Concurrent Task Scheduling and Dynamic Voltage and Frequency Scaling in a Real-Time Embedded System with Energy Harvesting

Energy harvesting is a promising technique to overcome the limit on energy availability and increase the lifespan of battery-powered embedded systems. In this paper, the question of how one can achieve the prolonged lifespan¹ of a real-time embedded system with energy harvesting capability (RTES-EH) is investigated. The RTES-EH comprises a photovoltaic (PV) panel for energy harvesting, a supercapacitor for energy storage, and a real-time sensor node as the embedded load device. A global controller performs simultaneous optimal operating point tracking for the PV panel, state-of-charge (SoC) management for the supercapacitor, and energy-harvesting-aware real-time task scheduling with dynamic voltage and frequency scaling (DVFS) for the sensor node, while employing a precise solar irradiance prediction method. The controller employs a cascaded feedback control structure, where an outer supervisory control loop performs real-time task scheduling with DVFS in the sensor node while maintaining the optimal supercapacitor SoC for improved system availability, and an inner control loop tracks the optimal operating point of the PV panel on the fly. Experimental results show that the proposed global controller lowers the task instance drop rate by up to 63% compared with the baseline controller within the same service time (i.e., from sunrise to sunset).¹The lifetime of a battery is usually less than five years, and in this paper we propose to use supercapacitor instead of battery for embedded systems to prolong the lifespan of the whole system to more than 20 years.