Abstract
Wave Dragon is a wave energy converter of the overtopping type. The waves are focused onto a ramp by two reflector arms and overtop into a reservoir above the mean sea level. The potential energy of the water in the reservoir is converted into electrical energy by a set of low-head hydro turbines and generators.
Wave Dragon will be built next winter as a full scale pre-commercial demonstrator device offshore the Welsh coast with a power output of 7 MW, called the Wave Dragon MW. After its deployment in 2008 it will be the world's largest wave energy converter.
The complete power train from the hydro turbines to the electricity feed into the grid will be described, and the main design approaches for the components will be discussed. For a reliable and cost optimal solution a number of different turbine/generator arrangements have been investigated, taking layouts with direct driven permanent magnet generators into consideration as well as induction generators combined with gearboxes.
For controlling the generator and feeding the electric energy into the grid a number of options like full back-to-back AC/DC/AC converter (transistors based LSC and GSC) or transistor based LSC with step-up chopper (DC/DC converter) and diode rectifier have been evaluated. The main objective of this paper is to discuss the control methodology of the power electronics. Results found in simulations and in experimental investigations are shown.
Finally, based on these results a recommendation for an optimal power takeoff train in terms of control accuracy, overall efficiency, reliability, purchase cost, maintenance requirements and power quality is given.