A Novel Trapezoidal EMF Flux Switching Brushless DC Motor for a Pedal-Assist E-Bicycle

Recent pollution levels worldwide have led the world to search for a clean and efficient way of transportation as an alternative to internal combustion (IC) engine vehicles. In this paper, the design of a novel trapezoidal electromagnetic force (EMF) flux-switching brushless dc (FS BLDC) hub motor for a pedal-assist E-bicycle is proposed. The proposed motor is similar to a flux-switching permanent magnet (FSPM) motor. However, the EMF of FSPM motor is sinusoidal making it necessary to use encoders for position sensing. The proposed FS BLDC motor has a trapezoidal back-EMF and it is operated like a brushless dc (BLDC) motor. Further, ferrite permanent magnets (PMs) are used in the motor to make it economical. The hub-drive based E-bicycles usually employ conventional BLDC motors which have less rotor outer diameter for placing the PMs. Hence, a conventional FSPM motor is redesigned with a trapezoidal EMF, which has more magnetic loading due to the placement of magnets in the stator. Further, a 2-D finite element (FE) analysis of the proposed 24-slot, 20-pole trapezoidal EMF outer rotor FS BLDC motor is carried-out and the results are presented. In addition, a prototype is fabricated, experimental validation is carried-out and the results are presented.