Note: Descriptions are shown in the official language in which they were submitted.
CA 02634450 2008-06-18
1
1 RELATED CASE
[ 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.
CA 02634450 2008-06-18
2
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.
CA 02634450 2008-06-18
3
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
3-D
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.
CA 02634450 2008-06-18
4
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
CA 02634450 2008-06-18
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
CA 02634450 2008-06-18
6
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
CA 02634450 2008-06-18
7
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
CA 02634450 2008-06-18
8
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
CA 02634450 2008-06-18
9
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.
CA 02634450 2008-06-18
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
CA 02634450 2008-06-18
11
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
CA 02634450 2008-06-18
12
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.
CA 02634450 2008-06-18
13
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
CA 02634450 2008-06-18
14
1 corner in a rollable seal.
CA 02634450 2008-06-18
1 BRIEF DESCRIPTION OF DRAWINGS
[ 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
CA 02634450 2008-06-18
16
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.
CA 02634450 2008-06-18
17
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.
CA 02634450 2008-06-18
18
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
CA 02634450 2008-06-18
19
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
CA 02634450 2008-06-18
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
CA 02634450 2008-06-18
21
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
CA 02634450 2008-06-18
22
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-
CA 02634450 2008-06-18
23
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
CA 02634450 2008-06-18
24
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
CA 02634450 2008-06-18
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.
CA 02634450 2008-06-18
26
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.
CA 02634450 2008-06-18
27
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
WEC 10
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.
CA 02634450 2008-06-18
28
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.
