Abstract
In this paper, a novel discrete control strategy is proposed to improve power-capture performance of wave energy converters (WECs) with a hydraulic power take-off (PTO) system. In this novel discrete control strategy, separate switching valves are introduced such that each chamber of hydraulic cylinders can be actively and independently connected to a high-pressure gas accumulator or a low-pressure gas accumulator by controlling the switching action of the switching valves. Thus, it increases the flexibility of the PTO system and makes the PTO system more controllable. The effectiveness of the novel discrete control on improving power-capture performance of a raft-type WEC and the optimal switching command of the switching valves for maximizing power capture are studied. Benefit brought by the novel discrete control is investigated in terms of power improvement and the control effect of the novel discrete control is compared with that of load control and latching control. Results show that the novel discrete control can effectively improve power-capture performance of the raft-type WEC and theoretically the corresponding benefit reaches a peak value of 2 and 2.5 in regular and irregular waves, respectively. The novel discrete control has an advantage over load control and can be complementary to latching control.