Robust disturbance observer design for a power-assist electric bicycle

Electric bicycles (EBs) have greatly extended the scope of application for traditional bicycles by providing assistive power with a motor. Commercially available EBs set the assistive torque proportional to the torque provided by the rider. This simple approach is lack of flexibility and does not fully utilize the assistive capability. For example, under uphill riding condition, the proportional assistance might be insufficient if the slope is steep and/or the rider has a large body weight. A robust disturbance observer based power-assist scheme is proposed for uphill riding in this paper. The robust design guarantees the robust stability of the overall system under plant uncertainties. The disturbance observer provides flexible assistive power through estimating and compensating for the changing environmental disturbances, such as gravitational force and frictional force. The proposed approach is shown to be effective through experimental results.