Direct drive wave energy converter (DDWEC) needs fewer moving parts since the translator in the linear generator is directly coupled with the wave energy converter. Many linear generators are used to achieve high power density in DDWEC and transverse flux linear generator is a decent choice to achieve high power density, which is suitable to be used in typical low-speed high thrust application, like DDWEC. In this paper, a field modulated transverse flux linear generator (FMTFLG) is proposed. The magnetic gear effect is ensured by the interval arrangement of silicon steel sheets and nonmagnetic sheets and the machine operation principle and field modulation mechanism are discussed in detail. The results show that the air gap flux density distributions and harmonics can be modulated and the field modulated transverse flux linear generator is proved to achieve higher thrust density than its conventional counterpart.

This paper presents the optimal energy management scheme for island microgrid applications with direct-drive wave energy converter (DDWEC) and hybrid energy storage system (HESS). Because the motion of the wave is irregular, resulting in frequent and violent changes in the power captured by the generator. HESS plays a very vital role in smoothing out such fluctuations and maintaining a stable DC bus voltage. This paper reduces the times of battery charging and discharging by Optimal Energy Management Scheme (OEMS) to extend its service life. Two-loop control is used where the outer loop controls the DC bus voltage stabilization and the inner loop uses MPC (Model predictive control). MPC helps to handle sudden changes in power generation and load power demand. HESS is used to compensate the difference in average and instantaneous power between the wave generation system and the DC load. MPC aims to regulate the battery and supercapacitor (SC) currents to track the dynamic current reference. The proposed optimal energy management scheme and control structure are verified by simulation results.

Typically, direct-drive wave energy converter (DDWEC) is coupled with a permanent magnet linear generator (PMLG) to transfer energy from mechanical energy to the grid. In order to reduce the current ripple of PMLG, an improved model predictive current control is proposed in this paper. The extended voltage vectors are used to reduce the d-axis and q-axis current tracking errors of the PMLG. In order to reduce the calculation time caused by expanding the voltage vectors, a cascaded optimization algorithm is proposed in this paper, and only 11 voltage vectors calculations are required for each calculation cycle. Simulation results show that the control method proposed in this paper can reduce the current ripple, which is beneficial to improve the stability of the whole wave power generation system.