A rule-based and a model predictive power management strategy are evaluated in experiments for power management of a fuel cell/ultracapacitor hybrid. The two degrees of freedom provided by use of two dc/dc convertors enable independent low-level control of the DC BUS voltage and the current split between the fuel cell and ultracapacitor. The high-level control objectives are to respond to rapid variations in load while minimizing damaging fluctuations in fuel cell current and maintaining the ultracapacitor charge (or voltage) within allowable bounds. Experiments show that both strategies can be tuned to meet these control objectives; however the predictive nature of the model predictive scheme coupled with its ability to aggressively push the ultracapacitor to its constraint line results in smoother fuel cell current transients.

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