Multi-purpose Electromagnetic Energy Harvesting System

Abstract

This thesis proposes a multi-purpose electromagnetic energy harvesting system that harnesses mechanical energy from diverse types of mechanical motion sources and converts it into low power electrical energy. The harvested electrical energy is either used to supply power to low-power electronic devices or stored in an internal storage battery for later use. The proposed energy harvester can be i) mounted on a human’s knee, elbow, or hip, ii) hand-cranked, as well as iii) installed on any enclosure with fixed and movable parts (e.g., doors and/or windows). When mounted on a knee or hip, the device is actuated only during the so-called negative energy cycle of the motion and does not disturb the motion in the forward direction. The key building blocks of the proposed multi-purpose electromagnetic energy harvesting system is a new brushless AC electromagnetic generator, an adaptive motion translation mechanism and a smart power management system. The brushless AC generator consists of a new structure with a detachable rotor arrangement comprising mainly Neodymium rare-earth magnets mounted on an adjustable height rotor shaft and a stator made up of top and bottom flanges and a single continuous coil arrangement on a non-magnetic spool worn on a center magnetic stator core. The stator and rotor arrangement is carefully designed to allow for variable air gap so that the initial amount of torque required to move the rotor is adjustable and the amount of the generated output voltage can be controlled. Finite-element modeling magnetics (FEMM) simulation tool was used for the optimization of the new brushless generator, selecting the different generator materials, and determining the placement of the key components to achieve an efficient and truly adjustable system to the variation of frequencies and torque conditions. Furthermore, a gearbox was used as a mechanical up conversion mechanism to multiply the relatively low human motion to up to 5000 RPM at a walk pace of about one step per second. For this purpose, a three-stage spur gear system was designed using a roller-clutch at the front end to only allow motion during the negative cycle. The gearbox, when assembled together with the generator, works together with the adjustable height rotor to create the desired effect – adaptive, multi-purpose energy harvesting system. The power management design was optimized to maximum energy harvesting at rated RPM. When an external load is detected, the harvested power is routed to the external load, else, the power is routed to the internal storage battery for later use. The completed system generates between 2.5 watts and 7.5 watts of electrical power at an overall system efficiency of up to 84%.