Low-Loss Design and Analysis of Magnetic-Field Modulated Brushless Double-Rotor Machine

Due to the existence of large permanent magnet (PM) loss caused by its magnetic-field modulated (MFM) rotor in a traditional MFM brushless double-rotor machine (MFM-BDRM), a low-loss MFM-BDRM with the sinusoidal permeance characteristic of an MFM rotor is proposed and investigated in this paper. Since fan-shaped magnetic and nonmagnetic blocks in traditional MFM rotor cause many harmonic permeances and further produce large harmonic loss in the PMs, the ideal sinusoidal permeance model of an MFM rotor is first established and investigated by the analytical method. Considering that tangential leakage flux among magnetic blocks in the analytical method is difficult to calculate accurately, the influence of key parameters of the proposed MFM rotor, like the span ratio of magnetic block, minimum length of inner and outer air gap, on the electromagnetic performance of MFM-BDRM is further investigated and optimized by the finite-element method. Finally, to completely evaluate the performance of the proposed MFM-BDRM, a traditional MFM-BDRM with the same size is designed to compare performances under different operating conditions.