Portable appliances are an integral part of modern lifestyle. The energy source for most of these devices is batteries. Energy capacity of the battery limits the operating time between charges from the mains. In cases where continuous operation of the system is critical, the users are compelled to carry extra batteries. One of the solutions proposed to extend operation time utilizes user biomechanical energy to charge the battery.

This research presents a new biomechanical energy harvesting system based on the regenerative braking concept applied to the human natural motion. In previous studies the optimal braking profile was determined by an off-line procedure using an external load which was kept constant during a walking cycle. The new concept of this study optimizes the maximum amountf energy that can be extracted during human motion while minimizing the subject's effort. This is achieved by a 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 adaptive torque variation according to bio 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 breaks).

The concept presented in this research was verified by simulation model and experimental prototype. 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. The study was published by two articles in the most prestigious conferences in the field of power electronics.