Back-EMF optimization of a Rotor Permanent Magnet Flux-Switching Machine Through Air-gap Harmonic Design

Unlike the stator permanent magnet (PM) flux-switching (FS) machine, the sinusoidal degree of the no-load back electromotive force (back-EMF) in the rotor PMFS machine is not high, which will decrease the utilization rate of the inverter voltage, and the torque performances. Hence, this paper presents a method to sinusoidal the back-EMF of the rotor PMFS machine with a T-shaped rotor module by optimizing the key harmonics of the air-gap flux density $(B_{r})$. The presented method has the benefit of optimizing the back emf without sacrificing the output torque performance of the machine. Firstly, the magnetomotive force (MMF)-permeance model is analyzed to investigate the no-load $B_{r}$, which contributes to the back-EMF, and is obtained by introducing the winding function theory. Then, based on the Maxwell stress tensor method, it is possible to obtain the devotion of the harmonics of the $B_{r}$ to the torque. After that, the design method to reduce the back-EMF is realized by minimizing the harmonics of $B_{r}$ which generates more to the third harmonic of the back-EMF and maximizing $B_{r}$ which generates more to the torque.