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Recently, linear generators have been implemented in direct drive wave energy conversion (DD-WEC), thus simplifying the structure and improving system efficiency. Since DD-WEC is a typical low-speed application, linear generators with multi-pole design all encounter problems such as low power density and low efficiency. Similar to the magnetically geared machine, field-modulated permanent magnet transverse flux linear generator (FM-PMTFLG) has been a suitable candidate for DD-WEC, due to the high power density capability ensured by the ‘magnetic gear effect’. However, for solely PM excited generators, there is a tradeoff between high power density and wide speed operation. Hence, field-modulated hybrid-excitation permanent magnet transverse flux linear generator (FM-HE-PMTFLG) is proposed. In order to improve the thrust performance, the partitioned staggered translator (PST) topology is introduced. The simulation results show that PST topology can achieve better thrust performance than partitioned translator (PT) counterpart. Compared with PT topology, PST topology reduces the magnetic flux leakage and has advantages of higher thrust density, less thrust ripple, higher flux linkage and better total harmonic distortion (THD) of back-EMF.

Direct drive wave energy conversion (DDWEC) device ignoring intermediate transmission mechanism can simplify the structure and improve the efficiency. Usually, linear generator used in DDWEC need a low-speed design for low-frequency wave condition. However, the linear-rotating axial flux permanent magnet generator (AFPMG) proposed in this paper combines the merits of magnetic lead screw (MLS) and axial flux generator to convert the low-frequency reciprocating wave motion into high-speed rotating motion to generate power. Four similar configurations (12s10p, 12s11p, 12s13p and 12s14p) are detailed. The results show the output voltage and power density of the power generation system can be improved in this topology and 12s13p configuration can be a decent candidate for DDWEC.

A novel hybrid excitation axial flux permanent magnet generation (HE-AFPMG) is proposed to improve the electromagnetic performance of conventional axial flux permanent magnet generation and suite the demands of direct drive wave energy conversion. Firstly, the configuration of the HE-AFPMG is introduced. Then operation principle based on open-circuit field distribution and qualitative analysis of field modulation are following. Finally, the electromagnetic performances under no-load and load conditions are analyzed. Meanwhile, the influence of the application of electric excitation on generator is also investigated. It verifies the validity of generator and confirms the excellent field-regulation capability. According to the results, it is proved that the addition of electric excitation field can not only reduce the harmonic component of back EMF, but also broaden the range of load torque.