Energy-efficient power assist control with periodic disturbance observer and frequency estimator

In this paper, energy-efficient power assist control problem for almost-periodic motions is considered. Specifically, we focus on the electric power assisted bicycles. Previously, it was shown that the energy efficiency improves by flattening the pedaling torque pattern. To cope with the frequency fluctuation of our motion, we introduce the periodic disturbance observer and a frequency estimator and suppress the pulsation of the human pedaling torque based on a disturbance observer framework. The effectiveness of the proposed method is demonstrated through experiments with an actual bicycle.