Hybrid control strategy for efficiency enhancement of a raft-type wave energy converter

Abstract

To improve the wave energy capture performance of a raft-type wave energy converter, a novel hybrid control strategy consisting of a passive control strategy and an active control strategy is proposed. In the passive control strategy, a nonlinear stiffness mechanism is introduced to generate a nonlinear passive control force. The passive control strategy has the advantage of broadening the capture width, whereas the active control strategy, which uses nonlinear model predictive control, is mainly utilized to improve the capture efficiency. Considering the high dimensions of the dynamic model, a dimension reduction strategy is given. Moreover, a mechanism for selecting the initial value is proposed to avoid the local optimum. Then, a dimension reduction nonlinear model predictive control controller is proposed to obtain the optimal active control force. Finally, the wave energy capture performance is evaluated for both regular and irregular waves. Numerical simulation results show that the wave energy capture performance can be improved using the novel hybrid control strategy.