Finite element modeling and analysis of external rotor brushless DC motor for electric bicycle

This paper describes finite element modeling and analysis of 3-phase brushless DC motor for direct-drive application with low speed and high torque capability. The motor is intended to be used as traction drive in an electric bicycle. The proposed motor has external rotor configuration with surface mounted NdFeB magnets. Motor transmission is gearless so that it will increase motor efficiency and reduce overall system weight. Calculation of motor parameters are made by means of finite element method i.e. Opera 2d software. Three motor designs having fractional slot and pole numbers are considered for this project. Their electromagnetic characteristics and performances such as cogging torque, line-line back-emf, phase back-emf, torque output, torque ripples, inductances, iron saturation level and magnet demagnetization issue are computed and analysed. From the FE results, it is observed that 9-slot/10-pole pm motor is the best choice and should be built as a prototype motor and configured into the wheel hub of an electric bicycle.