Investigation of a magnetic-field modulated brushless double-rotor machine with the same polarity of PM rotor

Owing to getting rid of brushes and slip rings, the magnetic-field modulated brushless double-rotor machine (MFM-BDRM) can be a promising candidate for the electrical-continuously variable transmission (e-CVT) in hybrid electric vehicles (HEVs). However, since there are many magnetic-field harmonics with the high rotating speed in the air gap, the PM loss is a big problem in traditional MFM-BDRMs. Therefore, a new MFM-BDRM with the same polarity of PM rotor is proposed, which has advantages of reducing PM loss, saving PM material and keeping good electromagnetic performance. The magnetic field distribution in the air gap, the back electromagnetic force (EMF) and torque performance of the proposed MFM-BDRM are investigated. To obtain the optimum design scheme, the influence of PM pole-arc coefficient on the torque performance is investigated. Then the torque performance is further optimized by the span ratio of magnetic blocks. To evaluate the overall performance of this new MFM-BDRM, a traditional MFM-BDRM with the same size is designed to compare their performances.