The present paper deals with the activities and the results achieved under a cooperative research project between IFP, D2T, LMS, G2Elab and Renault focused on Hardware-inthe- Loop (HIL) applications to hybrid power-trains conception and assessment. The main goal of this study is the evaluation of hybrid propulsion concepts and the benefits of different degrees of hybridization in a flexible architecture, by using a chain of simulation platforms: from the co-simulation to the highdynamic engine-in-the-loop test bed, through a virtual version of the last one. This paper focuses on the implementation issues of an energy management strategy (EMS) for a parallel hybrid architecture. The EMS is developed from the optimal control theory, using Pontryagin's Minimum Principle (PMP). The resulting Equivalent Consumption Minimization Strategy (ECMS) is implemented in real time and tested in an experimental environment (HyHiL test bench). In particular, a possible integration of the three way catalytic converter constraint in the optimization is presented.