A fuel cell vehicle can benefit from being hybridized with an energy storage (ES) device (battery or ultracapacitor). The benefits could include improved vehicle performance and fuel economy and lower system cost. Previously, the degree of hybridization benefits from (a) fuel cell efficiency characteristics (b) fuel cell downsizing, (c) displacing fuel cell tasks with the ES functionality, or (d) energy recovery through regenerative braking were not well understood. To take advantage of these potential benefits, we must define the attributes of the ES system relative to the fuel cell. We have recently studied the role of batteries and ultracapacitors in hybrid fuel cell vehicles to understand their potential impact on fuel economy and performance. We also studied the impact of fuel cell performance and control strategy on the benefits of hybridization. This paper addresses (1) the impact of fuel cell efficiency characteristics on vehicle system efficiency; (2) the fuel economy trend that results from downsizing different fuel cells; and (3) the ES required to meet the performance requirements of midsize hybrid fuel cell cars.
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