Triple-Mode, Hybrid-Storage, Energy Harvesting Power Management Unit: Achieving High Efficiency Against Harvesting and Load Power Variabilities

This paper presents a triple-mode, hybrid storage, energy-harvesting power management unit (EH PMU) that interfaces a photovoltaic cell, a regulated load, and a rechargeable battery. The objective is to maximize the end-to-end conversion efficiency of the EH PMU against temporal mismatch and variabilities of harvesting and load power. To minimize the involvement (charging or discharging) of a battery in the voltage conversion process, the proposed hybrid energy storage employs both battery and capacitor, which increases transient energy buffering capability and reduces the overall power conversion loss. Measurement results with 65-nm test chips show that the proposed EH PMU can achieve up to 2.2× higher end-to-end conversion efficiency than the conventional dual-mode architectures under testing cases emulating realistic load and harvesting power variabilities. We also devised a framework for the system design to guide capacitor sizing, buffering voltage range selection, and end-to-end efficiency tradeoffs.