Performance Analysis of an Axial Magnetic-Field-Modulated Brushless Double-Rotor Machine for Hybrid Electric Vehicles

The series-parallel hybrid electric vehicles (HEVs) are widely developed due to the advantages of high fuel economy and good driving performance. The electronic continuously variable transmission, which is a key part of the HEV, can be based on planetary gear or compound structure machine (CSM). The axial magnetic-field-modulated brushless double-rotor machine (AMFM-BDRM), which can be connected with a traditional permanent-magnet synchronous machine to form a CSM, is investigated in this paper. The axial tilting torque is analyzed, and the necessary condition for avoiding it is given. Compared with the single-sided topology, the double-sided AMFM-BDRM is recommended to eliminate the axial tilting torque. The influences of winding turns, diameter ratio, ferromagnetic block and permanent-magnet (PM) dimensions, air-gap length, phase current, and internal power-factor angle on the power factor and electromagnetic torque are analyzed, and it is found that the increase of power factor is sometimes at the expense of sacrificing the electromagnetic torque. The effects of speed and PM segmentation on losses are investigated, and the circumferentially double-segmented PM is selected. The influences of dissymmetry on air-gap flux density, no-load back electromotive force, electromagnetic torque, and axial magnetic force are analyzed, and it is found that the offset, tilt, and PM position deviation of the PM rotor have different degree effects on machine performances. Experiments are carried out, and the correctness of the analysis and simulation results are verified.