A New Magnetic-Field-Modulated Brushless Double-Rotor Machine

In this paper, a new magnetic-field-modulated brushless double-rotor machine (MFM-BDRM) is proposed, solving the contradictory problem of the electromagnetic performance and the mechanical strength of an MFM rotor in the traditional MFM-BDRMs. The operating principle of the proposed MFM-BDRM, including the speed and torque relations of the stator, the MFM rotor, and the permanent magnet (PM) rotor, is investigated by an analytical method. The magnetic field distribution law in the air gap, the back electromotive force, and the torque performance of the proposed MFM-BDRM are investigated. To obtain the maximum torque density, the influence of some key parameters, such as PM pole-arc coefficient, span ratio, and thickness of magnetic units, on the maximum torque is investigated. Besides, due to the rich magnetic-field harmonics with high rotating speed in the air gap, the distribution law of iron loss in the proposed MFM-BDRM is investigated. The PM-split method along the circumferential direction is employed to reduce the PM loss. Finally, the overall performance of this new MFM-BDRM is evaluated, including loss, efficiency, power density, and so on.