WO2012076851A1

WO2012076851A1 - Wave energy converter

Info

Publication number: WO2012076851A1
Application number: PCT/GB2011/001705
Authority: WO
Inventors: Stephen John Packard; Malcolm Van Den Burgh
Original assignee: Trident Energy Limited
Priority date: 2010-12-10
Filing date: 2011-12-09
Publication date: 2012-06-14
Also published as: GB201021031D0; EP2649304A1; GB2486279A; GB2486279B

Abstract

A wave energy converter comprising: at least one float for immersion in waves and connected to an armature of a generator; a controller for operating the generator in a generation mode for converting wave energy into electricity or a damping mode in which wave motion is reduced more than in generation mode and the amount of wave energy converted into electricity is less than in generation mode.

Description

WAVE ENERGY CONVERTER

Description The present invention relates to the conversion of sea wave energy to electricity and in particular to a wave energy converter system comprising a wave energy converter and a controller.

Off-shore installations require maintenance and/or operations to be performed by humans. For this purpose humans must often land on off-shore installations, sometimes at short notice. Landing on an off-shore installation or working on an offshore installation can be made hazardous by the presence of waves. That is, wave motion can make access onto an off-shore installation or working on an off-shore installation hazardous. Additionally wave motion can destabilize an off-shore installation and potentially capsize the off-shore installation, particularly if the off- shore installation is a platform such as a floating platform.

The marine environment is becoming a more and more important source for renewal energy, in particular renewable electricity. One of the many difficulties of operating in the marine environment is the presence of waves. Waves can make access to off-shore installations difficult, dangerous or even impossible.

It would be advantageous to have a means for damping wave motion, both in terms of the amplitude of the wave and/or the motion of a platform which is moving due to wave action. This allows boarding of the platform in a safe way at any time, irrespective of the sea conditions, and work to be carried out on the platform irrespective of sea conditions and can reduce the chance of breakage or capsize of an off-shore installation, such as a platform, due to wave motion.

The wave motion can be defined in terms of the water surface wave motion which is the amplitude of the waves (e.g. wave surface), the frequency of the waves, the wave velocity or other characterizing properties of the wave which change with respect to time. The wave motion may be a surge, ridge, swell, ripple or another wave form or movement of the sea surface. The wave motion can also refer to the wave induced wave motion which is the motion of a platform, floats and any other component of the present invention floating on the sea surface which is moving relative to the sea bed due to the action of waves on the platform. The wave motion can be defined as a vibration of a component, e.g. a back-and-forth motion. A floating off-shore wind energy system stabilisation device is disclosed in DE

10 200 5040 808 Al . It has a control device to damp the floating off-shore wind energy system and components for operating a damping process. The off-shore device converts wave energy to electricity using a generator which is attached to different floats on the device. The generator can also be used as a motor to control the floats and damp the vibration of the floating off-shore wind energy system. In this way the platform movement is regulated. Electricity is generated when no active level of damping is required from the floats.

GB 1,560,499 discloses an apparatus for extracting energy from wave, and tidal motion. The apparatus comprises a float on a pivotal axis, allowing the float to rise, fall and pivot due to wave motion. Energy extracting means are attached to the float so that movement of the float due to the wave motion can be used to generate electricity. The float can be controlled to restrain its movement by locking one of the energy extracting means. This locks the float in position and might damp wave motion.

GB 2,442,719 discloses a wave and wind power generation system. It comprises a platform, a wind turbine and oscillating water columns (containing Wells turbines). A flow control valve can be used to control air flow in the column thereby to stabilize the platform.

GB 2,472,470 discloses a variable liquid column oscillator using wave energy to generate electricity. Control valves between air tubes and air chambers can be used to damp the motion of the variable liquid column oscillator itself to prevent damage in extreme waves.

WO 2010/110671 Al discloses a floating, anchored installation for energy production. The installation comprises wind and wave energy conversion devices used to generate electricity. Damper plates attached to the installation and completely independent of the wave energy converter devices are used to stabilize the installation.

In a first aspect of the present invention there is provided a wave energy converter system comprising: a wave energy convertor including at least one float for immersion in waves and connected to an armature or a stator of a generator; a controller for operating the generator in a generation mode for converting wave energy into electricity or a damping mode in which wave motion is reduced more than in generation mode and wave energy is converted into electricity and the amount of wave energy converted into electricity is less than in generation mode. In this way a marine energy converter which is designed for taking energy from the waves can be operated in a mode in which the marine energy converter reduces wave motion. The wave motion reduced may be water surface wave motion.

In this way the amplitude of a wave passing under the wave energy converter system can be reduced. This allows access to marine installations in the path of the wave downwind or down wave of the wave energy converter system. The marine installation may be fixed to the sea bed or floating.

Additionally or alternatively wave induced wave motion i.e. the wave motion of a platform (e.g. movement of the platform due to wave action) may be reduced thereby allowing easier working on the platform and/or reducing chance of damage to components on the marine platform and/or reducing the chance to capsize.

The wave energy converter may act to reduce fatigue loads on the wind turbine support structure and foundations. In generation mode, the conversion of surge energy into vertical motion which is converted into electricity reduces the cyclical loading on the wind turbine support structure and foundations. In damping mode the linear generator dampens wave conditions to minimise the cyclical loading on the wind turbine structure and foundations.

Advantageously, in damping mode electricity is still generated. This means that whilst damping wave motion the wave energy converter is still operating as a wave energy converter. This avoids the disadvantage of the need to store electricity or to provide a source of electricity to the wave energy converter in damping mode. In this way damping of the system can be provided more cheaply and/or for a longer duration, for example during winter storms.

Some prior art generate electricity in a generation mode and use stored energy for damping wave motion. The amount of energy that may be stored will be limited by the storage unit on each device. The limited stored energy may not be enough for continual stabilization of the device. Therefore, there is also a limited period of time for which the damping can be carried out, after which the device may not be able to be stabilized.

If the limitation of the available damping period was a problem, the amount of energy stored could be increased, but this would inevitably lead to larger storage devices which may adversely affect the layout or weight of the overall device and of course the cost.

The current invention solves this problem by generating electricity in the damping mode. This means that electricity can be continually generated, even when stabilization of the platform is required. There are many reasons why this capability is advantageous.

Generating electricity whilst in damping mode allows the motion of the device to be controlled whilst still converting wave energy into electricity. The main aim of the energy converters is to generate electricity, therefore this allows more effective electricity generation and no interruption of electricity supply to shore. As well as this, the electricity generation is more continuous which can lead to an overall higher power production and so increase efficiency.

There are a variety of reasons why the platform may need to be boarded, which requires the stabilization of the platform. It is more efficient to continue electricity generation whilst stabilizing the device. This allows maintenance and checks to be carried out, without adversely effecting the generation and supply of electricity.

There may also be prolonged periods of time for which damping mode is required. Lengthy maintenance may be required or there may be a storm which means the platform needs stabilization for an extended period of time. If the device could not generate electricity whilst also damping the device, the limited stored energy may not be enough, which would lead to failure of the damping and therefore no stabilization of the device. If this occurred, especially during a storm, it could lead to the device being damaged, destroyed and/or capsized which may also effect surrounding devices and their stabilization. Components of one damaged device could impact another device leading to destabilization of that device in a knock-on effect. Alternatively during or after a storm maintenance may be required, due to any damage caused by the storm, which would also require the stabilization of the device. If the energy stored by the device has been used, then maintenance of the device would not be able to be carried out until wave action had subsided.

Periods when maintenance cannot be carried out because of lack of stability would be expensive. It would also be very costly for a device to be

damaged/destroyed/capsized, especially if this affects surrounding devices. The present invention could reduce these effects and the corresponding costs due to the continual electricity generation and therefore longer possible stabilization time.

In an embodiment, in damping mode, the wave motion is reduced more than in generation mode by changing the operating parameters of the generator.

Changing the operating parameters of the generator allows specific control of the extent and/or character of the damping. It may only be necessary to apply a small amount of damping to adjust wave motion sufficiently which is more easily and efficiently carried out by controlling the operating parameters of the generator, rather than using the generator as a motor and/or controlling a separate entity, such as a valve.

Using the generator to control the damping is convenient because the implementation of the control uses a part of the device that is already there. It means the generator is multifunctional and is cheaper than providing a separate entity e.g. a valve. The addition of other entities would mean there are more possibilities for breakdown of a component and therefore, a greater likelihood maintenance will be required e.g. if a valve gets blocked. This is expensive to carry out and leads to reduced generation of electricity.

In an embodiment, in damping mode, coils of the generator are short circuited, or the total effective length of coils in the generator is changed, or current through the coils is controlled or current is injected from an external source into the coils such that the float experiences a force from the generator different to the force experienced in generation mode.

These are ways in which the generator of the wave energy converter system can change the character of waves thereby to change their amplitude, for example and/or their effect on the wave induced wave motion of a platform.

In an embodiment, there is a damping motor mode (i.e. an (active) damping mode in which the generator is driven as a motor. The generator may alternatively or additionally be driven as a motor during initialisation/stopping of a mode in which the float does not move relative to the stator (e.g. a passive mode)). In damping motor mode the linear generator is operated as a motor to drive the float. In damping motor mode the linear generator may actively dampen wave conditions to minimise the cyclical loading on the wind turbine structure and foundations.

In this way, the float can be driven to a position or held at a position specifically for damping the wave motion and/or the float can be moved so as to apply a force to the wave specifically to reduce the wave motion. In an embodiment the generator is driven as a motor using energy converted into electricity from the waves by the wave energy converter system. The energy may be stored in a storage unit such as a capacitor, a battery etc.. In an embodiment the generator is driven as a motor using electricity from a grid to which the generator is attached and to which, in generation mode and/or damping mode, the generator provides electricity.

In one embodiment, a plurality of wave energy converters are provided. A control system can drive one or more of the plurality of wave energy converters in generation mode and/or one or more of the wave energy converters in damping mode and/or damping motor mode.

In one embodiment power generated by a wave energy converter driven in generation mode is used to drive another wave energy converter in damping mode or damping motor mode.

The electricity generated in generation mode or damping mode may be used to operate the generator in damping motor mode or when otherwise being driven as a motor, for example to drive the generator as a motor during specific times of damping and/or in damping mode (to short circuit coils of the armature, and/or to change the total effective length of coils in the armature and/or to change current through the coils).

The present invention also relates to a marine platform comprising at least one of the above wave energy converter systems. In this way in damping mode or damping motor mode the motion of the platform may be reduced and/or the amplitude of waves passing under the platform may be reduced.

Particularly if the marine platform is a floating marine platform, the wave energy converter system can be used to damp the wave motion of the platform. That is, the motion of the marine platform due to the action of waves can be damped using the wave energy converter. For example, as a wave passes under the marine platform and the marine platform tends to fall at a first end and rise at the other second end, if the wave energy converter system is mounted at the first end, in damping mode and/or damping motor mode it can be driven so as to provide more buoyancy thereby to reduce the amount the first end of the platform falls. Conversely, if the first end of the platform were to be lifted up by the wave, in damping mode and/or damping motor mode the wave energy converter could be driven to reduce the amount of buoyancy provided by the float thereby reducing the amount of upward motion at the first end of the platform. During passing of the wave under the generator, the position of the float can be changed (e.g. in a feedback or feedforward manner) to provide additional or less buoyancy, as required.

In one embodiment a plurality of wave energy converters is mounted to the marine platform.

In one embodiment at least one wind energy conversion apparatus is mounted on the marine platform. The wind energy conversion apparatus may be the main source of renewable energy generated by the marine platform. Energy from the wind energy conversion apparatus may be used to drive the wave energy converter in damping mode and/or damping motor mode.

The invention may relate to a marine energy generation apparatus comprising a wind energy conversion apparatus and at least one of the above wave energy converters. The marine energy generation apparatus may be a wind farm comprising a plurality of wind energy conversion apparatus. The at least one wave energy converter may be present around at least part of the wind farm, for example may be positioned in a direction from which inclement weather is expected at the wave farm. In normal operation the at least one wave energy converter may be driven to generate electricity. In inclement weather the wave energy conversion apparatus may be driven in damping mode and/or damping motor mode thereby to damp the amplitude of waves and protect and/or allow access to one or more of the wind energy conversion apparatus of the wind farm.

The wind energy conversion apparatus may either be fixed to the sea bed in a static way or may be provided on a floating platform which is anchored to the sea bed.

The wave energy converter may act to reduce fatigue loads on the wind turbine support structure and foundations, either in generation mode or damping mode or damping motor mode. In generation mode, the conversion of surge energy into vertical motion which is converted into electricity reduces the cyclical loading on the wind turbine support structure and foundations. In damping mode the linear generator actively dampens wave conditions to minimise the cyclical loading on the wind turbine structure and foundations.

The invention will now be described with reference to the accompanying drawings in which:

- Figure 1 illustrates, in cross section, an example of a wave energy converter;

Figure 2 illustrates in perspective view a wind farm protected by a plurality of wave energy converters according to the present invention; and

Figure 3 illustrates a marine platform for a wind energy conversion apparatus and including wave energy converters according to the present invention.

Figure 1 illustrates, schematically in cross-section, a wave energy to electrical energy conversion apparatus 10. The apparatus comprises a float 1 which is connected to an armature 2 of a generator 3. The armature 2 is (co-axially) surrounded by a stator 4. The armature 2 is arranged for reciprocating movement in the stator 4. The armature 2 is configured as an elongate rod. The stator 4 of the wave energy converter comprises a plurality of coils. The coils coaxially surround the armature 2. The armature 4 is held substantially stationery relative to the sea bed 70. As a wave 20 passes under the generator 3, the float 1 rises up with the wave thereby moving the armature 2 relative to the coils in the stator 4.

The armature 2 comprises a series of permanent magnets. Movement of the permanent magnets of the armature 2 within the coils of the stator 4 results in generation of electricity.

A controller 30 is provided for controlling the generator 3 as described below. The apparatus of Figure 1 may be configured differently. For example, the stator may be in the form of an elongate rod with permanent magnets and fixed relative to the sea bed 70 and the armature comprising coils may be within the float 1. In such an embodiment, as the float moves up and down in the waves, the coils are moved relative to the permanent magnets thereby generating electricity.

In one embodiment the generator 3 is a linear generator.

The wave energy converter 10 may be as described in EP-A1- 1,196,690, EP- Al-1,646,785, EP-A 1-1, 196,691 or WO 2006/075147, the entire contents of all of which are hereby incorporated herein by reference thereto. The float 1 may be any type of float which provides enough buoyancy in order for the generator 3 to generate electricity on the passing of a wave 20 under the generator 3. The float 1 may be of the type described in WO 2007/042800, the entire contents of which is hereby incorporated herein by reference thereto.

A controller 30 is provided for controlling the generator 3. The controller 30 can operate the generator 3 in two modes. In a first mode (generation mode), the generator 3 is driven purely as a generator 3 and wave energy is converted into electricity. For example, the generator 3 is operated in such a way that as much energy as possible is extracted by the generator 3 from the waves. Operating parameters are changed to adjust, for example, the speed of the armature relative to the stator and the depth of the float relative to the wave surface.

The apparatus operates in generating mode is as follows. As a wave 20 arrives, the natural buoyancy of the float 1 causes the whole assembly comprising the float 1 and armature 2 to rise. This may be assisted by the pressure of the rising water acting against paddles or surfaces of the float 1.

Thus relative motion arises between the armature 2 and stator 4 of the (linear) generator 3 and alternating current is generated within the coils of the generator 3, the amplitude and frequency of which depend upon the vigour of the wave motion. The current is conducted to a shore station by a suitably armoured and flexible cable.

(Note, means, not shown, are present to prevent rotation of the wave energy converter

10 and therefore unwanted tensioning of the cable.)

Once the wave 20 has reached its zenith, and begins to fall, the weight of the float 1/armature 2 assembly causes the same also to fall. Power again is generated as the armature 2 traverses the stator 1. If the upthrust experienced by the generator 3 is substantially the same as the weight of the float 1/armature 2 assembly, electricity is generated reasonably consistently both upon the rise and fall phases of the wave 20. There is some natural phase lag between the ascending of the assembly relative to the waves, and its fall, due to the natural damping effect of the electromotive force generated. The load impedance presented to the generator 3, and the overall weight of the moving assembly, may be so selected as to optimise generation for any particular wave condition.

The apparatus of the invention thereby generates electrical energy.

The controller 30 can also operate the generator 3 in a damping mode in which wave motion is reduced more than in generation mode and wave energy is converted into electricity and the amount of wave energy converted into electricity is less than in generation mode.

In damping mode the controller 30 changes operating parameters of the generator 3 to reduce wave motion. The wave motion reduced may be one of two types of wave motion (water surface wave motion and/or wave induced wave motion) as discussed in more detail with reference to Figures 2 and 3. Wave motion may be the water surface wave motion of the wave 20 (as explained with reference to Figure 2), for example wave amplitude, frequence, velocity or other characteristic wave properties or it may be the wave induced wave motion of a platform or any other component of the present invention due to waves passing under the platform, including vibration of a component (as explained further with reference to Figure 3). To this end, various detection and measurement instruments may be provided with the wave energy converter 10. To achieve the best result knowledge of the wave period will enable the generator to be operated such that the float oscillates out of phase with the waves.

Detection and/or measurement means 17 is located to detect and/or measure the rate of movement of the armature 2 of the generator 3, and also the extent of its movement. The detection means 17 may comprise Hall effect detectors located adjacent to the magnetic armature 2 of the generator 3, so providing information on its movement as the series of armature magnetic fields passes the detection means 17.

By using two detectors with a phase displacement of 90°, i.e. in phase quadrature, information is made available in terms of direction, position and speed.

Alternatively, as an addition to or in place of use of the Hall effect components, the emf voltages generated by the stator 4 may be measured and assessed. In accordance with electrical engineering theory, the amplitude of these voltages provides information on the rate of movement, and the number of cycles generated in a particular movement of the armature 2 provides information on the overall distance travelled.

The signals so provided, by either or both of the Hall effects and the emf waveforms, are processed by the controller 30.

A further detector 21 (a wave sensor) is provided, for example on the same platform 40 as the generator 3. The detector 21 is capable of detecting the level of the surface of the water under it. This provides information regarding the speed, amplitude and wave length of waves and allows the calculation of when the wave front of a wave can be expected under the generator 3. This information along with the information from the detection and measurement means 17 is passed to the controller 30 which can control operating parameters of the generator 3 accordingly.

The detector 21 may be upwave and/or downwave of the generator 3 (mounted to the same or (a) different platform(s) to the generator 3). A downwave detector 21 detects information about the waves as influenced by the generator 3. Such information can be used to control the generator 3 in damping mode, for example in a feedback manner. Upwave and/or downwave information (e.g. one or more selected from predicted time of arrival, wave period, wave speed, wave amplitude) may be used in a control algorithm to alter the behaviour of the generator 3 in damping mode by means of changing the resistance, the stroke and/or the speed of the armature.

The float will produce its own waves due to reflection. By adjusting the pattern of the reflected waves to interfere with the underlying wave cycle, a calming effect will be achieved. The effect on the waves will not simply be downwave but will be in an arc radiating from the generator. If a number of generators are therefore coordinated in an array, the combined effect will be better than a generator operating in an uncoordinated manner.

The controller can drive the generator in damping mode and/or damping motor mode in a feedforward way, using a pre-determined algorithm which relates the characteristics of a wave front as sensed upwave of the generator to a particular operating characteristic needed of the generator to reduce wave amplitude downwave of the generator. For an array of generators, the controller may co-ordinate the control of each generator in a feedback or feedforward manner as described above in order to achieve a desired result (e.g. wave pattern) at a certain location.

A passive damping mode may additionally be provided which is a passive mode in which the float 1 does not move relative to the stator 4 and the float 1 and armature 2 merely act as a barrier to the passage of a wave or in an active mode in which the float 1 and armature 2 move relative to the stator 4 (and sea bed 70).

In damping mode (which may be termed an active mode in that the float moves) the resistance of the float 1 and armature 2 to movement relative to the stator 4 can be increased or decreased relative to generation mode. This can be achieved by short circuiting one or more of the coils of the stator 4, or by varying the total effective length of coils in the stator 4 or by changing the current through the coils of the stator 4. Current may be injected from an external source into the coils. This latter technique enables larger resistance to movement of the float by waves to be generated than is possible by short circuiting the coils.

In one embodiment in damping motor mode, current is passed through coils in the stator 4 thereby to drive the generator 3 as a motor. Energy may be provided from other generators operating in generation mode and/or damping mode, from a storage unit such as a capacitor or battery or from a grid to which the generator is attached and to which, in generation mode, the generator optionally provides electricity.

The controller 30 controls the generator 3 in damping mode and/or damping motor mode according to input parameters including the results from the detection and measurement means 17 and the wave sensor 21.

The controller 30 can automatically enter damping mode and/or damping motor mode depending upon signals received from, for example, the detection and measurement means 17 or the wave sensor 21 or in response to a signal received from an operator.

In the embodiment of Figure 2 it is likely the controller 30 will be set up to receive a communication from an operator that wave damping is required (for example to allow technicians access to a wind energy conversion apparatus). In the embodiment of Figure 3 an operator may provide a signal for the wave energy converter 10 to enter damping mode and/or damping motor mode. Alternatively, a detected motion of the platform 40 or signals from the detectors 17 may indicate that damping mode and/or damping motor mode should be entered (for example because a certain parameter is above a certain threshold parameter). In either case, the controller

30 then enters damping mode and/or damping motor mode and controls the operating parameters of the generator 3 to reduce wave motion.

In an embodiment it may be most effective if the generators act as motors and to ensure that the float or floats move out of phase with the waves.

It will be clear from the above that in damping mode and/or damping motor mode or passive damping mode, wave motion is reduced more than in generation mode (in generation mode wave motion may be reduced because energy is taken out of the wave). In damping mode the amount of wave energy converted into electricity is less than in generation mode for a given wave. That is, in generation mode the amount of energy converted into electricity is substantially optimised whereas this is not necessarily the case in damping mode. The efficiency of energy conversion in damping mode is lower than in generation mode.

In damping motor mode and passive damping mode no energy may be generated by the wave energy converter 10.

Energy may be used by the wave energy converter 10 in damping mode, for example by driving the generator 3 as a motor.

Energy generated by the wave energy converter during generation mode or damping mode may be used in damping mode. For example, the energy may be used to change the operating parameters of the generator 3 (for example short circuiting coils of the stator 4, changing the total effective length of coils in the stator 4, varying the current through coils in the generator 3).

Energy generated by the wave energy converter during generation mode or damping mode may be used in damping motor mode. For example, the energy may be used to drive the generator 3 as a motor.

Varying the current of coils in the generator 3 may include driving a current through coils in the generator 3 to drive the generator 3 as a motor or may, for example, be attaching a resistance to the coils thereby to increase the resistance of the generator 3 to movement of the armature 2 relative to the stator 4. The controller 30 may control the operating parameters of the generator 3 depending on the position of the wave 20 relative to the generator 3 as measured by wave sensor 21. The controller 30 may vary the operating parameters of the generator 3 according to one or more of the shape of the wave, the velocity of the wave, the amplitude of the wave and the wavelength of the waves. An energy storage unit 35 may be provided for storing energy generated by the wave energy converter 10 and for use in damping mode and/or damping motor mode.

In one embodiment a plurality of wave energy converters 10 (e.g. in an array) are provided. The electricity generated by one wave energy converter 10 may be used by the controller 30 for controlling the generator 3 of another wave energy converter 10 in damping mode and/or damping motor mode.

The wave energy converter 10 of the present invention can be used to damp wave motion of or in proximity to off-shore installations. Off-shore installations include, but are not limited to, a marine platform of any type, in particular a marine platform for the mounting thereon of one or more wind energy conversion apparatus (such as illustrated in Figure 3). In another embodiment the wave energy converter apparatus is useful in a marine energy generation apparatus 100 which comprises a wind energy conversion apparatus 50 (such as a turbine), such as illustrated in Figures 2 and 3.

In one embodiment, the wind energy conversion apparatus 50 is secured in permanent position relative to the sea bed (Figure 2). In that embodiment the wave energy converter 10 may be used to reduce the amplitude of waves, as desired, to allow operator access to one or more wave energy conversion apparatus 50.

Maintenance of wind energy conversion apparatus 50 can only be carried out if wave amplitude is below a pre-defined maximum limit. It may be unusual for waves of above the maximum pre-defined limit to arrive from a particular direction. If that is the case, it may only be necessary partly to surround the farm of wind energy conversion apparatus 50 on a side from which waves above the pre-determined maximum are likely. Alternatively a plurality of wave energy converters 10 may surround the wind farm.

If access to a particular wind energy conversion apparatus 50 is required, one or more of the wave energy converters 10 may be switched to damping mode and/or damping motor mode thereby to damp the amplitude of waves in the region of the wind energy conversion apparatus 50 needing attention. In this way the wave energy converter 10 of the present invention can be used to ensure that access to wind energy conversion apparatus 50 is possible during most weather conditions, including weather conditions at which the wave amplitude would otherwise be above the maximum allowable amplitude. During other times the wave energy converters) 10 may be driven in generation mode and/or damping mode and contribute to the energy converted by the marine energy generation apparatus 100. It will be appreciated that the wave energy converter 10 described above in relation to Figures 1 and 2 could be used to protect other types of off-shore structure and is not limited to protecting wind energy conversion apparatus 50.

Figure 3 shows a plurality of wave energy converters 10 attached to a marine platform 40. The marine platform 40 is a floating marine platform. The marine platform 40 is attached to the sea bed 70 via cables and anchors 60. The marine platform 50 is still affected by waves 20 and will have a wave motion as a result of those waves. Optionally the marine platform 50 may have mounted on it any type of marine installation including, but not limited to, a wind energy conversion apparatus 50.

The wave energy converters 10 may be installed both to convert wave energy into electricity (in generation mode and/or damping mode) either to generate electricity to be transmitted to the shore or to generate electricity to be utilized on the marine platform 40. The wave energy converters 10 may be driven in damping mode and/or damping motor mode in which case they are effective to damp the (wave induced) motion of the platform 40. In this embodiment, movement of the platform 40 may be detected (for example by an inclinometer or accelerometer 25 illustrated in Figure 1).

In Figure 3, the position of the wave results in a rotation of the platform 40 counter clockwise, as illustrated. This information is provided to the controller 30. The controller 30, if in damping mode and/or damping motor mode, then controls one or more of the wave energy converters 10 to provide more or less buoyancy than is normal. For example, if more buoyancy is required at a position (for example on the left hand side of the platform 40, as illustrated), the controller 30 ensures that the float 1 of a wave energy converter 10 at that position is further from the stator 4 than would be the case in generation mode. Thus, the float 1 will be more immersed in the wave 20 than is normally the case and thereby provide additional buoyancy. At that point a larger than normal upward force on the platform 40 will be present thereby helping to damp the motion of the platform 40.

Conversely, if less buoyancy is required at the position of a wave energy converter 10 (e.g. on the right hand side of the platform 40, as illustrated), the controller 30 ensures that the float 1 is closer to the stator 4 than normal. As a result, the float 1 would be less immersed in the wave 20 than normal (or out of the water, as illustrated) and the wave energy converter 10 at that position will provide less buoyancy at its location. As a result, the motion of the platform 40 will be reduced. The controller 30 may control the distance between the float 1 and the stator 4 either by increasing or decreasing the resistance to motion between the armature 2 and stator 4 or by driving a current through coils in the armature 4 and driving the generator as a motor.

One or more of the wave energy converters 10 may be controlled in the generating mode whilst others are in the damping mode and/or damping motor mode.

One or more of the wave energy converters 10 may be controlled in the damping mode whilst others are in the damping motor mode.

The controller 30 may automatically enter damping mode and/or damping motor mode when sensors associated with the controller 30 indicate that certain conditions have been met (e.g. to stabilize the platform in inclement weather when the inclinometer or accelerometer 25 indicate large movement of the platform).

Additionally or alternatively the controller 30 may enter damping mode or damping motor mode in response to a user signal. This could, for example, reduce the motion of the platform 40 during maintenance or at least during a time when an operator boards the platform 40.

In an embodiment the wave energy converters 10 mounted on the platform 40 can be operated in a similar manner to the wave energy converters as described in Figure 2. Thus, for example, in a wave farm one or more platforms 40 associated with one or more wind energy conversion apparatus 50 could surround other wind energy conversion apparatus 50 (either in fixed position relative to the sea bed or mounted on a floating marine platform) to reduce wave amplitude at the other wind energy conversion apparatus 50 thereby to protect and/or allow access to the wind energy conversion apparatus.

It will be apparent that the features of any above described embodiments can be combined with the features of any other described embodiment.

Claims

1. A wave energy converter system comprising:

a wave energy converter including at least one float for immersion in waves and connected to an armature of a generator; and

a controller for operating the generator in a generation mode for converting wave energy into electricity or a damping mode in which wave motion is reduced more than in generation mode and in which wave energy is converted into electricity and the amount of wave energy converted into electricity is less than in generation mode.

2. The wave energy converter system of claim 1 , wherein in the damping mode, the wave motion is reduced more than in generation mode by changing the operating parameters of the generator.

3. The wave energy converter system of claim 1 or 2, wherein in damping mode coils of the generator are short circuited, or the total effective length of coils of the generator is changed, or current through the coils is controlled or current is injected from an external source into the coils such that the float experiences a force from the generator different to the force experienced in generation mode.

4. The wave energy converter system of claim 1 - 3, wherein the controller is additionally adapted to operate the generator in a damping motor mode in which the generator is driven as a motor.

5. The wave energy converter system of any of claims 1-4, wherein the damping mode is an active mode in which the float moves relative to the stator of the generator.

6. The wave energy converter system of any of claims 1 - 5 wherein the controller is additionally adapted to operate the generator in a passive damping mode in which the float does not move relative to the stator.

7. The wave energy converter system of any of the preceding claims, further comprising a wave sensor for providing information to the controller about a wave front either upwave or downwave or both of the wave energy converter.

8. The wave energy converter system of claim 7, wherein in damping mode the controller controls the generator in a feedback or feedforward manner based on the information provided by the wave sensor.

9. A marine platform comprising at least one wave energy converter system of any of claims 1-8 mounted on the platform.

10. The marine platform of claim 9, on which is mounted at least one wind energy conversion apparatus.

11. A marine energy generation apparatus comprising a wind energy conversion apparatus and at least one wave energy converter system of any of claims 1-8.

12. The marine energy generation apparatus of claim 11 comprising a marine platform on which the wave energy converter and wind energy conversion apparatus are mounted.

13. The marine platform of claim 9 or 10 or the marine energy generation apparatus of claim 12, wherein the marine platform is a floating marine platform.

14. The marine platform of claim 9 or 10 or the marine energy generation apparatus of claim 12 or 13, wherein the wave motion reduced in damping mode is motion of the platform.

15. The wave energy converter system of any of claims 1 -8, the marine platform of any of claims 9, 10, 13 or 14 or the marine energy generation apparatus of claim 11 - 14, wherein the wave motion reduced in damping mode is the amplitude of waves.

16. A method of boarding a marine platform comprising instructing the controller of a wave energy converter system of any of the preceding claims to enter damping mode and boarding the marine platform.

17. A wave energy converter system, marine platform or marine energy generation apparatus substantially as hereinbefore described with reference to and/or as illustrated in the accompanying drawings.