This paper presents an approach for the preliminary design of complex physical systems in the framework of systems engineering. This approach is centered on the activities and actors involved in the pre-design tasks. It focuses on the modeling of design problems with DEPS (DEsign Problem Specification), a recent formalism for specifying and modeling design problems in engineering. This design methodology completes simulation-based analysis approaches, which are mainly used today for the design of physical systems. In particular, our approach allows the synthesis of pre-design architectures, which analysis/simulation approaches cannot do. Starting from the textual specification of the requirements, the proposed approach builds a formal model of the design problem and solves it using Constraint Programming. Ideas and concepts related to this approach are discussed: the issue of reusability of problem models, the concepts of problem, knowledge and solutions spaces as well as the formal specification of requirements and everything else that distinguishe a design problem model from a designed system model. An example of a Li-ion battery design for an electric vehicle acts as a practical use case for this article.