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The cogging torque in flux-switching permanent magnet machines (FSPMs) is high due to its unique structure and high air-gap flux density. The cogging torque principle in FSPM is different from that in traditional PM machines, which can not be correctly predicted by analytical consideration. The aim of paper is to present the investigation on cogging torque principle in FSPM by analyzing the flux density distribution and a simple cogging torque reduction technique, i.e., teeth notching. Various kinds of notching schemes and their influence on cogging torque are examined along with instantaneous torque and average output torque at different load conditions. Numerical optimization process combined with finite-element analysis, which gives more preciseness to calculations, is performed to minimize cogging torque. The results show that the cogging torque circle depends on the real flux density distribution in the machine rather than the number of stator/rotor poles and the presented method can greatly reduce the torque ripple at only slight cost of average output torque.