A Frequency-Response Design Method for the Control of Wave Energy Converters in Irregular Seas.

Abstract

In this paper we present a method of controlling wave energy converters (WECs) in irregular seas. The method controls the WEC so that its displacement frequency response achieves a predetermined characteristics, which is chosen to enhance performance. The design of the controller described is based upon a feedback structure, through deriving the control force from the required displacement of the WEC, rather than the actual displacement. The control setpoint (the required displacement) is synthesized from the incident wave, so prediction of the incoming waves is required, in common with other methods of control in irregular seas. The method is demonstrated using a linear time-domain model of a heaving cylinder. The control signal is generated using both impulse-response functions and transfer functions in order to compare the performance of each, in terms of control signal accuracy and power output, under conditions of reduced wave prediction time. The characteristics of the control force demand and power flow in the controlled system, and the effect on performance of errors both in synthesizing and predicting the incoming wave are investigated. The application of the controller design to a model incorporating non-linearity is also considered