In this paper, a control method for a permanent magnet linear synchronous generator (PMLSG) using an improved equivalent circuit model (IECM) is proposed for maximizing energy harvesting under irregular waves. Compared with the conventional equivalent circuit model, the IECM incorporates a new impedance to characterize the radiation impulse response and provides a method for controlling the PMLSG to conjugately match the external parameters in the hydrodynamic equation in real time under irregular waves. First, the hydrodynamic equations of DDWEC and the energy harvesting mathematical model of the PMLSG were analyzed. Then, the principle of maximizing energy harvesting using the IECM-controlled PMLSG under irregular waves and the calculation of IECM parameters are explained. Finally, it is verified that the harvested energy is maximized based on the superposition principle and through simulation. The results show that the proposed method enables the PMLSG to harvest the maximum energy from irregular waves over a long period of time.

Dual-port direct drive wave energy power generation systems (DP-DDWEPGS) have received widespread attention due to their smooth and zero-free output power, compared to single-port direct drive wave energy power generation systems (SP-DDWEPGS) which have the disadvantage of large out-put power fluctuations. To further enhance the performance of the DP-DDWEPGS, optimal power capture control is proposed to achieve maximum power point tracking. Meanwhile, a multiport converter is applied to the DP-DDWEPGS to solve the problem caused by an excessive number of switching devices in the overall system converter. The multiport converter fulfills all the functional requirements of the DP-DDWEPGS while reducing the number of switching devices. However, switch multiplexing of the multiport converter also introduces coupling relationships between each port and the wave force exhibits time-varying characteristics, necessitating advanced control methods with superior fast-tracking capability. Therefore, in this paper, a decoupling duty cycle optimization model predictive control for DP-DDWEPGS is proposed. Based on the characteristics of switching multiplexing, NSC finite control set model predictive control (FCS-MPC) decouples the current prediction and the cost function, reduces the number of candidate voltage vectors in each operation, and shortens the operation time by 70%. To address the issues of high ripple value and increased error due to decoupling in FCS-MPC, duty cycle optimization control is added, greatly reducing the fluctuations in electromagnetic force and power of the permanent magnet linear generator (PMLG). Based on the established simulation model, the feasibility and superiority of the multiport converter and decoupling duty cycle optimization model predictive current control method are verified.

The dual-port direct-drive wave energy converter (DPDDWEC) topology has recently been proposed as a solution to address the intermittent nature of wave energy. This paper introduces an Optimal Frequency Point (OFP) method for DPDDWEC, which can generate higher active power compared to the commonly used Spectral Peak Frequency point (SPFP) method. The analysis reveals that DPDDWEC systems exhibit multi-degree-of-freedom characteristics due to the coupling between the dual translators, induced by the electromagnetic spring force. By establishing a comprehensive state-space model for the dual-port system and deriving the kinematic relationships between the dual translators, the resonance conditions between the system and the waves are determined, optimizing wave energy capture. Furthermore, the power output from the driven translator is effectively harnessed to compensate for the reactive power of the driver translator. The proposed OFP method produces approximately 22.2% more active power than the SPFP method under single and double-degree-of-freedom (S/DDF) conditions with different wave environments. Finally, the feasibility and effectiveness of the proposed control method for the dual-port system are validated through simulation and experiment results.