This paper presents a Digital Filter method for real time prediction of waves incident upon a Wave Energy device. The method transforms waves measured at a point ahead of the device, to expected waves incident on the device. The relationship between these incident waves and power capture is derived experimentally. Results are shown form measurements taken on the Wave Dragon prototype device, a floating overtopping device situated in Northern Denmark. In this case the method is able to accurately predict the surface elevation at the device 11.2 seconds before the measurement is made. This is sufficient to allow advanced control systems to be developed using this knowledge to significantly improve power capture.
Time domain digital filters can be used to transfer a measurement of the waves ahead of a structure to a real-time prediction of the waves in the near future. Knowledge of the forcing, overtopping or other excitation caused by the next few waves may be used for fast control of a device. Studies show such a prediction can improve energy capture by 5 % (Tedd et al, 2005). This paper describes the general theory and application of this, and presents results from a specific case study of implementation on the Wave Dragon machine. Wave Dragon is a floating wave energy converter (WEC), extracting energy principally by means of overtopping of waves up a ramp and into a reservoir. Potential energy of the water at the higher head is extracted by several turbines within the reservoir. There is a fully automated, real sea prototype of the device deployed in Northern Denmark. Here the turbines are controlled to turn on and off in a cascading sequence to maintain the water level in the reservoir. This fast acting control could be improved with knowledge of the incoming overtopping flow.
