below the piston (5) enters at least one of the hydraulic pipes (13) through the first opening and exits at least one of the hydraulic pipes (13) through the second opening; the power extraction device wherein the housing (16) is in fluid communication with the first end of the cylinder (1) through a third opening at the bottom of the housing (16), whereby the cylinder (1), at least one of the hydraulic pipes (13), and the housing (16) together form a closed loop for the working fluid of the power extraction device. It further includes at least one front conduit having at least one one-way valve (17), and the one-way valve (17) is configured such that in response to the upward stroke of the piston (5) relative to the cylinder (1), the working fluid can pass from the first end of the cylinder (1) above the piston (5), through at least one of the front conduits, to the second end of the cylinder (1) below the piston (5). A power extraction device, characterized by this.

2. The power extraction device according to claim 1, wherein at least one of the front conduits and at least one of the one-way valves (17) are arranged on the piston (5).

3. The power extraction device according to claim 1, wherein at least one of the front conduits includes a return pipe (19) arranged outside the cylinder (1).

4. It further includes a regulator unit (30) arranged to be in fluid communication with a closed loop formed by the cylinder (1), the hydraulic pipe (13), and the housing (16). The regulator unit (30) is arranged to replenish the closed loop with the working fluid, monitor the working fluid, clean the working fluid, and / or add an additive to the working fluid to reduce friction and / or corrosion in the power extraction device. The power extraction device according to any one of claims 1 to 3.

5. The power extraction device according to claim 4, wherein the regulator unit (30) includes a fluid analysis chamber (31), a mixing chamber (32), a filter (33), a waste chamber (34), and / or an additive chamber (35).

6. It further includes a flywheel (14) arranged to rotate coaxially with the rotating shaft of the hydraulic turbine (4). The hydraulic turbine (4) and the flywheel (14) are separated by a partition wall (18) inside the housing (16). The power extraction device according to any one of claims 1 to 5.

7. It further includes a pressure tank (40) arranged to be in fluid communication with a closed loop between the hydraulic turbine (4) and at least one of the hydraulic pipes (13). The pressure tank (40) is arranged to provide a substantially continuous constant pressure to the working fluid delivered to the hydraulic turbine (4). The power extraction device according to any one of claims 1 to 6.

8. The generator (15) is arranged to rotate the hydraulic turbine (4) in order to control the rotational speed of the hydraulic turbine (4) when the working fluid does not rotate the hydraulic turbine (4), according to any one of claims 1 to 7.

9. The power extraction device according to any one of claims 1 to 8, further comprising at least one valve (11) arranged in at least one of the hydraulic pipes (13) and configured to allow the working fluid to pass from the first lower end portion to the second upper end portion in at least one of the hydraulic pipes (13).

10. The power extraction device according to any one of claims 1 to 9, further comprising at least one first bypass conduit (20) arranged to be in fluid communication with at least one of the hydraulic pipes (13) and the first end portion of the housing (16) or the cylinder (1) below the hydraulic turbine (4), and the at least one first bypass conduit (20) is configured to open at a predetermined pressure and allow the working fluid to pass from at least one of the hydraulic pipes (13), through at least one of the bypass conduits (20), to the housing (16) below the hydraulic turbine (4) or the first end portion of the cylinder (1), and is provided with a first relief valve (24).

11. The power extraction device according to any one of claims 1 to 10, further comprising at least one second bypass conduit (9) having a first lower end portion in fluid communication with the second end portion of the cylinder (1) and a second upper end portion in fluid communication with the housing (16) below the hydraulic turbine (4) or the first end portion of the cylinder (1), and the at least one second bypass conduit (9) is configured to open at a predetermined pressure and allow the working fluid to pass from the second end portion of the cylinder (1) below the piston (5), through at least one of the second bypass conduits (9), to the housing (16) below the hydraulic turbine (4) or the first end portion of the cylinder (1) above the piston (5), and is provided with a second relief valve (8; 21).

12. The power extraction device according to claim 11, wherein at least one of the second bypass conduits (9) with the second relief valve (21) is arranged on the piston (5).

13. The power extraction device according to any one of claims 1 to 12, further comprising a cylinder partition wall (53) that divides the second end of the cylinder (1) into two spaces, the partition wall having an opening with a high-pressure sealing portion (51) surrounding the piston rod (6), the bottom wall of the cylinder (1) having an opening with a low-pressure sealing portion (52) surrounding the piston rod (6), and the lower space (50) being in fluid communication with the first end of the cylinder (1) via at least one third bypass conduit (9) to allow the working fluid to pass in the direction from the lower space (50) to the first end of the cylinder (1).

14. The power extraction device according to any one of claims 1 to 13, wherein the piston rod (6) includes a first section (61) attached to the piston (5) from above, a second section (62) parallel to the first section and disposed outside the cylinder (1), and a third section (63) joining the first and second sections above the cylinder (1), and the cylinder (1) includes a pair of sliding connection portions (64) arranged such that the cylinder (1) can slide along the second section (62) of the piston rod (6).

15. The power extraction device according to any one of claims 1 to 14, wherein the piston rod (6) is arranged to be attached to a separate marine structure.

16. A point absorption type wave energy converter comprising a floating device (66) and the power extraction device according to any one of claims 1 to 15.

17. A method of using the power extraction device according to any one of claims 1 to 15 in a point absorption type wave energy converter for generating electrical energy from the wave power in a body of water.

18. The method according to claim 17, wherein the generator (15) is used to rotate the hydraulic turbine (4) to control the rotational speed of the hydraulic turbine (4) when the working fluid does not rotate the hydraulic turbine (4).

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