A new magnetic-field modulated brushless double-rotor machine

With the advantage of independent speed control of two rotors, the double-rotor machine (DRM) can be a promising candidate for the electrical-continuously variable transmission (e-CVT) in hybrid electric vehicles (HEVs). Since the DRM with brushes and slip rings has problems of extra losses, low reliability, and maintenance, the brushless DRM would be a preferable selection. In this paper, a new magnetic-field modulated brushless double-rotor machine (MFM-BDRM) is proposed, solving the problem of the weak mechanical strength of MFM rotor in traditional MFM-BDRMs. The magnetic field distribution law in the air gap, the back electromagnetic force (EMF) and torque performance of the proposed MFM-BDRM are investigated. To obtain the maximum torque density, the influence of some key parameters, like PM pole-arc coefficient, span ratio and thickness of magnetic blocks, on the maximum torque is investigated. Besides, due to the rich magnetic-field harmonics with the high rotating speed in the air gap, the distribution law of core loss in the MFM-BDRM is investigated. Finally, the overall performance of this new MFM-BDRM is evaluated, including loss, efficiency, power density, etc.