Internal-model-based velocity tracking control of a submerged three-tether wave energy converter

Abstract

Control algorithms play an important role in the design of wave farms and individual wave energy converters (WECs). Advanced control systems can significantly increase the performance of any oscillating WEC, while also improving the investment attractiveness of the entire wave energy industry. Whilst the majority of effective controllers have been tested in simulations, many cannot be implemented in real life as they heavily rely on future (predicted) knowledge of the incident wavefront. In order to overcome this problem, several causal control strategies have been developed to maximise power output of the WEC. One such example is a simple and effective real-time controller based on the concept of the internal model control (IMC), where the performance of the WEC is tuned to the dominant wave frequency from the spectrum. This controller has been previously applied to the floating heaving buoy with one degree of freedom. In the current study, the IMC approach is extended to the three-tether submerged WEC, where several motion modes contribute to power generation. The performance of the controller is compared with another existing acausal solution in order to quantify its effectiveness.