Design and analysis of ferrite based permanent magnet motor for electric assist bicycle

Abstract

Electric powered bicycles have been making their way into the world market for few years now. Typically DC, brush-less DC and PMSM motors are used as traction motors in electric bicycles. This paper describes finite element modeling and analysis of low cost ferrite based permanent magnet motor. This motor is intended to be used as traction drive in an electric assisted bicycle. The electric drive train consists of outer rotor motor along with planetary gear unit. The compact design arrangement of the planetary gear unit with motor provides better overload capability. The cogging torque is reduced by choosing a slot-pole combination with lower slots/pole ratio. Also, the phase winding and shape of permanent magnets are modified so as to obtain sinusoidal back-EMF even with a concentrated winding. Thus, torque ripple in the motor is minimized while keeping copper loss low. Prototype of the designed motor is being fabricated which is to be mounted on the rear wheel of the bicycle.