A compact digitally controlled fuel cell/battery hybrid power source

A compact digitally controlled fuel cell/battery hybrid power source is presented in this paper. The hybrid power source composed of fuel cells and batteries provides a much higher peak power than each component alone while preserving high energy density, which is important and desirable for many modern electronic devices, through an appropriately controlled dc/dc power converter that handles the power flow shared by the fuel cell and the battery. Rather than being controlled to serve only as a voltage or current regulator, the power converter is regulated to balance the power flow to satisfy the load requirements while ensuring the various limitations of electrochemical components such as battery overcharge, fuel cell current limit (FCCL), etc. Digital technology is applied in the control of power electronics due to many advantages over analog technology such as programmability, less susceptibility to environmental variations, and low parts count. The user can set the FCCL, battery current limit, and battery voltage limit in the digital controller. A control algorithm that is suitable for regulating the multiple variables in the hybrid system is described by using a state-machine-based model; the issues about embedded control implementation are addressed; and the large-signal behavior of the hybrid system is analyzed on a voltage-current plane. The hybrid power source is then tested through simulation and validated on real hardware. This paper also discusses some important issues of the hybrid power source, such as operation under complex load profiles, power enhancement, and optimization of the hybrid system. The design presented here can not only be scaled to larger or smaller power capacities for a variety of applications but also be used for many other hybrid power sources.