Comparison and analysis of dual stator permanent magnet vernier machines with different pole/slot combinations for low speed direct drive applications
Permanent magnet vernier machine (PMVM) based on flux modulation principle has attracted increasing attention in low speed direct drive applications due to its high torque capability. A dual stator PMVM topology with sandwiched spokearray PM rotor is presented to produce higher air gap flux density and larger torque in this paper, and the space utilization and the energy conversion efficiency are improved significantly. Two representative dual stator PMVMs (DS PMVMs) are designed with this topology, the pole/slot combinations and gear ratios of which are 18 slots/30 poles and 18 slots/28 poles, 5 and 3.5, respectively. In order to reveal the advantages of the proposed topology and assess the torque characteristics of the proposed machines with different pole/slot combinations, the electromagnetic characteristics of these two machines are quantitatively compared and analyzed by using finite element method (FEM) The results demonstrate that the 18 slots/28 poles DS PMVM can offer higher output torque, lower torque ripples, lower cogging torque and higher power factor owing to its optimal pole/slot combination. In addition, the unbalanced magnetic pulls (UMPs) of the two machines are also investigated, and the UMP of the 18 slots/30 poles DS PMVM is smaller than that of its counterpart due to its symmetrical winding.