Optimum Performance of Direct Hydrogen Hybrid Fuel Cell Vehicles
- Publisher: eScholarship, University of California
UCD-ITS-RR-09-12, Engineering | UCD-ITS-RR-09-12 | Engineering
Proton Exchange Membrane fuel cell (PEMFC) technology is one of the most attractive candidates for transportation applications due to its inherently high efficiency and high power density. However, the fuel cell system efficiency can suffer because of the need for forced air supply and water-cooling systems. Hence the operating strategy of the fuel cell system can have a significant impact on the fuel cell system efficiency and thus vehicle fuel economy. The key issues are how the fuel cell back pressure and air flow through the fuel cell are controlled. One approach is fixed back pressure control. The other is optimum varying back pressure control. In both cases, the air flow stoichiometry is optimized. In this paper, a dynamic forward-looking vehicle model with a dynamic fuel cell system model is employed. The effects of different fuel cell system operation modes and different power split strategies on fuel economy of fuel cell hybrid vehicles are simulated. The simulation results of light duty vehicles on various driving cycles indicate a significant improvement in fuel economy for optimum varying back pressure operation compared to high fixed back pressure operation. For various fuel cell system operation modes, the load leveling control can significantly improve fuel economy on some aggressive driving cycles such as US06. The vehicle with a small fuel cell system becomes more efficient during low speed or low power demand driving by avoiding low fuel cell output power region.