Supercapacitor-based reconfigurable energy management unit for autonomous wireless sensor nodes

Wireless sensor nodes require longevity, zero maintenance, and self-sufficiency. However, constraints on power, system volume, and cost are prohibitive to satisfy these requirements. In this paper, a reconfigurable energy management unit (EMU) is introduced that works within the constraints to meet the requirements. With multi-directional energy flow control, the EMU achieves the unification of photovoltaic (PV) energy harvesting with maximum power point tracking (MPPT), energy storage, voltage regulation, and energy recycling for dynamic voltage scaling (DVS). Supercapacitors are employed for energy storage to enhance operation lifetime. A reconfigurable DC-DC converter architecture is implemented to accommodate flexible voltage conversion and multi-directional energy flows. Functionality is implemented and verified using a CMOS 0.35-μm process. The PV cell voltage is well controlled from 1 V to 5 V to achieve MPPT under varying illumination conditions. Meanwhile, the output voltage is regulated from 1.2 V to 3.3 V with no additional regulator. Energy recycling improves DVS down-tracking by over 15 times.