Thermal modeling of fuel cell hybrid electric vehicles -

Abstract

The goal of this thesis is to model the behavior of a fuel cell hybrid electric vehicle (FCHEV) taking into consideration the effect of temperature on the overall vehicle performance. The fuel cell is intended to be the main energy provider in the vehicle. It receives humidified hydrogen from the tank and compressed air from the environment to deliver the required power. The battery on the other hand, is available to complement the existing fuel cell. In addition to the above main components, the auxiliary systems consisting of a humidifier, a compressor and two cooling systems (one for the fuel cell and another for the battery), are designed. Water management in the fuel cell is critical; where low humidity causes the dryness of the membrane while excess humidity causes its flooding. So a humidifier is used to keep the membrane of the fuel cell at a good humidity level. A compressor receives the air intake from the atmosphere, and compresses it to reach the fuel cell operating pressure. Finally, the fuel cell and the battery are cooled separately since they have different operating temperatures. The total power demand of the vehicle is derived from the specifications of the vehicle, the car speed and the road inclination angle. An energy management system is then combined to this model to distribute the power between the fuel cell and the battery pack with an aim to reduce the fuel consumption in the vehicle. The overall model is then tested with three different car sizes. Each car runs through two different driving cycles (UDDS and HWFET) and with two battery modes (charge depletion (CD) and charge sustaining (CS)). Furthermore, the road inclination angle is increased and the car performance is observed when the car goes through the same runs as described above.