Design Optimization and Comparative Study of Novel Magnetic-Geared Permanent Magnet Machines

This paper presents a novel magnetic-geared permanent magnet (MGPM) machine with dual-layer PM excitations, referred as dual-layer MGPM (DL-MGPM) machine. The key is to employ both the outer rotor and the modulation ring with PM-iron sequences, in which the PMs are separated by iron segments one by one, and can provide PM excitation and flux modulation simultaneously. Both the outer rotor and the modulation ring can achieve flux modulating, namely, bidirectional flux modulating, which can couple the magnetic fields excited by the two sets of PMs and armature currents effectively. The proposed DL-MGPM machine, as well as its existing counterpart which employing all the PMs on the outer rotor and referred as single-layer MGPM (SL-MGPM) machine, are optimal designed using finite element method coupled with genetic algorithm. The electromagnetic performances of the DL-MGPM machine and the SL-MGPM machine are investigated in detail and quantitatively compared. The results show that the proposed DL-MGPM machine can achieve higher torque density than the SL-MGPM machine, and is more suitable for low-speed high-torque direct-drive applications.