Influence of Rotor Pole Number on Performance of Novel Slot Permanent Magnet Machines with Complementary Rotors

In this paper, the influence of rotor pole number on the performance of a new kind of slot permanent magnet (PM) machine with complementary rotors is investigated. The major merit of this novel machine concept is the use of complementary rotors, which consist of an inner rotor and an outer rotor that are mechanically staggered by 180 electrical degrees, to provide complementary paths for the PM excitation flux. Two layers of PMs are employed, located on the inside and outside of the slots. Meanwhile, with only salient poles, the rotors are mechanically robust. The investigation is based on 12 stator pole machines with 10, 11, 13 and 14 rotor poles. Electromagnetic performance measures including flux linkage, back electromotive force (EMF), torque characteristics, loss and efficiency are comprehensively studied using the finite element method (FEM). The results show that the machine with 11 rotor poles can achieve the largest torque density and rated efficiency, as well as minimum ratio of cogging torque to rated torque.