Research on Surface-Mounted Permanent Magnet Machine with Negative Salient Pole

In this work, a surface-mounted permanent magnet (SPM) machine with negative salient pole is proposed, to improve the electromagnetic characteristics without increasing magnet usage and processing difficulty. To achieve negative salient pole, several notches are added into the q-axis flux path in the proposed SPM machine, the q-axis inductance decreases, while the back electromotive force (EMF) is almost not affected. Hence the armature reaction magnetic field under q-axis current excitation is weakened, as well as the saturation of stator core. Therefore the output torque is enhanced by the negative salient pole, while the core losses and magnet eddy-current losses are suppressed. Both the torque improvement and losses reduction are validated by finite element analysis (FEA) results, compared with the conventional SPM machine.