Maximum power point tracking control strategy for built-in direct-drive wave energy converter

The built-in direct-drive wave energy converter (BD-WEC) converts the mechanical energy of the buoy into electrical energy. The conventional maximum power point tracking (MPPT) control strategy is difficult to implement on the BD-WEC due to the cyclic variation and over-zero transients in the input power of the core power generation unit (CPGU). This manuscript derives the numerical relationship between the capacitor voltage at the rectifier output end of the permanent magnet synchronous generator (PMSG) and the average output power of the PMSG in the time domain is derived, and the P-V curves at the output of the PMSG are obtained for different wave frequencies and CPGU weights. An MPPT control strategy for BD-WEC is proposed, which uses the perturbation and observation (P&O) algorithm to autonomously track the maximum power point of the CPGU, and ensures the safe operation of high-weight CPGU through parallel position control. A prototype of the BD-WEC was manufactured in the laboratory, and MPPT control was implemented through a digital signal processor (DSP). Simulation and prototype experimental results show that the proposed MPPT control strategy can increase the energy conversion efficiency of a 90 kg CPGU to 32.5 % when the wave frequency is 0.143 Hz.