Load characteristics and control of a hybrid fuel cell / battery vehicle

The polymer electrolyte membrane fuel cell (PEMFC) has been projected to be the fuel cell of choice for future automotive applications. Among the most challenging aspect of this application is the occurrence of severe and frequent changes in power demand. This paper will present a model aimed at mimicking the load expected in a fuel cell vehicle, including a DC motor, DC-DC converters and a rechargeable battery for peak-shaving and regenerative braking. The model also includes the kinematics of the vehicle (rotational and translational inertia as well as a simple wind resistance model), and thus can be connected to standardized drive cycle scenarios. In contrast to simple lab focused loads (resistive, constant current, constant voltage or constant power) where load impedance is directly manipulated, the manipulated variable within this load is the gain signal to the DC-DC converter. Based on this model we develop a control system architecture consisting of a number of low level regulatory loops, a power distributor for peak-shaving and finally a high level loop for tracking vehicle speed.