Power optimisation of a point absorber wave energy converter by means of linear model predictive control

Abstract

This study presents a model predictive control (MPC) scheme for a wave energy converter (WEC); in particular, for a buoy-type point absorber. The WEC is a two-body system which is taut-moored to the sea floor with three cables. Much research has been done recently to achieve optimal operation of WECs. The goal is to maximise the power conversion without violating system limits. In practice, there are physical constraints on position, velocity and the power take-off (PTO) force. MPC is a promising and beneficial approach to achieve this goal. It poses a control formulation including constraints in a natural way. Furthermore, MPC can exploit predictions for the sea motion a standard MPC approach always needs a reference trajectory. For one-body point absorber, an optimal velocity trajectory can be calculated. However, an optimal trajectory is not easily available for the two-body case. The proposed formulation in the presented work does not require an optimal trajectory. For this reason it is possible to apply this MPC scheme to a two-body model as well. This work demonstrates that the proposed control algorithm optimises the power extraction without violating the system constraints. Finally, the performance of MPC is compared to linear passive load control through simulation.