Direct-drive wave power generation systems based on permanent magnet linear generators (PMLGs) produce fluctuating electromagnetic power under irregular wave excitation, which may affect DC-bus voltage stability and load-side power quality. To smooth the fluctuating output power, this paper develops an empirical mode decomposition (EMD)-based power allocation strategy for a battery–supercapacitor hybrid energy storage system (HESS). In the proposed strategy, EMD is used to decompose the fluctuating electromagnetic power into low-frequency and high-frequency components according to their time-scale characteristics. The low-frequency component is assigned to the battery for energy buffering, while the high-frequency component is assigned to the supercapacitor for transient power compensation. Finite-control-set model predictive current control (FCS-MPCC) is adopted on the generator side to improve the current response of the PMLG, and an MPC-based HESS controller is designed to track the assigned power commands and regulate the DC-bus voltage. Simulation results show a battery power-tracking error of 3.93 W and a DC-bus voltage standard deviation of 0.108 V; compared with LPF, EMD reduced the load-step voltage deviation by 11.94%. Experiments confirm that the PMLG back-EMF follows the translator velocity, the storage currents track their references, and the DC-bus voltage remains within ±2 V of its reference.

An adaptive super-twisting algorithm (ASTA)-based variable-damping strategy coordinated with five-vector model predictive current control (FV-MPCC) is proposed for a dual three-phase permanent magnet linear generator (DTP-PMLG) wave energy conversion system. In the upper-level controller, the power take-off (PTO) damping coefficient is adjusted online based on the captured power gradient, and finite-time convergence of the power-gradient variable is established via Lyapunov analysis. In the lower-level controller, four active voltage vectors and one zero voltage vector are applied in each sampling period, so that the d–q–x–y current components are directly included in the action-time calculation. Therefore, q-axis current tracking and x–y harmonic-current suppression are achieved simultaneously. Simulation results under two irregular-wave conditions show that the proposed variable-damping law approaches the optimal fixed-damping performance without requiring prior sea-state-specific damping selection, increasing the mean captured power by 2.38% and 3.44% relative to the optimal fixed-damping cases. Experimental results further confirm that the proposed FV-MPCC reduces the d-axis and q-axis current ripples by 35.92% and 40.66%, respectively, compared with conventional MPCC.

Direct‐drive wave energy converters (DDWECs) commonly employ linear generators because this configuration can reduce intermediate components and provide high conversion efficiency, a simple structure and convenient maintenance. For DDWEC applications, a six‐phase permanent magnet transverse flux linear wave generator (PM‐TFLWG) can improve the fault‐tolerant capability of the system using the additional degrees of freedom provided by the multiphase winding. However, for a flat linear generator, the end effect affects both the post‐fault control performance and the thrust ripple characteristics. Therefore, this paper proposes a fault‐tolerant control strategy for a six‐phase PM‐TFLWG considering the end effect, and the influence of dq‐axis current on electromagnetic thrust is analysed. An ANSYS simulation model is established, and the phase‐A open‐circuit fault is experimentally tested. The simulation results indicate that a nonend‐phase fault causes a larger thrust reduction and thrust ripple than an end‐phase fault. The proposed strategy restores the thrust amplitude and reduces the thrust ripple under different single‐phase open‐circuit faults. After fault‐tolerant control, the experimental mean thrust increases from 150.3 to 179.8 N close to 180.7 N under the normal condition.

In the past decades, various linear generators have been applied in direct drive wave energy converter (DDWEC). However, linear generators have the demerit of low power density in low-speed applications. The transverse flux linear generator (TFLG) can achieve higher power density due to the decoupling of electromagnetic loads and the use of laminated silicon steel sheets in primary to reduce iron loss. Also, the magnetic field-modulated machine is a suitable solution in low-speed large thrust application scenario. In this article, a TFLG used in DDWEC is proposed. In addition to the magnetic field modulation effect, another highlight of this topology is the use of permanent magnets (PMs) in the slots, which further enhances power density. The simulation results prove that the proposed TFLG reaches large power density and has relatively low thrust ripple. Tangential magnetization type can achieve higher power density than its radial counterpart, but it is difficult to fix the slot PM in tangential magnetization type. The power density per PM volume of the TFLG prototype is 975.1 kW/m3, and the thrust ripple is 2.62%.