This thesis is dealing with the development of a tool for supporting decision on problems related to ElectroMagnetic Compatibility (EMC) in big systems such as motor vehicles. To understand which parameters had to be taken into account in order to get consistent results from the measurements implemented on vehicle was the highest difficulty. We have been focussed on characterising the bundles in vehicles. We have been as well tackling the study of the behaviour of the ground plane linked to very strong electrical direct currents. In order to address these aspects we have been using the PEEC method (PEEC for Partial Element Equivalent Circuit) because of its easy implementation as well as of the possibility of using it for a wide range of frequencies. The report is composed of three chapters. The first one presents the bases of electromagnetism applied to big systems' EMC. A particular attention is turned to ground planes which are used as return conductor as well as voltage reference. In the second chapter, we present the PEEC method and the methodology which was set up for developing the software in order to obtain the best performances possible. This software has been validated on a set of test cases. The tool's application to an industrial case is dealt with in the last chapter and enables to understand the phenomena of resonance created by the different elements connected by a bundle. The modelling of the components allows completing the model thus generated.
