Comparison of flux-switching and doubly-salient permanent magnet brushless machines

This paper compares the topology, operation principle and electromagnetic performance of 12/10-pole flux-switching and 12/8-pole doubly-salient permanent magnet (PM) 3-phase brushless machines, including airgap field distribution, flux linkage, back-emf, cogging torque, winding inductance and electromagnetic torque etc. It is found that the most significant difference is in the flux linkage waveform. In the doubly-salient PM machines, the phase flux linkage is unipolar, which compromises the back-emf per coil and torque capability, while its phase back-emf waveform is more trapezoidal and hence it is more suitable for brushless DC operation. In the flux-switching PM machines, the phase flux linkage is bipolar, and hence it exhibits significantly higher torque density. Both phase flux linkage and phase back-emf waveforms of flux-switching PM machines are essentially sinusoidal, which makes it most appropriate for brushless AC operation.