UC Davis Institute of Transportation Studies

In the area of analysis, a modeling tool for fuel cell vehicles needs to address the transient dynamic interaction between the electric drive train and the fuel cell system. Especially for vehicles lacking an instantaneously responding on-board fuel processor, this interaction is very different from the interaction between a battery (as power source) and an electric drive train in an electric vehicle design. Non-transient modeling leads to inaccurate predictions of vehicle performance and fuel consumption. Applied in the area of development, the existing programs do not support the employment of newer techniques, such as rapid prototyping. This is because the program structure merges control algorithms and component models, or different control algorithms are lumped together in one single control block and not assigned to individual components as they are in real vehicles. In both cases, the transfer of control algorithms from the model into existing hardware is not possible. The simulation program developed in this dissertation recognizes the dynamic interaction between fuel cell system, drive train and optional additional energy storage. It provides models for four different fuel cell vehicle topologies: 1) A load following fuel cell vehicle; 2) A battery hybrid fuel cell vehicle; 3) An ultra-capacitor hybrid fuel cell vehicle in which the ultra-capacitor unit is coupled via a dc-dc converter to the stack; 4) An ultra-capacitor hybrid fuel cell vehicle with direct coupling between fuel cell stack and ultra-capacitor. The structure of the model is a causal and forward-looking. The model separates the modeling of control algorithms from the component models. The setup is strictly modular and encourages the use of rapid prototyping techniques in the development process. The first half of the dissertation explains the model setup. In the second half of the dissertation, the simulation of different hybrid vehicle designs illustrates the capabilities of the model.