Design and Analysis of a Magnetic-Field Modulated Brushless Double-Rotor Machine—Part I: Pole Pair Combination of Stator, PM Rotor and Magnetic Blocks

The magnetic-field modulated brushless double-rotor machine (MFM-BDRM) is a promising candidate for the power splitting device in hybrid electric vehicles. Due to its special operating principle, the magnetic field modulation principle, various harmonic magnetic fields are produced in the MFM-BDRM. Therefore, it is crucial for the design of MFM-BDRM to reduce the influence of nonworking harmonic magnetic fields on the electromagnetic performance of MFM-BDRM, like back electromotive force (EMF) and torque ripple. In this paper, first, the distribution law of permanent-magnet (PM) and armature modulated magnetic fields is analyzed. Second, since the analysis and calculation method of harmonic back EMF in a traditional PM machine is not suitable for the MFM-BDRM, the formation mechanism of harmonic back EMF in the MFM-BDRM is further investigated. Third, combined with the characteristic of modulated magnetic field and formed harmonic back EMF in the MFM-BDRM, the optimal pole pair combination of stator, PM rotor, and magnetic blocks is investigated. Finally, analysis and calculation of a specific MFM-BDRM by analytical and finite- element method shows the MFM-BDRM with the optimal combination can obtain very sinusoidal no-load and load back EMF and quite low torque ripple.