Research on a novel axial-flux magnetic-field-modulated brushless double-rotor machine with low axial force and high efficiency

The axial-flux magnetic-field-modulated brushless double-rotor machine (MFM-BDRM) is a possible alternative as a power-split device for hybrid electric vehicles (HEVs). However, the existence of large axial force may lead to assembly problems and rich inner air-gap harmonics could result in high PM loss and low efficiency. This paper proposes a novel axial-flux MFM-BDRM with improved PM rotor structure. 2-D analytical method to predict the magnetic-field distribution of the proposed MFM-BDRM is developed and the design procedure of the proposed machine is illustrated. The impact of key geometrical parameters on axial force and torque is investigated. To evaluate the advantage of the proposed machine, a comparison is made with a conventional one with respect to electromagnetic performances. Results show that the proposed machine is effective in reducing PM eddy loss and axial force by 60% and 35%, respectively.