Real-time latching control strategies for the solo Duck wave energy converter in irregular waves

Highlights: • Three real-time latching control strategies are defined and compared. • Suggestions are given on how to choose the time step for predictive strategies. • The non-predictive strategy captures the same power as the predictive ones. • The non-predictive control strategy is most favorable for solo Duck WECs. • Latching control does not cause additional fatigue damage to the PTO. As a point absorber, the solo Duck wave energy converter (WEC) shows high power capture efficiency within a narrow bandwidth around the natural period. In this paper, real-time latching control is applied to the solo Duck WEC in irregular waves to improve its performance in sea states away from the natural period. Two predictive latching control strategies, in which one is close-to-optimal and the other is sub-optimal, and one non-predictive strategy are considered. The improvement of the WEC performance due to latching control is studied. Compared to the performance under simple resistive control, the three latching control strategies show almost equivalent control effect, leading to an average increase of the maximum relative capture width by around 70% and an average decrease of the optimal power take-off (PTO) damping coefficient by around 60%. Since the non-predictive strategy requires no prediction of future excitation force and WEC motion, it can be identified as the best choice for the solo Duck WEC under latching control. Although latching control leads to significant increase of fatigue load on the WEC hull like other advanced controls, it does not cause additional fatigue damage to the PTO.