A Novel PMSM with Optimized Asymmetric Eccentric Air-Gap for High-Power Electric Motorcycle

Abstract

In order to improve power density of high-power electric motorcycle driving motor, the air-gap length is usually minimized, which aggravates the influence of armature reaction on air-gap magnetic field. Considering the fact of unidirectional driving of electric motorcycle, the eccentric air-gap is used in each pole air-gap magnetic field strengthened area to suppress armature reaction, thus an asymmetric eccentric air-gap structure is designed. The torque and efficiency of motor are improved by asymmetric structure optimizing to improve the comfort, load capacity and battery life of vehicle, the ratio of maximum air-gap to minimum air-gap is eventually determined to be 3.2. The results of simulation and experiment show that, for the specified rotation direction, the distortion of air-gap magnetic density and back electromotive force (back-EMF) caused by armature reaction can be significantly suppressed by the determined asymmetric structure, hence the torque ripple and iron loss are reduced by 70.66% and 20.9% under rated load, respectively. Meanwhile, the proposed motor can provide a wide speed range and superior speed control performance, thus, verifying the validity and feasibility of the proposed asymmetric eccentric air-gap structure.