Electrical Power Take off

Electrical machines have traditionally been designed to be driven at high speed rotary motion, typically from an internal combustion engine. This corresponds to an airgap speed within the machine of upwards of 60 m/s, allowing for easy conversion into a rapid change in flux. A typical wave energy converter, however, can expect to produce linear oscillatory motion with velocities in the region of 0.5-2m/s. Previously the trend for both wave energy and tidal energy converters has been to match the motion of the device to that required by the traditional high speed rotary electrical machines by complex systems of hydraulics, pneumatics or gearboxes. These mechanical linkages were required to rectify and step up the velocity.

A direct drive system is one where there are no intermediate mechanical systems between the primary moving element of an energy converter and the electrical machine. Directly coupling the moving element of the electrical machine to that of the energy converter in this way places special requirements on the electrical machine, in the form of slower speeds, higher forces and a variable power input not present in schemes with extra mechanical systems. It is these special requirements which have previously led the engineer to use 'off the shelf high speed rotary electrical machines and create innovative solutions to match the required and provided motion within the energy converter. Figure 1.9 shows that these extra mechanical steps significantly increase the complexity of the overall power train.

Figure 1.9: Alternative power take off schemes Wind turbines also produce a slow speed motion, and current practice is to use a conventional high speed induction or synchronous generator, operating at 1500 rpm driven by a step up gearbox. Research in this area has allowed direct drive generators to be proposed, using electrical machines capable of running with airgap speeds of 5-6 m/s [43].

Figure 1.9: Alternative power take off schemes Wind turbines also produce a slow speed motion, and current practice is to use a conventional high speed induction or synchronous generator, operating at 1500 rpm driven by a step up gearbox. Research in this area has allowed direct drive generators to be proposed, using electrical machines capable of running with airgap speeds of 5-6 m/s [43].

The concept of direct drive marine energy converters is hence an extension of slow speed electrical machine research. The principle was highlighted in the heaving buoy wave energy converter illustrated in Figure 1.5, where the float of the device is intended to follow the movement of the water surface. The linear generator translator is coupled directly to the float and so too follows the motion of the waves. The device is slack moored, making it appropriate to use in deep water. Energy is removed by developing a force between the moving element and the submerged drag plate, which will remain stationary or nearly stationary. As is clearly demonstrated, the direct drive system offers a very elegant method for power take off in this example, with an absolute minimum of moving parts.

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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