Improving the efficiency of air-flow energy harvesters combining active and passive rectifiers

The architecture of air-flow energy harvesters generally consists of a first rectifying stage followed by a DC-DC regulator to convert and to store the incoming energy. This paper presents a circuit designed to improve the efficiency of the rectifying stage combining a MOSFET-based active rectifier in parallel with a passive full-wave bridge. Such system exploits the low forward voltage of the Schottky diodes to compensate the drawback of the inefficient passive rectification due to the bulk diodes of the MOSFETs when the power generated by low air-flow speed is not sufficient to activate the control circuitry of the active rectifier. The hybrid rectifier concept was firstly analyzed by SPICE simulations and next validated by means of experiments. Results show a conversion efficiency improvement between 10% and 30%. Moreover an energy harvester equipped with the hybrid rectifier shows an increase of the collected energy from 7% to 11% with respect to a scavenger using the active topology.