Optimal sizing of batteries and ultracapacitors for fuel cell electric vehicles

Fuel cell electric vehicles with a single energy storage system can be heavier than vehicles with a hybrid energy storage system. This happens because different sources exhibit different specific energy and power values. With a hybrid energy storage system is possible use determined sources to supply high peaks with high specific power and other ones for long peaks power with high specific energy. For this reason hybrid energy storage systems can be lighter. A sizing methodology based on nonlinear optimization is proposed in this article. The goal of the methodology is to find the lowest mass for the hybrid energy storage system. The maximum values that the specific energy and power can reach, related to Ragone plots, are constraints of the optimization problem.