Unconventional wearable energy harvesting from human horizontal foot motion

Abstract

This paper presents an unconventional flat-type linear permanent magnetic generator based energy harvesting system which employs a cascaded boost-buck two-stage converter, with a maximum power control algorithm optimized for low frequency human horizontal foot motion, for Li-Ion battery charging. The dynamic model of the linear generator is built and the analytical equations for maximum power generation of non-resonant applications like human foot motion are derived. A double-sided stator linear machine with moving permanent magnet and soft magnetic spacer is designed. The Finite Element Analysis (FEA) is carried out on the designed geometric model to estimate the real-time voltage of energy harvester. A cascaded boost-buck converter with appropriate control is proposed to abstract maximum power from the linear generator and charge the Li-Ion battery with constant current at the same time. Under the typical human horizontal foot motion velocity of 4.5 m/s, the proposed energy harvester with the designed power conditioning circuit has power density as high as 8.5 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> .