Design method of a magnetic-field-modulated brushless double-rotor machine used for HEVs

The magnetic-field-modulated brushless double-rotor machine (MFM-BDRM), composed of a stator, a permanent-magnet rotor and a modulating ring rotor, is a novel machine used for hybrid electric vehicles (HEVs). As a three-port machine, the energy transfer relations among three ports of the MFM-BDRM are complicated. Furthermore, the special operating principle of the MFM-BDRM, the magnetic field modulation principle, is quite different from that of traditional machines. Therefore, investigating the design method of MFM-BDRM is valuable for its applications. First, the power flow of the MFM-BDRM system is analyzed on the base of the HEV background. Then different working modes of the MFM-BDRM are obtained. By analyzing the speed and torque relations among three ports, the design principle of the MFM-BDRM is proposed. In the design process, the analytical methods of the fundamental flux, stator frequency and q-/d- axis inductance, which are different from traditional machines, are proposed. The influence of some key parameters, like combinations of PMs and magnetic blocks, the span and thickness of magnetic blocks, on the electromagnetic performance is discussed. Finally, a favorable solution with the higher power density and the lower torque ripple is determined.