PELAMIS WEC - INTERMEDIATE SCALE DEMONSTRATION
V/06/00188/00/00/REP DTI URN 03/1434
Contractor Ocean Power Delivery Ltd.
Prepared by Dr. Richard Yemm
The work described in this report was carried out under contract as part of the DTI New and Renewable Energy Programme, which is managed by Future Energy Solutions. The views and judgements expressed in this report are those of the contractor and do not necessarily reflect those of the DTI or Future Energy Solutions.
First Published 2003 © Crown Copyright 2003 dti EXECUTIVE SUMMARY
The Pelamis Wave energy Converter (WEC) is an innovative concept for extracting energy from ocean waves and converting it into a useful product such as electricity, direct hydraulic pressure or potable water. The system is a semi-submerged, articulated structure composed of cylindrical sections linked by hinged joints. The wave-induced motion of these joints is resisted by hydraulic rams that pump high-pressure oil through hydraulic motors via smoothing accumulators. The hydraulic motors drive electrical generators to produce electricity. The complete machine is flexibly moored so as to swing head-on to the incoming waves and derives its 'reference' from spanning successive wave crests.
This project, which has been part funded by the UK DTI New & Renewable Energy Programme, has successfully demonstrated the complete Pelamis WEC system at 1/7th scale. This is a vital step on the path towards proving the system at full-scale and onwards commercialisation. The intermediate scale system has shown that the full Pelamis WEC system can be implementedusing 100% availabletechnology.
PROGRAMME SUMMARY
Early in the Pelamis WEC development programme OPD identified a requirement for an intermediate scale ‘systems’ demonstrator with which to develop and provethe full-scale Pelamis hydraulic, control and data acquisition systems. The model was conceived tothe OPD ethos of systematically tackling each aspect of technical risk before committing to a full-scale prototype. It is seen as absolutely critical to the overall success of the technical programme that as little immature technology as possible is incorporated within the first full-scale prototype. The step to a full-scale technology demonstrator must be as pure an engineering exercise as possible, rather than an uncertain part of the research and development process.
A scale of 1/7th was chosen for the intermediate scale model to match the wave climate in the Firth of Forth. This scale is large enough for functionally realistic systems to be tested while remaining small enough to avoid the need for specialist handling equipment. The DTI-supported programme reported here was to build the 7th scale machine, integrate and commission the full power take-off, control and data-acquisition systems, then to deploy and test the whole machine in representative conditions.
The complete machine was successfully tested in a range of conditions in the Firth of Forth. All tests confirmed the functionality and expected behaviour of the system. Though the scope and nature of the tests was not as broad as had been originally intended a wide range of useful data and operational experience was obtained. The key results from these tests are presented later in this report.
The 7th scale machine represents a cheap, rugged test platform with which to continue onward development and verification of all aspects of the full-scale control and data
I acquisition systems. OPD will be using the machine extensively during final design, build and deployment of the full-scale prototype machine.
SPECIFIC PROGRAMME OBJECTIVES
1. To build, commission and demonstratea 7th scale full-system model of the Pelamis WEC
2. To develop and demonstrate a robust preliminary SCADA system for the future full-scale technology demonstrator
3. To validate numerical simulations of the complete system
4. To test the complete SCADA system in a broad range of conditions in active control mode, passive 'fail-safe' control mode and fora range of partial failure scenarios
5. To thereby address remaining key areas of technical risk via a cheap, robust but realistic full-system model
6. To allow OPD engineers to work closely with the project partners for the full- scale programme
7. To give the OPD team valuable experience working with complex systems in the field.
MAIN PROGRAMME CONCLUSIONS
The resulting demonstrator has proven the fundamentals of the complete system and the main conclusions from the programme are as follows:
1. A complete Pelamis WEC system has been built, commissioned and tested.
2. The 7th scale machine is, in all respects, a working wave power demonstrator apart from the final step of power generation. The programme has been of enormous benefit to the technology andthe OPD development team.
3. Tests were conducted with the system inthe Firth of Forth. All tests were carried out with the machine under tow behind a support vessel. The model was towed via a representative mooring system to allow it to respond in the correct way. It is intended that initial tests with the forthcoming full-scale demonstrator will be carried out in the same way. The 7th scale trials have provided invaluable experience of working in this mode.
4. The functionality and operation of the proprietary OPD hydraulic power take-off and conversion system has been validated. Active and passive control systems
II have been demonstrated in the laboratory using a joint systems test rig. The control algorithms have been tested onthe 7th scale machine at sea. The results of all these tests have been used to validate the simulation code and to direct the onward design programme.
5. The functionality and flexibility of the embedded control and data-acquisition systems has been validated.
6. The individual joint control modules have successfully demonstrated robust active and failsafe characteristics. However, early tests showed that the network software was not robust enough for extended operation and a complete re-write has been carried out. The new software is currently being evaluated.
7. Further tests in controlled wave tank conditions should be carried out to generate specific performance data and further verify the active and passive control modes and algorithms
8. The project has proven that OPD can work with a wide range of suppliers to delivera complex system, and can deploy and operate such a system in the field.
9. The programmehas been invaluable for ‘marinising’ the technology and the OPD team.
10. The Pelamis WEC is now ready to proceed to full-scale technology development and demonstration.
DISCUSSION OF DEVELOPMENT ISSUES ADDRESSED
The successful build, commissioning and test of the 7th scale machine represents a major milestone in the Pelamis WEC development programme. Until this point the machine had only existed as tank test models, paper designs and in the form of a full machine simulation. The 7th scale machine is, in all respects apart from scale and power generation, a complete Pelamis WEC system, and as such proves that the concept is technically realisable. The programme has been of enormous benefit to the technology and the OPD team.
The 7th scale machine is the first model that has had to be essentially autonomous with outside intervention limited to data-retrieval and reprogramming. Successful deployment, test and retrieval of the machine have given OPD extensive experience of these tasks, most of which will be similar forthe full-scale prototype.
Testing of the 7th scale system was carried out with the system under-tow behind a support-vessel, the machine was towed via a representative mooring system to ensure the response was realistic. This allows a ‘hands-on-the-pram’ approach to be used and simplifies deployment and retrieval systems and procedures. As a result of this experience the programme for the first full-scale machine has been modified to include a
III period ofsea-trials under-tow before the full-scale machine is installed on site. This is now seen as a vital part of the commissioning of the full-scale prototype and would have been overlooked had the 7th scale machine not been built. Experience with deployment, tow and retrieval of the 7th scale machine has led to several key innovations and detailed design improvements to the full-scale mooring systems that will allow faster, safer installationand removal of the full-scale system, in a far wider range of wave conditions.
Tests in the field have given OPD the requisite experience with operating complex systems, off-site in the marine environment. In particular, remote communications, re programming, and data acquisition have been successfully carried out.
The functionality and adaptability of the proprietary OPD hydraulic power capture and conversion system has been thoroughly proven, both through the development of the onshore systems test rig and through tests in the field with the complete machine. The results have been used to direct the detailed design of the full-scale system.
To assess the results from both the test rig and the whole machine the numerical simulation code has been extensively modified and extended. The system now includes full modelling of the hydraulic system including control valve characteristics, hydraulic compressibility and flow losses. This has allowed much more detailed modelling of the full-scale system to be carried out. This has led to significant improvement and optimisation of the full-scale hydraulics design. Both active and passive fail-safe algorithms have been developed and implemented on both the machine and the simulation. This has allowed validation of the numerical simulation code.
The project has identified that increased robustness is required in the control software, and this is being addressed inthe onward programme. A complete software re-write was commissioned, and the new code is currently being evaluated. The 7th scale machine will continue to be the main test-bed for the improved software, an onward test programme is in progress.
Perhaps the most important milestone for OPD is demonstration that the development team can work together with a wide range of suppliers to build and commission a complete Pelamis WEC system and test it inrepresentative conditions.
KEY REMAINING RISKS & DEVELOPMENT MILESTONES
The final key development milestone before proceeding to the first full-scale prototype machine is proof of the full-scale joint hydraulic & electrical systems. An intensive programme is currently underway to demonstrate and prove the functionality and operability of a full-scale joint power take-off system in the laboratory.
Once this key development milestone has been passedthe Pelamis WEC will be ready for the first full-scaleprototype test.
IV TABLE OF CONTENTS
1. INTRODUCTION...... 1 1.1 ThePelamis WEC Concept 1.2 Project objectives 1.3 This report
2. 7th SCALE MACHINE SUMMARY...... 3 2.1 General configuration 2.2 Structure 2.3 Hydraulic system 2.4 Electrical & wiring system 2.5 Control system 2.6 Data acquisition system 2.7 Mooring system
3. SYSTEM SIMULATION & JOINT SYSTEMS TEST RIG 15 3.1 Simulation work 3.2 7th scale joint systems test rig 3.3 Power take-off and control model validation
4. TEST METHODOLOGY & KEY RESULTS...... 22 4.1 Data acquisition & communications systemtests 4.2 Generaltest format 4.3 Discussion of test results 4.4 Ongoing & further work
5. PROJECT CONCLUSIONS...... 31
6. THE ONWARD PROGRAMME...... 32 6.1 Onward 7th scale programme 6.2 Full-scale joint systemstest rig 6.3 Full-scale prototype machine
V 1. INTRODUCTION
1.1 The Pelamis WEC Concept
The Pelamis WEC is a semi-submerged, articulated structure composed of cylindrical sections linked by hinged joints (Figure 1.1). The wave-induced motion of these joints is resisted by hydraulic rams which pump high pressure fluid through hydraulic motors via smoothing accumulators. The hydraulic motors drive electrical generators to produce electricity. The complete device is flexibly moored so as to swing head-on to the incoming waves and derives its 'reference' from spanning successive wave crests.
Figure 1.1 - Artists impression of a Pelamis WEC wave-farm
A novel joint configuration is used to induce a tuneable cross-coupled resonant response that greatly increases power capture in small seas. Control of the restraint applied to the joints allows the resonant response to be 'turned-up' in small seas where capture efficiency must be maximised or 'turned-down' to limit loads and motions in survival conditions. Electrical power from the joints is fed down a single umbilical cable to a junction on the seabed. Several machines can be connected together and linked to shore through a single seabed cable.
The core theme of the Pelamis concept is survivability. The fundamental survivability mechanisms employed are the use of length as the source of reaction (to allow the system to de-reference in long storm waves) in conjunction with a finite diameter to induce full submergence and emergence in large, steep waves, thereby limiting loads and motions. The system is slack moored and does use mooring reaction in order to absorb power. The
1 moorings have a motion envelope large enough to accommodate extreme wave motions inaddition tothe low frequency wave-group induced response.
1.2 Project objectives
This project, which has been supported by the UK DTI New & Renewable Energy Programme under grant reference V/06/00188, had the following objectives:
1. To build, commission and demonstrate a 7th scale full-system model of the Pelamis WEC
2. To develop and demonstratea robust preliminary SCADA system for the future full-scale technology demonstrator
3. To validate numerical simulations of the complete system
4. To test the complete SCADA system in a broad range of conditions in active control mode, passive 'fail-safe' control mode and for a range of partial failure scenarios
5. To thereby address remaining key areas of technical risk via a cheap, robust but realistic full-system model
6. To allow OPD engineers to work closely with the project partners for the full- scale programme
7. To give the OPD team valuable experience working with complex systems in the field.
1.3 This report
This report summarises all aspects of work carried out under the project. The main body is set out as follows:
Section2 : A general description of the 7th scale Pelamis WEC machine and its key systems
Section 3 : Details of the joint system test rig and simulation codes
Section4 : A discussion of tests conductedand key results.
Section 5: Discussion of development milestones achieved
Section 6: A brief summary of the onward Pelamis WEC development programme
Section 7: Project conclusions including recommendations forfuture work
2 2. 7th SCALE MACHINE SUMMARY
The outline design of the 7th scale machine and its systems are summarised in the following six sections:
1. General configuration 2. Structure 3. Hydraulic systems 4. Electrical systems 5. Control & data-acquisition (DAQ) systems 6. Deployment/retrieval systems
2.1 General Configuration
The configuration chosen for the 7th scale machine was the same as the intended configuration for the first full-scale machine. This is in common with the current configuration of the 33 rd and 20 th scale models. Standardisation of machine configuration and dimensions is important to allow direct comparisonbetween test results.
Figure 2.1 - Generalview of the 7th scale machine on test in the Firth of Forth
The approximate dimensions and configuration of the 7th scale machine are as follows:
• Overall length: 17m • Diameter: 0.5m • Segments: Four equal length segments • Joints: Three-off, two degree-of-freedom joints • Nose: 5m long drooped conical nose • Tail: Flat
The joint systems are functionally identical to the full-scale design withthe same relative ram areas, control valves and accumulator/reservoir sizes. The only key difference is that the rams are external rather than internal and the ram control manifolds could not be mounted directly onto the rams due to scale differences. No hydraulic motor-generator set is included - accurately modelling these at 7th scale is not feasible. Instead, this system is simulated using a pressure compensated flow regulator. This valve delivers a flow-rate proportional to the demand signal, irrespective of the inlet pressure. As far as the control system is concerned this is identical to the motor-generator set. Power for the controllers and control valves is provided by sets of 24V batteries at each joint. See Section 2.4 for details.
3 Each jointsystem has an independent controller linked to a common centralisedhub. The hubacts as the communication bridge between shoreand the individual joint controllers via an externalEthernet or radio modem link, as will be the case for the full- scale machine. This communication link serves both for data acquisition and for access tothe joint controllers for remote reprogramming. See Section 2.5 for further details.
The model was provided witha mooring system representative of the full-scale system. Details of the mooring configuration cannot be given hereas this is currentlythe subject of a patent application.
4 2.2 Structure
The main structural tubes are made from filament wound glass-fibre tube. All other components are bonded and/or mechanically linked to the main tube segments. This form of construction was deemed to be the most cheap, versatile and robust construction option, while remaining easy to modify and repair. To allow for variable ballasting a second 100mm internal diameter glass-fibre tube was bonded to the inner surface of the main tube. External access from one end of each segment allows a mixture of steel ballast slugs and wooden spacers to be inserted to give the required floatation and trim.
Due to space and accessibility constraints a decision was taken to mount the rams externally, in a cut out bay in the end of each tube segment. The ram mounts and sides of the apertures are linked using an aluminium alloy fork assembly to form an accurate, rigid structure connecting the main bearing and ram mounts. The structure includes a longitudinal web that extends approximately 1 metre into the tube section. These sub- assemblies were then mechanically secured to the main tubes using large dowel pins and bolts, before bonding and fibre-glassing in place. Various external and internal bulkheads complete the main structure. Partial bulkheads were then added inside to provide a secure bay for the batteries.
The complete joint system hydraulics and control system was designed to be mounted on the underside of a large hatch near each segment end. All hoses enter through the hatch lid directly into the main manifold (Figure 2.2). A purpose made hatch coaming was moulded, fitted and bonded in place. Sealing is effected using a neoprene gasket seal. Apertures for the various signal and power cabling were provided inthe internal faces of the ram bays to afford protection and give a clear cable run. Figure 2.3 onthe following page showsvarious views of the structure during construction.
Figure 2.2 - General joint arrangement showing external hydraulic rams with hoses connecting to hydraulic packs through the hatch covers
5 Figure 2.3(a) - Pull-wound fibreglass tubes on delivery, large tubes form the main segments, the small diameter tubes formthe ballast tubes.
Figure 2.3(b) - Tube segments during construction. Rigid sub-frames for bearing and ram mounting were pre-fabricated, then fibre-glassed and doweled into the ends ofthe main tubes as shown in the right hand image.
Figure 2.3(c) - The ballast tubes (bottom left) and hatchways (yellow) were then added. Finally, the ends of the units were faired using closed cell foam and over-glassed.
6 2.3 Hydraulic systems
Ocean waves perform work on the Pelamis by moving adjacent cylindrical sections relative to each other. This relative angular motion is resisted and reacted against by sets of hydraulic rams that pump oil into high-pressure accumulators for short-term energy storage. Hydraulic motors use the smooth supply of high-pressure oil from the accumulators to drivegrid-connected electrical generators.
The 7th scale prototype employs a hydraulics system functionally identical to that intended for use at full scale. This enables control algorithms developed and tested at 7th scale to be transplanted into the full-scale system without major changes. There are however three main differences between the hardware implementations.
• The lower flow and pressure regime at 7th scale allows direct-acting poppet valves to be used without a piloting system as required at full scale where intermediate pilot valves under electronic control must be used to provide the hydraulic pressure to open larger valves. • The externally mounted 7th scale rams are connectedvia flexible hoses to a single manifold that houses the complete set of valves and hydraulic transducers and fixes directlyto the high-pressure accumulator, reservoir, and filter. This manifold is contained in an electro-hydraulic power pack including all instrumentation, data-acquisition, control electronics andwiring. The use of flexible hoses between the rams and the control manifold has consequences due to the low pressure- stiffness of the hose. The full-scale rams will be housed internally and will each have a dedicated manifold attached, thus removing the need for flexible hoses between the poppet valves and the ram chambers. • Due to the non-linear scaling of power with geometry, the 7th scale prototype can only absorb ~0.1% of the power of the equivalent full-scale machine. It is therefore impractical to convert this small amount of absorbed power into electricity. The hydraulic motor and generator of the full-scale system is represented at 7th scale by a proportional throttle valve that dissipates absorbed energy as heat. The oil flow through the valve is controlled electronically in much the same way as flow through the hydraulic motor at full scale.
Each joint has its own self-contained electro-hydraulic power pack including all instrumentation, data-acquisition and control electronics and wiring. Views of various components prior to assembly and an annotated view of a complete pack are shown below in Figures 2.4 & 2.5 on the following page. The complete system is mounted to the underside of the hydraulics bay hatch to allow easy removal and replacement. Connection the to pack is through a single 31-way IP68 connector for all data and signals and through a single 3-way power connector for power supply and charging.
7 Figure 2.4 - Hydraulic system components prior to assembly
LP reservoir
HP accumulator Control/DAQ electronics box
Power switches Oil filter
Charging socket & vent Control valves
Throttle valve
Power connector
Figure 2.5 - Annotated view of an assembled jointsystem power take-off pack
The pack is enabled using a pair of IP68 switches on the outside of the hatch lid. The first powers up the instrumentation and control electronics, the second enables the main drivers for the hydraulic valves. This is to allow safe power up for initial tests. All units were filled andpressure tested before installation in the model. Figure 2.6 shows the power packs undergoing calibration and communication tests on the 7th scale prototype. Water-tight communications cables extend between joints to connect adjacent controllers. The complete joint assembly in-service is shown in Figure 2.7.
Figure 2.6 - Joint systems undergoing commissioning trials
Figure 2.7 - Joint system in service showing independent powerpacks for each joint half
The hydraulic system was originally developed and tested using a laboratory rig as described in Section 3.2.
9 2.4 Electrical & wiring systems
As mentioned earlier it is not possible to realistically reproduce the electrical generation elements in the 7th scale system. It was decided to use batteries to provide power for the electro-hydraulic valves and control and data acquisition system. The batteries were specified to provide sufficient capacity to allow the system to run at full load for in excess of 8 hours. Sealed lead acid batteries are used, charging is via a combined sealed charging socket and vent on the external face of the power packhatch lid.
Each joint system was provided with an independent set of batteries to minimise inter joint wiring. Each joint system is effectively galvanically isolated as will be the case for the full-scale machine. The data communication links are designed to copewith this.
Power is enabled to each joint unit in turn using two switches, one to power up the joint controller, the second to enable the control valves. An emergency power shut-off is included to allow all power packs to be disabled from the nose or tail of the machine in the event of malfunction.
Communication along the length of the machine is provided using link wires incorporating IP68 sealed connectors across each joint. Individual transducers are wired back to each joint controller box.
2.5 Control system
The hydraulic valves of each joint are controlled by a field programmable gate array (FPGA) based micro-controller mounted on apurpose built PCB with all necessary signal conditioning circuitry. The micro-controller and surrounding electronics take a number of transducer signals as inputs, samples them and then passes the values on to the control program running onthe FPGA. The control program processes the inputs and determines the appropriate control output. Drive signals are then sent to the various controlvalves.
The six individual joint controllers are independently linked back to a host controller. The host acts as the hub for data acquisition and communications with the outside world. A PC-104 format computer is used, as this allows for easy incorporation of further data acquisition and GPS functions, and is easily sealed within a compact enclosure.
Interconnection between joint systems and the host controller is via various internal wiring-looms. Each joint controller has a dedicated communication link back to the host controller sited at the rear of the device. As mentioned above 24V DC power is supplied to each joint controller locally but a generalised grounding scheme is used. As mentioned above there is a separate power safety loop to switch off all units in the event of problems. An array of transducers for control and diagnostics have been integrated anda complete joint controller system has been tested on the bench.
Communication with the shore or the support boat is via an Ethernet link and a duplex radio modem running off a serial port on the host controller. This will be similar to the
10 system used for the full-scale prototype machine. For the majority of tests conducted to date the communication link has only been used for remote reprogramming. All sampled data has been stored on a model-mounted hard disk attached to the PC-104 host, for subsequent download. However, the communication software has been set up to be run at a wide range ofbandwidths allow real-time data retrieval for tests in wave tanks and for the full-scale system. Control programs are downloaded to eachjoint controller via the host computer.
A range of transducers are employed to sense important physical quantities and pass on proportionate voltages to the analogue to digital converters housed on each joint controller. The most important input signals for active control of the machine are position and accumulator pressure. It is envisaged that a degree of redundancy in these signals will be built into the full-scale system. The role of the control software is to process input signals and demand an appropriate output valve state to achieve a desired response. The basic control algorithms initially implemented on prototype machines will provide an approximation to a given mechanical impedance at the joint in which they are installed.
Control algorithms originally developed using simulations have now been implemented on the 7th scale system. Results have shown the system to be operating as designed for and capable of providing the desired response. Aspects of the system such as valve transient response have been characterised in the context of controlling the full joint system. The experience gained in the development and testing of control strategies and the diagnostics and characterisation of the full system is and will continue to be invaluableto the full-scale development programme.
2.6 DAQ system
A range of transducers are employed to sense important physical quantities and pass on proportionate voltages to the analogue to digital converters (ADCs) housed on each joint controller. Allowance is made for a further set of digital transducers to provide monitoring of alarm conditions such as compartment flooding. The full set of transducers required at full-scale is installed in the 7th scale prototype thus making the 7th scale data acquisition system essentially transplantable into the first full-scale machine.
At full-scale it is intended to use only fully interchangeable factory calibrated transducers. Two of the 7th scale sensing systems were specially constructed by OPD for reasons of cost and practicality. The impact on the prototype electronics is minimal as the signals from the OPD transducers are conditioned locally to use the same excitation voltage output and signal ranges as those transducers intended for use at full scale.
• Joint angle is measured by a potentiometer coupled to the joint motion via a mechanical linkage. Position measurement at full scale will be by linear transducers mounted inside the hydraulic rams. It was originally the intention to use functionally equivalent rotary transducers at 7th scale. However, since all the conditioning electronics for the units intended for use at full scale are integral to the transducer, the
11 impact on the electronics design of replacing them with conditioned potentiometers for 7th scale is minimal. The cost saving was significant.
• High (accumulator) and low (reservoir) pressures are measured using pre-calibrated transducers with integrated conditioning electronics. Pressure transducers are mounted directly on the hydraulic manifolds.
Position and oil pressure are control signals vital for the operation of the power take-off control system. Other signals were included for general condition monitoring and analysis of system response andperformance.
• Joint moment is measured using strain gauges attached to the spiders of each joint. Four gauges comprise a full bridge circuit for each degree of freedom. This configuration allows both bending moment and axial loads to be derived. Electronic connections are housed on the spiders next to the gauges and potted. The moment measurement system was calibrated by applying known weights to a lever arm attached tothe spiders while inplace on the joints.
• The temperature of the hydraulic oil at the hottest part of the hydraulic circuit is measured using a PT100 probe fitted to the hydraulic manifold. The temperature of the electronics box is measured using a PT100 pad stuck onto an internal surface. PT100 platinum resistors offer higher precision and reliability than conventional thermocouples.
• The batteryvoltage is measured through a conventional potential divider.
• A float switch housed at the bottom of each hatch cavity detects any significant water ingress.
Figure 2,8 - Instrumentation transducers (Joint angle - left Joint moment - right)
The position and force sensors are housed outside the hatch and their connection to the joint controller is through a bulkhead connection. Other transducers are housed in the hatched compartment and are connected to the joint controller through cable glands on
12 the electronics box. All transducers and electronics, both inside and outside the hatched enclosure, are sealed to IP68 standard and are capable of sustained full immersion without failure.
Mooring force and position, and nose slamming pressure transducers are additional sensors catered forby the system but have not yet been incorporated.
In addition to controlling the hydraulic power take-off system, each joint controller acts as a data collection and communication system. The complete set of transducers in each joint are sampled at 32Hz by the joint controllers. While some of the transducer signals are used as inputs to the control program that in turn determines the demand valve states for the power take-off system, all the sampled data is transferred by Ethernet connection via a DSP card to the hub computer housed at the rear of the device.
As mentioned above, the communication software is capable of transmitting data at a range of bandwidths. A direct Ethernet link will be used to provide full remote data retrieval in real time during future 7th scale tests in wave tanks and at full scale via a connection through the mooring system.
The final element ofthe data collection system was a non-directional Neptune Science Inc Mini Wave Sentry wave buoy. This was to allow the general wave conditions for each test to be logged for subsequent analysis. The buoy logs acceleration data over 8.5 minute intervals before processing and transmitting spectral data, via a UHF radio modem, to the base station located on shore. The precise location of the buoy, as determined by GPS, is also transmitted. Depending on weather conditions, the buoy can operate upto a range of 5 kilometres fromthe base station.
The automated transmission wave measurement buoy was first tested in the OPD offices using a spring suspension system and then at sea during the first launch of the 7th scale prototype.
Thegraph on the right of the screen-grab shown in Figure 2.9, shows a plot of the energy density against frequency for a single logging period on the 31 st of October 2001. As can be seen from the sharp edge at the low frequency end of the graph, the waves in the testing area just outside Granton harbour were purely locally wind generated. This resembles a secondary spike on a mixed swell/wind sea offshore. The position of the buoy at a number of waypoints duringthe test period is shown on the left.
13 Figure 2.9 - Screen grab from the Neptune Sciences Inc. Mini Wave Sentry buoy
This spectra indicates a significant wave height of 0.71m corresponding to 5m at full scale. The dominant period is 4.92s corresponding to an 11s period at full scale. This represents an incident wave power of ~135kW/m at full scale.
2.7 Mooring system
All tests to date have been carried out with the machine under tow behind a support vessel. However, the model was towed via a mooring system representative of the current full-scale design to ensure the correct response. Details ofthe mooring system used cannot be given here as they are currentlythe subject of a Patent application.
14 3. SYSTEM SIMULATION & JOINT SYSTEMS TEST RIG
Work on this programme included significant numerical simulation of the joint power take-off system and the complete machine. This is summarised below along with details of the laboratory based joint systems test rig used to validate the numerical code and prove the joint system prior to installation in the 7th scale machine.
3.1 Simulationwork
Numerical modelling and simulation has played a vital role in the development and design of the Pelamis since its inception. Models of the machine’s dynamics and hydrodynamics have been used to calculate annual average power absorption at given potential sites, allowing economic viability to be confirmed. Structural loads have been derived from numerical models and various device configurations tried out in the virtual environment offered by computer simulations. All this has contributed immensely to the design process.
The 7th scale programme differed from previous experimental work in that the focus was on the realisation and understanding of the proposed electro-hydraulic power take-off system and communications systems rather than on the fundamental dynamics, survivability, and power capture of the Pelamis as a whole. Efforts are still underway to further improve the understanding of every aspect of the Pelamis using a combination of model testing and computer simulation.
It was intended that the 7th scale programme provide an increased understanding and experience of systems functionally similar to those to be installed on the full-scale machine. As explained earlier, the 7th scale hydraulics system is functionally identical to that of the full-scale machine and is controlled in the same manner. Experiments carried out on the 7th scale system can therefore be used to develop and verify mathematical models of components and full simulations of the control and hydraulics in operation. These computer models can then be used, after altering the appropriate parameters, to model the full-scale hydraulics system. The determination of full-scale component parameters and verification of the simulation at full-scale will be carried out as part of a full-scale joint system test rig programme (see Section 6.2).
As part of the general development programme OPD has developed a suite ofsoftware simulation tools, including detailed modelling of the Pelamis WEC dynamics and hydrodynamics. Before this project the power take-off (PTO) system has been represented by a simple impedance function e.g. a moment is applied to each joint proportional to angular position and velocity. Control of this type is relatively straightforward to model both mathematically and experimentally. Pure linear control allows frequency domain methods to be applied, offering very fast computation over a range of conditions. However, control of the joint motion of the Pelamis uses a proprietary hydraulics and control strategy. It was vital to gain an understanding of this quite different form of control, and of the effects of real components on system behaviour. As part of this programme, the simulation software was therefore extended to
15 include realistic PTO models and control. This tool now facilitates rapid development and optimisation ofcontrol algorithms in the risk free and cheap virtual environment of computer simulations.
The control software is structured suchthat moments applied at the joints are provided by a separate routine from the rest of the programme. Previously, jointangles and velocities were read in each time-step and a moment proportionate to these was output. This allowed subroutines simulating the microcontroller and the hydraulics system to be created separately before substitution in place of the old joint restraint routines.
The controller and the power take-off models are programmed in separate subroutines with information passing to and from the control subroutine in exactly the same way as for the real microcontroller. This separation allows for the easy translation of control programmes between simulations and actual hardware. All parameters are read in from files on the initialisation of simulation; users define the simulation conditions by editing these files. The PTO parameters include geometry; valve characteristics, fluid resistances, and cracking pressures; accumulator volumes, pre-charges, and starting pressures amongst others. Control parameters depend on the particular control algorithm to be implemented, for example, spring and damping coefficients are required for the algorithms demonstrated in this report. The hexadecimal valve word tables contained in the controller parameter files are expressed in the same format as in the real microcontroller, again allowing for ease of porting between simulated and real systems.
The joint angles used by the control system are effectively ‘sampled’ from the routines handling hydrodynamics in the same way that a real microcontroller samples transducer signals. The control subroutine applies a control algorithm passes its control outputs, in the form of valve control words, to the PTO modelling subroutine. The PTO subroutine then models the physical hydraulic system and provides the resulting applied joint moment to the rest of the program along with its own variables such as chamber pressures, flows etc.
A mathematical model of the PTO system was developed for inclusion in the simulation software. It is designed to work in conjunction withthe control software as written for the simulation such that complete separation exists between the control algorithm and the modelling of its effects.
The power take-off system consists of 4 double-acting hydraulic cylinders configured to pump oil into a high pressure accumulator, from which oil flows steadily through a motor or, in the 7th scale system, a throttle valve. The flow of oil to and from each cylinder is controlled via a set of control valves. As with all mathematical modelling, the level of detail, and therefore the computational effort required, should be set appropriate to the accuracy of results required. However, a model that is less demanding computationally is not necessarily easier to formulate.
16 Elements and effects were treated as follows: • Valves are modelled using conditional statements and orifice flow models. Effects include: passive and active operation, cracking pressures, fluid resistance curves, and operating delays. • Accumulators are modelled using gas laws with heat transfer accounted for by applying a suitable polytropic index. This could be extended to a more general heat transfer model. • Oil compressibility is modelled within ram chambers as a volumetric spring based on a constant bulk modulus. An ‘effective bulk modulus’, combining the compressibility of oil, entrained gas, and pipework etc. is often used when describing hydraulic systems.
The complete simulation was verified for a number of simplified cases, prior to detailed comparisons with the results obtained from the laboratory-based 7th scale joint systems test rig described in the following section.
17 3.2 7th scale joint systems test rig
The 7th scale hydraulic system was developed and tested using a laboratory rig shown in Figure 3.1, below. This rig, initially actuated by hand, was adapted for actuation by a ball-screw operating under closed-loop control. This actuator performs the role of the waves by applying a moment to the joint that is resisted and reacted against by the rams. Pressure transducers were fitted to each ram chamber volume to allow measurement of pressure at every point in the system. Signals used by the control system, such as accumulator and reservoir pressure, and angular position, were also measured using a dedicated data acquisition system.
The second generation prototype hydraulics, constructed from a number of line bodies and a prototype manifold, can also be seen inthe left picture. Thetest rig continues to be used to develop and test control algorithms. Figure 3.1 (right) shows the rig being usedto test and develop control software using one ofthe complete power packs from the 7th scale prototype.
Figure 31 - The 7th scale jointsystems test rig
The large forces and small travel of the rams leads to sensitivity to lost motion due to backlash or compressibility. Energy taken to bring oil contained in a ram chamber up to accumulator pressure is lost when the ram is depressurised. For this reason it is important that the ram pressurises with as little stroke as possible.
18 Oil itself is, for our purposes, a stiff medium with a typical bulk modulus of 1.5 x 109 A- resulting in less than 2% of the maximum stroke being lost. However, air entrained inthe oil can dramatically reduce the effective bulk modulus as can the use of flexible hoses.
As has been mentioned previously, flexible hoses are required in the 7th scale prototypeto link the externally mounted rams to the internally mounted hydraulics system. It was found that the highly flexible polyester braid hoses initially installed on the model gave rise to a greater lost motion than had been foreseen. Bleeding difficulties associated with the small and convoluted geometry left entrained air that further exacerbated the problem of low effective bulk modulus.
Tests were carried out on a range of hoses and hard piping using the laboratory rig. It was found that steel braid hose offered 1.7 times the pressure stiffness of the polyester hose that was originally chosen for its flexibility. Hard pipe, similar to that used in car brake systems, offers nearly five times the stiffness (see Figure 3.2).
Pressurisation of hoses at constant stroke speed
Time (s) Hard steel pipe ------Steel braid — Polyester braid
Figure 3.2 - The effect of hose stiffness on 'lost motion'
It should be noted thatthe problems associated with flexible hoses at 7th scale do not exist in the full-scale system because the valves controlling flow to and from the rams will be housed in manifolds attached directly to the rams. Pressurisation cycles will therefore occur only in the ram chambers. Although short lengths of flexible hose will still be required to take oil to and from the ram manifolds, these will be held at roughly constant pressure so that no pressurisation losses will ensue.
A power pack taken from the 7th scale prototype was used for an extensive set of tests designed to demonstrate the operation of the PTO system and to verify the mathematical model developed for computer simulation.
Typical test results are shown in Figures 3.3.
19 Chamber Pressures
------Ram 4ann ------Ram 3ann Ram 2 ann Rami ann ------Ram 4 lull ------Ram 3 lull ------Ram 2 full ------Ram 1 full
1 2 3 4 5 6 Time (s) Applied moment
E -500 -1000 -1500
-2000 Time (s) Figure 3.3 - Individual chamber pressures through a wave cycle (top) along with the resulting applied joint moment (bottom). The quantised control method can clearly be seen.
20 3.3 Power take-off & control model validation
The power take-off (PTO) model can be run in isolation by providing, as input, measured time-series of both jointangle and the state demanded by the actual microcontroller. The corresponding control signal is passed to the PTO subroutine which models the hydraulics system, effectively under the control of the real microcontroller.
The PTO and controller models can be run in conjunction by providing only the joint angle time-series as input and allowing the simulated controller to carry out the control algorithm and provide control commands to the PTO subroutine which, in turn, models the hydraulic system. Whilst the control algorithms running in the real and simulated microcontrollers should be identical, the outputs can differ due to different control inputs. Slightly different calibrations on real transducers measuring pressures and positions can lead to differences in input signals between real and simulated controllers. Moreover, since control is based on pressure measurements taken from the hydraulic system, disagreement between the real and modelled PTO system results in discrepancies in controller output for a given position time series. Different clock rates and filtering can also add to discrepancies. However, the cumulative effect of the discrepancies discussed above is steady state errors rather than divergent ones.
The controller and PTO subroutines were substituted into the dynamic and hydrodynamic simulation of the Pelamis to form part of the simulation of software. The complete simulationwas validated inan extensive test programme usingthe joint test rig.
Since wave surface elevation cannot be measured during sea trials, it is not possible to recreate results from sea trials using the simulation. It is intended that the 7th scale machine be further tested under repeatable conditions in a large wave basin to allow these comparisons to be made.
21 4. TEST METHODOLOGY & KEY RESULTS
The 7th scale prototype has now undergone 8 sea-trial programmes and has effectively proven the functionality of all systems working both independently and together in the context of the entire machine underrepresentative operating conditions.
4.1 Data acquisition and communications system tests
As described in Section2.6, all transducer signals in each joint are logged continuously to the on board computer via communications links running down the length of the machine. This same communications system is also used for the remote re-programming of the jointcontrollers.
Early shore and sea borne trials concentrated on demonstration of these systems, before actively controlled tests were conducted. The data acquisition system has, after the elimination of some significant software stability problems, operated effectively and to specification during all tests to date. It is currently undergoing extended robustness testing in preparation for use on the full scale prototype. Its capability is also undergoing expansion to allow full multi-degree of freedom control of all the joints from a single control device and programme. Proof of the communications and data acquisition system’s operational effectiveness and an understanding of the requirements for robustness have pavedthe waytowards a confident full scale implementation.
Remote re-programming of the joint controllers has been demonstrated successfully during sea trials. Both parameter and complete programme changes have routinely been made ‘mid-wave’ without interruptingmachine operation.
22 4.2 General test format
All tests were carried out with the model under tow behind a rigid inflatable (RIB) support vessel. A second RIB was used to control the model during deployment and to act as a safety standby during testing. The model was loaded onto a flatbed truck in two sections of two units. It was then shipped to Granton Harbour where it was deployed using a Hiab arm on the truck (Figure 4.1). The two halves were then mated alongside a pontoon before switch on and test (Figure 4.1).
Figure 41 - Launch, fina assembly and initialisation
After this the model was towed from the harbour using the two rigid inflatable boats (RIBs) - one as the lead, and one as the trail tug (Figure 4.2). Once the model was in sufficient depth the mooring system was deployed and the test conducted.
Figure 4.2 - Tow out usingtwo rigid inflatable boats
23 The model was then tested for a period of typically 4-6 hours before recovery to the harbour. Figure 4.3 below shows various views of tests in progress.
Figure 4.3 - 7th scale trials in progress on the Firth of Forth
24 4.3 Discussion of test results
The 7th scale build, commissioning & test programme has been a major success. The primary function of the 7th scale machine was to develop and demonstrate the complete Pelamis WEC system, and to provethat the proposed control and data acquisition system could be robustly implemented. For the first time, a fully representative system has been successfully demonstrated. The 7th scale joint system test rig proved invaluable for characterising and ‘de-bugging’ the hydraulic system and control algorithms and programs. The development of this rig led directly to the inclusion ofa full-scale joint systems rig in the onward development programme. Basic power take-off (PTO) and control concepts and algorithms have been proven, subtle issues relating to the PTO and control system have been discovered and have become a key focus the onward developmentprogram.
The gathering of detailed experimental results across a broad range of wave conditions was not one of the key objectives - tests focussed on demonstrating the various elements of the system functioning as a whole, and that the PTO and control system chosen were stable and effective. Part of the reason for this lies in the fact that accurate collection of time series wave data was not feasible. Detailed assessment of the hydrodynamic performance of the Pelamis WEC system is better performed using smaller scale models in the test tank, where repeatable wave conditions allow meaningful assessment and comparison of machine performance. Despite this a significant quantity of test data was acquired.
A total of eight sea-trial programmes were conducted in the Firth of Forth as part of this project. Tests of the full system to date have, in general, suffered from weather related delays or cancellation. The tests have been carried out over periods of one to two days with commitment to the test made the day before. As such, the tests are highly weather dependent and despite the use of forecasts often conditions have been too calm to carry out meaningful tests, or too rough to allow tests to be carried out safely. Testing in severe conditions has been avoided due to safety considerations. As further demonstration of survivability was not one of the primary objectives of this programme it was felt that it was unwise to test in very rough conditions. All functionality and performance data can be gathered in moderate seas. Indeed, the most severe test of the functionality of the joint restraint system is in very small waves where the wave induced moments are small. On three occasions tests have had to be cancelled due to calm conditions, on two occasions tests were abandoned before or after launch due to severe conditions. Also, due to tidal cycles our launch and retrieval requirements put restrictions on suitable dates for testing.
The following overall results and conclusions were drawn from the tests, these points is discussed more fully below with reference to example test results.
• Fully active joint control of the complete Pelamis machine was demonstrated in a range of conditions.
25 • The quantised moment control was seen to perform satisfactorily, confirming that linear jointimpedances canbe approximated by stepped functions. • A representative range of joint impedance functions were applied. However, areas for improvement were identifiedand are to be tackled in the onward programme. • While the control and data acquisition system performed adequately, several software stability issues were discovered. • While the open sea trials were beneficial in terms of general operating experience, it is concluded that tests of this kind are best undertaken in the controlled environment of a wave tank where possible.
All testing was carried out using fully active joint control. The individual joint controllers were programmed to implement the required joint impedance function. Impedance and other control parameters were varied from the overseeing control computer, in these tests this was carried onboard the test support vessel. The controllers updated the parameters in real time without any loss in continuity of control.
kMM Andhra
Sway -taint Aituhm
TT
Figure 4.4 - Results from one of the trials.
26 The top two graphs in Figure 4.4 show joint angles for the ‘heave’ and ‘sway’ joints respectively. The three traces correspond to the three independent joints. The lower two plots show the corresponding joint moments. The irregular nature of the incoming waves can clearly be seen. It is this unsteady nature of the input that OPD’s proprietary PTO and conversion system is designed to copewith.
The use of quantised control of applied joint moment has been demonstrated for the first time on a full system model. Figure 4.5 below shows a typical record of the joint controller in operation on the 7th scale machine in the Forth. The solid line shows the quantised demand, the fainter dashed line shows the achieved joint moment indicating that the system is effective in applying the required impedance. Figure 4.6 shows the joint impedance function for the same tests. The discrete moment levels can be clearly seen.
Figure 4.5 - Quantised control demand and achieved jointmoment for tests in the Forth.
Sway 3 Impedance Function (one cycle) Sway 3 Impedance Function (many cycles)
600
z -0.3 z -0.3
-1000 Velocity (rad/sec) Velocity (rad/sec)
Figure 4,6 - Quantised impedance functions from tests in the Forth.
27 Undesirable slowly varying joint angle offsets can develop, particularly in small seas at higher damping levels, typical examples are shown in Figure 4.7. This effect is predominantly due to the quantisation of joint moment leading to asymmetries in net centring force. These offsets can be crudely controlled by increasing the stiffness term. However, this involves significant reactive power and reduces the overall efficiency of the system, more elegant solutions to this phenomenon are currently under development and will be demonstrated in future tests.
Heave angles
------H1 pos ----- H2 pos H3 pos
Time (sec)
Sway angles
----- S1 pos — S2 pos S3 pos
Time (sec) Figure 4.7 - Undesirable slowly varying joint angle offsets with the model at high impedancevalues. Control of these is the subject of further work.
Although the control and data acquisition system generally performed satisfactorily, system robustness was not good enough for a long term offshore installation. The individual joint controllers were highly robust and on many occasions demonstrated automatic switching to the desired failsafe condition when the SCADA program crashed. General limitations of the communications and control software led to the decision to completely re-specify, and rewrite, the entire control code. It was precisely this kind of issue that the 7th scale model was conceived of to address, and this alone justifies the considerable investment in the programme.
28 4.4 Ongoing and Further Work
As mentioned in the previous section tests of the full system to date have, in general, suffered from weather related restrictions, delays or cancellation. This makes targeted testing of specific control algorithms, parameters and characteristics inefficient. Verification of the time domain simulation ofthe power take-off system and complete machine requires full knowledge of the incident wave conditions. The power take-off simulation has been fully validated using the joint system test rig but it is not possible to validate the whole machine simulation for the 7th scale machine without having full control over the wave conditions.
When the programme was conceived there were no wave tank facilities available to test the machine in a ‘realistic’ environment. Since the programme started suitable facilities at NAREC and Ecole Centrale de Nantes in France have been built and commissioned. The wave-making systems at these tanks can generate seas of up to 1m high at period between 2-4 seconds (7m, 6-11 s at full-scale), exactly the target test range for the 7th scale machine. In addition, the Nantes tank allows multi-directional mixed sea spectra to be generated.
It is now therefore the intention to test the 7th scale machine under laboratory conditions in this large scale tank testing facility. This will allow detailed power capture tests and verification of the full machine simulation to be carried out. The tests will allow the preliminary control algorithms and DAQ system data-rates and formats for the full-scale prototype to be fully verified, this will significantly reduce the chance of serious commissioning delays on the prototype programme, and will dramatically increase confidence in the system for the first months of open sea testing of the full-scale prototype.
The 7th scale machine has yet to undergo full mooring tests. All tests to date have been with the system under tow behind a support vessel - while the port authority permits the towing of the 7th scale machine behind a support boat, it does not allow installation on an anchored mooring for even small periods of time. The machine was towed via a representative mooring system to ensure that the dynamic response was realistic, but OPD remain keen to carry out tests on a fixed mooring to allow comparison with tests at other scales. The existing towing arrangement also allowed for testing of other important aspects of the mooring system, in particular, deployment and retrieval activities are similar to those that will be used at full scale. Simulations and tank testing of smaller models are currently providing the data required for development of the Pelamis mooring system.
The simulation and test rig continue to be used to further develop and test control algorithms prior to testing at sea or in the wavetank.
Knowledge and experience gained from the 7th scale programme have been crucial to the continuing Pelamis development programme, now advancing to implementation of the full scale prototype. The implementation of control hardware and software, made at 7th
29 scale, is directly applicable to full scale systems. The control electronics hardware, proven and tested under the 7th scale programme, is now being installed with confidence on the full scale joint prototype.
Finally, it is worth noting that the 7th scale machine has had a very positive effect on external perception of the company.
As full scale development proceeds, the 7th scale prototype will continue to provide a vitaltest bed for new control software.
30 5. PROJECT CONCLUSIONS
The following general project conclusions canbe drawn:
1. A full Pelamis WEC system has been built, commissioned and tested. The 7th scale machine is, in all respects, a working demonstrator apart from the final step of power generation.
2. The programme has resulted in major advances in the technology, and has been of enormous benefit tothe OPD development team.
3. Tests were conducted with the system in the Firth of Forth. All tests were carried out with the machine under tow behind a support vessel. The model was towed via a representative mooring system to allow it to respond in the correct way. It is intended that initial tests with the forthcoming full-scale demonstrator will be carried out in the same way, as such the 7th scale trials have provided invaluable experience of working in this mode.
4. The functionality and operation of the proprietary OPD hydraulic power take-off and conversion system has been validated. Active and passive control systems have been demonstrated in the laboratory using a joint systems test rig. The control algorithms have been tested on the 7th scale machine at sea. The results of all these tests have been used to validate the simulation code and to direct the onward design and development programme.
5. The functionality and flexibility of the embedded control and data-acquisition systems has been validated.
6. The individual jointcontrol modules have successfully demonstrated robust active and failsafe characteristics. However, early tests showed that the SCADA was not robust enough for extended operation, and a complete re-write has been carried out. Thenew software is currently being evaluated.
7. Further tests in controlled wave tank conditions should be carried out to generate specific performance data and further verify the active and passive control modes and algorithms.
8. The project has proven that OPD can work with a wide range of suppliers to delivera complex system, and can deploy and operate such asystem in the field.
9. The programme has been invaluable for ‘marinising’ the technology and the OPD team.
10. The Pelamis WEC is now ready to proceed to full-scale technology development and demonstration.
31 6. THE ONWARD PROGRAMME
The onward programme is summarisedbelow:
6.1 Onward 7th scale prototype
The overall programme has been extended to allow for tank testing the 7th scale machine in the Nantes multi-directional wave basin. These tests will primarily be for verification ofthe preliminary control algorithms to be used on the full-scale prototype. However, the tests will also provide essential data for full validation of the numerical simulation software.
This work is being supported by the DTI New & Renewable Energy Programme under grant reference V/06/00203.
6.2 Full-scale joint system test rig
This development task will focus on confirming the functional operation and reliability of a full joint system for the Pelamis WEC prototype. A complex electro-hydraulic system such as the Pelamis power take-off system would not be cleared for service in the offshore or aerospace industries before it had completed a rigorous test programme in the laboratory - wave energy systems should not be treated any differently.
A full joint system test is the only effective way to minimise the overall risk of the offshore demonstration phase. Various simplified test rig configurations were considered but it was concluded that representative tests would only be possible using a rig with the same configuration, geometry and load/motion limits as the full-scale joint.
The rig will be actuated by an independent hydraulic servo system using a pair of rams mounted outside the power take-off cylinders. This will give them the necessary mechanical advantage to overcome system friction and flow losses. A servo position control drive-system will allow accurate simulation of in-service conditions. The drive system has been specified to deliver the full angle, velocity, moment and continuous power ratings of the full-scale joint.
The programme will have the following main objectives:
1. Build and test a full-scale Pelamis joint system 2. Confirm functionality of joint control modes 3. Confirm functionality of power conversion and electrical systems 4. Determine pressure drops through all hydraulic flow paths to ensure inlet cavitation and local overpressure are avoided 5. Confirm the thermal stability of the system for a range of normal and failed operating states 6. Confirm suitability of the chosen hydraulic fluid 7. Preliminary assessment of static and dynamic seal performance and likely service life
32 8. Determine full-cycle conversion efficiency of the complete system at a range of mean power levels 9. Conduct a three-month cycle test to increase confidence in reliability before the first offshore test 10. Allow the OPD team to work closely with the full-scale hydraulics contractor and to gain experience of assembling, testing, operating and maintaining the full joint system
The DTI New & Renewable Energy Programme is supporting the above under grant reference V/06/00191.
6.3 Full-scale prototype machine
Once all key elements of the system have been developed and tested the final phase of the RD&D programme will the building, installation and testing of the first full-scale prototype machine.
The programme will have the following objectives:
1. Build, install & test a full-scale, grid-connected Pelamis WEC prototype 2. Confirm all key performance parameters including: - survivability - power capture - power conversion efficiency - power quality - power deliveryto shore - system reliability, availability, operability and maintainability 3. Provide key design drivers for optimisingthe systemfor production units
The full-scale prototype programme is being part-funded by the DTI New & Renewable Energy Programme under grant reference V/06/00198.
33