Efficient Charging of Supercapacitors for Extended Lifetime of Wireless Sensor Nodes

This paper describes an efficient charging method for a supercapacitor-operated, solar-powered wireless sensor node called Everlast. Unlike traditional wireless sensors that store energy in batteries, Everlast´s use of supercapacitors enables the system to operate for an estimated lifetime of 20 years without any maintenance. The novelty of this system lies in the feed-forward, pulse frequency modulated converter and open-circuit solar voltage method for maximum power point tracking (MPPT), enabling the solar cell to efficiently charge the supercapacitor and power the node. Experimental results show that by its low-complexity MPPT, Everlast can achieve over 89% conversion efficiency with lower power overhead than the state-of-the-art by two orders of magnitude, while enabling charging a supercapacitor up to 400% faster than direct charging. This makes Everlast particularly applicable to miniature-scale, high-impedance energy harvesting systems.