Harvesting-aware charge management in embedded systems equipped with a hybrid electrical energy storage

A sustainable energy supply trend for portable embedded devices is energy harvesting, although its variability necessitates having energy storage systems (ESSs) besides. Requirements like energy and power capacities motivate the using of two or more complementary ESSs (e.g. battery and supercapacitor) in the form of a hybrid ESS (HESS). The capacity of most ESSs is divided into two instantly available charge (IAC) and instantly unavailable charge (IUC) parts. This paper first defines the concept of effective power as the sum of external applied power and internal charge migration power between IAC and IUC. It then proposes an adaptive charge/discharge management method, aware of energy harvesting, to use the possibilities of storing the surplus harvested energy into the HESS IUC part and extracting that stored energy to face with energy shortage. Simulation results show up to 20% improvements in the system lifetime in comparison to the state-of-the-art HESS charge management policies.