A two-body buoys power generation system using the field-modulated tubular linear permanent magnet generator (FM-TLPMG) is proposed for direct-drive wave energy conversion in this paper. The traditional linear generator has disadvantages of large weight and low-power density caused by the slow speed of ocean wave. The FM-TLPMG can overcome these disadvantages in some extent through accelerating the speed of the traveling magnetic field. In order to design a suitable FM-TLPMG for the direct-drive wave energy conversion in a short time, ocean wave theory is applied to analyze hydrodynamic problems of the two-body buoys and calculate the operating velocity of FM-TLPMG in the sea. A 2-D analytical model for FM-TLPMG design is presented to obtain the electromagnetic field distribution by solving the Laplace and Poisson equations for each region. The analytical result has been compared with the finite-element analysis and shows its validation for the design.

A field-modulated tubular linear generator with quasi-Halbach magnetization (FMTLG) is proposed for ocean wave energy conversion. The FMTLG equipped with field-modulated technology and quasi-Halbach arrays can overcome the disadvantages of heavy weight and inefficiency caused by the low speed ocean waves to some extent. In order to design and optimize FMTLG in a short time, the open-circuit magnetic field distribution is established with analytical method. The finite elements method (FEM) results show that the back-EMF of FMTLG is 43% higher than that of quasi-Halbach magnetization linear generator (TLPMG). A novel assistant tooth of FMTLG makes the cogging force 8 times smaller than the TLPMG. Finally, a prototype is manufactured to verify the simulation results by the experiments.

In this paper, a permanent magnet (PM) slotless tubular linear generator based on magnet field analysis model is presented for wave energy conversion. To improve air flux density and efficiency of the generator, two improved Halbach PM Arrays (T-PM structure and claw-PM structure) applied in the slotless linear generator is proposed and compared with Halbach PM Arrays. Combined with axisymmetric dimensional finite-element method (FEM), no-load electromagnetic performance is analyzed. Finally, due to test and analysis model results of prototype concordant with the FEM results, the generator model and the analysis method are correct.

To improve the power density and reliability of radial (RS-TLPMG) and quasi-Halbach (QH-TLPMG) magnetization tubular linear surface-mounted permanent magnet generators under realistic sea-state conditions, a novel tubular linear generator with multilayer interior permanent magnets (MI-TLPMG) for wave energy conversion is proposed and analyzed in this paper. Using finite element analysis (FEA), a comprehensive comparison of air gap flux density, flux linkage, back electromotive force (back-EMF), load, and no-load performance is investigated to verify the advantages of the proposed machine. The FEA results indicate that MI-LTPMG with a flux-concentrating effect has higher back-EMF, air gap magnetic flux density, flux linkage, and output power than do the other two machines. Finally, a prototype is manufactured and measured on the test platform and wave tank. The experiment and simulation results show a great agreement with each other.

Aiming at the problem of unstable output power of wireless charging systems for autonomous underwater vehicles (AUVs), a magnetic coupler (MC) with an arc-shaped core structure is introduced and an output power stabilization control strategy based on mutual inductance identification algorithm is proposed. Firstly, an arc-shaped MC with high tolerances, excellent magnetic coupling and weak electromagnetic interference (EMI) is designed for the cylinder-shaped AUV. Based on ANSYS Maxwell simulation, an analysis of the magnetic field and comparative misalignment tests are carried out for the arc-shaped and the double dipole core structures. Secondly, a mathematical model of the LCC-S type magnetically coupled resonant wireless power transfer (MCR-WPT) system is developed, and a particle swarm parameter identification algorithm with adaptive inertia weights is proposed. Finally, the output power is steadily controlled by real-time adaptation of the duty cycle for the Buck-Boost circuit. The results show there is a maximum error within 2.5% in mutual inductance identification when the load is changed from 0 Ω to 12 Ω and the mutual inductance is changed from 25 μH to 50 μH. The system output power is steady at around 680 W with a maximum fluctuation rate of 4.90%, which verifies the efficiency of the power stabilization control strategy.

Direct-drive wave energy converter (DDWEC) is more widely used due to its simple structure and high conversion efficiency. Different kinds of linear machines are used in DDWEC to improve the power density. Among them, transverse flux linear machine uses perpendicular magnetic flux path and axial stacked silicon steel sheets to reduce iron loss and enhance power density. In this paper, a flux-reversal transverse flux permanent magnet linear generator is proposed. The winding connection type of this configuration is elaborated. Circumferential three-phase type, axial three-phase type and the proposed one are compared to obtain higher power density and lower thrust ripple. The proposed three-phase winding configuration has the lowest thrust ripple (0.76%) and decent average thrust (247.01N). A prototype was manufactured and an experimental testing platform was built. The measured back EMF values in the experiment showed a consistent trend with the FEA values. Owing to the convenience in changing the armature winding connection and excitation winding connection, the proposed machine has high design flexibility. The proposed machine is suitable to be used in high power density and low thrust ripple applications. When the proposed machine uses dual three-phase winding or six-phase winding, it also has high fault tolerance ability.