Fuel Cell Hybrid Electric Drive Train Design

Fuel cells, as discussed in Chapter 14, are considered to be one of the advanced power sources for applications in transportation. Compared with the IC engines, fuel cells have the advantages of high energy efficiency and much lower emissions. This is because they directly convert the free energy in fuel into electrical energy, without undergoing combustion. However, vehicles powered solely by fuel cells have some disadvantages, such as a heavy and bulky power unit caused by the low power density of the fuel cell system, long start-up time, and slow power response. Furthermore, in propulsion applications, the extremely large power output at sharp acceleration and the extremely low power output at low-speed driving lead to low efficiency, as shown in Figure 15.1.