GB2410299A

GB2410299A - An ocean power converter

Info

Publication number: GB2410299A
Application number: GB0402826A
Authority: GB
Inventors: Thomas Tsoi Hei Ma
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-01-22
Filing date: 2004-02-10
Publication date: 2005-07-27
Anticipated expiration: 2024-02-10
Also published as: GB2410299B; GB0402826D0

Abstract

An ocean power converter comprises a submarine vessel 10 which is tethered horizontally by a cable 14. The vessel has at least one variable control surface, or swash plate, 36 for inducing a pitching or yawing action. A gyroscopic energy conversion module 20 is installed onboard. The module comprises a circular housing 22 with an internal ring track or groove 21, a moveable frame 30 supported resiliently by springs 33 and flexible seals 31 revolving about an axis 32, and a spinning rotor 40 supported within the revolving frame to rotate about another axis 42. An electric generator 44 is driven by the spinning rotor. The module also comprises an electric motor 46 for driving the rotor at times when it is not gaining rotational energy from the ocean current. A flexible coupling 26 is provide between the shaft 32 of the revolving frame and the shaft 34 of the swash plate.

Description

241 0299 - 1 -

OCEAN POWER CONVERTER

Field of the invention

The present invention relates to a device for converting ocean or river currents energy to electricity.

Background of the invention

0 Most developments of tidal power have concentrated on the conversion of the energy in the tidal stream into a form which can be converted to electrical energy by conventional high speed rotary generators. Examples such as the Seaflow_ rotor concept and the Stingray_ reciprocating wing concept employ high ratio gearbox or hydraulic power system to convert low speed rotating or reciprocating motion (typically 0.5 to 5 m/s) to high speed suitable for the generator running at an air-gap velocity of typically 50 m/s or higher. This mechanical interface required for speed conversion is the most complicated and costly part of a tidal energy converter. In addition, hydraulic systems contribute to energy losses and require regular maintenance which is difficult on the high sea.

Summary of the invention

In order to mitigate at least some of the above problems, there is provided in the present invention a submarine vessel tethered or towed for extracting energy from ocean or river currents, the vessel having at least one variable control surface for inducing pitching or yawing . , motion of the vessel in the ocean current and an energy conversion module installed on-board the vessel comprising a circular housing with an internal ring track or groove, a moveable frame supported resiliently within the housing to revolve about an axis substantially concentric with the said ring track, a spinning rotor supported within the said - 2 revolving frame to rotate about another axis which is perpendicular to the said revolving axis of the frame and which lies in the same plane as the said ring track in the housing such that the spindle of the spinning rotor engages loosely at both ends within the said ring track while revolving with the said revolving frame around the ring track, and an electric generator driven by the said spinning rotor for converting the rotational energy of the rotor to electricity, characterized in that the said control surface lo of the submarine vessel is set into periodic motion at the same frequency as the rotation of the said revolving frame in the energy conversion module thereby inducing the submarine vessel into periodic pitching or yawing motion at the said frequency, and further characterized in that the phasing of the said periodic motion of the control surface relative to the said rotation of the revolving frame is positioned such that the said spinning rotor gains rotational energy by synchronized transfer of angular momentum from the periodic tilting motion of the axis of the resiliently supported revolving frame which is the precession axis of the spinning rotor forcing the spindle of the spinning rotor to tilt by gyroscopic action into rolling contact with the side walls of the ring track thus driving the rotor while revolving in precession motion around the ring track, the said tilting motion being forced by the induced periodic pitching or yawing motion of the submarine vessel in the ocean current.

In the invention, the submarine vessel is deliberately set into periodic pitch and yaw motion against the ocean current in such a way that the induced energy is converted to rotational energy transferred synchronously to the spinning rotor of a gyroscopic device. This converts, in one step, low frequency oscillation to high speed rotation suitable for power generation using a generator of small size and high efficiency driven at high speed by the spinning rotor. Compared with other known tidal energy 3 converters, the invention does not rely on intermediate mechanical interface for speed conversion, therefore has low cost and low energy loss, and can be completely sealed and maintenance free.

The energy used for moving the control surface is small in comparison with the pitching and yawing energy induced in the vessel as a result of moving the control surface. The induced energy then becomes the excitation energy applied to lo the energy conversion module. Furthermore, by coupling the movement of the control surface directly with the precession of the gyroscope, no additional control system is necessary for achieving synchronization with smooth transfer of rotational energy to the rotor, which will happen automatically by design.

The said energy conversion module further comprises an electric motor for driving the rotor at times when the rotor is not gaining rotational energy from the ocean current.

For compactness, this may be integrated with the said electric generator into a combined generator/motor unit.

Preferably, the axis of the revolving frame which is the precession axis of the spinning rotor is supported resiliently along the longitudinal axis of the submarine vessel for it to be tilted in response to both pitching and yawing of the vessel relative to the flow direction of the ocean current. In this case, the precession axis will be forced to wobble in elliptical or circular motion energised by the pitching and yawing motion of the submarine vessel in the ocean current.

Preferably, the control surface is a rotating swash plate mounted on a shaft along the longitudinal axis of the vessel and driven directly by the revolving frame of the energy conversion module. As the swash plate is rotated through a complete revolution, the submarine vessel is - 4 induced to changing pitch and yaw, wobbling in elliptical or circular motion at the frequency of the revolving frame.

In the invention, the spinning speed of the rotor is variable and its precession speed about the revolving frame axis is also variable. Because of the mechanical coupling between the revolving frame and the control surface, the excitation tilting frequency exerted on the frame axis is always the same as the precession frequency, which is the lo condition for the rotor to gain rotational energy by synchronized transfer of angular momentum in response to the forcing frequency of the pitching or yawing motion of the submarine vessel.

The invention makes use of a known principle of a gyroscopic device described in Patent US3726146 and marketed under the trade name Powerball_. This is a body-building ball for hand and wrist exercise composed of gyro ball mounted on ring track. In use, under swinging of the hand, the rotation speed of the gyro ball can be increased from hundreds of RPM to thousands of RPM, resulting in a great force exerted on the hand. When applied correctly, the swinging frequency of the hand would be synchronized with the precession frequency, gaining speed in step with one another.

In the present invention using a similar principle in the energy conversion module, the forcing frequency of pitching and yawing of the submarine vessel is always matched to the precession frequency of the spinning rotor so that the two will gain in speed in step with one another, and the rotational energy transferred to the rotor will be converted to electricity by the generator. Of course, the phasing of the periodic motion of the control surface influencing the tilting motion of the precession axis must be correctly positioned in order to ensure smooth and efficient transfer of rotational energy to the rotor. - 5

The invention differs from other known gyro-based energy conversion devices such as those described in Patents GB2058938 and US4300871, where the method of energy conversion relies on capturing the reactive movements of the precession frame by connecting the frame to a reciprocating piston pump operated at low speed, and the pumped fluid is used to power a hydraulic motor to drive a rotary generator at high speed. As explained earlier, such mechanical interface for speed conversion is complicated and costly.

lo Also the hydraulic system contributes to energy losses and require regular maintenance which is difficult on the high sea. All these problems are mitigated by the present invention.

Preferably, a controller is provided for varying the electrical load on the generator according to the energy I available from the rotor such that there is sufficient residual rotational energy in the rotor to sustain the spinning of the rotor for an indefinite period against bearing and windage losses. To reduce such losses, the energy conversion module may be housed within a sealed chamber which is evacuated of air.

The submarine vessel of the present invention may be additionally provided with a water turbine connected to the said revolving frame in the energy conversion module for assisting the precession motion of the revolving frame, driving the said spinning rotor while the spindle of the spinning rotor is tilted into rolling contact with the said ring track at the correct frequency and phasing induced by the said control surface.

An energy conversion farm made up of a large array of submarine vessels of the present invention tethered horizontally may be deployed in rows and stacks against the ocean current for extracting energy from the current.

Another array of submarine vessels tethered vertically may - 6 - be deployed under the ocean waves for extracting energy from the vertical heaving motion of the waves. In the latter case, the submarine vessel is tethered at a fixed depth and is designed with control surfaces that are reversible so that the vessel continues to wobble in the same direction against both upward and downward column flows produced by the oscillation of the waves. The invention may also be towed by a boat through a current relative to the boat for supplying electricity to the boat.

Brief description of the drawing

The invention will now be described further by way of example with reference to the accompanying drawings in which Figure 1 shows a schematic cross-sectional view of a preferred embodiment of the submarine vessel for use in ocean currents, Figure 2 shows a controller for regulating the energy transfer within the energy conversion module on- board the vessel of Figure 1, Figure 3 shows a schematic cross-section view of the submarine vessel of Figure 1 with the addition of a water turbine, and Figure 4 shows a schematic view of an alternative embodiment of the submarine vessel for use under ocean waves.

Detailed description of the preferred embodiment

Figure 1 shows a submarine vessel 10 tethered horizontally in a submerged position by cable 14. The vessel 10 has at least one variable control surface 36 for inducing pitching or yawing motion of the submarine vessel in the ocean current. An energy conversion module 20 is installed onboard the vessel 10. The module 20 comprises a circular housing 22 with an internal ring track 21, a moveable frame 30 supported resiliently by springs 33 and - 7 flexible seals 31 within the housing 22 to revolve about an axis 32 substantially concentric with the ring track 21, a spinning rotor 40 supported within the revolving frame 30 to rotate about another axis 42 which is perpendicular to the revolving axis 32 of the frame 30 and which lies in the same plane as the ring track 21 in the housing 22 such that the spindle 41 of the spinning rotor 40 engages loosely at both ends within the ring track 21 while revolving with the revolving frame 30 around the ring track 21, and an electric lo generator 44 driven by the spinning rotor 40 for converting the rotational energy of the rotor 40 to electricity. In the invention the control surface 36 is set into periodic motion driven by the revolving frame 30 at the same frequency as the rotation of the revolving frame 30 thereby inducing the submarine vessel 10 into periodic pitching or yawing motion at the said frequency. Furthermore, the phasing of the said periodic motion of the control surface 36 is positioned such that the spinning rotor 40 gains rotational energy by synchronized transfer of angular momentum from the periodic tilting motion against the flexible seal 31 of the axis 32 of the resiliently supported revolving frame 30 which is the precession axis of the spinning rotor 40, forcing the spindle 41 of the spinning rotor 40 to tilt by gyroscopic action into rolling contact with the side walls of the ring track 21 thus driving the rotor 40 while revolving in precession motion around ring track 21.

It would be clear from the above that the ratio of rotor speed versus precession speed is fixed when the spindle 41 is forced into rolling contact with the ring track 21, and is determined by the diameter ratio of the ring track 21 and the spindle 41. Thus, the energy conversion module 20 serves as a speed conversion device from oscillating motion directly to rotating motion, and at a very high step-up ratio and high efficiency. - 8

The energy used for moving the control surface 36 is small in comparison with the pitching and yawing energy induced in the vessel 10 as a result of moving the control surface 36. The induced energy then becomes the excitation energy applied to the energy conversion module 20.

Furthermore, by coupling the movement of the control surface 36 directly with the precession of the revolving frame 30, no additional control system is necessary for achieving synchronization with smooth transfer of rotational energy to lo the rotor 40, which will happen automatically by design.

The energy conversion module 20 further comprises an electric motor 46 for driving the rotor 40 at times when the rotor is not gaining rotational energy from the ocean current. For compactness, this may be integrated with the electric generator 44 into a combined generator/motor unit, which could be one or both of the units 44 and 46.

In Figure 1, the axis 32 of the revolving frame 30 which is the precession axis of the spinning rotor 40 is supported resiliently along the longitudinal axis of the submarine vessel 10 for it to be tilted in response to both pitching and yawing of the submarine vessel 10 relative to the flow direction of the ocean current shown by the dashed line arrows. In this case, the precession axis 32 will be forced to wobble in elliptical or circular motion energised by the pitching and yawing motion of the submarine vessel.

Figure 1 shows a control surface for the submarine vessel 10 provided by a rotating swash plate 36 mounted on a shaft 34 along the longitudinal axis of the vessel 10 and driven directly by the revolving frame 30 of the energy conversion module 20. As the swash plate 36 is rotated through a complete revolution, the submarine vessel 10 is induced to changing pitch and yaw, wobbling in elliptical or circular motion (as shown by the solid-line arrow) at the frequency of the revolving frame 30. A flexible coupling 26 - 9 - is provided between the shaft 32 of the revolving frame 30 and the shaft 34 of the swash plate 36 to take up any misalignment between the two shafts.

Alternatively, other designs for the control surface may be used, including elevators for inducing pitch upwards and downwards, and rudder for inducing yaw to the left and I to the right. Various methods may be used for actuating the control surface synchronized with the precession frequency, lo including gears, cranks, levers and oscillating mechanisms.

The actuator may be driven directly by the revolving frame 30, or remotely triggered by sensors detecting the rotation of the revolving frame 30.

In the present invention, the spinning speed of the rotor 40 is variable and its precession speed about the revolving frame axis 32 is also variable. Because of the mechanical coupling 26 between the revolving frame 30 and the control surface 36, the excitation tilting frequency exerted on the frame axis 32 is always the same as the precession frequency, which is the condition for the rotor to gain rotational energy by synchronized transfer of angular momentum in response to the forcing frequency of the pitching or yawing motion of the submarine vessel 10.

In the invention, the forcing frequency and the precession frequency will gain in speed always in step with one another, and the spinning rotor 40 will gain rotational energy to be converted to electricity by the generator 44.

Of course, the phasing of the periodic motion of the control surface 36 influencing the tilting motion of the precession axis 32 must be correctly positioned in order to ensure smooth and efficient transfer of rotational energy to the rotor 40.

In the invention, the inertia mass and speed range of the rotor 40 could influence the effective amplitudes of - 10 pitch and yaw of the vessel 10, which must be taken into account in determining the rated power that can be extracted from the ocean current.

Figure 2 shows a sensor 38 which measures the speed or frequency of precession of the frame 30 Another sensor 48 measures the spinning speed of the rotor 40. Signals from one or both sensors 38, 48 are fed to a controller 28 which varies the electrical load on the generator 44 according to lo the energy available from the rotor 40 such that there is sufficient residual rotational energy in the rotor 40 to sustain the spinning of the rotor against bearing and windage losses. To reduce such losses, the housing 22 may be sealed and evacuated of air.

The motor 46 is required to drive the rotor 40 up to a minimum speed for the gyro effect to take hold, after which the rotor speed could be selfsustaining by regulating the generator 44 alone even in small current streams. If the current is very weak, the rotor may slow down or stop, then it must be restarted using the motor 46 when there is sufficient current.

In Figure 2, the generator 44 feeds electricity into an external power grid 24 connected to the energy conversion module 20 via the controller 28 and sliding contacts (not shown) between the revolving frame 30 and the housing 22.

The same grid 24 may supply electric power to the motor 46 when required. Alternatively, the generator 44 may be used to charge an on-board battery (not shown) which then supplies the motor 46 when required.

The present invention may be applied to the Stingray_ reciprocating wing concept described earlier in the Background Section. In this case, a hydrofoil wing is triggered to move up and down in a tidal current by changing the angle of attack of the wing at a variable frequency - 11 depending on the speed of the current. By attaching the energy conversion module 20 of the present invention to the pivot support of the wing arm and using the precession frequency of the gyro as the triggering frequency for changing the angle of attack of the wing, the gyro would oscillate with the wing arm always at the correct frequency for smooth transfer of energy to the spinning rotor 40, thus generating electricity directly without relying on the hydraulic interface for speed conversion used previously.

Figure 3 shows the submarine vessel 10 of Figure 1 with the addition of a water turbine 56 connected to drive the revolving frame 30 in the energy conversion module 20. This extracts more energy from the current stream and transfers the energy to the spinning rotor 40 by assisting the precession motion of the revolving frame 30, driving the spinning rotor 40 while the spindle 41 of the spinning rotor is tilted into rolling contact with the ring track 21 at the correct frequency and phasing induced by the rotating swash plate 36. Of course, the size of the water turbine 56 and the size of the rotating swash plate 36 must be optimised such that the driving torque generated by the turbine 56 at the rolling contact of the spindle 41 with the ring track 21 does not exceed the frictional torque created by the tilting force exerted on the spindle 41 at the said rolling contact caused by the induced pitching and yawing of the submarine vessel by the rotating swash plate 36. This ensures no slipping will occur at the rolling contact.

Figure 4 shows two submarine vessels 110, 112 tethered vertically under the crest and the trough respectively of an ocean wave. The crest and trough represent the vertical heaving motion of the wave which is strongest at the surface and gets weaker progressively below the surface. The vessels 110, 112 are tethered by cables 16, 18 respectively at a fixed depth close to the surface where the heaving energy of the wave is still strong. - 12

In Figure 4, each submarine vessel is provided with two control surfaces 136, 138 one at each end of the vessel, and these are reversible so that the vessel continues to wobble in the same direction against both upward and downward column flows produced by the oscillation of the wave, represented instantaneously by the respective dashed-line arrows relative to the vessels 110 and 112. The control surfaces 136, 138 are rotating swash plates similar to that of Figure 1 but with an additional feature of being mounted lo pivotally between two incidence angles relative to each of the rotating shafts 132, 134 respectively. These will be flipped automatically by the changing direction of the current flow as shown in the vessels 110, 112 respectively, and will exert a tilting couple on the vessel always in the same sense so that the vessel will continue to wobble in the same direction throughout the up and down oscillation of the wave. Of course, the length of the vessels 110, 112 should be small in relation to the amplitude of the wave for the heaving current to flow effectively past the vessels.

The ocean power converters shown in Figures 1, 3 and 4 enable conversion of tidal and wave energy to electricity using a generator of small size and high efficiency driven at high speed by the spinning rotor 40. Compared with other known tidal and wave energy converters, the invention does not rely on intermediate mechanical interface for speed conversion, therefore has low cost and low energy loss, and can be completely sealed and maintenance free. - 13

Claims

CLAIMS l

1. A submarine vessel tethered or towed in a submerged position for extracting energy from ocean or river currents, the vessel having at least one variable control surface for inducing pitching or yawing motion of the vessel in the ocean current and an energy conversion module installed on-board the vessel comprising a circular housing with an internal ring track or groove, a moveable frame lo supported resiliently within the housing to revolve about an axis substantially concentric with the said ring track, a spinning rotor supported within the said revolving frame to rotate about another axis which is perpendicular to the said revolving axis of the frame and which lies in the same plane as the said ring track in the housing such that the spindle of the spinning rotor engages loosely at both ends within the said ring track while revolving with the said revolving frame around the ring track, and an electric generator driven by the said spinning rotor for converting the rotational energy of the rotor to electricity, characterized in that the said control surface of the submarine vessel is set into periodic motion at the same frequency as the rotation of the said revolving frame in the energy conversion module thereby inducing the submarine vessel into periodic pitching or yawing motion at the said frequency, and further characterized in that the phasing of the said periodic motion of the control surface relative to the said rotation of the revolving frame is positioned such that the said spinning rotor gains rotational energy by synchronized transfer of angular momentum from the periodic tilting motion of the axis of the resiliently supported revolving frame which is the precession axis of the spinning rotor forcing the spindle of the spinning rotor to tilt by gyroscopic action into rolling contact with the side walls of the ring track thus driving the rotor while revolving in precession motion around the ring track, the said tilting motion being forced by the induced periodic pitching or yawing motion of the submarine vessel in the ocean current.

- 14 -

2. A submarine vessel as claimed in claim 1, wherein said energy conversion module further comprises an electric motor for driving the rotor at times when the rotor is not gaining rotational energy from the ocean current.

3. A submarine vessel as claimed in claims 1 and 2, wherein the said electric generator and electric motor are integrated into one or more combined generator/motor units.

lo

4. A submarine vessel as claimed in claim 1, wherein the axis of the revolving frame which is the precession axis of the spinning rotor is resiliently supported along the longitudinal axis of the submarine vessel for it to be tilted in response to both pitching and yawing of the vessel relative to the flow direction of the ocean current.

5. A submarine vessel as claimed in claim 1 and 4, wherein the control surface is a rotating swash plate mounted on a shaft along the longitudinal axis of the vessel and driven directly by the revolving frame of the energy conversion module.

6. A submarine vessel as claimed in any preceding claim, wherein a controller is provided for varying the electrical load on the generator according to the energy available from the rotor such that there is sufficient residual rotational energy in the rotor to sustain the spinning of the rotor against bearing and windage losses.

7. A submarine vessel as claimed in any preceding claim, wherein a water turbine is additionally provided connected to the said revolving frame in the energy conversion module for assisting the precession motion of the revolving frame, driving the said spinning rotor while the spindle of the spinning rotor is tilted into rolling contact with the said ring track at the correct frequency and phasing induced by the said control surface.

- 15 -

8. A submarine vessel as claimed in any one of claims 1 to 7, wherein the vessel is tethered horizontally against the ocean current for extracting energy from the current.

s

9. A submarine vessel as claimed in any one of claims 1 to 7, wherein the vessel is tethered vertically under the ocean waves for extracting energy from the vertical heaving motion of the waves.

JO

10. A submarine vessel as claimed in any one of claims 1 to 7, towed by a boat through a current relative to the boat for supplying electricity to the boat.