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Description
As a promising member of permanent-magnet brushless motors, flux-modulated permanent-magnet (FMPM) motors have aroused considerable attentions due to the outstanding low-speed large-torque characteristics. With the increasing demands of high quality PM motor, the high efficiency transmission in motor operation is one of the important performance evaluation indexes of motor. And then, the analysis, calculation and reduction of the motor losses have been one of the research subjects for the FMPM motors, such as the iron loss. In previous studies, the reduction of iron loss is often realized by optimizing the topologies of stator and rotor or improving the winding configuration. Yet, it is worth noting that, to the FMPM motors, the abundant harmonics often exist in the air-gap due to the flux modulation effect. So it can be inferred that the low-loss design of the FMPM motor is closely related to the air-gap harmonics. In this paper, an outer-rotor FMPM (OR-FMPM) motor is selected and researched, in which a low-iron-loss design is carried out considering the air-gap harmonics. In the motor, two rectangular PM pieces are artfully placed with V shape in one stator pole, which can enhance the flux-focusing effects and further increase the flux density in the air-gap. In order to reduce the iron loss of OR-FMPM motor, flux barriers are adopted purposely to adjust the harmonics which have a great influence on the iron loss, considering the relationship between iron loss and air-gap harmonics. Then, the electromagnetic performances of both the existing motor and proposed motor are compared to verify the reasonability of the low-iron-loss design. The results indicate that the iron loss of the motor can be reduced significantly, when maintain an almost consistent the output torque. Finally, a prototype is manufactured to verify the rationality of the proposed motor and the effectiveness of the proposed low-iron-loss design, which offers a new perspective on the low-iron-loss design of PM motors.
