Hybrid system components pre-sizing and energy management strategy methods are important to ensure successful product development. These methods rely on optimization algorithms, which use mathematical models and are built on a set of assumptions. For hybrid vehicle█s architecture where energy storage system is passively connected to the DC bus, one common assumption is to consider its voltage as constant hence ignored. In this context, is first presented the interest of not neglecting that aspect for some high power consuming hybrid vehicle applications. As their management system needs to be fed with reliable information of the DC bus voltage, a method is proposed for its evaluation during preliminary design by optimization.