Check out the simulation-based design for hybrid vehicles article by Michael Jensen of Synopsys:
Combining technologies in a standard vehicle, where electronic and software control is used in non-drive source applications, is a complicated design challenge. A hybrid vehicle has this same design challenge of integrating non-drive automotive electronics source systems, with the added complexity of electronic and software control of the vehicle drive. Because of this integration requirement, hybrid vehicles are among the most complex systems to design, manufacture, and maintain.
As vehicle complexity increases, so do concerns about reliability. Designing hybrid vehicle systems, therefore, requires a systematic, organized approach to development. To ensure system reliability, this organized approach requires that reliability issues be an integral part of the design process from the very beginning. A Robust Design methodology provides the organized framework needed to design reliable hybrid vehicle systems.
Read the entire article on Automotive DesignLine