A fuel-cell-battery hybrid for portable embedded systems

This article presents our work on the development of a fuel cell (FC) and battery hybrid (FC-Bh) system for use in portable microelectronic systems. We describe the design and control of the hybrid system, as well as a dynamic power management (DPM)-based energy management policy that extends its operational lifetime. The FC is of the proton exchange membrane (PEM) type, operates at room temperature, and has an energy density which is 4 - 6 times that of a Li-ion battery. The FC cannot respond to sudden changes in the load, and so a system powered solely by the FC is not economical. An FC-Bh power source, on the other hand, can provide the high energy density of the FC and the high power density of a battery. In this work we first describe the prototype FC-Bh system that we have built. Such a prototype helps to characterize the performance of a hybrid power source, and also helps explore new energy management strategies for embedded systems powered by hybrid sources. Next we describe a Matlab/Simulink-based FC-Bh system simulator which serves as an alternate experimental platform and that enables quick evaluation of system-level control policies. Finally, we present an optimization framework that explicitly considers the characteristics of the FC-Bh system and is aimed at minimizing the fuel consumption. This optimization framework is applied on top of a prediction-based DPM policy and is used to derive a new fuel-efficient DPM scheme. The proposed scheme demonstrates up to 32% system lifetime extension compared to a competing scheme when run on a real trace-based MPEG encoding example.