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Aquamarine Power’s Oyster hydro-electric wave energy device incorporates a 315kW high-efficiency grid-connected inverter system from Control Techniques.

The Oyster marine energy generator sits just off the shore in Orkney and comprises a large buoyant steel flap hinged to a base that sits on the seabed.

As waves roll over the device, the flap oscillates backwards and forwards, driving two hydraulic pistons attached to each side.

High-pressure water from the two pumping cylinders – clean, salt-free water in an enclosed system – is pumped ashore, driving a Pelton wheel with spoon-shaped buckets that harness the energy of the high-pressure water.

This is attached to a flywheel (to smooth out variations) powering a standard induction generator.

Control Techniques inverters take the generated power and provide an interface with the grid.

Testing of the demonstration-scale wave energy device commenced at the New and Renewable Energy Centre in March last year and it is now installed and working offshore at Billia Croo near Stromness in Orkney.

The Oyster was officially turned on in November 2009 to generate power for the national grid and local homes in Orkney and beyond.

The Oyster is installed at the European Marine Energy Centre’s test site in Orkney, where two Control Techniques inverters provide a clean supply to the grid, with low harmonic distortion.

The AC output from the generator is normally equally split via sharing chokes in order to produce a clean output to the grid.

Being a demonstration unit, Aquamarine Power has fitted many strain gauges, pressure monitoring and other feedback devices at all key points on the system to provide a complete picture of the system performance and all of these signals are fed back to the programmable logic controller.

The Pelton turbine’s speed is monitored by an encoder and this is fed back to the inverter.

’The next generation of Oyster drives, which will have three operating “flaps”, are already in development and we are looking at an output of 2.4MW per unit,’ said Paul Smith, lead electrical engineer at Aquamarine Power.

The units that make up the system are from the Unidrive SPM range, which can be used to implement high-efficiency grid-tie inverters for renewable energy systems, including wave, tidal, photovoltaic and wind.

Control Techniques

Control Techniques, an Emerson Industrial Automation company, is a world leader in the design, production and marketing of electronic variable speed drives for the control of electric motors. Our strategy is to concentrate on delivering drives and servo products that enhance the productivity of our customers’ machines and processes.

We operate through a global network of drive and application centres that both distribute product and add value by building our drive products into custom designed systems and by offering the highest levels of customer service.

Our Control Techniques drive centres also provide us with invaluable feedback and market intelligence so that we can further improve our products and service. This customer focused strategy will enable us to continue to grow profitably.

Our competitive edge is based on our unique focus on drives, our strength in research and development, our investment low-cost manufacturing and an effective worldwide marketing strategy.

Emerson Industrial Automation, a business of Emerson, is a global technology provider that enables productivity, efficiency and quality gains for customers across a spectrum of industries. Our products include alternators, electric motors and drives, electrical distribution devices and mechanical power transmission, fluid automation and ultrasonic joining solutions. Visit our website for more details.

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