Dynamic Energy Burst Scaling for Transiently Powered Systems

Abstract

Energy harvesting is generally seen to be the key to power cyber-physical systems in a low-cost, long term, efficient manner. However, harvesting has traditionally been coupled with large energy storage devices to mitigate the effects of the source's variability. The emerging class of transiently powered systems avoids this issue by performing computation only as a function of the harvested energy, minimizing the obtrusive and expensive storage element. In this work, we present an efficient Energy Management Unit (EMU) to supply generic loads when the average harvested power is much smaller than required for sustained system operation. By building up charge to a pre-defined energy level, the EMU can generate short energy bursts predictably, even under variable harvesting conditions. Furthermore, we propose a dynamic energy burst scaling (DEBS) technique to adjust these bursts to the load's requirements. Using a simple interface, the load can dynamically configure the EMU to supply small bursts of energy at its optimal power point, independent from the harvester's operating point. Extensive theoretical and experimental data demonstrate the high energy efficiency of our approach, reaching up to 73.6% even when harvesting only 110 µW to supply a load of 3.89 mW.

Wearable, energy-opportunistic vision sensing for walking speed estimation

“…If the application is divided into several tasks in which only some of the peripherals are used, each task has its own optimal supply voltage for lowest energy consumption. The idea of Dynamic Energy Burst Scaling (DEBS) is to supply each task with its optimal supply voltage, or in other words to track the load's optimal power point in order to minimize its energy consumption [8].…”

“…Transiently powered systems operate efficiently in adverse harvesting conditions, requiring only limited storage capacity and input power to reliably execute power-hungry applications. The recently-proposed Energy Management Unit (EMU) [8] allows a transient system to operate in an energy-proportional manner. As opposed to traditional duty-cycling, an EMU-based system is energy driven, meaning that as the available energy increases, so does application's execution rate.…”

Energy-driven computing: Rethinking the design of energy harvesting systems

“…If expression (2) is violated, the system does not fail as the photo is stored in NVM and, when the supercapacitor is later charged again, another photo will be captured. Gomez et al [5] propose a system based on a similar concept, whereby tasks in a wireless sensing system (e.g. sampling data, transmitting data, etc) are not performed until there is enough energy stored in a small (80µF) capacitor.…”

“…This means that it usually only makes a single snapshot per supply failure, which removes wasted snapshots (increasing efficiency) and ensures a valid snapshot is always made (improving reliability). To detect the drop in ++ , a voltage interrupt is used where the hibernation threshold, 5 , is chosen such that [9]:…”

A scan-chain based state retention methodology for IoT processors operating on intermittent energy

“…One approach to operate reliably in such a setup, is to split the operation of a IoT node in atomic tasks, e.g., take one sample, process a few samples, transmit the processed samples. Each atomic task has then a known energy requirement and as soon as sufficient energy for a task was harvested on a tiny energy buffer, the task is executed [3]. While this scheme guarantees reliable operation, it can only be applied when the maximal required energy of a task can be reasonable bounded, which is often not the case for the processing tasks due to data-depended execution times.…”