A Novel Piecewise Velocity Control Method Using Passivity-Based Controller for Wave Energy Conversion

By studying the working principle of a maximum power point tracking (MPPT) method called active phase control (APC), we found that not only was the phase difference between the wave excitation force and the velocity reduced, but also the magnitude of the velocity increased. For the direct-drive wave energy converter with a permanent magnet linear generator (PMLG), the velocity of the PMLG in the no-load state is larger than that in any power generation states. According to this characteristic, a novel piecewise velocity control (PVC) method and its trajectory planning scheme for a sealed-buoy wave energy converter (SBWEC) are proposed to obtain the maximum power extraction condition. Considering the irregularity of ocean waves and that the proposed method needs to frequently change the operating state of the PMLG, a passivity-based controller (PBC) is designed. With energy modification and damping injection, rapid convergence and asymptotic stability of the system are guaranteed, so that the proposed MPPT method can be perfectly implemented. The comparative simulation results for regular and irregular waves demonstrate that it is an effective and promising power control method.