A Hill-Climbing-Method-Based Maximum-Power-Point-Tracking Strategy for Direct-Drive Wave Energy Converters

Based on the mechanical model of direct-drive wave energy converters, the relationship among the average output power of a direct-drive wave energy converter, its inherent mechanical impedance, and the equivalent mechanical impedance of the generator is analyzed in the frequency domain to obtain the maximum power extraction condition. In addition, the curves of the average output power of the system under the power control with two degrees of freedom with respect to the control variables are obtained. Based on the characteristics of the curves, a maximum-power-point-tracking (MPPT) strategy is proposed, and the hill-climbing method is used to realize the MPPT. Additionally, the iterative equations and the control flow of the MPPT algorithm are provided. Based on the oscillation phenomenon caused by the measurement error of the average power of actual systems, a window function-based processing method for mean value filtering is proposed, which can further improve the steady-state performance of the hill-climbing-based MPPT strategy. Simulation and experimental results demonstrate that it is an effective and promising power control strategy for direct-drive wave energy converters.