Expanding the Definition of the Degree of Hybridization of Fuel Cell Electric Vehicles

Electric vehicles have become increasingly important as an alternative drive system solution, supporting the effort to overcome the economic, ecological and social challenges in the automotive sector. Besides battery electric vehicles, fuel cell electric vehicles (FCEV) also offer locally emission free mobility. The drive system of fuel cell electric vehicles consists of a fuel cell system, an electric motor, power electronics, a hydrogen storage system as well as a rechargeable electrical energy storage system (REESS), typically a battery. The quantified power ratio between the fuel cell system and the REESS is referred to as the degree of hybridization (DoH), although inconsistent definitions are used. Therefore, existing definitions of the DoH regarding the power ratio of FCEVs are evaluated and compared to definitions used in context of the hybridization of internal combustion engine vehicles. The existing definitions of the DoH of FCEVs are not suitable as optimization criteria of fuel cell drive systems as they don’t support a distinct differentiation and characterization of FCEVs. Thus, a new definition of the DoH is proposed considering the ratio of the energy contents of the hydrogen storage system and the REESS, effectively adding a second dimension. The DoH of existing FCEVs is then evaluated using the proposed definition and enables the characterization and clustering of the different vehicles. While this two-dimensional DoH can be used as optimization criteria during the design and optimization of fuel cell drive systems, the aforementioned clusters can be assigned to already established qualitative DoH definitions used to describe types of hybrid electric vehicles. This supports customers to be able to more easily distinguish between different types of FCEVs.