Patent Application
20120096846
The present invention relates to a wave energy conversion system. In particular the present invention relates to a wave energy conversion system which includes a control means for determining a desired damping in response to a sensed parameter of a wave absorber. The control means is operable for selectively activating one or more actuators to achieve the desired damping.
Wave energy converters are known in the art. Examples of such arrangements include those described in our earlier patents EP1439306, EP1295031 and EP1036274. Such arrangements are usefully deployed in a maritime environment and generate energy from wave motion.
To provide such generation it is known for such converters to employ power take off systems. Typically such systems comprise a hydraulic circuit which is driven by the wave energy which in turn drives a power generator to generate electricity. The hydraulic circuit is controlled such that it remains at a constant pressure so that the electrical power generated by the generator is of a stable frequency. By generating power at a stable frequency permits the power to be readily used in a power grid without the need for complex power electronics. The main disadvantage of constant pressure power take off systems of the type known heretofore is that wave energy absorption is not maximised.
There is therefore a need for a system which optimises wave energy absorption.
These and other problems are addressed by providing a power take off system which includes a control means for determining a desired damping in response to a sensed parameter of a wave absorber. The control means is operable for selectively activating one or more actuators to achieve the desired damping.
Accordingly, a first embodiment of the invention provides a wave energy conversion system as detailed in claim 1. Advantageous embodiments are provided in the dependent claims.
These and other features will be better understood with reference to the followings Figures which are provided to assist in an understanding of the teaching of the invention.
The present invention will now be described with reference to the accompanying drawings in which:
The invention will now be described with reference to an exemplary system which is provided to assist in an understanding of the teaching of the invention.
Referring to
The hydraulic pumps 120 are driven by at least one wave absorbing system 105 for facilitating the conversion of wave energy to, in this exemplary arrangement, electrical energy. Wave energy absorbing systems are known in the art, an example of which is shown in our earlier patent EP 1295031 and replicated in
While the wave absorbing system of EP 1295031 is described as employing a power take off system—an example of which is described in FIG. 7 of EP 1295031, the specific implementation described utilises hydraulic pumps, the damping force of which is not controlled to the response of the wave absorber to wave action thereon. The present inventors have realised that in order to maximise wave absorption it is possible to control the damping of the pumps to the response of a wave absorber to wave action thereon. In this exemplary embodiment, the response of the wave absorber to wave action thereon is provided as a sensed characteristic representative of the velocity of the wave absorber. In this way the actual response will be better suited to the conditions prevalent. It will be appreciated by those skilled in the art that the velocity of the wave absorber 115 varies depending on the ocean conditions where the wave absorbing system 105 is moored. The operating characteristic of the system 100 may be dynamically varied during operation as the velocity of the wave absorber 115 changes due to changing ocean conditions. The damping provided by the hydraulic pumps 120 may be varied during a unitary wave period thereby ensuring that the output response changes rapidly and does not have to wait for the next wave period to begin before taking effect. A wave period is the time taken for two consecutive wave troughs to pass a given point. A typical wave pattern will have crests formed by a volume of water between consecutive troughs. A control unit 147 or controller is provided and is operable to vary the damping at different instances during the wave period. Alternatively, the operating characteristic of the system 100 may be tuned by estimating/approximating the velocity of the wave absorber resulting from the prevalent ocean conditions.
The system 100 of
In one exemplary arrangement each hydraulic pump 120 provides a predetermined constant damping force. The constant damping force provided by each hydraulic pump 120 can be chosen to be different to that of the other pumps, or indeed selected ones can have the same and others different. The mechanism for varying the operating characteristic may be for example the selective use of pumps having different dimensions. As there are a plurality of pumps it is possible, in accordance with the teaching of the invention to selectively activate individual ones of the pumps to optimise the response characteristic of the system to the operating conditions of the wave energy absorber 115.
One preferred arrangement is effected by the control unit 147 activating a combination of pumps 120 in a predetermined sequence such that the damping force provided by the pumps is matched to the velocity of the wave absorber 115. As the velocity of the wave absorber 115 increases the control unit 147 dynamically activates a certain combination of pumps 120 so that the damping force of the system 100 also increases. Similarly, as the velocity of the wave absorber 115 decreases the control unit 147 dynamically activates a certain combination of pumps 120 so that the damping force decreases. In this exemplary arrangement, three pumps 120 are provided each providing a different damping force when activated. As three pumps 120 are provided the pumps 120 may be activated in seven combinations, which in turn provide seven different combinations of damping forces from which the control unit 147 can select from. While it will be appreciated that this is a specific example and the teaching should not be restricted to such an exemplary arrangement for the purposes of understanding the number of combinations that are possible it will be seen the seven combinations of damping forces are provided by the following combinations of pumps:
In this exemplary arrangement, the control unit 147 actives the pumps 120 so that the system 100 has a constant load resistance such that:
R=F/V
p
Where:
R is the load resistance,
F is the damping force provided by the active pumps 120, and
Vp is the velocity of the wave absorber 115.
Referring now to the graph of
The control unit 147 activates the pumps 120 such that there is a substantially linear relationship between the damping force F of the pumps 120 and the velocity Vp of the wave absorber 115. The inventors of the present application have realised that by maintaining a substantially predetermined relationship between F and Vp, in this case, a linear relationship, it is possible to significantly enhance the quantity of wave energy which may be absorbed by the system 100, and therefore the efficiency of the overall system. For example, if the velocity Vp is within a first range, the control unit 147 may activate pump 120A such that the system 100 has a corresponding first damping force. If the velocity Vp is within a second range, the control unit 147 may activate pump 120B such that the system 100 has a corresponding second damping force. If the velocity Vp is within a third range, the control unit 147 may activate pumps 120A and 1208 such that the system 100 has a corresponding third damping force. If the velocity Vp is within a fourth range, the control unit 147 may activate pumps 120C such that the system 100 has a corresponding fourth damping force. If the velocity Vp is within a fifth range, the control unit 147 may activate pumps 120A, 120B and 120C such that the system 100 has a corresponding fifth damping force. If the velocity Vp is within a sixth range, the control unit 147 may activate pumps 120A and 120C such that the system 100 has a corresponding sixth damping force. If the velocity Vp is within a seventh range, the control unit 147 may activate pumps 120B and 120C such that the system 100 has a corresponding seventh damping force. Thus, it will be appreciated by those skilled in the art that the control unit 147 may be configurable to dynamically activate and/or deactivate predetermined pumps 120 at different instances during a single wave period so that there is a substantially linear relationship between F and Vp. In other words, the controller or control unit 147 is configured to dynamically activate various combinations of pumps during the time period for two consecutive wave troughs to pass a given point. The control unit thereby achieves a tuning of the response of the PTO throughout the passage of individual waves. In this way the response of the device is not restricted to a single response characteristic for a single wave. A single wave may require a modification of the damping forces at multiple iterations during the passage of that single wave. It will be appreciated by those skilled in the art that as the pumps 120 are selectively activated and/or deactivated it is possible to vary the operating characteristic of the system 100 to the sensed characteristic. At least one of the pumps 120 may be activated and another one of the pumps 120 deactivated simultaneously. Alternatively, at least two pumps 120 may be activated simultaneously, and at least two pumps 120 deactivated simultaneously. The pumps 120 may be operated in a sequence.
In this exemplary arrangement, the system 100 comprises a network 118 of hydraulic pumping circuits 119 which are driven by wave energy for pumping fluid from reservoirs 123 to the power generator 121. The pumped fluid drives the power generator 121 to generate electrical energy. Each pumping circuit 119 has an associated damping force. The pumping circuits 119 are selectively activated and/or deactivated for actively varying the damping force of the PTO system 100 to be dynamically matched with the velocity of the wave absorber 115 of the wave absorbing system 105.
Each pumping circuit 119 comprises a hydraulic pump 120 with corresponding wave absorbing rams 124 axially moveable in cylinders 122 and operably coupled to the wave absorbing system 105 by a coupling shaft 126. As the submerged wave absorbing body 115 oscillates due to wave energy it provides a driving force to the rams 124 via the coupling shaft 126, which in turn forces the rams 124 to oscillate. Position sensors 125 sense the movement of the rams 124. The control unit 147 is in communication with the position sensors 125 for calculating the velocity of the rams 124, which in turn calculates the velocity of the wave absorber 115. Depending on the velocity of the wave absorber 115 certain pumps 120 are activated so that there is a substantially linear relationship between the damping force of the system 100 and the velocity of the wave absorber 115. The oscillating rams 124 pump fluid from the reservoirs 123 to the power generator 121. The pumping circuits 119 are in fluid communication with the power generator 121 via a primary hydraulic circuit 128. Each pumping circuit 119 comprises a main line 130 extending between the pump 120 and the primary circuit 128 and coupled thereto by a coupling valve 133. A supply line 132 extends between each reservoir 123 and corresponding main line 130 which ensures that the reservoirs 123 are in fluid communication with the pumps 120. A flow control means, in this case, a bidirectional pneumatic valve 140 is located in each supply line 132 intermediate the main lines 130 and the reservoirs 123, and are selectively controlled for activating and/or deactivating the corresponding pumps 120. It will be appreciated by those skilled in the art that the activated pumps 120 contribute to the damping force of the overall system 100. Deactivated pumps 120 do not contribute to the damping force of the overall system 100.
The damping force of each pumping circuit 119 is set by the dimensions of the pumps 120. In this exemplary arrangement three pumping circuits 119 are provided and each pumping circuit 119 has a different damping force as the pumps 120 have different dimensions. The transverse cross sectional area of the rams 124 and the corresponding cylinders 122 progressively increase from the first pump 120A to the third pump 120C. While the preferred arrangement includes three pumping circuits 119 it will be appreciated by those skilled in the art that any desired number of pumping circuits 119 may be provided. It is not intended to limit the invention to this described arrangement. It will be appreciated by those skilled in the art that the pumping circuits herein described are exemplary of the type of circuitry that may be employed to match the response of the PTO to the climatic conditions of the wave absorbing system.
The control unit 147 is operably coupled to the pneumatic valves 140 by electrical cables 150 for providing control signals to the pneumatic valves 140 which selectively activate and/or deactivate the pneumatic valves 140, which in turn selectively activates and/or deactivates the corresponding pumps 120. The control unit 147 comprises a microprocessor 152 and a memory chip 154 which stores a control algorithm. The microprocessor 152 calculates the velocity of the wave absorber 115 by communicating with the position sensors 125 and generates an optimised damping force which the system 100 needs to have in order to optimise wave absorption. Tables containing velocity data and corresponding damping force data may be preloaded to the memory chip 154 which can then be read by the microprocessor 152 for selecting the optimum damping force. The control unit 147 controls the pneumatic valves 140 based on the velocity of the wave absorber 115 so that the overall damping force of the system 100 is set at the optimised value. The control unit 147 may be operable to communicate with local and/or remote data systems for receiving data for populating the tables in the memory chip 154. This data may then be used for estimating/approximating/determining the appropriate damping force of the system 100. The data systems which supply data to the control unit 147 may include a weather system. The data received by the control unit 147 may be historical data representative of seasonal wave conditions. Additionally or alternatively, the data may be real-time data representative of real-time wave conditions. It will be appreciated by those skilled in the art that the data received may be any type of data which can be used for selecting an optimum damping force. The control unit 147 may be in wireless communication with the data systems.
A pressure accumulator 160 is operably coupled to the primary circuit 128 via an interconnecting circuit 165 for maintaining the pressure in the primary circuit 128 constant. It will be appreciated that wave energy varies significantly depending on the conditions in the ocean. In periods of large swells, the wave energy absorbing system 105 generates a large amount of kinetic energy which drives the pumps 120 at a high rate so that the fluid in the primary circuit 128 is under high pressure. In periods of relatively small swells, the kinetic energy generated by the wave energy absorbing system 105 is significantly less than periods of large swells resulting in less kinetic energy and as a consequence the pumps 120 are driven at a slower rate resulting in the fluid in the primary circuit 128 being under less pressure. The pressure accumulator 160 regulates the pressure within the primary circuit 128 so that the pressure in the primary circuit 128 remains substantially constant. Overflow wells 170 are in fluid communication with each main line 130 via outlet lines 173 for receiving fluid from the primary circuit 128 when pressure in the primary circuit 128 exceeds a threshold level. A unidirectional valve 175 is provided in each outlet line 173 for controlling the flow of fluid to the overflow wells 170.
In operation, the pumps 120 are operably coupled to the wave absorbing system 105. The submerged wave absorber 115 of the wave energy absorbing system 105 is forced to oscillate by the wave energy, which in turn provides a driving force which drives the rams 124 to pump fluid to the power generator 121. The pumped fluid to the power generator 121 drives the power generator 121 to generate electricity. The control unit 147 dynamically activates one of seven combinations of pumps 120 sequentially so that there is a substantially linear relationship between the damping force of the system 100 and the velocity of the wave absorber 115. As the wave absorber of this specific example generates energy from relative motion of two devices in response to passing waves its movement effects a driving of the rams to move bi-directionally. In other words, the wave absorber 115 pushes the rams 124 of the pumps 120 in an upwardly direction when the wave absorber 115 moves towards the surface of the water, and pulls the rams 124 in a downwardly direction when the wave absorber 115 sinks to a lower depth. In certain instances, it may be desirable to increase the potential energy which the wave absorber 115 provides by urging the wave absorber 115 to a lower depth. The pumps 120 may be controlled by the control unit 147 to drive the wave absorber 115 downwardly. It will therefore be appreciated that while the wave absorber 115 drives the pumps 120 for the majority of the time, in certain instances the pumps 120 drive the wave absorber 115 to increase the potential energy of the wave absorber 115. It will therefore be understood that the wave absorber 115 drives the pumps 120 for major portion of an operating cycle of the wave energy conversion system 100, while the PTO drives the wave absorber 115 for a minor portion of the operating cycle.
It will be understood that what has been described herein is an exemplary embodiment of a wave energy conversion system. While the present invention has been described with reference to exemplary arrangements it will be understood that it is not intended to limit the teaching of the present invention to such arrangements as modifications can be made without departing from the spirit and scope of the present invention. For example, in the exemplary arrangement the predetermined relationship between F and Vp has been described as being substantially linear. It will be appreciated by those skilled in the art that the relationship between F and Vp may be non-linear. It will be understood that the invention is to be limited only insofar as is deemed necessary in the light of the appended claims.
The words comprises/comprising when used in this specification are to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0811280.7 | Jun 2008 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2009/057638 | 6/18/2009 | WO | 00 | 10/25/2011 |
