Ocean wave energy is sustainable and renewable energy, wave energy conversion (WEC) effectively solves the disadvantage of traditional power system with fossil energy. WEC system is the power generation process that converts wave kinetic energy of undulation and swing into electric energy, and direct‐drive WEC system (D‐DWEC) converts wave energy into electric power directly by linear generator to improve the efficiency. At present, the research of WEC system has the characteristic of interdisciplinary, multi‐system integration, engineering application, and commercial operation. This paper summarizes the types, principle, and classification of WEC system, mainly focusing on the aspects of the kinds and characteristics of linear generators used in D‐DWEC system, power post‐processing, and power control methods. At the end of the paper, giving the development trend and challenges of D‐DWEC technology, the research of ocean complementary energy generation platform with offshore wind, solar and ocean wave energy is analysed. It shows that the platform has advantages owing to stable power output, efficient utilization, ocean saving‐space, and power generation cost reduction.

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.

Coastal waves are an abundant nonpolluting and renewable energy source. A wave energy converter (WEC) must be designed for efficient and steady operation in highly energetic ocean environments. A direct-drive wave energy conversion (D-DWEC) system with a tubular permanent magnet linear generator (TPMLG) on a wind and solar photovoltaic complementary energy generation platform is proposed to improve the conversion efficiency and reduce the complexity and device volume of WECs. The operating principle of D-DWECs is introduced, and detailed analyses of the proposed D-DWEC’s floater system, wave force characteristics, and conversion efficiency conducted using computational fluid dynamics are presented. A TPMLG with an asymmetric slot structure is designed to increase the output electric power, and detailed analyses of the magnetic field distribution, detent force characteristics, and no-load and load performances conducted using finite element analysis are discussed. The TPMLG with an asymmetric slot, which produces the same power as the TPMLG with a symmetric slot, has one fifth detent force of the latter. An experiment system with a prototype of the TPMLG with a symmetric slot is used to test the simulation results. The experiment and analysis results agree well. Therefore, the proposed D-DWEC fulfills the requirements of WEC systems.

So as to the efficient and low-cost utilization of offshore renewable energy, a novel direct-drive wind-wave complementary energy generation (D-D WWCEG) platform based on a tubular permanent magnet (PM) linear-rotary generator (TPMLRG) with dual stator is proposed in this study. According to the demand of the load and the energy storage, the D-D WWCEG system has stable output power, few non-operating hours and good anti-disturbance performance under different sea conditions by energy storage. Firstly, combine the design steps of traditional motors, the design process of TPMLRG is given, and the key parameters of linear power generation module (LPGM) and rotating power generation module (RPGM) are optimized by combining the finite element analysis (FEA) and multi-objective optimization method. The magnet field, thermal distribution and the magnetic properties of the PMs are analyzed by multiple coupled models. Secondly, the direct circuit - direct circuit converter (DC/DC) circuit for energy storage is designed and tested, the results show that under a wide fluctuation input voltage, a constant charging current of 0.2A is obtained for the lithium battery. Finally, based on the optimized parameters of TPMLRG, the energy conversion efficiencies of LPGM and RPGM are respectively obtained as 61.0% and 49.8%.

This paper presents a tubular permanent magnet (PM) linear generator (TPMLG) with one single stator and double translators for complementary energy generation platform. Moreover, groups of Halbach PM magnetized structure for double translators is applied to increase the radial air gap flux density and to decrease the axial air gap flux density in the TPMLG. Based on the linear generator model and finite element method (FEM), the radial air gap flux density and axial air gap flux density in the two translator of the TPMLG is calculated and analyzed comparatively. Magnet field distribution of the TPMLG with groups of Halbach PM magnetized structure is illustrated, no-load performance at constant velocity and at sine velocity is analyzed, respectively, and comparing with the radial magnetization PM, the detent force is analyzed contrastively. Finally, this study proposed an experiment system consisting of a TPMLG with a single translator, a cylindrical float and wave flume to verify the analysis results. Through comparative analyses, the proposed TPMLG with double translators and groups of Halbach PM magnetized structure fulfill the requirements of complementary energy generation platform systems.