Dynamic Characteristics and Test Results of a Wave Power Takeoff System With Mechanical Motion Rectification and Transmission

In this paper, innovative ocean wave power takeoff (PTO) system is presented to enhance the electrical energy generation from oscillating wave motions. This PTO system, mainly consisting of dual-ball screws, a gearbox with mechanical motion rectification and a permanent magnet synchronous generator (PMSG), can convert bidirectional irregular motions from a floating wave buoy into unidirectional steady generator rotations. Systematical operating principles, design, and prototyping details of the PTO system are presented and analyzed. A hydrodynamic-mechanical-electrical model of the system is established by reasonably representing power switches attached to the PMSG as an equivalent external resistance. The overall dynamics of the system are then analyzed in the frequency domain. Three power control strategies are proposed to maximize the wave power absorption by changing the equivalent external resistance. The effectiveness and relatively high-energy conversion efficiency of the PTO system have been demonstrated based on lab bench test results. The levelized cost of energy of a full-scale wave energy converter system is also calculated based on the proposed PTO system.