UC Davis Institute of Transportation Studies

Hybridization of fuel cells with additional batteries or ultracapacitors in a fuel cell vehicle reduces electrical and mechanical stresses on fuel cells and improves the overall drive train efficiency over a standard drive cycle. This paper primarily analyzes hybrid fuel cell vehicles with different drive train arrangements, and compares projected fuel economies of hybrid fuel cell vehicles with improved conventional vehicles and hybrid electric vehicles at three points in the future: 2015, 2030, and 2045. The key points addressed are as follows: drive train arrangements, control strategies, and the influence of energy storage sizing on vehicle fuel economy. The study shows that fuel cell vehicles having ultracapacitors coupled with fuel cells via a DC/DC converter with load-leveling control is the best approach in term of improving fuel economy and mitigating the stress on the fuel cell. Power-assist control is well suited for fuel cell-battery hybrids in terms of fuel economy improvement. Fuel cell vehicles achieve about twice the fuel economy of the improved conventional vehicles and only about 15 percent better fuel economy compared to the hybrid electric vehicles.