CA2634450A1 - Wave energy converter - Google Patents

Abstract

An ocean wave energy converter for electric power generation is proposed, which comprises a shell, with an open top, resting on the ocean floor, enclosing a piston reciprocating along its mainly vertical axis, a rollable annular seal, fixed to the piston and to the shell inner wall, enclosing a vented gas-filled chamber housing an assembly of hydraulic cylinders and fluid energy conversion equipment, with the piston operable in response to pressure changes from ocean waves. In the state of the art, the reciprocating part is designed to resonate at ocean wave frequency. In contrast to this, the special feature of the inventive wave energy converter is the piston is controlled via an inventive fluid power transformer to start and stop discretely in response to a computer algorithm sensing pressure along the seabed for on-coming waves for harvesting, and in this way a substantial improvement in power generation efficiency is achieved. A further object of the invention is to provide an ocean wave generator for recreational purposes by reversing piston function and using electricity to make waves.

Description

[ 1. ] This application claims priority from provisional patent application Ser. No. CA 2 408 3 855 titled Ocean Wave Energy Converter filed Oct. 30, 2002, the teachings of which are incorporated herein by reference.

SUMMARY OF THE INVENTION

[ 2.] The invention relates to ocean wave energy converters ("WEC"s) particularly for 7 application near shore, and more particularly to WEC(s) comprising hydraulic fluid means for converting energy from recurring waves to electric energy.

9[ 3.] Known WECs are mainly for application in deep water where heavy storms are known to play havoc with even the largest of WECs, and long transmission distances add 11 appreciably to power generation costs. The known problem of a WEC having to shield itself from destruction by ocean storms is not solved by the prior art, which is a serious 13 shortcoming with global warming and the weather becoming more volatile.

[ 4.] Known WECs are formed by two or more parts, a first part stationary with the ocean floor and a second part displaceable in a vertical direction relative to the first part, which responds to pressure changes from recurring ocean waves, using hydraulic fluid 17 energy means for converting wave force to power an electric generator.
These are usually resonant devices where mass and spring are adjusted to vary frequency to 19 approximate that of the ocean wave. Those for deep water application, use a float, on or near the ocean surface, flexibly connected to a rod of a hydraulic cylinder fixed to 21 the ocean floor, whose piston reciprocates as waves pass over and pumps fluid to a motor to drive an electric generator. Those for near-shore application are divisible into 23 two groups, those mainly exposed above the ocean waves, and those mainly concealed below the ocean waves. Those above the surface disclose an assembly of floats of different sizes, hinged together, sometimes into a large platform, responsive to a wide range of wave heights and frequencies, intended for recovering 27 the heaving potential of wave energy through movement of hydraulic cylinders near hinges connecting the floats, unfortunately leaving much of the kinetic energy to slip 29 by under the floats.

1 [ 5.] Those mainly concealed below the ocean surface, which rest on the ocean floor concealed below the wave trough at locations of significant wave height, comprise two 3 main types: those with equipment chambers sealed from atmosphere and pressurized, and those with a conduit or snorkel to the surface to communicate with atmosphere.
In the former, inventor Burns discloses in a continuation-in-part application, in W020040003380, an improvement to a WEC initially comprising a chamber with a 7 flexible membrane over the top of a piston, pressured with gas to adjust piston position to about mid-range of operation in a calm sea. A long lever, positioned approximately 9 horizontal, is connected at one end to the underside of the piston and the opposite end to a double-acting hydraulic cylinder near a fulcrum. The lever reciprocates as waves 11 pass over and the hydraulic cylinder pumps fluid from both sides of the piston for use on shore.

13 [ 6.] It is known that gas pressure for WECs that rest on the ocean floor, must be varied for changing tide, increased for rising tide so the piston returns to top position, and reduced for low tide, so the piston returns to bottom position - varied with the tide to avoid piston stalling at the two extremes. Subsequently, inventor Burns filed W02007019640 for 17 a WEC suited for deep water, citing that his earlier improved device can be relatively expensive to construct and maintain. In the latter type WEC, those able to 19 communicate with the surface, inventor Gardner disclosed a WEC in US
6,256,985, that can be sealed and/or vented to atmosphere. Like Burns, Gardner uses the gas-21 pressurized chamber like a spring to keep the piston operating within its range.
Gardnerteaches means for hydraulically adjusting compression of a mechanical spring, 23 and/or in combination, varying the volume of the chamber, to achieve a variable spring force to vary resonant frequency.

[ 7.] It is known resonant devices require damping for limiting swings during excessive resonance. Known resonant devices which employ linear electric motor technology 27 disclose means for electrically damping swings, to slow and limit excessive swings and avoid WEC destruction, and include a fail safe mechanical brake in the event of loss 29 of transmission. The WEC device of Gardner is particularly vulnerable to damage from ocean storms because the piston and shell are on a pedestal above the ocean floor.

1 [ 8.] Unfortunately, known WECs which depend on resonance for satisfactory performance are not well suited for near-shore applications where wave height and frequency vary 3 considerably, because of the need for frequent adjustment of mass and springs and/or gas pressure to approximate the frequency and intensity of the ocean waves.

9.] The inventive WEC, while similar to the near-shore WECs just discussed, overcomes the inherent disadvantages of a resonant device operating in a mixed wave 7 environment. On deciding to solve this problem by using discrete switching and furthering the research in the related case device with the objective to reduce the 9 proposed WEC device to practical use, it was necessary to proceed simultaneously on three main fronts: a) Undertake efficiency studies to quantify fluid transmission 11 efficiency and substantially improve on the prior art; b) Simulate WEC
operation on a computer model, progressively explore possibilities and reject non-productive 13 schemes; and c) Develop the physical model and wave energy enhancements in and improve on state of art WEC survivability in a ocean storm environment.
More particularly, the computer simulation included means to estimate the energy of the on-coming wave, optimal state estimation of the overall WEC system, optimal control that 17 would cause the WEC to follow the idealized state estimation model, and network reduction to reduce switching complexity in the hydraulic fluid piping system.
The 19 discrete switching simulation included a kind of energy swing circuit between the power-stroke and return-stroke, operated in parallel with and independent of the fluid 21 power transformer, to enhance power generation efficiency, analogous to a gas-pressurized shock absorber effect in an automobile.

23 [ 10.] It is an object of the invention to provide an improved WEC system characterized by an inventive fluid piping network with minimal fluid valve switching and computer controlled discrete switching that starts and stops piston movement on sensing an on-coming wave, capable of producing electric energy substantially more efficiently than 27 state-of-art. When strategically positioned near shore below wave trough level at a location of significant wave height, the inventive WEC converts potential and kinetic 29 energy of select ocean waves by a hydraulic fluid system powering an electric generator transmitting power to consumers on shore by cables on the ocean floor.

1 ( 11.] The aforementioned advantages of the inventive WEC include the following: The piston is inherently protected from damage from floating debris by a robust surrounding 3 shell; Energy of changing tides is stored and recovered automatically;
Piston displacement is switched discretely on sensing strength and proximity of the on-coming wave; and electric power is generated substantially more efficiently by judicially selecting waves for harvesting.

7 12.] The following further objects are apparent from viewing drawings of the invention:

[ 13.] The entire column of water up to the wave crest forces down on the piston and 9 transfers force through the stroke distance to the hydraulic fluid system for conversion to electric energy.

11 [ 14.] The kinetic energy of waves moving horizontally is adjustably deflected down to add force to the piston or allowed to pass by safely when forces would be excessive, or the 13 extra power would be surplus to requirements.

( 15.] The piston has an economical, reliable, friction-free, water-tight seal.

[ 16.] The ballast can be readily interchanged when experimenting to maximize generation efficiency, or to improve wave aesthetics when operating in wave making mode, with 17 one of different curve and/or fin design, for more concentrating or less concentrating of wave force.

19 [ 17.] The shell is buoyant with the ballast removed and the piston can be extended above shell top position for additional buoyancy, then floated to shore on high tide, and lifted 21 onto dry land for ease of maintenance.

[ 18.] The inventive WEC can shelter itself from damage from heavy ocean storms by 23 lowering the piston to the bottom position, and further by venting and flooding the gas filled chamber.

[ 19.] The inventive WEC is able to boot itself up from a cold start, like known thermal power generation plants, with electric energy via the underwater cables from a small motor-27 generator set on shore, sufficient to charge the pressure accumulator with energy to 1 run a sump pump to drain flood water after a heavy ocean storm, and to reset the piston to top position to restart generation.

3 20.] The inventive WEC provides a reliable electric energy supply with high availability in a corrosive seawater environment, with shell and ballast made of virtually indestructible 5 high-strength reinforced concrete, moving parts made of stainless steel, and the interior sprayed regularly with fresh water to remove traces of salt which is drained to 7 a sump and pumped to the outside, the fresh water itself being produced by reverse osmosis with power by the WEC.

9 21.) In the context of the invention, the following terms are used to assist in comprehension:

11 [ 22.] "terminal" or "line terminal" means a connection point of a hydraulic fluid line to a port of a hydraulic fluid device, such as 'input terminal' means a point of flow into a 13 device such as a hydraulic motor, pump, accumulator, 'fluid power transformer', etc., and "outlet terminal" means a point of flow out of a hydraulic device.

[ 23.] "cylinder assembly switching state" means valve positions setting the number of cylinders in groups for operation below the piston thereby adjusting the ratio of wave 17 pressure to fluid pressure at the terminal of the cylinder assembly, where state one means all cylinders in operation, providing lowest fluid pressure and highest fluid flow 19 in communication with the fluid power transformer, analogous to shifting gears for the best choice for vehicle load and roadway grade with economy benefits of higher gears, 21 and may also include in the alternative, a second group by-passing the fluid power transformer and communicating directly with an accumulator for that purpose.

23 [ 24.] "fluid power transformer" means a device of a known configuration (Class C) or an inventive configuration (Class A of Class B) that transforms fluid power from one particular combination of pressure and flow at the input terminals to another combination of pressure and flow at the output terminals, analogous to an electric 27 power transformer.

[ 25.] "fluid transposing switch" means a switching device for use with a fluid power 1 transformer comprising four two-way valves, with position indicator means, for transposing the fluid lines to the motor with the fluid lines to the pump in the 3 configuration where a pump serves in place of a fluid motor operating in regenerative mode.

26.] "fluid piping network switching state" means a particular set of fluid control valve positions and motor displacement settings that facilitate hydraulic fluid flow through the 7 fluid power transformer during the power-stroke and return-stroke power production cycle as shown on a schematic drawing.

9 [27.] "fluid energy swing" means a system for transferring fluid energy between the power-stroke and the return-stroke by communication between the hydraulic cylinder 11 assembly and an accumulator without need for hydraulic rotatory equipment.

[ 28.] "ocean-wave-degree" means a unit of measurement in units of time or distance, 13 equivalent to the period of an ocean wave divided by 360, the number of degrees in a wave cycle, used in a context analogous to degrees-before-top-dead-center as commonly shown on a scale on an engine block for advancing ignition timing for internal combustion engines. For example, a wave period of 18 seconds computes to 17 a wave speed of 20 ocean-wave-degrees per second.

[29.] "wave state vector" means a two-dimensional vector representation of the wave within 19 the computer control system, which includes separate vectors for the wave peak and the wave trough. The wave peak vector defines the location of the vertical axis of the 21 wave crest in units along the x-axis corresponding to distance in feet from piston center, and the elevation of the wave crest in units along the y-axis corresponding to 23 elevation in feet relative to the top of shell opening. The wave trough vector defines the location of the vertical axis of the wave trough in units along the x-axis corresponding to distance in feet from piston axis center, and elevation of the wave trough represented in units along the y-axis corresponding to elevation in feet relative 27 to the top of shell opening. The wave peak vector minus the wave trough vector equals the wave vector, the real component of which equals the horizontal distance 29 between the peak axis and trough axis of the wave and the imaginary or quadrature 1 component equals the wave height in absolute terms. The wave vector is used within the computer to select those waves that can be harvested efficiently as they approach 3 the WEC. Other wave vectors are computed to monitor distant waves as they approach from further off-shore.

30.] "Vector Drive" means a system with computer control for optimal functioning of the WEC, which includes sensing a train of on-coming waves, computing their wave state 7 vectors, setting the switching states for the cylinder assembly and the fluid power transformer for various operating conditions as they develop, initiating and controlling 9 the transmitting of energy during the power-stroke-return-stroke power production cycle, and transmitting electric power across the underwater cables to a user on shore.

11 [ 31.] Operation overview of Vector Drive is explained with reference to the power-stroke shown as it would begin in FIG. 2. An optimum state estimator algorithm within the 13 WEC control computer computes the wave vectors and the energy capability of the WEC for a complete power-stroke-return stroke cycle, and uses that dynamic model to control WEC operation. The fluid energy passes from the cylinder assembly below the main piston, through the fluid power transformer to the accumulator during the 17 power-stroke and from the accumulator back through the fluid power transformer to the cylinder assembly to lift the piston during the return-stroke. As the wave crest moves 19 over the top of the piston, seconds in advance of the axis of the crest aligning with the axis of the piston, say 30 - 35 ocean wave degrees in advance of top-dead-centre of 21 the vertical axis of the piston, the computer switches the fluid piping network and the fluid flow by displacement control of the hydraulic rotating devices as shown in FIG. 6 23 or FIG. 7, to start the piston in motion and achieve maximum force-times-distance through the power-stroke, similar to that of an engine when ignition is applied say 30 -35 mechanical degrees in advance of top-dead-centre for maximum torque.
Similarly during the return-stroke, shown as it would begin in FIG. 3, seconds before the wave 27 trough axis aligns with the piston axis, the computer switches the fluid piping network and the fluid flow by displacement control of the hydraulic rotating devices as shown 29 in FIG. 8 or FIG. 9, and hydraulic cylinders return the piston to top position, while discharging seawater like a combustion engine discharges exhaust gases. When 1 wave heights are less than design maximum for the converter, the stroke is reduced so as not to waste energy for an unnecessarily long return-stroke. Consider an ideal 3 system with no losses and the WEC operating in a calm sea with the shell submerged.
The fluid energy generated during power-stroke equals the fluid energy consumed to return the piston to top position. Energy for hydraulic fluid system losses, is drawn from storage in an accumulator, analogous to fuel drawn from the fuel tank for engine 7 losses while idling a combustion engine. Selecting the appropriate "cylinder assembly switching state" is analogous to shifting gears up and down, in 9 accordance with wave height, to keep cylinder operating pressure as close as possible within the high efficiency operating range of about 20% pressure variation between 11 input and output for the preferred fluid power transformer, which in turn is optimally adjusted to facilitate flow and minimize fluid transmission losses.

13 [32.] Computer optimal control techniques are commonly used in state-of-art motor vehicles.
The operation of the main power piston of the inventive WEC is analogous to the operation of the pistons in an internal combustion engine. The inherent variable-piston-displacement feature of the WEC is analogous to the displacement-on-demand 17 feature of current-art efficiency improved combustion engines, where it is claimed under light load conditions up to 4 cylinders of an 8 cylinder engine will shut down 19 automatically to improve efficiency up to 25 percent. Optimal WEC operation follows concepts analogous to state-of-art motor vehicle terms like spark-advance before top-21 dead-center, combustion monitoring, feedback to adjust the ignition timing forthe next power-stroke to maximize efficiency, supercharging, displacement on demand, gear-23 shifting, etc. In high-end automobiles, the engine and transmission control systems adapt to changing conditions, seemingly learning as the car is driven along, and readjusting to changing situations, a control strategy commonly known as sub-optimal adaptive computer controi. The proposed invention uses state-of-the-art optimal 27 control systems for monitoring power conversion operation to maximize efficiency and computer graphics for displaying performance, and the on-coming wave. An algorithm 29 in the computer control system provides a running state estimate of the ocean wave as it approaches within about one wave length of the converter. Optimal control is 31 achieved with state-of-art computer control devices commonly called PLC and DCS

1 controls, which receive input from sensors on all aspects of the inventive WEC and particularly pressure along the seabed under the on-coming waves.

3 33.] An important object of the invention is to transmit hydraulic fluid energy substantially more efficiently than state-of-art fluid transmission through to the electric generator, and particularly through the fluid power transformer, where losses are concentrated in state of art devices. The fluid power transformer serves to transfer energy from the 7 converter piston during the power-stroke to the accumulator and from the accumulator to the converter piston during the return-stroke. The fluid power transformer is 9 optimally adjusted to facilitate flow and minimize energy losses: during the power-stroke output pressure is amplified to match pressure in the accumulator as pressure 11 gradually rises as energy is accumulated. Flow is continually adjusted to optimally control piston velocity throughout the power-stroke to maximize energy in each stroke, 13 minimize energy losses, and maximize overall efficiently. Part of the flow during the power-stroke is directed to a low pressure accumulator to provide a pressure float for the return-stroke to minimize return-stroke energy. At the bottom of the power-stroke, the fluid power transformer is switched to facilitate the return-stroke and the optimizing 17 function repeated to minimize the energy expended to discharge the seawater into the lowest point in the wave trough, return the piston to the top position and await the next 19 wave crest to move into position, and then open the valves to begin the power-stroke.
[ 34.] Efficiency of the inventive WEC is substantially improved with the inventive fluid power 21 transformer over the state-of-art, over the entire range of operating conditions, including boosting and reducing pressure, for both forward and reverse power flows.
23 For efficiency comparison, the best choice of fluid power transformer state-of-art for the inventive WEC application consists of a variable displacement driving motor rotatably coupled to a variable displacement pump. Driving torque equals driven torque. Flow times pressure at the input terminals is approximately equal to flow times 27 pressure at the output terminals when losses are small. An ideal fluid power transformer has no losses. Known state-of-art fluid power transformers pass all the 29 energy through two rotary devices rotatably connected in series such that losses of the driving motor compound the losses of the driven pump resulting in high overall losses.

1 For example, 80% transmission efficiency for each rotary unit compounds to an input requirement which computes as (1/0.80/0.80) to 1.56 per unit input for 1.0 per unit 3 output, or 64% transmission efficiency overall, and 36% losses.

[ 35.] In contrast the inventive fluid power transformer is configured so both rotary devices 5 are connected at a common terminal, that being the input terminal when output pressure is to be increased, and that being the output terminal when output pressure 7 is to be reduced, and a third terminal being the low pressure out flow terminal when output pressure is to be increased, and being the low pressure inflow terminal when 9 output pressure is to be reduced, with the result that for pressure changes of less than 50% most of the power transmitted by-passes the rotary devices and in this way 11 substantially lower losses and substantially higher transmission efficiency is achieved which is apparent from the shaft torque being much lower than state-of-art, for the 13 same power flow. In the inventive fluid power transformer, the discharge device can be a pump or driven motor in regenerative mode, which is driven by the input motor.
(The said low pressure terminal connects to a low pressure accumulator which is switchable to a reservoir at atmospheric pressure.) For example when output pressure 17 is boosted relative to input pressure, (through fluid flow is reduced in proportion), the driving motor needs only supply a motor load equivalent to the pumping or driven 19 motor load (regenerative motor load) which is the product of the incremental increase in output pressure and total output flow plus losses for pumping. For example to boost 21 pressure 10%, power losses by the output motor operating in regenerative mode, as measured at the input shaft to the regenerative motor, are the product of 10%
pressure 23 boost and 90% fluid flow and the efficiency factor for this condition which, to use 80%
efficiency to be consistent with the prior art example, computes as (.10x.90/.80) to approximately 0.1125 per unit input to the shaft of the regenerative output motor. Total fluid power to the input motor including losses computes as (0.1125/0.80) to 0.1406 27 per unit, of which 0.09 per unit is transmitted by the regenerative motor through to the fluid powertransformer output terminals. Total losses forthe inventive fluid transformer 29 compute to 0.0506 per unit or 5.06%, and overall transmission efficiency computes to approximately 95% compared to 64% efficiency for the aforementioned state-of-art 31 fluid power transformer - with the result that 48% more energy is available for 1 generation.

[ 36.1 For example to boost pressure 20%, power losses by the output motor operating in 3 regenerative mode, as measured at the input shaft to the regenerative motor, are the product of 20% pressure boost and 80% fluid flow and the efficiency factor for this condition which, to use 80% efficiency to be consistent with the prior art example, computes as (.20x.80/.80) to approximately 0.2000 per unit input to the shaft of the 7 regenerative output motor. Total fluid power to the input motor including losses computes as (0.2000/0.80) to 0.2500 per unit, of which 0.16 per unit is transmitted by 9 the regenerative motor through to the fluid power transformer output terminals. Total losses for the inventive fluid transformer compute to 0.09 per unit or 9%, and overall 11 transmission efficiency computes to approximately 91 % compared to 64%
efficiency for the aforementioned state-of-art fluid power transformer - with the result that 42%
13 more energy is available for generation.

[ 37.] Similarly for a 50% boost in output pressure, power to the input shaft of the regenerative motor computes as (0.5x0.5/0.80) to 0.3125 per unit, fluid power to the input motor computes as (0.3125/0.80) to 0.3906 per unit, of which 0.25 per unit is 17 transmitted by the regenerative motor through to the output terminals.
Total losses compute as (0.3906-0.25) to 0.1406 per unit or 14.06%, and overall transmission 19 efficiency computes to about 86% for a pressure boost of 50%, compared to 64%
efficiency for the aforementioned state-of-art fluid power transformer ---with the result 21 that 34% more energy is available for generation.

[ 38.] From 42% more to 34% more electric power can be generated by the inventive fluid 23 power transformer in the pressure change range of 20% to 50%, compared to state-of-art fluid transformation means. It is preferable that maximum hydraulic system transmission efficiency be realized by selecting a cylinder switching state so the fluid pressure transformer operates within a pressure change range of about 20%.

27 [ 39.] The same holds true when output pressure is reduced relative to input pressure and fluid through-flow is increased, the additional flow coming by way of the output motor 29 in regenerative mode pumping from the low pressure terminal, as the configuration is 1 essentially the same as if flow through all elements of the fluid power transformer are reversed and the fluid transformer is viewed from the opposite direction.

3 40.] For purposes of this proposal the fluid power transformer with the aforementioned inventive configuration is known in this document as the Class A configuration because it is substantially higher efficiency than the state-of-art configuration which is known in this document as the Class C configuration. It is preferred that the 7 hydraulic motor units have a reversible variable displacement feature with a plus-100-percent-to-minus-100-percent range for added flexibility. In an alternative inventive 9 configuration to the aforementioned Class A configuration, a further inventive fluid power transformer configuration comprises a pump in place of a motor operating in 11 regenerative mode. The motor and pump are rotatably connected by a common shaft and fluid lines connected by way of fluid transposing switch comprising four 2-way 13 valves so the pump is always in place of the regenerative motor and the inventive configuration including said transposing switch is known in this document as the Class B configuration.

[ 41.] The vector drive is the overall control system for the wave energy converter which 17 includes the cylinder assembly below the piston, the fluid power transformer(s), the accumulator(s) and the hydraulic motor(s) that drive the electric power generator(s).

19 [ 42.] The vector drive takes ocean power in the form of alternating ocean waves of variable frequency, computes the wave particulars, and converts wave power to alternating 21 current electric power of constant frequency in synchronism with the electric utility receiving the power. The vector drive of the inventive WEC is analogous to a mirror 23 image of known electric power system art, where variable frequency drives take power from a constant frequency source, convert it to direct current power and then invert it to variable frequency alternating current power to drive an induction motor at a predetermined speed and direction which corresponds to the frequency and phase 27 sequence, respectively, of the power produced. The inventive vector drive for ocean wave generation, where electric power is used to generate waves, is the mirror image 29 of the inventive vector drive for power generation.

1 [ 43.] In the known electric power system, inertia effects are minimized for fast response by using induction motors and extremely fast solid-state circuitry for switching voltage and 3 current. Similarly, in this inventive WEC, inertial effects are minimized for fast piston response. The underside of the converter piston is fixed to a rigid structural aluminum frame, with mass kept to a minimum, allowing the piston to respond quickly when the valves are opened to begin the power-stroke, and stop quickly at the end of the power-7 stroke, then restart quickly into the return-stroke to exhaust water from the converter chamber into the wave trough, and stop again at top position - a total of 2 stops and 9 2 starts per WEC cycle.

[44.] The fluid power transformer in combination with the accumulator going through power-11 stroke and return-stroke functions analogous to a flywheel in a combustion engine, except that fluid transfer losses are much higher than bearing losses and judicious 13 operation is required to minimize fluid power losses. It is another object of the inventive WEC to provide means for energy exchange without significant efficiency losses, in the nature of a fluid energy swing more closely analogous to a flywheel effect, between the piston and an accumulator directly without rotary hydraulic motors 17 or pumps. This fluid energy swing is analogous to a gas-pressurized shock absorber added into a motor vehicle, completely independent of other functions. The variability 19 comes with increasing or reducing the gas pressure and the number of hydraulic cylinders in the energy swing circuit.

21 [ 45.] It is known WECs lose effectiveness as piston dimension in the direction of the on-coming wave increases to about 1/4 wave length. In the preferred arrangement, the 23 shell and the piston are elliptical with wall thickness increased near the minor diameter to strengthen the shell in the direction of the incoming wave. An elliptical converter harvests a wider swath through an incoming ocean wave, restricted only by its minor axis, whereas a circular converter, where both major and minor diameters are the 27 same, becomes less effective as its width increases beyond 1/4 wave length.
An elliptical rollable annular seal functions smoothly like a circular seal, without a 29 tendency to rotate, and a pressure surface approximately 78% of a rectangular piston surface, without the disadvantage of reduced reliability that would result from a sharp 1 corner in a rollable seal.

[ 46.] The invention is explained in greater detail below by means of examples of the 3 operation shown in the drawings.

[ 47.] FIG. 1 is a perspective view of three WECs with their deflectors fully raised, resting on 5 the ocean floor near shore, connected by cables laid on the seabed to a utility on shore.

7[ 48.] FIG. 2 is a perspective view of a WEC with the piston at top position and the deflector fully raised to capture as much energy as possible from an on-coming ocean wave 9 during a power-stroke.

[ 49.] FIG. 3 is a perspective view of the WEC with the piston at the lower limit of the power-11 stroke and the deflector at its lowest position to enable seawater to be discharged into the wave trough during the return-stroke.

13 [ 50.] FIG. 4 is an exploded view of the WEC showing the component parts in perspective view.

15 [ 51.] FIG. 5 is a perspective view of the assembly of hydraulic cylinders with the piston removed.

17 [52.] FIG. 6 is a schematic representation of the hydraulic fluid energy conversion equipment with the piston and cylinder assembly of FIG. 5 represented by a piston with a single 19 cylinder below, with the WEC as shown in FIG. 2, operating in power-stroke, with pressure being boosted through the fluid power transformer and fluid flowing to 21 storage in the accumulator.

[ 53.] FIG. 7 is a schematic representation similar to FIG. 6 operating in power-stroke, 23 except with pressure being reduced through the fluid power transformer and fluid flowing to storage in the accumulator.

[ 54.] FIG. 8 is a schematic representation similar to that of FIG 6, except with the WEC as shown in FIG. 3, operating in return-stroke with pressure from the accumulator being 27 boosted through the fluid power transformer and fluid flowing to the cylinder assembly 1 to lift the piston to top position.

[ 55.] FIG. 9 is a schematic representation similar to FIG. 8 with the WEC
operating in the 3 return-stroke, except with pressure from the accumulator being reduced through the fluid power transformer and fluid flowing to the cylinder assembly to lift the piston to top position.

[ 56.] FIG. 10 is a schematic representation similar to FIG. 6 with the WEC
operating in the 7 power-stroke, with pressure from the accumulator being boosted through the fluid power transformer comprising a motor rotatably connected to a pump, after passing 9 through a fluid transposing switch.

[ 57.] FIG. 11 is a schematic representation similar to FIG. 7 with the WEC
operating in the 11 power-stroke, with pressure from the accumulator being reduced through the fluid power transformer comprising a motor rotatably connected to a pump, after passing 13 through a fluid transposing switch.

[ 58.] FIG. 12 is a schematic representation similar to FIG. 8 with the WEC
operating in the return-stroke, with pressure from the accumulator being boosted through the fluid power transformer comprising a motor rotatably connected to a pump, after passing 17 through a fluid transposing switch.

[ 59.] FIG. 13 is a schematic representation similar to FIG. 9 with the WEC
operating in the 19 return-stroke, with pressure from the accumulator being reduced through the fluid power transformer comprising a motor rotatably connected a pump, after passing 21 through a fluid transposing switch.

[ 60.] FIG. 14 is a schematic representation similar to FIG. 6 with the WEC
operating in 23 power-stroke, except represented by a piston with multi-cylinder assembly below divided into two groups, each represented by a single cylinder, with one cylinder connected to transfer fluid directly to an fluid energy swing accumulator introduced in this arrangement, and with pressure from the second cylinder as before being boosted 27 through the fluid power transformer and fluid flowing to storage in the high pressure accumulator.

1 [61.] FIG. 15 is a schematic representation similar to FIG. 14 except with the WEC operating in return-stroke as shown in FIG. 8 with fluid from the energy swing accumulator 3 acting to return the piston to top position.

[ 62.] This invention utilizes certain principles and/or concepts as are set forth in the claims appended hereto. Those skilled in the arts to which this invention pertains will realize that these principles and/or concepts are capable of being utilized in a variety of 7 embodiments which may differ from the exact embodiments utilized for illustrative purposes herein. For this reason this invention is not to be construed as being limited 9 solely to the illustrative embodiments, but only to be construed in view of the claims.
DETAILED DESCRIPTION

11 [ 63.] The operation of the invention is explained with reference to the drawings. Three WECs 10a,b,c are shown in FIG. 1 resting on the ocean floor 20 near shore 21 with a 13 significant wave 22 passing over them, each slightly offset to the wave crest for smoother electric power flow to the utility. WECs act independently, alternatively communication to atmosphere can be shared via vent piping 12. A canister 11 connected to WEC 10a,b,c by conduits 12a,b,c serves as an alternate communication 17 vent to atmosphere where high waves may be overtopping the vent on the WECs, making it possible to shut off the vent at 10a,b,c. The on-coming wave first 19 encountered the most seaward WEC 10a which has completed the power-stroke and is about to lower the wave deflector. The next most seaward WEC 10b is shown part 21 way through the power-stroke, and least seaward WEC 10c is shown just moments before encountering the on-coming wave. Power and system control cables 23 layed 23 on the ocean floor 20 connect the WECs 10 to a electrical distribution surface structure 24 of an underground electrical distribution system on shore. Fiber-optic lines (not shown) continue underground to a computer control center at some distant location.
A line of pressure sensors 25 layed along the seabed to detect the pressure of the on-27 coming wave close to each WEC connect to the electrical distribution box 24. A
computer within the WEC 10, or at some remote location, computes the ocean wave 29 vectors to establish height, speed and distance from the WEC.

1 [ 64.] WEC 10 is shown in FIG. 2 with the deflector raised in readiness for the power-stroke.
The control computer senses the vertical axis 26a of the wave peak 26, and the vertical 3 axis 27a of the wave trough 27 shown on FIG. 1, computes the wave state vector, and if the wave is within a range suitable for harvesting, initiates the power-stroke using the ocean-wave-degree algorithm. At some point, say 10 degrees, before the wave crest moves over top-dead-center of the piston 32 vertical axis, the fluid power transformer 7 is switched by the computer to allow fluid to flow from the hydraulic cylinder assembly under force from the wave 22 on the piston 32, through to the accumulator(s) 225, 9 shown on FIG. 6, where energy from the power-stroke is stored.

[ 65.] On completion of the power-stroke, the deflector 38 is lowered by the computer for the 11 return-stroke as shown in FIG. 3, in readiness to discharge seawater from the piston chamber 32a into the wave trough 27. The control computer senses the vertical axis 13 27a of wave trough 27 and if the wave trough 27 is suitable for discharging the WEC, initiates the return-stroke using the ocean-wave-degree algorithm for the return-stroke.
At some point say 30 degrees before the wave trough moves over top-dead-center of the piston 32 vertical axis, the fluid power transformer is switched to allow fluid to flow 17 from the accumulator(s) 225 to the hydraulic cylinder assembly 50 to apply force to lift piston 32 and discharge seawater from the piston chamber 32.

19 [ 66.] The exploded view in FIG. 4 shows component parts of the WEC shown in FIG. 2, and 3. The shell 31 is preferably elliptical, with the underside resting securely on the ocean 21 floor 20 and the shell axis nearly vertical. The deflector 38 is secured at hole 41 a with pins 41 to the hydraulic cylinder 39 to a hole 41b in vertically operated sliders at 23 opposite ends of the shell. After the shell is sunk to the ocean floor, a ballast of two or more parts 34a,b is installed on beams that project from the shell. Fingers 42a at the ends of the beams 42 and horizontal pins near the top of the ballast 34a,b lock the ballasts 34a,b to the shell 31. The curvature 43 and fins 44 on the ballast 34a, on the 27 seaward side, opposite the deflector 38, direct wave force to the top of the shell where it adds force to the piston 32 to enhance power production. The rollable annular seal 29 33 has a lip 33a that fixes to the piston 32 and an outer surface 33b that fixes to the inner surface of the shell 32b to form a water seal 1 [ 67.] When the WEC is used for producing waves for recreational purposes, it is turned to face shore 21. The curvature and fins on the ballast 34b on the deflector 38 side direct 3 seawater to the opening at the top of shell 31. In a single motion the deflector 38 moves up and angles forward, as the piston 32 moves up and thrusts seawaterforward to send a strengthened wave towards shore 21. It is proposed to vary the aforementioned single motion by varying the discrete switching, deflector angle 7 adjustment, and piston velocity control features, to send waves at faster speeds to catch up to the wave ahead.

9 68.] The computer 231 controlling the WEC 10 adjusts the wave deflector 38 to add wave velocity energy to the piston 32 for enhancing power generation. The deflector 38 is 11 adjusted vertically by extending four hydraulic cylinders at the same rate:
two 39 at opposite ends of the shell 32 along the major axis of the ellipse, and two below the mid 13 point of the deflector 38 adjacent to the vertical plane through the minor axis of the ellipse of the shell 32. The deflector 38 is rotated by further extending the two cylinders 45a,b adjacent to the minor axis. Alternatively, the deflector 38 can be rotated about its main axis 38a as it is being raised or lowered, by coordinating cylinder sets 39,45 17 so clearance is maintained between the deflector 38 inner surface 38b and upper edge of shell 31.

19 [ 69.] The piston 32 is similar to a mirror image of the shell 31 on a reduced scale, inverted within the shell 31. The stroke of the piston 32 is limited to about twice the vertical 21 dimension of the piston rim and about 2/3 the depth of the shell 32b. The rollable annular seal 33 is fabricated as it would fit about as shown in FIG. 3 between the piston 23 32 and the shell 31 a at the bottom of the stroke so the seal 33 has no circumferential tension.

[ 70.] A vent 35 attached to the side of the shell 31 serves as a hydraulically adjustable snorkel. Piston 32 movement causes air below the piston in the chamber of cylinder 27 assembly 50 to communicate with atmosphere.

[ 71.] The assembly of hydraulic cylinders 50 comprising individual cylinders 51 a-n shown in 29 FIG. 5 are mounted on a base plate 52 which is fixed to the inside bottom of the shell 31, preferably after all WEC equipment is installed and shop tested. The cylinder rods 1 51A-N are fastened to the structural framework 53. At least four castors 55a-d mounted on the framework 53, projecting from a members 54a-d below the bottom of 3 the piston 32, roll in contact with the shell 32b as the piston 32 moves vertically and keeps the axis of piston 32 coincident with the axis of shell 32b.

5 72.] It is preferable in WECs with multi-cylinders that cylinders be switchable in two or more groups to adjust pressure ratio between an ocean wave and the output pressure of the 7 cylinder assembly, such ratio adjustment being inversely proportional to the reduced number of cylinders in operation to the maximum number of cylinders in operation, said 9 ratio adjustment enables fluid pressure adjustment such that the fluid power transformer operates within the plus or minus 20 percent pressure change range.

11 [ 73.] The underside of the piston 32 is secured to the top side of the structural framework 53 by way of access through a hatch (not shown) on the top of the piston 32.
The lip 13 33a of the flexible seal 33 is secured to the top of the piston 32 and the skirt 33b is secured to the inner wall of the shell 32b with the piston 32 in the bottom most position 15 as shown in FIG. 3. It is known art to manufacture flexible seals with reinforced fabric formed over a mold. The annular seal is fully described by measurements of the major 17 and minor axes of the piston and of the shell, and the length of the skirt, by the distance from the bottom of the stroke to the top of the shell. The piston is preferably 19 fluted to enable the annular seal to fit wrinkle-free against the piston as the outer side of the seal rolls into contact with the piston under pressure from seawater as the piston 21 moves up in the return-stroke.

[ 74.] Any seawater that inadvertently enters the chamber if cylinder assembly 50 drains to 23 a sump at the bottom of the shell 31 and is automatically pumped to the outside.
Intermittent pressure-spraying with de-salinated water produced by a small reverse-osmosis fresh water generator keeps traces of salt from settling on equipment within the WEC. Exterior parts can be fabricated in corrosion resistant reinforced concrete 27 for the ballast and the shell, stainless steel, and aluminum for the cylinders and carbon filament or aluminum for the deflector 38.

29 [ 75.] Simulations on the shop floor prove out WEC functions and aid investigation for 1 optimum economy of scale for the prototype for a particular ocean wave site.
For example, to simulate the WEC idling in a calm sea, the piston chamber is partially filled 3 with water, and the piston operated within displacement limits to raise and lower water to the shell brim. Energy of the return-stroke is equal to the energy from the power-stroke, and except for fluid power transformation losses, the WEC could idle indefinitely. Energy of a power-stroke is the product of stroke-distance and ocean head 7 above piston position. Ocean head includes potential head and the forward thrust of wave velocity, or velocity-head, deflected down to the piston. A scale model of the 9 WEC prototype tested in a wave tank can provide an estimate of velocity head parameters for the prototype.

11 [ 76.] An alternative inventive fluid transfer arrangement for further efficiency enhancement, known in this document as a fluid energy swing, from the power-stroke as shown by 13 arrow 251 to the return-stroke as shown by arrow 261, is shown in FIG. 14 and 15.
The assembly of cylinders 221 below the piston is shown divided into two groups. A
first group communicates through line 421 to 2-position fluid valve 414 and line 422-424 with a separate accumulator 425, storing energy from the power-stroke to provide 17 energyforthe return-stroke without incurring losses from fluid pressure transformation.
The fluid energy swing is adjustable from approximately zero to 100 percent of the 19 energy required to return the piston to top position, depending on numbers of cylinders (each with a single-pole double throw fluid switch 414) in the group and accumulator 21 pressure. The second group of cylinders communicates through fluid line 201 to the fluid power transformer similar to that shown in FIG. 6 - 13.

23 [ 77.] The discrete switching methodology of the inventive WEC maximizes transmission efficiency through the fluid power transformer using a single symmetrical piping network with only one fluid valve for all fluid flow combinations for boosting and reducing fluid pressure in power-stroke and return-stroke. The duality principle was 27 applied to develop the network shown in figures FIG. 6-9. The duality of pressure-boost and pressure-reduce, when flow is reversed for power-stroke and return-stroke, 29 shows in two identical pairs, FIG. 6 and 9, and FIG. 7 and 8. The pairs themselves are identical except for the position of the two-position fluid valve 214, which is shown in 1 its fluid flow-through positions, known in this document as a boost/reduce switch.
Computer control adds a duality dimension to the fluid network by setting rotary 3 displacement electrically to control magnitude and direction of flow through the network. In summary, the four views of the fluid piping network, shown in FIG.
6-9, are exactly the same when the extra particulars of fluid flow arrows and fluid flow-through position of the boost/reduce switch 214 are deleted.

7 78.] The surprise outcome: Simplicity in fluid piping, in fluid switching and high transmission efficiency of the inventive discrete switching methodology applied to the fluid power 9 transformer is apparent in FIG. 6-9. Fluid pipes shown in 3-D, show a piping network with only one cross-over (nearthe boost/reduce switch), distinguishing the fluid system 11 network from electrical system wiring which is shown schematically in single line representation in the top most layer. This seemingly unconventional form of 13 presentation in patent disclosure applications, schematic in part for some components while showing the piping in 3-D, fluid valve in flow-through position, and arrows showing fluid flow through the network, is an efficient means for explaining the functionality of the inventive network, particularly for artisans who prefer a fluid power transformerwith 17 a pump in place of a motor in regenerative mode. This additional inventive feature is shown with similar clarity in FIG. 10-13, where a four-element fluid transposition switch 19 310 with elements 311-314 is incorporated into the network for those applications where a pump 322 is preferred to a motor in regenerative mode 222, 223, 222, 223, 21 respectively as shown in FIG. 6-9. (A four-element fluid transposition switch 310, is analogous to a known art 4-pole double throw electric power switch. Other switches are 23 single-pole on-off 215, 415, and single-pole double throw 214, 216, 414. ) [ 79.] Arrows in figures FIG. 6-13 show the direction of flow through the fluid power transformer in boost and reduce configurations for power-stroke and return-stroke.
Flow transducers 211-213 and valves 214-216 connect with multi-conductor control 27 lines in shrink-wrap 232 to the control computer 231, monitor pressure and displacement, flow to and from the cylinder assembly 221, accumulators, and through 29 motor and pump units 222, 223. The explanation follows known art by showing wiring as multi-colored wiring from connectors of transducers and sensors bundled in shrink-1 wrap cable 232 terminated at a connector at the computer 231. All hydraulic motors are fully controllable electrically and are equipped with pressure sensors at inlet and 3 outlet ports, double swing swash-plate fluid displacement actuators with position sensors, and shaft speed indicators.

80.] A signal from a flow transducer 211 on the fluid line of the cylinder assembly is used by the computer to control fluid flow and piston speed during the power-stroke arrow 7 251 and return-stroke arrow 261. Biasing flow in favor of boosting pressure through the fluid power transformer, where receiving-end pressure is about the same as the 9 sending-end pressure, avoids pressures being in balance and there being no flow and the piston seemingly frozen in power-stroke or return-stroke. The target receiving 11 device is inclined to accept flow when the incoming pressure is incrementally higher.
[ 81.] During the power-stroke, shown in FIG. 6, 7, the force of the wave presses down as 13 shown by arrow 251 on the piston 252 onto the cylinder assembly 253 which is schematically represented by a piston and single cylinder 210. Pistons 254, within the cylinders 253 force fluid 255 from cylinder assembly 221 through fluid line 201. In the case where the pressure of the high pressure accumulator is higher than the pressure 17 from the cylinder assembly, the computer sets the boost/reduce switch 214 to "boost", connecting flow pipe 201 to 203 and designates the lower motor 222 as driving motor, 19 as shown in FIG. 6. The computer adjusts the displacement setting to provide power for the motor by drawing from the cylinder assembly and discharging to the low 21 pressure accumulator 224. The pumping is done from the cylinder assembly to the high pressure accumulator 225 by the second motor 223 put in regenerative mode by 23 computer control of the displacement setting on the second motor 223.

[ 82.] When the pressure of the high pressure accumulator is lower than the cylinder assembly, the computer sets the boost/reduce switch 214 to the "reduce"
thereby connecting flow pipe 206 to 203 and designates the upper motor 223 as the driving 27 motor, as shown in FIG. 7. In the "reduce" position, the motor inlet is connected to the cylinder assembly 221 through pipe 201 and the motor outlet to the high pressure 29 accumulator 225. Simultaneously the computer switches the displacement setting of the second motor 222 to regenerative mode to cause it to pump fiuid from the low 1 pressure accumulator 224 to the high pressure accumulator 225. In summary, the two fluid switching states for the power-stroke are identical except for the position of the 3 fluid boost/reduce switch 214.

[ 83.] During the return-stroke, the force from the cylinder assembly is pressing up as shown by arrow 261 under the piston 252 to discharge seawater, as shown in FIG. 8, 9. In the case where the pressure of the high pressure accumulator is lower than the pressure 7 from the cylinder assembly, the computer sets the boost/reduce switch 214 to "boost", and designates the lower motor 222 as driving motor, as shown in FIG. 8. The motor 9 222 inlet is connected through pipe 203 and boost/reduce switch 214 to pipe 206 to the high pressure accumulator 225 and the motor outlet through pipe 204 and 205 to 11 the low pressure accumulator 224. The power of motoring is used to drive the second motor 223 in regenerative mode. The regenerative motor 223 displacement is 13 siniultaneously switched to pump fluid from the high pressure accumulator 225 to the cylinder assembly 221. The boost/reduce switch 214 is shown to be on the same side to that shown in FIG. 7, which reflects the change of view of the fluid flow through the switch from power-stroke 'reduce' to return-stroke 'boost'.

17 [ 84.] During the return stroke, if the pressure of the high pressure accumulator is higher than the pressure of the cylinder assembly, the computer sets the boost/reduce switch 214 19 to "reduce", and designates the upper motor 223 as the driving motor, as shown in FIG. 9. The motor inlet is connected to the high pressure accumulator and outlet to the 21 cylinder assembly. The power of motoring is used to drive the second motor 222 in regenerative mode to pump fluid from the low pressure accumulator 224 to the cylinder 23 assembly. The boost/reduce switch 214 is shown to be on the same side to that shown in FIG. 6, which reflects the change of view of the fluid flow through the switch from power-stroke 'boost' to return-stroke 'reduce'.

[ 85.] The aforementioned figures FIG. 6- 9, are the switching states for what is known in this 27 document as a Class A fluid power transformer where both motors are capable of operating in regenerative mode according to displacement set by the control computer.
29 It may be preferable to use a pump in place of the regenerative motor, inter alia, a pump may be more efficient than a motor driven in regenerative mode, and switch the 1 pump into the regeneration motor location each time regeneration is required. This is done by inserting a fluid transposing switch ahead of the motor and pump as shown 3 in figures FIG. 10 - 13 and toggling the transposing switch such that the pump is always in the position of the regenerative motor as evidenced by comparing FIG. 10 to FIG.
5 6; 11 to 7; 12 to 8; and 13 to 9. The following figures FIG. 10-13 show that the fluid transposing switch makes it possible to use the most efficient rotating equipment 7 available, in what is known in this document as a Class B fluid power transformer, without any loss of flexibility, functionally identical to figures FIG. 6- 9, and independent 9 of other functions of the inventive WEC.

[ 86.] It is shown in FIG. 10 that the fluid transposing switch 310 is in the transpose position.
11 Each of the four fluid switches 311-314 are connected to transpose motor 323 and pump 322 to align with the motor and regenerative terminals shown in FIG. 6.

13 [ 87.] It is shown in FIG. 11 that the fluid transposing switch 310 is in the straight though position and no transposition is required. Each of the four fluid switches 311-314 that 15 make up switch 310 is connected straight through to the motor 323 and pump 322 as shown in FIG. 7.

17 [ 88.] It is shown in FIG. 12 a transposition is required so that the motor 323 and pump 322 are in the same configuration as the motor and regenerative motor in FIG. 8.

19 [ 89.] It is shown in FIG. 13 no transposition is required as the motor 323 and pump 322 are in the same configuration as the motor and regenerative motor in FIG. 9.

21 [ 90.] The fluid transposition switch has an auxiliary function, that of transposition switching the electrical sensors and displacement controls for the motor and pump simultaneous 23 with the fluid transposition. This requires a two-position double-throw switch of the requisite number of poles, plus auxiliary contacts to control the fluid transposition 25 switch. It is preferable that this electrical switching be done entirely within the control computer, where the first part of an algorithm performs the electrical sensor and 27 displacement control transposition, and the second part, the fluid line transposition, is done by an electrical pulse to each valve 311-314 in the fluid transposition switch 310.

1 [ 91.] It is apparent from the discussion of FIG. 6-13 that the two inventive fluid power transformers (Class A and Class B) are functionally equivalent, and would perform 3 equally well for the four main operating conditions, boosting and reducing pressure in the power-stroke and return-stroke. It may be preferable to reduce the low pressure accumulator 224 to atmospheric pressure reservoir 226. A two-position double-throw fluid valve switch 216 at the inlet to the charging pump 516 is switchable to allow the 7 low pressure accumulator 224 to communicate through pipe 208 with the oil reservoir 226 at atmospheric pressure.

9 92.] In the conversion of fluid power to electric power generation, it is preferable during the power-stroke to send about half the fluid energy directly through on-off switch 215 to 11 the hydraulic motor that powers the electric generator and thus avoid the power transformation losses that would otherwise occur if all the energy was sent to storage 13 and then drawn back for generation. A fluid power switch 215 inserted into the cylinder assembly line 202 is kept open for direct generation during power-stroke as shown in FIG. 6, 7, 10 and 11, and kept closed during return-stroke as shown in FIG. 8, 9, 12 and 13.

17 [ 93.] The generator 510 is preferably powered by two hydraulic motors 511, 512, rotatably coupled 513, at least one of which is supplied directly from the cylinder assembly 19 during the power-stroke through an open valve 215 as shown in FIG. 6, 7, 10 and 11.
The second motor is switchable to lead the change-over to operate from the high 21 pressure accumulator 225 during periods of transition, which is at a different pressure than the flow from the cylinder assembly 221 via line 201. These hydraulic motors are 23 operated at constant speed for constant frequency electric power generation. The cylinder assembly valve is closed 225 at the end of the power-stroke and fluid is then supplied from the accumulator 225 for the duration of the return-stroke and during periods of piston inactivity. The computer program has a forward looking state-27 estimator algorithm to estimate the steady level of power that can be produced for a particular on-coming wave condition and determines the best estimate for the power 29 production settings. Such optimal control and optimal state estimator features are known to be programable in state-of-art computer PLC and DCS systems.

1 [ 94.] Power is imported from the utility system on shore, or from a motor-generator set, over the under water cables to an electrical box 514 start the WEC into operation.
Electrical 3 control lines connect the control computer 231 to a computer on shore. A
small electric motor 515 drives a pump 516 to charge the accumulators and hydraulic equipment from a reservoir 226.

[ 95.] Sufficient power is imported to operate the electric motor-pump-set to charge the high 7 pressure accumulator 225 to build up an energy reserve sufficient to run the through a few power-stroke return-stroke cycles and give the computer algorithms time 9 to adjust to ocean wave conditions. After fluid energy in the high pressure accumulator 225 is considered sufficient to sustain continuous electric power production, the fluid 11 line to the turbine is opened, the hydraulic turbines 511, 512 are started and electric generator 510 is brought up to speed and synchronized at the electrical control panel 13 514. Power is exported to shore by increasing turbine displacement to increase power generation.

[ 96.] The aforementioned drawings and discussion have been simplified to assist in comprehension with some details omitted for brevity. A WEC operates continuously 17 when waves are favorable, making it cost-effective to apply high efficiency hydraulic equipment and computer technology to the maximum extent possible. It is known that 19 it is preferable, for greatest efficiency and flexibility, that for optimal state estimation all possible parameters be measurable (accessible and observable) to formulate the 21 computer model for optimal computer control. A comprehensive computer model includes motor speed and fluid displacement indicators, fluid pressure and metering 23 sensors, and fluid valve position indication at all possible points of measurement. It is known good practise for example, that auxiliary contacts on electrically operated devices such as fluid valves in this case, ensure that the devices have responded as required and are in the required position. The hydraulic motors and pumps are 27 preferably the full-range reversible type, actuated with electronic signals, with displacement indicators. The computer on board the WEC is subordinate to a master 29 computer on shore, allowing the master computer to log, review and improve the performance of the slave.

1 [ 97.] The inventive WEC is essentially a computer controlled wave energy harvesting device that relies on a state estimator model of an incoming wave, as determined from 3 pressure transducers on the ocean floor, to set the strategy for the harvesting of each wave cycle. The WEC's, forward looking, discrete switching synchronizes itself to the waves coming on shore, and adjusts itself to harvest only those waves with energy above a predetermined threshold.

Claims (3)

1. A system for converting energy from recurring ocean waves to electrical energy, comprising a wave energy converter and a control computer, said wave energy converter comprising:

a. a shell having a circular or elliptical inner surface about a mainly vertical centre axis, with the bottom end closed, fixed with relation to the ocean floor, with top end open to the sea above and enclosing a converter piston coaxial within said shell, with a rollable annular seal between said shell inner surface and said piston, secured to keep seawater out of a gas-filled chamber vented to atmosphere, below said piston, said piston operable axially in said shell in response to variations in water pressure on said converter piston as ocean waves pass over;
b. a means for deflecting horizontal wave forces downward onto said piston;

c. a means for converting axial forces on top of said converter piston to an assembly of hydraulic cylinders below said converter piston connected so as to pump fluid through a hydraulic fluid system as said converter piston reciprocates in power-stroke and return-stroke cycles in near synchronism with crest and trough of waves passing over;

d. a mean a for converting energy in said hydraulic fluid system to electric energy;
e. said hydraulic fluid system including at least one accumulator, and a fluid power transformer comprising a fluid piping network, including a two-position fluid switch, a motor rotatably coupled to a second motor operable in regenerative mode, all connected to communicate fluid with said cylinder assembly and means for converting fluid energy to electric energy;

f. a means for transferring said electric energy to a receiving device onshore, in the nature of an electric power user or distributor; and g. said control computer comprising means for sensing physical features of on-coming waves, algorithms in optimal state estimation and optimal control, discrete switching, and displacement control for fluid flow through rotary hydraulic devices.

2. The system for converting energy from recurring ocean waves of claim 1, wherein said hydraulic fluid system includes at least one accumulator, a fluid power transformer comprising a fluid piping network, including a two-position fluid switch, a four element two-position fluid transposition switch, a motor rotatably coupled to a pump, all connected to communicate fluid with said cylinder assembly and means for converting fluid energy to electric energy.

3. The system for converting energy from recurring ocean waves of claims 1 and 2, wherein said hydraulic fluid system includes at least one accumulator and fluid power transformer essentially as set out in claims 1 and 2, and which includes a said cylinder assembly particularly divided into at least two groups of cylinders, one group with means for further fluid energy exchange with another accumulator directly without rotary hydraulic motors or pumps.