Decentralized Power Management in a Hybrid Fuel Cell Ultracapacitor System

This paper addresses decentralized control of a hybrid energy system consisting of a fuel cell (FC) and an ultracapacitor. Separate controllers are developed for the FC and the ultracapacitor for power management rather than one central controller. Explicit communication between controllers, such as exchange of locally sensed information, is absent. The former operates the FC in a load-following mode, while attenuating transient fluctuations in fuel utilization. The latter allows the ultracapacitor to be used as an energy buffer. The paper proposes a simple energy-conservation-based approach where the FC controller estimates the energy gap that is compensated for by the capacitor, based on its own transient response history. Accordingly, it modulates its own output power. The capacitor control, in turn, imparts robustness to the collective performance of the controllers by either dissipating excess energy or regulating the load voltage. Together, synergistic power management is achieved within a decentralized framework. An experimental test stand is developed to validate the approach and experimental results are provided. This paper considers one power source and one energy storage element, and further research must be done to translate this approach to power networks.