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Design, Control, and Validation of a Charge-Sustaining Parallel Hybrid Bicycle

Traffic congestion, energy, and environmental considerations are boosting the interest for light electric vehicles. Electrically power-assisted cycles (EPACs) have great potential: they are cost effective, safe, easy to use, and have a small footprint. The two biggest disadvantages affecting EPACs are the need to recharge them and the added weight to the bicycle. To address these issues, a novel hybrid electric bike is presented. This contribution represents the first complete instance of a real-time electric bicycle-human body synergic control. The idea is to recover energy from the cyclist when she is most efficient and return it during low-efficiency pedaling. A control-oriented analysis of the cyclist's metabolic efficiency is carried out to guide the design of the control algorithm. Three features are employed for this purpose: an ad hoc-defined equivalent cycling efficiency based on oxygen consumption, a dynamic model for the state of fatigue (SoF), and heart rate (HR) measurements. The analysis of the equivalent cycling efficiency and SoF dynamics guide the design of a charge-sustaining assistance algorithm. The algorithm is designed and tuned through simulations. The proposed system is tested on subjects, and it is shown that it is capable of maintaining the battery charge; further tests indicate that improvements up to 25% in equivalent cycling efficiency and reduction in peak HR and SoF can be achieved for urban cycling.