Impact of Ultra-Capacitor Sizing Optimization on Fuel Cell Hybrid Vehicle

Abstract

Fuel Cell/Ultra-Capacitor vehicle is a hybrid system, where the two energy sources produce electricity to supply the traction motors. An accurate sizing is a key factor to achieve the driving performances and the economical viability. The Fuel Cell (FC) is the main energy source; it ought to be able to supply power during steady speed. The hydrogen tank is sized depending on the required autonomy. The Ultra-capacitor (UC), as a second energy source, assists the FC during fast power demand periods and recovers the braking energy. Two different methods for UC sizing are presented in this paper: (1) a full sizing where the UC is capable to deliver the total energy needed during the maximum acceleration and (2) an optimized sizing where the FC participates with the UC to realize the maximum acceleration. The FC/UC vehicle system is modelled and simulated using a random drive cycle. Simulation results obtained with the two sizing methods demonstrate a compromise between the UC size and the FC durability.