Biomechanical energy harvesting system with optimal cost-of-harvesting tracking algorithm

This paper presents an innovative biomechanical energy harvesting system based on the regenerative braking concept applied to the human natural motion. To determine optimal braking profile previous studies used an off-line procedure based on constant external load to determine the optimal braking profile. The new concept of this study continuously optimizes the maximum amount of energy that can be extracted during human motion while minimizing the subject´s effort (metabolic rate). This is achieved by an energy harvesting system equipped with a programmable braking profile and a unique power extraction algorithm, which adaptively changes the braking profile to obtain the optimal ratio of energy to effort. These are facilitated by a BLDC generator that is connected to boost converter. A digital current programmed control of the boost converter enables an adaptive torque variation according to bio (measure of effort) and electrical feedbacks. This study focuses on the human knee joint as the energy source since the most of this joint work during level walking is negative (muscles are acting as brakes). Since this work is preliminary and more oriented to the novel concept of adaptive profile and optimal power extraction, the operation of the energy harvester is demonstrated on a full-scale laboratory prototype based on a walking emulator. The results exhibit ultimate power extraction capabilities as well as adaptation to the walking pattern.