APPARATUS FIELD

Embodiments herein relate to platforms and arrangements for support and control of apparatus for the harvesting and generation of electrical power from water currents, and more particularly, to a structure for supporting underwater turbines that engage one or more generators depending on variation in the current of water flowing thereby. BACKGROUND

Generating electrical power from the harvesting of fluid energy is a type of alternative energy that is commonly found in locations with water currents. An example of such is the generation of electricity from hydro-electric dams, rivers and tidal flows.

US Patent 7,768, 145 to Drentham Susman discloses a water current power generator and turbine unit. The system comprises at least one submerged turbine connected to a generator assembly above the surface of the water. The submerged turbine is oriented such that a longitudinal axis of the turbine is substantially parallel to the direction of the flow of the water and a turbine blade surface faces the water current. The flow of water around the turbine causes rotation of the turbines in which in turn causes co-rotation of a fluid pump for pumping fluid to the generator for generating electricity. A single generator is provided and power output varies in accordance with the water velocity.

US Patent 7, 199,484 (the '484 patent) to Brashears discloses an underwater electrical generator including a stator core and counter-rotating turbine blades with permanent magnets. The turbine has a longitudinal axis that is substantially parallel to the direction of the flow of water. The flow of water around the turbine blades causes rotation thereof. The blade angle can be feathered to alter the blade rotation. The extent of power generation is varied by moving the apparatus to greater or lesser currents. The generator is tethered to the floor of the water body and pivots with direction of current.

Published PCT application WO 2010/033147 or US20100148512A1 , to Pitre, discloses a prolate or ellipsoid body having a helicoid screw turbine thereabout. The body and turbine are tethered for operation in a submerged location. Within the interior of the helicoid screw is a generator for generating electricity. The helicoid screw has a longitudinal axis that is parallel to the direction of the flow of the water. The water flows around the helicoid screw causing the helicoid screw to rotate, causing the generator to generate electrical power. The tethered body aligns with the current, the power generator output is sized for expected current.

In Applicant's patent US 9,279,407, the entirety of which is incorporated herein, a pair of turbines are arranged and supported in a V-shape structure. The turbines are contra-rotating, providing symmetry and counteracting the respective turbine's reactive torque of the current of fluid flowing thereby. System performance is optimized by location in a pre-determined current, controlling the operative angle between the longitudinal axis of the turbine and the direction of the current flow and by controlling a pitch ratio of the turbine. Control surfaces can manipulate the system orientation.

As above, many current fluid power platform technologies comprise a bladed turbine, anchored to the floor of the water body, and coupled to a single large generator sized for the expected current. While many such turbines are conveniently anchored near the floor of the water body, this is also where current velocity is generally lowest.

Additionally, as bladed turbines can have a large vertical extent, sweeping from a high elevation to a low elevation, the current velocity near the bottom of the turbine section may be significantly lower than that near the top. For example, it is not unknown that the current velocity across the height of a turbine to exceed 15%. For example, the velocity at bottom of a turbine can be 3.25 m/s and 3.75 m/s at the top. This uneven velocity results in an unbalanced stress being exerted on the bearings of the turbine, which can result in maintenance issues over time.

Further, the generators are adapted to the design conditions. Tidal power platform designs incorporate a single, large generator connected to the turbine to convert the mechanical motion of the turbine into electrical power. A consequence of using a large generator is that a high velocity is required in order to apply sufficient force to rotate the turbine and drive the generator. Additionally, should current velocities be higher than design, so as to drive the generator to produce power above its power rating, the rotational speed of the turbine must generally be reduced, such as by feathering the turbine blades, in order to prevent damage to either the generator or power conditioning equipment. Such performance compromises for bladed turbines and generator inflexibility result in reduced power efficiency. Further, such generators are often limited to only begin producing once a minimum flow velocity is achieved, and must mitigate turbine speed at higher flow velocities, effectively giving up the power generation potential.

The bladed turbines currently employed are also typically mechanically coupled to the generators. This can be problematic in situations where extremely high flow speeds are present, as mitigating flow using methods such as braking can cause excessive mechanical wear, and feathering the turbine blades may not be enough to sufficiently mitigate the rotational speed of drives the turbines.

Further, as a result of variable power generation, most current fluid power platforms have to condition the power to 60Hz and 1 15kV, or other grid specifications, before transmission to the utility grid.

Additionally, the power generation arrangement for most current fluid power platforms is uni-directional and the platform must be re-oriented in order to harness flow in varying directions, necessary with tidal flows. Further, the submerged location and system for anchoring such platforms are inconvenient for servicing and are inflexible as to depth. SUMMARY

Herein, in general, a power generation system is provided that can adapt to variable fluid current flows, harvest power therefrom and generate electrical output suitable for the local utility grid. The power generation platform can be depth adjusted in the current stream to access the greatest current, yet remain submerged to avoid shipping and be raised to surface periodically for ease of maintenance. As the electric power generated is a function of current velocity cubed, it is extremely beneficial to locate the turbine in high-velocity areas. In tidal environments, the energy that can be harvested from the current is generally optimal closer to the variable surface of the water body. Applicant further recognizes an advantage to retain some ease of access and maintainability. As in most marine environments, there are trade-offs between operability and maintainability.

An electrical generation system is based on the use of a turbine having or turbines having helical screws supported in a frame and angularly oriented relative to the direction of the flow of the water current. Each turbine is restrained underwater and operatively connected to a generator. The generator can then be connected to an electrical grid or to storage facilities.

Each turbine is located within the currents and water flowing thereby causes rotational movement of the helical screw. The rotational movement of the screw is transferred, through one or more means, to the generator for converting the mechanical rotational energy into electrical energy.

In an embodiment, the helical screws or turbines are supported in an overall structure or frame and the turbines are submerged in the current. Herein, two helical turbines are arranged in a structure having a V-shape, providing the angular orientation to the current. The turbines are supported from a, tubular hull. The hull has a longitudinal axis that aligns with the current. The alignment of the hull with the current, and the turbines supported therefrom, align each turbine within the current at an operative angle relative to the direction of the current, the angle being the angle between the longitudinal axis and the direction of the current. Each of the two helical turbines is operatively connected to a generator. The generators can be conveniently located with the hull. The hull is submerged, hence the submerged generators also employ appropriate water lubricated seal technology as known to skilled marine technicians. The frame comprises the hull having fore and aft structural support members for supporting the helical turbines.

Proximal or hull ends of the helical turbines converge at an apex at the hull, also at the location of generators housed therein. Outriggers extend from the hull for supporting end bearings at distal end of the turbines . Buoyancy is provided at various portions of the structure. The overall structure has a positive buoyancy provided by one or more of the hull, turbines and outriggers. . While some elements can have a neutral or native buoyancy, an overall positive buoyancy is provided so that the system can float to surface of the body of water if not anchored. The hull has a longitudinal axis that is aligned with the current, positioning the turbines at the operative angle for power generation. The apparatus generates energy with the flow in both directions negating the need to rotate or otherwise re-align the unit.

In a fully submerged embodiment, the unit is submerged when in operation in both low and high tide scenarios. Such an arrangement is optimal for location in which there is shipping overhead and minimum depth restrictions are in place. The unit is secured with cables to the sea floor so that the minimum depth is provided even at maintained at low tide. For servicing purposes, the winch can be is actuated to loosen the cables and the unit floats to the surface. It is then winched down again for normal operations. This is also the best solution for tidal developments which are prone to rough seas.

Anchor cables remain under tension so that regardless of the water level as the tides rise and fall, the water flows over the restrained structure. In other words, the unit is submerged. When the unit is at the surface, maintenance access is provided to the central hollow pipe-like hull that can contain the power generation and conditioning equipment when the tides are at their lowest. This arrangement also allows for access to the screws and generators. A winch can be attached to at least one anchor cable, so that it is quite easy to adjust the winch cable to raise and lower the unit.

This unit can serve in all in-current tidal applications and adds to the economy of the technology in general. This unit, equipped with a pair of 12 foot diameter by 55 foot long turbines can produce over 2 MWs of power in a 5 m/s liquid flow, such as those available in the Bay of Fundy, Nova Scotia, Canada.

In one broad aspect, a fluid power apparatus is provided having a buoyant frame having a longitudinal axis and having first and second helical turbines supported thereon. The first helical turbine is rotatable about a first turbine axis, and the second helical turbine is rotatable about a second turbine axis, the first and second turbine axes diverge from one another and have a frame end of the each of the first and second turbine axes intersecting at the frame's longitudinal axis. At least one pump is driven by the first and second helical turbines to convert rotational motion thereof to produce a pressurized drive fluid having a produced fluid rate variable with rotational motion. A plurality of electrical generators is provided, each generator having a fluid driven motor connected thereto for driving its generator, and a controller fluidly connects the drive fluid to one or more of the plurality of motors, the number of motors connected commensurate with the produced fluid rate.

In embodiments the controller monitors the fluid rate and actuates the number of motors to consume the produced fluid rate. Each generator can be operated at a design rotational speed to generate grid frequency.

In another broad aspect, a method for generating power from a variable flow of current using a fluid power platform comprises, anchoring the power platform in the variable current; converting the variable flow of current into a fluid drive fluid; driving a plurality of generators using the drive fluid; and controlling the number of driven generators. If the instant power output exceeds the combined power output of at least one active generator of the plurality of generators, adding an additional generator to the at least one active generator; and if the instant power output is below the combined power output rating of the at least one active generator by a difference of at least the power output rating of one of the at least one active generator, deactivating one of the at least one active generators. BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a perspective view of an embodiment of a fluid power platform disclosed herein having a central hull, fore and aft bracing members, and two helical turbines supported thereon;

Figure 2 is a plan view of the fluid power platform of Figure 1 ;

Figure 3 is a front plan view of the fluid power platform of Figure 1 ; Figure 4 is a side plan view of a helical screw of the fluid power platform of Figure 1 ;

Figure 5 is a schematic representation the hull of the fluid power platform of Figure 1 , depicting hydraulic pumps, a plurality of hydraulic motors and generators, and other components;

Figure 6a is a side view of an embodiment illustrating a fluid power platform anchored and floating near surface at high tide; Figure 6b is a side view of the fluid power platform of Figure 6a wherein the winch has retracted the anchor lines sufficiently so that the platform floats near surface at low tide;

Figure 6c is a side view of the fluid power platform of Figure 6a floating at surface at high tide, and depicting the range of motion of the platform;

Figure 7A is a flowchart of an embodiment of the process to determine whether a hydraulic motor/generator pair should be added or removed from the system;

Figure 7B is a flowchart of an embodiment of the process to manage variation in the power production at about the threshold of the current number of motor/generator pairs currently in operation in the system;

Figure 8 is a plan view of an embodiment wherein a plurality of helical turbines is provided along an extended transverse structure; and

Figure 9 is a perspective view of another embodiment of a power platform a central hull, fore and aft bracing members, and two helical turbines supported therebelow. DETAILED DESCRIPTION OF THE EMBODIMENTS

In Applicant's patent US 9,279,407, the entirety of which is incorporated herein, a pair of turbines are arranged and supported in a V-shape structure. The turbines are contra-rotating, providing symmetry and counteracting each other's reactive torque of the current of fluid flowing thereby. System performance is optimized by controlling the operative angle between the longitudinal axis of the turbine and the direction of the current flow and by controlling a pitch ratio of the turbine. Control surfaces can manipulate the system orientation.

Turning to the present embodiment, and with reference to Figs. 1 - 6, embodiments of the fluid power platform can be applied to harvest power from offshore oceanic environments having bi-directional tidal currents, such as coves, inlets and bays along a coastline, or oceanic environments having unidirectional currents, such as the Gulf Stream.

In the tidal context, the platform is secured in the current such as being anchored to the ocean or sea floor. Accordingly, a fluid power platform is disclosed for generating electrical power or electricity using two or more helical rotors or turbines subject to currents in a body of fluid such as water. Rotation of the turbine converts the kinetic energy of the flowing fluid into electrical power or electricity. In an embodiment, the system can comprise two or more turbines each operatively connected to one or more hydraulic pumps, such as via a direct connection by shaft or flexible drive cable. The drive fluid from the hydraulic pumps is in fluid connection to a plurality of hydraulic motors, each of which is operatively connected to a corresponding generator. The fluid power platform is placed within a flowing current of fluid and the turbines are caused to rotate by the fluid flowing thereby, actuating the hydraulic pumps which flow hydraulic drive fluid to a specified arrangement of hydraulic motors, which in turn drive their respective generators. To maintain optimal utility characteristics, such as frequency, the generators are operated at their optimal rotational speed (rpm). Thus, as variable current speeds, result in variable flow rates of drive fluid, one or more generators can be added or subtracted to matched the turbine output.

As illustrated in Fig. 1 , an embodiment of a fluid power platform 10 is provided for generating electrical energy or power from a flowing current C, in this case water. The platform 10 comprises a fluidly sealed and buoyant central hull 12 having a longitudinal axis 13 two or more aft bracing members 18 located at the aft end of the hull 22, together forming a frame 1 1.

Platform 10 also comprises at least two helical turbines 50,50, such as Archimedes screws, each converging and connected at a proximal or hull end of the turbine to the hull. The hull ends can merge with the hull at cowlings or forward bracing members 16, acting as outriggers, located at the bow end of the hull 20The turbines are further supported at the opposing distal end of each turbine to a respective aft bracing member 18. As the flow can be bi-directional, the terms forward and aft are for the illustrated orientation. The platform 10 generates energy from current C flowing in either direction, reducing the need to orient the unit. Anchor points 24 can be located at various locations about the frame 1 1 . The frame 1 1 has a positive buoyancy and floats to the surface if not anchored. Buoyancy can be provided by any or all of the hull, the turbines and bracing members. The turbines 50,50 themselves can be foam-filled or hollow for achieving about a neutral or positive buoyancy. The lightweight turbines 50,50 result in further weight, material, and supportive structure savings in the system. A winch 26 or similar cable managing device, located on the platform 10, can be used to extend or retract one or more anchor lines 27, thereby elevating or lowering the platform. Each of the forward and aft cables can be operated with their own winch or by one winch, or a shown in Fig. 6C, one winch is applied to one cable whilst a second cable is fixed and merely pivots as the other line is pulled in or played out.

Sealable access ports 14 can be positioned on the hull 12 to allow access into the interior of hull 12 for maintenance and other purposes when the platform 10 is floating at surface. The platform 10 is formed in a planar, horizontal arrangement, residing generally within a narrow elevation of the environment such that there is little difference between the current velocities at the top of the turbines 50,50 compared to the bottom. This results in a balanced force exerted on the bearings of the turbines. As the horizontal profile length and width of the platform 10 is larger than its vertical profile, the platform 10 is able to maintain the turbines 50,50 within the fast-flowing currents closer to the water's surface while at the same time maintaining a sufficient distance from the surface to allow traffic to pass thereabove.

Turning now to Fig. 5, turbines 50,50 are each operatively connected to at least one hydraulic pump 28 located inside the frame 1 1 . In the depicted embodiment, a hydraulic pump 28 is located within each forward bracing member 16. The hydraulic pumps are selected for low input rotational speed for direct connection to the turbines while producing conventional output drive fluid pressures and flows, such as at 5,000 psi. Pumps requiring higher input speeds can implement intermediate gear bow of other rotational interface.

The pumps 28 convert rotational motion of the turbines to produce a pressurized drive fluid having a produced fluid rate variable with rotational motion. A plurality of electrical generators 32 are provided, each generator having a fluid driven motor 30 connected thereto for driving its respective generator 32. A controller fluidly connects the drive fluid F to one or more of the plurality of motors 30, the number of motors 30 connected commensurate with the produced fluid rate F.

Hydraulic pumps 28,28 are fluidly connected to a plurality of hydraulic motors 30 via fluid lines 34, which are in turn each operatively connected to and drive a respective generator 32. Valves or other isolating means, such as proportional control valves 29, can be located between the fluid line 34 and each motor 30 to selectively connect and/or disconnect each motor 30 from the fluid line 34. The generators output electrical power or electricity to at least one transformer 36 also located inside the hull 12.

As stated above, depending on the pump selection, the helical turbines 50,50 can first be connected to a speed increaser, such as a gearbox, which is then connected to the hydraulic pumps 28,28 in order to convert the relatively slow rotation of the turbines 50,50 to a rotational speed sufficient to drive the pumps 28,28 so as to provide a desired flow rate of hydraulic drive fluid F. Alternatively, the turbines 50,50 can be directly connected to the pumps 28,28, which are configured to convert the slow rotation speed of the turbines to a sufficient drive fluid flow rate.

In a preferred embodiment, each of the plurality of hydraulic motors 30 is paired with one of the plurality of generators 32, forming a motor/generator pair 33. A reservoir 35 containing hydraulic drive fluid F is located inside the hull 12 and fluidly connected to the fluid line 34 to supply drive fluid F to the hydraulic pumps 28,28 and receive return and excess drive fluid F from the hydraulic motors 30. Components familiar to one of skill in the art and common to hydraulic actuation systems such as coolers, manifolds 38, pressure filters, suction filters, and the like can be incorporated into the hydraulic system so as to ensure effective and efficient operation.

With reference to Fig. 2, helical turbines 50,50 can be closely spaced to the hull, the hull ends basically extending directly from the apex at the hull for minimizing the amount of structure required to support the turbines, or spaced farther away using longer bracing or outrigger structure as needed to optimally locate the turbines in the current C. The helical turbines 50,50 are preferably arranged in a structure having a V-shape such that their axes of rotation, or turbine axes 51 a, 51 b, are oriented to be angularly offset, or non-parallel, to a direction of the flowing current C. That is, an operative angle a between the direction of the flowing current C and the axes 51 a, 51 b of the helical turbines 50,50 is between the range of 0 and 90 degrees, although practically, a is typically about 25 to 35 degrees for optimal performance of the turbines. Optimal performance of the turbines 50,50 is dependent on factors including the available surface area for exposure to a current C passing thereby. In turn, the surface area of the turbines 50,50 exposed to the current C is a function of the operative angle a and a pitch ratio of the turbines. For illustrative performance data based on operative angle and pitch, some empirical data is show in Table 1.

Other factors that affect the exposed surface area and power production are length of the turbines, outer diameter of the turbines, inner diameter of the turbines, pitch of the helicoid blades, and the number of turns or twists of the helicoid blade. Increasing the surface area of the turbines 50,50 exposed to the current C affects the force acting thereon for rotating the helical turbines 50,50 about their axes 51 a,51 b.

Helical turbine 50 can comprise a shaft 52 of a length L having at least one helicoid blade 54 extending along the entire length of the shaft 52. The at least one helicoid blade 54 defines an outer diameter OD and a pitch P, the length of one full twist or turn of the helicoid blade 54. Each twist or turn of the helicoid blade 54 presents a surface area 56 for exposure to the current C. The relationship between the pitch P and the outer diameter OD can be defined as a pitch ratio PR, such that PR=P/OD. The rate of rotation of various helical turbines of 6 feet (1 .8 m) in length, having an outer diameter of about 9 inches (23 cm), and having various pitches and operative angles a ranging from 27° to 45°, is set out in Table 1 below. TABLE 1 - RATE OF ROTATION (in rpm)

With reference to Fig. 1 and Fig. 9, the rotational movement of a single helical turbine 50 about its axis has an associated reactive torque T acting on the frame 1 1 , placing a rotating load thereon. Accordingly, embodiments herein can comprise a first helical turbine 50 rotatable about its axis 51 a in a first direction and a second helical turbine 50 rotatable about its axis 51 b in a second direction opposite the first direction. The opposite rotation of the second helical turbine 50 creates a balancing torque (T) on the frame 1 1 for substantially counteracting the reactive torque T generated on the frame by the helical turbine. Helical turbines 50,50 of opposing turns can be provided in pairs for countering reactive torque. While a single pair is shown, as shown in Fig. 8, a plurality of pairs of helical turbines 20,20 can be provided along a transverse (shown) or longitudinal (not shown) extended structure such as a barge or structure between floating platforms.

Anchor lines 27 can be attached to anchor points 24 located at various points on the exterior of the power platform 10, and preferably aligned along the line of the intended current C, to anchor the platform to the floor of the body of water and provide the foundation so as to be able to restrain the positively buoyant platform 10 from floating to the water surface.

As depicted in the embodiment in Figs. 6A to 6C, for raising and lowering the system, at least one of the anchor lines 27 can be attached to at least one winch 26, which extends or retracts the anchor line 27. The at least one winch 26 can be located on the body of the platform 10 or on the floor of the body of water. This permits one or control the elevation of the power platform 10, to rise and descend, to maintain the turbines 50,50 within the area of highest current velocity, or to float at surface for retrieval or maintenance. As shown in Fig. 6A, the anchor line 27 connected to the winch 26 is retracted or extended to a sufficient length to allow the platform 10 to float near surface at high tide. Fig. 6B depicts the winch 26 having sufficiently retracted the anchor line 27 from the position in Fig. 6A to allow the platform 10 to float near surface at low tide. Fig. 6C illustrates only one anchor line being drawn in and played out, and the other of fixed length, to show a range of positions of the platform 10, from floating at surface to submerged near the floor of the water body, as the winch 26 retracts and/or extends the anchor line 27 respectively .

As described above, a plurality of generators 32 can be located inside the frame 1 1 which are driven by a plurality of hydraulic motors 30. In a preferred embodiment, each of the plurality of hydraulic motors 30 is paired with one of the plurality of generators 32, forming a motor/generator pair 33. The motor/generator pairs 33 can be individually connected to, or disconnected from, the fluid line 34 so as to dynamically adjust the instant generation capacity of the power platform 10 accordingly with the velocity of the current C flowing past the turbines 50,50 and resulting hydraulic energy produced by the pumps 28. The generators 32 can be of equal or differing power outputs. For example, and with twenty motor/generator pairs per turbine, the arrangement can comprise 20 generators rated for 50kW output, totaling 1 MW. Alternatively, the arrangement can comprise a 12.5kW, a 25kW, a 75kW generator, and 17 50kW generators. Such a configuration allows for the instant generation capacity of the power platform 10 to be stepped up or down in finer increments.

The output frequency of the generators 32 can be chosen to match the frequency of the power grid that will receive the power generated by the fluid power platform 10. Each generator is operated at a design rotational speed to generate grid frequency. By outputting power at the utility gird specifications, power conditioning is minimal or not required at all. The generators 32 typically have an optimal input speed or rpm, such as 1800 rpm for producing power for North American (60Hz) grids and 1500 rpm for European (50Hz) grids. A rotational speed of 1800 rpm for a generator having 2 pairs of poles will output 60 Hz (North America) , and similarly at generator at 1500 rpm will output 50 Hz (United Kingdom). The output of the generators 32 are connected to at least one transformer 36, which steps up the voltage of the electrical power produced by generators 32 to a magnitude suitable for transmission to the utility or power grid.

A controller 60 can be used to monitor the operating parameters of the fluid power platform 10, including the power output of the generators 32, the rotational speed of the turbines 50, the rate of drive fluid being output by the pumps 28,28, the rate of drive fluid used, and pressures in fluid lines 34. Controller 60 can also be configured to connect or disconnect additional generators 32 from the fluid line 34 according to fluid power the various parameters, as further described below.

In use, the length of anchor lines 27 are adjusted by the at least one winch 26 such that the turbines 50,50 are located in the area of greatest current flow velocity, which is typically about 7 meters below surface. The flow of current C past turbines 50,50 applies force to the helicoid blades 54,54 and causes the turbines 50,50 to rotate after a minimum force is reached and resistive frictional and reactive torque is overcome. The rotation of the turbines 50,50 actuates the at least one hydraulic pump 28, which pumps hydraulic drive fluid F through fluid lines 34. The flow of drive fluid F drives selected numbers of the hydraulic motors 30 fluidly connected to the fluid line 34, which in turn drive the generators 32 coupled to the hydraulic motors. Typically, as the platform 10 is beginning or restarting operations, one motor/generator pair 33 is connected to fluid line 34. Various controls can be implemented to manage off-spec power generation.

In a preferred embodiment, various parameters of the platform 10 such as rate of fluid output by the pumps 28, rate of fluid consumption by the motor/generator pairs 33rpm or frequency of the generators 32 are monitored such as by a controller 60.

Simply, in an embodiment, given an instantaneous turbine input to the pumps for producing a nominal output of 10 fluid units, and each motor/generator pair consumes 1 fluid unit, one could allocate 10 motor/generator pairs for power production. If the fluid output rate of the pumps 28 exceeds the combined fluid consumption rate of the currently active motor/generator pairs 33 by a threshold amount, at least one additional motor/generator pair 33 is connected to the fluid line 34, for example by opening a valve 29 located between the motor 30 and fluid line 34. If the fluid output rate of the pumps 28 is lower than the combined fluid consumption rate of the currently active motor/generator pairs 33 by a threshold amount, for example a magnitude of at least the fluid consumption rate of one of the active motor/generator pairs 33, at least one motor/generator pair 33 is disconnected from the fluid line 34, for example by closing a valve 29 located between the motor 30 and the fluid line 34.

For example, if the platform 10 is currently running one 12.5kW generator consuming 0.025 m ³ /min of hydraulic drive fluid, one 25kW generator consuming 0.05 m ³ /min, and one 50kW generator consuming 0.1 m ³ /min, resulting in a total fluid consumption rate of 0.175 m ³ /min, and the current velocity about the turbines 50,50 is such that the pumps 28 are outputting 0.190 m ³ /min of fluid, the controller 60 can disconnect the 12.5kW and 25kW motor/generator pairs 33 and connect one additional 50kW motor/generator pair, such that the combined fluid consumption rate of the motor/generator pairs 33 becomes 0.2 m ³ /min.

Similarly, as an alternate allocation process, or when the pump output is closely matched by the consumption of the numbers of motor/generator pairs, then another parameter, such as rotational speed rpm or frequency, can be monitored. For example, the rpm of each of the generators 32 can be monitored, such as by the controller 60, and a motor/generator pair 33 can be removed if the rpm of the generators fall below a threshold difference from the optimal rpm, and added if the rpm of the generators rise above a threshold difference from the optimal rpm. In this manner, the fluid power platform is capable of adjusting its power output according to the surrounding current velocity, while maintaining peak generator efficiency and on-spec power characteristics, thereby harnessing the power generation potential of variable and higher velocity currents rather than implementing a purposeful and counterproductive downgrading of the rotational speed of the turbines 50,50 in order to avoid the risk of burning out a generator, as is the case in traditional large single-generator configurations.

With reference to Figs. 7A and 7B, a general methodology of an embodiment of a control system is provided. In an example embodiment, operations begin at step 102, as an initial number of motor/generator pairs 33 are connected to fluid line 34. For example, one motor/generator pair 33 can be connected at the start of operations. At steps 104 and 106, controller 60 obtains the current drive fluid production rate P of the pumps 28,28 and the current aggregate drive fluid consumption rate C of the motor/generator pairs 33, respectively. Consumption rate C should be known for a given motor/generator pair. The drive fluid rate P can be measured or determined from other parameters such as pump speed.

At step 108, controller 60 calculates P - C. If the result is greater than, or equal to, a first threshold value T1 , typically a positive number, controller 60 proceeds to step 1 14 and determines whether there are additional motor/generator pairs 33 which can be connected to fluid line 34. While the number of generators is preferably in excess of the expected maximum turbine generation capability for the environment, then serendipitously, if maximum power generation is being achieved, and then some, and no motor/generator pairs 33 are available, then the system could manage the pump output by dumping excess fluid through a relief vale to a reservoir. Alternatively, one could manage turbine input through braking or applying fluid resistance or other means.

In case of emergency, such as a power system failure, the controller could disconnect all motor/generator pairs 33 from the fluid line 34, allowing the drive fluid to circulate freely in a loop back to the reservoir.

In the usual course of events, If controller 60 determines that motor/generator pairs 33 are available, it proceeds to step 1 16 and connects at least one motor/generator pair 33 to the fluid line 34, depending on the magnitude of P - C and the rated fluid consumption rate of the motor/generator pairs 33 to be connected. Controller 60 then returns to steps 104 and 106 to obtain new values for P and C. If, at step 108, controller 60 determines P - C is below T1 , it proceeds to step 1 10. At step 1 10, if controller 60 determines that P - C is equal to, or less than, a second threshold value T2, typically a negative number, it proceeds to step 120 and disconnects at least one motor/generator pair 33, depending on the magnitude of P - C and the rated fluid consumption rate of the motor/generator pairs 33 to be connected, before returning to steps 104 and 106. At step 1 12, if P - C is greater than zero but below the first threshold value T1 , that is, if pumps 28,28 are producing excess fluid that cannot be used up quickly enough by the active motor/generator pairs, but not at a rate that exceeds T1 , then controller 60 proceeds to step 122 and actuates a relief valve to remove the excess fluid, for example, by returning it to the reservoir 35. In this manner, controller 60 adjusts the number of active motor/generator pairs 33 accordingly with the velocity of fluids flowing about the turbines 50,50 such that the motor/generator pairs 33 consume drive fluid at about the same rate it is being flowed by pumps 28,28.

With reference to Fig. 7B, once drive fluid production P is generally balanced with the instantaneous fluid consumption C, controller 60 proceeds to monitor one or more operational parameters of the motors and generators to further fine tune operation of the platform 10, as set out in flow chart 200. At this stage, controller 60 first obtains the current operating parameter(s) of the motors and generators, for example, RPM, frequency, and/or temperature. If the measured operational parameter(s) is above an acceptable value, controller 60 proceeds to step 208 and determines whether at least one additional motor/generator pair 33 is available. If no additional motor/generator pairs are available, controller 60 proceeds to step 210 and disconnects all motor/generator pairs 33 from the fluid line 34. If motor/generator pairs 33 are available, controller 60 connects at least one additional motor/generator pair and returns to step 202 to obtain new values for the operational parameter(s). If, at step 204, controller 60 determines the measured operational parameter(s) is not above acceptable values, it proceeds to step 206 and determines if the parameter(s) is below acceptable values. If the operational parameter(s) is below acceptable values, then controller 60 proceeds to step 214 and disconnects at least one motor/generator pair 33 and returns to step 202. If the operational parameter(s) is not below acceptable values, then controller 60 returns to step 104 and returns to monitoring and controlling the flow of drive fluid. In this manner, controller 60 adjusts the number of active motor/generator pairs 33 accordingly with the velocity of fluids flowing about the turbines 50,50 such that the motor/generator pairs 33 operate within acceptable operational parameters.

To enable control of motor/generator pairs 33, and in an embodiment, valves 29 are proportional flow control valves which allow for the varying of fluid flow through the valve. The proportional control valves 29 can be electrically actuated, and enables the controller 60 or an operator to vary the fluid flow through the motors 30 and gradually increase the speed of the motor/generator pair 33 to the desired rpm. When engaging a motor/generator pair, the proportional valve can ramp up the motor speed and generator driven thereby, to the generator's design rotational speed over a ramp up time. Connecting the motor/generator pairs 33 to the fluid line 34 in this fashion imposes less stress on the motor and generator compared with introducing the motor to the full flow of drive fluid from the fluid line all at once. Further, constant speed motor/generator sets are known for emergency power implementations. For example Eaton Aerospace provides a servo-controlled, variable-displacement, inline axial piston hydraulic motor integrated with a three stage, brushless generator. As the power output and fluid consumption of the individual generators 32 is relatively low, a further advantage of the current system is that the platform 10 is able to begin producing power at lower fluid current velocities compared to traditional large, single-generator turbine configurations. The fluid power platform 10 disclosed is thus able to produce power in a wider range of current velocities relative to current singe-generator platforms.

The output of the generators 32 can all be connected to at least one transformer 36 which steps up the voltage of the generated power to one suitable for distribution in a power grid, for example 10 kV to 30 kV. As generators 32 are selected to produce power at a frequency which matches that of the grid to receive the generated power, further power conditioning is not required before the transformed power is sent to a high voltage power line connected to the receiving power grid. A multitude of power platforms 10 can output their generated power to the high voltage power line, allowing for the convenient connection of power platforms 10 to a power grid on an ongoing basis.

In situations where current velocities are such that the drive fluid F produced by pumps 28,28 would exceed its total fluid consumption capacity, that is the combined fluid consumption rates of all of the motors 30 in the platform 10, excess drive fluid F is simply cycled through the system and relieved to the hydraulic reservoir. The motor/generator pairs 33 can also all be disconnected in the event that all the generators 32 are active and exceed their optimal rpm by an amount greater than the threshold difference.

The platform 10 disclosed offers several advantages compared to existing fluid power generation systems. First, as the tidal platform 10 does not incorporate a large generator or require power conditioning, the per-megawatt cost of producing power is substantially less than that of existing technologies. Additionally, the power-to-weight ratio of the present platform 10 is far less than that of existing technologies, again due in part to the lack of a single large, heavy generator. Further, the helical turbines 50,50 used in the platform 10 are less susceptible to damage from debris compared to bladed turbine systems, as most debris simply rolls through between the helicoid blades of the turbines as opposed to potentially striking and damaging the blades of a bladed turbine. Further still, the present platform 10 is more visually perceptible to marine life, such as fish, as opposed to bladed turbines, as it is easier for marine life to avoid the solid profile of a screw rather than the rotating blades of a turbine. Additionally, the relatively flat profile of the platform 10 allows the system to operate at an optimal depth of about 7 m below surface and not obstruct marine traffic overhead.

In an alternative embodiment, bracing members 16, 16, 18, 18 can be shaped and oriented such that the turbines 50,50 are vertically lower than the central hull 12. Such an embodiment allows the platform 10 to float on the water surface when sufficient slack is provided in the anchor lines 27, while at the same time maintaining the turbines 50,50 submerged at a sufficient depth to take advantage of the current C underneath. Example Embodiment

In an example embodiment, a 1 MW fluid power platform 10 used to generate power for the North American energy grid comprises forty generators 32 capable of producing up to 50kW at 60Hz at 1800 rpm, the motor/generator pairs are located inside hull 12. Two Archimedes screws 50,50, each 55 feet long, 12 feet in diameter and angled at about 35 degrees, are connected to two hydraulic pumps located the hull. The overall frame has a footprint of about 92 feet long by 90 feet wide. Each pump can be rated for an industry standard of 5000 psi, located inside the hull 12. Such a platform is capable of producing power from a current flow velocity of less than 1 m/s to over 5m/s.

The platform is maintained at a vertical position of 7 meters below water surface so as to take advantage of faster current velocities while allowing traffic to pass overhead. The voltage of the power produced by the generators 32 is about 60V, which is transformed up to about 1 1 kV by transformer 36.