Modelling of hybrid energy harvester with DC-DC boost converter using arbitary input sources for ultra-low-power micro-devices

Abstract

This work involves the modeling of three arbitrary input sources representing Hybrid Energy Harvesters (HEH) using a DC-DC Boost converter. These sources are combined in parallel and targeted at scavenging passive human power, therefore the three suitable ambient sources are motion, thermal and indoor light. Multiple sources mitigate limitations caused by single source harvesters but suffer impedance mismatches which greatly limit the total combined power that could have been harvested. A Boost Converter with suitable parameters has been designed and integrated to the HEH and PSPICE software has been used for both the modeling of arbitrary sources as well as the integration with the Boost Converter. An input source as low as 18 mV to 907 mV was able to be boosted into a 310 mV-27.9 V output when suitable parametric values were selected for the Ultra Low Power (ULP) HEH. A duty ratio of 0.5, with 10 kΩ load, 22 μH inductor as well as a switching frequency of 25 kHz was selected to be slightly above the audio range as well as being high enough to reduce passive component sizes. While VO/ VS of the boost converter is linear, PO/PIN is a function of third order polynomial. Therefore, at the HEH's lowest combined configuration of 1 K temperature difference, 0.25 g of vibration and 100 lux of indoor lighting, a combined 14 μW can be harvested. At its maximum of 10 K heat difference, 1 g vibration and 1000 lux of indoor lighting a combined 187 μW can be harvested. At its minimum, this enables possibility of battery-less applications in powering a quartz watch at 5 μW while at its maximum capacity powering a pace maker of ~50 μW as well as micro devices of ~100 μW solely from passive human activity. Once a 33 mF input capacitor is placed between the sources and converter, an output power of between 9.61 μW-78 mW can be obtained.