Comparison of the Performances of Different Geared Brushless-DC Motor Drives for Electric Bicycles

In this paper, we compare the technical performance of geared brushless-dc motor electric bicycle drive systems with both self-control mode and hysteresis-band (direct torque) control, where the operating cycle profiles used are based on actual road tests. In most cases, for a given gear ratio, hysteresis- band (direct-torque) control gives a better efficiency than self- control mode. However, with self-control, higher gear ratios can be used to increase the drive efficiency, where a drive with hysteresis-band control could not deliver the torque-speed combinations required by the riding profile. Furthermore, the improvement of the efficiency with use of a high-speed instead of a high-torque motor with a larger gear ratio or of increased battery voltage is not very significant, but comes with much larger physical dimensions of the gear.