Robust Control of Solid Oxide Fuel Cell Ultracapacitor Hybrid System

Mitigating fuel starvation and improving load-following capability of solid oxide fuel cells (SOFC) are conflicting control objectives. In this paper, we address this issue using a hybrid SOFC ultracapacitor configuration. Fuel starvation is prevented by regulating the fuel cell current using a steady-state invariant relationship involving fuel utilization, fuel flow, and current. Two comprehensive control strategies are developed. The first is a Lyapunov-based nonlinear control and the second is a standard H_∞ robust control. Both strategies additionally control the state of charge of the ultracapacitor that provides transient power compensation. A hardware-in-the-loop test stand is developed where the proposed control strategies are verified.