WAVE ENERGY CONVERTER CONTROL

Abstract

A method of controlling energy conversion and/or applied wave loads for a membrane power conversion wave energy converter (WEC) having a longitudinal axis and at least one cell having a membrane. The method includes acquiring data and determining a value relating to a local sea state at the WEC or to a WEC state of the WEC. Depending on the value determined from the acquired data, one or both of the vertical position of the at least one WEC cell relative to a free surface at still water and/or the angle of incidence of the WEC is adjusted.

Claims

1. A method of controlling energy conversion and/or applied wave loads for a membrane power conversion wave energy converter (WEC) having a longitudinal axis and at least one cell having a membrane, said method comprising: acquiring data and determining a value relating to a local sea state at the WEC and/or to a WEC state of the WEC; and depending on the value determined from the acquired data, adjusting one or both of the vertical position of the at least one WEC cell relative to a free surface at still water and/or the angle between the longitudinal axis of the WEC and an incident wave direction.

2. A method according to claim 1 wherein the WEC comprises a plurality of cells each with a respective membrane and wherein the method comprises adjusting the submergence of the plurality cells simultaneously without substantially altering the inclination of the membranes relative to the horizontal direction.

3. A method according to claim 1 comprising acquiring data to determine a local sea state value by acquiring data relating to one or more of: tidal conditions; weather conditions; wave height; wave period; wave direction; wave energy; sea current strength/direction; wave loads on the WEC; WEC depth, fluid pressure/volume/flow rate within a WEC, WEC valve positions and loads, WEC membrane position, loads and shape, turbine/generator speed/torque and energy conversion of the WEC.

4. A method according to claim 1 comprising identifying an optimal value or optimal range for the vertical position and/or an optimal value or optimal range for the angle of incidence for the determined local sea state value, comparing a current vertical position and/or current angle of incidence and, if it/they deviate(s) from the optimal value(s)/range(s), adjusting one or both of the vertical position and/or the angle of incidence to match the optimal value(s) or to be within the optimal range(s).

5. A method according to claim 4 comprising over-writing the optimal value or optimal ranges for the vertical position and/or angle of incidence with a revised optimal value or revised optimal range based on measured loads and/or WEC energy conversion.

6. A method according to claim 1 comprising acquiring data to determine a WEC state value by acquiring data relating to one or more of: cell volume; membrane loads, structural loads, cell fluid pressure, WEC valve positions, cell membrane position and shape, turbine/generator speed/torque.

7. A method according to claim 6 comprising determining if the WEC state value has an optimum WEC state value or is within an optimal WEC state value range and, if the WEC state value deviates from the optimal WEC state value or is outside the optimal WEC state value range, adjusting one or both of the vertical position and/or the angle of incidence, wherein the vertical position and/or angle of incidence is adjusted until the WEC state value matches the optimal) WEC state value or is within the optimal WEC state value range.

8-34. (canceled)

35. A method of controlling energy conversion and/or applied wave loads for a membrane power conversion wave energy converter (WEC) having a longitudinal axis and at least one cell having a membrane, said method comprising: acquiring data and determining a local sea state value relating to a local sea state at the WEC and a WEC state value relating to a WEC state of the WEC; and depending on the values determined from the acquired data, adjusting one or both of the vertical position of the at least one WEC cell relative to a free surface at still water and/or the angle between the longitudinal axis of the WEC and an incident wave direction, wherein the WEC state value is a power conversion WEC state value and/or a load WEC state value.

36. A method according to claim 35 wherein the WEC comprises a plurality of cells each with a respective membrane and wherein the method comprises adjusting the submergence of the plurality cells simultaneously without substantially altering the inclination of the membranes relative to the horizontal direction.

37. A method according to claim 35 comprising acquiring data to determine a local sea state value by acquiring data relating to one or more of: tidal conditions; weather conditions; wave height; wave period; wave direction; wave energy; sea current strength/direction; wave loads on the WEC; WEC depth, fluid pressure/volume/flow rate within a WEC, WEC valve positions and loads, WEC membrane position, loads and shape, turbine/generator speed/torque and energy conversion of the WEC.

38. A method according to claim 35 comprising identifying an optimal value or optimal range for the vertical position and/or an optimal value or optimal range for the angle of incidence for the determined local sea state value, comparing a current vertical position and/or current angle of incidence and, if it/they deviate(s) from the optimal value(s)/range(s), adjusting one or both of the vertical position and/or the angle of incidence to match the optimal value(s) or to be within the optimal range(s).

39. A method according to claim 38 comprising over-writing the optimal value or optimal ranges for the vertical position and/or angle of incidence with a revised optimal value or revised optimal range based on measured loads and/or WEC energy conversion.

40. A method according to claim 35 comprising acquiring data to determine a WEC state value by acquiring data relating to one or more of: cell volume; membrane loads, structural loads, cell fluid pressure, WEC valve positions, cell membrane position and shape, turbine/generator speed/torque.

41. A method according to claim 40 comprising determining if the WEC state value has an optimum WEC state value or is within an optimal WEC state value range and, if the WEC state value deviates from the optimal WEC state value or is outside the optimal WEC state value range, adjusting one or both of the vertical position and/or the angle of incidence.

42. A method according to claim 41 wherein the vertical position and/or angle of incidence is adjusted until the WEC state value matches the optimal WEC state value or is within the optimal WEC state value range.

43. A method of controlling energy conversion and/or applied wave loads for a membrane power conversion wave energy converter (WEC) having a longitudinal axis and at least one cell having a membrane, said method comprising: acquiring data and determining a value relating to a WEC state of the WEC; and depending on the value determined from the acquired data, adjusting one or both of the vertical position of the at least one WEC cell relative to a free surface at still water and/or the angle between the longitudinal axis of the WEC and an incident wave direction. wherein the submergence and/or angle of incidence is adjusted until the WEC state value matches an optimal WEC state value or is within an optimal range.

44. A method according to claim 43 wherein the WEC comprises a plurality of cells each with a respective membrane and wherein the method comprises adjusting the submergence of the plurality cells simultaneously without substantially altering the inclination of the membranes relative to the horizontal direction.

45. A method according to claim 43 comprising acquiring data to determine a WEC state value by acquiring data relating to one or more of: cell volume; membrane loads, structural loads, cell fluid pressure, WEC valve positions, cell membrane position and shape, turbine/generator speed/torque.

46. A method according to claim 45 comprising determining if the WEC state value has an optimum WEC state value or is within an optimal WEC state value range and, if the WEC state value deviates from the optimal WEC state value or is outside the optimal WEC state value range, adjusting one or both of the vertical position and/or the angle of incidence.

47. A method according to claim 46 wherein the vertical position and/or angle of incidence is adjusted until the WEC state value matches the optimal) WEC state value or is within the optimal WEC state value range.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0108] Embodiments will now be described by way of example only, with reference to the Figures, in which:

[0109] FIG. 1 shows an aerial view of a WEC;

[0110] FIG. 2 shows an open loop example of a method/system;

[0111] FIG. 3 shows a closed loop example of a method/system;

[0112] FIG. 4 shows an example for reducing biofouling;

[0113] FIGS. 5a and 5b show a first example of an adjustment actuator;

[0114] FIGS. 6a and 6b show a second example of an adjustment actuator;

[0115] FIGS. 7a and 7b show a third example of an adjustment actuator;

[0116] FIGS. 8a and 8b show a fourth example of an adjustment actuator;

[0117] FIGS. 9a and 9b show a fifth example of an adjustment actuator;

[0118] FIGS. 10a and 10b show a sixth example of an adjustment actuator; and

[0119] FIG. 11 shows an example of an adjustment actuator for varying the angle of incidence.

DETAILED DESCRIPTION AND FURTHER OPTIONAL FEATURES

[0120] FIG. 2 shows an open loop example for controlling energy conversion and/or applied wave loads for a fully submerged membrane power conversion wave energy converter (WEC) having a longitudinal axis and a plurality of cells each having a respective membrane. The WEC is associated with a control system having a controller.

[0121] In a first step, the method comprises acquiring 1 data relating to wave loads at a sensor mounted on the WEC. In this embodiment, a further step involves acquiring 2 tidal data from an internet source at a remote location.

[0122] The controller of the control system may apply a transfer function 3 to the internet tidal data to determine the current tidal height at the WEC. The controller then uses the wave load data and the current wave height data to determine 4 a local sea state value at the WEC.

[0123] The controller comprises a memory containing a data set (lookup table) comprising an optimal range for the submergence depth and an optimal range for the angle of incidence (i.e. for the angle of incidence between the incident wave direction and the longitudinal axis of the WEC) for the each determined local sea state value.

[0124] The method comprises determining 5 the current submergence and current angle of incidence (e.g. using depth/angle of incidence sensors or from historical data stored in the memory) and if they are not within the optimal ranges, the method comprises adjusting 6 the submergence and the angle of incidence to be within the optimal ranges using an adjustment actuator associated with the WEC.

[0125] Although not shown in FIG. 2, the method further comprises over-writing the optimal ranges (e.g. overwriting the upper and/or lower limits of the ranges) for the submergence depth and/or angle of incidence with a revised optimal range based on measured loads and WEC energy conversion.

[0126] For example, if measured loads (measured using the wave load sensor) exceed a threshold load value, the lower limit (smallest depth) of the optimal submergence range can be increased (i.e. the WEC lowered to towards sea bed) to reduce loads to within acceptable limits. In this way, the data set of optimal ranges can be updated over time based on observed operating conditions.

[0127] FIG. 3 shows a closed loop example for controlling energy conversion and/or applied wave loads for a partially submerged membrane power conversion wave energy converter (WEC) having a longitudinal axis and a plurality of cells each having a respective membrane. The power off-take system of the WEC is exposed. The WEC is associated with a control system having a controller.

[0128] The method comprises acquiring 7 data relating to membrane loads using a membrane-mounted sensor, and using the control system controller to determine 8 a power conversion WEC state value.

[0129] The method comprises determining 9 if the power conversion WEC state value is within an optimal power conversion WEC state value range. If the value is within the desired range, the depth and angle of incidence of the WEC is maintained 10. However, if the power conversion WEC state is outside the optimal WEC state value range, the method comprises adjusting 11 one or both of the submergence and the angle of incidence using an adjustment actuator associated with the WEC.

[0130] The submergence and/or angle of incidence is adjusted until the power conversion WEC state value is within the optimal power conversion WEC state value range. This can be ascertained by acquiring 12 further data after adjusting the submergence/angle of incidence to determine a revised power conversion WEC state value and determining 9′ if the revised power conversion WEC state value is within the desired power conversion WEC state value range. This is repeated until the revised power conversion WEC state value is within the optimal power conversion WEC state value range.

[0131] FIG. 4 shows a method of reducing biofouling of a membrane power conversion wave energy converter (WEC) comprising a plurality of cells each having a respective membrane.

[0132] The method comprises acquiring 13 data relating to wave loads using a sensor mounted on the WEC and acquiring data about local weather conditions. This data is used to determine 14 a local wave condition value and a local weather condition value.

[0133] The local wave condition and local weather condition values are compared 15 to a threshold (maximum wave load) wave condition value and a threshold (maximum cloud cover) weather condition value and where both of the values are below the threshold values, an adjustment actuator is used to raise 16 the WEC such that the cell membranes are exposed for a predetermined time period greater than 6 hours.

[0134] If the local wave condition and local weather condition values are above the threshold values, the submergence depth is maintained and the method is repeated after a predetermined delay until at least the local wave condition value is below the threshold wave condition value.

[0135] The exposure method is repeated at monthly intervals. Every third month, the predetermined time period is increased to 24 hours.

[0136] FIG. 5 onwards show examples of adjustment actuators that can be used in the exemplified methods shown in FIGS. 2-4.

[0137] FIG. 5a shows a first example of an adjustment actuator on a WEC 20. The adjustment actuator comprises opposing one buoyancy elements 21a, 21b each having an internal chamber 22a, 22b.

[0138] Each buoyancy element 21a, 21b has an open lower end 23a, 23b (the lower end being the end closest to the sea bed) and the adjustment actuator comprises a pump 24a, 24b and a valve 25a, 25b mounted on the (sealed) upper ends 26a, 26b of the buoyancy elements 21a, 21b which are exposed to air.

[0139] The valves 25a, 25b are used to bleed air from the internal chambers 22a, 22b under hydrostatic pressure thus allowing the water level within the internal chambers 22a, 22b to rise (as shown in FIG. 5b). This reduces the volume of air within the internal chambers 22a, 22b thus reducing the buoyancy of the WEC and thus causing the WEC to move towards the sea bed. The pumps 24a, 24b can be used to pump air into the internal chambers 22a, 22b of the buoyancy elements 21a, 21b thus increasing the volume of air within the chambers 22a, 22b, and increasing the buoyance of the WEC so that it moves away from the sea bed (as shown in FIG. 5a).

[0140] The example shown in FIGS. 6a and 6b is similar to that shown in FIGS. 5a and 5b except that the lower ends 23a′, 23b′ of the buoyancy elements 21a, 21b are sealed and the pumps 24a′, 24b′ are mounted on the sealed lower ends 23a′, 23b′.

[0141] The valves 25a, 25b can be used to allow flow of air into and out of the internal chamber 22a, 22b whilst the pumps 24a′, 24b′ can be used to allow flow of water into the internal chambers 22a, 22b to effect a change in mass of the buoyancy elements 21a, 21b (and thus the WEC). As the volume of water (ballast) in the buoyancy elements 21a, 21b increases, the mass increases and the WEC moves towards the sea bed (as shown in FIG. 6b). It should be noted that the height of the water (ballast) within the internal chambers 22a, 22b of the buoyancy elements 21a, 21b may be raised above the mean free surface at still water.

[0142] A third example of an adjustment actuator is shown in FIGS. 7a and 7b. The buoyancy elements 21a, 21b are sealed and filled with air. Each buoyancy element comprises a winch 28a, 28b around which a tether 29a, 29b is wound. Opposing ends of the tethers 29a, 29b are affixed to a moorings 30a, 30b. The tethers 29a, 29b can be lengthened (FIG. 7a) or shortened (FIG. 7b) suing the winch to adjust the vertical position of the WEC.

[0143] In a fourth example shown in FIGS. 8a and 8b, the tethers 29a′ and 29b′ are formed of resilient springs. In static equilibrium the downwards forces (acting towards the sea bed) of the tension within the elastic tethers 29a′, 29b′ are equal to the buoyant force of the buoyancy elements 21a, 21b (as shown in FIG. 8a). To move the WEC towards the seabed, ballast (water) within the internal chambers 22a, 22b is increased (e.g. using a water pump and an air bleed valve—not shown) as shown in FIG. 8b.

[0144] In a fifth example shown in FIGS. 9a and 9b, the tethers 29a″, 29b″ comprise a non-buoyant tether which may be a chain. The balance between the weight of the tethers 29a″, 29b″ (which will be less when the chain is supported on the sea bed-see FIG. 9b) and the weight of the WEC (which can be varied through the variation of the amount of ballast (water) within the buoyancy elements 21a, 21b) can be used to control the submergence depth of the WEC.

[0145] In a final example shown in FIGS. 10a, 10b, the adjustment actuator comprises opposing pinon gears 31a, 31b which cooperate with respective racks 32a, 32b extending vertically from the sea bed.

[0146] The adjustment actuator is configured to simultaneously raise and lower the plurality of cells towards or away from the sea bed without substantially altering the inclination of the membranes relative to the horizontal direction.

[0147] It should be noted that the tether embodiments shown in FIGS. 7a, 7b, 8a, 8b, 9a and 9b may be combined with the pinion/rack embodiment shown in FIGS. 10a-10b to provide a WEC with pinion gears which cooperate with respective racks on the tethered buoyancy elements.

[0148] FIG. 11 shows an adjustment actuator to adjusting the angle of incidence of the WEC 20. In this embodiment, the WEC 20 is attached to the sea bed at a pivot 33. A winch 34 is affixed to a corner of a lateral end of the WEC 20. The winch 34 is attached to a tether 35 which is also attached to a fixed mooring 36. The tether 35 can be shortened by the winch to increase the angle of incidence or lengthened to decrease the angle of incidence.

[0149] In other embodiments, instead of a fixed pivot, a second winch/tether/mooring arrangement is provided at the opposing lateral end at the opposite corner and as one tether is reduced in length, the other is increased.

[0150] It will be understood that the disclosure is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.