It is well known that the air-gap magnetic field of the permanent magnet synchronous generator (PMSG) is difficult to adjust. To overcome this challenge while maintaining the brushless feature of PMSGs, a hybrid excitation synchronous generator (HESG) based on inherent third harmonic field induction is proposed in this paper. The HESG adds a set of third harmonic windings with a pitch of 1/3 of the armature winding in the stator core and a set of harmonic windings with the same pitch as the third harmonic winding in the rotor core. Due to electromagnetic induction, the third harmonic field established by third harmonic windings in the stator induces the harmonic electromotive force (EMF) of six times the frequency in the rotor harmonic winding. This harmonic EMF is directly provided to the rotor excitation winding after rectifying by the diode rotating rectifier. The HESG has armature windings and third harmonic windings in the stator, and excitation windings, harmonic windings and permanent magnets in the rotor. In this article, the mechanism of stator third harmonic winding EMF, rotor harmonic EMF, and the brushless excitation are elaborated. The experimental results of adjustable armature winding voltages with controlling the stator third harmonic winding current have proven the feasibility of the proposed brushless excitation principle based on the third harmonic.
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